The Tricon evaporators - Elettra Sincrotrone Trieste
Contents
1. iv Symbol legend HV High Voltage Vy hot filament voltage Ir hot filament current Vg grid voltage Ic grid current Va anode evaporating material voltage I anode evaporating material current UHV Ultra High Vacuum R evaporating point substrate distance 1 Theory of operation 11 Thenew TriCon concept The evaporation in UHV of material mainly metals by means of electron bombardment is a well established technique The main scheme of such a source is that of a vacuum diode see Fig 1 electrons are emitted from a hot filament cathode by thermionic effect and are accelerated towards a higher potential electrode anode The energy transfer by electron bombardment on the anode can lead to very high surface temperature up to 3000K if the material has very high vapor pressure at least 10 10 Torr before the melting point it is possible to maintain the evaporating material in the solid state and obtain good evaporation rates from a relatively simple device nie Fig 1 Scheme for a conventional electron bombardment source substantially a c vacuum diode hot filament the cathode red and the evaporating material in form of rod the anode blue are shown a 3D view b top view c lateral view The main disadvantage is the strong limitation of the anode current due to space charge effect very high anode voltages gt 2000V short distances between filament and anode high thermioni2. the correct position refer to Par 4 4 10 3 Low evaporation rates from rod In case of very high temperature to be reached i e gt 1700 C to obtain good evaporation rates some thermal dispersion through the anode support can occur Due to the continuous anode length reduction the evaporation point will get closer to the Mo material holder and a decrease in the evaporation rate will be observed at constant anode power thus some increase in the anode power can be necessary to obtain the same evaporation rate If still the problem remains or low temperature are needed for the used evaporating material the position of the anode is not correct see Par 4 4 33
3. 5W e V4 1000V 1200V or lower in case of low evaporating temperature required lt 1000K This values should permit to work far from strong evaporation or melting temperatures of the used material however lower Ir and or Vg and or Va values must be used if necessary Best results in terms of reproducibility are obtained if two or more zero level conditions are determined for different VG and Va values Moreover as voltage values used in current evaporation are usually different from those of the Zo conditions a useful practice during operation is to note the Vg Ic and Va I values at the beginning of each evaporation session After several evaporation session the original anode position can be found by setting the Zo voltage or user defined conditions and moving the anode linear feedthrough until the correct current values are obtained A retraction of the anode will produce an Ig increase and an IA decrease An insertion of the anode will produce an Ig decrease and an I increase up to a saturation of I4 this means the anode tip distance from the Zo position is 26mm The original position can be reproduced within 0 1mm and the effective material consumption can be easily in situ monitored Define the Zo level after a complete source degas 4 5 Inspection of the evaporation zone removing the stainless steel cap When the source is in air there is the possibility to control the grid filament anode zone without removing the co
4. the electrodes 12 replace the stainless steel cap see Par 4 5 the Ta shield and diaphragm control the position of the diaphragm hole see Par 3 32 10 Troubleshooting 10 1 Rod tip melting If melting of the anode tip is reached there will be the formation of a sphere at the top of the rod this will produce a decrease of the anode length thus reducing the anode current IA in those working condition The anode tip surface will be increased and the required power for the correct evaporation rate will consequently be higher Moreover this situation is really unstable as the sphere will reduce its dimensions continuously during evaporation thus changing electrical field distribution inside the source and consequently the bombarding electron distribution on the tip itself An equilibrium situation will be reached when the material forming the sphere has been totally evaporated in this way the source will work at its best performance level 10 2 Strange anode current If the anode has been inserted or extracted too much with respect to the correct working position the anode current will be higher or lower than the original one respectively and very high or very low working grid voltage will be needed This is an anomalous situation that must be corrected to avoid rod bending damaging of source internal parts strong degassing Provided the procedure to find the zero level condition has been performed move the anode to find
5. TriCon electron bombardment evaporation source User s manual version 3 1 May 9 2000 Dr R Verucchi INFM UdR of Modena Read the Manual carefully This manual replaces any previous version The TriCon evaporation source is not an ordinary device even if based on well known physical principles its use without a careful reading of this manual will damage seriously both the source and the power supplies Take the time to read the manual in order to understand what is different and how it works Operations with the TriCon source are not more difficult than in usual sources they are simply different So please read carefully the manual and spend some minutes to verify how the new triode electrodes configuration has been realized making an inspection of the evaporation zone this will help you to understand why some precautions are necessary and how high performances can be achieved The triode electrodes configuration applied in an evaporation source based on electron bombardment is protected by the italian patent n GE98 A 000096 deposited on November 1998 18 by INFM and R Verucchi ii Table of contents 1 Theory of ODeratiOEL oeeeeeeee etant een Neve Hasen ond du uot eu eva veu S uu a ev evt voa us ev dennen 2 1 1 The mew Trion conceptiei eni ea oae dod Sede eee eet tes Bade dedique 2 1 2 Pertotmatibes sende ETE Mee EE 5 Source descriptions eoo n RS Geis e RR PPM dash tande beende e
6. a shown in Fig 3 are for a 1mm Iron rod a and a 2mm 2 Vanadium rod b Rods of different diameter will show very different performances For what concern the role of the distance R the well known IR flux dependence on the distance have to be taken into account It is very difficult to connect the anode power to the material temperature in the Tab 1 some indicative data are shown for both evaporation from rod and crucible However the shape the dimensions of the rod or rock like crystal used are fundamental in determining the anode power for the required temperature i e vapor pressure Material Evaporation from rod 2mm Evaporation from crucible Anode power Temperature Crucible power Temperature 1100 1200 C large irregular rock 12W like crystal 1700 1900 C Rod 2mm 12W 1500 C 1000 C Rod 1mm Rod 2mm 1500 1600 C 1500 1600 C Large irregular rock like crystal 1000 C 1300 1400 C Rod 1 5mm 2700 C Powder copper phthalocyanine Rod 2mm 1500 C Large irregular rock like crystal wafer 1400 C 1700 C Rod 2 2mm 0 2mm thin foil 3mm wide 2400 2600 C Rod 2mm 1900 C Rod 2mm 2700 3000 C Tab 1 Temperature vs anode power for several elements for evaporation from rod or crucible 2 Source description Air side UHV side b Fig 5 The TriCon
7. and M2 screws a b c d Plane perpendicular to the source main axis Mo electrode Mo screws e f g ig 16 Filament replacement a d top view e f lateral view a New filament from a 50mm long wire 13mm coil b place the coil on the electrodes and fasten the two Mo screws c cut the wire in excess d shape the wire to reproduce the original form e the wire can be in whatever vertical position but must be bent downward f and then slightly upward g 6 now remove the old filament unscrew do not remove the two M2 Mo screws If they are blocked wet the screwdriver tip with some alcohol drops and gently unfasten the two screws 7 now install the new filament ig 16b the wire must be positioned between the Mo M2 washer and the Mo threaded 3mm cylinder Fasten the two screws then cut away the wire in excess among the two electrodes ig 16c 8 if necessary bend the filament in order to reproduce the old filament shape pressing laterally the coil with your finger ig 16d 3l 9 now push the coil downward see ig 16e and then slightly upward see ig 16f with respect to a plane perpendicular to the source main axis as shown in ig 16f 10 replace the grid electrode assembly avoiding to touch the filament position the grid in order to reproduce the original configuration 11 replace the cooling shroud source part remember to replace the gasket Insert the flange avoiding to touch
8. ans of six M6 nuts tightened on the supplied special studs The six M6 nuts on the main flange grants joining of the two source parts so to remove the TriCon source from the vacuum chamber do not unscrew the nuts on the source flange air side remove only those on the vacuum chamber flange side Before inserting the source in the UHV system and after any kind of in air operation on the source perform a careful inspection of the electrodes zone see Fig 10 and Par 4 5 Moreover e verify the grid filament distance to be about 2mm the distance between grid and the top of the two filament electrodes Mo 3mm cylinder to be about 1mm e verify the grid and filament perpendicularity to the main source axis e verify that the grid and the filament distance with respect to the Ta cylinder and shroud internal walls is higher then 1mm e verify the resistance between filament grid anode to be higher than 20M in any case e verify the resistance between filament and ground grid and ground anode and ground to be higher than 20M O in any case e verify filament resistance it should be about 0 4 10 e verify the correct position of the Ta diaphragm 12 Evaporating material rod Mo electrodes Fig 10 Particular of the electrodes zone 3 1 Source substrate distance and beam divergence To evaluate the correct distance R mm between the source i e the real evaporating point and the growing substrate
9. ays necessary whatever the crucible dimensions are Move the linear motion feedthrough in order to put the anode in a position where extraction of the evaporating material holder is possible as previously described in Par 5 1 then insert the crucible in the material holder and tighten the two material holder screws to fix the crucible By using the linear motion feedthrough put the crucible with its external lower edge 1mm over the filament plane i e 4mm from the Mo tube edge The crucible can be filled with the evaporating material when it is positioned in the source or before Do not let fall pieces of material inside the Mo tube otherwise electrical shorts or mechanical damaging of the edge welded bellows of the linear motion feedthrough will occur Do not fill completely the crucible volume maximum material quantity is about 4 of the total volume but may be lower for materials which tends to wet the crucible walls 5 3 Anode positioning and centering An important operation with the TriCon source is to put the anode in the correct position from the point of view of the main source axis and distance from the grid The correct axial anode lateral 21 position have to be found to reach the best electrical field uniformity inside the source as well as to establish the necessary distance between the HV anode and the grounded internal walls of the Mo tube Do no bother about the anode movement or apparent absence of rigidity the poor
10. be damaged Adjust the position of the Ta diaphragm on the Ta shield in order to center the hole on the main source axis 4 6 Evaporating material cooling down In case of evaporation from rod no problems will occur for every working condition if a quick or sudden cooling occurs In case of evaporation from crucible instead great care must be taken for the cooling down procedure to prevent crucible cracks due to a sudden temperature reduction If the evaporating material is in a liquid state in a ceramic or metallic crucible and interactions among the crucible material and the melted substance occur anode power must be decreased very slowly In case of crucible breaking the internal part of the TriCon source could be irremediably damaged Take also into account that some material after having been melted must remain in liquid state 19 5 Evaporating material mounting The source is equipped with two Mo material holder 3cm long see Fig 13 respectively designed for Imm and 2mm diameter rod This last is also used for crucible supporting To mount the evaporating material first remove the stainless steel cap see Par 4 5 in order to see the evaporation zone Unscrew the three M3 grains for anode positioning 1 turn will be enough to leave the anode totally free Then use the following procedures for rod or crucible mounting material M2 hole herel Fig 13 Sketch for the Mo material holder lateral view the materia
11. c emission filament temperature gt 2400K can only partially overcome the problem Moreover due to the continuos material consumption the anode filament distance progressively increases thus producing a reduction of the anode current this requires a continuos increase of the anode voltage or and of the hot filament temperature until a repositioning of the anode is absolutely necessary e g by means of a linear motion feedthrough It is difficult to obtain a reproducible working condition however an active closed loop control on the evaporation rate acting on the filament temperature or anode voltage is possible by a direct measure of the evaporated material flux c Fig 2 Scheme for the TriCon electrodes configuration the presence of the grid green between cathode red and anode blue shows the triode structure of the source The gray cylinder around the blue anode is set at ground potential a 3D view b top view c lateral view The TriCon source has a different electrodes structure it is the configuration of a triode Italian Patent pending n GE98 A 000096 November 18 1998 As shown in Fig 2 the anode is surrounded by a metal tube set at ground potential and the electron emitting filament is positioned around it A grid set at a positive potential is located between the filament and the anode on the top tube edge The main advantages are e absence of space charge current limitati
12. cedures this is the last step The filament power supply will be set at a negative voltage and the grid will grounded in such a way electrons will hit the internal walls in the evaporation zone Remember now Va is the negative referring voltage at which the filament is set and the grid is grounded If the original TriCon power supply is used set Vc 0Vand turn the DEGASS switch from OFF to ON When the degassing operation has been performed set Vg 0V and turn the DEGASS switch from ON to OFF power supply switch in NORMAL If the original TriCon power supply is not used change the electrical connection control Fig 11b for the right scheme and always set Vc 0V before changing the filament referring voltage 6 4 1 Evaporation from rod Set Ip 3 8A set V Z0V and turn the DEGASS switch from ON to OFF then set Va 100V Vc 10V Slowly increase Vg up to about 250V whilst observing the chamber pressure and the Ic value the maximum current must be 50mA some internal power supply fuses could broke The maximum Ig value at Ig 3 8A will be lower than 30 40mA so set VG 10V increase the filament current by 0 1A then again increase Vg up to 250V Repeat the sequence until the maximum Ig 50mA value is reached Time required for this operation is 60min or higher 6 4 2 Evaporation from crucible Set Ir 3 8A set Vc 0V and turn the DEGASS switch from ON to OFF then set Va 50V Vc 10V Slowly increase Vg up to about 250V whilst observing the chamb
13. crease slowly the grid voltage up to 240 250V whilst observing the grid current and the system pressure do not exceed the suggested maximum pressure The maximum power on the grid is 6W i e 240V and 25mA the maximum current is about 30mA Increase the grid power with great care to avoid arc formation pressure can reach values in the high 10 mbar range Do not care of Ig variation during degassing do not vary Ir in order to correct grid current value just wait for slow degassing as time required is about 60 120min 6 3 Anode degassing After the filament and grid degassing this is the most critical stage as high voltage are involved while system pressure is usually in the high 10 mbar range Material melting have to be avoided possibly even if the crucible is used use the correct anode maximum power an indicative temperature vs anode power table is given in Tab 1 even if different material in different shapes will have different performances The presence of the crucible requires a different degassing procedures as described hereafter 6 3 1 Evaporation from rod Set Ir 4 1A V4 300V Vc 20V Increase V to reach in sequence 500V 800V 1000V whilst observing the anode current and the chamber pressure Slowly increase Va to reach about 80 90 of the anode power that will be used during operation or power required for material tip melting If very high power are requested gt 15W higher anode voltages and Ir can be us
14. current for the Ta 0 25mm filament is 4 1A even if higher values up to 4 7A can be necessary if very high temperature 22700K have to be reached Set Va 1000V or lower if you are using low melting point material then increase slowly the grid voltage whilst observing the anode current increase The required anode power should be reached slowly perform a waiting step at 50 and 80 of the requested power to leave the system reach a thermal equilibrium In case of very high evaporation rates or temperature close to the material melting point great care must be taken whilst reaching the desired anode power a strong pressure increase and a sudden anode current decrease are observed if material melting occur see Par 10 1 Tip melting must be avoided to obtain the best source performances The main advantage of the TriCon source is the possibility to control the anode power i e the evaporation rate adjusting only the grid voltage once you have set the filament current and the anode high voltage the desired anode power is reached and maintained constant just varying Va As can be seen in Fig 15 the evaporation rate is kept constant for long time by varying the grid voltage in order to preserve the 10w anode power if an I decrease is observed due to the anode consumption increase the Va to set the correct anode current Grid voltage variations may be different from those shown in Fig 15 as it depends on the several working condition Always
15. deposition 9 2 Filament replacing If the correct turning on procedure are followed the Ta filament life will be several hundreds of hours see Par 4 3 The Ta filament can be even gently touched moved bent without breaking it in case of a W wire this can not be done Use a Ta 0 25mm wire unless the source is used in a strongly oxidizing atmosphere in case of different material take into account that 5A is the maximum filament current that can be applied to the source electrical feedthroughs To replace the filament use a wire 50mm long and bend it to form a 13mm coil see ig 16a Then observe the following procedure 1 remove the water connections from the source 2 remove the stainless steel cap see Par 4 5 3 carefully unscrew the 6 M6 nuts on the main CF35 source flange then dislodge the CF35 double sided flange with the cooling shroud Avoid to damage or touch the internal electrodes Now the electrodes zone is accessible 4 remove the whole grid electrode assembly taking note of its original position first unscrew with an allen key the M2 grain which holds the grid molybdenum electrode stainless steel barrel system on the electrical feedthrough then gently take away the whole from the white MACOR cylinder avoiding contacts among grid and the filament 5 observe the shape of the filament coil it should be oval shaped see ig 16c or d it must be reproduced on the new filament 30 Mo electrodes
16. e of the linear motion mechanism c five electrical feedthroughs 3000V 5A welded on the CF35 flange see Fig 7 Filament Filament Grid and two not used The electrical connections one MHV connector and a 6 pins connector for the power supply are positioned on the stainless steel plate d the linear motion for the shutter a small edge welded bellows located on the CF35 flange connected by a mechanical arm with the on off lever on the bottom source air side In the UHV side are present see Fig 5b Fig 8 e a Molibdenum Mo tube O D 10mm I D 8mm with a Tantalum Ta shield inserted on its top the anode a stainless steel cylinder 4mm 12cm long with the Mo material holder screwed on it is inside the Mo tube and screwed on the main HV feedthrough f On the basis of the Mo tube near the CF35 flange are located a brown VESPEL ceramic cylinder for anode centering and correct positioning see Par5 3 and a white MACOR ceramic cylinder to hold and grant electrical insulation among the 5 pins coming from the CF35 flange c On the MACOR cylinder are located the two filament and the grid electrodes Each of them is composed of a stainless steel connector inserted into the MACOR cylinder and on the rod of an electrical feedthrough contact is granted by a M2 grain and of a Mo 3mm with a M2 hole on the top By means of M2 screws the filament and the grid are fixed on the Mo cylinders d The grid is a Ta woven mesh not w
17. ed provided the system pressure is in the low 107 mbar range If very low anode power are requested lt 5W use lower Ip Time required for the operation is about 60 120min 6 3 2 Evaporation from crucible Set Ir 3 9A Va 100V VG 20V if grid is present Increase Va to reach in sequence 500V 800V 1000V whilst observing the anode current and the chamber pressure Reach about 80 90 of the anode power that will be used during operation or power required for material melting If very high power are requested gt 15W higher anode voltages and Ir can be used provided the system pressure is in the low 10 mbar range set Ir 3 9A V4 500 then increase Ir of 0 1A and increase Va to reach in sequence 500V 800V 1000V Repeat the procedure until the necessary Ir value is reached If very low anode power are requested 5W use lower Ir 24 If the crucible is empty power as high as 50 70 Watt maximum can be set be careful 60 70 Watt corresponds to more than 2000K If the crucible is filled reach the melting point in a good pressure environment e g 10 mbar and after the chamber bakeout Take great care of the cooling down procedure to avoid crucible breaking see Par 4 6 Time required for this procedure are 2 3 hours for a new empty crucible 30min 2hours for a filled crucible In case of a new crucible always perform a degassing before filling it 6 4 Internal walls degassing After the previous three degassing pro
18. elded handle it carefully The cooling shroud see Fig 6b and Fig 9 it is a 316LN stainless steel tube connected to a double sided tapped CF35 flange by means of two tubes entirely located on the UHV source side The CF35 flange on the vacuum side will be connected to the CF35 main chamber flange The tube is closed at the top side by a hollowed stainless steel cap hole 6mm 2 this is also the support for a Ta shield and a diaphragm for the beam monitor electrodes and for the shutter The tube has three longitudinal holes to allow the presence of the shutter mechanical arm 1mm stainless steel bent rod and of the two electrical contacts for the beam monitor 6 special studs are screwed on the CF35 flange The Ta diaphragm can be set in the correct position using 10 the two M2 screws which hold the diaphragm itself on the Ta shield tighten them after any centering operation Ta shield Cooling shroud Ta diaphragm b Stainless steel cap Fig 9 Double sided CF35 flange with the cooling shroud a cutaway view b to show the stainless steel cap the Ta diaphragm and shield the shutter When the two main parts are disassembled they must be joined before inserting the source on the UHV chamber see Fig 5 The cooling shroud without the stainless steel cap must be inserted axially on the main flange do not forget the gasket with the supplied special 6 M6 studs with silver coverage alread
19. ende aah dS ele andes Reen 24 6 3 LByVaporauon from tod mesana denkende oenen aasde eisen deen 24 6 3 2 Evaporation from crucible ns o o ERE DRE UE RCHOES MU ERES SARI VERRE TS Uode ep HART 24 6 4 Internal walls de PASSIDIE ssnstinin on toe durer d e gea itae ae ubera eter nantes 25 64 1 Evaporation from rod sss one EU RES URAR VASA CNN EARS EKER NE ER UN Eee 25 G42 Evaporation Tromicpucible uie cuf iat E E eas 25 7 Evaporation procedure essssooesesosecesoscoesssocesssooseesooecesosecesosoosessooesssooesssoocessssecsssscossssoossesss 26 pM U De M PED MP M T MUERE 26 72 Evaporation OM TOi aao opens tese qoas eso eer Motus pea bed vos org e aang bies iui Dur aste poseer QUEE RC 26 iii 7 5 Evaporation Trom crucibles csser sariin UY PREPARA ASIA Eaa en tenten vae e ba dese 27 8 Some practical suggestions ip M P PERS NES NIE e coi Sn EUM I Mein Fu eM d tpe EOSYE geeen 29 95 MaTntendlicE oeconomica dore ea uta eme esena eSEE sn cedi Dex o dene ant dea daneen 30 9 1o Internal gatis clean Dennen oC eR T dE 30 9 PANIC DG TEIN ACT eec E Dee e m EE 30 10 gt FroubleshooUBE uie iiti sop kh Posi Eo vo0 i02 RqpUeTVEyL Enc os P kae psa EN eu EE RE Po EYE T iMd ou osobi anapa osde Rep saus URN 33 TOOE Rod p melintas tab apto vadis setatis oim eset iua e stab pe didolun 33 10 2Stfange anode ulii 33 10 3 Low evaporation rates from TOG terit tacto VEM 200 dsl aetid vi vagus siaratehbehean ina teansste 33
20. er pressure and the Ic value the maximum current must be 50mA some internal power supply fuses could broke The maximum Ig value at Ip 3 8A will be lower than 30 40mA so set Vc 10V increase the filament current by 0 1A then again increase Vg up to 250V Repeat the sequence until the maximum Ig 50mA value is reached Time required for this operation is 60min or higher 25 7 Evaporation procedure While the procedures are substantially the same for evaporation from rod or crucible great care must be taken for what concern the thermal properties of the material to be evaporated i e melting point vapor pressure vs temperature thermal conductivity best performances are obtained through a knowledge of this information Moreover source damaging can be avoided taking into account chemical reactions between source and evaporating materials For starting conditions see Par 4 1 and 4 2 then turn on the filament see Par 4 3 7 1 Shutter Open the shutter only for evaporation rate measurement or to perform film deposition The shutter is moved by the lever on the top of the 50mm linear motion mechanism in the air side it is a two position movement which corresponds to opened and closed shutter At the end of the mechanical arm in the air side of the source there is an adjustment system composed of two M3 nuts do not regulate the mechanism contact the 2M Strumenti service 7 2 Evaporation from rod The typical working
21. ible mounting the same procedure must be observed in order to correctly position the crucible itself Centering grain grain Holding grain grain Holding grain grain Centering grain rain Centering grain grain 88 Fig 14 Horizontal cutaway of the VESPEL cylinder to put in evidence the different M3 grains screwed into 22 6 Degassing procedure When the source is inserted in a UHV system a bake out is necessary to reach the best performances from the point of view of low degas levels during normal operation The maximum bakeout temperature is 180 C if the bake out is performed by tapes avoid direct contact with the source parts When the source is hot do not move any mechanical part Furthermore a specific degassing procedure have to be done to clean the source internal walls and electrodes The degassing operation should be performed before the main UHV system bakeout and after this to assure best performances and low degas pressure after the bakeout Four consecutive steps must be performed in the following sequence i filament degassing by direct heating ii grid degassing by electron bombardment iii anode i e the evaporating material degassing by electron bombardment iv source internal walls degassing by electron bombardment All operations will increase the UHV system pressure To avoid shorts and arc formation between electrodes inside the source do not exceed 2x10 mbar chamber pre
22. l or the Insert crucible must be inserted from the right The left part is M2 threaded in order to screw the device on the stainless steel cylinder 5 1 Rod With the two material holders supplied it is possible to insert cylindrical rod with diameter in the 0 8 3mm range Move the anode to the uppermost position the material holder is now at the level of the Ta cylinder on the top of the Mo tube Unscrew the material holder by means of flat end pins then extract it carefully without touching the grid and or the filament Never mind if the material holder together with the 4mm stainless steel rod are extracted see Par 5 for more details this is due to the coupling among them that is stronger than that of the rod and the HV feedthrough Unfasten the two Mo M2 screws located on the material holder see Fig 13 they are very short do not unscrew them completely If the two screws are blocked wet the tip of the screwdriver with some alcohol drops and gently unfasten the two screws The rod can be inserted in the material holder for a maximum minimum length of 8mm 3mm then gently tighten the two Mo M2 screws alternatively to reach a good mechanical contact among the rod and the material holder After material mounting just screw the material holder on the central rod or the whole central stainless steel rod on the HV feedthrough 20 It is possible to insert material inform of foils wafers or even with no regular sha
23. l melting point e Record the zero level conditions after the degassing see Par 4 4 e Low degassing level during evaporation can be reached only after the UHV system bakeout with a proper degassing procedure and using water cooling during evaporation e Once the filament current and the anode voltage have been set the anode current will be controlled by the grid voltage Par 7 e Record the initial value of Vc Ig and Va IA before starting any evaporating session e Rarely you will need high filament current gt 4 2A and or high anode voltage gt 1300V control the thermal properties of the evaporating material e After evaporation from crucible cool down the anode slowly to avoid cracks and or source damaging see Par 4 6 and 7 3 29 9 Maintenance Use gloves while performing any kind of mechanical operation on the UHV parts of the TriCon source avoid any direct contact whit skin 9 1 Internal parts cleaning After several evaporating session the internal parts of the source will be covered by coatings Typically the cooling shroud internal surface the Ta cylinder internal external surface the stainless steel cap are the most dirty parts the latter two can be cleaned after removing them from the source see Par 4 5 while the cooling shroud can be cleaned also with the two source CF35 flange joined together taking care to not touch the electrodes The Ta diaphragm and the Ta shield too can show material
24. lament is a 0 25mm Tantalum wire one coil self sustaining see Fig 10 Tantalum has been chosen because of its thermionic emission properties and its ductility it can be easily shaped and its substantially unaffected by stress release during heating However in case of strong current increases wire bending can occur and shorts can occur so the following turning on procedure must be followed every time the filament is turned on This will ensure long filament life and absence of deformation See Fig 11a for electrical connections Set the filament voltage and current potentiometer fully counterclockwise set the grid voltage Vg l0V and the anode voltage Va 100V Filament current Ir must be increased in step of 0 25A maximum current increasing step is 0 33A every 30sec or every 45sec if filament is new as shown in Tab 3 Faster step and higher current increase will result in filament deformation 16 Ta filament life Current step Total time 0 25A 245sec gt 12min 0 33A in the 0 2A range gt 30sec gt 3min 0 25A in the 2 5A range gt 30sec 24min Tab 3 Filament turning on procedure parameters The typical working condition for the supplied filament are current in the 3 8 4 4A range typically 4 A maximum 4 7A applied voltage depends on the filament life As you can see from Fig 12 after several hundreds of working hours there will be an increase in the filament resistance i e an increase in Vr t
25. mA or at 1000V and 10mA Remember you are using a real effusion cell so the beam monitor can not be used as there are no charged particles in the evaporated material flux 28 8 Some practical suggestions The TriCon source is an advanced evaporating source evaporating procedures are different from those of a conventional diode source maybe easier but surely different Some brief suggestions for a correct use will therefore be given to summarize the procedures explained in this manual e To insert the evaporating material the Ta shield and the stainless steel cap must be removed and repositioned after the filling operation with a careful check of the electrodes zone see Par 4 5 e After evaporating material mounting always set the rod in the correct position see Par 5 3 and control the position of the Ta diaphragm e Crucible mounting usually requires grid removal see Par 5 2 and Fig 10 e Beware of irregular or large rods do not fill the whole crucible volume Par 5 e Perform the necessary controls before the TriCon source installation on the UHV chamber see Par 3 e Minimum UHV system pressure required 10 mbar Never turn on the filament or give tension to the electrodes if the pressure is higher then 2x10 mbar e Follow the filament turning on procedure see Par 4 3 e Perform a source degassing before and after the UHV system bakeout see Par 6 Be careful whilst reaching temperature close to the materia
26. mechanical fiting among the 4mm Z central anode rod and the HV electrical feedthrough mounted on the CF16 flange is necessary to allow anode centering and electrical contact without stress transfer to the main external ceramic The source is provided with a three point centering system located in the VESPEL cylinder three M3 grains 120 spaced are transversally screwed into and can touch the central anode Observing the anode from the top of the source screw and unscrew the three grains until the correct axial position of the evaporating material tip is found i e when the anode tip is at the center of the Ta shield Sometimes only two of the three grains have to be moved to reach the correct central location Five M3 grains are present on the VESPEL cylinder but two are used to hold the insulating cylinder on the Mo tube The three grains necessary for anode centering can be easily distinguished from the other two observing Fig 14 Do not tighten firmly the three grains on the central anode otherwise the anode itself will be blocked and the linear motion could be damaged due to the strong mechanical strains the anode must be free to move for the whole evaporating material length Verify that the anode position is correct within 0 5mm of lateral movement for the whole length use the linear motion feedthrough If the evaporating material is in form of irregular rocks avoid electrical shorts among the HV anode and the Mo tube In case of cruc
27. nden ITI EUR RH eth e imde UNE 7 See Installation s ssccsessssscessicsoorsssoecsnesssesccsssesooooesceesnsssesocooossoonessss cobres ooessooecsboessesocs OLTRE eed ceshe ssoss 12 3 1 Source substrate distance and beam divergence A eneen Ce eae 13 3 2 Electrical connections 3o dente e edet abe toit tekent bola edet ario e pui e iedereens 15 4 Common Procedures cete ee Ud RON PEREEEUFOR EGRE REED UA I vase cae EN UE seses o EON AP ERR NUN SERA 16 4 15 oS Carts conditons eeens Oboe de eha ertsen ton idet essc pet DN ERAN 16 DR Ege m M 16 43 Turnie on the hot filament ono ee epo t een ele au Gels 16 44 Zo Zero level Conditions 7 4 o aee cce eeu 18 4 5 Inspection of the evaporation zone removing the stainless steel cap 18 4 6 Evaporatmg material cooling down iiie etel reioc Ged eae 19 5 Evaporating material mounting sos ees retener eroe enean Pone Pi So Pede Pa Ee oe ern YE Eee a anra e e rh Fee PE e dera n 20 SX nm M 20 SE iD arne 21 5 3 Anode positioning and centering i55 uoc det RE EIE aandere PARIS NUR DRUNK dco esi ue ee feed ads 21 6 De gassing proc dure sisaiicesccnsdessiccdsesiscacdisnssvcecussatedesssarddcudins sdessanssecsevendsidesincssseonsssartalecseseds 23 6 I Pilamentdegassrmg me Een ee 23 OA WTAE AS SUI sce ica iG cass sa Snc a eens M Ee 24 6 3 Anode degassing asresten
28. o obtain the desired Ir see Fig 12 Remember rarely you will need Ir values higher than 4 3A for your evaporations Ta 0 25mm filament characteristics 5 O New filament ie ge 4 1000 hours d E m 4 amp 3 Q x 5 gt oO 2 1 Vr V 0 fi L fi fi L fi 0 1 2 3 4 Voltage V Fig 12 Current voltage characteristic for the Ta 20 25mm filament new and after 1000 working hours The region where thermionic emission occur is shown in the inset 17 4 4 Zo Zero level conditions One of the main feature of the TriCon source is the possibility to obtain evaporation always in the same working condition see Par 1 1 Moreover in case of evaporation from rod it is possible a direct and precise evaluation of the anode consumption during evaporation When an evaporating material rod is mounted its tip must be positioned by means of the linear motion feedthrough at the grid level i e with the evaporating material tip just outside 0 5mm of the Ta foil cylindrical shield on the top of the Mo central cylinder see Fig 2 and Fig 10 When the source is in UHV conditions anode position reproducibility can be performed by measuring the operation parameters Ic I4 in well defined working conditions and or before any evaporating operations For example e Iy 4 10A or the filament current used in your evaporation experiment e VG 40V 50V or lower in case of low anode power required
29. oling cell double sided CF35 flange from the main source flange To perform this the Ta shield diaphragm and the stainless steel cap have to be removed from the stainless steel shroud 1 Put the shutter in the open position and unscrew the two M2 grains in order to loosen it from the mechanical arm stainless steel rod 1mm 2 18 2 remove the two M2 nuts they are tightened on two M2 grains with two M2 washers holding the Ta shield now gently remove the Ta shield together with the Ta diaphragm it is not necessary to remove it from the Ta shield 3 remove the third M2 nut and its washer that holds the stainless steel cap 4 displace the Imm mechanical arm from the shutter 5 dislodge the cap from the cooling shroud the three M2 grains will remain tightened on the shroud itself Now the evaporation zone can be seen with the grid over the filament the internal Ta cylinder with the evaporating material and material holder inside of it After the required operations reinstate the source cap on the cooling shroud and tighten the M2 nut the one opposite to the shutter mechanism Insert the mechanical arm in the proper shutter hole and position the Ta shield on the cap tightening the two M2 nuts Tighten the two M2 grains on the shutter when the shutter is closed it must be parallel to the Ta diaphragm and far 1mm from this one Be careful if the shutter touches the Ta diaphragm the linear motion for its movement will
30. ons due to the high electrical field created by the grid in the filament region e high anode current even at low filament temperature 2200 2300K and low anode voltage 600 1200V e high electrical field uniformity inside the source good electrons distribution on the anode surface e fine tuning of the anode current once the filament power i e temperature and the anode voltage are set the anode current power is regulated by variations of the positive grid voltage The precision is higher than in conventional electron bombardment sources with the possibility to work very close to the material melting point with higher evaporation rates the anode current reduction due to its length reduction is counterbalanced by a grid voltage increase it is possible to work with the same evaporating condition up to a reduction of 1 5 2mm of the anode length anode power stability means evaporating rate stability it is possible to maintain this last constant just by variation of the grid voltage without changing anything else the anode length can be easily monitored when the source is in situ with a precision of 0 2mm superior reliability and reproducibility of the performances higher and easier to obtain than in the conventional diode sources evaporation from crucible it acts as a real Knudsen cell material evaporation is obtained by crucible walls heating due to electron bombardment of its external surfaces Evap
31. or the thickness monitor some parameters have to be known If the distance L between the substrate and the top of the source i e the shutter or the Ta diaphragm is known R L 30 mm if the distance between the UHV chamber CF35 flange and the substrate is Lo R L2 90 mm A typical working distance is R 100mm For what concern the beam divergence it depends on the hole diameter of the Ta diaphragm see Tab 2 In case of evaporation from crucible the TriCon source inclination can lead to different results from those reported in Tab 2 Ta diaphragm hole Z mm Beam divergence 1 0 9 1 9 2 8 4 7 2 3 4 3 8 5 6 5 7 Tab 2 Beam divergence vs the diameter of the Ta diaphragm hole 13 Anode Filament Grid evaporating material Anode Filament Grid evaporating material Fig 11 Sketch for the electrical connections for the normal a and internal wall degassing b working condition Vr Ir filament low voltage power supply Vg Ic grid 250V power supply V A IA anode evaporating material HV power supply The ground symbol refers to the UHV chamber ground 14 3 2 Electrical connections In Fig 11a are described the electrical connections between the power supply and the source electrodes all the power supply negative connections are referred to the chamber ground level The use of the TriCon power supply is strongly recommended to ens
32. oration from semiconductors and insulating material too can be obtained Olron 1mm rod V 1000V Evaporation rate A min 5 3W Tip melting Evaporation rate A min 4 5 5 0 14 16 18 20 22 Anode power W Anode power W Fig 3 Evaporation rates source substrate distance of 10cm vs anode power for a 1 mm Fe rod 1000V anode voltage a 2 mm V rod 1200V anode voltage An additional power supply 250V 50mA is necessary with respect to the diode like sources The power dissipated by the grid is usually low 4W even at the higher voltages so degassing and heat irradiation from the grid can be disregarded The TriCon concept has been inserted into a complete source designing shown and described hereafter The whole project has been developed and supported in 1997 1998 by INFM Istituto Nazionale di Fisica della Materia at the Physics Department of the University of Modena Italy O Silicon crucible A Germanium EE V 471500V crucible V 1200V 40 30 I A I A 20 10 Evaporation rate A min Evaporation rate A min 40 60 14 16 18 20 22 Anode power W Anode power W Fig 4 Evaporation rates source substrate distance of 10cm vs anode power for crucible filled with a Si b Ge 1 2 Performances Evaporation have been obtained from several materials as shown in Tab 1 Evaporation rates depends on the material thermal properties and on the source substrate distance dat
33. pe as rocks in this case absolutely avoid contacts between the material itself and the Mo tube whose internal diameter is 8mm Avoid material pieces with external dimension that are larger than 3x3 mm or with strong longitudinal deformations it could be even impossible to center the anode for the whole material length Minimum and maximum lengths for rod or rocks are 5mm and 55mm Remember that the maximum anode linear excursion is 50mm See the scale on the metal plate on the air side of the TriCon source 5 2 Crucible The crucible is shaped in order to be positioned on the molybdenum 2mm material holder If the used crucible has an outside diameter of 9mm or higher the grid must be removed to avoid shorts among the grid itself and the HV anode However it is strongly recommended to always remove the grid when using the crucible contact 2M Strumenti service for further information To remove the grid first unscrew with an allen key the M2 grain which holds the grid molybdenum electrode stainless steel barrel system on the electrical feedthrough then gently take away the whole from the white MACOR cylinder and remove it from the top of the cooling shroud avoiding contacts among grid and the filament Put the grid assembly in a safe place Remove the tantalum cylinder inserted on the top of the molybdenum central tube there is a tight mechanical fitting among the two tubes so extraction have to be done firmly This operation is alw
34. rmal equilibrium Set Ip 3 8A Va 200V the grid is usually not present so leave the Vg value to zero or to about 20V if grid is present Increase slowly the anode voltage up to about 500 600V where the anode current is about 70 80 of the maximum current at the highest anode voltage 3000V So you can evaluate the anode power that can be obtained if Va gt 600V if the anode current is insufficient set again Va 200V and increase the filament current by 0 1A then reach the V 600V 27 value to evaluate the power increase Take care when material melting has to be reached as it will cause a strong pressure increase After having reached the requested anode power i e crucible temperature wait at least for 5 10 minutes to reach a reliable working condition from the point of view of the crucible temperature Depending on the evaporating material and its state and or quantity the evaporation rate can vary to maintain it constant just maintain the anode power constant itself acting on Ip and or Va Usually the power is constant without needing of further adjustment if large power variations or high I4 instability occur it means something is not working in the ideal condition e g some melted material is falling down from the crucible The same evaporation rate can be reached at the same anode power provided the anode voltage is the same or within 20 otherwise strong differences are possible if e g 10W are obtained at 500V and 20
35. source air side a and b vacuum side are put in evidence Fig 6 The TriCon source with the two parts not assembled the CF35 main flange a and the CF35 double sided flange with the cooling shroud b Shutter motion CF35 flange Fig 7 Sketch of the rear view source air side view to show the pins for electrical connections on the main CF35 flange The HV anode feedthrough is mounted on a CF16 flange at the bottom of the linear motion feedthrough not shown here MACOR cylinder Stainless steel connectors Mo central tube VESPEL a cylinder Mo electrodes Fig 8 UVH side of the main CF35 flange assembly a with an expanded view of the electrodes zone b The source is composed of two parts Fig 6 i e two CF35 flange assemblies that must be mounted together by means of special studs 1 the motion and electrical feedthrough CF35 flange the main flange see Fig 5a On the air side it is composed of see also Fig 6a a the 5cm UHV linear movement located on the main source axis with an edge welded bellow and a millimetric scale located on a stainless steel plate the movement is obtained 2 by means of a M6 screw on which is mounted a M8 hexagonal nut Remember 1 complete turn lmm movement counterclockwise rotation anode insertion clockwise rotation anode extraction b the High Voltage HV feedthrough on a CF16 flange located at the source bottom on the CF16 flang
36. ssure and do not use anode voltages higher than 1000V when pressure is in the 10 mbar range Moreover in case of strong pressure increase degassing time have to be prolonged and intermediate stages at increasing power are necessary a complete degassing procedure can request from 12 to 24 hours or more depending also on the pumping system of the UHV chamber Before starting read Par 4 1 and see Fig 11a and b for electrical connections Blow away the water from the cooling shroud to avoid formation of high pressure high temperature water vapor inside of it Moreover take into account that the source external parts can easily reach a temperature of about 70 C on the main flange be careful while touching it Open the shutter before any degassing operation After that wait several hours before closing the shutter or starting using the source for evaporation 6 1 Filament degassing See Par 4 3 for filament turning on During this operation the pressures can rise up to 10 mbar If the filament is new reach a current Ip 4 5A If the filament is not new just reach the current that will be needed for normal evaporation there is no need to exceed it 23 Typical time required for the filament degassing is 30 60 min After that you will not observe a pressure reduction as both grid and walls have been heated by radiation in the meantime 6 2 Grid degassing After the filament degassing set Vg 20V Va 100V Ir 4 1A then in
37. take note of the Va I and Vg Ic values when starting an evaporation session When Vg is 80 100 greater than the original value e g V changed from 80V to 140 160V it is 26 due to an anode length reduction of about 1 2mm or higher so the anode must be repositioned by means of the 50mm motion feedthrough to set the tip in the right position see Par 4 4 Decrease Vg of about 30 and insert the anode until I reaches the desired value Perform this procedure until the original Va value 2V has been reached Do not perform this procedure with anode power close to the tip melting point Reposition the anode only if the grid voltage is 80976 10040 higher than the original value Nichel 2mm rod 10W 1kV 3 0 85 gt 2 5 TriCon substrate distance 4 7 cm ot 2 0 480 gt E 15 a 4 e 2 gt E 1 0 75 t o zI 2 Oo Ss ie J EDS LE Dep film 192 74 1 61 min 0 0 L Lil S L Lo Lp od LO N L 70 20 40 60 80 100 120 Time min Fig 15 Evaporation rate left axis from a Ni 2mm rod vs time it is maintained constant 1 6 0 1 A min by variation of the grid voltage right axis for a total time of two hours 7 3 Evaporation from crucible This crucible is acting like a Knudsen cell that is the material evaporation is obtained by heating the crucible and not by direct electron bombardment of the evaporating material The desired temperature must be reached slowly to reach a good the
38. ure safe and reliable operations In case of use of different power supplies always respect the shown electrical connections Electrical connections shown in Fig 11a are those for normal operation and for the filament grid and anode degassing grid power supply switch in NORMAL while those shown in Fig 11b are for the case of internal walls degassing grid power supply switch in DEGASSING as described also in Par 6 4 15 4 Common procedures The hint of this paragraph is to describe some operations that are common for several working procedures as well as to give suggestions that are useful in most of practical situation 4 1 Starting conditions Before every operations check connections between the source and on the power supply Turn all potentiometers fully counterclockwise The UHV system pressure must be in the 10 mbar range or lower never turn on the filament or give voltage to the electrodes when the source is in air 4 2 Water cooling Check the presence of a water flow If evaporation has to be performed be sure the water flow is cooling the shroud from at least 15 minutes If degassing has to be performed water has to be blown out from the cooling circuit as well as connecting tubes have to be removed A water flux of 0 5 l min is sufficient for a good cooling action the maximum water pressure is related to the type of water connections chosen 4 3 Turning on the hot filament The supplied fi
39. y screwed on the cooling shroud flange carefully insert the shutter mechanical arm into the central hole of the cooling shroud and do not touch internal electrodes with the stainless steel cylinder Then fix the two flanges by means of six M6 nuts and tighten them gently to avoid possible damaging to the electrical feedthroughs perform a stronger tightening when the source has already been inserted into the UHV system See Par 4 5 for complete source mounting stainless steel cap Ta shield and diaphragm shutter 11 3 Installation The source mounting on a UHV system requires the presence of a CF35 flange with not threaded holes and standard internal diameter requirements use M6 nuts do not use M6 plates Depending on the evaporation material type and form care must be taken in positioning the source e g vertical or off vertical downward or upward facing Evaporation from rod If a rod is installed in the source the device can be mounted in every position vertical upward or downward or horizontal In case of vertical mounting with the source pointing downward more care must be taken to avoid evaporating material tip melting with possible drop falling outside from the source or inside it Evaporation from crucible In case of the presence of a crucible a horizontal mounting will produce a material fall out from the source so a minimum inclination of about 10 20 upward should be used The source is fixed by me
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