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2. 3 2 2 Environmental Requirementsand Concerns 55 In addition to the necessary floor space ceiling height is also a site consideration as illustrated in FIGURE 3 2 Approximately 2 9 m 115 in from floor to ceiling or 1 1 m 42 in from the top of the Dewar to the ceiling is required to insert the transfer line into the Dewar If this height is not available at the probe station the transfer line can be inserted in another room and then transported with the Dewar to the probe station Transfer line 2 9m 115 in Pressurized gas tank 1 52m 60 in Vacuum pump 0 4m 16 3 in a 1 3 2 2 Environmental Requirements and Concerns FIGURE 3 2 Suggested elevation There are several environmental considerations that may affect probe station operation probe measurements or the safety of the user The following sections discuss vibration considerations electrical noise ventilation and safety considerations 3 2 2 1 Vibration Place the probe station away from major sources of vibration to avoid problems when landing probes and to avoid electrically noisy probe contacts We recommend placing it on a concrete floor on the lowest floor of the building and away from elevators lar
3. Sample stage A 4 K radiation shield Radiation shield A 4 4K shield stage Second shield Radiation shield stage Second shield stage Model CPX Probe Station 7 r Vacuum chamber base ko Sample stage Cryogen Stage 4 Stage 1 3 flow control input connector connector bh Bottom exhaust Side exhaust 7 Bayonet FIGURE 2 4 Refrigerator 2 2 1 ProbeStation 15 2 2 1 3 Micro manipulated Stages Up to six micro manipulated stages can be installed on the CPX The micro manipulated stage includes x y and z micro manipulated translation stages with micrometer or hand dial controls probe arm base top feedthrough for user configurable signal connector bellows probe arm arm shield braids probe arm sensor provided on one arm and optional planarization adjustment FIGURE 2 5 and FIGURE 2 6 Probe arm sensor Y axis embedded in end micrometer of probe arm Z axis micrometer Probe arm sensor connector X axis hand dial FIGURE 2 5 Micro manipulated stage Signal connector _ feedthrough NU 7 Probe arm Bellows base Planarization Arm shield assembly braids optional FIGURE 2 6 Micro manipulated stage showing optional planarization assembly
4. 6 0 c cece cece eee e eens 55 32X NIDPAUION seige dereer nora aeee an Be cb tn aeaay an eid am eects 55 3 2 2 2 Electrical Noise 0 0 ccc cece cece cece cece cece eee eee ee ee ees 56 3 2 2 3 VentilatioN serieren issi e EEE AUE EEE EE E ERRER RE 56 3 2 2 4 Safety Compliant sserri sprost cece eee e ee eee e RA ANER ENA 56 3 2 3 Power Requirements 0 eee c cece cece eee e eee e nett eet ten ene nneeeees 56 3 2 4 CryOgen REQUIFEMENTS i scccerccesviees En E aaa E E Ea VE cas 57 3 2 5 Vacuum Requirements ssssusissrsusesrrrrserrrrererrrrrersrrrrrerer en 57 3 2 6 Gas REQUIFEMENES riris iaci ioro yn nan E RERE O E ETTEN a 57 3 3 Unpacking the Probe Station serres ireas s iera kitrrddi rrari ee ee een ESAR REENA NE 58 3 3 4 Shipping COMTAIMERS eesi cccr is erian ir ghabeacadhales EUNT a ves bagi sales eas EEE 58 3 3 2 Inspecting for Shipping Damage 00 cece cece e cece eee e eee e eee eee ee 59 333 Reguired TOOIS eoii cen en EEE R E deagucunnhanaget sated haat 59 3 3 4 Moving and Lifting the Probe Station sssssiessrrerrirererrrerrren 59 3 3 5 Uncrating the System and Stand ccc cece eee e eee ee eee en eee teen nna 60 3 3 6 Uncrating the Console and Accessories 0 c cece cece ee eee eee e eee eo 61 3 3 7 Unpacking the Probe Station ccc cece ee een e cece eee ene e eee e enna 61 3 3 8 Unpacking the Instrument Console Crate 0 0 e cece eee e eee e eee
5. ce cece e ee eee 140 6 3 1 3 Test the Vacuum Pumping System the Connection to the Probe Station and the Probe Station Vacuum Chamber 140 6 3 1 4 The Impact of CryopUMPING 6 eee cece eee eee arvava 141 6 3 1 5 Vacuum Chamber Leak Test 0 cece cece eee nent ee eens 141 6 3 1 6 Will Not Achieve 10 2 Torr cee cece cee cece e eect teeters 141 6 3 1 7 Will Not Achieve 10 3 Torr ec cece eee c cece e cette eee eee 142 6 3 1 8 Will Not Achieve Less Than 10 3 Torr or Cool to 4 2 K 142 6 3 2 Transfer Line Troubleshooting cc cee eeee cece eee eee takk sinet 143 6 3 2 1 Soft Transfer NE si sec asissadeeveiasd hater EREEREER NOE eee 143 6 3 2 2 Plugged Transfer Line 0 0 ccc cece cece cece teeta teste eens 143 6 3 2 3 Stuck Foot Valve Control KnNOD 0 cece e cece eee nee e teens 144 6 3 3 Refrigerator Cooling Troubleshooting cece eee ees 144 al akeShore www lakeshore com vi TABLE OF CONTENTS 6 3 3 1 Refrigerator Does Not Begin to Cool cece eee e ener ees 144 6 3 3 2 Sample Stage Will Not Cool 2 0 0 0 ccc cece cece eee ee eee ees 145 6 3 3 3 4K Shield Stage Will Not Cool 1 2 2 ccc cece c cece eee eee e teens 145 6 3 3 4 Sample Stage Does Not Reach 4 3 K Base Temperature 145 6 3 3 5 Takes Too LONG tO COO eee cece raana EEAO 146 6 3 3 6 Micrometer Valve Problems ccc cee e ee eeee eee
6. Low input horizontal 1 2 Hz to 1 7 Hz 7 s Vertical 70 to 85 Isolation efficiency at 5 Hz Horizontal 75 to 90 7 3 Vertical 90 to 97 Isolation efficiency at 10 Hz Horizontal 90 to 97 Additional details Gross load capacity 640 kg 1400 Ib Net load capacity 160 kg 350 Ib Finish Medium texture black powder coat Facilities required 552 kPa 80 psi nitrogen or air 40 psi required for CPX TABLE 2 3 Specifications for the TMC stand Copyright Technical Manufacturing Corporation Used with permission 2 3 14 Pump Line Vibration Isolator PS PLVI 40 or 25 2 4 Considerations for DC RF Electrical Measurements 2 4 1 Grounding Shielding and Isolation for DC RF Measurements 2 3 14 Pump Line Vibration Isolator PS PLVI 40 or 25 35 Vacuum pumps are a common source of vibration that can impact sensitive measurements There are two pumps commonly associated with the probe station the turbo pumping system used to evacuate the chamber and the 2 K base temperature option pump A pump line vibration isolator can minimize the vibration from either of these pumps When operating at cryogenic temperatures lt 77 K the cryopumping action of the refrigerator will maintain sufficient vacuum in the chamber so that the evacuation valve can be closed and the turbo pump turned off When operating the refrigerator at elevated temperatures however the vacuum pump nee
7. Open the vacuum isolation valve on the probe station vacuum chamber Power on the pumping system using steps 3a 3c in section 6 3 1 1 If vacuum levels come down to lt 10 2 Torr within 10 min of pumping you can assume all the connections are made securely If vacuum levels come down to lt 5 x 10 4 Torr within 1 h of pumping with the gauge located on the T inlet of the vacuum turbo pump you can assume all connections are made securely and there are no large leaks If vacuum levels come down to lt 5 x 10 5 Torr within 2 h of pumping you can assume all connections are made securely there are no large leaks and the chamber is free of moisture If the pressure listed in step 7 is achieved then you have verified that the vacuum pumping system and probe station vacuum chamber are functioning properly 6 3 1 Vacuum Troubleshooting 141 9 Continue through the remainder of section 6 3 1 and if these pressures are not achieved contact Lake Shore for technical assistance 6 3 1 4 The Impact of Cryopumping Any time cryogen is flowing through the refrigerator gas molecules in the chamber will freeze onto the cryogen cooled surfaces cryopump An otherwise functioning probe station can cryopump well enough to overcome a poor initial vacuum or keep up with a very small leak for some time Although this can be beneficial in some circumstances it can also mask vacuum problems and create unexpected results such as condensation on the sample T
8. The following tables provide specifications for the ZN50 DC RF probes You can find more information on the ZN50 DC RF probes in section 2 3 2 and application infor mation in section 2 4 ZN50 551 500 stripline probe body mount requires a ceramic blade selectable below TABLE 1 8 ZN50 probe body Part number s A Maximum frequency s aE gi i ote Z 3 ZN50R 03 W ZN50R 10 W Tungsten 10 ZN50R 25 W 25 ZN50R 03 P7 1 3 ZN50R 10 P7 Paliney 7 Maximum irene 10 l ZN50R 03 BECU frequency 1 GHz with 3 ZN50R 10 BECU MWC 09 00K NM cable 10 ZN50R 25 BECU BeCu 25 ZNS5OR 100 BECU 100 ZN50R 200 BECU 200 TABLE 1 9 ZN50 probe tips 1 5 3 ZN50 DC RF Part cube Connector Feedthrough Measurement Maximum Maximum Cables number ieee lie type type configuration frequency temperature Ultra miniature ZN50 G cryogenic SMA BNC Shielded 50 MHz 475K coaxial Ultra miniature ZN50 T cryogenic SMA 2 lug triaxial Low leakage 50 MHz 475K coaxial Semirigid Loss less MWC K SMA z 1GHz 475K 009 00K microwave compatible compression High frequency GHz 75 coaxial seal S21 gt 10 dB up to 1 GHz except for a 40 dB spike between 400 MHz and 800 MHz depending on probe model and placement S11 lt 3 dB up to 1 GHz TABLE 1 10 ZN50 DC RF cables Ea akeShore www lakeshore com 6 CHAPTER 1 Introduction 1 5 4 GSG Microwave m Coplanar waveguide probe with ground signal ground GSG c
9. www lakeshore com 104 CHAPTER 4 Basic Operation 4 6 Imaging and Probing the Sample 4 6 1 Using the Microscope to Image the Sample Model CPX Probe Station Aclear image of the sample is necessary for properly landing the probe tip Landing the tip with a poor image can result in intermittent contact scratches on the sample or probe damage If you cannot obtain a proper image please refer to section 6 3 4 Lake Shore recommends that you practice imaging the sample and landing probes before cooling the refrigerator Remember to raise the probes 3 mm to 4mm above the sample after practicing Each probe type and sample surface behaves slightly differently when landing probes The instructions below are general guidelines Lake Shore recommends developing a standard operating procedure for your lab that is optimal for the probes and samples being used see section 2 6 7 The plan can be developed by repeating steps 5 6 and 7 in section 4 6 2 until contact resistance measurements are repeatable Thumbscrew Hand dial Zoom gt Shaft collar 12 camee om p Focus gt slal FIGURE 4 15 Microscope controls Follow this procedure to use the microscope to image the sample 1 Remove the dust cap from the bottom of the microscope 2 Loosen the thumbscrew on the vertical microscope shaft swing the microscope over the center of the viewport and tighten the thumbscrew This process is rep
10. densation on the sample it may be necessary to leave the turbo pump running Oper ating with LN also affects the vacuum performance of the transfer line which may need to be pumped out more frequently to maintain acceptable performance If the probe station is going to be operated or pre cooled routinely with LN itis beneficial to have a dedicated LN transfer line The configuration of the transfer may differ based on your specific application Consult Lake Shore for more information It is tempting to save nitrogen by shutting off flow to the 4 K shield stage but it is not rec ommended because the radiation shield would not be cooled Operating without a prop erly cooled radiation shield will increase base temperature and increase the temperature gradient between the sample and sample stage 5 2 3 1 Filling the PS LN2 Liquid Nitrogen Dewar This section assumes that the PS LN2 option has been assembled according to section 3 4 4 5 Familiarize yourself with section 4 5 1 before starting this procedure 1 Slowly open the vent valve to relieve any pressure in the Dewar Leave the vent valve open Attach the liquid port on the PS LN2 to the LN source with a temporary fill line Open the liquid valve Turn on the LN source to initiate filling Continue filling until the level gauge reads three quarters full Turn off the LN source Remove the fill line from the liquid port Close the vent valve and liquid valve The 68 kPa 10 p
11. ie Controller FIGURE 2 14 Turbo pumping system 2 3 Configurations Options and Accessories 2 3 1 Probing Configurations 2 3 2 DC RF ZN50 Probe Configurations 2 3 Configurations Optionsand Accessories 23 This section illustrates and describes optional components for the probe station Awide selection of probes cables sample holders and options make it possible to configure the probe station to meet a variety of specific measurement applications Each of the six probing positions in the CPX can be configured with a user specified arm assembly and probe Arm assemblies are made up of several components and can be optimized for different probes and measurement techniques They share the same basic requirements of a micro manipulated stage welded stainless steel bellows probe arm and base cable and probe mount The micro manipulated stages translate the probe in x y and z axes and are common to all probe configurations If the system is not fully populated when ordered additional arm assemblies can be ordered as MMS 09 options and added in the field A probe arm and base are included with each assembly whether ordered with the system or separately Stages ordered with microwave cables will include planarization assemblies Additional planarization assemblies can be ordered for reconfiguration in the field Additional arm and base assemblies will facilitate reconfiguration of the system if different cables are routinely excha
12. 6 3 1 2 Test the Vacuum Pumping System Along with the Connection to the Probe Station 1 Remove the NW 40 blank off plate from the inlet T on the vacuum pumping system Set aside the NW 40 blank off plate it is no longer needed Use the NW 40 centering ring and clamp to connect the NW 40 flexible stainless steel vacuum line to the inlet T of the vacuum pumping system Fully close the vacuum isolation valve in this step we are only checking the vacuum ofthe connection up to the probe station Power on the pumping system using steps 3a 3c in section 6 3 1 1 Observe the vacuum gauge reading If the connections are all made securely the reading should come down to lt 10 5 Torr within 10 min of pumping Do not continue to the next steps if this pressure is not achieved see section 6 3 1 or contact Lake Shore for technical assistance see section 6 5 for contact information If 10 5 Torr is achieved turn off the scroll and turbo pump and perform steps 8a 8e in section 6 3 1 1 6 3 1 3 Test the Vacuum Pumping System the Connection to the Probe Station and the Probe Station Vacuum Chamber q gt Leave the vacuum pumping system connected to the probe station as inthe previous section Make sure that the vacuum pumping system is vented to atmosphere use the manual vent valve on the side of the turbo pump and the probe station vacuum chamber is vented to atmosphere use the purge valve and procedure in section 3 4 3 1
13. 600 Ib to 363 kg 800 Ib Transfer line box 1 63 m 64 in x 0 76 m 30 in x 0 13 m 5 in 8 kg 18 Ib PS V81 DP crate optional 0 66 m 26 in x 0 56 m 22 in x 0 91 m 36 in 61 kg 135 Ib PS LN2 box optional 0 56 m 22 in x 0 56 m 22 in x 1 04 m 41 in 48 kg 106 Ib Weight may vary depending on configuration and options ordered Model CPX Probe Station TABLE 3 2 Shipping container size and weight 3 3 2 Inspecting for Shipping Damage 3 3 3 Required Tools 3 3 4 Moving and Lifting the Probe Station A WARNING 3 3 2 Inspecting for Shipping Damage 59 Upon receipt of the system check for signs of rough handling such as damage to the shipping container or broken shock indicators attached to the outside and inside of the shipping container If any physical damage is suspected do not open containers before photographing the damage and informing the shipping agents and Lake Shore or your local representative Contact information for Lake Shore service is given in section 6 5 Shipping containers and shipping materials should be kept in the event you would need to return your probe station FIGURE 3 3 If you suspect damage take a photo of the packed shipment specifically damaged areas Left Probe station Right Console and accessories The following tools are required to unpack the crated probe station and are not included with the shipment Clean safe work space Lifting equipment or four pers
14. F7 a 81 akeShore www lakeshore com 16 CHAPTER 2 System Overview 2 2 2 Cryogen Dewar Major components of the cryogen Dewar and pressurized gas system include the and Pressurized Gas Dewar pressurized gas tank and transfer line The cryogen Dewar provides either liquid helium or liquid nitrogen used for cooling the refrigerator of the probe station System The pressurized gas is used to facilitate the transfer of the cryogen to the probe Station FIGURE 2 7 illustrates the system components Transfer line f Pressurized gas tank ASEE Cryogen Dewar To probe station FIGURE 2 7 Cryogen Dewar and pressurized gas system Model CPX Probe Station 2 2 2 Cryogen Dewarand Pressurized Gas System 17 2 2 2 1 Transfer Line The vacuum insulated transfer line carries liquid cryogen from the Dewar to the probe station The supply leg is 12 7 mm 0 5 in in diameter and incorporates a foot valve and filter at the bottom The foot valve is used to regulate flow through the transfer line and the filter prevents ice from entering the line The foot valve control knob is located at the top of the supply side leg so it can be accessed when the line is cold The target leg is designed to form a gas tight seal when properly inserted into the bayonet onthe probe station refrigerator FIGURE 2 8 illustrates the transfer line Pump out port ee Foot valve control Transfer knob line Braided
15. When landing a microwave probe tip you may need to rotate the sample stage slightly to align the microwave probe points with the landing pads To do this you can use the sample stage rotation hand dial to rotate the sample stage in either direction turning the hand dial counterclockwise rotates the sample stage clockwise Fifteen full turns of the hand dial will provide approximately a 5 rotation of the sample stage This is intended to fine tune the landing of your microwave probe and is not for major adjustments El akeShore www lakeshore com 106 CHAPTER 4 Basic Operation 4 6 4 Using the Planarization Assembly Model CPX Probe Station sample rotation hand dial FIGURE 4 16 Sample stage rotation hand dial There are three points on a GSG microwave probe tip All three points must be landed on appropriately sized pads for the probe to meet its specified performance The planarization assembly rotates the probe arm about its x axis so the three probe points land simultaneously on the sample Planarization hardware is included on all CPX probe assemblies that were initially configured with microwave cables or probes Probe assemblies can be upgraded in the field if microwave probes are purchased later The planarization assembly can be ordered as GSG TPM See section 5 3 8 for installation We recommend that you planarize the probe on a metallic test substrate prior to evacuating and cooling the system Gold plated pads are
16. because the back side of the sample is held at system ground They are recommended for routine measurements especially when samples are patterned on highly insulating substrates or leakage current is not a concern They are constructed out of solid metal making them the most thermally and electrically conductive The smallest thermal gradient between the sample stage and sample mounting surface can be achieved with the standard SH 1 25 G grounded sample holder The maximum operating temperature is 475 K when using the grounded sample holder 2 3 5 2 Isolated Sample Holders Isolated holders have a nonconductive sample mounting surface that electrically isolates the sample from system ground They are recommended for measuring samples with electrically conductive features on the back side They are constructed similarly to grounded holders but have a sapphire disk attached to the top surface The sapphire is an excellent electrical insulator and retains good thermal conductivity at cryogenic temperatures Moderate thermal gradients between the sample stage and sample mounting surface should be expected The maximum operating temperature is 400 K 2 3 6 Vision System Configuration 2 3 6 VisionSystem Configuration 29 2 3 5 3 Coaxial Sample Holders Coaxial holders offer the ability to define the voltage potential on the conductive sample mounting surface in addition to isolating it from system ground They are useful when it is desired to maint
17. equipment It must be clearly indicated on both the shipping carton s and any correspondence relating to the shipment The user should retain any shipping carton s in which equipment is originally received in the event that any equipment needs to be returned RMAs are valid for 60 days from issuance however we suggest that equipment needing repair be shipped to Lake Shore within 30 days after the RMA has been issued You will be contacted if we do not receive the equipment within 30 days after the RMA is issued The RMA will be cancelled if we do not receive the equipment after 60 days All shipments to Lake Shore are to be made prepaid by the customer Equipment serviced under warranty will also be returned shipping prepaid by the customer Equipment serviced out of warranty will be returned FOB Lake Shore Lake Shore reserves the right to charge a restocking fee for items returned for exchange or reimbursement Numerics 2 K base temperature 32 4 K shield 14 anchor points 25 attaching braid block 73 controller settings 81 diagram of 14 exhaust valve 97 ground return path 46 split flow 14 temperature limits 83 A assembly 63 Dewar pressure controller 71 liquid nitrogen Dewar 71 low temperature option 70 oil less air compressor 71 pneumatic vibration isolator 70 pump line vibration isolator 70 turbo pumping system 67 82 vision system 64 B BECU probe tips cleaning 133 C cables 5 adjusting semirigid cables 121
18. pressure less than 21 kPa to 28 kPa 3 to 4 psi will not provide enough cryogen to the refrigerator Excessive Dewar pressure pressure greater than 34 kPa 5 psi will raise the temperature of the cryogen in the Dewar m Probe arm position placing probe arms in the fully retracted x axis position presents a greater heat load as more of the arm s length will be outside of the radiation shielding extend the probe arms into the probing area to reduce the heat load m Extra heat load on the sample stage can be caused by arm braids touching improperly temperature control heater left on microscope light left on or all probe arms positioned all the way out in the x axis m Improper temperature controller setup if the temperature controller inputs are reconfigured it is common for the wrong temperature response curve to be selected for a sensor El akeShore www lakeshore com 146 CHAPTER 6 Maintenance and Troubleshooting Model CPX Probe Station 6 3 3 5 Takes Too Long to Cool FIGURE 6 7 illustrates a typical CPX refrigerator cooling curve for helium The system cools slowly at first because the heat capacity of the materials is high near room temperature As the materials cool their heat capacity drops and the system cools more quickly This impacts warm up time and temperature control time constants Please note that cooling with nitrogen takes significantly longer than cooling with helium If the cooling cycle takes signi
19. section 3 5 3 2 and then install the probe to the probe arm Rz WISE FIGURE 3 18 CPX with probe mount installed 3 5 3 1 Install the ZN50 Probe Mount 1 Follow the procedure in section 3 5 2 2 Flex the probe mount braids so that the copper braid block will be in approximately the correct position for attachment FIGURE 3 19 3 Ifdesired apply a small amount of Apiezon N brand grease to the end of the dowel and the bottom of the braid block FIGURE 3 19 The grease enhances the thermal contact between the probe and the probe arm however some users prefer to keep the sample area free of all greases Specified system performance does not require grease on the bottom of the probe arm braid block or on the probe dowel 3 5 3 InstallingaZN50 Probe 73 FIGURE 3 19 Left To install the probe mount bend the probe mount braids Right Apply grease to the end of the dowel 4 Slide the dowel of the probe mount into the end of the probe arm and using the 1 5 mm hex driver tighten the set screws that hold the probe mount in place 5 Attach the braid block The braid block is used as a thermal connection between the probe tip and the anchor location Use this procedure to attach the braid block to the 4 K shield before installing the probe tip to minimize the chance of accidentally hitting the probe tip a Using the x axis hand dial and y axis micrometer move the probe arm to expose the braid block mounting holes in t
20. 0 ccc cece cece eee e eee e eee e eee 121 5 3 6 1 Removing a Microwave Cable cccc cece cece eee e eee e ees 121 5 3 6 2 Installing a Microwave Cable cc cece cece e eect e eens 121 5 3 6 3 Adjusting the Fit of Microwave Cables cccc cece cece 121 5 3 7 Reconfiguring an Optical Fiber Assembly 00 0 0 cece cece erreen 123 5 3 7 1 Removing an Optical Fiber cece eee cece e eee eee enna 123 5 3 7 2 Installing an Optical Fiber Assembly ccc cece cece 123 5 3 8 Installing the Planarization Assembly 0 cece eee eeeee ee eee een ees 126 Chapter 6 6L General erea are odes aaecet essa N A ee tee ne ata te ate ate niece tearing 129 Maintenance and 6 2 MAINTENANCE si fesnicsciceenenne eh ce o pa EAE E ENEA RE EEA 129 6 2 1 Preventive Maintenance Schedule cccc ccc cece e eee e es 129 Troubleshooting 6 2 2 Cleaning the Vacuum Chamber Exterior 0c cece e cece eect ee eees 130 6 2 3 Cleaning the Vacuum Chamber Interior cccc cece eee rere 130 6 2 4 Viewport Window Maintenance cece ccc cece eee e cece eee eeenne eee eees 131 6 2 4 1 Cleaning the Viewport WINdOWS 0 00 cece cece cece ener eens 131 6 2 4 2 De fogging the Viewport WINdOWS 00 cece cece cece eee 131 6 2 5 O RING MAINTENANCE cece eee eee eter t eee e es 131 6 2 5 1 Re greasing O RINGS seis nadia an a EEEE A TEE 131 6 2 5 2 Accessing Other
21. 2 13 in outer window and 50 mm 2 in inner window Outer clear fused quartz 99 IR transmittance Inner IR absorbing with narrow band visible light transmittance Optical resolution microscope 7 1 zoom 4 um 16 1 zoom 4 um Selectable equipment TABLE 1 4 Optical Maximum sample size overall Up to 51 mm 2 in SH 1 25 G grounded sample holder Up to 32 mm 1 25 in and 475 K SH 1 25 I isolated sample holder Up to 32 mm 1 25 in and 400 K SH 1 25 C coaxial sample holder Up to 32 mm 1 25 in and 400 K SH 1 25 T triaxial sample holder Up to 32 mm 1 25 in and 400 K SH 2 00 G grounded sample holder Up to 51 mm 2 in and 475 K SH 2 00 C coaxial sample holder Up to 51 mm 2 in and 400 K SH 2 00 T triaxial sample holder Up to 51 mm 2 in and 400 K Selectable equipment TABLE 1 5 Sample holder a akeShore www lakeshore com 4 CHAPTER 1 Introduction 1 4 Standard Equipment Flow cryostat 4 2Kto475K Sample stage temperature sensor Lake Shore Model DT 670 SD 1 4H calibrated silicon diode Sample stage heater 50W Cooled radiation shield and cooled IR absorbing window above the sample Radiation shield temperature sensors Three Lake Shore Model DT 670C CU silicon diodes Radiation shield heaters Two 100 W and one 50 W Removable top lid with viewport G50 mm 2 in window Temperatur
22. 340 A Calibrated 1 50W 500 Banana plug 4K shield stage stage2 Silicon diode Model 340 B DT 670 2 100 W 25Q BNC 1 Radiation shield stage3 Silicon diode Model 332 A DT 670 2 100 W 250 BNC 2 Shield stage stage 4 Silicon diode Model 332 B DT 670 1 50W 500 Banana plug Probe arm Platinum Model 340 C PT 100 250 Model CPX Probe Station TABLE 4 1 Temperature controller configuration 4 5 7 Temperature Control Summary 103 Model 332 loop 1 Model 332 loop 2 Model 340 loop 1 Model 340 loop 2 Power up Off Off Disabled Disabled Control mode Manual PID Manual PID Closed Closed Filter Off Off Max temperature 475K 380K Max heater current 1A Setpoint ramp off off off off TABLE 4 2 Model 332 and 340 initial settings Maintaining 5 A Cooling sample Returning Refrigerator sample Sample stage A 7 ooon SE areen bas Operating sample stage with refrigerator to4 2K RRE 4 2K stage 6 K and up remaining to room i 42Kto6K refrigerator cold temperature 5 to 9 turns Z turnsopen Foot valve a 2 turns open 3 to 4 turns open 4K shield stage 2 turns open Closed ope 4 3t04 4 K TRE Dewar pressure 34 kPa 5 psi 28 kPa 4 psi 28 kPa 4 psi 28 kPa 4 psi 28 kPa 4 psi 6 89 kPa 1 psi A i Micrometer 6 to 8 turns 6 turns open settings ee 1 to 3 turns 1 to 3 turns
23. 5 K to 475 K GSG microwave probe with semirigid coaxial cable 1 5 Kto 475 K Temperature control heaters Sample stage 50W Radiation shields Two 100 W and one 50 W Probe arm Measurement only Selectable equipment TABLE 1 1 Temperature Travel X axis 51mm 2in Y axis 25 mm lin Z axis 18 mm 0 7 in Translation scale X axis 20 um Y and Z axes 10pm Planarization 5 Sample stage sample holder 7 5 5 in plane rotation Included with microwave probes TABLE 1 2 Probe arm adjustments 1 3 3 Frequency Range 1 3 4 Optical 1 3 5 Sample Holder 1 3 3 FrequencyRange 3 ZN50 DC RF probe frequency range Tungsten with cryogenic coaxial cable 0 to 50 MHz Tungsten with semirigid coaxial cable Oto 1GHz Paliney 7 with cryogenic coaxial cable 0 to 50 MHz Paliney 7 with semirigid coaxial cable Oto 1GHz BeCu with cryogenic coaxial cable 0 to 50 MHz BeCu with semirigid coaxial cable Oto 1GHz GSG microwave probe frequency range Low frequency with K connector 0 to 40 GHz Mid frequency with 2 4 mm connector 0 to 50 GHz High frequency with 1 85 mm connector 0 to 67 GHz Selectable equipment 21 gt 10 dB up to 1 GHz except for a 40 dB spike between 400 MHz and 800 MHz depending on probe model and placement 11 lt 3 dB up to 1 GHz TABLE 1 3 Frequency range Optical viewport located on top lids O54 mm
24. FIGURE 2 22 left is an image of the same device illuminated with a coaxial light Its flat two dimensional appearance and low contrast result from all of the light coming from the axis of the microscope It would be difficult to properly land a probe using this image FIGURE 2 22 Left Uneven surface through a Zoom 70 with a coaxial light Right Uneven surface through a Zoom 70 witha ring light 2 3 7 Turbo Pumping System PS V81DP Aturbo pumping system is required to properly evacuate the probe station s vacuum chamber Chamber vacuum lt 10 3 Torr at room temperature is required for the CPX to operate within specifications Lake Shore offers turbo pumping systems as the PS V81DP option for the CPX The components and specifications for these pumping stations are listed in TABLE 2 2 Pumping systems can also be sourced locally Turbo pumps with similar base pressure and pumping speed to those listed in TABLE 2 2 are recommended A vacuum line and fittings to adapt the pump system to the CPX probe station s NW 40 vacuum isolation valve must also be provided Lake Shore recommends using a turbo pump controller with safety interlocks to improve usability of the probe station and prevent accidental damage to the probe station and pump Lakeshore www lakeshore com 32 CHAPTER 2 System Overview 2 3 8 High Vacuum Option PS HV CPX 2 3 9 2 K Base Temperature Option PS LT Model CPX Probe Station Model and type Varia
25. FIGURE 5 19 6 Pullthe feedthrough and its attached optical fiber out of the probe arm Handle the fragile optical fiber carefully it should not be bent sharply or it may break 7 Ifyou are changing probe types remove the feedthrough extension and probe mount as necessary 5 3 7 2 Installing an Optical Fiber Assembly The optical fiber assembly includes the optical fiber terminations and feedthroughs To remove the optical fiber reference section 5 3 7 1 Follow this procedure to install an optical fiber assembly onto a probe arm assembly The procedure includes steps for installing the optical fiber probe mount 1 Orient the probe mount so the probe mount braids and braid blockare down 2 Slide the dowel end of the probe mount all the way into the probe arm The brass body of the probe mount should touch the copper end of the probe arm 3 Using the 1 5 mm hex driver secure the probe mount to the probe arm by tightening the probe arm set screws FIGURE 5 16 El akeShore www lakeshore com 124 CHAPTER 5 Advanced Operation FIGURE 5 16 Secure the probe mount to the probe arm 4 Lightly grease the feedthrough o ring FIGURE 5 17 and place it in the groove 5 Using the 2 5 mm hex driver attach the feedthrough extension to the probe arm base with four M3 screws FIGURE 5 17 6 Lightly grease the extension o ring and place it in the groove Do not loosen the nut between the cable and the flange FIGURE 5 17 F
26. Failure to vent large quantities of vaporized cryogen can result in a loss of consciousness or death Vaporizing cryogen displaces oxygen in its vicinity presenting an asphyxiation hazard There is a risk of oxygen deficiency if the oxygen level falls below 19 5 3 2 2 4 Safety Compliance The system is designed to be used in a laboratory environment therefore safety testing is done to laboratory standards For the CE mark normal use is defined as indoor use altitude to 2000 m temperature between 5 C and 40 C maximum relative humidity of 80 at 31 C and air quality pollution degree 2 nonconductive pollution of the sort where occasionally a temporary conductivity caused by condensation must be expected Electrical power is required for the operation of the instrument console vision system turbo pumping system and optional air compressor Most equipment is designed to operate over a range of line voltages Some equipment must be configured to operate at a specific voltage within the range listed This equipment is configured at Lake Shore to the voltage specified when the equipment is ordered Refer to section 6 4 1 for additional information on power requirements and configuration options The electrical equipment can be grouped as shown in TABLE 3 1 to distribute the system power requirements over multiple facility circuits TABLE 3 1 details the operational power requirements for each circuit The turbo pumping station and air c
27. Maximum relative humidity 80 for temperature up to 31 C decreasing lin early to 50 at 40 C Power supply voltage fluctuations not to exceed 10 of the nominal voltage Overvoltage category Il m Pollution degree 2 Ground the Instrument To minimize shock hazard the instrument is equipped with a three conductor AC power cable Plug the power cable into an approved three contact electrical outlet or use a three contact adapter with the grounding wire green firmly connected to an electrical ground safety ground at the power outlet The power jack and mating plug of the power cable meet Underwriters Laboratories UL and International Electro technical Commission IEC safety standards Ventilation The instruments have ventilation holes in its side covers Do not block these holes when the instruments are operating Do Not Operate in an Explosive Atmosphere Do not operate the probe station in the presence of flammable gases or fumes Opera tion of any electrical instrument in such an environment constitutes a definite safety hazard Do Not Substitute Parts or Modify Instrument Do not install substitute parts or perform any unauthorized modification to the probe station Return it to an authorized Lake Shore Cryotronics Inc representative for ser vice and repair to ensure that safety features are maintained Cleaning Clean only as directed in section 6 2 El akeShore www lakeshore com 10 CHAPTER 1 Introduction Dir
28. O RINGS eee ce eee e ence eee ee en eee eee enna 132 6 2 6 Cleaning the Sample Holder cece ccc ccc cece eee e nn es 132 6 2 7 Cleaning BeCu Probe TIPS 0 ce cece cece cece ete eee e eee e eens 133 6 2 8 Cleaning Microwave Probe Points cc cece eee cece eens 134 6 2 8 1 General Cleaning cece cece cece eee eee eee eee tenet ee ens 134 6 2 8 2 REMOVING Oxidation eee cece cent een eee EEANN 134 6 2 9 Probe Arm Maintenance ec cece cece eee e eee e eee ees 134 6 2 10 Vacuum Pump Maintenance cece cece eee e eee eeenen ne ees 135 6 2 10 1 Turbo PUMPS 4605528 eirrsancestena GEENA EE AERE EEDA 135 6 2 1 0 2 SEroll PUMPS precei ein eds x ite ie alg es Mine Gia eee a 135 6 2 10 3 Rotary Vane PUMPS cece cece eee eect eee en ene e ene e ened 135 6 2 10 4 Oil Mist Eliminators 2 0 0 0 cece cece e eens 135 6 2 10 5 Diaphragm PUMPS 0c cece t naka EE EEEE ERRARE NES 135 6 2 11 Pumping out the Transfer Line cece cece e cece eee e ene 135 6 2 12 Removing Condensation from Inside the Vacuum Chamber 137 6 3 Troubleshooting Procedures cece cece cece eee e eee e eee ees 138 6 3 1 Vacuum Troubleshooting 0 0 cece cece eee eee e eee EKARA TEREE 138 6 3 1 1 Test the Turbo Vacuum Pump Alone 0 c cece cece eee e eee 139 6 3 1 2 Test the Vacuum Pumping System Along with the Connection to the Probe Station
29. PS PLVI 25 oo ccc cece cece cece een eee e eee e eens 70 3 4 4 2 Assembling the Low Temperature Option PS LT 66 70 3 4 4 3 Assembling the Pneumatic Vibration Isolator PS PVIS 70 3 4 4 4 Assembling the Oil less Air Compressor PS OAC 2565 71 3 4 4 5 Assembling the Liquid Nitrogen Dewar PS LN2 005 71 3 4 4 6 Assembling the Dewar Pressure Controller PS DPC 71 3 5 Installing and Removing Probes ccc cece tittet tiskt eee oT KEAS NES 71 3 5 1 Probe Anchoring and Probe Temperature 0 00 c cece eee ee eee ee eee ee 71 3 5 2 Installing a Probe Prep Instructions for All Probe Types 00 0 eee 72 3 5 3 Installing a ZN50 Probe 2 cece cece ence eee en eee e eens 72 3 5 3 1 Install the ZN50 Probe Mount cee cece cece e eens 72 3 5 3 2 Install the ZN50 Probe Blade cece cece eee e eee ees 73 3 5 4 Removing a ZN50 Probe 6 ccc eee cece eee e eee e teen eee e enna 75 3 5 4 1 Removing the ZN50 Probe Blade ccccec cece eee eee e eens 75 3 5 4 2 Removing the ZN50 Probe Mount cc cece cece cece eee eee e ees 76 3 5 5 Installing a Microwave Probe 2 cece cece cece eee e eee n eens 77 3 5 6 Removing a Microwave Probe 6 ccc cece cece cece e eee eee e eee e eens 79 3 6 System Verification and Testing c eee eeeee cece cece e tenet eee eeennaeees 79
30. See TABLE 4 4 8 to 10 turns open valve open leave open Dual valve Not used Not used Open at base temp Not used Not used Not used Exhaust valve Not used Not used Not used Not used Y4 to 1 turn open Not used Sample stage Heater range Off Off Off See TABLE 4 4 Off 50W Nominal power See TABLE 4 4 100 4K shield stage i p Heater range off off off off off On 100 W rca tas Nominal power T _ 100 control 35 g Shield stage settings Heater range off off off off off On 100 W Nominal power 100 2nd shield stage Heater range off off off off off High 50 W Heater range 100 Higher rates of cryogen flow will shorten refrigerator cooldown time at the expense of more cryogen consumption Do not close the micrometer value completely as this may cause it to freeze closed TABLE 4 3 General mechanical and electronic control settings Sample Stage 6Kto10K 10Kto30K 30 K to 100 K 100 K to 250K 250 K to 325 K 325 Kto 475 K Micrometer valve 4 to 6 turns open 3 to 5 turns open 3 to 5 turns open 2 to 4 turns open 2 to 4 turns open 1to 2 turns open Nominal power 50 at 10 K 15 at 20 K 3 at 50K 10 at 200 K 40 at300K 30 at400K Heater range 500 mw SW 50W 50W 50W 50W Proportional P 250 300 300 175 175 150 Integral 1 75 50 50 20 15 15 Derivative D 0 0 0 0 0 0 TABLE 4 4 6 Kand up mechanical and electronic control settings for the sample stage EL akeShore
31. a period of between ten seconds anda few minutes and the exhaust port sounds as if it is breathing The oscillations almost always settle out when the refrigerator reaches temperature equilibrium If not choose a different Dewar pressure or foot valve operating point and re establish control Considerations when regulating with electronic temperature controls When operating with the electronic temperature controllers the following problems may cause unstable or erratic temperature readings Controller PID parameters are not tuned properly the controller tuning parameters listed in TABLE 4 4 are a good starting point but may need to be modified to achieve optimum control stability based on specific measurement conditions Heater range is important to tuning and also must be set properly Controlling too close to base temperature attempt to control a few kelvin higher in temperature then gradually lower the setpoint to identify the lowest practical electronic control temperature m Electrical noise ground loops and other electrical noise can impact the controller s temperature readings Establishing a high quality sample image can be difficult the first time the probe station is set up or after it has been reconfigured if the proper setup is not followed The electrical mechanical and optical components of the vision system must all be working together properly for the vision system to perform as expected This section will help iden
32. air compressor if used for the vibration isolation system Most equipment is designed to operate over a range of line voltages Some equipment must be configured to operate at a specific voltage within the range listed This equipment is pre configured at Lake Shore to the voltage specified when it is ordered If the probe station is to be operated using a voltage other than the original configuration some items may be reconfigured in the field while others may not In addition some items operate over the entire voltage range without modification Field configurable options are indicated in TABLE 6 2 Refer to the equipment s user manual for more information Voltage Voltage Frequency 3 vorta ORES tolerance range Hz inpue Held VAC 8 configurable 100 Lake Shore Model 332 120 46 10 150 50to 60 Yes temperature controller 220 240 100 Instrument Lake Shore Model 340 120 46 10 190 500 60 Yes Console temperature controller 220 240 100 Lake Shore Model 142 120 gt 750 50 to 60 No amplifier 220 240 Viewera V172SV monitor 100 to 240 432 50 to 60 Universal ee 10010240 96 47 to 63 Universal camera Vision System Microtech A20500 light 100 to120 50 to 60 source 190 No Microtech A20510 light 220 to 240 50 to 60 source Varian V81 AG rack Turbo atalier 100 to 240 210 50 to 60 Universal Pumping Varian SH 100 d Il 100 to 115 a t System ion aa 1084 50t060 Yes vacuum pump 200 to 230
33. and base using section 5 3 4 15 Install the micro manipulated stage using section 5 3 1 16 Attach the braid block following step 5 a c in section 3 5 3 1 17 Before initiating a cryogen transfer test probe arm reach It is very costly and time consuming to initiate cooldown only to find the probe mount braids prevent full probe travel You will need to install the planarization assembly if the micro manipulated stage was not configured with one and you intend to use microwave probes The planariza tion assembly allows the microwave probe to be rotated so that all three points on the microwave probe tip touch the sample at the same z axis position Follow this procedure to install the planarization assembly This section assumes that you have removed any probe from the selected stage to prevent damage to the probe The micro manipulated stage does not need to be removed for this operation 1 Center the probe arm with the y axis micrometer and raise the probe arm fully using the z axis micrometer This allows access to the mounting holes in the side of the probe arm base 2 Using the 3 mm hex driver loosen the four long M4 horizontal screws that attach the bellows to the z axis stage so the probe arm base can rotate FIGURE 5 21 Simply loosen them two to three rotations do not remove them FIGURE 5 21 Loosening the four M4 horizontal screws 3 Remove the lock nut from the end of the planarization assembly 4 Withthe moun
34. and down vertically with a total travel of 18 mm 0 71 in Turning the micrometer clockwise moves the probe down One complete revolution of the micrometer moves the probe 0 5 mm The graduated scale on the outside of the micrometer shows 0 01 mm divisions For those probe assemblies that are shipped with microwave probes planarization rotation of the probe arm is described in section 4 6 4 Installation of the planarization assembly is given in section 5 3 8 4 3 Sample Exchange CAUTION 4 3 1 Opening the Vacuum Chamber and Radiation Shield 4 3 Sample Exchange 85 Z axis micrometer FIGURE 4 2 Micro manipulated stage illustrating the axes This section covers the steps required to load and unload a sample Wear nitrile gloves when handling anything inside the probe station Hand oils will contaminate the surfaces resulting in poor vacuum and thermal performance The probe station should always be stored with the system under vacuum to help prevent contamination and oxidation This section is written assuming the chamber is under vacuum the vacuum pump is turned off and the vacuum isolation valve is closed Follow this procedure to open the vacuum chamber and radiation shield 1 Raise each probe 3 mm to 4 mm above the sample holder using the z axis micrometers 2 Centerall probes using the y axis micrometers 3 Retract all probes away from the sample stage using the x axis hand dials This will provide maximu
35. arm sensor should be monitored when probing a sample above this temperature SMA probe connectors mate with ZN50 series probes 2 Triaxial with ultra miniature cryogenic coaxial cable is for low leakage applications The triaxial signal connector on the probe arm base permits an active guard to be carried to the probe s ceramic blade The outermost contact connects electrically to the chamber to provide a shield The centermost contact is the signal contact and the contact between the signal and the shield is the guard contact The connector s signal to guard resistance is specified at gt 10 GO and is typically gt 50 GQ when itis clean and dry The impact of leakage current on measurement uncertainty is further reduced by proper guarding Teflon insulated ultra miniature cryogenic coaxial cable provides operation up to 50 MHz and 400 K with low thermal conductivity The probe arm sensor should be monitored when probing a sample above this temperature SMA probe connectors mate with ZN50 series probes 3 K connector with semirigid coaxial cable is for high frequency applications The SMA connectors on ZN50 series probes are physically compatible with the K connectors on 40 GHz microwave cables This cable configuration enables ZN50 probes to be used continuously up to 100 MHz and at selected bands up to 1 GHz ZN50 series and 40 GHz microwave probes can be interchanged without rewiring the probe arm Some limitations apply
36. as the convolutions in the bellows and it is difficult for the vacuum pump to remove them On some vacuum systems this problem can be overcome through a bake out process During bake out the chamber is heated to increase the energy in the water molecules so they move away from the surfaces and can be pumped out more quickly The CPX cannot be baked out because its components will not tolerate the high temperatures required However controlled warming and cycle purging can reduce the time it takes to recondition the vacuum chamber To dry out the vacuum chamber and check for damage follow the procedures below 1 Ifthe refrigerator is still cold close the purge valve and vacuum isolation valve to prevent more moisture from entering the system 2 Turn off and properly vent the turbo pump The turbo pump should not be used in this process until all visible water has evaporated from the chamber 3 Allow all stages of the refrigerator to warm to room temperature 300 K The temperature controllers can be used for warm up but they should be monitored closely in case any of the sensors were damaged Never heat any part of the probe station refrigerator above room temperature unless the vacuum chamber is under vacuum 4 Remove the chamber and radiation shield lids and sample holder 5 Wait 24 to 48 hours for the system to dry until there is no visual condensation on the inside or outside of the vacuum chamber Asmall fan or heat lam
37. be taken not to damage probes or cables by attempting to mate them improperly 2 92 mm plug socket FIGURE 2 33 K type 2 92 mm connectors published mode free to 40 GHz 2 4mm socket FIGURE 2 34 2 4mm connectors published mode free to 50 GHz plug socket FIGURE 2 35 V type 1 85 mm connectors published mode free to 67 GHz A microwave probe cable consists of a microwave semirigid coaxial cable with connectors permanently mounted on each end The center conductor is the signal path and extends to the center point on the probe tip The outer conductor is the reference ground path and extends to the two outer points of the GSG probe tip The outer conductor is also electrically connected to the microwave probe body so the measurement reference ground is electrically connected to the refrigerator through the probe mount braids Keep in mind that this electrical connection may be broken if desired by removing the anchors from the CPX 4 K shield stage however please note that this will also remove the thermal connection 2 5 3 Pad Construction and Impedance Matching 2 5 3 Pad Construction and Impedance Matching 47 The three points of a GSG microwave probe tip extend the 50 Q impedance of the semirigid transmission line down to the test substrate The landing pads on the measurement substrate should be 50 Q impedance coplanar waveguide structured If the substrate being tested has an impedance of something o
38. building on the knowledge and experience gained performing those operations explained in Chapter 4 Section 5 3 explains reconfiguration procedures that are not typically performed on a day to day basis but which are nonetheless essential to know The material in this chapter is written assuming that the user is an experienced oper ator of the CPX and understands the theory and operation of the CPX as discussed in Chapter 4 Wear protective gloves when performing the procedures in section 5 2 1 and in section 5 2 2 Various components of the probe station that you need to handle for these proce dures will be extremely cold Even when following good vacuum practices with well maintained equipment a small amount of residual gas remains in the vacuum chamber after it is evacuated The residual gas consists primarily of nitrogen and water vapor It is generally of little concern because it is cryopumped onto the refrigerator when it is cooled with helium However problems may occur with some materials if the residual gas condenses on the sample surface The following procedure is a simple but effective way to minimize the condensation onthe sample This is accomplished by cooling the 4 K shield stage first so that the majority of residual gas is attracted to it and not the sample If the sample stage is heated above 100 K and needs to be cooled again you will need to perform only steps 6 and 7 of this process Follow this procedure to reduc
39. case never force one of the controls or damage to the probe or refrigerator may result Instead remove the vacuum chamber lid and radiation shield section 4 3 1 and identify the restriction before proceeding The probe arm translation stage has a greater range of motion than is accommodated by the CPX sample stage and radiation stages When moving the probe beyond the opposite end of the sample holder take precautions to ensure nothing interferes with the probe or you may risk damaging the probe tip The following translation stage controls are used to position the probe Please note that these instructions apply only to stages like the one pictured in FIGURE 4 2 Other probe station models will operate differently The X axis hand dial is used to move the probe in and out in the probe arm axis witha total travel of 51 mm 2 in Turning the hand dial clockwise moves the probe toward the sample The graduated scale on the side of the stage shows 1 mm divisions The graduated scale on the hand dial shows 0 02 mm divisions The Y axis micrometer is used to move the probe from side to side along the plane of the sample perpendicular to the probe axis with a total travel of 25 mm 1 in Turning the micrometerclockwise moves the probe to the left One complete revolution of the micrometer moves the probe 0 5 mm The graduated scale on the outside of the micrometer shows 0 01 mm divisions The Z axis micrometer is used to move the probe up
40. connection or earth safety ground 3 AC noise can enter the measurement through electrical or magnetic coupling even when the leads are isolated Shielding section 2 4 1 3 and sample isolation section 2 4 6 2 should also be considered 2 4 7 Measuring Low Resistance 2 4 8 High Impedance Low Leakage Measurements 2 4 7 Measuring LowResistance 41 2 4 6 2 Sample Isolation for Low Noise Measurements Even with proper setup and isolation of the electronics it is sometimes impossible to reduce their interference with the sample when it is mounted on a grounded sample holder One solution is to use an optional coaxial sample holder to isolate the sample from the grounded refrigerator and vacuum chamber The FT BNC feedthrough and cable configuration can be used to bring a clean measurement ground reference directly to the sample plane This configuration can both isolate and shield the sample see FIGURE 2 28 2 4 6 3 Additional Considerations for Low Noise Measurements When designing a small signal or low noise experiment it is important to consider more than the electronics There are environmental factors that can limit measurement quality as well Three of the most common are 1 Contact quality poor probe to sample contacts can cause noise drift and poor repeatability in measurements Refer to section 2 6 for information on how to improve contact quality 2 Temperature stability the sample temperature changes relatively slowl
41. death or damage to the probe station CAUTION O CAUTION a CAUTION 4 5 Temperature Operation 4 5 1 Basic Cryogen Handling AWARNING AWARNING ATT Te CAUTION 4 5 2 Controls for Temperature Operation 4 5 Temperature Operation 95 Never purge the chamber unless all stages of the refrigerator are above 100 K Never vent the chamber to atmosphere unless all refrigerator stages are above 290 K Follow this procedure to purge the vacuum chamber This process assumes the turbo pump has been properly shut down according to section 4 4 3 1 Attacha dry nitrogen or inert gas line to the purge valve We recommend you purge to dry nitrogen instead of purging to air in order to increase and maintain the pumping efficiency of the system 2 Regulate the gas pressure to 6 89 kPa to 13 79 kPa 1 to 2 psi 3 Open the purge valve slowly In about one minute the pressure relief valve on the chamber will open and release gas If the system is going to be opened for sample exchange remove the vacuum chamber lid with the gas flowing The dry inert gas will prevent atmospheric air from entering the chamber this will speed vacuum pump down times Close the purge valve when the vacuum chamber lid is replaced If it needs to remain open for an extended period of time replace the chamber lid and shut the gas off This section describes basic temperature operation of the probe station advanced temperature operation will be discusse
42. displayed The flexible stainless steel vacuum line should immediately begin to stiffen The vacuum gauge should begin reading in approximately 3 min The turbo pump should reach full speed in approximately 5 min The chamber should pump below lt 10 3 Torr in approximately 30 to 60 min If it does not refer to section 6 3 1 8 for troubleshooting At this point in the process operation of the vacuum pump and isolation valve are dependent on the intended application Follow this procedure to shut down the turbo pumping system This procedure assumes that the system is sealed and under vacuum 1 Close the vacuum isolation valve 2 Press the stop button on the vacuum turbo pump controller to disengage the turbo pump 3 Switch the scroll pump knob from position 1 to position O to stop the roughing pump 4 Openthe manual vent valve located on the side of the turbo pump to vent the turbo pumping system In order to increase the lifetime of the turbo pump it is always recommended to vent the pumping system through the manual vent valve and not simply allow atmospheric air to rush into the inlet 5 You will hear hissing as the manual vent valve is opened and air rushes into the turbo pump Once the hissing ceases completely close the manual vent valve It is acceptable to leave the main power rocker switch in the on position when not operating the vacuum pumping system Remember you will always need to purge the vacuum chamber and ope
43. from the instrumentation This isolation is sufficient for most probe station applications Additional precautions may be necessary for very low noise measurements see section 2 4 6 The most common DC configuration consists of BNC signal connectors ultra miniature cryogenic coaxial cable and a grounded sample holder The grounded sample holder provides a direct electrical and thermal contact to the sample stage This is the most basic measurement configuration and it suits the needs of many DC research applications FIGURE 2 25 El akeShore www lakeshore com 38 CHAPTER 2 System Overview Coaxial BNC signal connector Cryogenic I coaxial cable m E h E ee eee SR O OOOO OOST ccc ZN50 Grounded probe sample holder Probe Probe arm shield e arm ee base AAAI e CONDUCTOR _ Sample stage Thermal ZA yl anchors 4K shield stage S77 Radiation shield stage S77 Second shield stage S77 Vacuum chamber base 19 pin Totemperature Shield connector controller chassis FIGURE 2 25 Basic configuration for DC measurements 2 4 3 Basic RF Electrical RF measurements can be made with similar configurations described for DC Measurements measurements in section 2 4 2 RF measurements are typically configured with either a BNC signal connector with ultra m
44. increase the signal voltage above the noise floor However in cryogenic systems like the CPX this can lead to unwanted heating of the sample AC measurement techniques like those used in lock in amplifiers are preferred in cryogenic applications because they can separate the signal from noise without excessive current Lake Shore offers the industry leading Model 370 AC resistance bridge for this and other low power resistance measurements For the ultimate low noise performance the optional Model 3708 preamplifier for the Model 370 has an input noise specification of 2 nV VHz The CPX can accommodate resistance measurements greater than 100 GQ but not without special consideration given to probe station configuration and external electronics High impedance measurements are difficult for several reasons The current used to excite the sample must be very small so even tiny amounts of leakage current can create a large percentage reading error High resistance lead arrangements are more susceptible to environmental fields which easily induce current noise Probe to sample contacts are difficult to establish and verify ES akeShore www lakeshore com 42 CHAPTER 2 System Overview Model CPX Probe Station 2 4 8 1 Grounding and Shielding Ageneral discussion of grounding and shielding is in section 2 4 1 These concepts become more important for high resistance measurements High resistance samples do not short circuit induced noise the w
45. installing semirigid 121 removing coaxial cable 119 removing semirigid 121 ZN50 DC RF cables 5 cables installing semirigid 121 calibration substrate 8 27 48 coaxial cables reconfiguration 119 connectors microwave 45 cooldown 75 foot valve control knob 96 pressure regulator 96 with helium 98 cooldown mechanical and electronic control settings 103 crogenic transfer 98 cryogen Dewar 16 18 33 handling 95 pressurizing 57 space requirements 54 cryogen Dewar handling 95 cryogen requirements 57 Hlndex D DC measurements 37 DC RF ZN50 probe configurations 23 DC RF measurements 35 small signal low noise 40 device characterization requirements 39 Dewar pressure controller 33 E electrical measurements 35 voltage limits 44 environmental requirements 55 F fiber optic probe 23 fiber optic probe probe arm modification 27 G gas requirements 57 ground loops 36 grounded sample holder 28 36 37 cleaning 132 grounding 35 36 high impedance measurements 42 vacuum chamber 35 grounding instrument console 35 ground signal ground 6 25 45 77 guarding 42 configurations for 42 l installation 53 coaxial cable 119 semirigid cable 121 translation stage 113 installation optical fiber 123 installation probe arm and base 118 installing microwave probes 77 installing probes 71 instrument console 20 21 grounding 35 power requirements 153 unpacking 62 verification 79 wiring 154 instrument console power
46. located where it can be contaminated with debris Other o rings will require routine maintenance only if their seal is broken regularly to reconfigure the probe station 6 2 5 1 Re greasing O Rings Follow this procedure to re grease o rings Wear nitrile gloves during this procedure 1 Remove the o ring using the plastic o ring removal tool provided in the tool kit 2 Clean off any old grease with a lint free wipe and isopropyl alcohol 3 Clean the o ring groove and mating surface with a lint free wipe and isopropyl alcohol 4 Inspect for small cuts or nicks replace immediately if found Inspect for excessive flattening replace immediately if found 6 Place asmall amount of high quality vacuum grease such as Apiezon N grease on one gloved finger Run the o ring through your fingers until the entire surface is lightly coated Remove any excess grease 9 Replace the o ring in the o ring groove do not allow the o ring to twist in the groove oa fo N El akeShore www lakeshore com 132 CHAPTER 6 Maintenance and Troubleshooting 6 2 6 Cleaning the Sample Holder AWARNING Model CPX Probe Station 6 2 5 2 Accessing Other O Rings The o ring on the vacuum chamber lid is easy to locate This section describes the location of the other o rings in the system if you need to access them for maintenance or service Viewport window the viewport window is sealed to the vacuum chamber lid with an o ring Bellows there is a
47. maintenance The oil level in a rotary vane pump should be checked at least every three months Insufficient oil will cause catastrophic failure of the pump If the oil level is low add only the type of oil recommended by the pump manufacturer Do not overfill the oil reservoir Overfilling may cause oil to exhaust from the pump or shorten the service life of the pump The oil in a rotary vane pump should be changed regularly The time between changes varies based on hours of use and the type of gases being pumped The oil itself can be an indicator of when it needs to be changed The oil turns darker with use and should be changed when it becomes noticeably darker than new oil It is a good idea to have oil filled pumps on an annual preventive maintenance schedule for oil change 6 2 10 4 Oil Mist Eliminators The exhaust of a rotary vane pump is often fitted with an oil mist eliminator filter There are a variety of oil mist eliminators that may or may not include an inspection view port or replaceable filter element If the eliminator is not serviced or replaced regularly oil will exhaust from the pump Consider scheduling service or replacement of the oil mist eliminator when the pump oil is changed 6 2 10 5 Diaphragm Pumps On smaller probe stations diaphragm pumps can be used as fore pumps for the turbo pump however even on smaller probe stations the seals in the pump wear down and should be replaced periodically Always follow the
48. manufacturer s recommendations to reduce potential down time The transfer line requires regular service approximately every 12 months or whenever it becomes soft section 6 3 2 More frequent service may be required when using liquid nitrogen because nitrogen does not cryopump the line as well as helium El akeShore www lakeshore com 136 CHAPTER 6 Maintenance and Troubleshooting An evacuation adapter is delivered with the transfer line to adapt the pump port on top of the transfer line to an appropriate vacuum pumping system The transfer line should be pumped with a turbo pump The Lake Shore Model PSV81 DP or equivalent pump you use to pump out the probe station vacuum chamber will be sufficient for this process It is also recommended that you check the transfer line for leaks as it is pumped if a leak detector is available to eliminate the possibility that a leak is the cause of the poor vacuum If the necessary pumping and leak checking equipment is not available on site the transfer line can be sent back to Lake Shore for service Otherwise follow this procedure to pump out the transfer line 1 Attach the evacuation adapter to the evacuation port on the transfer line FIGURE 6 2 2 Tighten the fitting nut using a 11 4 in wrench 3 Attach one end of the vacuum line to the port on the vacuum system and the other end to the NW 16 evacuation adapter 4 Pushin the plunger on the evacuation adapter and turn it clockw
49. needs to be cooled back down to a lower operating temperature The valve allows back pressure in the 4 K shield stage cryogen flow path to force cryogen into the sample stage Otherwise the warmer sample stage may block the flow of cryogen 4 5 2 2 Electronic Temperature Controls Model 340 and Model 332 temperature controllers provide the electronic control of the CPX refrigerator temperature They work with a Model 142 auxiliary amplifier which provides additional heating power The Model 340 and 332 operate a total of four closed loop PID proportional integral derivative control loops refer to Chapter 2 of the instrument manuals for details Each refrigerator stage includes a temperature sensor which is the control input for each loop and a heater which is the control output for each loop The controller balances its heater power against the cooling power of the cryogen flowing through the refrigerator at a desired temperature setpoint Since the controller cannot contribute cooling power the setpoint must be higher in temperature than the base temperature of the refrigerator for the controller to operate properly EL akeShore wwwiakeshore com 98 CHAPTER 4 Basic Operation CAUTION 4 5 3 Cooling the Probe Station with Helium Model CPX Probe Station If the controller is configured improperly the controller can provide enough heat to damage the refrigerator The controllers are configured at Lake Shore as describ
50. of this tube to your gaseous helium or nitrogen source capable of 68 9 kPa 10 psi 5 Connect the outlet to the vent port on the Dewar 6 Consult the pressure controller manual for further information Probes are installed at the ends of probe arms inside the chamber The chamber and radiation shield must be opened It may also be helpful to remove the sample holder to make more room to work inside the chamber The probes are packaged separately to protect the delicate tips Do not touch the tips Do not handle the alumina blade or the electrical conductors on the ZN50 probe with bare hands as this may reduce its isolation Wear nitrile gloves while changing blades In the CPX probe station the probe mount braids can be anchored to either the sample stage or the 4 K radiation shield stage FIGURE 3 20 The decision for which location to use can be made based on the specific application Thermally anchoring to the 4 K stage maintains the probes near the temperature of the 4 K shield stage while anchoring to the sample stage allows the probes to change with the sample temperature For most applications a probe cooled to or below the sample ES akeShore www lakeshore com 72 CHAPTER 3 Installation and Setup 3 5 2 Installing a Probe Prep Instructions for All Probe Types 3 5 3 Installing a ZN50 Probe SMA connector Model CPX Probe Station blade temperature is desired Therefore we recommend t
51. on the probe station The valve has two potential uses during operation It can be used to help maintain the cleanest possible vacuum in the chamber as described in section 4 4 1 2 and it allows separation from the pumping system to reduce vibration during cryogenic operation In the sequence of operations the vacuum isolation valve can always be opened safely if the vacuum level on each side of the valve is the same Manual Turbo Vent Valve turbo pump performance relies on precision blades that must be kept in balance at all times The vent valve on the turbo pump is used to vent the pump system while keeping the blades in balance The precision blades can be damaged if the pump system is vented through the turbo pump inlet by opening the vacuum isolation valve m Automatic Turbo Vent Value some turbo pump systems are programmed to automatically vent when they are turned off or lose power A few seconds after the pumping system is powered off an automatic valve will backfill room air through the pump safely venting the pump system and shutting the turbo pump down However ifthe pump vents while the refrigerator is cold water vapor will condense on the refrigerator and freeze into damaging ice It can take approximately a week to return the probe station to proper working order if this does happen please refer to section 6 2 12 Itis possible that the refrigerator may suffer irreparable damage Close the isolation valve when the ref
52. on the vacuum chamber Lake Shore offers the PS V81DP for evacuating the chamber Components and specifications for these options are in section 2 3 7 You should use these specifications as a guideline if you purchase the pumping system separately If you do not purchase the turbo pumping system option with the probe station you will need to provide a calibrated vacuum gauge during installation to verify vacuum levels For Operation Below 4 2 K a vacuum pump is also necessary when cooling the sample stage below 4 2 K However the turbo pumping system recommended for the vacuum chamber is not suitable for this application Lake Shore offers the PS LT option for CPX operation down to 2 K The PS LT option includes the pump lines and valves necessary to operate the system safely Components and specifications for the option are in section 2 3 9 Purchasing the PS VLT option in addition to the PS LT extends the base temperature down to 1 5 K The Lake Shore PS PLVI 25 pump line vibration isolator or equivalent is recommended when using the PS LT option Dewar Pressure most Dewars will not self pressurize sufficiently to provide the 4 5 liquid L h maximum cryogen flow rate of the probe station Room temperature bottled gas is commonly used to pressurize cryogen Dewars Typically helium gas is used to pressurize helium Dewars and nitrogen gas is used to pressurize nitrogen Dewars El akeShore www lakeshore com 58 CHAPTER 3 Installation and
53. out as is common in UHV applications or environ ments The sensors and associated wiring will not tolerate the high temperatures involved See section 6 2 12 for an alternative to baking out Follow this procedure to operate the CPX sample stage with inert gas 1 Thermally anchor all probes to the 4 K shield stage section 3 5 1 2 Use the z axis micrometers to raise all probes 3 mm to 4 mm above the sample Failure to do so will potentially cause damage to the probe tip or scratch the sam ple surface 3 Evacuate the vacuum chamber using the procedure in section 4 4 2 4 Leave the vacuum isolation valve open and the turbo pump running throughout this process 5 Close the micrometer valve to establish zero and then open it counterclockwise and six turns Install the exhaust valve assembly onto the exhaust port on the bayonet Close the exhaust valve completely Insert a 9 5 mm 3 in adapter tube into the bayonet Attach tubing from the adapter tube to the pressure regulator of an inert dry gas source helium or nitrogen 10 Set the gas pressure regulator to approximately 7 kPa to 14 kPa 1 to 2 psi 11 Turn on the gas flow Oo MND The sample stage can now be heated to the desired temperature using the tempera ture controller Some experimentation may be necessary to find the best setting of gas pressure and control settings Monitor the 4 K shield stage to ensure that it does not exceed 380 K or 350 K when using
54. outside of the probe station first remove the probe mount mount aes section 3 5 4 2 and then follow steps 5 8 in this section 7 P 1 Follow the procedure in section 3 5 2 2 Disconnect the SMA connector The strain relief to the SMA connector on the cryogenic coaxial cable must be held in place with tweezers or your fingers while removing the SMA plug FIGURE 3 23 J FIGURE 3 23 Disconnect the SMA You only need to loosen the screws in steps 3 5 Do not remove them This will keep them from dropping into the chamber a akeShore www lakeshore com 76 CHAPTER 3 Installation and Setup Model CPX Probe Station 3 Using the 1 5 mm hex driver loosen both of the M3 probe arm set screws two to three turns FIGURE 3 24 to rotate the probe to access one of the probe mount set screws FIGURE 3 24 Loosen the probe arm set screws Using the 1 5 mm hex driver loosen the visible probe mount set screw FIGURE 3 25 Rotate the probe mount to access the set screw on the other side of the probe mount and loosen that screw as well Gently work the blade up and down to release and remove it Avoid sideways force to minimize the chance of cracking the alumina Remove the blade from the system and place it back into its storage case making sure not to contact the delicate probe tip FIGURE 3 25 Loosening the probe mount set screws 3 5 4 2 Removing the ZN50 Probe Mount 1 If you have not yet removed the blade you wi
55. poor contact uncalibrated response Right Improvement shown in the S parameters after proper planarization and quality contact uncalibrated response 2 6 Contact Quality 2 6 1 Contact Material 2 6 2 Contact Area Model CPX Probe Station The movable probe tip contacts that make probe stations such flexible tools can also lead to poor measurement repeatability if contact quality is poor Low resistance ohmic contacts are the goal for most electrical measurements The following topics should be considered when establishing contacts and testing their quality The most repeatable probe contacts are formed between the metal probe tip anda metal pad patterned on the sample Contacting other materials like bulk semiconductors requires special considerations not covered in this manual Gold plated metal is the most common pad material used in probe station applications but any conductive metal that resists oxidation or reaction with the tip metal can be used to form low resistance contacts Lake Shore offers three probe tip materials that are compatible with different probing applications see section 2 3 2 1 In addition to contact material contact area is a major factor in the ultimate contact resistance Lake Shore offers probe tips with a variety of radii In general a larger tip radius will create a larger contact area but this may not translate to lower contact resistance as several factors dictate how much surface is actually in con
56. requirements 56 al akeShore 157 L landing the probe 105 leakage current 24 41 42 leakage low leakage measurements 41 light source 22 66 104 image quality 149 power requirements 56 153 light source troubleshooting 148 low resistance samples 41 M maintenance 129 probe arm 134 transfer line 135 vacuum pump 135 micro manipulated stage 15 23 microscope 8 22 assembly 64 blurred image 149 connections 66 focus 81 specifications 3 use 104 microwave cables 6 connectors 26 27 microwave compatible cables 26 microwave compatible probes 25 microwave connectors images of 46 microwave measurements 45 calibration 48 contact quality 50 frequency range 45 microwave cables and connectors 45 planarization 49 microwave measurements calibration 48 microwave probe configurations 25 microwave probes 25 care of 134 151 handling 77 image with cable 78 installing 77 removing 79 specifications 2 standard 25 temperature 25 microwave probes specifications 3 Model 142 21 power requirements 153 www lakeshore com 158 INDEX Model 332 21 default settings 103 electronic temperature controls 97 power requirements 153 verifying 80 verifying voltages 79 Model 340 default settings 103 electronic temperature controls 97 power requirements 153 N noise 56 electrical 147 low noise measurements 40 41 reducing 50 60 Hz 36 37 reducing 50 60 Hz noise 37 O opening radiation shield 85 oper
57. specifically recommended because the following procedure requires landing the probe on the substrate and visually verifying landing marks Soft gold plating allows the landing marks to be more visible Planarization assembly FIGURE 4 17 The planarization assembly CAUTION 4 6 4 Usingthe PlanarizationAssembly 107 4 6 4 1 Adjusting the Angle of the Planarization Assembly Follow this procedure to planarize a microwave probe any time it has been serviced or replaced 1 9 Use the z axis micrometers to raise all probes 3 to 4 mm above the sample Failure to do so will potentially cause damage to the probe tip or scratch the sample surface Loosen the four long M4 screws holding the bellows flange to the z axis stage assembly to allow the probe arm base to rotate Loosen them approximately two to three rotations Do not remove these screws Bring the probe close to the surface of the substrate but do not land the probe While observing the probe tip through the microscope turn the differential knob to adjust the angle as shown in FIGURE 4 18 visually noting the three points alignment to the x y plane FIGURE 4 18 Turn the differential knob to adjust the angle Check the angle by landing the probe making contact to a metallic substrate and then raising it again Marks made by the probe points on the metallization can be seen with the microscope at high magnification Repeat steps 4 and 5 until the probe points make t
58. stainless steel flex section Target side leg ra insert in bayonet FIGURE 2 8 Transfer line The transfer line is included with the probe station the following components in sections 2 2 2 2 and 2 2 2 3 are not included with the probe station They are however required for operation of the probe station and must be supplied by the customer El akeShore www lakeshore com 18 CHAPTER 2 System Overview 2 2 2 2 Cryogen Dewar Major features of a typical cryogen Dewar include the Dewar Dewar pressure gauge top withdraw port gas port gas shut off valve low pressure relief valve with shut off valve and high pressure relief valve FIGURE 2 9 illustrates a typical helium Dewar Gas port Gas shut L off valve Shut off valve E T tow a pressure Pressure relief gauge Top withdraw port Dewar t High pressure relief FIGURE 2 9 Cryogen Dewar top view Model CPX Probe Station 2 2 2 Cryogen Dewarand Pressurized Gas System 19 2 2 2 3 Pressurized Gas System The pressurized gas system typically includes the tank output pressure regulator pressure gauges and gas output FIGURE 2 10 illustrates the pressurized gas system Output pressure gauge M Tank pressure gauge Shut off Gas output Output pressure regulator Pressurized gas tank FIGURE 2 10 Pressurized gas system profile El akeShore www lakeshore com 20 CHAPTER 2 System Overview 2
59. that changes significantly with time or is overly sensitive to vibrations Too much pressure will obviously cause probe damage One way to ensure repeatable contact pressure is to monitor the distance the probe tip skates when being landed as described in section 4 6 2 This distance is likely different for each different probe material tip radius and sample material Another approach is to monitor the DC resistance of each pair of probes while landing Tip radius a larger tip radius normally provides a larger area of contact which consequently lowers contact resistance The larger tip can also tolerate slightly higher pressure before being damaged Smaller tips are normally chosen for probing smaller features but they can also be useful in scratching through electrically insulating oxide layers that may form on the sample surface For more information please reference section 2 4 8 Tip material Lake Shore offers several tip materials for different applications Not every tip material is compatible with every sample material For more information please reference section 2 3 2 1 Dirty or damaged tips some tip materials especially BeCu form an insulating oxide when exposed to air Tips also get dirty during normal use Bent or damaged tips generally make very poor electrical contact Clean and inspect probe tips for damage regularly For more information please reference section 6 2 7 El akeShore www lakeshore com 152 CHAPTER 6 M
60. that coaxial and triaxial sample holders contain Kapton insulation any chemicals used must be compatible with this Also for the coaxial and triaxial sample holders temperatures should not exceed 400 K m Tomount puta drop of the photoresist on three pads of the sample holder Center and align the wafer onto the sample holder and bake using the usual specifications for the resist m Toremove you can remove the sample by soaking in chemical remover Grooves in the sample holder permit the remover to flow under the sample 3 Silver paint if an electrically conductive mounting is required silver paint can be used in place of photoresists or VGE 7031 varnish Please note that the paint must be dried completely for best electrical conduction m To mount only a small amount of silver paint is needed for your sample Fora 25 mm Lin sample place a drop of the silver paint on three pads of the sample holder Center and align the wafer onto the sample holder The amount of silver paint used can be increased or decreased for larger or smaller samples respectively Silver paint may be air dried or baked according to manufacturer s recommendations m Toremove you can remove the silver paint by soaking it in acetone 4 3 3 5 Permanent Mounting Permanent mounting is generally considered a last resort if all other methods have failed to give adequate performance These methods generally do permanent damage to the sample sample holder or b
61. the fiber optic bundle m Check that the bulb is centered in the opening If the bulb is out of alignment refer to the light source manual for further information Do not lower or raise the microscope trying to improve illumination This will bring the sample out of the focal range of the microscope 6 3 4 3 Poor Image Quality Troubleshooting poor image quality can be challenging because the symptoms of a variety of problems are very similar The next four sections cover a variety of image quality issues The first three section 6 3 4 4 to section 6 3 4 6 are more likely to cause a blurred image that appears to have good color and contrast but does not focus sharply The causes listed in these sections are relatively easy to diagnose and should be checked first Low contrast images are explained in section 6 3 4 7 This problem is the most difficult to diagnose and is often related to the sample surface and the light source chosen for the system 6 3 4 4 Fog on the Viewport Fog normally indicates that the viewport window needs to be cleaned with an appropriate anti fog solution see section 6 2 4 In severe cases persistent fogging can indicate poor chamber vacuum see section 6 3 1 When checking for fog also check for smudges on the microscope lens or on any of the viewports and clean as needed section 6 2 4 6 3 4 5 Height Adjustment The range of focus of the microscope is quite short as small as 34 um on some systems It is comm
62. the top surface of a clean sample holder You have applied too much grease if the grooves onthe sample holder become filled Apiezon N grease is available from Lake Shore 2 Clamping a small amount of pressure applied with clamps can significantly improve thermal contact between the sample and sample holder Clamping can also be used to improve the effectiveness of grease as a thermal contact Users often make simple clamping fingers to fit their sample and hold them down with M3 screws in the tapped holes intended for the lifter tool 3 Adhesive Tape tape over the corners or edges of a sample with vacuum compatible tape that has a silicon adhesive Experience has proven that 3M brand Kapton tape with silicon adhesive will retain its adhesive properties to as lowas 4 K 4 Double sided Adhesive Tape if there is no room on the top surface for Kapton tape double sided tape can be placed between the sample and sample holder Some experimentation may be required to find a tape that does not harden and peel away at low temperatures With all of the adhesive methods the sample holder top surface can be cleaned with acetone applied to a soft clean cloth then rinsed with isopropyl alcohol Do not use abrasives or scrub the sample holder because the gold plating will be removed 4 3 3 4 Semi Permanent Mounting Semi permanent mounting gives better thermal contact than temporary mounting but it requires more time to mount and remove the sa
63. to its holding location as directed in section 5 3 2 Follow this pro cedure to remove a probe arm and base 1 Usingthe 3 mm hex driver loosen the four long M4 horizontal screws that attach the bellows to the z axis stage FIGURE 5 8 2 Grasp the square end flange of the bellows and with a twisting motion work the bellows end flange off the probe arm base This should be done slowly and with a great deal of control 3 Compress the bellows to make room to slide it carefully off the probe arm When you reach the end of the probe arm you will need to tilt it up to remove it from the probe arm FIGURE 5 8 Place the bellows on a clean lint free cloth or wipe FIGURE 5 8 Left Remove the four horizontal screws that attach the bellows to the z axis stage Right Compress the bellows to remove it from the probe arm 4 Ifyou have a planarization assembly attached to the probe arm loosen the two M3 screws that hold the planarization assembly to the arm base You may need to turn the z axis micrometer to access the screw that is behind the micrometer FIGURE 5 9 The planarization assembly will remain attached to the stage planarization assembly screws rE n FIGURE 5 9 Left Loosen the two screws holding the planarization assembly to the probe arm base Right Pull out the threaded dowels 5 The probe arm base is loosely secured to the z axis stage with two stainless steel threaded dowels Unscrew the threaded dowels and the
64. to three turns 3 Carefully loosen the connector plug from the probe connector socket 4 Grasp the microwave probe between thumb and forefinger on the sides of the probe body 5 Slide the microwave probe off the probe arm 6 Replace the microwave probe back into its storage case Microwave probes should always be returned to the storage case with the foam block holding down the flexible probe mount braids to prevent the braids from coming forward and contacting the delicate tips This section describes a sequence of short tests that can be used to verify that the probe station has been assembled correctly and is in good working order These tests should be done after making changes to the probe station configuration but before cooling down the system The goal is to find small problems before investing the time and resources into cooling the system These procedures assume that the station has been fully assembled as described in section 3 4 The instrument console is a housing cabinet that includes two temperature controllers Model 340 and Model 332 and the Model 142 linear amplifier 3 6 1 1 Verifying Voltages The console is shipped from Lake Shore with user specified line voltage selected Ifthe system is being moved or there is any reason to believe the voltage may not be appropriate for the installation site please verify line voltage settings The Model 332 and the Model 340 both have a voltage selection with the same desig
65. turned on before the fore pump brings the vacuum level down to an acceptable level the turbo controller is designed to prevent this from happening Lake Shore turbo pumping systems are shipped set to the pump manufacturer s factory defaults that work well for probe station operation 4 4 1 1 Vacuum Controls In addition to the obvious power switch configuration on the turbo pumping system there are three more valve controls that need to be understood for proper vacuum operation These are the purge valve vacuum isolation valve and turbo vent valve The purge valve and vacuum isolation valve are located on the probe station vacuum chamber and are always operated manually Some turbo pumping systems include an automatic venting feature for the turbo pump but most are manual Specific instructions for vacuum operation are included in the remainder of this section and section 4 5 General descriptions and recommendations for these controls are given below however your pump manufacturer s recommendations should always take precedence El akeShore wwwilakeshore com 92 CHAPTER 4 Basic Operation CAUTION Model CPX Probe Station m Purge Valve the purge valve shown in FIGURE 4 9 is used to backfill the chamber with dry nitrogen or inert gas It is most commonly used when warming or venting the system m Vacuum Isolation Valve the vacuum chamber and turbo pumping system are separated by the vacuum isolation valve located
66. vacuum chamber with a single 90 degree bend The total length of the microwave cable is approximately 279 mm 11 in Probe station layout inherently contributes some signal loss Lake Shore recommends the following for best performance 1 Calibrate the system as described in section 2 3 8 7 2 Retighten the connectors to manufacturer s specified torque after repeated thermal cycling 3 Keep external cables as short and direct as possible Microwave probes must be specified with the same frequency and connector type as the probe cable TABLE 2 4 summarizes the three microwave probe frequency ranges and associated connectors Highest rated eg comecar mast 40 GHz K type 2 92 mm Standard SMA connectors 50 GHz 2 4mm V 1 85 mm connectors 67 GHz V type 1 85 mm 2 4 mm connectors TABLE 2 4 Microwave probe frequency ranges and associated connectors For reference FIGURE 2 33 to FIGURE 2 35 show plug and socket head on views of the three types of connectors Note that all three types look very similar Side by side differences in the connectors can be seen primarily in the head on view in the thickness of outer conductor and spacing between the inner and outer conductor El akeShore www lakeshore com 46 CHAPTER 2 System Overview CAUTION 2 5 2 Ground Return Path Model CPX Probe Station The connector types are physically similar and can sometimes but not always be interchanged care should
67. valves on the dual valve assembly completely Attach the dual valve assembly to the inlet of the PS LT option vacuum pump Follow the steps in section 4 5 3 to initiate a helium transfer Follow the steps in section 4 5 4 to cool the sample stage to 4 2 K while reducing helium consumption 7 Slowly close the micrometer valve on the probe station until the temperature at the sample stage channel Aon the Model 340 temperature controller has risen to approximately 4 3 K to 4 5 K The gas flow coming out of the flexible stainless vacuum line should be minimal at this point OO WN Flowing too much LHe into the inlet of the PS LT pump can damage the pump Steps 8 to 9 should be done in a quick succession Failure to perform these in quick succession may cause the sample stage temperature to rise making the vacuum pump unable to reduce the temperature below 4 2 K 8 Using protective gloves attach the flexible stainless vacuum line to the dual valve assembly 9 Startthe pump and the sample stage temperature will immediately start to drop 10 Close the sample stage micrometer valve one quarter turn at a time to reduce the temperature to near 2 K 11 With some experimentation the micrometer valve can be used to lower the sam ple stage temperature to the specified 2 K minimum temperature The goal is to reduce helium flow enough that the pump can maintain low vacuum pressure while still maintaining sufficient cooling capacity 12 Use
68. 03 10 105 i f z Time h FIGURE 6 3 Typical CPX pump down curve 6 3 1 Vacuum Troubleshooting 139 6 3 1 1 Test the Turbo Vacuum Pump Alone Before going through an extensive troubleshooting process on the probe station it is advisable to verify proper pump and gauge operation The only components needed for this step are the turbo vacuum pump and an NW 40 vacuum blank off plate The turbo vacuum pump must be equipped with an NW 40 inlet connection anda vacuum gauge capable of reading pressures down to 10 8 Torr FIGURE 6 4 Turbo vacuum pump NW 40 connection Tand gauge 1 With the gauge located on a T at the inlet of the vacuum pump place the NW 40 centering ring blank off plate and clamp over the inlet of the vacuum pump T 2 Ensure the manual vent valve is fully closed 3 Power on the pumping system FIGURE 6 5 shows the PS V81DP control panel The steps to power on the pumping system are a Switch the main power rocker switch to the up position which powers on the entire unit b Switch the scroll pump knob from position O to position 1 to start the roughing pump c Press the start button on the turbo pump controller to engage the turbo pump If the controller is set in remote mode the turbo pump will automatically start and stop with the scroll pump knob FIGURE 6 5 a Main power rocker switch b Scroll pump knob c Start button 4 The turbo vacuum pump should start rotating up to its
69. 2 3 Instrument Console Major instrument console components include the temperature instrumentation and the Model 142 amplifier FIGURE 2 11 illustrates the instrumentation components Storage drawer Lake Shore Model 340 temperature controller Lake Shore Model 332 temperature controller Model CPX Probe Station Power strip Lake Shore Model 142 amplifier Lakeshore o Haese 7S FIGURE 2 11 Instrument console 2 2 3 InstrumentConsole 21 2 2 3 1 Temperature Instrumentation The temperature instrumentation includes two Lake Shore temperature controllers Model 340 and Model 332 and a Model 142 amplifier The instruments are housed in the instrument console FIGURE 2 12 illustrates the temperature instrumentation and provides a summary of the probe station component that is monitored or controlled by each controller input Sample stage Input A Control loop 1 Sensor HT Si diode Heater 50 W Probe arm any Input C Sensor Platinum RTD Radiation shield stage Input A Control loop 2 Sensor Si diode Heater 100 W powered by Model 142 channel 2 4 K shield stage Input B Control loop 2 Sensor Si diode Heater 100 W powered by Model 142 channel 1 8 akeShore 340 Temperature Controller Model 340 temperature controller Second shield stage Input B Control loop 1 Sensor
70. 2 for a test to check this 3 Locate the probe arm temperature sensor cable labeled DCO616 and connect it to the probe arm El akeShore www lakeshore com 64 CHAPTER 3 Installation and Setup 3 4 2 Assembling the FIGURE 3 7 illustrates the assembly of a single post microscope CCD camera and Vision System ring light The vertical post horizontal boom microscope and CCD camera are connected to the CPX baseplate The position of the shaft collar determines the height of the microscope above the sample and may require adjustment after assembly of the vision system S video Monitor cable Color CCD camera Horizontal boom swing arm Pa Hand dial Fiber optic cable Vertical post wee Chamber FIGURE 3 7 Assembly of the vision system onto the probe station 3 4 2 1 Assemble the Vertical Post Follow this procedure to install the vertical post onto the baseplate Depending on the microscope option and probe station model the microscope post will have either one or two shafts The Zoom 70 has one shaft and the Zoom 160 has two 1 Install the microscope vertical post as shown in FIGURE 3 8 To install the post remove the one or two M5 screws in the bottom of the post 2 Align the post so that one of the two screw holes on the vertical post mount is over the hole that is closest to the vacuum chamber The other screw hole will align with the third hole further away from the vacuum chamber 3
71. 27 EL akeShore wwwiakeshore com 78 CHAPTER 3 Installation and Setup Model CPX Probe Station A Eu FIGURE 3 27 Left Misaligned probe Right A properly aligned probe 6 Continue to slide the microwave dowel onto the probe arm until the microwave connector socket aligns with and contacts the connector plug on the semirigid cable The semirigid cable can be gently lifted or pushed to one side or the other to help align the two connectors 7 Carefully start threading the connector plug onto the probe connector socket The probe can be rotated slightly to better align it as you thread Refer to section 5 3 6 3 if the cable length seems inappropriate 8 Ifthe connector is properly aligned it will make good contact simply by finger tightening It is acceptable if the back of the copper probe body is not flush with the copper end of the probe arm Awrench should not be used to tighten the plug onto the microwave probe unless it is a calibrated torque wrench specifically designed for making microwave connections FIGURE 3 28 Microwave probe threaded onto a semirigid cable 9 Once the microwave connector is tight use the 1 5 mm hex driver to tighten both probe arm set screws If the probe body was rotated in order to ease the alignment of the microwave connectors when threading hold the microwave probe body with your thumb and forefinger as you tighten the set screws to vertically align the probe 3 5 6 Removing a Microwa
72. 3 6 1 Console Verification 06 c ccc cece cece e cece eee ne ee een enna 79 3 6 1 1 Verifying Voltages sesks 0 eee ene EEE EREAA HERAA enaes 79 3642 Verify POWEF ON iis cine yess ie ceee ceetinute cada vedas EANET SNRA EEEREN 80 3 6 1 3 Verifying the Model 332 and Model 340 Controllers 80 3 6 2 Temperature Sensor and Heater Test ccc ccc cece cece cece een eee eeees 80 3 6 3 Microscope Light and Focus Test 000 cece cece cece cece ence eee eeeeee ee 81 3 6 4 Testing theProbe Arm Reach cece cece hraki nett ee ee eeneeeeeeeenaes 81 3 6 5 Probe Continuity TeSt cece cece cece eee e eect eee eee ennee een nnaes 81 al akeShore www lakeshore com iv TABLE OF CONTENTS 3 6 6 Vacuum Chamber LeakTest 06 cee eee eee e teen ee nnneeee 82 Chapter 4 4 1 General ccc cccec ccc cececceuseueeueeveeveeveteuteneenetnetneeneentenenreneneees 83 Basic Operation 4 1 1 Common Operational Mistakes ccc cece cece eee e eee e tees nen en eee 83 4 12 Temperature LIMES vised saa scans cho oh tea Range Ahad cate ee TAKERS 83 4 2 Operating the Probe Arm Translation Stages ccceeeeeee cess ene eee tenes 83 4 3 Sample EXChange gvcccsa i nosetter edie cesvawasbhesevsdeieanede EATE TEASTA TANTAS 85 4 3 1 Opening the Vacuum Chamber and Radiation Shield 05 85 4 3 2 Removing the Sample Holder cc cece cece cece eee e eee ee ee teens
73. 45 2 5 2 GrOUNG REtUPA Path secs can rceeecassaaee nes E ANEAN OD T 46 2 5 3 Pad Construction and Impedance Matching eceeeee eee eee e es 47 2 5 3 1 Probe Crosstalk icssieetanwidvans egri epens a ai 47 2 5 4 Calibration with the CS 5 Calibration Standard 00 cece cece eee 48 2 5 5 Temperature Effects of Calibration 0 0 ccc cece cece cece een nen e eens 49 225 6 PlaMALlZAtlO M eseria ia e Ea EEE E EE E EEA 49 2 6 COn t QUIY creser ari ERAAN avivstansintes ed canine beac bane ANRE ARAA LA 50 2 6 1 Contact Maten all wieccosne seater se isnin arion r A ESE SERRE E 50 26 2 CONTIAT A enirir iE E a a A E a e AR EE ENS 50 26 3 OXICAUON korrast reniei hes EEE R RER ETETE TE EE AS 51 2 6 4 Four Lead Measurement s sssssrrssrssrsrerrrrsrrsersrrsresrrrerrrers 51 2 6 5 Ohmic versus Non ohmic Contacts cece cece e ee eee eee eens 51 2 6 6 Measuring Contact Quality 00 cece cece cece nett eee enn eect enna 51 2 6 7 Lab ProtOcGl orrori erorii yoti naeeiae ys etapa wed tye ahanwe teal A E EROARE 51 3 1 Genera recreia trni aa EE sy dea ehernd sash den nes saeue ERETO EARRA 53 3 1 1 Lake Shore Assisted Installation cece cece cece eee e eee e enna ee 53 3 2 Site REGUIFEMENTS face tncnechstadeacadenuginreaeee rah ietanercnnde E EREE tae ten des 53 3 2 1 Space Requirements and Suggested Layout 00 cece cece eee e eens 54 3 2 2 Environmental Requirements and Concerns
74. 5 left to the probe arm base with four M3 screws FIGURE 5 14 Cable feedthrough assembly 10 Install the probe arm and base using the steps in section 5 3 4 11 Install the micro manipulated stage using the steps in section 5 3 1 12 Install a ZN50 probe using section 3 5 3 Model CPX Probe Station 5 3 6 Reconfiguring Microwave Cables 5 3 6 Reconfiguring Microwave Cables 121 If you will be changing cables frequently it is recommended to have a probe arm available with the appropriate cable already installed then switch probe arms using the instructions in section 5 3 3 and section 5 3 4 However if a cable change is nec essary you can follow this procedure to do so 5 3 6 1 Removing a Microwave Cable Semirigid cables are used with microwave probes Follow this procedure to remove a semirigid cable from a probe arm assembly 1 Remove the micro manipulated stage using the instructions in section 5 3 2 2 Remove the probe arm and base using the instructions in section 5 3 3 3 Cutthe unwaxed dental floss that ties the cable to the probe arm thermal anchor 4 Using the 2 5 mm hex driver remove the four M3 screws that attach the cable feedthrough assembly to the probe arm base FIGURE 5 15 5 Pull the cable feedthrough assembly and its attached cable out of the probe arm The semirigid cable has bends that require some reorientation of the cable feedthrough assembly as the cable is removed 5 3 6 2 Installing a Micro
75. 86 4 3 3 Mounting Samples on the Sample Holder cee eeeeee cece eee eees 87 4 3 3 1 Sample Alignment and Position cece cece cece e eee e nee ee ees 87 4 3 3 2 Reducing the Risk of Cracking Wafers cceeeee cece eee e ees 87 4 3 3 3 Temporary MOUNntING seess irent nein ii A coven ent 88 4 3 3 4 Semi Permanent Mounting cece eee eee eee eens 88 4 3 3 5 Permanent MOUNTING seina cese n neee ines Maen TA 89 4 3 4 Mounting the Sample Holder onto the Sample Stage 65 89 4 3 5 Closing the Vacuum Chamber and Radiation Shield 000e sees 90 4 4 VACUUM OPeratlON sirean e a ai IPRA TARER ERNEA 91 4 4 1 Turbo Pump Overview ss sssssiesresresresseseesrrrerrsrerrrreerrrrerreet 91 4 4 1 1 VacUUM CONtrOlS scena n iaa paea AEE EEROR 91 4 4 1 2 Considerations for Using the Vacuum Isolation Valve 92 4 4 1 3 Vacuum Gauge Location cece e cence eee e eens 92 4 4 1 4 Vacuum Performance 6 cece eee eee cece eee e eens 93 4 4 2 Evacuating the Vacuum Chamber ccc cecee cece ee ee ee eee eenaeeeees 93 4 4 3 Shutting Down the Turbo PUMP cece eee eee eee eect eee enna e tees 94 4 4 4 Purging the Vacuum Chamber cceceecceee cece eee eect ennneeeeees 94 4 5 Temperature Operation ccc cc cece cece i Er euS ANEA eect tent tebe eee es 95 4 5 1 Basic Cryogen Handling 0 0 0 cece eee eee eee eee eee eet
76. APTER 6 Maintenance and Troubleshooting 6 2 8 Cleaning Microwave Probe Points CAUTION CAUTION 6 2 9 Probe Arm Maintenance Model CPX Probe Station The points on microwave tips are extremely delicate and require great care in both handling and cleaning 6 2 8 1 General Cleaning 1 Immerse the probe tip only in a bath of isopropyl alcohol or acetone in an ultra sonic cleaner 2 Cycle the ultrasonic cleaner on and off in very short bursts several times If you do not have an ultrasonic cleaner simply dip the tip into a bath of acetone Finish with a rinse in isopropyl alcohol 4 Allowthe probe to air dry thoroughly for several hours preferably overnight before use so that no liquid remains within the air gap between the points ora short will result w Never use high velocity compressed air directly on the probe tip the nozzle must be kept 10 in to 12 in away if used Do not use a brush or cotton swab to wipe the probe tip 6 2 8 2 Removing Oxidation 1 Tape a piece of clean card stock or heavy paper onto the sample holder 2 Touch the probe down on the paper slightly so that the ground points begin to flex and slowly drag the probe backward across the paper a distance of 1 mm Do not drive the tip forward into the paper or you will damage the points 3 Insevere cases touch the probe tips down onto a piece of smooth ceramic and drag the probe backwards 1 mm This process quickly removes the oxide but
77. Air Central pneumatic Compressor 47407 120 264 60 NG TABLE 6 2 Detailed power requirements a akeShore www lakeshore com 154 CHAPTER 6 Maintenance and Troubleshooting 6 4 2 Pin Outs The pin outs for the control and readout cables of the system are detailed in TABLE 6 3 EE Colora Function Pin I Connector A Red V 4 B Black V 2 Sample C White l 5 Sensor 1b D Green l 1 6 pin DIN No connection Gray tin Cable shield 3 E Red Signal Sample Heater 1 F Black Ground Dual banana Sample c Connector body Gray tin Ground Signal SAE EETE G Red V 4 H Black V 2 4K shield J White l 5 Sensor 2 19 pin K Green l 1 6 pin DIN connector No connection Gray tin Cable shield 3 bottom vacuum L Red Signal 4K shield flange Heater 2 M Black Ground Dual banana r 4K shield c Connector body Gray tin Ground Signal ebm N Red V 4 P Black vV 2 Rad shield R White I 5 Sensor 3 S Green l 1 6 pin DIN No connection Gray tin Cable shield 3 T Red Signal Rad shield heater 3 U Black Ground Dual banana Rad shield Connector body Gray tin Ground Signalc He IEIETE vV Not used A Red V 4 p Black un Second shield en 0 White l 5 6 pin DIN sree D Green 5 l No connection Gray tin Cable shield 3 bottom vacuum z flange second shield E Red Banana Second shield 8 F Black Banana Dual banana Second
78. Higher pressure 55 to 69 kPa 8 to 10 psi allows maximum flow during cooldown Lower pressure 21 to 34 kPa 3 to 5 psi is recommended for normal operation Dry pure gaseous nitrogen should be used for LN transfers and dry pure gaseous helium for LHe transfers Sample Stage Micrometer Valve this restricts the cryogen flow to the sample stage while permitting unrestricted flow to the 4 K shield and other radiation stages The valve is opened five to six turns when cooling the sample stage It is opened two turns or less when operating the sample stage either above or below the 4 K shield stage temperature The control does not have a stop on the open side therefore it can unthread if it is opened too far You should never need to open it more than nine turns If you inadvertently unthread it too far gently push up on the micrometer control and turn it in the closed direction 4 5 2 ControlsforTemperature Operation 97 FIGURE 4 11 Sample stage micrometer valve Dual Valve Assembly this is used only when operating the sample stage below 4 2 K as part of the PS LT option These valves work with the sample stage micrometer valve to create vacuum pressure on the helium in the sample stage which lowers its temperature Refer to section 5 2 2 for operating below 4 2 K FIGURE 4 12 Left Dual value assembly Right Exhaust valve assembly Exhaust Value Assembly this is used only when the sample stage was operated above 100 K and it
79. IGURE 5 17 Left Attaching the feedthrough extension to the probe arm base Right The nut between the cable and the flange SMA style shown 7 Ifthere is any cellophane tape on the optical fiber remove it 8 Insert the optical fiber tip into the feedthrough extension FIGURE 5 18 Handle the fragile optical fiber carefully it should not be bent sharply or it may break Pull the cable through until the feedthrough seats against the feedthrough extension 9 Using the 2 5 mm hex driver attach the feedthrough to the feedthrough exten sion with four M3 screws Model CPX Probe Station 5 3 7 Reconfiguringan Optical FiberAssembly 125 FIGURE 5 18 Insert the optical fiber tip into the feedthrough extension 10 Loosely wrap the fiber around the probe arm to take up any slack 11 Insert the optical fiber tip into the opening in the probe mount FIGURE 5 19 12 Using the 2 5 mm hex driver secure the tip by gently tightening the M3 screw FIGURE 5 19 FIGURE 5 19 Left Inserting the optical fiber tip into the opening in the probe mount Right Securing the optical fiber tip by tightening the M3 screw 13 Using unwaxed dental floss tie the fiber to the arm to keep it from unraveling during use FIGURE 5 20 FIGURE 5 20 Tie the optical fiber to the arm Lakeshore www lakeshore com 126 CHAPTER 5 Advanced Operation 5 3 8 Installing the Planarization Assembly Model CPX Probe Station 14 Install the probe arm
80. Move the crate materials out of the work area It is advisable to save these in the event you need to return the probe station 10 Move the probe station to its final location 11 Remove the cross braces from the red shipping brackets 12 Using an adjustable wrench take the screws out of the shipping bracket underneath the baseplate 13 Place your hands underneath the edges of the baseplate and lift up on the baseplate while gently pulling the red shipping bracket down and out This should be done with four people a person to lift each side of the station Use the steps in section 3 3 5 as a guide to uncrate the console and accessories The number of supports and braces may vary depending on the options and configuration you ordered Four lifting lugs are provided on top of the console to lift it up and off the crate base Use the wheels to roll it into its final location Before moving the console or moving on in this process however be sure to remove the crate and clean the area of any debris left over from the uncrating process You will need to unpack the probe station itself including removing any ties and packing paper Finally you will need to unpack the tools o rings and hardware 1 Remove the plastic wrap from the probe station arms and the bayonet 2 Using wire cutters cut the plastic ties from the x axis hand dials Remove the tape if any from the z axis micrometers Once you have removed the crate from the instrumen
81. Place the two M5 screws in their respective holes and finger tighten each one 4 Using the 5 mm hex driver tighten each one until secure 3 4 2 2 Assemble the Microscope and Horizontal Boom 1 Using the 3 mm hex driver remove the four M3 mounting screws FIGURE 3 8 from the microscope 2 Attach the microscope to the horizontal boom see FIGURE 3 8 with the screws that were removed in step 1 The microscope attaches beside the hand dial Model CPX Probe Station 3 4 2 Assemblingthe Vision System 65 Microscope FIGURE 3 8 Left Installing the microscope vertical post Middle Four M3 mounting screws on the vertical post Right Attaching the microscope to the horizontal boom 3 Slide the horizontal boom onto the vertical post as shown in FIGURE 3 9 You may need to turn the white plastic nut counterclockwise to allow it to slide easily If the microscope physically touches the vacuum chamber lid adjust the shaft collar before moving on section 6 3 4 5 describes how to adjust the shaft collar FIGURE 3 9 Installing the horizontal boom onto the vertical post El akeShore wwwilakeshore com 66 CHAPTER 3 Installation and Setup 3 4 2 3 Connect the Vision System 1 Connect the microscope electronics These consist of two parts a The 12 V DC power supply connects to the plug on top of the microscope b S video cable connect one end to the top of the microscope as well It will align in only one direction for the connect
82. RE 4 13 Left Bayonet compression fitting on the transfer line shoulder Right Opening the foot valve ANY Ele 4 5 3 2 Initiate the Helium Transfer 1 10 11 12 Remove the plug in the Dewar top port FIGURE 2 9 and slowly open the top withdraw port to relieve the pressure in the Dewar Lower the transfer line into the Dewar until the pressure just starts to rise FIGURE 4 14 Thread the 1 2 in compression fitting onto the top of the Dewar but do not fully tighten it so that the transfer line can still be inserted further into the Dewar Close the shut off valve isolating the low pressure relief valve from the Dewar The high pressure relief valve should never be closed or disabled Monitor the pressure and keep it between 48 kPa to 62 kPa 7 to 9 psi Use the shut off valve on the low pressure relief valve to maintain pressure Continue to lower the transfer line until the transfer line leg hits the bottom of the Dewar Do this slowly so that the Dewar pressure does not rise dramatically Fully tighten the 1 2 in compression fitting on the Dewar to secure the transfer line The Dewar pressure should be maintained at approximately 34 kPa 5 psi for the remainder of the cooldown Most helium Dewars will not self pressurize at these flow rates so regulated helium gas pressure must be introduced through the gas port on the Dewar Allow the transfer line to pre cool until a continuous plume of white vapor is ejected from t
83. Replace any o rings that look worn or flattened m Clean and lubricate the o rings section 6 2 5 2 in the micrometer valve stem especially if the leak increases when the valve is actuated m Clean and re grease the o rings between the probe arm base and bellows especially if the leak increases when planarization adjustments are made m Ifthe pressure relief valve assembly activates routinely verify that it reseats properly AWARNING 6 3 2 Transfer Line Troubleshooting 6 3 2 Transfer Line Troubleshooting 143 Never operate the probe station without a pressure relief valve installed If these troubleshooting procedures do not correct the problem a helium leak detector will be required to identify the exact source of the leak Transfer line problems most often fall into three categories the transfer line becomes soft it becomes plugged or the foot valve control knob freezes and will not operate 6 3 2 1 Soft Transfer Line The transfer line may have become soft if any of the following symptoms are observed m Reduced gas output from the transfer line Cooling time increases Cryogen consumption increases Transfer line starts to become noticeably cooler during operation Condensation appears on the braid during operation condensation and frost is normal near the bayonet fitting If the transfer line is soft it requires maintenance as described in section 6 2 11 Ifthe transfer line requires pumping more than every three to si
84. S YLH 4 a8e s pjalys puoras YLH 4 aqez INO CHT I a 1qe2 TINO ZT if Yd GND 3Ndyno HH OvE a N splays ajqe tA Y gl jeusis ud S 7 ndyno 4 N Dj aNd ai S splays 1qe2 Josuas J N i 49334 MOOT YLH A g N asejs pjaiys uoneipey YLH L 919000 8 N a s z ou ET poip s A d A a8e s pjalys uo1eipey N N J t cutee UlH W Plays ajge gt 4osu S J N o asels pjaiys Jy YLH 1 Vee l X y Xa f aLy wnunejd vA po p IS H Aue wie aqoid 2 asejs pjalys 17 5 dosuas Bee 493234 MOS d gt In a8ejs aides J a uod Japjo uod p 10p uuo euis uid 6T eds al Lies uid 9 aseds vaseis T sa8eis apoip is q a8ejs ajdues Yy Aue 4JayeaH 1osu s jeusis uid Ajquiasse we aqoid w0 0q Jaquiey gt WinndeA uolze 4s aqo1d FIGURE 6 10 Wiring diagram www lakeshore com _akeShore ae 156 CHAPTER 6 Maintenance and Troubleshooting 6 5 Technical Inquiries 6 5 1 Contacting Lake Shore 6 5 2 Return of Equipment 6 5 3 RMA Valid Period 6 5 4 Shipping Charges 6 5 5 Restocking Fee Model CPX Probe Station Refer to the following sections when contacting Lake Shore for application assistance or product service The Lake Shore Systems Service department is staffed Monday through Friday between the hours of 8 00 AM and 5 00 PM EST excluding holidays and company shut down days Contact Lake Shore Systems Service through any of the m
85. S 21 40 S12 50 60 6522 70 80 90 S parameters dB 0 10 20 30 40 30 60 Frequency GHz FIGURE 2 39 Calibrated S parameter response of 67 GHz GSG microwave probes Model CPX Probe Station 2 5 5 Temperature Effects of Calibration 2 5 6 Planarization 2 5 5 Temperature Effects of Calibration 49 There are temperature dependent losses in microwave feedthroughs semirigid cables and probe bodies and tips As the sample stage cools to 4 2 K for example there is approximately a 294 K temperature gradient set up over the length of the semirigid coaxial cable In addition the structures of a calibration or test substrate have a temperature dependent response Measurements have shown that there is approximately 1 to 2 dB less insertion loss at 67 GHz as measured in 21 S12 at 4 3 K compared to the same measurement at 300 K To illustrate this phenomenon FIGURE 2 40 shows the calibrated S parameter response of a pair of 67 GHz GSG microwave probes measured on a 50 0 through structure at 4 3 K temperature using a SOLT calibration that was performed at 300 K temperature Note the error in the calibration as compared to FIGURE 2 39 The error is due in part to the temperature changes in the arms and probes as well as the coplanar waveguide physically changing geometry which causes errors in the VNA calibration correction coefficients The calibration error is on the order of 1 to 2 dB for this particular calibrat
86. Setup ANIL TS 3 3 Unpacking the The following must be provided for each cryogen used a gas cylinder or other source of dry high purity gas an independent low pressure regulator capable of providing steady pressure between 13 8 kPa 2 psi and 69 kPa 10 psi and gas line and fittings to attach the regulator output to the gas port on the Dewar Lake Shore does not offer these components as accessories Gas cylinders must be anchored properly before use Tipping cylinders can cause serious injury or death Vacuum Chamber Purge Gas during system warm up and sample change operations it can be beneficial to purge the vacuum chamber with inert gas A purge valve with a Yin NPT connection is provided on the vacuum chamber for this purpose Dry nitrogen gas is recommended for most purge operations but other inert gasses can be used Helium is not recommended because it is difficult to pump out when re evacuating the system Aregulated nitrogen gas system like the one described in this section under Dewar pressure is sufficient for purging the vacuum chamber It is possible to share one nitrogen gas system between the functions because they are not used at the same time Vibration Isolation Lake Shore offers the PS PVIS vibration isolation option You will need to have access to pressurized air to provide steady pressure between 138 kPa and 280 kPa 20 to 40 psi The connector on the PS PVIS is a 6 4 mm 1 4 in OD push to connect fitti
87. Si diode Heater 50 W Control A Tune Remote O O O Control BRamp Alarm Control Zo Input Display Alarm Remote Escape Auto Heater Setup S iting Setup Format l Tune Range Mo CIC PID Curve Math Analo Setpoint MHP En Output nterface Enter Loop MMM mo Oc Heater Off Model 332 temperature controller FIGURE 2 12 Temperature instrumentation El akeShore www lakeshore com 22 CHAPTER 2 System Overview 2 2 4 Vision System Vertical i post Horizontal boom Major components of the vision system include the microscope color CCD camera monitor support and adjustment apparatus light and light source FIGURE 2 13 illustrates the vision system S video cable Monitor ia Color CCD camera ra Hand dial ra Monoscope Fiber optic cable Viewport a Chamber 2 2 5 Turbo Pumping System Optional PS V81DP or Equivalent Model CPX Probe Station FIGURE 2 13 Vision system with ring light shown Major components of the turbo pumping system typically include the controller turbo pump oil free dry scroll backing pump vacuum gauge and vent valve FIGURE 2 14 illustrates the PS V81DP turbo pumping system To probe station Vacuum gauge H woo pump Manual vent D Il Bali ry scroll pump
88. TION 4 2 Operating the Probe Arm Translation Stages This chapter describes the majority of daily operation Chapter 5 covers more advanced probe station operation It is assumed that the station has been installed and set up as described in Chapter 3 The following are some common mistakes that can be made while operating the probe station These mistakes can result in costly damage to the probes or refrigerator Please read this chapter thoroughly before operating the probe station for the first time so that these and other mistakes can be avoided Opening the vacuum chamber to atmosphere with a cold refrigerator Heating the refrigerator when not under vacuum Heating the refrigerator when not flowing cryogen Not raising the probe tips before evacuating the chamber Not raising the probe tips before changing temperature Not checking that all probe tips can contact the sample under test before initiat ing a cryogen transfer The maximum temperature limits for the multiple stages and components of the probe station are listed below Adhere to these limits at all times during probe station operation Sample stage 475K 4 K shield stage 380K Radiation shield stage 380K Second shield stage 380K Probe arms 350K Optional probes and sample holders may have lower maximum temperatures Failure to observe maximum temperatures may result in equipment damage Each probe assembly includes a micro manipulated translation stage with three a
89. User s Manual CPX Probe Station Lake Shore Cryotronics Inc 575 McCorkle Blvd Westerville Ohio 43082 8888 USA sales lakeshore com service lakeshore com www lakeshore com Fax 614 891 1392 Telephone 614 891 2243 Methods and apparatus disclosed and described herein have been developed solely on company funds of Lake Shore Cryotronics Inc No government or other contractual support or relationship whatsoever has existed which in any way affects or mitigates proprietary rights of Lake Shore Cryotronics Inc in these developments Methods and apparatus disclosed herein may be subject to U S Patents existing or applied for Lake Shore Cryotronics Inc reserves the right to add improve modify or withdraw functions design modifications or products at any time without notice Lake Shore shall not be liable for errors contained herein or for incidental or consequential damages in connection with furnishing performance or use of this material Rev 1 0 P N 119 050 30 April 2009 El akeShore wwwilakeshore com LIMITED WARRANTY STATEMENT WARRANTY PERIOD ONE 1 YEAR 1 Lake Shore warrants that this Lake Shore product the Product will be free from defects in materials and workmanship for the War ranty Period specified above the Warranty Period If Lake Shore receives notice of any such defects during the Warranty Period and the Product is shipped freight prepaid Lake Shore will at its option either r
90. W THE ABOVE WAR RANTIES ARE EXCLUSIVE AND NO OTHER WARRANTY OR CONDITION WHETHER WRITTEN OR ORAL IS EXPRESSED OR IMPLIED LAKE SHORE SPECIFICALLY DISCLAIMS ANY IMPLIED WARRANTIES OR CON DITIONS OF MERCHANTABILITY SATISFACTORY QUALITY AND OR FIT NESS FORA PARTICULAR PURPOSE WITH RESPECT TO THE PRODUCT Some countries states or provinces do not allow limitations on an implied warranty so the above limitation or exclusion might not apply to you This warranty gives you specific legal rights and you might also have other rights that vary from country to country state to state or province to province 7 TO THE EXTENT ALLOWED BY APPLICABLE LAW THE REMEDIES IN THIS WARRANTY STATEMENT ARE YOUR SOLE AND EXCLUSIVE REME DIES 8 EXCEPT TO THE EXTENT PROHIBITED BY APPLICABLE LAW IN NO EVENT WILL LAKE SHORE OR ANY OF ITS SUBSIDIARIES AFFILIATES OR SUPPLIERS BE LIABLE FOR DIRECT SPECIAL INCIDENTAL CONSE QUENTIAL OR OTHER DAMAGES INCLUDING LOST PROFIT LOST DATA OR DOWNTIME COSTS ARISING OUT OF THE USE INABILITY TO USE OR RESULT OF USE OF THE PRODUCT WHETHER BASED IN WAR RANTY CONTRACT TORT OR OTHER LEGAL THEORY AND WHETHER OR NOT LAKE SHORE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES Your use of the Product is entirely at your own risk Some countries states and provinces do not allow the exclusion of lia bility for incidental or consequential damages so the above limitation may not apply to you Limited Warranty Statemen
91. _ Temperature Baseplate instrumentation Turbo vacuum pumping system components FIGURE 2 1 CPX probe station major components El akeShore www lakeshore com 12 CHAPTER 2 System Overview 2 2 1 Probe Station The probe station provides the temperature measurement environment for the sample or device under test DUT It also provides the electrical and optical interface with the sample Major components of the probe station include the vacuum chamber refrigerator and baseplate the probe station is not mounted to the stand and probe arm assemblies FIGURE 2 2 illustrates the probe station components Probe arm assembly Probe arm assembly Baseplate Refrigerator Vacuum chamber FIGURE 2 2 Probe station Model CPX Probe Station 2 2 1 ProbeStation 13 2 2 1 1 Vacuum Chamber Vacuum is important for two reasons It provides thermal insulation for the cryogenic refrigeration used to cool the sample and radiation shields and it also prevents particulates and air in the chamber from condensing on the sample which may lead to sample contamination during measurements The vacuum chamber houses both the refrigerator and the radiation shield subsystems Major components of the vacuum chamber include the vacuum chamber lid chamber viewport vacuum isolation valve vacuum line purge valve pressure relief valve electrical feedthrough and auxiliary gauge port FIGURE 2 3 illustrates the vacuum chamber Chamber v
92. a ZN50 551 probe mount is required in the CPX for the ZN50 blades Semirigid microwave cables are limited to operation below 350 K and are more thermally conductive than ultra miniature coaxial therefore the probe arm sensor should be monitored when probing a sample above this temperature The cable s outer conductor is grounded to the thermal anchor point of the probe arm shield See section 2 4 3 for further information on the RF performance of the ZN50 probe 2 3 3 Microwave Probe Configurations 2 3 3 Microwave ProbeConfigurations 25 2 3 2 3 ZN50 Compatible Probe Mount All ZN50 series blades require a ZN50 551 probe mount that attaches to the probe arm and provides mechanical support and thermal anchoring for the blade The probe mount braids provide the thermal anchoring and can be connected or disconnected as desired for a particular measurement application When connected the probe is maintained at approximately the same temperature as the anchor point In the CPX there are two possible probe mount braid anchor points for each probe arm one on the sample stage and one on the 4 K shield stage Matching microwave probes and cables are available in three frequency ranges DC to 40 GHz DC to 50 GHz and DC to 67 GHz Each frequency range uses a different connector type but all use the same semirigid coaxial cable Probe arm planarization is necessary to ensure simultaneous contact of all three points of the microwave probe tip A pl
93. ain the back side of a substrate at a potential other than chassis ground They are recommended for applications such as guarding the sample to reduce leakage current bringing a bias voltage to the back side of the sample or isolating and shielding the sample to reduce noise Coaxial holders are constructed as laminations of metal insulator metal in the sample plane The insulator provides a layer to layer resistance of gt 30 GO and a layer to layer capacitance of lt 150 pF The conductive sample surface has a contact pin that can be driven at a user defined potential Wiring for the sample holder requires an FT BNC or FT TRIAX feedthrough option Moderate thermal gradients between the sample stage and sample mounting surface should be expected The maximum operating temperature is 400 K 2 3 5 4 Triaxial Sample Holder Triaxial holders offer the ability to define two different voltage potentials between the conductive sample mounting surface and system ground They are recommended when two of the features supported by the coaxial sample holder are used at the same time Examples include guarding to reduce leakage current and shielding to reduce noise or voltage biasing and guarding at the same time Triaxial holders are constructed as laminations of metal insulator metal insulator metal The insulator provides a layer to layer resistance of gt 30 GO and a layer to layer capacitance of lt 150 pF The conductive sample surface and center metal pl
94. aintenance and Troubleshooting Model CPX Probe Station Temperature change probe arms change length when their temperature changes necessitating lifting probe tips before changing temperature The probe arms must stabilize in temperature for approximately 10 to 15 min in addition to the sample stage before probes can be landed effectively If probes are landed too soon the position of the probe tip will shift degrading the quality of electrical contact 6 3 5 3 Loss of Continuity Loss of continuity is nearly always caused by bad contact between the probe tip and sample If the contact resistance is known to be good and there is no continuity between the signal connector and the probe the cause is likely a broken center conductor in the probe cable This is often caused when the back of the SMA plug on the cryogenic coaxial cable is not held steady when the ZN50 probe is installed Check the continuity of the center conductor by measuring the resistance between the center pin of the signal connector and the center of the SMA connector If the resistance is not approximately zero the cable must be replaced Refer to section 5 3 5 for the procedure to replace the cable 6 4 Service Reference 6 4 1 Power Requirements and Power Configuration Information This is the service reference section 6 4 Service Reference 153 Electrical power is required for the operation of the instrument console vision system turbo pumping system and
95. alibration FIGURE 2 38 shows the response of a pair of 67 GHz probes placed ona 50 Q through test structure on the CS 5 calibration substrate The measurements were made using a commercial VNA calibration using mechanical standards that places the measurement reference plane at the end of the VNA measurement cables that are connected to the input connectors of the 67 GHz probe arms FIGURE 2 38 shows the frequency dependent characteristics of the probe station with the 67 GHz probes and probe arms The performance looks very good with the transmission coefficients 21 S12 remaining above 10 dB and the reflection coefficients 11 S22 remaining below 10 dB over the entire frequency band The gradual sloping increase in loss the decrease in S21 S12 as the frequency increases is expected 10 i _ 10 4 SPS TS ri as ee 20 l 11 30 S 21 40 S12 50 60 22 70 80 90 0 10 20 30 40 50 60 Frequency GHz S parameters dB FIGURE 2 38 S parameter response of 67 GHz GSG microwave probes FIGURE 2 39 shows the response of a pair of 67 GHz probes placed ona 50 Q through test structure following a SOLT calibration using the CS 5 calibration substrate This calibration places the VNA measurement reference plane at the end of the probe tips and thus removes the losses of the associated cabling and probes from the measurement response of an unknown substrate 107 0 10 y mE 20 11 30
96. also removes some of the tip material and can result in reduced probe life 4 After removing oxidation clean the probe as described in section 6 2 8 1 The probe arms and stages require very little maintenance however some of the fasteners do need to be re tightened periodically due to thermal cycling or repeated movement Fasteners associated with thermal interfaces electrical conduction and mechanical stability should be checked regularly The instructions for re tightening these components are the same as those for installation or operation so they are not repeated here Tightening the braid block please reference step 5 in section 3 5 3 1 if you need to tighten a braid block Tightening the probe mount please reference step 4 in section 3 5 3 1 Tightening the arm shield braids please reference FIGURE 5 4 in section 5 3 1 Tightening the probe arm into the probe arm base follow this procedure to tighten the probe arm 1 Remove the micro manipulated stage using the instructions in section 5 3 2 2 Remove the probe arm and base using the instructions in section 5 3 3 3 Using the 10 mm wrench tighten the locknut that secures the threaded brass anchor of the probe arm to the hex standoff of the probe arm base while keeping the probe arm oriented properly 4 Install the probe arm and base using the instructions in section 5 3 4 5 Install the micro manipulated stage using the instructions in section 5 3 1 6 2 10 Vacuum P
97. amples in the CPX The FT BNC coaxial feedthrough is used to bring the guard voltage into the chamber and to the sample holder When the experiment requires guarding and back side voltage biasing or additional ground isolation the SH 1 25 T or SH 2 00 T triaxial sample holder is required in the CPX FIGURE 2 31 Triaxial sample holder SH 1 25 T The triaxial sample holder offers two layers of isolation between the sample and grounded refrigerator The FT TRIAX triaxial feedthrough is required to connect signals to the sample holder FIGURE 2 32 The coaxial and triaxial sample holders are almost identical in appearance however the difference is the number of electrical isolation layers which cannot be seen from the outside El akeShore www lakeshore com 44 CHAPTER 2 System Overview Triaxial signal connector Cryogenic coaxial cable oS ZN50 Triaxial i Probe sample holder Probe Probe arm shield g c i ryogenic arm T pai voltage coaxial cable base eaaaaaees ee a g Sample ness 4 K shield stage 77 Radiation shield stage 7 Second shield stage 77 Vacuum chamber base TI gt S77 Triaxial feedthrough a 77 Shield 19 pin To temperature connector controller chassis AWARNING Model CPX Probe Station FIGURE 2 32 Guarding wit
98. an be removed after the assembly is installed FIGURE 5 11 planarization assembly screws _ a FIGURE 5 11 Left Securing the planarization assembly to the probe arm base Right Taping the cable to the probe arm 5 Clean the o ring groove in the probe arm base FIGURE 5 10 Clean inspect and lightly grease the o ring with vacuum grease and place it in the groove Model CPX Probe Station CAUTION 5 3 5 Reconfiguring Ultra miniature Cryogenic Coaxial Cables 5 3 5 Reconfiguring Ultra miniature Cryogenic Coaxial Cables 119 6 Place the bellows over the arm grasp the square end and carefully twist it down until the flange meets the probe arm base FIGURE 5 12 7 Install the four long M4 horizontal screws that attach the bellows to the z axis stage assembly and tighten the screws evenly FIGURE 5 12 The four M4 screws holding the bellows flange to the z axis stage assembly should be installed to a torque of 112 N mm 16 ozf in The torque required is much lower than one might think would be needed We recommend using a torque wrench to ensure these screws are not over torqued If these screws are over torqued the z axis stage and bel lows may be damaged FIGURE 5 12 Left Placing the bellows onto the probe arm base Right Attach the bellows to the z axis stage If you will be changing cables frequently it is recommended to have a probe arm and base available with the appropriate cable already installed then s
99. anarization assembly is included on micro manipulated stages when microwave cables are ordered or it can be field installed 2 3 3 1 Microwave Compatible Probes There are three frequency configurations of microwave probes determined by the connector used The microwave probe must be specified with the same frequency and connector type as the probe cable All microwave probes are constructed with ground signal ground GSG geometry and are designed for use with coplanar waveguides The BeCu signal and ground points are 10 um to 12 um planar triangular structures The pitch or spacing between the probe points can be specified from 50 um to 250 um in 50 pm increments In general smaller pitches are recommended for higher frequency applications The point size is the same regardless of the probe pitch The probes have a room temperature current limit of 2 A due to heat generated in the probe tip Consult Lake Shore if this current limit is not sufficient for your application H GSG FIGURE 2 16 Approximate shape of microwave probe tip Separate probe mounts are not necessary for microwave probes because they are permanently mounted into a proprietary probe body The proprietary microwave probe body is optimized for thermal performance in cryogenic probe stations and includes both mechanical support and thermal anchoring for the probe Microwave probe bodies must be kept below 350 K at all times but due to the low thermal cross section of th
100. ane both have contact pins that can be driven at user defined potentials Wiring for these signals requires an FT TRIAX feedthrough option Moderate to medium thermal gradients between the sample stage and sample mounting surface should be expected The maximum operating temperature is 400 K The probe station s vision system is critical for distinguishing characteristics of the sample and properly landing probes The vision system can be optimized for the type of sample that is most frequently probed There are four configurations available for the probe station two different microscopes each with two lighting choices The choice of an appropriate lighting type is especially important because it strongly influences the behavior of the vision system 2 3 6 1 Microscopes There are two microscopes available for the probe station the standard Zoom 70 and the optional Zoom 160 The Zoom 70 has a ratio of magnification change zoom of 7 1 and the Zoom 160 has a ratio of magnification change zoom of 16 1 The maximum magnification of the vision system is different than the magnification ratio Vision system magnification is dependant on the microscope magnification and other factors such as the camera monitor size and the optical elements necessary to overcome the probe station s relatively large working distance Resolution is often a more useful specification than magnification when choosing a microscope Lake Shore specifies resolution for th
101. appropriately fitted cable will tighten to the probe connector while the probe arm touches flush or is less than 2 mm from the probe mount However there are two sit uations for which you may need to make adjustments of your semirigid high fre quency cables First if the connector plug does not smoothly tighten to the probe socket you will need to make an adjustment If there is too much tension or misalign ment in mating the semirigid cable to the connector the high frequency connectors may be damaged Second if you are able to tighten the connector plug to the probe socket but there is more than a 2 to 3 mm gap between the probe arm and the probe body then you will need to make an adjustment El akeShore www lakeshore com 122 CHAPTER 5 Advanced Operation A few adjustments can be made to change the relative positions of the cables and the probes These are listed in order of increasing difficulty The more difficult methods allow for more adjustment range First Method Rotate the Cable Feedthrough Assembly 1 Remove the micro manipulated stage following the steps in section 5 3 2 2 Remove the bellows following steps 1 to 2 in section 5 3 3 3 Remove the four M3 screws holding the cable feedthrough assembly to the probe arm base FIGURE 5 15 4 Rotate the feedthrough assembly into position and loosely start the four M3 screws leaving the cable free to rotate in the feedthrough The cable does not pass through the center of
102. at the cable and probe arm enter the radiation shield The copper arm shield braids go between the chamber and radiation shield Using the 3 mm hex driver secure the stage to the baseplate with the four M4 screws FIGURE 5 2 FIGURE 5 2 Left Prepare the o ring and groove Middle Guide the cable and probe arm through the arm port 9 10 Model CPX Probe Station Right Secure the stage to the table Using the 3 mm hex driver loosen the two bottom screws holding the front of the bellows onto the arm stage and lift the bellows up to align it to the arm port Using the 3 mm hex driver attach the bellows to the vacuum chamber Proceed ing in the following manner allows you to maintain equal pressure between the bellows flange and the arm port o ring seal a Loosely tighten two of the M4 screws on diagonally opposing sides that attach the bellows to the chamber FIGURE 5 3 Loosely tighten the remaining two M4 diagonally opposing screws c Fully tighten the first two diagonally opposing M4 screws that attach the bellows to the vacuum chamber d Using the x axis hand dial move the probe arm stage forward toward the vacuum chamber e Fully tighten the remaining two M4 screws that attach the bellows to the vacuum chamber 5 3 2 Removinga Micro manipulated Translation Stage 115 FIGURE 5 3 Loosely tighten two M4 screws to begin securing the bellows to the chamber 11 Attach the arm shield braids to the radiatio
103. ated PS HV CPX HVAC components Vacuum specifications radiation shields at room temperature with DUT at maximum sample stage temperature 10 5 Torr room temperature 10 6 Torr cold radiation shields with DUT at maximum sample stage temperature 10 6 Torr cold radiation shields with DUT at room temperature or below 10 7 Torr Load lock assembly option Allows sample exchange without warming the radiation shields or breaking vacuum significantly improving PS LL CPX efficiency and throughput by reducing cycle time to roughly 1 h Load lock also allows samples to be exchanged under controlled environmental conditions Overall temperature range limited from 10 K to 400 K when using this option PS SSVAC CPX Stainless steel vacuum chamber upgrade supplied in place of standard nickel plated aluminum vacuum chamber Optical fiber assembly Transmit or receive light or IR UV radiation Optical fiber terminated with SMA connector or compression PS FOA j z i feedthrough Optical fiber not included Optical fiber and probe cannot be used simultaneously PS Z16 16 1 zoom microscope upgrade provides 4 um resolution NOTE Consult Lake Shore for field upgrade PS LT 2 0 K base temperature stage pumping option includes system modifications stainless steel flex hose for pump connection and Varian DS402 rotary pump 12 3 CFM at 60 Hz with oil mist eliminator on output with oil return and inlet oil demister PS PLVI 25 Pump line vib
104. ation 83 above room temperature 112 closing the vacuum chamber and radiation shield 90 cooldown with helium 98 evacuating the vacuum chamber 93 from 4 2 Kto 6 K 100 from 6 K and higher 101 helium transfer 99 imaging and probing the sample 104 anding the probe 105 mounting samples 87 mounting the sample holder 89 nitrogen 111 opening vacuum chamber 85 planarization assembly 106 probe arm translation stages 83 reducing condensation 109 removing sample holder 86 sample alignment 87 sample exchange 85 sample rotation 105 temperature 95 temperature control 102 temperature controls 95 temperatures below 4 2 K 110 turbo pump 91 turbo pump shut down 94 vacuum 91 vacuum chamber purge 94 warm up 102 operation advanced 109 optical fiber 123 installing 123 Model CPX Probe Station removing 123 optical fiber assembly 8 optical specifications 3 o rings maintenance 131 P pin outs 154 planarization assembly 25 installation 126 use 106 power requirements 56 pressurized gas 16 19 probe area 84 probe arm installing 118 removing 117 probe arm adjustments 2 probe arm assemblies 15 probe arm maintenance 134 probe pitch 25 27 47 probe station 12 applications 2 assembly 63 description 1 floor plan 54 installation 53 major components 12 major subsystems 11 materials 2 operation 83 required equipment 4 site requirements 53 standard equipment 4 suggested elevation 55 unpacking 58 probe station diagram of 12 probe stati
105. ay low resistance samples do When measuring high resistance measurement electronics tend to convert common mode noise which is easily cancelled to normal mode noise which is difficult to separate from the signal 2 4 8 2 Driven Guards Driven guards are used to minimize the leakage current that typically flows between conductors in the leads used to connect the sample to measurement electronics The most common leakage path is between the signal leads and their respective shield or ground Properly configured a guarded measurement system can reduce leakage current by three orders of magnitude or more which would allow a system capable of accurately measuring 10 MQ to 100 MO to measure 10 GO to 100 GO Guarding works by surrounding signal leads with coaxial conductors and driving them with a guard voltage close to the signal voltage Very little current crosses the insulation resistance leaks because the voltage difference is low Guarding does not provide adequate shielding so the signal and guard are often surrounded by a shield requiring triaxial cable and connectors FIGURE 2 29 Measurement electronics Cryostat vacuum system ey ee E q SOF Somer Leta Sp ode en ae iy 1 Le ONE te eae tee eae tal Feedthrough triax Cable triax Driven guard FIGURE 2 29 Recommended circuit for measuring high resistance devices The entire experiment must be set up with guarding in mind A key element of most guarded syste
106. base eet CONDUCTOR F A coaxialcanie MMAYMYMYMYM4IW Y J INSULATOR CONDUCTOR amp x Thermal A sane sey lh anchors 4K shield stage S77 Radiation shield stage S77 Second shield stage S77 Vacuum chamber base Coaxial BNC 4 19 pi feedthrough Totemperature Shield ee controller chassis 2 4 6 Small Signal Low Noise DC RF Measurements ANIL TS Model CPX Probe Station FIGURE 2 28 Back side voltage bias with coaxial sample holder As measured signal magnitude decreases environmental noise becomes more of an issue Proper setup of the experiment is crucial to extracting small signals from the background noise The CPX offers several standard features and optional configurations that can help 2 4 6 1 Noise Isolation for Low Noise Measurements The noise isolation features described in section 2 4 1 4 may be insufficient when making low noise measurements Please consider the following when setting up a low noise experiment Never remove earth safety ground protection from electronic equipment 1 Make every effort to isolate other noisy components pumps compressors switching power supplies when they are added to the system 2 Electrical and electronic devices are connected through the power line mains even when isolated in the probe station Care must be taken to prevent noise from coupling through the power
107. be s SMA socket otherwise the cable s center conductor can be broken Hand tighten until snug If installing the ZN50 probes on arms configured with K connectors and semirigid coaxial cable refer to section 3 5 5 steps 5 to 8 for proper alignment of the connector 6 Before initiating a cryogen transfer see section 3 6 4 and section 3 6 5 to test probe arm reach and landing ability It would be very costly and time consuming to initiate a cooldown only to find that a probe mount braid is preventing the probes from landing Do not remove the tape covering the SMA plug on the cryogenic coaxial cable The tape prevents contact with the radiation shield curtains the flexible aluminized strips covering the openings or other conductive elements in the sample area which would short the guard signal to ground 3 5 4 Removing a The ZN50 series probes consist of a probe mount ceramic blade with SMA electrical ZN50 Probe connector and probe tip You can simply remove the alumina probe blade on ZN50 probes if it has been damaged or if a different tip is desired You will need to remove SMA the probe mount if you are installing a different kind of probe than was previously connector installed itl 3 5 4 1 Removing the ZN50 Probe Blade LL blade You can remove the probe blade in the probe station or out of the probe station These z E steps describe removing the blade while it is in the station If you wish to remove the L774 blade from its mount
108. be filled with pre mix concrete to provide the vibration isolation This requires approximately 40 kg 90 Ib of concrete not included 1 Mix the concrete according to directions provided with the concrete 2 Fillthe bucket with the mixture 3 After the concrete has cured turn the bucket handle side up and place it on the three rubber pads included with the kit FIGURE 3 17 4 Forthe PS PLVI 40 connect the bucket between the turbo pumping system and the probe station s vacuum isolation valve 5 Forthe PS PLVI 25 when directed connect the bucket between the PS LT rotary vane pump and the probe station FIGURE 3 17 Pump line vibration isolator 3 4 4 2 Assembling the Low Temperature Option PS LT The low temperature option consists of a rotary vane pump dual valve assembly fittings flexible stainless steel vacuum line and an oil exhaust filter with an oil return line Follow this procedure to assemble the exhaust filter with oil return line to the rotary vane pump 1 Remove the centrally located screw from the pump side of the oil exhaust filter 2 Remove the elbow fitting with the orange push to connect fitting from the end of the oil return tube 3 Attach the elbow fitting to the centrally located tapped hole in the pump side of the oil exhaust filter You will need to hold the fitting stationary then use a 9 mm wrench to rotate the nut until the fitting is secure 4 Remove the gas ballast plug and screw the retur
109. chanical and should be relatively easy to identify Follow this procedure to find the issue m Close the purge valve Close the turbo vent valve if it is not closed automatically Check the alignment of the vacuum chamber lid Verify that the chamber lid o ring is properly seated Verify that the seals and clamps are properly installed on the vacuum line al akeShore www lakeshore com 142 CHAPTER 6 Maintenance and Troubleshooting Model CPX Probe Station m Examine any changes that were made to the system since it was last used to verify that the system was reassembled properly m Look for any parts that may have been damaged including bellows vacuum line valves fittings etc 6 3 1 7 Will Not Achieve 10 3 Torr Systems achieving between 10 2 Torr and 10 3 Torr in the vacuum chamber can be more difficult to troubleshoot because these smaller leaks can be hidden m Examine any changes that were made to the system since it was last used especially removal of probe arm assemblies to verify that the system was reassembled properly Remove clean inspect for damage grease and reinstall o rings that were used in the change m Remove clean inspect for damage grease and reinstall the vacuum chamber lid o ring Make sure the o ring is not twisted m Check the torque on fasteners between the bellows and arm base see section 5 3 4 Do not overtighten these fasteners or new leaks can be created m Asanaid in identifying the source
110. d be determined first Signal paths signal return paths and shielding build off of that foundation In most cases earth ground is the ground reference for the experiment The vacuum chamber is typically tied to earth ground to form a shield around the sample and probes The CPX is configured this way if it is assembled according to the instructions in Chapter 3 The shield conductor in one of the temperature controller cables is used to give the chamber a low impedance path to earth ground FIGURE 2 24 Grounding the vacuum chamber through the instrument console is not appropriate for all experiments so the connection is designed so that it can be changed easily The outer shell of the BNC and triax signal connectors and FT BNC feedthrough connector are electrically connected to the vacuum chamber Any one of these connectors can be used to establish a ground reference through the measurement electronics if the ground connection to the instrument console is removed If the vacuum chamber ground reference connection is removed from the instrument console it is important to reestablish the ground reference through the measurement instrumentation Leaving the chamber ungrounded often causes unpredictable measurement results El akeShore www lakeshore com 36 CHAPTER 2 System Overview Signal connector The probe station refrigerator and included grounded sample holder are also electrically connected to the vacuum chamber This will
111. d in Chapter 5 Before performing any of the operations the system must be closed and evacuated as described in section 4 4 2 Often there are multiple ways of performing some of these procedures but we have chosen steps that represent a good balance between ease of operation and minimizing helium consumption Liquid cryogen is a safe effective and economical cooling source when handled with appropriate respect Please follow the operating instructions and carefully read each warning and caution before performing cooling operations This information is provided to protect both operator safety and the probe station from damage Wear cryogenic gloves safety glasses long sleeves and long pants Due to the extremely low temperatures of liquid nitrogen 77 K and liquid helium lt 4 3 K caution should be exercised when handling or transferring it Failure to comply may result in severe frostbite injury All cryogen Dewars should be clearly labeled and operated in accordance with the manufacturer s instructions The pressure relief devices should be periodically inspected and any ice formation removed Do not use cryogenic gases in confined spaces ensure that the room is ventilated As liquid cryogen vaporizes it expands and displaces oxygen Failure to vent large quantities of vaporized cryogen can result in a loss of consciousness or death Never cool the system if the vacuum chamber is not evacuated The CPX uses five mechanical con
112. d in section 3 2 3 to section 3 2 6 is not included witha standard CPX probe station or as part of the installation and training service Some of that equipment can be purchased from Lake Shore as options or accessories those model numbers are listed in the relevant sections El akeShore www lakeshore com 54 CHAPTER 3 Installation and Setup 3 2 1 Space The CPX probe station and associated electronics console are relatively compact Requirements and However the vacuum pumping station cryogen Dewar and transfer line can take considerable space during operation Some consideration should be given to the floor Suggested Layout plan before placing the probe station The site must have enough space to provide access to all controls without posing a risk to the operator A suggested floor plan is illustrated in FIGURE 3 1 The suggested layout can be mirrored or rearranged to fit in the available space However the angle of the transfer line and mating bayonet are fixed and the vacuum pumping station must be within 2 m 79 in of the vacuum chamber for optimum performance Probe station Pressurized gas tank an Vacuum pump Instrument console SONIC 5 ol 7 Dewar ZS FIGURE 3 1 Suggested floor plan Model CPX Probe Station Instrument Probe station 1 1m 42 in console
113. d statement of limited warranty FIRMWARE LICENSE AGREEMENT The firmware in this instrument is protected by United States copy right law and international treaty provisions To maintain the war ranty the code contained in the firmware must not be modified Any changes made to the code is at the user s risk Lake Shore will assume no responsibility for damage or errors incurred as result of any changes made to the firmware Under the terms of this agreement you may only use the Model 340 firmware as physically installed in the instrument Archival copies are strictly forbidden You may not decompile disassemble or reverse engineer the firmware If you suspect there are problems with the firmware return the instrument to Lake Shore for repair under the terms of the Limited Warranty specified above Any unauthorized duplication or use of the Model 340 firmware in whole or in part in print or in any other storage and retrieval system is forbidden TRADEMARK ACKNOWLEDGMENT Many manufacturers and sellers claim designations used to distin guish their products as trademarks Where those designations appear in this manual and Lake Shore was aware of a trademark claim they appear with initial capital letters and the or symbol Apiezon is a registered trademark of M amp I Materials Ltd Cernox is a trademark of Lake Shore Cryotronics Inc Dust Off is a registered trademark of Falcon Safety Products Inc Kimwipes is a regi
114. d the second shield stage should be less than 50 K Wait at least 20 min to give the refrigerator and probe arms time to stabilize in temperature before making repeatable measurements Stabilization occurs approximately 20 min after all refrigerator stages reach base temperature Reduce helium flow and Dewar pressure to 27 kPa 4 psi for normal operation Refer to the following sections for more information on operating the probe station once base temperature is reached If the system does not cool as expected refer to troubleshooting information in section 6 3 3 4 5 4 Operating the Follow this procedure to operate the sample stage from 4 2 K to 6 K Because it is Sample Stage from difficult for the electronic controller to achieve stable temperature control in this 4 2 Kto6K range temperature is maintained using the mechanical controls This procedure will also help minimize the consumption of cryogen while in this range and it assumes that the sample and 4 K shield stages have stabilized below 5 K 1 Model CPX Probe Station Reduce the pressure in the Dewar to 28 kPa 4 psi This reduces the temperature of the cryogen and makes it easier to regulate flow and temperature of the sample stage Reduce cryogen flow for best efficiency To do this perform the following steps a Close the transfer line foot valve one half turn wait 2 min to see if the temperature rises at the 4 K shield stage channel B on the Model 340 temperatu
115. djustable light source and power supply must specify sample illumination at time of order NOTE Coaxial illumination is recommended for highly reflective materials High efficiency helium transfer line with foot valve for precise flow regulation Instrument console Basic tools and spares kit for standard operation TABLE 1 6 Standard equipment 1 5 Required User Micro manipulated Stages Probes Probe Tips and Cables Configurable We understand that today s researcher requires flexibility Our wide selection of probes cables sample holders and options make it possible to configure a probe sta Equipment tion to meet your specific measurement applications 1 5 1 Up to Six XYZ Precision Micro Description man i pu ated Stages Micro manipulated stage with thermal radiation shields stainless steel welded bellows MMS 09 and feedthrough ports includes probe arm and base probes probe tips and cables sold separately TABLE 1 7 Micro manipulated stage Model CPX Probe Station 1 5 2 ZN50 DC RF Probes 5 1 5 2 ZN50 DC RF The ZN50 DC RF probes are ideal for DC biasing low high frequency measurements Probes low noise shielded and low leakage guarded measurements The ZN50 probe base incorporates a pair of copper braids that anchor to the 4 K stage to minimize heat loss The SMA connector is mounted directly to a replaceable alumina ceramic blade with a 50 Q stripline routed to the probe contact
116. ds sop Seaunbheshawedvawed inh Rees tava arden dauias tee phe dees 156 6 5 1 Contacting Lake ShOre icscsdisccesves cteeounetana dare ERENER ETEA 156 6 5 2 Return of EQUIPMENT arrr ssid neii rrari EEE aay suede Waa REAA 156 6 5 3 RMA Valid Period n nnnnsaunnnnnnnnunsunsrerenrrerrrrrrrrrrrrrrerrrrrrn 156 6 5 4 Shipping Charges 00 cece cece anan E IGOA A E a TERERAA 156 6 5 5 Restocking FEC wisyvnedscawediceen AEREE ATE ORE ONAA NA 156 MEX agern ae ARE EEE EENAA ER E EEA 157 Model CPX Probe Station 1 1 General 1 2 Product Description 1 1 General 1 Chapter 1 Introduction This chapter serves as a brief introduction to the components that make up a com plete testing environment with the CPX station at the core of that system Also cov ered is a brief description of the testing environment and the types of applications for the probe station Features m High stability operation from 1 5 K to 475 K m Sample can be maintained at room temperature while system cools reducing potential for condensation m Multiple radiation shields optimized to minimize cryogen consumption m Sample stage with 5 in plane rotation m Measurements from DC to 67 GHz Optional high vacuum to 10 7 Torr Optional load lock assembly m Accommodates up to 51 mm 2 in diameter wafers m Configurable with up to six thermally anchored micro manipulated probe arms m Probe arms with 3 axis adjustments and 5 theta planarization m Cabl
117. ds to be left connected and operating so vibration isolation is recommended The PS PLVI 40 pump line vibration isolator is recommended for isolating the turbo pump for this application It includes a bucket with NW 40 fittings a 1 m flexible stainless steel vacuum line and clamps Avibration isolator is also recommended any time the PS LT base temperature option is used with the CPX because the pump must be left running during operation The PS PLVI 25 pump line vibration isolator includes a bucket with NW 25 fittings a 1m flexible stainless steel vacuum line and clamps Nearly every DC or RF measurement done in a CPX has some unique configuration or requirement Although it is impossible to predict every application this section provides information on how to optimize the probe station for some of the most common measurement challenges The quality and repeatability of DC and RF measurements is greatly influenced by the integrity of the ground system Components of the probe station are integral to the overall ground system but so are signal sources and meters making the actual sample measurements Careful consideration should be given to how these components work together when setting up any experiment The following sections describe features of the probe station that relate to grounding shielding and isolation with some suggestions on how to use them effectively 2 4 1 1 Ground Reference The ground reference of a measurement system shoul
118. e www lakeshore com 128 CHAPTER 5 Advanced Operation Model CPX Probe Station 6 1 General 129 Chapter 6 Maintenance and Troubleshooting This chapter covers maintenance troubleshooting and field service instructions Instructions for contacting Lake Shore and arranging product service are in 6 1 General 6 2 Maintenance CAUTION 6 2 1 Preventive Maintenance Schedule section 6 5 This section includes both a preventive maintenance schedule and maintenance instructions unless those instructions are included elsewhere in this manual During all chamber cleaning procedures wear nitrile gloves to create a biological barrier between your hands and the inside of the vacuum chamber Failure to comply will result in poor probe station performance Use this table as a foundation in developing a time table for probe station component maintenance Tailor the schedule to fit your own probe station use Maintain a safe clean work space Clean the top surface of the sample holder Inspect for condensation during cooling Observe changes in cooling behavior Close and evacuate the vacuum chamber when finished Clean the inside of the vacuum chamber Clean the sample holder Pump out the chamber overnight or over the weekend Clean BeCu probe tips Tighten probe arm components Pump out the transfer line Change the tip seals of the scroll pump PSV81 DP Clean micr
119. e Dewar must have the following features 127 mm 0 5 in top withdraw liquid port gas port with shutoff valve and safety pressure relief valves one of which should be approximately 68 9 kPa 10 psi The Lake Shore Model PS LN2 option provides a 50 L nitrogen Dewar The CPX can require a cryogen flow rate as high as 4 5 liquid L h therefore a Dewar pressurization system is normally required Requirements for a gas pressurization system are described in section 3 2 6 The CPX includes a transfer line capable of transferring either liquid helium or liquid nitrogen from the Dewar to the probe station The transfer line supply leg is approximately 1 7 m 5 5 ft long refer to FIGURE 3 2 You will need to provide 60 L of liquid helium during installation This amount is needed to demonstrate the temperature capability of the probe station For the Vacuum Chamber the probe station vacuum chamber provides thermal insulation for the internal refrigerator as it cryogenically cools the sample being tested It also prevents condensation or other contamination from affecting the sample High quality vacuum equipment is necessary for good cooling performance and for keeping the sample clean You must provide a vacuum pumping system including appropriate gauges and vacuum lines for the CPX It must have the ability to attain at least lt 10 3 Torr in the probe station while at room temperature A vacuum isolation valve with an NW 40 flange is included
120. e and o rings are used for maintenance or configuration changes 3 3 9 Unpacking the Options 3 4 Assembling a Basic Probe System Configuration 3 4 1 Connecting the Console to the Probe Station 3 3 9 Unpackingthe Options 63 There are various options that you may have purchased with your probe station and most of these will be packed in the crate with the instrument console m PS PLVI the pump line vibration isolator will be packed in the crate with the con sole The bucket will typically not be packed in a box but will be bubble wrapped and shrink wrapped The bellows and associated hardware will be bubble wrapped and packed in the accessories box m PS OAC the air compressor is also packed along with the console It will be packed in a box from its supplier Please follow supplier directions to unpack it m PS LN2 the liquid nitrogen Dewar may be shipped inside the crate with the con sole or it may be shipped separately depending on the options purchased and space available in the crates It will also be shipped in a box from its supplier Please follow supplier directions for unpacking it from its box m PS LT the pump portion of the low temperature option is packed alongside the console It will be bubble wrapped and shrink wrapped The smaller associated items will be packed in the accessories box m PS PVIS the pneumatic isolator is integrated into the TMC stand and it will not be crated separately Use the follo
121. e condensation on the sample 1 Evacuate the chamber as described in section 4 4 2 2 Cycle purge the vacuum chamber using the guidelines in section 4 4 4 but use dry argon instead of nitrogen for this process 3 Re evacuate the system to achieve a lower base pressure than achieved initially instep 1 4 Control the sample stage at 290 K using control settings in TABLE 4 3 and TABLE 4 4 loop 1 on the Model 340 temperature controller 5 Cool the refrigerator by following the instructions in section 4 5 3 with the fol lowing exception when instructed to open the micrometer valve six turns as found in step 4 section 4 5 3 1 open it only two turns The temperature control ler will keep the sample stage warm while the remainder of the refrigerator cools to base temperature At this point any residual gas in the chamber will condense on the 4 K shield stage 6 When the 4 K shield stage is cooled to less than 10 K open the micrometer valve six turns to begin cooling the sample stage and turn off the heater The sample stage will not begin cooling until step 7 is completed 7 The warm sample stage acts as a flow restriction and will cool very slowly Force liquid helium into the sample stage to speed up the cooling process Follow this procedure to do this El akeShore www lakeshore com 110 CHAPTER 5 Advanced Operation 5 2 2 Operating the Sample Stage Down to 2 K CAUTION Model CPX Probe Station a Reduce cry
122. e control knob on the transfer line can become stuck if the foot valve is blocked with ice It can also become stuck if the transfer line is inserted into a Dewar with the valve closed completely Do not force the foot valve control knob when it is stuck This can damage the delicate foot valve Ice build up in the foot valve has the same causes as described in section 6 3 2 2 Follow the same instructions to remedy and prevent the foot valve from freezing Remember the transfer line must be removed from the Dewar to melt the ice because the foot valve is at the bottom of the transfer line supply leg Heating the foot valve control knob at the top will not help The foot valve can also become stuck if the transfer line is inserted into a Dewar with the valve closed Thermal contraction of the valve parts can jam the valve The remedy is the same as for an ice blockage remove warm open and reinsert the transfer line Many refrigerator cooling issues are actually symptoms of vacuum problems or transfer line problems It is advisable to review section 6 3 1 and section 6 3 2 before proceeding with this section The most common refrigerator cooling problems are listed below 6 3 3 1 Refrigerator Does Not Begin to Cool Use this section if neither the sample stage nor 4 K shield stage begin to cool The first step is to make sure that all temperature controller heater loops are turned off or have a O K setpoint Both the Model 332 and 340 have tw
123. e controllers One Lake Shore Model 340 with 3462 expansion card one Model 332S and one Model 142 200 W 2 channels 100 W each power supply independent regulation of sample stage radiation shields and probe arm temperature monitoring Electroless nickel plated aluminum vacuum chamber Diameter 279 mm 11 in Removable top lid with clear fused quartz viewport G54 mm 2 13 in window Probe ports 6 surround the sample thermal radiation shield Pump port NW 40 pump sold separately Gas purge and 0 5 psi safety pop off port NW 25 Option port High vacuum Spare ports NW 40 and NW 25 Machined aluminum base plate 610 mm x 737 mm 24 in x 29 in Support stand Heavy duty welded steel stand optional pneumatic vibration isolation system available Temperature sensor installed and wired to a 6 pin feedthrough included on one probe arm Grounded sample holder SH 1 25 G accommodates up to a 32 mm 1 25 in sample with a G25 mm lin probe area Optics Zoom 70 microscope 7 1 zoom with 4 um resolution Color CCD camera S video or composite output format Swing arm Optics can be manipulated to view any part of the sample or wafer and can be retracted and swung away to allow access to the top of the vacuum chamber for sample exchange Video monitor High resolution 17 inch Sample illumination Coaxial via optical fiber or ring light from an a
124. e cooling 1 Follow section 5 2 3 2 to begin cooling the probe station with nitrogen 2 Allow the sample stage and 4 K shield stage to cool below 85 K This may take approximately two to three hours 3 Purge nitrogen from the transfer line Remove the transfer line from the probe station and nitrogen Dewar Use a heat gun to warm both ends of the transfer line and melt the ice Wipe both ends of the transfer line dry with a clean cloth Insert the withdraw leg of the transfer line a few inches into the helium Dewar and tighten the 1 2 inch compression fitting Do not allow the transfer line to contact liquid Regulate the helium Dewar to 21 kPa to 28 kPa 3 to 4 psi f Allow helium gas to flow for several minutes clearing nitrogen from the transfer line anov 2 4 Purge nitrogen from the refrigerator a Wait forall stages of the refrigerator to warm to 80 K to 85 K Loosen the 12 inch compression fitting c Finish inserting the withdraw leg of the transfer line into the helium Dewar started in step 3 Check to make sure gas is flowing but do not wait fora plume to form d Tighten the 1 2 inch compression fitting If gas ceases to flow from the target side of the transfer line this is an indication that a blockage has occurred Remove the transfer line from the Dewar and repeat the process starting at 3b above e Immediately insert the target leg into the probe station bayonet The initial flow of helium gas wil
125. e eee 61 3 3 8 1 Unpacking the Instrument Console cccc cece cece 62 3 3 8 2 Unpacking the Vision System 0 0 0 0 cece eee ee ee ee eee eee eee naae 62 3 3 8 3 Unpacking the Transfer Line c ce eeee cece teen e eect enna 62 3 3 8 4 Unpacking the Turbo Pumping System Option 665 62 3 3 8 5 Unpacking the Tool Kit and Spares Kit cc cece eee eee eens 62 3 3 9 Unpacking the Options cece cece eee cece cence tenet nena 63 3 4 Assembling a Basic Probe System Configuration ccce cece eee e cece eens 63 3 4 1 Connecting the Console to the Probe Station 0 cece cece eee e eens 63 3 4 1 1 Complete the Connections to the Probe Station 68 63 3 4 2 Assembling the Vision System cece cece e een e eee eee nent eee enna 64 3 4 2 1 Assemble the Vertical Post cc cece cece eee eee eee ees 64 3 4 2 2 Assemble the Microscope and Horizontal Boom 64 64 3 4 2 3 Connect the Vision SysteM 0 cece cece eect enn rii ueris 66 3 4 3 Assembling the Turbo Pumping System cc cece eee eeee eee eee eaeees 67 3 4 3 1 Prepare the Probe Station Before Attaching the Vacuum 68 3 4 3 2 Prepare the Turbo Vacuum Pump Components 65 68 3 4 4 Assembling Probe Station Options ccc cece cece eee eee e eens 70 3 4 4 1 Assembling the Pump Line Vibration Isolator PS PLVI 40 or
126. e eee eneeees 146 6 3 3 7 Erratic Temperature ReadingS cece ee eee cece eee eeae tees 147 6 3 4 Image System Troubleshooting 0c cece cece cece e eee e eee eees 147 6 34 NO WMASE mrem iusto E E See ledes mee toe eA ATIO 147 6 3 4 2 Insufficient Sample Illumination 0 0 cece cece cece eee 148 6 3 4 3 Poor Image QUAIILY cas case sda gereeias aden oetweaanderecnvesennees 148 6 3 4 4 Fog on the VieWport cccc cece cece cece eee e eee e eee eeeeennee 148 6 3 4 5 Height ACjUStMent dees wiseasece awa daccetvs iai EE ENN 148 6 3 4 6 Vibration in the Image System ccc cece cece eee e ee ee eee e ees 149 6 3 4 7 Poor contrast IMAGES xc osicisos eetendiean palmer eis ceameres anne 149 6 3 4 8 Mage Orientation serere an e a EE AAEE aed adacs 150 6 3 5 Probe Troubleshooting ccssrrrrisiterii ttin ninr tit TEn N EE 150 6 3 5 1 Bent or Broken Probe TIPS 0 0 cece cece cece eee ence nena ee 150 6 3 5 2 Poor or Non Ohmic Electrical Contact cece eee cence es 151 6 3 5 3 Loss Of GONTINUILY eoo oen sedan EKTA ner AUEK EAE S 152 6 4 S rvice Re feErENC Errori ienie E EE EEE EEEE ENEA EENEN 153 6 4 1 Power Requirements and Power Configuration Information 153 6 4 2 PIN OULSS cicsncnaticeeninan rehearing chpha vaguest deatenaeana EEEE E eds 154 6 4 3 Instrumentation Wiring Diagram cc cece cece ee cece eect eee e eee e ees 154 6 5 TEChniGall INQUIRIES j dcsscin
127. e eens 95 4 5 2 Controls for Temperature Operation 0 cece cece cece eect eee e eee ees 95 4 5 2 1 Mechanical Refrigerator Controls 0 00 cceeeeeeee eee eeeneeees 95 4 5 2 2 Electronic Temperature Controls c cece cece cece eee ene ene ees 97 4 5 3 Cooling the Probe Station with Helium 00 cece cece cece eee eeee eee eees 98 4 5 3 1 Prepare the Systm cn cererea orra e EA 98 4 5 3 2 Initiate the Helium Transfer ssussussissirsirsrrrirrrerrereen 99 4 5 3 3 Allow the Sample and Radiation Shield Stages to Cool 100 4 5 4 Operating the Sample Stage from 4 2 KtO6K 00 eect eee ees 100 4 5 5 Operating the Sample Stage 6 K and Above 0 ccc cece cece eee e eee 101 4 5 6 Returning to Room Temperature cece eee ee eee teen cette eeeee 102 4 5 7 Temperature Control SUMMALY 0 cece e cece eee ee eee e eee e nena ates 102 4 6 Imaging and Probing the Sample cece eee cece e eee eee e eens 104 4 6 1 Using the Microscope to Image the Sample cece eeeeeeeee eee 104 4 6 2 Landing the Probe si ssiecicess onnesta nya nantan AAAA EAEE 105 456 3 SAMPple ROtALION vs cc cavsasassede Rie Ernan A E LARS REEE AIUREA 105 4 6 4 Using the Planarization Assembly c cee ceeee cece ene teen enna 106 4 6 4 1 Adjusting the Angle of the Planarization Assembly 107 Chapter 5 BL GEM eral wud on dvnatsws co E doubles nectar s
128. e in 120 V PA SEN Probe arm modification with temperature sensor installed and wired to a 6 pin feedthrough PS PAB 09 Probe arm and base cS 5 Calibration substrate for GSG probes pad size 50 m2 calibration type SOLT short open load through LRL line reflective line LRM line reflective match pitch range 75 to 250 pm Calibration substrate for GSG probes pad size 25 ppm2 calibration type SOLT short open load through LRL line reflective line LRM line reflective match pitch range 40 to 150 pm TABLE 1 15 Equipment options Cs 15 Model CPX Probe Station 1 7 Safety Considerations 1 7 Safety Considerations 9 Observe these general safety precautions and all warning a cautions throughout this manual during all phases of instrument operation service and repair Failure to com ply with these precautions or with specific warnings elsewhere in this manual vio lates safety standards of design manufacture and intended instrument use Lake Shore Cryotronics Inc assumes no liability for customer failure to comply with these requirements The CPX probe station protects the operator and surrounding area from electric shock or burn mechanical hazards excessive temperature and spread of fire from the instrument Environmental conditions outside of the conditions below may pose a hazard to the operator and surrounding area Indoor use Altitude to 2000 m Temperature for safe operation 5 C to 40 C
129. e into the microscope The coaxial light configuration guides light from the light source along the same path coaxially with the light returning from the sample This allows the vision system to image very highly reflective samples such as those patterned on polished silicon FIGURE 2 21 left is an image of four gold circles 10 um to 100 um in diameter patterned on a highly reflective surface illuminated with a coaxial light Although the image appears relatively flat and has modest contrast it is more than adequate for properly landing probes FIGURE 2 21 right is an image of the same sample illuminated with a ring light The image is darker and even lower in contrast because nearly all of the light is cleanly reflected away from the microscope It would be difficult to properly land a probe using this image FIGURE 2 21 Left Highly reflective surface through a Zoom 70 with a coaxial light Right Highly reflective surface through a Zoom 70 witha ring light Model CPX Probe Station 2 3 7 Turbo Pumping System PS V81DP 31 The ring light surrounds the end of the microscope with light from the source which illuminates the sample from all directions The light scatters as it reflects off of textured or uneven surfaces giving images contrast and the appearance of a third dimension FIGURE 2 22 right is an image of a surface mount device illuminated with a ring light The natural appearance of the sample is preferred by many operators
130. e probe points the probe tips can safely probe substrates that are higher in temperature With the thermal anchor point for the probes located alLakeShore www lakeshore com 26 CHAPTER 2 System Overview Model CPX Probe Station onthe 4 K shield stage in the CPX probe station the microwave probes can safely probe a substrate on the sample stage up to 475 K as long as the 4 K shield stage is maintained at 300 K or less Refer to section 3 5 1 for more discussion on thermal anchoring FIGURE 2 17 Microwave probe 2 3 3 2 Microwave Compatible Cables and Connectors A microwave probe cable consists of a microwave semirigid coaxial cable with connectors permanently mounted on each end There are three frequency configurations for the probe cables determined by the connector used The cable is fed through the probe arm base with a compression seal to minimize signal loss The outer conductor of the semirigid coaxial cable is grounded by the thermal anchor of the probe body The microwave probe must be specified with the same frequency and connector type as the probe cable FIGURE 2 18 Microwave cable Thought should be given to the measurement equipment that will be used with the microwave probes as the connections on existing measurement equipment may dictate the connectors on the microwave probe arms 1 Kk connector 2 92 mm with semirigid cable this is the general purpose microwave connection rated for continuous mode free ope
131. e sample holder from the sample stage FIGURE 4 4 Using tweezers or your fingers pull the cable plug out of the sample holder socket The cable can be left as shown in FIGURE 4 4 Be very careful that the tweezers do not slip off the cable plug and onto the wire where they can accidentally pull the wire out of the connector Veas TEEN ME A FIGURE 4 4 Left Disconnecting the triaxial sample holder Right Cable plug left out after disconnecting 2 Screw the lifter tool into the sample holder There are two holes available for the lifter Use the most convenient FIGURE 4 5 3 Using the 2 5 mm hex driver loosen the four M3 screws Be careful not to drop them inside the chamber 4 Lift the screws out with tweezers or leave them in their holes and lift them out with the sample holder Model CPX Probe Station 4 3 3 Mounting Samples on the Sample Holder 4 3 3 Mounting Samples onthe Sample Holder 87 5 Using the lifter tool lift out the sample holder and screws Store the sample holder ina clean place until needed 6 Ifthe probe station is not going to be used immediately it should be reassembled and evacuated FIGURE 4 5 Lifter tool screwed into a lifter tool hole The sample must be properly mounted to the sample holder so that the two are in close thermal contact If the sample is not properly mounted the sample can deviate from the temperature read by the sample stage temperature sensor causing errors in mea
132. e sensor and heater Prior to heating or cooling the system it is important to verify that the sensor heater cabling and temperature controller are all configured properly If any of the control loop wiring is mixed up ora sensor is malfunctioning it is possible for the system to overheat and become damaged during warm up You can check the instrumentation wiring diagram if your probe station does not perform as these tests suggest Use steps 1 4 to prepare the system for the sensor and heater test Then use TABLE 3 3 to run the sensor and heater test 1 With the system stabilized at room temperature verify that all sensors read within a few degrees of each other Only the sensors on the sample stage and 4 K shield stage are accurately calibrated so some discrepancy in the readings can be expected 2 Install the radiation shield lid and vacuum chamber lid 3 Use the z axis micrometers to raise all probes up 3 mm to 4 mm above the sample stage Do not allow the temperature on any stage to raise more than 10 K above room temperature when the system is not being actively cooled Carefully observe all temperature readings and be ready to turn the heater off if any stage raises more than 10 K above room temperature 4 Use TABLE 3 3 to set the sample stage s sensor and heater 5 Monitor the temperature reading Within 10 min the stage should raise approximately 5 K and begin to stabilize The heater output for the chosen stage should the
133. e two different microscopes in Chapter 1 The specified resolution indicates the smallest feature that can be reasonably distinguished on the sample s surface The sample s texture and contrast also affect resolution Although the Zoom 160 always offers a higher magnification than the Zoom 70 the useable resolution of the two microscopes is often similar This is primarily a result of the relatively large working distance between the microscope and sample which limits the resolution of the Zoom 160 FIGURE 2 20 compares the resolution of the two microscopes under similar conditions in a TTPX probe station Although the Zoom 160 image has visibly more resolution in this comparison it is ES akeShore www lakeshore com 30 CHAPTER 2 System Overview important to note that these results are difficult to duplicate during actual measurements Factors such as the sample surface texture and normal levels of room vibration can quickly degrade the resolution of the Zoom 160 to match that of the Zoom 70 FIGURE 2 20 Left Best case resolution approximately 2 um obtained obtained with Zoom 160 and coaxial light on a TTPX probe station Right Typical resolution approximately 3 um obtained with Zoom 70 and coaxial light on a TTPX probe station 2 3 6 2 Lighting Types There are two types of lights available for each microscope coaxial and ring The primary difference between the two is in the way light is reflected off of the sample surfac
134. e uses can normally be wiped clean when the probe is landed If the probe or pad is allowed to form a thick oxide film tarnish more aggressive action is necessary Pre cleaning or over travel of the probe tip scratching may be required to create forces large enough to break the film The larger softer tips that help increase surface area may not be as good at scratching through oxidation therefore a compromise is often necessary Controlled electrical current can also be used to break through any remaining insulating barrier Afour lead measurement technique is frequently used during resistance measurements to eliminate the effect of unwanted contact and lead resistance In this technique the two excitation current leads are separated from the two voltage measurement leads all the way down to the probe tips A reasonable amount of contact resistance and small changes in contact resistance will not appear in the voltage measurement because there is no current flowing through the voltage contact However this technique will not overcome contacts that have too much resistance or are non ohmic Ohmic contacts result from a good interface between two conductive surfaces They are called ohmic because they exhibit a linear relationship between current and voltage like a resistor Non ohmic contacts are typically formed when oxides or other contamination is present between the conductive surfaces They exhibit a non linear relationship between cur
135. e warmed the system to room temperature 1 Using the camera setup menu reset the camera controls to their factory preset values 2 Remove the vacuum chamber lid and radiation shield lids 3 Re establish the sample image with the lids off al akeShore www lakeshore com 150 CHAPTER 6 Maintenance and Troubleshooting 6 3 5 Probe Troubleshooting Model CPX Probe Station This should provide an image with very high quality and contrast If it does not go back through the assembly procedures section 3 4 2 and the earlier parts of section 6 3 4 and try to identify the problem The image obtained with the chamber and shield lids off is better than can be expected with them on The viewport optics will always degrade image quality no matter how well the system is optimized Experiment with different sample materials first with the lids off then add the lids back on one ata time First try a very reflective sample such as a piece of polished silicon wafer Then experiment with a sample that absorbs light Finally try a sample that has high contrast and image on the three dimensional details in the sample holder itself This investigation will establish the limits in capability of the probe station and its configuration of microscope and light source Optimize the light intensity and camera settings for the type of sample most commonly tested in the probe station If the results do not meet expectations for the equipment purchased co
136. eans listed below However the most direct and efficient means of contacting is to complete the online service request form at http www lakeshore com sup serf html Provide a detailed description of the problem and the required contact information You will receive a response within 24 hours or the next business day in the event of weekends or holidays If you wish to contact Systems Service by mail or telephone use the following Lake Shore Cryotronics Inc 575 McCorkle Blvd Westerville Ohio 43082 USA Phone 614 891 2243 option 6 Fax 614 818 1608 e mail sysservice lakeshore com The probe station is packaged to protect it during shipment Please use reasonable care when removing it from its protective packaging and inspect the probe station carefully for damage If it shows any sign of damage please file a claim with the carrier immediately Do not destroy the shipping container it will be required by the carrier as evidence to support claims Call Lake Shore for return and repair instructions All equipment returns must be approved by a member of the Lake Shore Systems Service department The service engineer will use the information provided in the service request form and will issue a Return Material Authorization RMA Once the RMA has been approved you will receive appropriate documents and instructions for shipping the equipment to Lake Shore You will be given an RMA number This number is necessary for all returned
137. eated for fine positioning providing the first axis of motion 3 Rotate the hand dial until the microscope is over the center of the viewport This process is repeated for fine positioning providing the second axis of motion 4 Turn on the monitor camera and light source 5 Adjust the light source to 50 to begin As the image is refined use the least amount of light necessary to view the sample Turn the light source off during extended measurements to reduce thermal radiation to the sample 6 Zoom the microscope to its lowest magnification setting to begin As the image is refined zoom as necessary to obtain the desired view 7 Focus must be adjusted repeatedly as the image is zoomed in and further refined It is necessary to focus clearly on the sample surface in order to properly land probes 8 The shaft collar is set at Lake Shore for relatively thin samples If thicker samples are outside of the focal range of the microscope the shaft collar should be raised 4 6 2 Landing the Probe CAUTION CAUTION 4 6 3 Sample Rotation 4 6 2 Landingthe Probe 105 The camera has a specified working distance which is the distance from the sample to the lens Raising or lowering the microscope outside this working distance will not improve magnification or resolution Follow this procedure to manipulate a probe to the sample and make contact The sample stage and probe arms should be at a steady temperature before landing a pr
138. ect current power line Alternating current power line Alternating or direct current power line Three phase alternating current power line Earth ground terminal Protective conductor terminal Frame or chassis terminal On supply O Or 220 2 il Off supply m A A FIGURE 1 1 Safety symbols Model CPX Probe Station Equipment protected throughout by double insulation or reinforces insulation equivalent to Class II of IEC 536 see Annex H CAUTION High voltages danger of electric shock background color yellow symbol and outline black CAUTION or WARNING See instrument documentation background color yellow symbol and outline black Chapter 2 System Overview 2 1 General Chapter 2 illustrates the major CPX components options and accessories necessary to provide the features and specifications listed in Chapter 1 2 2 Major This section is intended as a reference for identifying assemblies operator interfaces Components and controls called out in later chapters A CPX probe station comprises the probe station itself and four major sub systems FIGURE 2 1 illustrates an overall view of the full system Each major component is detailed in the following sections Vision system Vision system components Probe station Cryogen Dewar and Probe arm assemblies pressurized gas system Refrigerator Transfer line Pressurized gas tank Instrument console Vacuum chamber
139. ed in conjunction with a vector network analyzer VNA to characterize the measurement setup out to the tips of the GSG probe Lake Shore offers two calibration substrates CS 5 for 75 um to 250 um probe pitch and CS 15 for 50 um to 150 um probe pitch Each substrate is capable of calibrating SOLT short open load through LRL line reflective line and LRM line reflective match See section 2 5 for more information on microwave calibrations 9 INI SIIVLSNANI S 53 s j IE Bi FIGURE 2 19 CS 5 calibration substrate Optical fiber compatible probe arms can be ordered as PS FOA options The option is configurable to accommodate a variety of fiber types and applications Each option includes a probe arm and base with vacuum feedthrough and mount Lake Shore offers the choice of several optical fibers or customers can install their own fibers in the field Contact your Lake Shore sales representative for more information El akeShore www lakeshore com 28 CHAPTER 2 System Overview 2 3 5 Sample Holders Model CPX Probe Station Sample holders attach to the top of the sample stage to provide a good mounting surface for the wafer or device under test They can be removed easily to facilitate careful sample mounting One grounded sample holder is included with the system but it can be interchanged with any of the optional sample holders as long as the appropriate feedthrough wiring option is installed for coaxia
140. ed in the temperature controller configuration table TABLE 4 1 However the controller settings should be re verified any time the system is moved serviced or reconfigured section 3 6 1 3 The sample stage is the only stage actively controlled during normal operation The other control loop setpoints should be set to zero or the heaters should be turned off The sample stage control operates with different control settings at different temperatures Nominal values for helium operation are described in each of the following sections and summarized in the temperature controller configuration table TABLE 4 3 and TABLE 4 4 Some adjustments to these settings will be required during operation Control of the other three stages is generally limited to warming the system for sample exchange They are most often operated by turning the heater output on and off Follow this procedure to cool the sample and radiation shield stages This procedure assumes the probe station and transfer line are at room temperature and that the vacuum chamber has been evacuated following section 4 4 2 It is tempting to save helium by shutting off flow to the 4 K shield stage but it is not rec ommended because the radiation shields would not be cooled Operating without prop erly cooled radiation shields will increase base temperature and increase the temperature gradient between the sample and sample stage 4 5 3 1 Prepare the System 1 Use the z axis micrometer
141. ee e eee eee e eee eeeeees 29 2 3 5 4 Triaxial Sample Holder eee ee cece cece eee eee eee e eee eees 29 2 3 6 Vision System Configuration 1 0 0 0 cece cece e eee e eee ee d eenee eset ene nnas 29 a akeShore www lakeshore com TABLE OF CONTENTS Chapter 3 Installation and Setup Model CPX Probe Station 2 3 6 1 MICIOSCOPES 4 242 cdacacaad ve sinh cannes Gade se deniuise AAE Ww ieee es 29 2 3 6 2 Lighting TYPES ost aeecescundenresearednent ETE SERA EEEE AE 30 2 3 7 Turbo Pumping System PS V81DP 2 0 00 0 cece cece ence eee e eens 31 2 3 8 High Vacuum Option PS HV CPX 2 0 0 0 cece cece cece cence eee reren 32 2 3 9 2K Base Temperature Option PS LT cece cece e cece eee e enna ee 32 2 3 10 Load lock Assembly Option cc cece eee ence eee een i esia ienis 33 2 3 11 Liquid Nitrogen Dewar PS LN2 6 c cece cece cece eee e eee rerne 33 2 3 12 Automatic Dewar Pressure Controller PS DPC ccc cece eee 33 2 3 13 Pneumatic Vibration Isolation Option PS PVIS cece cece eens 33 2 3 14 Pump Line Vibration Isolator PS PLVI 40 or 25 00 0 cc cece cece eens 35 2 4 Considerations for DC RF Electrical Measurements cceeeeeee resene 35 2 4 1 Grounding Shielding and Isolation for DC RF Measurements 35 2 4 1 1 Ground Reference 23 2 30e cu saeeactee iis dg taezinaalte EE REEE EANA 35 2 4 1 2 Avoiding Ground LOOPS ccc c
142. eeeee cent ene eee eee nnee eee e enna 36 P E SNIEIGING Er E P E E E A 37 24 1 4 NOISE Isolation ei enere yrii ia ap O R i 37 2 4 2 Basic DC Electrical Measurements 0 ccc c eee e cece eee e eee e ene ee 37 2 4 3 Basic RF Electrical Measurements 6 00 cece cece cece ee eee ene eee e eens 38 2 4 4 Conductive Back Side Features 6 c cece cece cece cece ee eeeeeeeee ee 39 2 4 5 Back Side Voltage BiaSiNg ccc cece e cece eee eee sinis rAr enna 39 2 4 6 Small Signal Low Noise DC RF Measurements 0 c0ceee ence ee ene 40 2 4 6 1 Noise Isolation for Low Noise Measurements 000eeeee ee 40 2 4 6 2 Sample Isolation for Low Noise Measurements 000000 ee 41 2 4 6 3 Additional Considerations for Low Noise Measurements 41 2 4 7 Measuring Low Resistance ce cece eee eee eee eee e ene eeneneea 41 2 4 8 High Impedance Low Leakage Measurements 00 ceeeeeeeee eens 41 2 4 8 1 Grounding and Shielding 00 cc cece cece ee cece een ee eee ena 42 2 4 8 2 Driven GUATS ii c sacs i pctieaa sa pec ew eassaverseedan acter sda i 42 2 4 8 3 Guarded Probe Station Configurations cece eee eee eee 42 2 4 8 4 Measurement Voltage Limits cee eee eee eee e eee rena 44 2 5 Considerations for Microwave Measurement 0 cece cece eee e eee eeeeees 45 2 5 1 Microwave Cables and Connectors 6 eee ee eee eee e eee eee ee
143. em 31 major components 22 power requirements 56 turbo pumping system basic operation 91 U unpacking 58 crates 60 instrument console 61 moving and lifting the probe station 59 options 63 tools required 59 V vacuum chamber 13 cleaning 130 closing the shields 90 diagram of 13 evacuating 93 ground reference 35 purging 58 94 removing condensation 137 shielding 37 vacuum levels 93 vacuum requirements 57 vacuum gauge 22 image of 68 installing 68 location 92 vacuum requirements 57 vacuum troubleshooting 138 Vector Network Analyzer 27 48 vibration isolation 8 33 55 70 low noise measurements 41 viewport window maintenance 131 vision system 22 assembly 64 power requirements 56 153 troubleshooting 147 unpacking 62 voltage biasing 39 43 W warm up 102 purging 94 removing condensation 137 sensors and heaters 14 transfer line 143 wiring diagram 154 Z ZN50 compatible probe cables 24 ZN50 compatible probe mounts 25 ZN50 probe tip material 23 ZN50 Probes 23 al akeShore 159 www lakeshore com 160 INDEX Model CPX Probe Station
144. epair or replace the Product if it is so defective without charge to the owner for parts service labor or associated customary return shipping cost Any such replacement for the Product may be either new or equivalent in performance to new Replacement or repaired parts will be warranted for only the unexpired portion of the original warranty or 90 days whichever is greater 2 Lake Shore warrants the Product only if it has been sold by an autho rized Lake Shore employee sales representative dealer or original equipment manufacturer OEM 3 The Product may contain remanufactured parts equivalent to new in performance or may have been subject to incidental use 4 The Warranty Period begins on the date of delivery of the Product or later on the date of installation of the Product if the Product is installed by Lake Shore provided that if you schedule or delay the Lake Shore installation for more than 30 days after delivery the Warranty Period begins on the 31st day after delivery 5 This limited warranty does not apply to defects in the Product resulting from a improper or inadequate maintenance repair or cal ibration b fuses software and non rechargeable batteries c soft ware interfacing parts or other supplies not furnished by Lake Shore d unauthorized modification or misuse e operation outside of the published specifications or f improper site preparation or mainte nance 6 TO THE EXTENT ALLOWED BY APPLICABLE LA
145. er is desirable to prevent thermal gradients across the wafer but because of their size differences in thermal expansion can cause the wafer to crack when cooled There are two common methods for reducing the risk of cracking wafers Flexible Mounting flexible mounting methods like vacuum compatible grease allow the sample and sample holder to expand and contract at different rates Be careful at very low temperatures because some types of grease freeze and become solid al akeShore www lakeshore com 88 CHAPTER 4 Basic Operation Model CPX Probe Station Reduce Gradients cool and warm the system slowly using the setpoint ramp feature of the temperature controller to reduce temperature gradients across the sample Consult the temperature controller manual for details on the setpoint ramp feature 4 3 3 3 Temporary Mounting Temporary mounting is the most common mounting technique among probe station users It is easy and fast but still gives reasonable results for most applications These are the four most common methods for temporarily mounting samples 1 Vacuum Compatible Low Vapor Pressure Grease Apiezon N grease works well to improve thermal contact at cryogenic temperatures Apiezon N grease has a specified operating range of 1 K to 300 K At lower temperatures it freezes changing its physical and thermal properties At warmer temperatures 316 K it melts and becomes less tacky To use grease brush a very light coat on
146. er when all refrigerator stages are at their temperature setpoints and the probe arm is above 290 K If the probe station is not going to be cooled within the next 6 h do the following a Raise the transfer line so the bottom of the Dewar side leg is out of the liquid cryogen in the Dewar but still inside the Dewar b Open the shut off valve to the low pressure relief valve on the Dewar The Dewar pressure will drop c Asthe Dewar pressure approaches atmosphere remove the transfer line from the Dewar and store it where it will not be bent or dropped d Close the top of the Dewar and leave the low pressure relief valve open If the probe station is going to be out of service for any length of time a Ifthe vacuum chamber was opened reinstall the radiation shield lid and vacuum chamber lid Close the purge valve and disconnect the gas line Open the vacuum isolation valve Turn on the turbo pump for approximately 15 min Close the vacuum isolation valve Turn off the turbo pump hoang The temperature controller configuration table TABLE 4 1 and the mechanical and electronic control settings table TABLE 4 3 and TABLE 4 4 summarize the typical settings needed to maintain CPX temperature control Temperature Input controller Auxiliary Temperature sensor Control rear panel amp Sensor type controller channel Sensor curve loop Power limit Resistance connection channel Sample stage stage 1 Silicon diode Model
147. es shields and guards minimize electrical noise and thermal radiation losses m Options and accessories for customization to specific research needs The Model CPX is a versatile cryogenic micro manipulated probe station used for non destructive testing of devices on full and partial wafers upto 51 mm 2 in in diameter The CPX is a platform for measurement of electrical electro optical para metric high Z DC RF and microwave properties of materials and test devices Nanos cale electronics quantum wires and dots and semiconductors are typical materials measured in a CPX A wide selection of probes cables sample holders and options makes it possible to configure the CPX to meet your specific measurement applica tions The CPX operates over a temperature range of 4 2 K to 475 K With options the base temperature can be extended down to 1 5 K The probe station provides efficient tem perature operation and control with a continuous refrigeration system using either helium or nitrogen Vapor cooled shielding optimizes efficiency and intercepts black body radiation before it reaches the sample A control heater on the sample stage along with the radiation shield heaters provide the probe station with fast thermal response The CPX is user configured with up to six ultrastable micro manipulated probe arms Each arm provides precise 3 axis control of the probe position to accurately land the probe tip on device features The sample stage p
148. f a pair of ZN50 probes configured with K connectors and semirigid cable Special consideration must be given to the choice of a sample holder if the sample is constructed with conductive features patterned on the back side of the substrate Lake Shore offers optional isolated sample holders that have a non conductive top surface for this application Isolated sample holders also work for samples constructed on a uniformly conductive substrate However coaxial sample holders should also be considered for this case as described in section 2 4 5 FIGURE 2 27 Isolated sample holder Experiments such as device characterization often require voltage biasing The biasing voltage can be introduced through a probe if the bias contact is available on the top surface but doing so prevents the use of the probe for other purposes Voltage biasing can be done through the sample holder if the bias contact is available on the back side of the sample or if biasing is done directly through the substrate An optional coaxial sample holder and FT BNC feedthrough and cable configuration allows convenient back side biasing as illustrated in FIGURE 2 28 ELakeShore www lakeshore com 40 CHAPTER 2 System Overview Triaxial signal connector T Cryogenic l I coaxial cable ZN50 Coaxial ED mi Piate sample holder I pies Probe arm shield U Bias voltage Cryogenic
149. f you suspect a leak We recommend cleaning sample holders between uses to ensure samples make good thermal contact Considering the many possible methods used to mount samples onto the sample holders a variety of methods are necessary to clean them Chemical solvents are recommended over mechanical removal methods The gold plating on the top surface of many sample holders is delicate and will not hold up to abrasives scrubbing or scratching Follow the manufacturer s recommendations for removing sample mounting materials such as photoresist Be sure that all chemicals are compatible with the materials in the sample holder Most solvents and removers are compatible with the copper and gold grounded sample holders Coaxial and triaxial sample holders also contain Kapton and solder Isolated sample holders use sapphire Only work with volatile or toxic chemicals xylene acetone etc in a well ventilated area or under a fume hood To remove the sample mounting material m Apiezon N grease can be removed using xylene with an isopropyl alcohol rinse m Silver paint can be removed by soaking in acetone 6 2 7 Cleaning BeCu Probe Tips CAUTION 6 2 7 Cleaning BeCu ProbeTips 133 m VGE 7031 varnish can be removed using equal parts ethanol and toluene After removing the mounting material wipe with a lint free cloth to remove any solvent residue Finish with an isopropyl alcohol rinse Probe tips made of beryllium copper BECU
150. ficantly longer than the times represented in the cooling curve FIGURE 6 7 investigate the possible causes listed in section 6 3 3 2 to section 6 3 3 4 In addition be sure to pre cool the transfer line as shown in FIGURE 4 14 The cooling curve pictured below was performed following the procedure given in section 5 2 1 The sample stage cooldown was purposely cooled slowly allowing the radiation shields to cool first so that the majority of residual gas was attracted to them and not the sample 250 200 150 100 Stage temperature K 50 00 00 00 00 20 00 00 40 00 01 00 00 01 20 00 01 40 00 02 00 00 Time h FIGURE 6 7 Typical CPX refrigerator cooling curve for helium 6 3 3 6 Micrometer Valve Problems The most common problems with the micrometer valve are that it can become stuck or difficult to turn In either case the valve should never be forced open or closed because it can be easily broken Cooling the system with the valve closed completely can cause it to stick as the valve body contracts around the stem Operating instructions always specify opening the valve before cooling If the valve does become stuck the refrigerator must be warmed before the valve can be opened Warming the valve handle will not help because the valve body is inside the refrigerator not near the handle 6 3 4 Image System Troubleshooting 6 3 4 Image System Troubleshooting 147 6 3 3 7 Erratic Temperature Readings The CPX sa
151. from the box Remove the protective metal sheath that is taped on covering the transfer line outlet The transfer line is best stored by hanging it on hooks on a wall See FIGURE 3 6 for an image of the transfer line The transfer line box also contains the evacuation adapter which is used to pump out the transfer line yearly or as needed as part of routine maintenance Do not misplace or inadvertently discard the evacuation adapter shipped with the transfer line See FIGURE 3 6 for an image of the evacuation adapter FIGURE 3 6 Left Transfer line Right Evacuation adapter 3 3 8 4 Unpacking the Turbo Pumping System Option If you purchased the turbo pumping system from Lake Shore open the box and remove all plastic wrap and ties Remove the flexible stainless steel vacuum line from the plastic bag The NW 40 fittings necessary to connect the turbo pumping system to the probe station will also be included in the instrument console crate The turbo vacuum system can be left on the floor near the probe station or placed on a cart 3 3 8 5 Unpacking the Tool Kit and Spares Kit The tool kit and the spares kit come wrapped in plastic bags in the accessories box In each kit is a form that lists the included components part numbers and their use on the probe station Retain these forms for reference or for use when ordering additional items The hex keys and lifter tool are needed during assembly and operation The 8 mm wrench hardwar
152. g efficiency and throughput by reducing cycle time to roughly 1 h Load lock also allows samples to be exhanged under controlled environmental conditions The overall temperature range is limited from 10 K to 400 K when using this option The load lock option includes an electrically isolated adapter for the sample stage slide on sample holders a modified 4 K shield and a modified radiation shield that provides easy load lock access Lake Shore offers a 50 L liquid nitrogen laboratory storage Dewar as the PS LN2 option The Dewar has a 12 7 mm 0 5 in top withdraw port that is compatible with the probe station transfer line Constructed of durable stainless steel the Dewar includes a pressure gauge gas port gas valve and 68 9 kPA 10 psi pressure relief valve for safe and convenient operation Dry nitrogen gas is required to pressurize the Dewar during cryogen transfer The option does not include a nitrogen fill line gas pressure regulator gas lines or fittings Liquid nitrogen will only cool the refrigerator down to 78 K The PS DPC automatic Dewar pressure controller provides a digital readout and digital regulation of the pressure in a helium or nitrogen Dewar It regulates over the normal operating range of the probe station from approximately 3 4 kPA 0 5 psi to 68 9 kPA 10 psi The digital pressure setpoint ensures fast repeatable Dewar pressure settings The controller connects between the regulated gas source and Dewar and
153. ge motors or moving equipment If floor vibration is a concern the Lake Shore PS PVIS vibration isolation system is available to order along with the probe station The probe station turbo pumping system can be a source of vibration The vacuum pump is often turned off when the refrigerator is cooled to below 77 K Additional vibration isolation may be needed if working outside of that range The Lake Shore PS PLVI 40 pump line vibration isolator or equivalent is recommended for reducing Vacuum pump vibration El akeShore www lakeshore com 56 CHAPTER 3 Installation and Setup AWARNING 3 2 3 Power Requirements 3 2 2 2 Electrical Noise Place the probe station away from major sources of electrical noise to avoid interference with probe measurements Common electrical noise sources in buildings are power distribution panels high capacity power lines communications distribution centers and RF radio transmitters Line power quality can also impact electrical measurements done in the probe station When possible avoid long or indirect power routing circuits that are shared with motors or other noisy loads unbalanced overloaded and poorly grounded circuits When poor quality power circuits are unavoidable an isolation transformer for measurement instruments may be required to achieve optimum performance 3 2 2 3 Ventilation Place the probe station in a well ventilated area to avoid the risk of asphyxiation from liquid cryogens
154. ground the back side of the sample substrate during normal operation The quality of this ground is very dependent on sample mounting technique Optional sample holders are available to completely isolate the sample if necessary Cryogenic coaxial cable r Probe Probe Probe arm shie arm Totemperature Shield base panana d Sample stage Thermal A a anchors L Sample holder 4 K shield stage Radiation shield stage S77 Second shield stage S77 Vacuum chamber base pr 77 19 pin Feedthrough connector controller chassis AWARNING Model CPX Probe Station FIGURE 2 24 DC RF ground reference 2 4 1 2 Avoiding Ground Loops Ground loops are one of the most common noise sources in measurement systems like a probe station A ground loop occurs when two or more places on the probe station are connected separately to ground The loop area is exposed to magnetic fields generated by AC power lines in the lab The changing field induces line frequency noise in the loop that can permeate through the measurement setup As mentioned in section 2 4 1 1 there are multiple places on the probe station that connect electrically to the vacuum chamber and therefore have the potential to form a ground loop Most of these points are connected to provide high frequency
155. h back side voltage bias 2 4 8 4 Measurement Voltage Limits The CPX probe station is specified for signal voltages below 60 VDC and 30 Vims referred to as non hazardous live voltage The sensor heater and power supply voltages entering the probe station are all below this voltage More importantly testing criteria established for the CE mark assumes there will be no hazardous live voltage operating in the probe station Many of the guarded sources electrometers and other pieces of electronic test equipment used in DC or RF measurements are capable of operating from hundreds of volts to over thousands of volts The CPX probe station is not specifically designed to ensure operator safety when these voltages are present Because Lake Shore has no way to predict how the hazardous live voltages would be configured or operated it is impossible for us to guarantee safety in the event of improper operation accidental misconnection or component failure The CPX does not include the safety interlocks current limits or earth safety ground system that are necessary for safely working with hazardous live voltages 2 5 Considerations for Microwave Measurements 2 5 1 Microwave Cables and Connectors 2 5 Considerations for Microwave Measurements 45 Lake Shore offers microwave configurations with ground signal ground GSG probe geometry optimized for substrates patterned with coplanar waveguide structures Both signal and ground traces of the micr
156. he 4 K shield stage FIGURE 3 20 b Position the braid block over the holes in the 4 K shield stage using tweezers c Using the 2 5 mm hex driver attach the braid block to the 4 K shield stage with the two M3 captive screws see FIGURE 3 20 for an image of the mounted braid block The probe mount braids can touch neighboring probe braids or the stage it is anchored to but should not touch adjacent stages In the CPX probe station the probe mount braids can be anchored to either the sample stage or the 4 K radiation shield stage FIGURE 3 20 FIGURE 3 20 Braid block mounting holes 3 5 3 2 Install the ZN50 Probe Blade Follow this procedure to install the blade inside the probe station You may find it easier to install your blade outside of the probe station to do this you will need to remove the probe mount section 3 5 4 2 and follow the procedures in step 3 El akeShore wwwiakeshore com 74 CHAPTER 3 Installation and Setup CAUTION 1 Using the 1 5 mm hex driver loosen the set screws on the probe arm so that the probe mount can rotate freely FIGURE 3 21 Rotate the mount so that you have access to the mount set screw Insert the blade a Verify that the mount set screws are out far enough that the blade can slide in easily If they are not unscrew them slightly to accommodate the blade Slide the new blade all the way into the probe slot FIGURE 3 22 Its bottom edge should be square and flush with
157. he next step 5 Attach the other end of the vacuum line to the vacuum isolation valve on the probe station FIGURE 3 16 FIGURE 3 16 Use the clamp provided to attach the vacuum line to the probe station To minimize the transfer of vibration to the probe station position the turbo pumping system so that the vacuum line has at least one 90 bend in it Do not remove or exchange the plastic clamp and centering ring installed between the isolation valve and the vacuum chamber These electrically isolate the chamber from the turbo pumping system This eliminates most of the electrical noise that might otherwise be coupled from the turbo pumping system to the probe station and also eliminates a potential ground loop in the system 6 Connect the power cord to the turbo pumping system see TABLE 3 1 30 El akeShore_ www lakeshore com 70 CHAPTER 3 Installation and Setup 3 4 4 Assembling Probe Station Options Model CPX Probe Station Some options require some assembly while others come fully assembled This section explains how to assemble the options and attach them to the probe station 3 4 4 1 Assembling the Pump Line Vibration Isolator PS PLVI 40 or PS PLVI 25 The PS PLVI 40 is for the PS V81DP turbo pumping system The PS PLVI 25 is for the PS LT low temperature option The pump line vibration isolator includes a bucket with NW 40 or NW 25 fittings and 1 m flexible stainless steel vacuum line The bucket must
158. he target side leg FIGURE 4 14 middle This should take approxi mately 5 min Use a clean cloth to wipe any ice crystals from the tip of the transfer line Immediately after wiping away the ice crystals quickly insert the transfer line into the bayonet on the probe station FIGURE 4 14 right Push the transfer line in until it stops then hand tighten the bayonet compression fitting The transfer is started listen for a whooshing sound at the beginning of the transfer as the liquid cryogen is evaporating in the refrigerator EL akeShore www lakeshore com 100 CHAPTER 4 Basic Operation FIGURE 4 14 Left Inserting the transfer line into the Dewar Middle Plume indicating the process of precooling the transfer line is complete Right Inserting the transfer line into the bayonet on the probe station 4 5 3 3 Allow the Sample and Radiation Shield Stages to Cool 1 2 CAUTION w Wait for all stages to cool to below 100 K Close the vacuum isolation valve Close the isolation valve when the refrigerator is cold to prevent the chamber from being vented if the pump is accidentally turned off or if the vacuum pump loses power Venting the chamber when the refrigerator is cold can damage the probe station Turn off and vent the turbo pump see section 4 4 3 Allow the stages to cool down The sample stage should be 4 5 Kto 5 K the 4 K shield stage should be below 5 K the radiation shield stage should be 15 K to 20 K an
159. he target vacuum levels in this section are all given with the assumption that the refrigerator is at room temperature because it is difficult to troubleshoot a vacuum leak when the refrigerator is cold 6 3 1 5 Vacuum Chamber Leak Test If you have achieved the pressures in section 6 3 1 1 and section 6 3 1 2 but have failed to achieve the pressures listed in section 6 3 1 3 follow this procedure and the procedures through the end of this section to identify vacuum integrity issues in your probe station If a calibrated gauge is not available for step 1 the gauge from the pump cart can be moved for this test as shown in FIGURE 6 6 fi te igi vallum iS gauge FIGURE 6 6 Vacuum gauge on the chamber 1 Installa vacuum gauge on the chamber side of the vacuum isolation valve 2 Pump outthe vacuum chamber as described in section 4 4 2 3 Allow the pump to run for 2h 4 Log the gauge reading at the chamber 5 Ifthe system did not reach lt 10 3 Torr refer to section 6 3 1 6 to section 6 3 1 8 6 Close the vacuum isolation valve 7 Turn off the vacuum pump 8 Wait 10 min compare the gauge reading at the chamber to the reading recorded instep 4 9 Ifthe two readings are not the same order of magnitude or the pressure reading continues to rise there may be a leak in the vacuum chamber 6 3 1 6 Will Not Achieve 10 2 Torr If the system will not achieve at least 10 2 Torrin the vacuum chamber the problem is likely me
160. hermally anchoring the probe mount braids to the 4 K shield stage so that the thermal mass of the probes and probe arms will be cooled initially and remain cold when changing sample stage temperature This will allow the sample stage to change and stabilize in temperature more quickly Thus the default location for mounting is to the 4 K shield Follow this procedure to prepare for installation of all probe types then use the unique instructions for each individual probe type 1 Open the vacuum chamber and radiation shield using the guidelines in section 4 3 1 2 Ifyou purchased semirigid cables or coaxial cables there will be safety ties on the arms Cut these off and remove the ties from all four cables Be careful not to cut the Kapton tape on the coaxial cables You may need to use the x axis hand dial to move the probe arms in or out so that the ties are more accessible 3 Using the x axis hand dial extend the probe arm into the chamber until the probe arm set screws are accessible The ZN50 series probes consist of a probe mount ceramic blade with SMA electrical connector and probe tip Use the procedure in section 3 5 3 1 to install a ZN50 probe If the probe mounts are already installed see FIGURE 3 18 go to section 3 5 3 2 and begin with installing the probe blade If the probe mount is not installed please be aware that some probe station users find it easier to first install the blade to the probe mount outside the station
161. hooting Procedures 6 3 1 Vacuum Troubleshooting Model CPX Probe Station 13 Use the procedures in section 3 6 to ensure basic functionality of the probe sta tion and vacuum pump The following procedures should only be performed by skilled operators who are familiar with the required process and equipment Damage to the probe station can result if these procedures are not done properly If you require assistance contact Lake Shore service or your local representative before beginning these procedures Contact information is in section 6 5 The CPX should be able to achieve a vacuum of lt 10 3 Torr at room temperature with an appropriate vacuum system and the gauge located on the chamber If your vacuum does not perform similar to the curve illustrated in FIGURE 6 3 the following sections describe some common problems and simple diagnostic procedures to remedy this If the problem is caused by a very small leak it may be necessary to use a leak detector to troubleshoot it properly Leak detector operation is not covered in this manual Consult your leak detector user s manual Suspect poor vacuum if you observe any of the following symptoms m Refrigerator will not cool to base temperature Cooling time increases Condensation appears on sample surface Condensation appears on any internal viewport surface Excessive condensation appears on exterior of chamber viewport 10 10 10 10 107 10 Pressure Torr 1
162. hree uniform marks on the metallization If the adjustment range of the differential knob is inadequate the probe must be manually rotated in the probe arm inside the vacuum chamber by loosening the probe arm set screws and manually rotating the probe body Once the probe has been properly planarized raise the probe again to avoid damage Carefully tighten the four M4 screws holding the bellows flange to the z axis stage assembly The screws do not need to be tightened securely They hold these pieces in proper alignment but are not required to seal vacuum The four M4 screws holding the bellows flange to the z axis stage assembly should be installed to a torque of 112 N mm 16 ozf in The torque required is much lower than one might think would be needed We recommend using a torque wrench to ensure these screws are not over torqued If these screws are over torqued the z axis stage and bellows may be damaged Check the planarization once more to be sure tightening the bellows screws did not change the angle 10 See section 2 5 for more information on making microwave measurements a akeShore www lakeshore com 108 CHAPTER 4 Basic Operation Model CPX Probe Station Oe 5 1 General 5 2 Advanced Temperature Operation AWARNING 5 2 1 Reducing Condensation on the Sample 5 1 General 109 Chapter 5 Advanced Operation This chapter is separated into two parts Section 5 2 provides advanced operation procedures
163. iber optic cable 3 4 3 Assembling the Turbo Pumping System Before assembling the turbo vacuum pump with the probe station it is a good idea to test the turbo vacuum pump alone section 6 3 1 1 FIGURE 3 13 shows the assembled turbo pumping system and the connections of the turbo pumping system components Most of these components have already been assembled vent D Il Bi m a i ry scroll pump To probe station Vacuum gauge E Pa Turbo pump Soo Controller FIGURE 3 13 Assembled turbo pumping system and its connections al akeShore www lakeshore com 68 CHAPTER 3 Installation and Setup 3 4 3 1 Prepare the Probe Station Before Attaching the Vacuum The probe station is shipped under vaccum you need to release this vacuum Follow this procedure to release the vacuum 1 Attach a dry nitrogen or inert gas line to the purge valve We recommend you purge to dry nitrogen instead of purging to air in order to increase and maintain the pumping efficiency of the system 2 Regulate the gas pressure to 6 89 kPa to 13 79 kPa 1 to 2 psi 3 Open the purge valve slowly In about one minute the pressure relief valve on the chamber will open and release gas 4 Close the purge valve completely 5 The gas line can be left in place or removed 3 4 3 2 Prepare the Turbo Vacuum P
164. iewport Probe arm port Lid Vacuum isolation valve i Auxillary gauge port other side Purge valve Pressure Vacuum line relief valve Probe arm port to vacuum pump Vacuum chamber Ports for bayonet bottom exhaust and electrical feedthrough FIGURE 2 3 Vacuum chamber El akeShore www lakeshore com 14 CHAPTER 2 System Overview Sample stage Sensor HT Si diode Heater 50 W 4 K shield stage Sensor Si diode Heater 100 W Radiation shield stage Sensor Si diode Heater 100 W Second shield stage Sensor Si diode Heater 50 W 2 2 1 2 Refrigerator The CPX uses an open flow cryogenic refrigerator The refrigerator contains several features to optimize performance and efficiency One notable feature is that the sample stage and radiation shields have separate flow paths split flow This enables the sample stage to be operated above or below the temperature of the 4 K shield stage Major components of the refrigerator include the sample stage 4 K radiation shield stage radiation shield stage radiation shield radiation shield viewport second shield stage and second shield A temperature sensor and heater on the sample stage provide a means of sample temperature control Temperature sensors and heaters on the lower stages allow temperature monitoring and quick warm up to room temperature for sample exchange FIGURE 2 4 illustrates the refrigerator va Radiation shield viewport
165. in the part number have a normal shelf life of about one month before they develop an oxide layer which may impede good electrical contact If discoloration of the tips or a change in electrical properties becomes noticeable use the following procedure to clean the tips Tungsten and Paliney 7 are less prone to oxidation so they will not need regular cleaning We suggest using Tarn X a liquid tarnish remover commonly available in the United States The probe tips are very delicate Do not touch them during this procedure Failure to comply may result in damaged or broken probe tips Follow this procedure to clean BeCu probe tips 1 Wearing gloves remove the probe from the probe arm 2 Place asmall drip cup under the probe tip 3 Wearing gloves dispense one full strength drop of liquid tarnish remover just above the probe tip letting the cleaner run down the tip and into the drip cup FIGURE 6 1 Do not allow the cleaner to contact any part of the probe body Probe Ss 6 Drop of liquid ra Probe tip Drip cup Pa FIGURE 6 1 Method for cleaning probe tips 4 For heavily oxidized probe tips repeat step 3 as necessary 5 Within 30s drip three or four drops of deionized or distilled water applied in the same manner to rinse the probe tip clean 6 Rinse with three or four drops of isopropyl alcohol 7 Allow the probe to dry thoroughly before use 8 Reinstall the probe a akeShore www lakeshore com 134 CH
166. iniature cryogenic coaxial cable or a K connector with semirigid cable as described in section 2 3 2 2 The useable frequency range of a ZN50 configured with a BNC signal connector with ultra miniature cryogenic coaxial cable is DC to 50 MHz While performance beyond 50 MHz is certainly possible steps should be taken to understand the losses at the particular frequency of interest The useable frequency range of the ZN50 configured with K connectors and semirigid cables provides continuous operation up to 100 MHz and selected band operation up to 1 GHz This configuration has reasonable frequency response out to 1 GHz as long as the band between 200 MHz and 400 MHz can be avoided FIGURE 2 26 can add additional information it shows the forward transmission response of a pair of ZN50 probes configured with K connectors and semirigid cable While the probes do have a response out to 1 GHz the separation of the ground path from the single signal tip of the ZN50 blade causes a large dip in transmission forward gain at 0 3 GHz 300 MHz Depending on the configuration of the probes and measurement setup this dip can vary from approximately 200 MHz to 400 MHz Model CPX Probe Station 2 4 4 Conductive Back Side Features 2 4 5 Back Side Voltage Biasing 2 4 4 Conductive Back Side Features 39 Forward transmission dB o 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 Frequency GHz FIGURE 2 26 Typical forward transmission response o
167. ion ii FIGURE 5 5 Left and Right Use a wrench to remove the arm shield braids from the radiation shield 4 Using the 3 mm hex driver remove the four M4 screws that attach the stage base to the baseplate FIGURE 5 6 If necessary use the x axis hand dial to move the stage forward to access all of the screws 5 Using the 3 mm hex driver detach the bellows from the chamber by removing the four M4 screws FIGURE 5 6 6 Supporting the bellows in one hand carefully pull the probe arm out guiding the arm shield braids so they do not get stuck on the arm port FIGURE 5 6 WALA AIII WT FIGURE 5 6 Left Removing four screws from the stage base Middle Detaching the bellows from the chamber Right Carefully remove probe arm cables and thermal anchor from the chamber 7 Slide the stage back and use the 3 mm hex driver to secure the stage to its hold ing location with two M4 screws FIGURE 5 7 This is an optional step and is given to provide you with a convenient work space 8 Ifanother arm is not to be installed in this location install a blank over the arm port Do not leave the chamber open to atmosphere MNO baseplate oe screw FIGURE 5 7 Secure the micro manipulated stage to its holding location Model CPX Probe Station 5 3 3 Removinga Probe Armand Base 117 5 3 3 Removing a Probe This procedure assumes that you have removed the micro manipulated stage and Arm and Base secured the stage
168. ion FIGURE 3 10 Attach the other end of this cable into the s video connection on the monitor 2 Attach the monitor power supply to the monitor This is a 12 V DC connection 39 soa FIGURE 3 10 Attach the s video cable to the microscope 3 Connect the fiber optic The steps vary depending on whether you are using the ring light or the coaxial light Ring Light a Screw the light source adapter onto the bottom of the microscope using the three screws supplied FIGURE 3 11 Finger tighten only b Insert the fiber optic cable into the light source Finger tighten only FIGURE 3 11 c Connect the power cord to the light source see TABLE 3 1 for power requirements MICRO TECH INSTRUMENTS INC FIGURE 3 11 Left Installing the ring light onto the adapter Middle Tighten the ring light thumbscrews Right Fiber optic cable attached to the light source Model CPX Probe Station 3 4 3 Assembling the Turbo Pumping System 67 Coaxial Light a hoang Using the 0 05 in hex driver loosen the set screw on the fiber optic cable fitting to the microscope FIGURE 3 12 Remove the protective metal fitting Insert the fiber optic cable Secure the set screw Insert the fiber optic cable into the light source Finger tighten only Connect the power cord to the light source TABLE 3 1 FIGURE 3 12 Left Loosen the set screw on the fiber optic cable fitting Middle Remove protective fitting Right Insert the f
169. ion that spans 40 MHz to 67 GHz and represents a 294 K temperature change from the calibration temperature to the measurement temperature This example represents a wide band measurement over a large change in temperature and is described here as an extreme case the error will be less for narrower band measurements or for measurements over smaller temperature variations For the most accurate measurements it is recommended to performa calibration at the actual measurement temperature o rS val a whi pi ii ron N saa Et yen a S parameters dB S 0 10 20 30 40 s0 60 Frequency GHz FIGURE 2 40 Calibrated S parameter response of 67 GHz GSG microwave probes measured on a 50 Q through structure at 4 3 K after calibration with a CS 5 substrate at 300 K Another concern with microwave probes is that the probe must be rotated to ensure that the three points of the probe ground signal and ground are in the same plane as the sample this is referred to as planarization FIGURE 2 41 shows the S parameters for a probe station before and after the contacts are properly planarized and good contacts established al akeShore www lakeshore com 50 CHAPTER 2 System Overview S parameters dB 0 10 20 Frequency GHz Frequency GHz 0 10 20 Li 30 11 40 SAL 50 S12 60 on 22 S parameters dB 90 m 100 l 40 50 60 0 10 20 30 40 50 60 FIGURE 2 41 Left Improperly planarized test with
170. ise approxi mately two turns to engage the plug Do not force it as you may strip the threads Start the vacuum and let it run for 5 min Pull the plug out to begin pumping out the transfer line 7 Evacuate the transfer line fora minimum of 12 h If the transfer line has been opened or vented it may need to be pumped for several days especially if it has been exposed to damp air 8 Push the evacuation adapter plunger back in to reseat the plug into the transfer line 9 Turn off and properly vent the pump 10 Turn the plunger counterclockwise to disengage the plunger from the plug 11 Using a 114 in wrench remove the evacuation adapter from the transfer line Do FIGURE 6 2 Top Evacuation adapter attached to the evacuation port on the transfer line Right Pumping out the transfer line Model CPX Probe Station 6 2 12 Removing Condensation from Inside the Vacuum Chamber CAUTION CAUTION 6 2 12 Removing Condensation from Inside the Vacuum Chamber 137 Opening the vacuum chamber to atmosphere when the refrigerator is at cryogenic temperatures allows water vapor to condense on the refrigerator and freeze into ice It is possible for the refrigerator or turbo vacuum pump to suffer irreparable damage when this occurs It can take as long as a week to return the probe station to proper working order The time is required because water molecules are easily attracted to the surfaces inside the probe station such
171. it is powered by a 9 V battery or the included wall plug power supply The PS PVIS option is available for vibration sensitive applications The flow cryostat in the probe station produces very little vibration typically lt 1 um therefore vibration is not a problem for all users The additional isolation is recommended when probing extremely fine detail when making measurements that are very sensitive to electrical noise or when there are likely to be outside vibration sources near the probe station The option adds active pneumatic vibration isolation to the CPX s integrated stand Typical performance and general specifications are given in FIGURE 2 23 and TABLE 2 3 The stand requires a regulated source of compressed air or nitrogen to operate The PS OAC oil less air compressor option is available for use with the PS PVIS 110 V operation only El akeShore www lakeshore com 34 CHAPTER 2 System Overview Model CPX Probe Station 10 0 1 Acceleration Transmitted Acceleration Input 0 01 Transmissibility 0 001 10 Frequency Hz 90 FIGURE 2 23 Vibration isolation performance for the TMC stand with option PS PVIS pneumatic vibration isolation system Copyright Technical Manufacturing Corporation Used with permission Isolator natural frequency 1000 Isolation amplification High input vertical 1 2 Hz High input horizontal 1 0 Hz Low input vertical 1 5 Hz to 2 0 Hz
172. l triaxial It is often desirable to order more than one holder so one sample can be mounted while another is being measured Different models are optimized for different electrical measurement applications All of the holders are thermally conductive so the sample temperature remains close to the sample stage temperature but there are some trade offs between thermal conductivity and electrical characteristics TABLE 2 1 shows the temperature gradients that are typical between the sample stage temperature sensor and the top of each sample holder The gradients are given for base temperature which is the worst case gradients are smaller at higher temperatures type model size difference at 4 2 K temperature Grounded SH 1 25 G 32 mm 1 25 in 0 1K to 0 2 K 475K Isolated SH 1 25 I 32mm 1 25 in 1K 400 K Coaxial SH 1 25 C 32 mm 1 25 in 1K 400 K Triaxial SH 1 25 T 32mm 1 25 in 1Kto2K 400 K Grounded SH 2 00 G 51mm 2 in 0 1K to 0 2 K 475K Coaxial SH 2 00 C 51mm 2 in 1K 400 K Triaxial SH 2 00 T 51mm 2 in 1Kto2K 400 K Temperature difference between the top of the sample holder and the sample stage temperature sensor Additional temperature difference can be expected between the sample and sample holder depending on mounting technique and experimental heat load TABLE 2 1 Sample holder summary 2 3 5 1 Grounded Sample Holders Grounded holders are the most common type and are referred to as grounded
173. l warm the stages but should clear nitrogen from the refrigerator 5 Allow the probe station to cool normally with the sample stage micrometer valve open six to eight turns If either the sample stage or 4 K shield stage do not cool after 10 min to 20 min anice blockage has formed in that flow path The system must be warmed to room temperature and dried before re cooling Refer to section 6 3 3 1 Some probe station models can be operated above room temperature using inert gas instead of liquid cryogen as a cooling source Pump the vacuum chamber continu ously during this operation to prevent outgassing from contaminating the sample and spoiling the vacuum A vacuum line vibration isolator PS PLVI 40 or equivalent is recommended for vibration sensitive operation Heaters in the CPX should never be turned on when the chamber is not under vacuum or when the refrigerator is not being actively cooled CAUTION CAUTION CAUTION 5 3 Probe Arm Assembly Reconfiguration 5 3 1 Installing a Micro manipulated Translation Stage MMS 09 5 3 ProbeArmAssemblyReconfiguration 113 The maximum temperature for the sample stage is 475 K the 4 K shield stage is 380 K the radiation shield and second radiation shield stage is 380 K and the probe arm is 350 K Optional probes and sample holders may have lower maximum temperatures Failure to observe maximum temperatures may result in equipment damage The CPX is not designed to be baked
174. lcohol Do not clean the viewports during this step Top edge of the radiation shield mating surface Mating surfaces of the radiation shield lid Any surface that shows fingerprints Any surface likely touched during sample exchange Sealing surface of the vacuum chamber lid Main chamber o ring Main chamber o ring groove The radiation curtains are very fragile do not soak them or rub them as they can come off or break 3 Clean and lubricate the chamber components m Clean the viewport windows section 6 2 4 m Lubricate the main chamber o rings with a thin layer of high quality vacuum grease section 6 2 5 m Clean the sample holder section 6 2 6 4 Reassemble the probe station Sample holder Probes Main chamber o ring Radiation shield lid Vacuum chamber lid 5 Pull vacuum for 30 min prior to loading a sample To minimize the risk of contamination the radiation shield lid and vacuum chamber lid should remain in place except when working in the chamber Lake Shore also recommends that you store the chamber under vacuum to reduce oxidation 6 2 4 Viewport Window Maintenance CAUTION 6 2 5 O Ring Maintenance 6 2 4 Viewport Window Maintenance 131 Viewport windows require extra consideration It is important to protect the optics as they are your only way to view and photograph the activity on the sample holder 6 2 4 1 Cleaning the Viewport Windows The viewport windows on the radiation shield lids and vacu
175. ll need to disconnect the SMA connector The strain relief to the SMA connector on the cryogenic coaxial cable must be held in place with tweezers while removing the SMA plug Using the x axis hand dial and the y axis micrometer move the probe arm to expose the braid block mounting holes in the 4 K shield stage Using the 2 5 mm hex driver loosen the two captive screws on the braid block FIGURE 3 20 Pull the braid block out Using the 1 5 mm hex driver loosen both M3 probe arm set screws two to three turns and slide the dowel out of the probe arm FIGURE 3 21 Pull the probe mount out of the probe station 3 5 5 Installing a Microwave Probe CAUTION 3 5 5 Installinga Microwave Probe 77 The K connector 2 4 mm connector and the V connector all look very similar however they may not mate to a connector of different frequency rating and the probe or cable may be damaged if forced to thread to an improper mate See section 2 5 1 for more information Contact Lake Shore if you are still unsure of your probe station s microwave configuration Unlike the ZN50 blade and optical fiber assemblies that use a separate probe mount the microwave probe has an integrated mount that attaches to the probe arm and includes probe mount braids and a braid block for attachment to the thermal anchor point GSG microwave probe tips are extremely delicate the slightest touch on the probe tips can disturb the ground signal ground GSG transmi
176. m access to the sample stage 4 Recommended connect a tank of dry inert gas such as nitrogen or argon to the purge valve and follow the instructions for purging the vacuum chamber section 4 4 4 Input 6 9 kPa to 13 8 kPa 1 to 2 psi into the chamber during the remainder of this procedure Alternate to release the vacuum to atmosphere slowly open the purge valve by turning the hand knob on the top of the valve counterclockwise 5 Using the 2 5 mm hex driver unlock the four captive quarter turn fasteners on the vacuum chamber lid al akeShore www lakeshore com 86 CHAPTER 4 Basic Operation FIGURE 4 3 Left Vacuum isolation valve on the probe station Right Probe station vacuum chamber lid removal 6 Pull up gently on the lid to remove it A light bump may be required to release the o ring seal if the chamber was closed for a long time 7 Place the vacuum chamber lid in a safe place where it will not get scratched or contaminated 8 Using the 2 5 mm hex driver loosen the eight M3 screws from the outer edge of the radiation shield lid The screws are captive and stay with the radiation shield lid 9 Place the radiation shield lid with the vacuum chamber lid Bumpers are built into the radiation shield lid for it to rest on 4 3 2 Removing the Follow this procedure to remove the sample holder Sample Holder 1 Ifyou are removing an optional triaxial or coaxial sample holder disconnect the signal cable before removing th
177. maximum operational speed 5 Ifthe vacuum gauge readout is not currently displayed on the turbo controller front panel push the measures button on the controller front panel to cycle through various pump diagnostics until the vacuum gauge readout is displayed El akeShore wwwilakeshore com 140 CHAPTER 6 Maintenance and Troubleshooting Model CPX Probe Station The Eyesys Mini IMG gauge reads pressures from 10 3 Torr down to 10 9 Torr so there will be no vacuum pressure reading until the pressure has reached below 10 3 Torr 6 7 If the connections are all made securely the vacuum gauge reading should come down to lt 10 6 Torr within 10 min of pumping Do not continue to the next steps if this pressure is not achieved contact Lake Shore or your vacuum pump manufacturer directly for technical assistance If 10 6 Torr is achieved turn off the scroll and turbo pump a Press the stop button on the vacuum turbo pump controller to disengage the turbo pump b Switch the scroll pump knob from position 1 to position O to stop the roughing pump c Open the manual vent valve located on the side of the turbo pump to vent the turbo pumping system You will hear hissing as the manual vent screw is opened and air rushes in to the turbo pump d Once the hissing ceases completely close the manual vent valve It is acceptable to leave the main power rocker switch in the on position when not operating the vacuum pumping system
178. microwave probes The following sections describe the procedures to reconfigure the probe arm assem blies of your probe station These reconfigurations will not necessarily need to be done daily but you may find them essential for some research situations Follow this procedure to add a probe arm stage to your probe station 1 Use the micrometers and hand dial to center the x y and z axis stages in the probe station 2 Using the 3 mm hex driver remove the four M4 screws on the arm stage plate if present and set the plate aside 3 Using the 2 5 mm hex driver remove the two M3 screws in the slide insert from the bottom of the new stage see FIGURE 5 1 4 Position the slide insert onto the arm stage location so that it is facing as illus trated FIGURE 5 1 and secure the insert to the arm stage location El akeShore www lakeshore com 114 CHAPTER 5 Advanced Operation FIGURE 5 1 Left Remove the screws from the slide insert Right Secure the slide insert to the arm stage location 5 6 Using the 3 mm hex driver unscrew the four M4 screws from the arm port blank on the vacuum chamber if present Remove the blank and set it aside Clean the o ring groove in the probe arm port FIGURE 5 2 Clean inspect and lightly grease the o ring with vacuum grease and place it in the groove Slide the stage onto the probe arm location and carefully guide the cable and probe arm through the arm port FIGURE 5 2 Take care th
179. mple 1 VGE 7031 varnish you can use VGE 7031 varnish in temperatures ranging from 2 K to 470 K and it is compatible with the grounded isolated coaxial and triaxial sample holders VGE 7031 varnish is available through Lake Shore m To mount only a small amount of varnish is needed for your sample Fora 25 mm 1 in sample place a drop of the varnish on three pads of the sample holder Then center and align the wafer on the sample holder The amount of varnish used can be increased or decreased for larger or smaller samples respectively VGE 7031 varnish may be air dried or baked according to manufacturer s recommendations m Toremove you can remove the sample by soaking in ethanol or toluene A solution of equal parts of ethanol and toluene has also been very successful at removing samples mounted with VGE 7031 varnish Grooves in the sample holder permit the remover to flow under the sample 2 Photoresist or PMMA material the most common semi permanent mounting tech nique is photoresist or PMMA material common to the semiconductor processing industry It offers excellent adhesion yet is still removable CAUTION 4 3 4 Mounting the Sample Holder onto the Sample Stage CAUTION 4 3 4 Mounting the Sample Holder onto the Sample Stage 89 The photoresist chemical remover and bake procedures must be compatible with the wafer and devices These processes are compatible with grounded and isolated sample holders Please note
180. mple stage is a stable temperature control platform and reasonable temperature control can be achieved over the entire temperature range Short term temperature control of a few tens of millikelvins should be expected around base temperature As the system approaches maximum temperature short term control stability degrades somewhat but should remain below 1 K in a properly tuned system Long term stability is very dependent on consistent helium flow which requires well regulated Dewar pressure Considerations when regulating with mechanical flow controls When operating at or near base temperature the mechanical flow controls are used to regulate temperature At these temperatures electronic temperature control is not appropriate because there is insufficient cooling power for the controller to work against The following problems may cause unstable or erratic temperature readings to occur when controlling with mechanical flow controls m Change in Dewar pressure this can be caused when there is not adequate regulation of the pressurizing gas source or if you rely on a pressure relief valve to regulate Dewar pressure m Shield stages not stabilized sample stage temperature will not regulate properly until the shield stages stabilize m Irregular cryogen flow there can be a combination of control settings that cause irregular cryogen flow through the refrigerator If this condition occurs the exhaust gas pressure will oscillate with
181. ms is the excitation source Keithley Instruments Model 6220 DC precision current source is an excellent example of a guarded source that can combine with a precision voltmeter or electrometer to make high resistance measurements The critical elements needed to carry the guarding inside the probe station are described in section 2 4 8 3 2 4 8 3 Guarded Probe Station Configurations Within the probe station guarded configurations begin with triaxial signal connectors which are part of the ZN50 T DC RF cable configuration for probe arms 2 4 8 High Impedance LowLeakage Measurements 43 FIGURE 2 30 Triaxial connector 1 The center pin carries the signal It is connected internally to the center conductor of the cryogenic coaxial cable that is attached to the ceramic blade signal conductor and probe tip 2 The middle ring carries the guard voltage It is connected to the outer conductor of the cryogenic coaxial cable that is attached to the ceramic blade reference plane 3 The outer shell is available for shielding the external cable It is connected to the vacuum chamber The shield is not carried inside the vacuum chamber in this configuration The chamber itself provides shielding For best performance the sample must be guarded in addition to the cables There is a potential leakage path through the sample substrate to a standard grounded sample holder The SH 1 25 C or SH 2 00 C coaxial sample holder is recommended for guarding s
182. n V81 T turbo pump and controller 4 x 10 9 Torr blanked off specification 10 7 Torr typical in a PS V81DP configuration Pumping speed 50 L s NW 40 flange Turbo pump Base pressure Model and type Varian SH 110 dry scroll pump Fore pump Pumping speed 110 L min Base pressure 5 x 10 2 Torr Model Varian EyeSys Chamber gauge Type Vacuum gauge Range 10 2 to 10 8 Torr Gauge readout Model Integrated Capacity One vacuum gauge 46 cm 18 in wx 56cm 21in dx Size 64cm 25 in h general Weight 22 kg 48 5 Ib Power 100 120 V or 220 230 240V Size NW 40 Included Vacuum Length 1m for specified system performance accessories line Type Flexible stainless steel Clamps Size NW 40 TABLE 2 2 PS V81DP option components The high vacuum option ensures that condensation does not accumulate in the sample environment during cooldown This is critical for measuring organic semiconductors and for high Z and low current applications The high vacuum option includes an HVAC port Varian V301 turbo pump kit and related HVAC components The option increases vacuum to as low as 1077 torr The nominal base temperature for the sample stage on a standard CPX is at the boiling point of helium which is approximately 4 2 K under normal atmospheric conditions Lower temperatures can be achieved on the sample stage if pressure on the helium in the sample stage is dropped below atmospheric pre
183. n fuse casing From the back of the console look at the voltage selection window to find the voltage setting If you find you need to change the voltage contact Lake Shore for assistance You can find contact information in section 6 5 El akeShore www lakeshore com 80 CHAPTER 3 Installation and Setup 3 6 2 Temperature Sensor and Heater Test CAUTION Model CPX Probe Station 3 6 1 2 Verify Power On All controllers are plugged into the power strip inside the console First plug in the power strip see TABLE 3 1 for power requirements then verify that all the power on switches in the back of the controllers are in the on position On the front right hand side of the console you will find a rocker switch This is the main power switch For some consoles turning this on will automatically trigger the power to the Model 142 linear amplifier for others you may have to physically press the switch on the linear amplifier 3 6 1 3 Verifying the Model 332 and Model 340 Controllers The control settings for the Model 332 and 340 are set at Lake Shore however it is good to verify them for safety purposes and to acquaint yourself with the controllers You can use TABLE 4 1 and TABLE 4 2 in section 4 5 7 to assist you in verifying or resetting them You can find more information on the controllers in their manuals Each of the four refrigerator stages in the CPX sample 4 K shield radiation shield and second shield has a temperatur
184. n line worst case configuration of 10 dB across the entire frequency band This crosstalk should be negligible for most measurements however if the devices to be measured require in line probe to probe placement less than 150 um crosstalk could affect the accuracy of the measurement 10 0 10 20 30 40 50 60 70 80 90 S mae 21 S12 ms 22 S parameters dB O 10 20 30 40 50 60 Frequency GHz FIGURE 2 37 Frequency response of 67 GHz microwave probes located 150 um across from each other and landed on the 50 A pads of a CS 5 calibration substrate El akeShore www lakeshore com 48 CHAPTER 2 System Overview 2 5 4 Calibration with The following concepts are used with permission from the CS 5 instructions the CS 5 Calibration For the most accurate microwave measurements using a vector network analyzer dard VNA calibration is required to eliminate the frequency dependent losses of the Standar associated connectors cables and probe tips The CS 5 or CS 15 calibration substrate can be used for this purpose The CS 5 can be used for pitch ranges of 75 to 250 um and the CS 15 can be used for pitch ranges of 50 to 150 um Standard elements for calibrating a microwave measurement system consist of opens shorts matched loads and throughs These four elements have electrical characteristics that are very different from one another so that each one by itself contributes an important part to the c
185. n line fitting into the gas ballast Screw it in firmly but do not overtighten Secure the oil exhaust filter to the out exhaust using the NW 25 clamp 6 Fit the oil return tube into the orange push to connect fitting on the oil exhaust filter Attach the other end to the orange push to connect fitting on the return line fitting For the push to connect fitting be sure to push in pull out and then push in again to ensure a secure fit oi 3 4 4 3 Assembling the Pneumatic Vibration Isolator PS PVIS The pneumatic isolator is integrated into the TMC stand To assemble the isolator fit the 1 4 in OD compressed air tube into the red push to connect fitting on the isolator Flow 172 kPa to 241 kPa 25 to 35 psi compressed air into the stand Consult the TMC manual for further instruction 3 5 Installing and Removing Probes CAUTION 3 5 1 Probe Anchoring and Probe Temperature 3 5 Installingand Removing Probes 71 3 4 4 4 Assembling the Oil less Air Compressor PS OAC The air compressor comes fully assembled and simply needs to be plugged in see TABLE 3 1 for power requirements The air compressor line will be attached to the red push to connect fitting under the table when you are ready to level the TMC table 3 4 4 5 Assembling the Liquid Nitrogen Dewar PS LN2 The PS LN2 liquid nitrogen Dewar option is packed in a cardboard box and included in one of the larger shipping crates Parts included with the option come f
186. n o ring sealing each end of each bellows They can be accessed by following the instructions in section 5 3 2 and section 5 3 3 Signal connector feedthrough there is an o ring between each signal connector feedthrough and its probe arm base It can be accessed using the instructions in section 5 3 5 as a guide Probe arm temperature feedthrough there is an o ring between the probe arm base and the 6 pin feedthrough used for the probe arm temperature sensor This port will be blanked off if there is not a sensor on the arm It can be accessed using instructions in section 5 3 6 3 third method as a guide Vacuum chamber ports the NW 40 and NW 25 gauge ports the load lock port and the high vacuuum port on the CPX chamber each have an o ring sealing the blank off flange to the chamber Vacuum chamber base there is an o ring sealing the vacuum chamber to its base Accessing this o ring requires dropping the refrigerator out of the vacuum chamber This operation is not recommended for routine maintenance Please contact Lake Shore service before attempting to drop the refrigerator if you suspect a leak Vacuum chamber base feedthroughs there are a number of electrical and mechanical feedthroughs located on the base of the vacuum chamber and each contains an o ring The seals on these feedthroughs are not normally broken during reconfiguration of the probe station Please contact Lake Shore service before attempting to service these o rings i
187. n pull both dowels out FIGURE 5 9 Access to the threaded dowels may be to the side of the z axis stage as shown in FIGURE 5 9 or to the top of the z axis stage 6 Liftthe probe arm and base off the z axis stage Pull the probe arm and base out ofthe stage al akeShore www lakeshore com 118 CHAPTER 5 Advanced Operation 5 3 4 Installing a Probe If the probe arm base has not been removed from the stage remove it using the Arm and Base instructions in section 5 3 3 Then follow this procedure to install a probe arm assembly 1 Insert the probe arm base into the z axis stage Orient the probe arm base as shown in FIGURE 5 10 and hold it in place Precise alignment is not necessary 2 Insert the two threaded dowels into the z axis stage FIGURE 5 10 Tighten until snug Access to the threaded dowels may be to the side of the z axis stage as shown in FIGURE 5 9 or to the top of the z axis stage FIGURE 5 10 Inserting the threaded dowels into the z axis stage The probe arm base is loosely captured by the dowels It is free to rotate even when you secure the dowels 3 Ifyou havea planarization assembly using the 2 5 mm hex driver tighten the two M3 screws to secure it to the probe arm base FIGURE 5 11 4 Ifthe probe arm has a flexible cable use a non residue tape like Kapton to tem porarily tape the cable to the probe arm to easily pull the cable through the bellows Place the tape near the end of the cable so it c
188. n reduce below 100 and begin to stabilize This demonstrates that the sensor and heater are functioning properly and that the control loop is closed If you are not flowing cryogen the temperature will settle to a temperature above the actual setpoint 6 Turnthe sample stage heater off 7 Set the temperature setpoint to zero 8 Repeat steps 4 to 7 for the remaining stages one at a time If any of the stages do not raise 5 K and stabilize the most likely reason for the failure is the cabling there may be a cable plugged into the wrong connector Refer to the wiring diagram in section 6 4 3 If the wiring diagram does not reveal the problem contact a Lake Shore representative for assistance Controller Model 340 Model 340 3 6 3 Microscope Lightand Focus Test 4K shield stage Radiation shield stage Second shield stage Model 332 Model 332 Loop and channel Loop 1 input A Loop 2 input B Loop 2 input A Loop 1 input B 5 Kabove 5 Kabove 5 K above 5 Kabove Temperature setpoint room temperature room temperature room temperature room temperature Heater On max heater range On On On high Heater indicator light Channel 1 light on the Model 142 linear amplifier Channel 2 light on the Model 142 linear amplifier 81 TABLE 3 3 Controller settings for temperature sensor and heater test 3 6 3 Microscope Light and Focus Test Follow this procedure to ensure that the microsco
189. n shield Use tweezers to lift an arm shield braid Slide the spade lug under the hex screw head and washer FIGURE 5 4 Using the 8 mm wrench tighten the hex screw FIGURE 5 4 Use the same procedure to attach the other braid to the other side of the awning anoow 12 Remove anything temporarily fastening the cable to the end of the probe arm Take care not to remove the tape that electrically insulates the SMA connector FIGURE 5 11 27 S ath S FIGURE 5 4 Left Slide the spade lug under the hex screw head and washer Right Tighten the hex screw 5 3 2 Removing a This section provides directions for removing a micro manipulated translation stage Micro manipulated Before removing the micro manipulated translation stage find a small tray in which to put the hardware removed from the system Translation Stage 1 Using the x y and z axes center the probe arm in the chamber 2 To prevent damage to a ZN50 or microwave probe remove it from the probe arm using the instructions in section 3 5 4 and section 3 5 6 respectively Do not remove optical fiber probes they should be left in place 3 Use an 8mm wrench to loosen the hex screws that hold the spade lugs at the ends of the arm shield braids to the radiation shield FIGURE 5 5 but do not fully remove these screws Slide the spade lugs from under the screw heads and let the arm shield braids fall El akeShore wwwiakeshore com 116 CHAPTER 5 Advanced Operat
190. n the vacuum isolation valve before restarting the pump Never vent the turbo pump through the vacuum isolation valve whether the pump is turned on or turned off Although this will not immediately destroy the vacuum pump it will likely stall the pump and decrease its life Always close the vacuum isolation valve turn off the pumping system and open the turbo vent valve if the valve is not configured to open automatically The purge valve shown in FIGURE 4 9 is used to backfill the chamber with dry nitrogen or inert gas It is most commonly used when warming or venting the system During warm up backfilling with inert gas can speed the warm up process section 4 5 6 step 7 When opening a warm system backfilling with dry nitrogen gas will prevent moisture and contaminants from entering the chamber which will reduce pump down time and improve vacuum quality If the system is accidentally left open for a long period of time it should be cycle purged to reduce contamination In this technique the chamber is evacuated purged with dry argon and evacuated again The vacuum chamber is not designed for positive pressure and should never be pressurized above 2 1 kPa 0 5 psi The pressure relief valve on the chamber is set for 0 5 psi and should never be disabled or modified Failure to comply may result in injury or death The vacuum chamber should only be backfilled with dry nitrogen or inert gas Failure to comply may result in injury or
191. nector into the hole in the probe arm near the arm shield braids 3 Push the cable in until it comes to the end The cable may come out of the exit hole by itself If not use small tweezers to pull it out being careful not to damage the fragile center conductor al akeShore www lakeshore com 120 CHAPTER 5 Advanced Operation 4 Push the wire through the feedthrough opening in the probe arm base FIGURE 5 13 cable insert comes cable out here here FIGURE 5 13 Left The feedthrough o ring in the groove Right Coaxial cable orientation for inserting into the probe arm base arm shown off of base for clarity 5 6 1 CAUTION 7 8 9 With the cable extending approximately 25 mm 1 in from the probe arm base solder the cable ends to the BNC or triaxial connector FIGURE 5 14 The recom mended solder is tin silver Sn 96 Ag 4 with no clean flux On either connector type solder the copper crimped outer conductor to the con nector body and then solder the small center conductor to the center pin Solder the outer pin first so that the fragile center conductor will not be inadvertently broken off Use minimal heat to avoid melting the dielectric between the shield and center conductor Test the continuity of the newly soldered arm using section 3 6 5 as a guide Clean and re grease the top surface of the o ring if necessary Using the 2 5 mm hex driver attach the cable feedthrough assembly FIGURE 5 1
192. net end before inserting it 3 Allow the transfer line to warm up and dry out after each use before cooling again If the transfer line becomes blocked with ice 4 Remove it from the bayonet and the Dewar 5 Allow it to warm to room temperature 6 Pass low pressure dry nitrogen gas through the line until it is dry El akeShore www lakeshore com 144 CHAPTER 6 Maintenance and Troubleshooting CAUTION 6 3 3 Refrigerator Cooling Troubleshooting Model CPX Probe Station Repeated ice blockage in the transfer line may indicate excessive contamination in the Dewar itself Water vapor and other gas can contaminate the cryogen if the Dewar is not maintained properly Dewars should be stored under positive pressure pressurized only with dry pure gas and decontaminated before refilling If the transfer line remains plugged after it has been warmed and dried the blockage may be from another cause The transfer line target side leg is tapered to properly engage the bayonet on the probe station The taper is perfectly shaped to pick up plaster paint or other foreign material if the transfer line is bumped into walls or equipment in the lab Inspect the bayonet end of the transfer line If it is blocked remove the debris with a wooden toothpick never use a metal tool Ifthe end is bent or otherwise damaged contact Lake Shore service or your local representative for assistance 6 3 2 3 Stuck Foot Valve Control Knob The foot valv
193. ng A 6 4 mm 1 4 in tube 3 7 m 12 ft long is provided Lake Shore offers the PA OAC oil less compressor option for the vibration isolation system but it is only available for 120 V line power The following sections describe the unpacking of each component shipped with the Probe Station probe station Please report any shortages or potential shipping damage prior to arranging Lake Shore assisted installation or within five days of shipment It is important that you read and understand this section thoroughly before starting the process Clear enough space to complete all steps safely 3 3 1 Shipping The standard components of the model CPX will be shipped in two crates and one box Containers one crate contains the probe station itself the second crate contains the instrument console and the box contains the cryogen transfer line Most of the accessories and options configured with the CPX are contained in the crate with the instrument console The PS V81 DP and PS LN2 are two options that are shipped in separate containers TABLE 3 2 lists approximate size and weight of the standard shipping containers The weight of the crates varies in the ranges listed below depending on probe station configurations and options ordered CPX probe station crate 1 22 m 48 in x 0 91 m 36 in x 1 22 m 48 in 318 kg 700 Ib to 386 kg 850 Ib Instrument console and accessories crate 1 22 m 48 in x 0 91 m 36 in x 1 22 m 48 in 272 kg
194. nged on the same micro manipulated stage The probe arm and base can be ordered as PS PAB 09 options Those needing optical fiber assemblies will also need to order PS FOA options with the probe arm and base On typical systems one arm is provided with a temperature sensor for monitoring nominal arm temperature Additional sensors are available as PA SEN temperature sensor options but must be ordered with the arm and base assembly Probing configurations are divided into three basic groups DC RF section 2 3 2 microwave section 2 3 3 and optical fiber section 2 3 4 DC RF ZN50 probes are commonly used for electrical probing in the CPX ZN50 series probes can be used for a wide variety of DC and RF probing measurements as well as other electrical functions like carrying biasing voltage or excitation current The probes can be used in the continuous frequency range from DC to 100 MHz and selected frequency bands up to 1 GHz depending on cable connector selection See section 2 4 1 and section 2 4 3 for further information on the DC and RF performance of the ZN50 probe 2 3 2 1 ZN50 Probes ZN50 series probes consist of a probe mount ceramic blade with SMA electrical connector and probe tip Lake Shore offers a large selection of ZN50 probe blades with different tip materials and point radii sharpnesses ZN50 probes all share the same basic frequency response and temperature limits but they can be limited in operation by the choice of
195. nt teense een ene 20 2 2 3 1 Temperature Instrumentation cece eect eee e eee e eee 21 2 2A NVISION SYSTE ai aiei niae Saran ures Wen e ES AE vated ete int 22 2 2 5 Turbo Pumping System Optional PS V81DP or Equivalent 22 3 Configurations Options and Accessories 6 ccc ccc ete e eee e eee e ees 23 2 3 1 Probing Configurations 0 0 cee cece eect ene EERE seen enna 23 2 3 2 DC RF ZN50 Probe Configurations c ccc ceee cece srra rri iater raras 23 2 32 0 ZNSO PODES er rerien aeo a wndacca sad sed obese deed am 4 aba see be 23 2 3 2 2 ZN50 Compatible Probe Cables and Connectors 0 00000 24 2 3 2 3 ZN50 Compatible Probe Mount cc cece cece eee ee eee e eee e tees 25 2 3 3 Microwave Probe Configurations cceeceee cece eeee eect ee enneeees 25 2 3 3 1 Microwave Compatible Probes ccc cece cece cece e eens 25 2 3 3 2 Microwave Compatible Cables and Connectors 00eeees 26 2 3 3 3 Microwave Calibration Substrate ccceceee cece cette teens 27 2 3 4 Optical Fiber Assembly 0 cece cece cece e eect ee ee ene eee n enna 27 2 3 5 Sample Holders cece cece e eee beeen eben ene neen eae 28 2 3 5 1 Grounded Sample Holders ccccc cece eee cece cece eens 28 2 3 5 2 Isolated Sample Holders cece ccee cee eee eee teen eee e ene 28 2 3 5 3 Coaxial Sample Holders ccc cece cece e
196. ntact Lake Shore service for assistance section 6 5 6 3 4 8 Image Orientation Follow this procedure to change the orientation of your image 1 Below the threaded joint to the CCD camera is a rotating joint Using a 5 64 in hex driver loosen the three set screws on this joint FIGURE 6 9 2 Rotate the camera so the image on the monitor is oriented logically The objective is to rotate the camera until the monitor image corresponds to the expected image the bottom left probe appears in the bottom left of the monitor screen 3 Retighten the set screws after adjustment FIGURE 6 9 Loosening the camera rotating joint to adjust the camera image orientation The three most common issues that arise with probes fall in three categories bent or broken probe tips poor or non ohmic electrical contact or a loss of continuity 6 3 5 1 Bent or Broken Probe Tips Probe tips by nature are delicate and must be handled with care both inside and outside the probe station The following are ways that probe tips can be broken or bent 6 3 5 ProbeTroubleshooting 151 Landing landing probes is probably the most important step in achieving reliable repeatable electrical measurements Too little contact pressure will result in unstable measurements but too much will damage probes ZN50 probe tips damaged during landing are often bent upwards Carefully follow instructions in section 4 6 2 to prevent probe damage Develop and follow a protocol sui
197. o control loops If this has been verified then the problem is most likely with the Dewar or transfer line If the cryogen transfer is initiated and it does not create a plume FIGURE 4 14 check for the following common problems m Insufficient Dewar pressure Dewar empty Transfer line not reaching cryogen in the Dewar Transfer line foot valve closed Transfer line plugged If the cryogen transfer is initiated and creates a plume as shown in FIGURE 4 14 the problem is more likely a blockage in the refrigerator itself If the refrigerator becomes blocked with ice m Remove thetransfer line m Allow the refrigerator to warm to room temperature m Pass low pressure dry nitrogen gas through until it is dry 6 3 3 Refrigerator Cooling Troubleshooting 145 6 3 3 2 Sample Stage Will Not Cool If the 4 K shield stage cools but the sample stage does not there are two potential problems that are easy to remedy and should be checked first m Micrometer valve is not opened sufficiently m Sample stage temperature control is on If you have the micrometer valve open sufficiently and the sample stage temperature control is off then your problem may be a result of the following m Sample stage warmer than 4 K shield stage when the 4 K shield stage is cold and the sample stage remains above 100 K it can become difficult for cryogen to enter the sample stage cooling line refer to step 7 in section 5 2 1 for instructions on how to use the exhau
198. obe Failure to do so will potentially cause damage to the probe tip or scratch the sample surface 1 Swing the microscope away from the viewport 2 Use the z axis micrometers to raise all probes 3 to 4 mm above the sample Fail ure to do so will potentially cause damage to the probe tip or scratch the sample surface 3 Position the probe tips over the sample or landing pads using the x axis hand dial and y axis micrometer 4 Swing the microscope over the viewport 5 Adjust the microscope to fill the monitor with the sample image and focus at the height of the landing pads or landing surface 6 Use the z axis micrometer to move the probe tip up and down until the tip begins to come into focus At this point the tip is only 30 um to 60 um away from the sample 7 Continue lowering the probe slowly stopping to position it as needed so the tip lands on the outside edge of the landing pad 8 Once it lands on the pad which is indicated by a forward movement known as skating continue lowering it until it skates on the pad by a consistent amount A typical amount of skating is 20 um to 25 um which is roughly the same as two scale graduations on the z axis hand dial 9 The desired position of the probes with respect to the edge of the pads and the desired amount of skating should be determined and used as a lab standard to ensure consistent results Raise all probes 3 mmto 4 mm above the sample before changing temperature or vacuum
199. obe tip damage CAUTION 3 6 5 Probe Continuity Test Follow this procedure to ensure that the probes have been installed correctly and will transmit a signal when probing a sample The radiation and vacuum chamber lids do not need to be installed This procedure should be performed whenever a probe arm or probe has been changed 1 Land each probe tip on the top surface of the grounded sample holder 2 Using a multimeter measure continuity resistance between each adjacent pair of probes 3 Abad probe assembly can be identified if it does not show continuity low resistance with the probes on either side 4 Ifa probe assembly appears bad first re land the probe to make sure it is touching the sample stage then refer to section 6 3 5 ES akeShore www lakeshore com 82 CHAPTER 3 Installation and Setup 3 6 6 Vacuum Chamber Leak Test CAUTION Model CPX Probe Station Follow this procedure to verify vacuum chamber integrity 1 Test the turbo vacuum pump along with the connection to the probe station section 6 3 1 2 2 Test the turbo vacuum pump connection to the probe station and the probe station vacuum chamber section 6 3 1 3 Failure to turn off and properly vent the vacuum before opening the vacuum isolation valve may result in damage to your vacuum pumping system 4 1 General 83 Chapter 4 Basic Operation 4 1 General 4 1 1Common Operational Mistakes 4 1 2 Temperature Limits CAU
200. of the leak place a few drops of isopropyl alcohol on the suspected area and look for an observable change in the vacuum gauge reading 6 3 1 8 Will Not Achieve Less Than 10 3 Torr or Cool to 4 2 K Systems capable of achieving 10 3 Torr but unable to achieve and hold between 3 x 10 4 Torr and 9 x 10 4 Torr or unable to cool to a base temperature of 4 2 K are the most difficult to troubleshoot because the symptom can be caused by several different problems Contamination in the vacuum chamber and very small leaks are the most common issues associated with this level of performance Suspect contamination if m The system has been left open for extended periods of time m The system has been worked on and good vacuum practices were not followed m The system has been overheated or operated when not under vacuum m The system has been vented to atmosphere while cold To minimize the effects of contamination m Follow the guidelines in section 6 2 3 m Follow the guidelines in section 6 2 12 Suspect a very small leak if m The pump passed a blank off test m The system is clean and poor vacuum persists m Performance degrades the longer the system is cold m Sudden changes in vacuum reading are observed when the sample stage is heated especially warming above 77 K The best way to proceed if you suspect a leak m Follow the instructions in section 6 3 1 7 in hopes of sealing the system even if the exact source is not identified m
201. ogen flow by closing the foot valve until it is 1 to 2 turns open Locate the exhaust valve assembly and open the valve c Using protective gloves attach the exhaust valve assembly to the exhaust port on the bayonet using the NW 16 clamp and centering ring included d Close the exhaust valve then open it approximately one quarter turn The sample stage will begin to cool more quickly The 4 K shield stage tempera ture will rise but you should not allow it to rise above 20 K Open the foot valve additional turns if necessary e When the sample stage reaches 100 K you can open or completely remove the exhaust valve assembly 8 Operate the probe station normally The sample stage of the CPX can be operated below 4 2 K the boiling point of liquid helium at atmospheric pressure by decreasing the pressure of the helium flowing to the sample stage and therefore reducing its boiling temperature This process requires the PS LT option A vacuum line vibration isolator PS PLVI 25 or equivalent is recommended for vibration sensitive operation The vacuum turbo pump used to evacuate the vacuum chamber is not suitable for operat ing the probe station below 4 2 K Follow this procedure to operate the sample stage below 4 2 K 1 Using the clamp and centering ring provided install the flexible stainless vacuum line onto the sample stage exhaust port on the bottom of the probe station Do not attach the other end until step 8 Open the
202. older sample mount surface at system ground m Isolated sample holder backside contact not needed sample mount surface is electrically non conductive and isolated from ground m Coaxial sample holder backside contact can be made sample mount surface is isolated from ground m Triaxial sample holder guarded backside contact can be made sample mount surface has guarded isolation from ground Separate Maximum Measurement Maximum Part number A feedthrough sample configuration 7 temperature required diameter SH 1 25 G Grounded i 475K i 0 SH 1 25 1 Isolated 32 mm 1 25 in SH 1 25 C Coaxial Yes 400 K SH 1 25 T Triaxial Yes SH 2 00 G Grounded No 475K SH 2 00 C Coaxial Yes 51mm 2in 400K SH 2 00 T Triaxial Yes Coaxial sample holders require one FT BNC or FT TRIAX feedthrough as listed below Triaxial sample holders require one FT TRIAX feedthrough as listed below TABLE 1 13 Sample holders FT BNC Coaxial feedthrough and coaxial cable installed and wired FT TRIAX Triaxial feedthrough and coaxial cable installed and wired TABLE 1 14 Feedthroughs El akeShore www lakeshore com 8 CHAPTER 1 Introduction 1 6 Equipment Options High vacuum option Ensures that condensation does not accumulate in the sample environment during cooldown This is critical for measuring organic semiconductors and for high Z and low current applications Includes HVAC port Varian V301 turbo pump kit and rel
203. ompressor should be powered from a separate circuit to isolate electrical noise from the sensitive electronic instruments It is also recommended that the circuit protection used for the circuits powering the turbo pumping system be capable of handling high inrush currents The turbo pumping system will draw high inrush currents when powered on Circuit protection capable of handling these short duration inrush currents is required to prevent nuisance tripping of the safety devices Operational current required AAC Probe station equipment 100 VAC 120 VAC 220 VAC 240 VAC Instrument console 9 4 6 2 3 8 3 1 Circuit 1 isi aE VRON Sytem 7 2 6 0 3 3 3 0 monitor camera and light source ae PS V81DP turbo pumping station 6 2 6 3 1 3 Circuit 2 Air compressor 120 VAC only 2 2 Model CPX Probe Station TABLE 3 1 Power requirements 3 2 4 Cryogen Requirements 3 2 5 Vacuum Requirements 3 2 6 Gas Requirements 3 2 4 Cryogen Requirements 57 The CPX is a cryogen flow open cycle refrigerator Liquid cryogen must flow continuously through the refrigerator during operation Liquid nitrogen can be used to cool the sample to 78 K and liquid helium is necessary to cool the sample below 78 K The system can be used at ambient temperatures for measurements with no cryogens The cryogen must be provided in an appropriate Dewar designated for the correct cryogen either helium or nitrogen Th
204. on specifications 2 probes 5 frequency range 3 installing a ZN50 72 misaligned 78 removing 71 removing a ZN50 75 troubleshooting 150 probing configurations 23 R refrigerator 14 83 cryopump 141 diagram of 14 electronic controls 97 mechanical controls 95 103 troubleshooting 144 vacuum controls 92 refrigerator cooling curve 146 refrigerator electronic controls 103 RF measurements 38 40 S safety considerations 9 sample permanent mounting 89 semi permanent mounting 88 temporary mounting 88 sample exchange 85 sample holder 7 28 alignment of sample 87 cleaning 132 coaxial 29 for samples with conductive back side features 39 grounded 28 isolated ground 28 mounting samples 87 removing 86 specifications 3 voltage biasing 39 sample holders isolated 39 sample rotation 105 sample imaging and probing 104 service reference 153 shielding DC RF measurements 37 space requirements 54 specifications 2 split flow 14 superconducting magnet 12 T temperature control summary 102 temperature controls 95 temperature instrumentation 21 temperature specifications 2 testing the system 79 microscope 81 probe arm reach 81 probe continuity 81 sensor and heater 80 transfer line 17 image 62 pumping out 135 space requirements 54 troubleshooting 143 unpacking 62 transfer line cryogen 57 triaxial sample holder 29 troubleshooting 138 image system 147 probes 150 refrigerator cooling 144 transfer line 143 turbo pumping syst
205. on for a microscope that is set up for thick samples to be incapable of focusing on the sample holder or thin samples Follow this procedure if the microscope does not focus on the sample surface 1 Set the microscope focus knob to the middle of its range 2 Loosen the nylon thumbscrew on the horizontal boom 3 While supporting the microscope with one hand to prevent it from falling use the 3 16 in hex driver to loosen the shaft collar section FIGURE 6 8 4 Slide the microscope and collar up or down a few millimeters and tighten the shaft collar and thumbscrew Attempt to focus again 6 Continue adjusting the height until the sample can be focused eal 6 3 4 ImageSystem Troubleshooting 149 FIGURE 6 8 Microscope focus adjustments 6 3 4 6 Vibration in the Image System The most common reason for a blurred image on a properly focused microscope is vibration Vibration can come from many sources including vacuum pumps motors and fans running in the vicinity of the probe station Vibrations can also affect the microscope directly Make sure the electrical wires and fiber optic bundle going to the microscope are not stretched tight and do not pass over the vacuum line or any other vibration source Isolate the light source from the probe station to verify its fan is not causing the blurred image Finally verify that the nylon set screw is tight on the shaft Vibration from vacuum pumps vacuum pumps used with the probe sta
206. ons capable of lifting at least 22 7 kg 50 Ib each Box cutter knife Phillips head screw driver battery powered if available Adjustable wrench Small diagonal wire cutters If space and equipment is available the loaded shipping crates should be moved to the installation site intact They can be moved easily with a pallate jack while the contents remain protected If the CPX must be moved after it is uncrated it should be strapped to a dock cart for transport Use lifting equipment or four people one for each side of the probe station throughout this procedure The probe station weighs over 91 kg 200 Ib and is uneven in its weight distribution Failure to comply may result in injury Ea LakeShor e www lakeshore com 60 CHAPTER 3 Installation and Setup A WARNING 3 3 5 Uncrating the System and Stand Model CPX Probe Station The probe station has a high center of gravity and is not mounted to its stand The probe station should never be moved unless the shipping brackets are in place between the baseplate and the stand N FIGURE 3 4 Proper lifting These steps will assist you in safely removing the probe station from its crate 1 Using a Phillips screw driver remove the screws from the top of the crate containing the probe station Remove the screws that fasten the wood and foam stabilizer to the long side crate walls Remove and save the stabilizer Remove the screws around the perimeter of b
207. ontact Probes geometry m User specified pitch spacing m Optimized low thermal conductivity coaxial leading to low thermal conductivity tips m Include a copper braid assembly to cool the probe to near sample temperature m Limited to 475 K Separate theta planarization module with 5 rotation mechanism is provided Maximum ae ve bss plead ld oe 50 GSG 050 40A 55I E GSG 100 40A 55I E 100 GSG 150 40A 55I E K 40 150 GSG 200 40A 55I E 200 GSG 250 40A 55I E 250 GSG 050 50A 55I E 50 _ GSG 100 50A 55I E 100 GSG 150 50A 55I E 2 4mm 50 150 GSG 200 50A 55I E 200 GSG 250 50A 55I E 250 GSG 050 67A 55I E 50 GSG 100 67A 55I E 100 GSG 150 67A 55I E 1 85 mm 67 150 GSG 200 67A 55I E 200 GSG 250 67A 55I E 250 TABLE 1 11 GSG microwave probes 1 5 5 GSG Microwave m Loss less compression seal Cables m Semirigid with Teflon dielectric type temperature frequency thes Semirigid Loss less SMA ere JOH MWC 009 240 microwave compression 475K JA 50GHz ee E coaxial seal MWC 009 185 1 85 mm 67GHz TABLE 1 12 GSG microwave cables Model CPX Probe Station 1 5 6 Sample Holders 7 1 5 6 Sample Holders Typical sample holder configuration characterized by Leakage resistance between m Top surface and guard m Guard and ground Capacitance between m Top surface and guard m Guard and ground Types of sample holders m Grounded sample h
208. order of a magnitude higher than measured here All probe station vacuum specifications are made with the gauge located on the vacuum chamber itself For more accurate vacuum pressure readings the gauge can be moved to an available port on the vacuum chamber 4 4 2 Evacuating the Vacuum Chamber 4 4 2 Evacuatingthe Vacuum Chamber 93 4 4 1 4 Vacuum Performance Aroom temperature vacuum level of lt 10 3 Torr in the vacuum chamber is required for the probe station to meet its specified base temperature and cooling time Each probe station is tested prior to shipment to ensure it can achieve appropriate vacuum level and cooling specifications with a PS V81DP turbo pump option If the system will not reach a vacuum level of lt 10 3 Torr within 1 h or it takes more than 10 min for the turbo pump to reach full speed suspect a leak or other problem with the vacuum system and refer to section 6 3 1 8 for troubleshooting information Even with properly functioning equipment and good maintenance vacuum performance of the probe station may degrade with time The probe station may need to be warmed up and re evacuated if it has been in continuous operation for several days or ifthe sample is warmed and cooled frequently To keep the vacuum system operating efficiently refer to section 6 2 1 fora preventive maintenance schedule After closing the vacuum chamber lid follow this procedure to evacuate the system This process assumes that the vacuum p
209. osition the 90 bend in the cable to give or take length from the vertical section and add or subtract it from the horizontal section Keep pres sure on the inside radius as the bend is made to prevent the cable from kinking 5 Install the cable assembly using the instructions in section 5 3 6 2 You may need to use the first method of this section for a final adjustment Model CPX Probe Station 5 3 7 Reconfiguring an Optical Fiber Assembly 5 3 7 Reconfiguring an Optical Fiber Assembly 123 6 Test the fit Ifthere is not enough adjustment with this method go to the third method 7 Install the probe arm and base to the micro manipulated stage using the instruc tions in section 5 3 4 8 Install the micro manipulated stage to the probe station using the instructions in section 5 3 1 Third Method Adjust the Arm Length 1 Remove the micro manipulated stage following the instructions in section 5 3 2 2 Remove the probe arm and base using the instructions in section 5 3 3 3 Remove the cable assembly using the instructions in section 5 3 6 1 4 Forthe probe arm that has the temperature sensor remove the 6 pin feedthrough receptacle using section 5 3 5 1 as a guideline Mark the four sensor wires so that they can be replaced in their original pin locations 5 Usinga10mm wrench loosen the locknut located on the end of the probe arm nearest the probe arm base 6 Rotate the probe arm in full revolutions to lengthen or shorten i
210. oth Low temperature solder and filled epoxy Stycast are permanent mounting options that are compatible with vacuum Follow this procedure to mount the sample holder onto the sample stage 1 Raise each probe 3 mm to 4mm above the sample holder using the z axis micrometers 2 Centerall probes using the y axis micrometers 3 Retract all probes away from the sample stage using the x axis hand dials This will provide maximum access to the sample stage 4 Lower the sample holder onto the sample stage using the lifter tool FIGURE 4 6 5 Ifmounting an optional triaxial or coaxial sample holder align the socket on the sample holder with the cable location 6 Using the 2 5 mm hex driver fasten the sample holder to the sample stage by starting all four M3 screws in a few threads before tightening any screws to pre vent cross threading 7 Tighten the four screws securely this is the source of thermal contact between the sample holder and the sample stage It is best to tighten all four screws a little at a time until snug Do not over tighten as damage to the sample stage threads is costly to repair El akeShore www lakeshore com 90 CHAPTER 4 Basic Operation FIGURE 4 6 Left Fastening the sample holder onto the sample stage Right Connecting the signal cable on a triaxial or coaxial sample holder 8 CAUTION If mounting an optional triaxial or coaxial sample holder connect the signal cable after mounting the
211. oth short walls of the crate and remove both short walls Make sure a second person holds onto each of the panels as you remove the screws to make sure the panels do not fall on you or the probe station Remove both long walls leaving the wooden cross braces shown in FIGURE 3 3 left If there are tie down straps remove them Remove the cardboard surface protectors that protected the baseplate from the tie down straps Remove the red shipping brackets that are screwed into the legs of the stand and the crate Using a utility knife remove the plastic wrap covering the probe station To avoid scratching the bellows begin by cutting the plastic wrap where it covers the vacuum isolation valve FIGURE 3 5 3 3 6 Uncrating the Console and Accessories 3 3 7 Unpacking the Probe Station 3 3 8 Unpacking the Instrument Console Crate 3 3 6 Uncrating the Console and Accessories 61 FIGURE 3 5 Remove the plastic wrap 8 Liftthe probe station off the crate base see FIGURE 3 4 Use one of the following methods a Lifting equipment Screw lifting eyelets into the four 1 2 13 in threaded holes in the top of the baseplate FIGURE 3 4 You may need to remove the set screws in the threaded holes before doing this The lifting eyelets on the instrument console can be removed and used for this purpose b Four people capable of lifting 23 kg 50 Ib each Each person should grasp one end of the cross braces as shown in FIGURE 3 4 9
212. owave probes Lubricate micrometer valve o rings Lubricate chamber lid and probe arm o rings Clean the viewport windows Clean the vacuum chamber exterior TABLE 6 1 Preventive maintenance schedule El akeShore www lakeshore com 130 CHAPTER 6 Maintenance and Troubleshooting 6 2 2 Cleaning the Vacuum Chamber Exterior 6 2 3 Cleaning the Vacuum Chamber Interior CAUTION Model CPX Probe Station The exterior of the probe station chamber should be kept generally clean and clear of dust and other possible contaminants Surfaces may be wiped down using damp lint free cloths like Kimwipes Isopropyl alcohol on a lint free cloth is recommended to loosen adhesives and other residue Dust on the exterior may also be removed with a commercially available compressed air product such as Dust Off Failure to keep the chamber clean and store it under vacuum will result in poor probe station performance due to contaminants and moisture in the chamber A dirty chamber requires longer pump down times more helium to cool and results in higher base temperatures If the CPX chamber is not properly maintained it will be increasingly difficult to operate the 4 K shield stage below 5 K 1 Prior to cleaning remove the following Vacuum chamber lid Radiation shield lid Main chamber o ring Sample holder Probes 2 Wipe down the following surfaces with a lint free wipe like Kimwipes and iso propyl a
213. owave structures must be patterned on the top layer of the substrate to facilitate top side probing Measurements can be performed on both passive and active devices to characterize performance metrics such as S parameters noise figure or load pull parameters Proper use of GSG microwave probes is more complex than of DC RF probes Proper probe alignment of the GSG points with respect to the test substrate is required as is the proper probe planarization with respect to the plane of measurement Also calibration may be desired to separate the frequency dependent losses of the measurement setup from the actual device under test The remaining sections in this chapter describe details of the microwave probe measurement setup as well as concepts and techniques that are important for making good microwave measurements in the probe station Microwave cables form transmission lines that carry high frequency signals from the signal connection point outside the vacuum chamber to probe points near the cooled sample The type and quality of microwave cables and their associated connectors determine the frequency range and overall performance of microwave measurements in the probe station Properly installed the cables provide a low loss broad band electrical path with minimal crosstalk Also they need to be compatible with the cryogenic temperatures and vacuum for the CPX The geometry of the CPX requires that the cables extend 229 mm 9 in into the
214. p may speed this step 6 Reinstall the sample holder radiation shield lids and vacuum chamber lid Using section 4 4 2 as a guide evacuate the chamber 8 Warm the refrigerator stages slightly above room temperature to help evacuate the water molecules Monitor the stage temperatures closely until they stabilize in case any of the sensors were damaged Stages should be warmed to the follow N ing temperatures m Sample 475K 4 K shield 380 K C m Radiation shield 380 K m Secondshield 380K Do not allow the sample stage to exceed 475 K the 4 K shield stage radiation shield stage or the second radiation shield stage to exceed 380 K or the probe arm to exceed 350 K Temperatures exceeding this could cause damage to your probe station 9 Use the vacuum pump to evacuate the probe station for 24 to 48 hours 10 Ifthe vacuum chamber can attain lt 10 3Torr then go to step 13 11 Cycle purge the refrigerator several times with dry argon gas using the instruc tions in section 4 4 4 as a guide Allow the argon gas to remain in the chamber for at least 30 min during each cycle before evacuating Allow the vacuum pump to run for several hours during each cycle 12 If the station can attain lt 10 3 Torr then go on to step 13 if not contact the Lake Shore service department because the system may have a vacuum leak or other damage El akeShore www lakeshore com 138 CHAPTER 6 Maintenance and Troubleshooting 6 3 Troubles
215. pe focuses properly on the sample stage See section 2 3 6 1 for a sample of approximate focal clarity when you use the focus aid with the Zoom 70 and Zoom 160 1 Place apiece of sample material or sample substrate on the sample holder We recommend using an optical target such as the U S A F optical target for resolution verification 2 Install the radiation shield lid and the vacuum chamber lid see section 4 3 5 3 Refer to section 4 6 1 to use the microscope to image the sample 4 Ifthe microscope will not focus on the target refer to section 6 3 4 5 Ifthe image is not oriented as desired refer to section 6 3 4 8 3 6 4 Testing the Follow this procedure to check the probe arm reach Probe Arm Reach 1 Remove the vacuum chamber lid and radiation shield lid section 4 3 1 2 Use the z axis micrometers to raise all probes up 3 mm to 4 mm above the sample stage Slowly move one probe towards the sample stage using the x axis hand dial Watch for interference of the probe cable connector and blades 5 Using the x and y micrometers to adjust position move the probe it should travel smoothly until the probe tip reaches all sides of the specified 25 mm 1 in diameter probe area see FIGURE 4 1 for probe area 6 Retract the probe and repeat for all other probes PO Check arm reach one probe arm at a time Retract the previously checked arm before advancing a second arm into the sample area Failure to comply may result in pr
216. ple stage to elevated temperatures to reduce thermal gradients It is sometimes difficult to re cool the sample stage after operating it above 100 K Please refer to section 5 2 1 if the sample stage cools too slowly 1 2 wn Use the z axis micrometers to raise all probes 3 mm to 4 mm above the sample Reduce the pressure on the Dewar to between 21 kPa and 34 kPa 3 to 5 psi This reduces the temperature of the cryogen and makes it easier to regulate flow and temperature of the sample stage Reduce cryogen flow for best efficiency To do this perform the following steps a Close the transfer line foot valve one half turn wait 2 min to see ifthe temperature rises at the 4 K shield stage channel B on the Model 340 b Repeat step a until you see the temperature at the 4 K shield stage rise to approximately 0 5 K above base temperature c Open the foot valve approximately one quarter turn and wait 1 min to see if the temperature at the 4 K shield stage stops rising d Repeat step c until you see the temperature at the 4 K shield stage stabilize at approximately 5 K to 10 K Close the sample stage micrometer valve completely then open it as shown in TABLE 4 4 The valve may need to be more open in the beginning if the sample stage needs to cool significantly Change the setpoint Model 340 loop 1 to the desired temperature Use the controller settings given in TABLE 4 4 to set the P and D heater range settings If the con
217. probe cable All ZN50 blades require a ZN50 551 probe mount for the probe arm The three probe tip materials are 1 Tungsten this is the stiffest hardest and potentially sharpest probe tip material Best for probing fine detail or scratching through hard oxide layers to make electrical contact with underlying layers 2 Beryllium Copper softest and most compliant probe tip material Makes low resistance contacts to conductive surfaces like gold pads especially with larger diameter tips 3 Paliney 7 least reactive probe tip material Least likely to form resistive oxides especially at elevated temperatures El akeShore www lakeshore com 24 CHAPTER 2 System Overview Model CPX Probe Station FIGURE 2 15 ZN50 probe and mount 2 3 2 2 ZN50 Compatible Probe Cables and Connectors ZN50 probe cables with their signal connector and probe connector dominate the electrical characteristics of DC RF configurations Each combination has different electrical properties but they are all compatible with the ZN50 series of probes 1 BNC feedthrough with ultra miniature cryogenic coaxial cable is for general purpose DC RF applications The BNC signal connector on the probe arm base is easy and economical to interface Shielding at system ground potential is carried to the probe s ceramic blade Teflon insulated ultra miniature cryogenic coaxial cable provides operation up to 50 MHz and 400 K with low thermal conductivity The probe
218. qUIDMENt 0 0 cece cece cece ence eee e eee e eens 4 1 5 1 Up to Six XYZ Precision Micro manipulated Stages 4 1 5 2 ZN50 DG RE PrODE S 44 c c csd tiit ernie Sankaa ea awedbs Molgeandalgadadaundeagaeaun 5 1 5 3 ZNSODC RF Cables ccc ccc ccc ccc cece een teen nate eee ee ene ee ennaes 5 1 5 4 GSG Microwave Probes ccccc cece cece cece cece teen eee eeneeeeeeaee 6 1 5 5 GSG Microwave Cables cccc cece eee cence cence en nn enna 6 1 5 6 Sample Holders ocni aa eee EER EEEN 7 EQUIPMENT Options 4 iosnc srsiaaesderseeatieadantngcbesnes E EERE EINE EKERI eet 8 Safety Considera GONS cece cece ELEn eee eee e eect nee teen nnneeeee ena 9 GENER all perenras ea EEEE EAER RR ass dy alaiale Acne yea EAER EERE RRES 11 Maj r COMpPOMeNts proroirersreieuni sin nr EA E ENRETE KEAR RA REEE ETRE 11 22 1 PRODSStAUOM sc sccorvonte ree casmaveiie heearbaabseecieeyeiaageeeminty ETS 12 22 11 VACUU CN aM DOP pa e enine aerae an E A 13 2 212 REMISENAUOL orak aena ENEA DELALA T RECEA NATE 14 2 2 1 3 Micro manipulated Stages ssssssrsrrrrsrrreserrerrsrrirrirssssrerev 15 2 2 2 Cryogen Dewar and Pressurized Gas System 00 ccee eee ence eee enna 16 De 22 Tanster ING sea ous ap sete cette tents FAAEE n EE 17 22 22 CONVO EN DEWA sseparata aains os aaen anan Oa a EEEE ERNES 18 2 2 2 3 Pressurized Gas SYSt M 2 eee eee eee nina e eee e eee eect eennaees 19 2 2 3 Instrument Console 66 e cece eee e ne
219. ration from DC to 40 GHz K connectors mate to SMA connectors making this a configuration that allows easy exchange between the microwave probes configured with K connectors and ZN50 probes that have SMA connectors This configuration can also be used with external measurement cables with either K connectors or SMA connectors The semirigid microwave cable is limited to operation below 350 K 2 2 4mmconnector with semirigid cable this microwave connection is rated for continuous mode free operation from DC to 50 GHz 2 4 mm connectors mate to 2 3 4 Optical Fiber Assembly 2 3 4 Optical FiberAssembly 27 precision higher frequency V connectors 1 85 mm This configuration can be used with external measurement cables with either 2 4 mm or V connectors The semirigid microwave cable is limited to operation below 350 K 3 V connector 1 85 mm with semirigid cable this is a precision microwave connection rated for continuous mode free operation from DC to 67 GHz V connectors mate to 2 4 mm connectors This configuration can be used with external measurement cables with either 2 4 mm or V connectors The semirigid microwave cable is limited to operation below 350 K 2 3 3 3 Microwave Calibration Substrate For the most accurate microwave measurements especially when performing wide band frequency measurements the frequency dependent losses in the probes and cables should be removed using a calibration substrate A calibration substrate is us
220. ration isolator includes NW 25 fittings 1 m stainless steel bellows clamps and rings placed between pump cart and system requires one bag of cement PS V81DP Turbo pumping system includes Varian V 81 turbo pump cart with oil free dry scroll backing pump vacuum gauging for high vacuum and foreline controller and adaptors specify 120 V 60 Hz or 220 V 50 Hz PS PLVI 40 Pump line vibration isolator includes NW 40 fittings 1 m stainless steel bellows clamps and rings placed between pump cart and system requires one bag of cement 1 5 K base temperature assembly includes adapter 4 K shield and Model SH 1 00 G 25 mm 1 in grounded sample holder NOTE Must be PS VLT CPX purchased in addition to PS LT maximum sample size limited to 25 mm 1 in with this option additional sample holders sold separately 50 Hz operation may increase base temperature PS DPC Automatic Dewar gas pressure controller regulates Dewar liquid flow PS LN2 Nitrogen Dewar with stainless fittings gauges and adaptors allows LN use with the LHe transfer line Pneumatic vibration isolation system gimbal piston isolator actuators and supports isolator natural frequency vertical 0 8 Hz PS PVIS horizontal 1 0 Hz isolation efficiency at 5 Hz vertical 80 to 97 horizontal 60 to 90 efficiency at 10 Hz vertical 90 to 99 horizontal 70 to 95 requires 40 psi nitrogen or air PS OAC Oil less compressor for PS PVIS only availabl
221. re controller 4 5 5 Operating the Sample Stage 6 K and Above 3 4 5 5 Operating the Sample Stage 6 K and Above 101 b Repeat step a until you see the temperature at the 4 K shield stage rise to approximately 0 5 K above base temperature c Open the foot valve approximately one quarter turn and wait 1 min to see if the temperature at the 4 K shield stage stops rising d Repeat step c until you see the temperature at the 4 K shield stage stabilizes at approximately 5 K to 10 K Regulate cryogen flow to the sample stage a Close the sample stage micrometer valve on the probe station one half turn wait 2 min to see if the temperature rises at the sample stage channel Aon the Model 340 temperature controller Repeat step a until you see the temperature at the sample stage rise c Atthis point the sample stage micrometer valve can be used to regulate the sample stage temperature within a range of approximately 1 K to 2 K above base temperature Follow this procedure to maintain sample temperature above 6 K This procedure assumes that you have cooled the refrigerator to base temperature see section 4 5 3 and wish to bring it up to the temperature your experiment requires Cooling the system to base temperature stabilizes the temperature of the 4 K shield and radiation shield stages making it easier to regulate the temperature of the sample stage It is recommended to keep the radiation shields cold even when raising the sam
222. rent and voltage more closely resembling a diode This is undesirable because signals resulting from the contact cannot easily be subtracted from the desired signal of the sample Measuring contact quality is always recommended for critical measurements to make sure the contact resistance is low and the contact is ohmic Both contact resistance and ohmic behavior can be checked at the same time The most common DC technique is to excite two probe contacts at a time with different positive and negative currents and plot the measured voltage IV curve A linear curve with a low slope indicates a good contact Non linearity in the curve indicates a non ohmic contact If the test cannot be performed on the actual device probing technique can be verified by landing two probes on one sample pad and making an IV curve prior to probing the device Inthe case of a microwave measurement contact resistance increases the series resistance of the microwave circuit However the film between the probe and measurement pad can form a capacitor This capacitance will change the S parameters of the device as measured by a network analyzer A level response on the network analyzer is typically the best measure of contact quality Lake Shore recommends developing a lab protocol to ensure consistent contacts The protocol should include probe handling routine cleaning landing probes and measuring contacts The probe landing instructions given in section 4 6 describe
223. rigerator is cold to prevent the chamber from being vented if the pump is accidentally turned off or the vacuum pump loses power Venting the chamber when the refrigerator is cold can damage the probe station 4 4 1 2 Considerations for Using the Vacuum Isolation Valve If the probe station is going to be cryogenically cooled with liquid helium it is best to close the isolation valve and turn off the vacuum pump when the refrigerator temperature is less than 100 K The cooled radiation shields act as a cryopump creating a better vacuum than the turbo pump In the case where cryopumping reduces the vacuum pressure in the chamber below that of the turbo pump it is even possible to draw outside contamination in through the vacuum system Turning the pump off also minimizes vibration at the sample If the probe station is going to be operated without cryogenic cooling see section 5 2 4 itis best to leave the vacuum isolation valve open and the pump running during operation This is because at elevated temperatures the system will slowly outgas and degrade the vacuum The pump line isolation option PS PLVI 40 should be used if measurements are routinely made at elevated temperatures to reduce vibrations due to the vacuum pump 4 4 1 3 Vacuum Gauge Location For convenience the vacuum gauge on the PS V81DP pump option is located on an NW 40 T immediately at the inlet of the turbo pump Vacuum pressures in the probe station chamber will be a half
224. rn fas teners until they lock into place Do not attempt to tighten the fasteners as the vacuum force will draw the lid down and form a tight seal aD CAUTIO N The quarter turn fasteners should never be forced if they do not engage smoothly push down firmly on the vacuum chamber lid before engaging them FIGURE 4 8 Left Placing the o ring in the chamber groove Right Placing the chamber lid onto the o ring 4 4 Vacuum The vacuum system is one of the biggest variables in the probe station hardware Operation configuration Clean consistent vacuum is critical to probe station performance and should be given careful consideration during operation This section outlines some of the operating characteristics of a typical vacuum system using the Lake Shore Model PS V81DP option as an example refer to section 2 3 7 for equivalent specifications Most of the principles described here are applicable to other vacuum systems Please take time to become familiar with the components of your turbo pumping system and their operation before continuing 4 4 1 Turbo Pump The most difficult part of operating a turbo pumping system is keeping the proper Overview sequencing The turbo pumping system option offered by Lake Shore includes a vacuum controller for automatic sequencing of turbo turn on and turn off operations The vacuum controller has safety limits to help prevent damage to the vacuum equipment For example the turbo pump may be damaged if it is
225. rovides in plane rotation to allow alignment of patterns with stage axes Proprietary probe tips in a variety of sizes and materials minimize thermal mass and optimize electrical contacts to the device under test DUT Probe tips are thermally linked to the sample stage to minimize heat transfer to the DUT For increased versatility CPX options include temperatures down to 1 5 K high vac uum load lock assembly vibration isolation systems LN Dewar kit higher magnifi cation microscope turbo pumping system and optical fiber assembly El akeShore www lakeshore com 2 CHAPTER 1 Introduction 1 2 1 Applications 1 2 2 Materials 1 3 Specifications 1 3 1 Temperature 1 3 2 Probe Arm and Sample Stage Adjustments Model CPX Probe Station Electrical and electro optical measurements over a wide temperature range RF and microwave Parametric testing Shielded guarded low noise characterization High Z Non destructive full wafer testing Nanoscale electronics carbon nanotube transistors single electron transistors molecular electronics nanowires etc Quantum wires and dots quantum tunneling Single electron tunneling Coulomb blockade Basic semiconductor devices including organics LEDs and dilute magnetic semi conductors Operating temperature range overall 1 5 K to 475 K ZN50 DC RF probe with low RF cryogenic coaxial cable 1 5 K to 475 K ZN50 DC RF probe with high RF semirigid coaxial cable 1
226. s to raise all probes 3 mm to 4 mm above the sample Failure to do so will potentially cause damage to the probe tip or scratch the sam ple surface 2 Turn offall temperature controller heater outputs or set all control setpoints to O K Both the Model 332 and Model 340 have two control loops 3 Close the sample stage micrometer valve to establish zero When you feel a spongey stop the valve is closed do not over torque as the valve is delicate 4 Openthe sample stage micrometer valve by opening it counterclockwise six to eight turns 5 Ifinstalled remove the exhaust valve assembly or open the valve completely 6 If present remove any protective cap from the end of the cryogen inlet port on the bayonet 7 Unscrew the bayonet compression fitting from the port removing the two metal parts and the o ring If the o ring does not come out use a finger or the plastic o ring positioning tool to gently remove the o ring from the port 8 Prepare the transfer line by placing the bayonet compression fitting onto the transfer line shoulder FIGURE 4 13 9 Close the transfer line foot valve FIGURE 4 13 to establish zero 10 Open the transfer line foot valve five turns 11 Place the 1 2 in compression fitting included in the CPX spares kit on the with draw leg of the transfer line with the o ring toward the bottom the o ring will hold the fitting on the transfer line 4 5 3 Cooling the Probe Station with Helium 99 FIGU
227. sample holder to the sample stage FIGURE 4 6 Using twee zers push the cable plug into the sample holder socket Be very careful that the tweezers do not slip off the cable plug and onto the wire where they can accidentally pull the wire out of the connector If you are using microwave probes make sure rotation and planarization are within range section 4 6 3 and section 4 6 4 4 3 5 Closing the Follow this procedure to close the vacuum chamber and radiation shield Vacuum Chamber and Radiation Shield Lake Shore recommends that you practice imaging the sample and landing the probes section 4 6 before closing the vacuum chamber and radiation shield for cooldown 1 Using the 2 5 mm hex driver attach the radiation shield lid to the radiation shield Model CPX Probe Station body Start all M3 screws in a few threads before tightening any screws to pre vent cross threading FIGURE 4 7 Securely tighten all eight screws this is the source of thermal contact between the lid and shield body FIGURE 4 7 Attaching the lid to the radiation shield body Clean the o ring groove in the vacuum chamber Clean inspect and lightly grease the o ring with vacuum grease and place it in the groove FIGURE 4 8 Make sure that the o ring does not twist as it is being installed Place the vacuum chamber lid onto the o ring FIGURE 4 8 4 4 Vacuum Operation 91 5 Push down squarely on the vacuum chamber lid and turn the quarter tu
228. shield Connector body Gray tin Ground N Ac Singlebanana A Red V 4 Probe arm B Black V 2 Probe arm 6 pin G White I 5 sensor connector D Green l 1 6 pin DIN No connection Gray tin Cable shield 3 E F Not used a In control cable b Sample sensor depending on model either TG GaAlAs diode or Cernox thermometer c Drain wire connected to single banana which plugs into chassis next to heater output of controller The other end of the drain wire is con nected to the body of the 19 pin mating connector Both leads of a spare sample stage heater are tied to this pin 6 4 3 Instrumentation Wiring Diagram Model CPX Probe Station TABLE 6 3 Pin outs for the control and readout cables of the system FIGURE 6 10 shows the system wiring diagram It details the electrical interconnec tions between the probe station and instrument console Lake Shore part numbers of individual cables are also shown Contact Lake Shore if you need replacement cables 155 iagram D iring 6 4 3 InstrumentationW J y dwe ZyT J POW 4Ja 0 14U09 4nzes d OVE J POW J3 10147U02 ainjesaduiay ZEE J POW m TZITA ml 79960 p O T4JIVIH 0
229. shielding for the measurement signals The shield connections can be the source of line frequency noise if they are allowed to create a ground loop Minimizing the effect of ground loops can be difficult some experimentation may be required to achieve the best results One of the biggest difficulties is that signal sources and acquisition electronics often operate with one lead internally referenced to earth ground so the overall grounding system must take this into account The best approach is to make the system a poor receiver for the noise Never remove earth safety ground protection from electronic equipment 2 4 2 Basic DC Electrical Measurements 2 4 2 Basic DC Electrical Measurements 37 1 Electrically isolate any parts of the systems that do not require grounding for safety or performance 2 Attach cable shields at only one end of the cable if the shield conductor is not being used to establish a return path for the signal 3 Add resistance in series with reference ground leads in cases where some common mode voltage is present 4 Reduce the loop area of any ground loops that remain by routing cables close together or twisting wires 5 Make sure power lines to equipment have a direct low impedance path to earth ground so that no voltage is present between equipment grounds 6 Ground strap instrumentation chassis to provide low impedance between components of the system 2 4 1 3 Shielding Shielding reduces noise ind
230. si pressure relief valve will maintain safe pressure in the Dewar until the LN is used o N Oy Or ew 5 2 3 2 Cooling the Probe Station with Nitrogen Cooling the probe station with nitrogen is nearly identical to cooling with helium Familiarize yourself with section 4 5 1 for safety information and section 4 5 2 for explanation of the probe station controls 1 Prepare the system as described in section 4 5 3 1 2 Initiate a nitrogen transfer using section 4 5 3 2 as a guide Allow the pressure relief valve to regulate pressure in the Dewar to 68 kPa 10 psi during this pro cess 3 Allow the sample stage and 4 K shield stage to cool below 80 K Reduce Dewar pressure to 34 kPa 5 psi 5 Leave the turbo pump running during operation P El akeShore www lakeshore com 112 CHAPTER 5 Advanced Operation 5 2 4 Operating Sample Stage Above Room Temperature CAUTION Model CPX Probe Station 6 When operation is completed use section 4 5 6 as a guide to return the system to room temperature 5 2 3 3 Pre Cooling with Nitrogen Prior to Helium Transfer The total amount of helium required to cool the probe station can be reduced if it is pre cooled with nitrogen first This process takes at least two hours longer than cool ing with helium This process also creates potential for blockages to form in the trans fer line or refrigerator cooling path Ifa blockage occurs the system must be warmed to room temperature before r
231. ssion line geometry thereby degrading performance Due to the high cost of replacement microwave probes we highly recommend that users become comfortable with probing techniques using ZN50 probes prior to installing and probing with microwave probes to avoid damage to the microwave probe tips Lake Shore provides two ZN50 25 BECU and two ZN50 25 W probe tips in the spares kit Follow this procedure to install a microwave probe If a ZN50 or optical fiber probe mount is installed in your probe station you will need to remove it first section 3 5 4 2 or section 5 3 7 1 1 Follow steps 1 4 in section 3 5 2 2 Remove a microwave probe from its storage case 3 Grasp the microwave probe between thumb and forefinger on the sides of the probe body so that the dowel is extending outward from your hand and the braid block is dangling below your hand FIGURE 3 26 FIGURE 3 26 Proper handling of a microwave probe 4 Using the 1 5 mm hex driver loosen the set screws on the probe arm and slide the dowel of the microwave probe into the probe arm FIGURE 3 21 5 Asyou slide the microwave dowel onto the probe arm note the relative height of the microwave connector socket on the probe and the microwave connector plug on the semirigid cable If the relative heights of the two connectors do not match the semirigid cable can be gently bent using the thumb and forefinger to align the connector plug with the height of the connector socket FIGURE 3
232. ssure reducing the boiling point of the helium Lake Shore offers the PS LT option which can reduce the temperature of the CPX sample stage to 2 K The option contains everything necessary to establish and regulate temperatures between approximately 2 K and 4 2 K The main component to the PS LT option is a Varian DS 402 rotary vacuum pump or equivalent which is used to pump on the sample stage exhaust port A flexible stainless steel vacuum line bellows and necessary fittings are included to safely connect the vacuum pump to the probe station The option also includes a set of cryogenic compatible valves ina dual valve assembly that can be used to regulate temperature The PS LT option can be ordered with the probe station or added later because it does not require changes to the internal refrigerator The option can be easily removed for standard operation within minutes Electronic temperature controllers are not capable of controlling sample stage temperature when using the PS LT option The included dual valve assembly is required to regulate temperature between 2 K and 4 2 K 2 3 10 Load lock Assembly Option 2 3 11 Liquid Nitrogen Dewar PS LN2 2 3 12 Automatic Dewar Pressure Controller PS DPC 2 3 13 Pneumatic Vibration Isolation Option PS PVIS 2 3 10 Load lockAssemblyOption 33 The load lock assembly option allows for sample exchange without warming the radiation shields or breaking vacuum significantly improvin
233. st valve assembly to aid in cooling the sample stage m Sample stage cooling line is blocked with ice follow the instructions in section 6 3 3 1 to remove ice blockage 6 3 3 3 4 K Shield Stage Will Not Cool If the sample stage cools but the 4 K shield stage does not there are two potential problems that are easy to remedy and should be checked first m Exhaust valve not open m Temperature control was left on for either the 4 K shield stage or radiation shield stage after the refrigerator was warmed up to room temperature There are also two potential problems that require more time to remedy m The 4Kshield stage cooling line is blocked with ice follow the instructions in section 6 3 3 1 for removing ice blockage Cooling with nitrogen when cooling with nitrogen it is important to open the micrometer valve allowing cryogen to flow to the sample stage while cooling the 4 K shield stage this operation seems counterintuitive but it is effective 6 3 3 4 Sample Stage Does Not Reach 4 3 K Base Temperature The sample stage should be able to cool to 4 3 K within 10 min after the radiation shield cools and stabilizes A large number of problems can prevent the sample stage from reaching base temperature because every subsystem needs to be optimized simultaneously Common problems are m Poorvacuum m Soft transfer line m Insufficient cryogen flow foot valve or micrometer valve not open sufficiently m Insufficient Dewar pressure
234. stered trademark of Kimberly Clark Worldwide Stycast is a trademark of Emerson amp Cuming Tarn X is a registered trademark of Jelmar Inc Teflon and Kapton are trademarks of DuPont De Nemours Copyright 2009 Lake Shore Cryotronics Inc All rights reserved No portion of this manual may be reproduced stored ina retrieval system or transmitted in any form or by any means electronic mechanical photocopying recording or otherwise without the express written permission of Lake Shore Model CPX Probe Station Chapter 1 Introduction Chapter 2 System Overview Table of Contents Ld General vai ccnndhs areon e E neniseeaphea sag enhawieesid nea EE ETRAS 1 1 2 PrOdUCt Descriptio ere ses cies caandeinenaneeeed sae hens bra AE REOR 1 1 2 1 Applications preciser nieri mort n y r ET aba bene EE EE AE EERS 2 LA Mave rials eerie E r T E bd EEE EA ATEEN 2 1 3 Specificati nS 25 2 te lt useeeis ini en nenian a OA NE EE AE EA ESEA 2 1 3 1 Termper tUre pierino ca beter EGEE dawn heed oe eke ele ade ieee 2 1 3 2 Probe Arm and Sample Stage Adjustments 0 ccc cece cece cece ee eee ee 2 1 3 3 Frequency RANGE corsia cceeriatvesd cance segs Laceteeads chante san nae ehh ke 3 13 4 OptlCal irecssrnGiaws coathenan th eatwenaueenee te E ARREA AATRE AN 3 1 3 5 Sample Holder c03cocsereccaa segeaa went ee dees bie E E ERE ETA EE 3 Standard Equipment irssi cccertowswsse ccta ret itane a rE A pa E EDGARS 4 Required User Configurable E
235. surement data The temperature error can be significant especially at cryogenic temperatures Before choosing a method to mount your sample it is important to understand how to align your sample and how to minimize the risk for cracking wafers Additional sample holders can be ordered so that new samples can be mounted while others are being probed 4 3 3 1 Sample Alignment and Position Remove the sample holder from the sample stage section 4 3 2 for best access and ease of alignment Align the patterning of the wafer parallel to the grooves in the sample holder This ensures that the probe arms will intersect the wafer patterns at right angles Whole 25 mm 1 in wafers must be centered on the sample holder in order to fit onto the sample stage to take advantage of the probe area see FIGURE 4 1 for an image of the probe area Smaller samples should also be centered to allow easy access by all probes Extra care must be taken aligning samples when using GSG microwave probes because each probe must land all three points on the sample see section 4 6 3 After the sample holder is secured in the probe station test the alignment to be sure that all probe points can contact the sample section 4 6 3 and section 4 6 4 Remember to lift the probes before evacuating the chamber 4 3 3 2 Reducing the Risk of Cracking Wafers Larger whole wafers pose the most difficult challenge for sample mounting Good thermal contact with the sample hold
236. t Continued 9 EXCEPT TO THE EXTENT ALLOWED BY APPLICABLE LAW THE TERMS OF THIS LIMITED WARRANTY STATEMENT DO NOT EXCLUDE RESTRICT OR MODIFY AND ARE IN ADDITION TO THE MANDATORY STATUTORY RIGHTS APPLICABLE TO THE SALE OF THE PRODUCT TO YOU CERTIFICATION Lake Shore certifies that this product has been inspected and tested in accordance with its published specifications and that this product met its published specifications at the time of shipment The accuracy and calibration of this product at the time of shipment are traceable to the United States National Institute of Standards and Technology NIST formerly known as the National Bureau of Standards NBS FIRMWARE LIMITATIONS Lake Shore has worked to ensure that the Model 340 firmware is as free of errors as possible and that the results you obtain from the instrument are accurate and reliable However as with any com puter based software the possibility of errors exists In any important research as when using any laboratory equipment results should be carefully examined and rechecked before final con clusions are drawn Neither Lake Shore nor anyone else involved in the creation or production of this firmware can pay for loss of time incon venience loss of use of the product or property damage caused by this product or its failure to work or any other incidental or conse quential damages Use of our product implies that you understand the Lake Shore license agreement an
237. t as necessary 7 Tighten the locknut while keeping the probe arm oriented properly 8 Forthe probe arm that has the temperature sensor replace the 6 pin feedthrough receptacle using section 5 3 5 2 as a guideline Replace all four wires in their original locations 9 Install the cable assembly using the instructions in section 5 3 6 2 10 Install the probe arm and base using the instructions in section 5 3 4 11 Install the micro manipulated stage using the instructions in section 5 3 1 If you will be changing cables frequently it is recommended to have a probe arm available with the appropriate cable already installed then switch probe arms using the instructions in section 5 3 3 and section 5 3 4 However if an optical fiber change is necessary you can follow this procedure to do so 5 3 7 1 Removing an Optical Fiber The optical fiber assembly includes the optical fiber terminations and the feedthroughs Follow this to remove an optical fiber from a probe arm and base 1 Remove the micro manipulated stage using the instructions in section 5 3 2 2 Remove the bellows following steps 1 to 2 in section 5 3 3 3 Cutthe unwaxed dental floss that ties the optical fiber to the probe arm thermal anchor 4 Using the 2 5 mm hex driver remove the four M3 screws that attach the fiber feedthrough to the feedthrough extension 5 Using the 2 5 mm hex driver loosen the M3 set screw on the probe mount to release the optical fiber tip
238. t console you will need to unpack the various items that were shipped in this crate Depending on your options these items may include the vision system transfer line turbo pumping system and the accessories box EiLakeShore wwwiakeshore com 62 CHAPTER 3 Installation and Setup Model CPX Probe Station 3 3 8 1 Unpacking the Instrument Console The CPX instrument console is a housing cabinet that includes two temperature controllers Model 340 and Model 332 and the Model 142 power amplifier All cabling is on the inside of the console To unpack the console remove the packaging and prepare the cables for routing The manuals and additional accessories will be located in the console packaging 3 3 8 2 Unpacking the Vision System The vision system is packed in the accessories box next to the console The microscope components are packed in bubble wrap and boxes The display is packed in its original packaging A separate box contains much of the rest of the optics the light source microscope CCD camera and power supply microscope vertical post and horizontal boom and miscellaneous support items Unpack these components and set them out in preparation for completing the system setup and assembly 3 3 8 3 Unpacking the Transfer Line To unpack the transfer line cut the bands holding the cover onto the bottom of the long flat box and remove the cover Cut the plastic ties holding the transfer line in place and lift the transfer line
239. table for the combination of probe type and pad material used in each application Failing to raise the probe tips the cautions throughout this manual instruct operators to raise probe tips before cooling or warming the system when applying field or applying vacuum and when moving probes in the x or y direction Probes that are damaged when vacuum is applied or while being moved when landed are generally the ones that are very severely damaged Probes damaged during temperature change often take on a characteristic curled shape Wait for the probe arm temperature to stabilize approximately 10 to 15 min after the 4 K shield stage stabilizes before landing the probes Storing when probes are not being used store them in their original packaging This is especially important for microwave probes because the weight of the probe body will cause damage to the tip if the probe is left loose Cleaning aggressive cleaning can easily damage probes If more than periodic tarnish removal for the BeCu ZN50 probes is necessary it is recommended to gently clean the probe tips under a microscope working away from the probe body 6 3 5 2 Poor or Non Ohmic Electrical Contact There are several important considerations for assuring good electrical contact between the probe and sample Pressure appropriate contact pressure is required for both establishing and maintaining good contact Too little pressure may result in high contact resistance resistance
240. tact Focusing on the metal to metal interface the true nature of the surfaces is not smooth but rough It would not be unusual for this roughness to be 1 um or 2 um Surface roughness causes the actual contact area to be much smaller than the physical contact area because conduction is through a few asperities high points The use of soft pad materials and steady contact pressure can minimize the effect of surface roughness Probe contamination is another factor that can reduce contact area Any foreign material picked up on the probe tip will prevent metal to metal contact Probes should always be handled with gloves and stored in their original shipping containers when not in use to prevent contamination Probes also cold weld pad metal to themselves after repeated landings Nonconductive materials are frequently attached to the pad material causing contamination Probe tips should be cleaned regularly to remove contamination Cleaning instructions are given in section 6 2 7 and section 6 2 8 2 6 3 Oxidation 2 6 4 Four Lead Measurement 2 6 5 Ohmic versus Non ohmic Contacts 2 6 6 Measuring Contact Quality 2 6 7 Lab Protocol 2 6 3 Oxidation 51 Oxidation is probably the biggest source of poor contact resistance in a well maintained probe station Oxidation builds up on the probe and pad metals over time to form an electrically insulating layer that prevents metal to metal contact The light oxidation that forms between routin
241. the action of skating the probe tip on the sample pad The amount of skate is one of the most important parts of the protocol More skate provides more wiping to clean away oxidation and more pressure to increase actual contact area Too much skate will damage the probe tip El akeShore www lakeshore com 52 CHAPTER 2 System Overview Model CPX Probe Station 3 1 General 53 Chapter 3 Installation and Setup 3 1 General 3 1 1 Lake Shore Assisted Installation 3 2 Site Requirements This chapter describes the process of preparing a site unpacking the probe station components and assembling them into the standard CPX configuration Finally it explains system checkout procedures Lake Shore personnel or trained representatives are available to assist with the installation process When installation and training services are purchased with the probe station the customer will be contacted and provided with the CPX site prep form and applications engineer contact information shortly after the order is placed To avoid delays in the installation process please read the form carefully as soon as it arrives Customers are responsible for completing section 3 2 through the end of section 3 3 before an installation trip can be scheduled This section describes the space utilities and equipment that must be provided at the installation site to properly install test and operate a CPX probe station Much of the equipment describe
242. the bottom of the probe mount Hold the new blade in position Positioning the blade so its bottom is flush with the bottom of the probe mount ensures that the SMA connector will not contact the probe mount During operation the body of the SMA connector may have a different voltage potential on it than the probe mount and therefore it should not touch the probe mount Using the 1 5 mm hex driver start the set screw and once the probe is secure tighten it just until you feel it touch the blade It is important that you do not overtighten the screw as you could crack the probe blade Rotate the probe mount and tighten the opposing set screw keeping the blade all the way back in its slot and flush to the probe mount FIGURE 3 22 Tighten the screw until the blade does not move with finger pressure Be careful not to over tighten as the alumina is delicate and will crack Rotate the probe back to the upright position FIGURE 3 22 Left Slide the blade into its slot Right Carefully tighten the probe mount set screws Model CPX Probe Station 3 5 4 RemovingaZN50Probe 75 4 Using the 1 5 mm hex driver secure the probe to the probe arm by tightening the probe arm set screws 5 Finger tighten the signal cable SMA nut onto the probe s SMA connector For the cryogenic coaxial cable the strain relief to the SMA connector must be held 0 CAUTIO N steady with tweezers while the plug is screwed onto the pro
243. the dual valve to regulate temperature between 2 K and 4 2 K 13 When you are finished with your experiment and no longer need the lower tem perature turn off the pump and quickly disconnect the flexible stainless vacuum line from the dual valve assembly 5 2 3 Operating with Nitrogen 5 2 3 Operatingwith Nitrogen 111 Most of the instructions in Chapters 4 and 5 are related to operating the probe station using liquid helium However most of the instructions can also be applied to operat ing with nitrogen The refrigerator is designed to operate with liquid nitrogen down to approximately 78 K This section describes the significant differences in operating with nitrogen Heat Capacity nitrogen has a lower heat capacity than helium so a higher flow rate is necessary to cool to base temperature lt 78 K This normally requires higher Dewar pressure of approximately 69 kPa 10 psi and longer cooling time Controller Settings the nominal controller settings given in TABLE 4 3 and TABLE 4 4 are for helium operation Some experimentation will be necessary to find appropriate settings for nitrogen It is very difficult for the temperature controller to control below 80 K when using nitrogen Restricting flow to the sample stage with the micrometer valve normally gives better results Cryopumping nitrogen is less effective at cryopumping than helium The vacuum chamber may need to be pumped longer to get acceptable results To help avoid con
244. the feedthrough assembly FIGURE 5 15 Rotating this assembly changes the position of the cable end that attaches to the probe FIGURE 5 15 Left Removing the four M3 screws that hold the feedthrough assembly to the probe arm base Right The off centered hole on the cable feedthrough assembly 5 Start but do not tighten all four feedthrough assembly screws 6 Gently push or pull both ends of the cable in the desired direction The cable should slide through the unwaxed dental floss holding it to the thermal anchor on the probe arm with some gentle wiggling of the probe end 7 The height of the connector above the feedthrough is not fixed Set the height necessary to adjust the probe end of the cable to approximately the correct height to mate with a microwave probe 8 Using the 2 5 mm hex driver tighten the four M3 screws on the cable feedthrough assembly 9 Test the fit If there is not enough adjustment with this method go to the second method 10 Install the bellows to the micro manipulated stage following steps 5 to 7 in section 5 3 4 11 Install the micro manipulated stage to the probe station using the instructions in section 5 3 1 Second Method Reshape the Microwave Cable 1 Remove the micro manipulated stage following the steps in section 5 3 2 2 Remove the probe arm and base using the instructions in section 5 3 3 3 Remove the cable assembly following the guidelines in section 5 3 6 1 4 Byhand carefully rep
245. ther than 50 Q the microwave signal will experience a discontinuity at the transition which will result in some of the energy being reflected back to the signal source Minimum pad size of 50 um x 50 um is recommended for proper probe landing with the spacing between the pads determined by probe pitch It is recommended to skate the tip forward approximately 15 um to 25 um for good electrical contact Gold plating is recommended to obtain consistent ohmic contacts for each point O BR FIGURE 2 36 Probe tip and pad geometry 2 5 3 1 Probe Crosstalk In the GSG probe construction the ground points on either side of the signal point help keep the microwave signals contained between them which minimizes crosstalk between adjacent probes Probe tips that are properly landed on measurement pads that have 50 O impedance radiate very little signal Poorly landed or open probe tips radiate significantly more Therefore properly land or move away any active probes that are not involved with the measurement or calibration Probes that are oriented across from each other in line have higher crosstalk coupling than probes oriented at 90 degrees To illustrate this FIGURE 2 37 shows the frequency response of a pair of 67 GHz microwave probes landed on the 50 Q pads of a CS 5 calibration substrate and located approximately 150 um directly across from each other The 12 and S21 transmission coefficients show the crosstalk between the probes in this i
246. tify which part of the vision system is causing the undesirable symptom so it can be remedied 6 3 4 1 No Image If there is no image on the monitor at all the problem is likely electrical It is important to remember that the camera light source and monitor are independent components and have separate power supplies and power switches m Remove lens cover if present El akeShore www lakeshore com 148 CHAPTER 6 Maintenance and Troubleshooting Model CPX Probe Station Verify the camera light source and monitor are all powered and turned on Turn the light source to 50 output Verify that the s video cable between the camera and monitor is plugged in Verify the monitor source is set to the s video input If the problem is not identified with these steps press the set setup button on the camera If the setup menu appears on the monitor the problem is likely in the optics rather than the electronics The following sections may help identify the problems with image system optics 6 3 4 2 Insufficient Sample Illumination Typically no more than 50 to 70 of the maximum light source setting is required to properly illuminate the sample If a higher output is required or the sample remains too dark at 100 output the light source may be out of alignment To verify proper alignment do the following m Turn off the light source and allow it to cool m Remove the fiber optic bundle from the light source m Remove any dust on the end of
247. ting holes on the planarization assembly bracket facing the mounting holes on the probe arm base thread the shaft through the hole for the planarization assembly shaft FIGURE 5 22 5 When the mounting holes in the bracket are aligned with the mounting holes on the probe arm base use the 2 5 mm hex driver to attach the planarization assem bly with the two M3 screws provided FIGURE 5 22 5 3 8 Installingthe Planarization Assembly 127 FIGURE 5 22 Left Thread the shaft through its mounting hole Right Attach the planarization assembly to the probe arm base 6 Using small pliers or an adjustable wrench thread the nut onto the bottom of the shaft until the end of the shaft is flush with the nut FIGURE 5 23 7 Adjust the planarization assembly from end to end to test the installation 8 Carefully tighten the four long M4 horizontal screws that attach the bellows to the z axis stage assembly and tighten the screws evenly FIGURE 5 12 3 CAUTION The four M4 screws holding the bellows flange to the z axis stage assembly should be installed to a torque of 112 N mm 16 in ounces The torque required is much lower than one might think would be needed We recommend using a torque wrench to ensure these screws are not over torqued If these screws are over torqued the z axis stage and bellows may be damaged FIGURE 5 23 Left Thread the nut onto the bottom of the shaft Right Tighten the four long horizontal M4 screws al akeShor
248. tion are a likely candidate for vibration because they are in close proximity to the probe station and are connected through stainless steel lines that transfer vibration Vacuum pumps and lines can be easily identified as the source of vibration by observing the microscope image when the pumps are off and lines disconnected If a pump or line is identified as a problem and it cannot be disconnected during operation the PS PLVI 40 pump line vibration isolation option is recommended Vibration from infrastructure if the vibration is intermittent it may be due to infrastructure sources such as HVAC systems or elevators In this case make sure that any vibration isolation options ordered with the probe station are properly installed and operating If the system did not include active vibration isolation it should be considered 6 3 4 7 Poor Contrast Images This section addresses images that are poor in contrast show little or no sample definition and have little response to small changes in light intensity This problem is difficult to troubleshoot primarily because of the geometry of the CPX itself The relatively long distance between microscope and sample and two optic viewports in between offer significant challenges to conventional image systems Because of this the light source and sample surface can have a big impact on image quality The first step to remedy the problem is to eliminate other possibilities The steps below assume you hav
249. troller is set for zone control mode these selections will be made automatically Wait for the temperature at the sample stage to stabilize Adjust the micrometer valve to achieve a heater power Model 340 loop 1 con sistent with the nominal heater power given in TABLE 4 4 Adjust the P and D settings as necessary to improve stability El akeShore www lakeshore com 102 CHAPTER 4 Basic Operation 4 5 6 Returning to Room Temperature 4 5 7 Temperature Control Summary Follow this procedure to return the probe station to room temperature and to prepare the station for sample exchange 1 Use the z axis micrometers to raise all probes up 3 mm to 4 mm above the sam ple stage Open the shut off valve to the low pressure relief valve to reduce the pressure in the Dewar to its lowest pressure Close the foot valve on the transfer line Frost buildup on the bayonet may prevent the transfer line from sliding out The frost can be gently thawed with a heat gun Warm the sample stage to a setpoint of 290 K by entering the appropriate controller settings given in TABLE 4 3 Warm the 4 K shield stage radiation shield stage and second shield stage to a setpoint of 290 K by entering the appropriate controller settings for each stage given in TABLE 4 3 Optional when all stages in the refrigerator are above 100 K the system can be purged with dry nitrogen gas to speed warm up section 4 4 4 It is safe to open the vacuum chamb
250. trols and four electronic control loops one for each refrigerator stage to establish and regulate temperature This section details the mechanical controls first followed by the electronic controls 4 5 2 1 Mechanical Refrigerator Controls The mechanical controls on the CPX are used to regulate the amount of cryogen flowing though the refrigerator and establish its nominal cooling behavior El akeShore www lakeshore com 96 CHAPTER 4 Basic Operation Model CPX Probe Station Transfer Line Foot Value Control Knob this is the primary means for setting the rate of cryogen flow into the refrigerator Both the sample and radiation shield stages are supplied by the same source so the foot valve sets the total for both paths The valve is generally opened counterclockwise six to nine full turns to allow maximum flow during system cooldown It is usually set to only one to two turns open after cooldown to help conserve cryogen The control does not have a stop on the open side therefore it can unthread if it is opened too far You should never need to open it more than nine turns If you inadvertently unthread it too far gently push it back together and rotate the control valve clockwise to re seat the threads Transfer line foot valve control knob close FIGURE 4 10 Transfer line foot valve control knob Pressure Regulator pressure is required in the Dewar to push cryogen through the transfer line into the refrigerator
251. uced in the probe cables by electric fields in the environment or other equipment in the experiment The probe station s vacuum chamber is the most important part of a shielding system The electrically conductive chamber surrounds the sample area and is often connected to the measurement system s ground reference as described in section 2 4 1 1 BNC and triaxial signal connector shells are electrically connected to the chamber to provide a shield contact for cabling DC RF probe cables are all made from cryogenic coaxial wire so the shielding can be carried inside the chamber and down the probe arm Outside the chamber shielding is recommended for all signal cables but the shielding must not be allowed to create ground loops as described in section 2 4 1 2 Itis often necessary to connect the shield at only one end of the cable 2 4 1 4 Noise Isolation Every attempt was made in the design and construction of the CPX to isolate potential noise sources so they do not interfere with measurements It is important to recognize these features so they are not inadvertently defeated when the probe station is re configured or set up for measurements Non conductive components are used to attach the vacuum isolation valve to the vacuum chamber to prevent electrical noise emanating from the pump from entering through the vacuum line bellows The temperature sensors and control heaters are electrically isolated from the refrigerator to prevent interference
252. ully assembled Several items necessary for operation and not included with the option must be assembled prior to use m Thecompression fitting for the withdraw leg of the transfer line is included with the spares kit and must be located and threaded to the top withdraw port of the Dewar m Dry nitrogen gas is required to pressurize the Dewar during operation A regu lated source of dry nitrogen must be adapted to the vent port on the PS LN2 The vent port comes with a 3 8 in NPT fitting An easily removable quick connect fit ting is recommended because the line may need to be removed to fill the Dewar m Atemporary nitrogen fill line must also be available to transfer LN from a larger storage Dewar or building source into the liquid port on the PS LN gt The transfer line included witht the probe station is not suitable for this purpose The liquid port comes with a 3 8 in flair fitting which is compatible with many flexible LN2 transfer lines available in the United States The fitting can be removed if it is more convenient to adapt to the 38 in NPT valve 3 4 4 6 Assembling the Dewar Pressure Controller PS DPC The Dewar pressure controller comes fully assembled Follow this procedure to complete the setup 1 Hang the Dewar pressure controller on the Dewar 2 Plug itinto the power source 3 Attach a 6 mm 1 4 in tube into the green push to connect fitting on the inlet in the Dewar pressure controller 4 Attach the other end
253. um chamber lid will need cleaning as they collect debris and smudges during normal operation Use cleaners recommended for glass optics A suggested cleaner is Eclipse High Purity Cleaning Fluid available through Edmund Optics Never use household cleaners on the optics windows some optics may be damaged by the chemicals in these cleaners 6 2 4 2 De fogging the Viewport Windows Some condensation on the outside of the viewport windows is normal however if there is condensation on the inside of the viewport windows refer to section 6 3 1 When the outside of the viewport window develops condensation during low temperature operation it is an indication that it needs to be treated with anti fog solution A suggested anti fog solution is Parker s Perfect anti fogging solution available through Edmunds Optics Follow this procedure to de fog the viewport windows 1 Apply anti fog solution to a small folded optical cloth 2 Wipe onto the surface of the viewport using a circular and overlapping motion 3 Allow the solution to dry until a slight haze appears 4 Apply a second coat using a new cloth and fresh solution to ensure complete and uniform coverage 5 Remove the final haze with a clean dry cotton cloth O rings are generally reliable and require very little maintenance Periodic cleaning and re greasing is all that is necessary under most circumstances This is especially true of the vacuum chamber lid o ring that is
254. ump Maintenance 6 2 11 Pumping out the Transfer Line 6 2 10 Vacuum Pump Maintenance 135 It is difficult to give specific instructions for all possible combinations of pumps that may be used with the CPX Refer to the information included with your selected vacuum pump for specific maintenance instructions and add them to the preventive maintenance schedule in section 6 2 1 of this manual Some general guidelines on Vacuum pump maintenance follow 6 2 10 1 Turbo Pumps Turbo pumps are generally considered maintenance free and contain no user serviceable parts or maintenance items Operate them according to manufacturer s instructions for the longest possible service life 6 2 10 2 Scroll Pumps Scroll pumps are frequently used because the fore pump for the turbo pump has replaceable seals called tips that wear with use As the tips wear pump performance degrades but this seldom causes pump failure The tips should be replaced when the pump no longer performs adequately Some manufacturers recommend replacing the tips every year depending on use to keep the pump operating to specification However a scroll pump can still be adequate for use as a fore pump even when it is performing well below its specification 6 2 10 3 Rotary Vane Pumps Rotary vane pumps are often used as the fore pump for turbo pumps or to pump on the helium exhaust port as part of a low temperature option These pumps contain oil and therefore require routine
255. ump Components If you purchased the turbo pump specified by Lake Shore follow this procedure to prepare it 1 Ifthe vacuum gauge FIGURE 3 14 is not already installed on top of the turbo vacuum pump remove the protective caps Then use the provided clamp and center ring to attach the gauge 2 Remove the blank off plate from the connector on top the vacuum gauge Attach the supplied cable to this connector see FIGURE 3 14 If not already done attach the other end of the cable to the connector on the back of the gauge controller FIGURE 3 14 Vacuum connector FIGURE 3 14 Left Vacuum gauge Right Back panel of the gauge controller 3 Attach the NW 40 flanges of the vacuum line to the T on the pump a Remove the clamp and protective cap from the fitting shown in FIGURE 3 15 The center ring may come out retain the ring to use in the next step Holding the center ring in place set the vacuum line against the ring Close the clamp around the fitting d Finger tighten the clamp with the screw See FIGURE 3 15 N Er Model CPX Probe Station 3 4 3 Assemblingthe Turbo Pumping System 69 L S gt gt Y i ZF G4 ZNN E AA a i FIGURE 3 15 Left Remove the clamp and protective cap Middle and Right Install the vacuum line to the pump 4 Remove the blank off plate from the NW 40 vacuum isolation valve The clamp and centering ring are used when the vacuum hose is attached in t
256. ump is off when beginning 1 Use the z axis micrometers to raise all probes 3 mm to 4 mm above the sample Failure to do so will potentially cause damage to the probe tip or scratch the sam ple surface 2 Close the purge valve completely FIGURE 4 9 3 Verify that the vacuum pump is turned off and properly vented close the manual vent valve 4 Open the vacuum isolation valve completely FIGURE 4 9 E TT Perri iii it FIGURE 4 9 Left Purge valve Right Vacuum isolation valve 5 Start the turbo pumping system The steps to power on the system follow a Switch the main power rocker switch to the up position which powers on the entire unit b Switch the scroll pump knob from position O to position 1 to start the roughing pump c Press the start button on the turbo pump controller to engage the turbo pump If the controller is set in remote mode the turbo pump will automatically start and stop with the scroll pump knob 6 Observe to be sure it starts rotating up to its maximum operational speed El akeShore wwwiakeshore com 94 CHAPTER 4 Basic Operation 4 4 3 Shutting Down the Turbo Pump CAUTION 4 4 4 Purging the Vacuum Chamber ZA WARNING AWARNING Model CPX Probe Station 7 Ifthe vacuum gauge readout is not currently displayed on the turbo controller front panel push the measures button on the controller front panel to cycle through various pump diagnostics until the vacuum gauge readout is
257. usnuet eae ddadehereaqadueds 109 Advanced 5 2 Advanced Temperature Operation ccc cece cece eee e eee e eee 109 Operation 5 2 1 Reducing Condensation on the Sample 00 cece cece eee e eee eee 109 5 2 2 Operating the Sample Stage Down to 2 K 1 eee eect eens 110 5 2 3 Operating with Nitrogen cece cece cece eee eee ent eee e ee ERRARE EIAS 111 5 2 3 1 Filling the PS LN2 Liquid Nitrogen Dewar eeeeee eens 111 5 2 3 2 Cooling the Probe Station with Nitrogen ceeee eee eee 111 5 2 3 3 Pre Cooling with Nitrogen Prior to Helium Transfer 112 5 2 4 Operating Sample Stage Above Room Temperature 00 eee eee 112 5 3 Probe Arm Assembly Reconfiguration cece cece cece nent eee eeeennees 113 5 3 1 Installing a Micro manipulated Translation Stage MMS O9 113 Model CPX Probe Station 5 3 2 Removing a Micro manipulated Translation Stage eeee eee 115 5 3 3 Removing a Probe Arm and Base 0 cece cece cece ee eee eee e eee e eee 117 5 3 4 Installing a Probe Arm and Base 0 00 cece eee e cece cece ence erreren 118 5 3 5 Reconfiguring Ultra miniature Cryogenic Coaxial Cables 119 5 3 5 1 Removing an Ultra miniature Cryogenic Coaxial Cable 119 5 3 5 2 Installing an Ultra miniature Cryogenic Coaxial Cable 119 5 3 6 Reconfiguring Microwave Cables
258. ve Probe CAUTION 3 6 System Verification and Testing 3 6 1 Console Verification 3 5 6 Removinga Microwave Probe 79 10 Attach the braid block using these steps a Use the x y and z axis micrometer controls to position the probe so that the braid block can be attached without disturbing the probe tips b Using tweezers or your fingers position the braid block over the mounting holes FIGURE 3 20 c Using the 2 5 mm hex driver attach the thermal braid block to the chosen location on either the sample stage or the 4 K shield stage very carefully so as not to contact the delicate probe tips 11 Before initiating a cryogen transfer see section 3 6 4 and section 3 6 5 to test probe arm reach and landing ability and see section 4 6 4 to planarize the microwave probe It would be very costly and time consuming to initiate a cooldown only to find that a probe mount braid is preventing the probes from landing Follow this procedure to remove a microwave probe from the probe arm 1 Detach the braid block using these steps a Usethex y and z axis micrometer controls to position the probe so that the braid block can be removed without disturbing the probe tips b Using the 2 5 mm hex driver loosen the two captive screws on the braid block until it is free Detach the thermal braid block very carefully so as not to contact the delicate probe tips 2 Using the 1 5 mm hex driver loosen both M3 probe arm set screws two
259. wave Cable Semirigid cables are used with microwave probes Follow this procedure to install a semirigid cable onto a probe arm assembly 1 Clean the o ring groove of the cable feedthrough in the probe arm base Clean inspect and lightly grease the o ring with vacuum grease and place it in the groove FIGURE 5 13 left 2 Carefully insert the cable into the probe arm base Continue inserting the cable reorienting the cable feedthrough assembly until it seats against the probe arm base 3 Using the 2 5 mm hex driver attach the cable feedthrough assembly to the probe arm base with four M3 screws Note that the cable does not pass through the center of the feedthrough assembly FIGURE 5 15 Rotating this assembly will change the position of the cable end that attaches to the probe section 5 3 6 3 4 Test fita microwave probe onto the probe arm section 3 5 5 Do not force the threading of the plug if it does not tighten smoothly 5 Ifthe cable length seems inappropriate use the instructions in section 5 3 6 3 to adjust the cable length 6 Remove the microwave probe you used for a test fit 7 Tie the cable to the probe arm thermal anchor using unwaxed dental floss FIGURE 3 28 8 Install the probe arm and base using section 5 3 4 9 Install the micro manipulated stage on the probe station using the steps in section 5 3 1 10 Install a microwave probe using section 3 5 5 5 3 6 3 Adjusting the Fit of Microwave Cables An
260. wing procedures to complete the assembly process If a Lake Shore assisted installation was purchased with the system the installer will begin at this point There are three cables with varying numbers of inputs and outputs to attach between the console power supply and the CPX probe station It is helpful to attach the cables in the order presented in section 3 4 1 1 The cables are already attached to the back of the controllers and each one is clearly labeled you will need to complete the connections to the probe station The information detailed in FIGURE 6 10 will assist you in making the correct connections and for troubleshooting 3 4 1 1 Complete the Connections to the Probe Station 1 Locate the main temperature control and sensing cable labeled DCO723 Attach the 19 pin connector to the refrigerator bottom of the vacuum chamber which has a corresponding 19 pin connection Note the orientation of the guiding lugs and rotate as necessary The outer shell should rotate and click into place fora secure connection 2 Locate the fourth stage cable labeled DC2048 This is one of three 6 pin connectors that are identical It will attach to a connection underneath the probe station labeled fourth stage The fourth stage cable and probe arm cable have identical 6 pin feedthroughs on the probe station If the fourth stage sensor and heater are not reading properly check that the plugs have not been reversed in error see section 3 6
261. witch probe arms using the instructions in section 5 3 3 and section 5 3 4 However if a reconfiguration of the ultra miniature coaxial cable is necessary follow this procedure to do so 5 3 5 1 Removing an Ultra miniature Cryogenic Coaxial Cable Ultra miniature coaxial cables are used with ZN5O probes Use the following steps to remove an ultra miniature coaxial cable from a probe arm assembly 1 Remove the micro manipulated stage using the instructions in section 5 3 2 2 Remove the probe arm and base using the instructions in section 5 3 3 3 Using the 2 5 mm hex driver remove the four M3 screws that attach the cable feedthrough assembly to the probe arm base FIGURE 5 13 4 Lift the cable feedthrough assembly approximately 25 mm 1 in from the probe arm base and unsolder the cable from the BNC or triaxial connector 5 Atthe other end of the cable grasp the cable near the SMA connector and pull it out of the arm while feeding the loose end into the center of the probe arm 5 3 5 2 Installing an Ultra miniature Cryogenic Coaxial Cable Ultra miniature coaxial cables are used with ZN5O probes Use the following steps to install an ultra miniature coaxial cable onto a probe arm assembly 1 Clean the o ring groove of the signal connector feedthrough in the probe arm base Clean inspect and lightly grease the o ring with vacuum grease and place it in the groove FIGURE 5 13 2 Insert the end of the coaxial cable without the SMA con
262. x months when using helium or more than two to three months when using nitrogen it may have a leak Contact Lake Shore service or your local representative for assistance If there is a single cold spot on the transfer line after it is pumped out there may bea physical touch between the inner line and the outer vacuum jacket of the transfer line In this case contact Lake Shore or your local representative 6 3 2 2 Plugged Transfer Line Suspect a plugged transfer line if it will not generate a cryogen plume when pre cooled as described in section 4 5 3 2 The most common cause of a plugged transfer line is an ice blockage however the bayonet end of the transfer line is susceptible to being plugged with foreign material The transfer line attracts water vapor from the air any time it is colder than its surroundings Any time that water vapor is allowed inside the line it will freeze and form an ice blockage The operating instructions in Chapter 4 are intentionally sequenced to minimize this risk but ice blockages can still happen They are especially common when working in high humidity pre cooling with nitrogen or changing helium Dewars during operation All of these cases expose the transfer line to greater than normal ice build up The best defense against an ice blockage in the transfer line is 1 Open the foot valve control knob six turns before inserting it into the Dewar 2 Use a heat gun to melt excessive ice off of the bayo
263. xes of motion that are described in this section All six available probes can be positioned ina25 mm 1 in diameter probe area in the center of the sample holder FIGURE 4 1 The CPX can accommodate 32 mm 1 25 and 51 mm 2 in sample holders but the probe area is the same for both sizes Individual probes can land outside the probe area in line with the probe arm Due to translation limitations individual probes cannot be landed on either side of the defined probe area The sample should be positioned and aligned on the sample holder to take best advantage of the probe area see section 4 3 3 1 for alignment El akeShore www lakeshore com 84 CHAPTER 4 Basic Operation CAUTION CAUTION Model CPX Probe Station Before evacuating the vacuum chamber or making significant temperature changes use the z axis micrometers to raise all probes up 3 mm to 4 mm above the sample Failure to do so will potentially cause damage to the probe tip or scratch the sample surface 25 mm Lin FIGURE 4 1 Probe area indicated with blue circle Normal motion of the translation stages remains smooth with constant turning force throughout the usable range It is normal however for additional tension to occur when the system is under vacuum as compared to when it is open Restrictions in motion are normally caused by the stage coming to the end of its travel Restriction can sometimes also be caused by interference inside the chamber In either
264. y in most applications and often does not contribute to measurement noise Small signals tend to have longer measurement intervals due to averaging so they are more susceptible to temperature changes It is important to properly tune the temperature controllers to improve temperature stability It is also important to allow the system to stabilize at the desired temperature longer before taking data It often takes several minutes after the sample stage temperature sensor stabilizes before the sample comes to equilibrium Cryogenic experiments are most often designed to cool the system to base temperature first Temperature is then increased between data points to provide the best sample temperature stability 3 Vibration isolation the vibration present in a typical probe station seldom contributes to measurement noise unless the probe to sample contact is poor When making small signal measurements the effect of vibration increases The slight change in contact resistance due to the vibration is larger compared to the signal Other noise sources such as the triboelectric effect in the probe cables can also become meaningful Lake Shore offers optional vibration isolation for probe stations and options for isolating vacuum pump lines that have the potential to induce vibration into the system One application that produces small difficult to measure signals is probing low resistance samples It is tempting to simply increase excitation current to

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