WT-1000B USER`S MANUAL
Contents
1. Frequency Ghz 1 0 533 Voltage w 2 088 Microwave DC Laser Control Monitor The Control Voltage versus Laser Power curve is measured in this window It serves for checking the stabilization of the laser The curves should increase monotonically and should remain below the Control Limit Semilab Operating Software I 27 WT Laser Control Monitor New Load Save Print 1 Control Limit 3 7 I Woltage 4 0 20 40 60 a0 100 Laser Power 9 Laser Power 5 Voltage M Laser Control Monitor Lifetime Time The lifetime as a function of the time curve is recorded in this window The measuring interval can be set between 0 250 sec by dragging the dT slider When dT is set to O the maximum available measuring speed is selected The Sampling determines how many measured values are averaged before recording a point on the plot AT Lifetime Time New Load Save Print Lifetime ps 0 2 4 E m 10 12 ej Time 3 Average p 1 8 606 D eviation 5 0 00 Lifetime Time Lifetime Laser Power The lifetime versus Laser Power curve is measured in this window The resulting curve logarithm of lifetime versus Laser Power is typically increasing and it can be fitted with straight line The slope of the line may be characteristic of the dominant contaminant in the wafer Semilab Operating Software HI 28 AT Lifetime Laser Power New Load Save Print Lifetime2. 100 E a or m gt 50 0 E Time Liz Voltage rr Transient Evaluation window The transient can be loaded printed or the current transient can be saved to disk to trn file format These functions can be activated using the self menu of the Transient Evaluation window There are four possibilities to illustrate the transient data They can be changed in the Mode drop down list The transient can be plotted on linear Linear or logarithmic Log scale It can also be illustrated as the output signal of a frequency scan Scan performed on the transient or as a function of the time cursor position Cursor LT The following information is displayed in the nfo area the amplitude of the transient and the lifetime evaluated with different methods The first method is the Semilab method text is black colored Here the number of points used for evaluation can be changed by the arrows pointing up down The name of the method than changes to e g LT SI 512 which means the lifetime calculated with the Semilab method from the first 512 points of the transient The transient itself 1s displayed in the plot area The axes of the plot area can be re scaled by the small arrows at the bottom and the right side of the plot By pushing the E button at the middle of the right side the original scaling can be set again The button allows you to select a rectangular area in the plot This handling is true for all appe
3. 256 wir Woltage m Amplitude 23 4 mY Thickness Correction Mm MA Frequency 10 168 GHz Laser Power 120 E11 ae a 0 04 Time ms Opto On 4 96 W Main window Recorders tab The window has four main parts Menu Bar at the top of the window just below the window title Toolbar below the Menu Bar Statusbar at the bottom of the main window and the working area between the Toolbar and the Statusbar The working area of the uPCD software consists of four or five tabs Details Statistics Lifetime and Recorder 6 3 2 Recorder tab There are the measuring parameters and the plot window which displays the transient in the Transient Recorder window The Microwave Frequency the Averaging the signal Range Y axis of the Scope window and the Time window X axis of the Scope window are automatically set by the Autosetting procedure Autosetting can be reached from Measure Autosetting menu item or clicking on the E icon on the Toolbar Semilab Operating Software I 16 LT transient evaluation method It defines the method for transient evaluation There are three different methods the so called Semilab method which was developed by Semilab the 1 e and the 1 e methods The Semilab method can be used with different number of points taken from the transient from the Time Cursor The Time Cursor is the vertical line in the Scope window which determines the point from where the recorded data are
4. p 0 1 0 316 1 3 162 10 31 62 100 Laser Povrer E11 Laser Power E 11 Litetime p Lifetime Laser Power 6 5 Toolbar The toolbar gives fast access to te following functions j Activates Autosetting procedure E Stops Autosetting procedure L Performs a measurement and adds data to the statistics iM Clears data from statistics M Update srt ti If checkbox 1s checked the transient is updated continuously
5. on the industrial computer and the other into socket on the WT 1000B main unit see image and table of interconnections later u PCD cable UTP cable for LAN connection An UTP cable for Local Area network connection is also delivered with the system It should be plugged to connector no 4 of the industrial PC and the other end to the LAN wall connector or HUB UTP cable for LAN connection Mains cable One mains cable is delivered for the industrial computer plug to connector no 2 on the industral PC back panel Besides this all other componets monitor printer etc have their own mains cables in their own package Mains cable Semilab Installation 12 Measurement head Industrial PC back panel For software installation and operation please refer to Chapter 6 u PCD Operating Software Semilab Installation 13 5 Hardware and software operation during the uPCD measurement WT 1000B is optimized for Si blocks and not for wafers The problem with the wafers is that the sensor is sensitive to the holder which is below the wafer This problem is solved for the WT 1000 because this system has a measurement stage This head has the same structure as the WT 1000 The operational software is the same also Bottom of the sensor of the sensor has to fit to the sample So during the measurement the whole measurement head 1s sitting on the surface of the sample s N The black plastic part of the sensor touches
6. operation of it If any part of the instrument got loose during shipment it can cause an inaccuracy in the result of measurement therefore tighten them before use Other components of the system Unpack all of other components of the system and please refer to their own manuals supplied with them for instructions 3 Installation Caution Be sure that the available power line voltage frequency corresponds to the setting on industrial computer 115 Vac or 230 Vac Line voltage selection Line voltage should be set manualy on the industrial computer only There 1s a red voltage selector on the backpanel of the industrial computer Please check swich position before connecting system to the mains Installation of system components For further information on system components computers monitor mouse keyboard and printer please follow the instructions found in their own manuals supplied with them System power and interconnections Caution All electrical conections of the system should be performed with switched off power and unpluged line cable The following list gives short description of the cables and their interconnection For socket numbering please refer to Image2 after the cable descriptions Semilab Installation 11 u PCD cable This cable makes connection between WT 1000B lifetime measuring system and the transient recorder in the measuring PC One end of this cable should be plugged into socket no 1
7. the sample Before the uPCD measurements do not forget to use the AutoSetting procedure which is described in Chapter 3 Semilab Operating Software HI 14 6 u PCD Operating Software 6 1 Introduction 6 1 1 Requirements For proper operation the following requirements should be fulfilled Software requirements e MS Windows 98 NT 2000 or XP Hardware requirements e Pentium compatible computer running the Microsoft Windows operating system e Optional windows compatible printer 6 2 Installation The software 1s installed on the computer shipped with the WT 1000B System The software is installed into C uPCDV directory The WinRt program should also be installed for correct operation The measuring program can be started by the following shortcut opt e Ed uP Semilab Operating Software HI 15 6 3 User Interface and basic operation 6 3 1 Main window Running the uPCD software the following window appears uPCD recorder v3 23 File View Edit Measure Options Macro Functions Access Help a OD T p E MILA UPDATE AUTAT set acto NEW BATCH CLEAR EXIT E10 ENGINEERING v Settings v Classification Details Statistics Lifetime Recorder LT Ranges TA 64 us Voltage E a ny 100 Settings Evaluation Sia p24 Time curs v Auto 5 us Offset oe fet mi mead Averaging
8. the sample increases due to the excess carriers generated by the illumination the resonance curve shifts and gets deformed Figure 3 3 blue line As the excess carriers recombine the conductivity of the sample returns to equilibrium and the resonance curve gets back to its original state Pretuned freqenc 3 5 1 E Voltage V s equilibrium e injected 10 10 1 10 2 10 3 10 4 10 5 10 6 Frequency GHz Figure 3 3 Resonance curves of the microwave probe with a sample underneath MWDC the DC signal in the function of microwave freqency When the sample is in equilibrium the curve is the red line When the sample is injected excess carriers are generated by the illumination the conductivity and reflectance is changed the curve is the blue line The vertical green line shows the freqency used during the measurement pretuned so that the change of the signal is maximal During measurement the microwave freqency is set to a predefined freqency vertical green line on Figure 3 3 As the curve gets back to the original state the measured signal of the antenna changes Because the recombination velocity is proportional to the number of excess carriers the recombination is exponential in time so the change of the signal 1s exponential too Figure 3 4 Semilab Theory 6 Voltage V 0 50 100 150 200 Time us Figure 3 4 Transient m
9. using viewing optics to inspect any part of the equipment around the connector and the stage under operation Semilab Theo 4 3 Theory of the u PCD measurement As the name implies the technique involves the optical excitation and the signal detection by the microwave system 3 1 Laser Excitation The pulse of an infrared semiconductor laser generates free electron hole pairs under the illuminated area on the sample Figure 3 1 Since the penetration depth of the 904 nm wavelength light is about 30 um in silicon the free carriers are generated close to the front surface of the sample 3 2 Detection Since the free electrons and holes recombine their concentration and so the conductivity of the sample decreases after the excitation The decaying conductivity can be monitored by detecting the microwave reflectivity because the reflected microwave power IS proportional to the conductivity of the sample Figure 3 2 It is measured as a measuring head O conductivity N free carrier concentration Figure 3 1 Laser excitation measuring head u wave antenna reflected u wave function of time Figure 3 2 Detection by micrwave Semilab Theory 5 The ring shaped microwave antenna is used near to its resonance freqency in the range of 10 0 GHz 10 5 GHz The sample and the antenna above it compose a resonator that s resonance curve can be seen on Figure 3 3 red line As the conductivity of
10. PAVE VOUS CS Cl CCH ON ese dad a ls i ada Sates Nal ie a Ua ale 10 installanom of SVSTCIN COMPONCIUS sai iT T GEES RA a 10 System power and INICFCONNCCHONS sare s2 creed cit catia eee aged Ur USE aa 10 Hardware and software operation during the uPCD measurement sseeeees 13 LP CD Operatino SOLEW AL ssion oe a Eaa 14 O MAMIE OCI LI OU ER IDR NRO DS we auras ated ashes dea RR 14 6 1 1 TCU CHI pass DO a ates Rae ANAE EIE A N T 14 De AVS eA TO WE a a5 a O E E oeeesebe ead eonmteas oa 14 6 5 User Interface and Dasic Operationerne ian AEEA 15 6 3 1 VLC 112 AE IAA a O ater nse A ean A E oats 15 6 3 2 RC CON Cie DO Dn aos a a oti tee mbar cetera cot enaptiasts 15 6 3 3 LES S POD pai aa RR EN EE EENE 18 6 3 4 CLS a ia ora ade a ad season dials een cannes ba ae ean nal a sunten tae 19 6 3 5 D T TS DD essere o a a E cea tab teat E A 20 Ord Men SN aTa E asses sauec E masa esteaumaeee E 20 6 4 1 TTI DU a pet a actos a a A sd ease 20 6 4 2 L TONE eee eee Te eR pa eee AM enor Tn meee NTE Peres re p 22 6 4 3 Measure men Interface I OF aner E a A Ze 6 4 4 COONS PIVA nt ot comida pa a D satan tae 22 6 4 5 MAT OT US oii a a e a 24 6 4 6 PUNC SI REP il rd ase sia hace baa aaa acces iadatet E 26 CS B16 lot ic ta ia ne mae Penn Aen CET an A REO ee Pe oP erent ne nnn aR Cen ne ee e 28 Semilab Introduction l I Introduction Welcome as a WT 1000B Wafer Tester owner The WT 1000B is a one point non contact minority carrier lifetime m
11. WT 1000B USER S MANUAL Date of revision 27 03 2008 SEMILAB Inc Budapest Hungary 1 Table of Contents BEAT CUNO IN isisi aeee aone ces bo ea ra che severe EDDIE raaraa aait 1 Product Hie He UG 5 seco eates bs hemeeaisdes assada a toate eae assesses Raios ia ne SUAS ements l PCC INC ALOU S arosi NT T EET O ETA l Salety INLORIM ALON aesae E E T dass 3 Theory of the u PCD measurement eeeeeecossssssececcccssssccceocccossscceeecosssssceceeesssssscceeesssssss 4 Sak Laer Exe Oa NAR UR ante esate see 4 k DAC 0 ea meee nen A a a e Cen en 4 Jo Eaua C0 q PRP nr er er NORA RAD ERES DN ORDENADO RR NO SEER CAES OI PTD DOE eee 7 54 Bulkand surface rc combinat Osroes Di 7 3 5 Lifetime measurement with the WT 1000B Wafer Tester 9 3 6 Automatic parameter setting in the u PCD measurement cc ccccceeeeeeeeeeeeees 10 PING AL AN AUION susscssvacsecseseuticssescsncssseusscdvenconcseususceseesctucseoeusedevenssuesessveceseesctucseooueesedasesdeseacdeses 9 aodu Goins Ra tad eos aie evan ade ee eee ee 9 SS LCV COM O UOL OVW scsi ye sitet E aa tet beeen eda cecum ea tia beeen are 9 TACTICS FCG ULI CIN CIS assis sian ia O aa asa id aaa 9 2 Unpacking inspection and preparing components of the system for installation 10 VE TA 000E mana Uni calc aA A ssa bedatat scdaaess ra a 10 Other components NC SVSTCUN inert eee endian 10 Dis MINS UME ON rar ta tage tiene E ect eta heat re oneness a ieee cnet aeons 10
12. ak The shortest time range is not used by the autosetting procedure A submenu appears After placing a sample under the head the optical sensor detects that If Used is checked a measurement is performed automatically after detecting the wafer The delay in millisecond units between sample detection and measurement can be set in Sense Delay input field Voltage on the optical sensor output 1s measured This voltage depends on the reflectivity of the material under the sensor There is a comparison level limit to decide if the empty stage or a sample is under the sensor Above the set limit it senses stage below that it senses wafer The default value is 4 5V Semilab Operating Software I 24 Lifetime Setup The upper and lower Warning and STOP levels can be set in the appearing input window for levels description please refer to 2 4 Trend menu Lifetime Setup Ls Upper limit STOP 25 Upper limit Ra 25 Lower limit ts 20 Lower limit 5 TOP Exlude below limit 0 eld Control STOP eld lower limit 72 Sequence limit NG Last HG field Control WARNING eld lower lirit 55 Sequence limit MG Last NG TLV Setup Total Lifetime Variation Setup Upd With Stat In case this option is activated when update checkbox is selected Update see Chapter 4 the continously measured data is added to the statistics Slope Correction The microwave DC level sometimes changes even d
13. aring plots 1n the software If the mouse cursor is on the plot area its coordinates appear in the Statusbar of this window The transient data can be copied to the clipboard by Edit Copy Data menu item or can be copied as an image by Edit Copy Picture In the View menu there is a possibility to show hide the fitted curve of the transient change transient and fitted curve line color and line width Right clicking below the Info area detailed measurement information appears Semilab Operating Software HI 22 a Tr iin adam A0 mebaze UL gs Save Transient Saves the actual transient to a trn file This file can be loaded later m the File Load menu of the Transient evaluation window Exit Closes uPCD lifetime measurement software 6 4 2 Edit menu Copy Data Copies current transient data to the clipboard Copy Picture Copies current transient as an image to the clipboard 6 4 3 Measure menu Interface for New performs a measurement and adds data to statistics see Statistics tab description in Chapter 2 1 Clear Statistic clears statistics Select a submenu appears where the active head can be selected for the Recorder window for Semilab WLL 5 five point system Autosetting at The point selected in Measure Select menu is used for automatic parameter setting In this case all the five heads will use the same settings Autosetting All The Autosetting procedure is performed at all the measuri
14. asured effective lifetime in the given position of the sample 3 4 Bulk and surface recombination The redistribution homogenisation of the free carriers takes place during and immediately after the excitation After this relatively fast event there are two main parallel processes until the thermal equilibrium is reached Figure 3 e bulk recombination e carrier diffusion to the sample surface and then surface recombination Semilab Theory 8 diff T surface diffusion of carriers surface to the surface recombination Excitation Redistribution of Thermal generation of carriers equilibrium excess carriers bulk recombination Figure 3 Block diagram of the sequence of processes during the u PCD measurement The measured lifetime characteristic of the whole recombination process as it is described with the following equations l l l gt Tomes Cou Tartt meas surf Cig E diff E D n p d Tout surf 2 8 where e Thy 1S the bulk recombination lifetime that is characteristic of material quality e Tap is the characteristic time necessary for carrier diffusion to one of the surfaces of the wafer from the place of excitation Itis determined by the wafer thickness and the diffusion constant of minority carriers e Tse IS the characteristic time of surface recombination determined by surface recombination velocity It is short for polished bare wafers S 50000 cms and long for
15. by the Measure Clear Statistic menu item or with the Ctrl L hotkey 6 3 4 Lifetime tab Lifetime tab 1s mainly used for inline applications Semilab WLL 1 and WLL 5 models Its purpose is to stop measurement and even the transport belt if a sample is found with lifetime out of the specified lifetime region uPCD recorder v3 26 aala File wiew Edit Measure Options Macro Functions Access Help SEMILAB ASET ASTOP NEW BATCH ue Miedo START STOP E E10 ENGINEERING Settings v Classification Details Statistics Lifetime Recorder Lifetime us U1 us BEE E E BeBe IN 0x00 OUT OxO1 BIN Ox0002 PICL6F877 SHR ISA interface OF on WinRT1 Lifetime Tab The ideal lifetime range is between the two orange colored line If the measured lifetime is in this region the colour of the plot is green The lifetime field in the Recorder window is also green If a sample found with lifetime out of the orange coloured Warning limits the plot and the lifetime display in the Recorder tab turns to orange color If a sample found with lifetime out of the red coloured STOP limits the plot and the lifetime display in the Recorder tab turns to red color Semilab Operating Software I 20 The WLL series in line lifetime testers have a 24V I O interface Both the Warning and the Stop levels are sent to this interface to control external device events Wa
16. ce recombination process should be suppressed i e the sample surface should be passivated There are two commonly used ways of surface passivation the thermal oxidation and the chemical passivation Depending on the efficiency of the passivation bulk lifetimes much longer than the diffusion lifetime can be measured Although the measured lifetime depends on both the bulk and the surface recombination processes in special cases it refers to either the bulk or the diffusion lifetime Approximately the bulk lifetime is measured if the measured lifetime is much shorter than the diffusion lifetime high contamination level independently of the surface recombination velocity The bulk lifetime is measured in the case of passivated surface as well The diffusion lifetime is measured if the surface recombination velocity is high bare sample and the bulk lifetime 1s much longer than the diffusion one low contamination level In this case the obtained lifetime map is very homogeneous since the diffusion lifetime depends only on the sample thickness and the diffusion constant of the minority carriers which parameters typically do not change a lot in a sample 3 5 Lifetime measurement with the WT 1000B Wafer Tester The WT 1000B Wafer Tester is a fully computer controlled equipment The measured transients are recorded by the transient recorder card Semilab Theo 10 Semilab s patented microwave antenna design provides unsurpassed sensitivity and m
17. characteristics and explains how to unpack install and start the operation of the WT 1000 system Operating software It presents the user interface and explains the capabilities of the software If you have any problem or question please do not hesitate to contact us SEMILAB Semiconductor Physics Laboratory RT H 1117 Budapest Prielle Korn lia u 2 Hungary Tel 36 1 382 4530 Fax 36 1 382 4532 E Mail semilab semilab hu Web site www semilab com Semilab Safety 3 2 Safety Information The WT 1000B Wafer Tester contains high power pulsed infrared laser source its radiation 1s invisible by human eyes The WT 1000B Wafer Tester equipment is a Class IM laser product classified according to EN 60825 1 standard because it is highly divergent It 1s safe for the naked eye potentially hazardous when optical instruments are used The laser diodes of the PCD units are built m the measuring head The invisible laser radiation 1s emitted down perpendicular to the sample placed below the measuring head During normal operation there is no risk of exposure to laser radiation Measuring head as well as laser diodes do not need any maintenance In case of removing any part of the protective cover from the industrial PC or dismounting the head unit scattered reflected invisible laser radiation might appear Normally it is not harmful but should be avoided viewing directly to the fiber connection the bottom of the measuring head or
18. e Industrial PC Windows operation system e Pheripherals keyboard mouse LCD monitor Facilities requirements Indoor environment Operating temperature between 15 C and 35 C Relative air humidity 10 to 80 Maximum height above sea level during operating 2000 m For detailed specifications of other components of the total system please refer to their own manuals supplied with them Specifications in next paragraphs concern the main unit only Power line supply Line type single phase phase neutral protective ground system Line frequency 50 60 Hz Input voltage 115 Vac or 230Vac 10 with manual selection Power consumption maximum 300 VA Power line connection 1 8 m long 3 wire 3 x 0 75 mm power cable with BS 1363 plug Class of hazardous electrical shocking class I protective conductor with green yellow color Overvoltage group II according to IEC 664 Semilab Installation 10 2 Unpacking inspection and preparing components of the system for installation WT 1000B main unit Unpack and remove the Wafer Tester WT 1000B the industrial computer and other units like the monitor the keyboard the mouse etc from the crates Check the crate contents according to the packing list Inspect the system if there is any damage observable Report damage to shipper immediately Be sure that the exterior of the instrument was not damaged Any deformation on the exterior of the instrument can influence the
19. easured on a sample As the carriers return to equilibrium exponentially the signal changes accordingly The signal is descending according to b case If the signal is higher right after illumination than in the eqilibrrum the signal is descending during recombination as it 1s indicated on Figure 3 5 b case The transient on Figure 3 4 belongs to this case a growing b descending signal signal 3 5 A 2 Voltage V s equilibrium J e injected 10 10 1 10 2 10 3 10 4 10 5 10 6 Frequency GHz Figure 3 5 The MWDC curves in egilibrium and after injection If the freqency is set to position a the signal grows during recombination to the original state if the freqency is set to b position the signal descends Semilab Theory fi In some cases the freqency is tuned to a position where the signal of the injected sample is below the signal of the sample in eqilibrium Left part of the graphs on Figure 3 3 In this case the transient is reversed the signal is growing by time during the recombination 0 5 P co gt ho Voltage V me 0 50 100 150 200 Time us Figure 3 6 Transient with increasing signal according to Figure 3 5 a case 3 3 Evaluation The measured microwave reflectivity decay is fitted with an exponential curve and the obtained time constant is recorded as the me
20. easurement speed allows the introduction of new evaluation principles The whole microwave system 1s integrated in the measuring head of the WT 1000B Figure 5 scope u wave trans rec generator circulator detector 7 antenna E wafer Figure 5 Microwave detection 3 6 Automatic parameter setting in the u PCD measurement The automatic setting AutoSetting of the measuring parameters should find an optimal setting taking into consideration the above problems The best possible wide band evaluation is necessary that is in a concrete Time Window the lifetime should be evaluated even if it changes orders of magnitude supposing that the Voltage Range and the microwave tuning is set correctly Because of this wide band behavior which also results in gathering noise from a broad frequency range the evaluation of the individual transients and hence the AutoSetting procedure requires signal to noise ratio much higher than one S N gt gt 1 The AutoSetting procedure works in serial mode 1 e the individual parameters are set in turn The parameters are set to their initial value e Afterwards the Voltage Range is decreased until the amplitude of the transient or its recorded first part 1s optimal for the A D conversion and at the same time the extreme values of the transient are also far from the scope boarders AutoRange Semilab Theory 1 e Due to the laser pulse there is a step at the beginning of the transie
21. easuring tool It is capable of monitoring defects and contamination both in the bulk and in the surface region of silicon blocks It is a useful tool for investigation and quality control of wafers blocks and solar cells Product Higlights e Fully automatic operation and data evaluation e Measurement selectable at any position on the sample e Measurement of mono and multi crystalline material e Patented chemical surface passivation option available e Wafers can be measured after each process step of solar cell manufacturing e 1 1 correlation with the standard Semilab WT 2000 Wafer Tester Specifications e Materials S1 Ge e Resistivity range 0 1 to 1000 Qcm e Laser 904 nm wavelength e Meas spot diam 3 mm e Microwave source variable frequency around 10 3GHz e Lifetime range 100 ns to 20 ms e Lifetime resolution 0 1 e Measurement time 30 ms data point e Single shot or continuous measurement There are four Chapters to introduce the WT 1000 Wafer Tester system to you There is a description about the theory of the measurements and you can study how to install and operate the system and how to use the software Safety Information Instructions about the safe way of operating the WT 1000 Theory of the measurements It describes the theory of the lifetime measurement with the u PCD technique Installation Semilab Introduction 2 It gives information about the system configuration specifications and the software
22. evaluated to avoid the initial distorted part of the transient The evaluated points are displayed with blue color and their number may be 64 128 256 512 or 1024 The whole recorded transient consists of 2048 data point In most cases it is recommended to use 1024 points The fitted lifetime is displayed near the LT drop down box in us units Time curs The above described Time Cursor is set automatic Auto by default 1 e the software automatically determines its position after recording a transient according to a built in algorithm If it 1s set manual checkbox is unchecked you can determine its position by dragging the cursor line by the mouse in the plot window It 1s recommended to use it in automatic mode to get reliable and reproducible results By the proper setting of the cursor the non exponential initial part of the decay e g due to redistribution of carriers is avoided and only the carrier recombination transient 1s analyzed The position of the Time Cursor is displayed near the Time curs checkbox in us units Averaging Averaging is the number of transients taken and averaged at a given position The possible values are 1 4 16 64 and 256 More averaging means an increased signal to noise ratio at the expense of longer time necessary for the measurement Amplitude The signal amplitude in the transient at the Time Cursor position is displayed also in the Settings panel in mV units It may happen when parameters are se
23. in the left bottom edit box and then the new menu item appears below the Macro menu item in the Macro menu Macro Syntax For more detailed information on macro possibilities refer to the Macro Syntax window by pressing the Be button in the Macro Edit window or Macro Macro Syntax menu item Macro Watch There is a debugger for macro language built in uPCD You can add watches by Macro Watch menu item On the appearing Watch Window use right mouse button to choose from the possibilities Semilab Operating Software H1I 26 Macro Syntax Load List Save List Modify Expression Modify value Insert Mew Expression Delete Expression Clear All Always On Top Clicking on Macro Syntax a list of all available variables functions and procedures appears Here you can check the sintax and finde sintax errors and set the editor fonts properies 6 4 6 Functions Menu Functions menu contains the measuring possibility of the following functions Microwave DC Plots the microwave reflection mV units versus the applied frequency Checking the Free Running checkbox at the top right the plot 1s repeatedly recorded The MWDC curve should be a non monotonic typically it has a minimum curve between the OV and the 5V limits measured on samples from a wide resistivity range from insulator to metal WT Microwave DC New Load Save Print E 5 4 l A 3 O ee eee ee tee a eel E 10 1 10 2 10 3 10 4 10 5 Frequency Ghz
24. ng points In this case all the heads use different settings Stop Autoset Stops Autosetting procedure Shortcut key Ctrl P 6 4 4 Options menu u PCD Interface here you can choose between 2 ports there is a possibility to use 2 measuring heads 24V I O Interface If the measuring system is equipped with 24V interface card WLL series only it 1s possible to send start stop signals to the main unit and control transport line according to measurement results If interface card is not installed select Not Used Semilab Operating Software HI 23 Serial TRG WID Triggering is also possible via a serial port or this port can be used for sending wafer ID s 1f you click the Settings button you can reach the Communication Setup panel Communication Setup Port com2 Baudrate J600 Parity Even Byte Size E bit Stop bits COM 2 SB00 E ven 8 2 2 bits Fast Transient Polarity Selector Exclude 50 us Time Range Optical Sensor Local Mode Only 1024 points are recorded by the Transient Recorder instead of the standard 2048 The microwave reflection changes with frequency see 3 6 Functions menu If the frequency is tuned before the peak the transient has negative polarity If the frequency is tuned after the peak the transient changes to positive polarity Polarity selector gives the possibility to force Autosetting to tune the frequency before or after the pe
25. nt that should be maximized by changing the microwave frequency in large steps with the necessary increase of the Voltage Range PreTuning e With this not optimal but adequate tuning an approximately optimal Time Window can be found which results in valid lifetime data within the Time Window Especially in case of strongly distorted transients it can occur that the resulting Time Window is longer than the optimal one After the Time Window setting the number of averaging 1s corrected to an approximate optimum value AutoTimeWindow e After setting the Time Window the fine tuning is performed by searching for the maximum of the correlation function that characterizes the energy of the transient weighted by an exponential decay of optimal lifetime value This way the tuning is independent of both the distortion and the fact that the evaluation is reasonable or not In general this process gives better microwave frequency than the PreTuning procedure Tuning e After the tuning procedure the Time Window is corrected if necessary and if the Time Window correction consists of more than one step then the tuning process is repeated followed by a new Time Window control Semilab Installation 9 4 Insatallation Introduction The WT 1000B Wafer Tester system is a computer controlled equipment which is suitable for recording storing and displaying minority carrier lifetime of silicon wafers System configuration Basic units e Measuring head
26. passivated wafers S lt 10 cms O Tneas 1S the measured lifetime e dis wafer thickness e D and D are diffusion constants of the minority carriers for electrons and holes e Sis the surface recombination velocity Semilab Theory 9 As described above in the equations the sample surface may have a large influence on the lifetime because of the surface recombination process Figure 4 shows theoretical data of the basic equation calculated for three different surface recombination velocities 10000 With chemical passivation SSIES S 10 cm s 1000 ah E 100 a Diffusion lifetime S 50000 cm s a 10 Without chemical passivation a 1 10 100 1000 10000 Bulk lifetime us Figure 4 Theoretical correlation curves of the measured lifetime versus bulk lifetime The two steps of the surface recombination process the free carrier diffusion to the surface and the recombination at the surface are described with two independent parameters Taiff and Toyrf If the surface recombination velocity is very high Tsurf is very small typically on bare surfaces the carrier diffusion is the limiting process 1 e Taiff describes the whole surface recombination process The longer the bulk lifetime is the more the diffusion lifetime determines the measured lifetime Figure 6 Since the aim of the measurement 1s to determine the contamination dependent bulk lifetime the surfa
27. rning and Stop limits can be set from Options Lifetime Setup menu For details please refer to ist description in chapter 3 4 Menu structure Options 6 3 5 Details tab Details tab is a sensible and useful combination of the Statistics and Lifetime tabs A uPCD recorder v3 26 File View Edit Measure Options Macro Functions Access Help i STOF s TOP P SEMILAB ras SSTOF NEW BATCH ote oe STEARAT STOP Ea E10 ENGINEERING v Settings v Classification Details statistics Lifetime Recorder Lifetime us NE LIZ j oo0o0o0o0o0o000000p0 Curent batch statistics Average lifetime 0 94 us Minimum lifetime 5 51 uz Maximum lifetime o r0 us Range 0 13 us Ul Yield Total number Yield Sequential MG Last NG Good 15 Invalid 0 Lifetime low E Lifetime high E Data file C WUP upd bet IN O00 OUT 0x01 BIN O OxO0002 PICL6F8 7 SHR ISA interface OK on WinRT1 Details tab 6 4 Menu structure 6 4 1 File menu View Transient The Transient Evaluation window appears with the last measured transient Semilab Operating Software HI 21 A Transient Evaluation File Edit View Into Settings Amplitude Mode 46 353 my LT 5 1 64 2222us g 150 LT 1 e 22 69 us LT I e 23 16 uz 200
28. se of a proper setting the fitted decay time should be about 1 5 1 10 part of the whole range Semilab Operating Software HI 18 6 3 3 Statistics tab uPCD recorder v3 23 File View Edit Measure Options Macro Functions Access Help lal UPDATE RPE O astor NEW BATCH CLEAR M OOO E10 ENGINEERING v Settings v Classification Classification Current batch statistics Average lifetime 15 81 us Minimum lifetirne 700 us Masimum lifetime 75 56 us PESE us Yield Total number eld Sequential NG Last MG 100 of 100 Good E rvalid 10 Lifetime low U Lifetime high 408 Data file AUPCD upa bet Opto On MIS Main Window with the Statistics tab active The Statistics tab contains the following important information fields Average lifetime shows the average lifetime of the displayed number of measurement Minimum lifetime displays the minimum measured value Maximum lifetime displays the maximum measured value Range difference between minimum and maximum lifetime Total number is the number all of the measurements Semilab Operating Software HI 19 New data can be recorded by 1 button in the Toolbar by the Measure New menu item or with the Ctrl N hotkey New batch of data can be started by E button in the Toolbar by the Measure New Batch menu item or with the Ctrl B hotkey Statistics can be saved and cleared by m button in the Toolbar
29. t manually that the beginning of the transient is out of the Voltage range thus the displayed Amplitude value 1s not of the whole transient One possibility is to drag the horizontal dashed line Offset and set to a position where the whole transient is inside the range If the transient amplitude is higher than one third of the Voltage range it is recommended to set to higher range Thickness Correction If the bulk lifetime is comparable to the characteristic lifetime coming from the surface recombination and diffusion the bulk lifetime can be calculated if wafer thickness and surface recombination velocity is known Click the button right from the Thickness Correction and type in the window the wafer thickness the surface recombination velocity and click the p or n type of the wafer If the checkbox on the left 1s selected the software calculates the bulk lifetime according to chapter 1 4 This calculated value is displayed in place of the measured lifetime Microwave frequency tuning The reflected microwave power depends on the microwave frequency As a consequence the measured transient amplitude also varies with it The tuning is finding the microwave Semilab Operating Software I 17 frequency where the signal has its maximum amplitude The microwave frequency can be modified within a 500 MHz range by dragging the slider or using the small arrows near the slider The basic frequency is 10 GHz Laser Power The excita
30. tion level number of excess carriers generated is proportional to the laser power By the application of different laser powers transients at high and low excitation levels can be measured and compared leading to valuable information on the contamination species or oxide quality In the default case high power is suggested 120E11 this way a good signal to noise ratio 1s achieved Range Laser Power The Laser Power can be changed easily with an order of magnitude low and high range Range Voltage plot window The Y axis of the Scope window is the signal amplitude the output voltage of the microwave detector Depending on the signal level different sensitivities can be selected such as 1 2 5 10 20 50 100 200 500 mV and 1 and 2 V In case of highly conductive material 0 1 1 Qcm the relative change in conductivity due to a given laser pulse is small As a consequence high sensitivity should be selected On the other hand measurements on wafers with high resistivity are normally performed with low sensitivity large amplitude range due to high amplitude The proper selection of the sensitivity range is when the signal amplitude is between the 50 and 70 of the whole range Use of Autosetting procedure is recommended Range Time plot window The X axis is the time elapsed after starting of the transient recording the zero point is before excitation The time ranges available are 0 05 0 1 0 2 0 4 1 2 4 10 and 20 ms In ca
31. uring the measurement and it results in a distorted transient shape The Slope Correction procedure takes the slope of the microwave DC level into account when evaluating the transient You can in this menu Load and Save the measurement settings and the Classifications for Classifications description please refer to 2 3 6 4 5 Macro menu The Macro language has been implemented in uPCD to give users a wider range of control over software capabilities It is a special program language that is mostly similar to BASIC or DOS batch programming Semilab Operating Software HI 25 6 4 5 1 Macro Clicking Macro Macro menu item the Macro Editor window appears CAMY DOCUMENTSSLOSDOCUMENTOS MANUALSWT 10005UPCD show m Mel ES int inputvaluedef 000 Enter delay between two measurements ma shat clear mesobj showcancel Repeated measuring sequence cycle uped update delap int iF mesobj result 0 then cycle To handle the macros you have the following tools Create new macro Deletes the selected macro Runs the selected macro Checks for Syntax Errors in the selected macro Lists all available macro variables functions and procedures Prints the selected macro Cuts the selected text from the selected macro Copies the selected text from the selected macro to the Clipboard e e e e e a l a Pastes text from the Clipboard to the selected macro You can also give menu access to the macros by typing a name
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