Thin Film Deposition & Vacuum Technology
Contents
1. Cold trap with coolant reservoir Sorption trap mee iii Throttling Safety shut off valve ma Modes of operation Vacuum chambers Manual operation Variable leak valve Vacuum chamber Electromagnetic operation Vacuum bell jar PO Hydraulic or pneumatic operation Shut off devices Electric motor drive Weight operated XK XO Xa Xe YA yA Shut off device general Shut off valve straight through valve Connections and piping Right angle valve SIE Flange connection general Stop cock Three way stop cock CRI XIX Small flange connection Table XVI Symbols used in vacuum technology extract from DIN 28401 continuation 51 J Bolted flange connection Clamped flange connection Threaded tube connection Ball and socket joint Spigot and socket joint Taper ground joint connection Intersection of two lines with connection Intersection of two lines without connection HH TYH Branch off point IE ici Combination of ducts Flexible connection e g bellows flexible tubing Linear motion leadthrough flange mounted lr Linear motion leadthrough without flange 4 r Leadthrough for transmission of rotary and linear motion sl dl Rotary transmission leadthrough Electric current leadthrough Table XVI Sy2. Figure 2 10 Substrate holder design the deposition source they often chipped and damaged the slides The remedy to this problem was to design a new holding system seen in figure 2 10 and switch the substrate from float glass slides to round mineral watch glass A lathe was used to craft the designed holder from Al and it was secured in place inside the vacuum using 4i inch steel bolts mounted seated on a 6 inch blank flange on the top of the chamber The design and implementation steps for the vacuum and deposition systems represent a substantial fraction of my thesis work However to fully comprehend the impact these developments made on the respective systems a deeper explanation of each individual piece of equipment is given in the next chapter 20 Chapter 3 Procedures amp Documentation 3 1 Equipment Documentation Purchasing equipment is an important aspect of all experimental physics research For further information regarding part numbers or companies from which equipment was purchased refer to appendix C The parts purchased for this project are detailed in this section 3 1 1 Silicon Heating Tape The purpose of the silicon heating tape is strictly for vacuum bakeout Capable of heating the chamber to 120 C the heat tape is primarily designed to reduce the water vapor content of the vacuum chamber Heating the chamber walls with the tape gives the sorbed or adhered water on the stainless steel the energy n
3. industry One of the most important applications of vacuum systems is the development of thin films Physical vapor deposition PVD is just one method of producing thin films Michael Faraday pioneered the first PVD process in the early 1800 s I Many sub processes fall under the description of PVD including electron beam sputtering thermal and plasma arc deposition methods At BYU Idaho the method used to produce thin films is a thermal evaporative deposition Thermal evaporation deposition is the most basic method used to produce thin films The first use of the term PVD was used in C F Powell J H Oxley and J M Blocher Jr s book Vacuum Coatings in 1966 3 They were not the first to use PVD methods for developing thin coatings either but their text helped to establish and clarify the PVD processes that were known by that time Since Powell Oxley and Blocher s publication scientists have devised many new methods for growing films Recent developments in the past few decades have produced methods capable of growing alloy films and processes suitable for large scale production in order to better meet the demands of consumers Today s society overlooks the importance of vacuum coatings in products they use The semiconductor industry relies heavily on thin film technology to produce flash memory and computer chips Companies developing optical products often use optical polarizers and beam splitters in their designs Other
4. Foundations of Vacuum Coating Technology William Andrew Publishing Noyes 2003 4 John F O Hanlon A User s Guide to Vacuum Technology John Wiley amp Sons Inc 3rd edition 2003 5 Wake Forest University Vacuum evaporation PDF Mar 2012 URL http users wfu edu ucerkb Nan242 L06 Vacuum Evaporation pdf 6 Problem Solving Problems Inc O ring and seal failure online URL http www pspglobal com abrasion html 7 D M Mattox Handbook of Physical Vapor Deposition PVD Processing William Andrew Publishing Noyes 1st edition 1998 8 Robert C Weast editor Handbook of Chemistry and Physics CRC Press Inc 66th edition 1985 9 Accuratus Ceramic materials character online URL http accuratus com materials html 38 10 Stanford Research Systems Quartz crystal microbalance theory and calibration PDF URL http www thinksrs com downloads PDFs ApplicationNotes QCMTheoryapp pdf 11 M A Herman H Sitter and W Richter Epitary Physical Principles and Technical Implementation Springer Verlag 2010 12 R F Bunshah Handbook of Hard Coatings Norwich N Y Noyes Publications and Park Ridge N J William Andrew Pub 2001 13 Jonathan Stolk Materials guide for thermal evaporation online Jan 2012 URL http www lesker com newweb menu_depositionmaterials cfm section MDtable 14 Dr Walter Umrath Fundamentals of vacuum technology Technical report Oerlikon L
5. We tried tungsten baskets and alumina coated tungsten baskets as suggest by the tables in appendix A and both kept melting see figure 2 6 The baskets kept breaking at the same spot along the wire so we began investigating the use of a stranded tungsten basket that holds a crucible which has proven to be hardier than the smaller baskets 15 Figure 2 6 Broken tungsten baskets An exploration of the theory behind Joule heating revealed the baskets were breaking because of the wire s small diameter Joule proposed that the heat lost by a wire filament with a known resistance and current passing through it is proportional to I R where R represents the resistance In our case we assumed all of the power P was lost in the form of heat through the filament Thus we approximate that P I R 2 3 Incorporating the definition of resistance which is R da where p is the resistivity of the material l is the length and Aes is the cross sectional area we end up with P Ip 2 4 Aes Using this equation in conjunction with values found in the CRC Handbook for the emissivity of tungsten 8 and the Stefan Boltzman law P oeAT 2 5 16 1 nr s 4 M Figure 2 7 Broken quartz crucibles where c is the Stefan Boltzman constant e is the emissivity A is the surface area of the black body and T is the temperature yields 2 T I lp a ie 2 T 218 This equation can then be used to approxima
6. le i Calcium Ca 839 E 1154 272 357 459 w w w Corrodes in air Carbon C 3652 S 1821 1657 1867 2137 E beam preferred Arc evaporation Poor film adhesion Cerium Ce 798 6 70 970 1150 1380 Ta W W Ta Cesium Cs 28 188 16 22 80 ss Chiolote NasAlsF w 290 800 Mo W nz 133 Chromium Cr 1857 Ss 720 837 977 1157 w w Films very adherent High rates possible Cobalt Co 1495 8 90 850 990 1200 W Nb w Alloys with refractory metals Adhesion poor Use interlayer Cr Evaporates using any Copper Cu 1083 892 727 857 1017 Mo W W jui Dysprosium Dy 1412 8 55 625 750 900 Ta Erbium Er 1529 Ss 9 07 650 775 930 W Ta 40 Europium Eu 822 s 524 m a 480 WTa Low tantalum solubility Gadolinium Gd 1313 790 1175 Ta gh tantalum solubility E EE EE EE seen Aloys with refractory metals Use E beam g 535 1167 Excellent films from E beam guns 19 32 807 kai DC RF Films soft not very adherent EME EE 2250 EZEXERH Ta w Use fine wire wrapped on tungsten Low rate required for ws IE IE w sot ans 487 597 W__ Wets tungsten and copper Use molybdenum liner 28 1850 2080 20 Ww Attacks tungsten Films hard smooth Preheat gently to a w Lanthanum La e Films will bum in air if scraped i i He M on Lithium L
7. 1 end Temperature m function T T u Temperature C V The purpose of this function is to calculate the Temperature and its uncertainty for a black body with a given emissivity eps This is done using a combination of Joule s power relation for resistive sheating and Ohm s law for resistors This function assumes an uncertainty in the voltage and current of 0 SA V respectively sig 5 67 10 8 Stefan Boltzmann constant 53 eps 0 41 Semissivity of W between 1700 2500 degree C eps u 0 05 Sthe rough uncertainty of the emissivity 0 00005141 Scrucible surface area _u 0 00000025 Suncertainty in the surface area u 0 1 Suncertainty in current u 0 1 Suncertainty in voltage There is a constant term in the partial derivative of T dT cons 1 4 C V sig eps A 3 4 oo Calculating T T C V sig eps A 1 4 Calculating the uncertainty in T Tu sqrt C u 2 dT cons V s ig eps A 2 Scurrent term V u 2 dT cons C sig eps A 2 voltage term eps u 2 dT cons C V sig eps 2 A 2 semissivity A_u 2 dT cons C V sig eps A 2 2 Sarea term end Vapor m function Pp Pp_u Vapor T T_u This function is designed to calculate th xperimental vapor pressure and its associated uncertainties due to heated Al at a given temperature as given by Wake Forest University s lab report Calculat
8. 25 flange can remain sealed The best practice for keeping a vacuum clean is to avoid putting anything in it that would contaminate its surfaces 2 2 Deposition System Design 2 2 1 The Original Experiment Designing a deposition system is remarkably difficult Knowing the difficulty it is understandable that flashing metal wire created the first films Essentially flashing or flash evaporation occurs when you run a high current through a wire so that it sublimates The original flashing experiment at BYU Idaho used a nickel silver alloy 14 Figure 2 5 Various boats and baskets wire wrapped around a tungsten wire Unfortunately during the flashing the tungsten sublimated and created a nonhomogeneous film on the glass substrate instead of the nickel silver Research done by Phillip Scott helped improve this process by exploring the use of boats and baskets see figures 2 5 and 2 6 In addition gradual Joule heating became the method for heating the deposition material With these improvements came an added ability to control the deposition process but there were still problems with homogeneity and sustainability 2 2 2 New Crucibles amp Improved Temperature Calculations Because of these improvements and a need for more uniform films for another research project we began developing films and to determine their thickness experimentally see chapter 4 Initially things went well but the baskets kept melting during use
9. RGA and single high voltage electrical feedthrough The current design can be seen in figure 2 1 While these are sufficient to achieve pressures suitable for PVD there is always room for improvement Vacuum Gauge Controller Vent Valve Viewport Vacuum Chamber Dry Nitrogen Gas Tank Type C Thermocouple Electrical Feedthrough Isolation Valve Figure 2 1 BYU Idaho Vacuum system The goal that drives development of the vacuum system is that of achieving the lowest base pressure possible It is far more difficult to achieve an ultra high vacuum than it is to reach a low vacuum Fortunately the oil diffusion pump that is used has a very high throughput rate of about 2 000 L s This makes it possible to achieve pressures as low as 1078 Torr with the current pump configuration Despite this advantage other elements of the system do more to limit the achievable pressure than the pump 2 1 2 Using a Viton Gasket A pitfall of the current design is lack of smaller ports to transfer materials in and out of the chamber The system has a cylindrical design with feedthrough ports along the sidewall and the chamber separates above the feedthroughs with a 25 outer diameter OD conflat flange CF this can be seen in figure 2 2 The Viton 10 Figure 2 2 25 OD CF Flange O ring that is used however makes this flange a possible source of significant leaking If a metal gasket and the secur
10. The in vacuum microdot cable was purchased separately All parts can be purchased directly from the company Description Part No Cost 6 Mhz Gold Coated Sensor Crystals 10pk 500 117 67 00 Vacuum Feedthrough 500 017 491 00 Single Head Sensor 500 042 375 00 Oscillator amp Transducer STM 2 500 408 620 00 30 Microdot Cable 500 024 80 00 10 Vacuum Microdot Cable 500 023 N A Notes The microdot cable shouldn t be further than 30 from the sensor head while using the STM 2 Despite this we ve tried to see if the STM 2 will still work with our 30 microdot cable Preliminary findings have yielded no significant results because the power supply couldn t heat the material to a temperature that a substantial deposition rate could be detected Additionally the water cooling for the sensor head should be used in the future to reduce noise and improve accuracy Power Supplies Several power supplies were used for thin film deposition at BYU Idaho but the only one purchased during my research was from TDK The website url that the technical details can be found at is http www us tdk lambda com hp productitml genh htm 45 Description Part No Cost 12 5V 60A Power Supply GENH 12 5 60 1890 00 Note s We purchased the additional USB option Viton O ring Viton is used because of its low permeation rate at low pressures and because it is resistant to m
11. add two more 18 AWG wires in parallel with my first 18 AWG wire In this case though I should note that my resistivty meter coefficients are different for this case I ll assume that the 18 gauge wire is hot 75 degrees Celsius amp the 10 gauge wire is still 750 degrees Celsius R10 1 117 304 8 R18 7 765 304 8 Current 39 0 Pow 237 9 Current 2 R10 Length1 1 3 Current 2 3 R18 Length2 Pow This means I m losing roughly 14 watts at full power which is roughly 6 of my total power input Not a surprising amount but I could use those extra 14 watts R wlength rconst rconst 304 8 wlength cmax 42 56 Manipulate Plot current 2 R l Length AWG10R 1 Wireswcurrent 2 Wires R Length AWG18R current 1 cmax AxesLabel Input Current AJ Power Loss W Frame True GridLines xpoint ypoint GridLinesStyle Directive Orange Dashed Wires 1 5 1 Length 0 1 2 AWG10R 0 9989 1 117 1 215 AWGI8R 6 385 7 138 7 765 xpoint 0 cmax 0 1 ypoint 0 200 01 wires 1 ann Length 05 a07 AWGIOR 0 9989 ETI7 1 215 AWGIBR 6 385 7 138 7 765 xpoint la E ann ypoint ss Blow Power Loss IF 57
12. industries also use thin film technology most of which is for cosmetic purposes such as mirrors and toys 1 2 Review of Theory At this point an in depth exploration of gas flow regimes will not be discussed but if the reader is interested they would benefit greatly from reading O Hanlon s A User s Guide to Vacuum Technology 4 Film quality and vacuum system pressure are inseparably connected Uniformity and purity are the main elements in determining a film s quality Uniformity is an issue that was not addressed during the development of the BYU Idaho deposition system Getting the system to function properly is a prerequisite to tasks concerning the film uniformity The purity of the material prior to deposition is the largest factor in determining the films purity The second biggest factor is most likely the gas composition and pressure of the system in which the film was developed Vacuum technicians know that these two elements of a vacuum system are difficult to control At BYU Idaho we focus on trying to analyze these factors rather than control them at the present time To analyze the gas composition in our vacuum system we rely on a 200 AMU residual gas analyzer RGA The RGA is a quadrapole mass spectrometer that can determine the atomic mass of gas molecules in a system by ionizing the particles and measuring the change in voltage of an electrode when the ionized gas collides with it The RGA uses the voltages to then produc
13. of one Realistically the emissivity of tungsten between 1700 and 2500 C is roughly 0 41 8 Using an accurate emissivity doesn t change the outcome of the early experiment 30 The uncertainty in the temperature calculations was the biggest factor affecting the deposition rate calculations Initial temperature calculations had an uncertainty of 75 C Improving the accuracy of temperature calculations may make this method reasonable Calculating the uncertainties associated with the composition of equations is a mathematical mess MATLAB code for analyzing the data and determining the x2 value is in appendix F This code accounts for the effects of slide outgassing while in vacuum by adding an empirically calculated amount as well as a coefficient for the black body emissivity and its related uncertainty The data from the experiment indicates that our model is far from accurate Data from eleven slides was analyzed to compare the theoretical deposition rate under the given conditions and deposition time to the experimentally calculated rate The reduced x value was around 3 3 x 107 This alludes to the inadequacy of the tested model in calculating the deposition rate of Al vapor Despite the results the experiment was useful in determining several areas of improvement for the deposition system and the process used for calculating rates 4 2 Effects of Slide Outgassing After measuring a post deposition slide mass that was less
14. quality This is known as film tribology The other side emphasizes applying methods for ensuring the desired film characteristics during deposition Film tribology requires additional equipment that we currently don t own Using this equipment characteristics of films such as adhesion hardness and homogeneity can be determined Some of the tribology methods are also an effective 35 at determining film thickness after deposition Students wanting to learn more about film tribology would find the Handbook of Hard Coatings helpful in their research 12 This book also contains ample information regarding many CVD and PVD methods and their theory An important step in building a quality deposition system is implementing preventative methods Better substrate preparation is one item requiring more attention and something that would definitely improve the film quality Typical substrate preparation often involves chemical etching and cleaning prior to deposition followed by heating during and after deposition to anneal the film and or bias the substrate surface These methods would also require new equipment Methods such as e beam or sputter deposition can also provide improved film quality and purity Ample resources regarding the best practices regarding film quality are available in many of the cited texts 5 2 Improved Deposition Rates During the rates experiment we made several questionable approximations to calculate our theoretica
15. 00 4750 00 ThO2Ir Replacement Filament O100RF 200 00 Replacement Ionizer Kit O100RI 450 00 46 For additional help diagnosing problems see http www thinksrs com support RGAsup htm Also the RGA pin diagram from ThinkSRS website is available below Filament Supply and Return pins RGA Pin Diagram Crucibles amp Heating Elements The current basket and crucible combination was purchased from Kurt J Lesker A wide variety of other options are available from their website if you want to try something different Description Part No Cost Stranded Tungsten Basket EVB8A3025W 34 00 Boron Nitride Crucible EVCIBN 34 00 Notes Kurt J Lesker suggests that you only heat their stranded tungsten crucible to 1800 C This is probably more of a precaution for the crucibles themselves rather than the tungsten Additional information about many of the common materials used for crucibles is available at http accuratus com materials html 47 Gas Leak Valve This item was made by Varian but was purchased from Ebay Eguivalent leak valves are sold by Kurt J Lesker and other companies but the cost is significantly greater than those sold on Ebay Description Part No Cost Varian Leak Valve N A 80 00 48 Appendix D Equipment Troubleshooting amp Repair O ring Construction Procedure This step by step process describes the procedure used to constru
16. 00 600 700 800 900 1000 O MELTING POINT In fl n D n n i ILI 1 il Mi I i H IBS HB amp a a a jn i 3000 4000 5000 6000 7000 ANS NE NUE TE Ne NS NE NE MENE ME L Sura i a p HS Nas ES HS UB dd HB S LE EET di gr md i EDU IUS m m it Na KA noa ins nem Wim i s EE MER E E t JE E H E is pr d f ER X puit ITI 1 zd DELL OU EHE TEE dS ce S n HH ul Hi L gt JM PRINCETON N J ES il mE RES HE sem mm Prepored By Richord E Honig RADIO CORPORATION OF AMERICA Temperature Degrees Kelvin HA DH in n A MS AS 200 300 400 500 600 800 1000 A POE Pee o RCA LABORATORIES 50 100 o 50 z i 1 i 6H wu YYOL NI 3YNSSIYA HOdVA aa Y 10 l 44 O MELTING POINT ESTIMATED S SOLID LIQUID 10 200 Appendix C Equipment Purchasing Information Type C Thermocouple Purchased from Kurt J Lesker which can be found online at www lesker com Description Part No Cost Type C CF Feedthrough TFT3CY00003 295 00 Alloy 405 426 Wire FTAWC056 10 00 Note s This is the type C thermocouple wire Quartz Crystal Microbalance QCM Purchased from Sycon Instruments which can be found online at www sycon com The QCM was purchased as a package with the STM2 and the out of vacuum BNC cable
17. 5 amps and then waiting a few minutes for the crucible to reach a thermal equilibrium with the W basket At the desired power output amp temperature turn the mechanical feedthrough clockwise to move the shield out of the way During deposition record the time elapsed power supply settings and the chamber pressure before and during the deposition process When done decrease the current output in the same manner that you increased it you can decrement the current in larger amounts and eventually turn off the power supply Lastly immediately after opening the chamber measure mass of the slide 28 Chapter 4 Thin Film Deposition Rates 4 1 Initial Rate Calculations A simple method for approximating the rate of deposition during deposition is done by weighing the slides pre and post deposition and then calculating the average rate by using equation 4 1 This method is difficult and is prone to many additional factors that don t affect rates calculated by equipment such as a QCM The purchase of the QCM actually came after this experiment failed to determine a realistic rate The rate calculated by the Langmuire Knudsen equation gives the rate in units of grams per square centimeter seconds The experimental rate should look like m Ria T 4 1 The mass m in the equation is the change in mass or the mass of Al deposited of the slide Measuring the slide pre and post deposition is an easy task but the scale used needs to
18. Thin Film Deposition amp Vacuum Technology THIN FILM DEPOSITION amp VACUUM TECHNOLOGY By Stefan Cannon Lofgran A senior thesis submitted to the faculty of Brigham Young University Idaho in partial fulfillment of the requirements for the degree of Bachelor of Science Department of Physics Brigham Young University Idaho April 2013 2013 Stefan Lofgran All Rights Reserved Brigham Young University Idaho Department Approval of a senior thesis submitted by Stefan Cannon Lofgran This thesis has been reviewed by the research committee senior thesis coor dinator and department chair and has been found to be satisfactory Date David Oliphant Advisor Date Ryan Nielson Committee Member Date Stephen McNeil Senior Thesis Coordinator ABSTRACT THIN FILM DEPOSITION amp VACUUM TECHNOLOGY Stefan Cannon Lofgran Department of Physics Bachelor of Science The study and development of thin films via physical vapor deposition has played a significant role in the development of optical coatings semiconduc tors and solar cells Closely related to the study of thin films is the de velopment of vacuum technology and systems capable of reaching pressures suitable for growing uniform films at reasonable deposition rates This paper explores the method of physical vapor deposition known as thermal evapo ration via resistive or Joule heating as a means for growing thin aluminum Al films o
19. and the substrate is the angle normal to the surface of the substrate and crucible r is the distance between the crucible and substrate and P and P are the system pressure and evaporant partial pressure in Torr respectively Another assumption of the Langmuire Knudsen equation is that the evaporant molecules will travel from the crucible where they are heated to the substrate without picking up any other gas particles in the chamber see figure 1 2 Subsequently a decrease in the base pressure of the vacuum will also reduce the number of particles picked up as they flow towards the substrate to be deposited The Langmuire Knudsen equation necessitates the use of other methods and equations to calculate an accurate deposition rate Among these is Stefan Boltzman equation for blackbody radiation P IV ocAT 1 3 where is the electrical power through the crucible J is the current V is the voltage o is the Stefan Boltzman constant e is the emissivity A is the surface area substrate holder mineral glass substrate evaporated material heating element Figure 1 3 Initial deposition system configuration of the black body and T is the temperature Solving for T we find a me 1 4 I also used an experimentally derived equation for determining the partial pressure of liquid AI given by 15993 log P 12 409 0 999 log T 3 52 x 10 9T 1 5 where P is the pressure in T
20. any chemicals Viton A is the standard material used for vacuum system seals A quick google search should provide several companies that are willing to sell Viton A cord stock which you can use to make your own O rings We are still working with a company called Quick Cut Gasket to make us some custom O rings but this process is time consuming and we haven t found a good fit yet When purchasing Viton cord stock make sure you buy stock that has a cross section CS 0 108 inches Heating Tape Purchased from BriskHeat at www briskheat com Description Part No Cost 1 x 96 Silicone Heat Tape BS0101080L 173 65 High Temperature Tape PSAT36A 16 00 Notes The high temperature adhesive tape is made to function up to 80 C but we ve used it past this temperature and it has held the tape in place at around 125 C Mineral Glass Slides Several companies sell mineral glass slides but they don t often refer to them as slides You will find better results for a Google search using the term watch glass Due to the effects of outgassing of the mineral glass it is best that you try and purchase the thinnest slides possible The substrate holder is designed to hold slides that are 1 or 25 4mm in diameter Residual Gas Analyzer RGA Replacement equipment amp more detailed documentation can be found at www thinksrs com Description Part No Cost 200 amu RGA RGA2
21. be capable of measuring differences of milligrams at minimum Calculating the filmed area of the slide required a more creative approach After projecting a filmed slide onto a wall and tracing the filmed area onto grid paper we were able to approximate the deposition area via a scale and the number of filmed squares on the grid paper Figure 4 1 shows a copy of the grid paper where the 29 Figure 4 1 Filmed slide projection shaded sguares represent the filmed area Assuming no angular dependence in the Langmuire Knudsen eguation further simplifies the theoretical model to look like MI y Cr MA PE P 4 2 This justification is acceptable given the crucible is positioned directly beneath and sufficiently far from the substrate 11 An appropriate distance should meet the requirement that the mean free path of molecules in the chamber be much greater than the distance between the crucible and substrate Black body temperature approximations include an emissivity factor relating to the fraction of power that is emitted as radiation For initial calculations we used an emissivity
22. ble of functioning properly under mild baking less than 80 C that should last long enough to order a new O ring 49 Appendix E Vacuum Symbols All symbols wit the exception of those marked with do not depend on the position These symbols may only be used in the position shown here tip of the angle pointing down The symbols for vacuum pumps should always be arranged such that the side with the constriction is allocated to the higher pressure Vacuum pumps Vacuum pump general Ejector vacuum pump Piston vacuum pump Diffusion pump Diaphragm vacuum pump Adsorption pump Rotary positive displacement pump Getter pump E Rotary plunger vacuum pump Sputter ion pump YBOSS E Cryopump Es Sliding vane rotary vacuum pump E Rotary piston vacuum pump Scroll pump E Liquid ring vacuum pump Evaporation pump o E Roots vacuum pump Accessories Turbine vacuum pump general Radial flow vacuum pump Condensate trap general y Axial flow vacuum pump a Condensate trap with heat exchanger e g cooled COO OQ OWOOOOGOVE O Turbomolecular pump U Gas filter general Table XVI Symbols used in vacuum technology extract from DIN 28401 50 Filtering apparatus general Right angle stop cock Baffle general Gate valve Cooled baffle Butterfly valve Cold trap general Nonreturn valve
23. certainty in the difference of mass measurement Calculating the difference in mass pre amp post deposition Post out Pre 9 SExperimental rate calculation Rex M A Time SExperimental rate m Rex u sqrt M u 2 1 A Time 2 mass term s 1 M A Time 2 2 Stime term A u 2 1 M A 2 Time 2 Sarea term end 55 Power Loss Calculator This file should provide an approximate power lost during Joule heating on standard annealed copper wire The purpose of which is to better estimate the power input provided by our power supply in order to better calculate the deposition rate of the material in our vacuum chamber Assumptions For this calculation I m assuming that the temperature of the wire doesn t change The length of the wire is also assumed to be fixed aka no thermal expansion I m also assuming that the gauge of the copper fixture inside the vacuum chamber is negligible As of the moment I m also assuming that the resistivity of my wires per 1000 ft values obtained from CRC F 114 is constant for both my 10 amp 18 AWG wire R10 0 9989 304 8 R18 6 385 304 8 Length1 1 Length2 0 7 Current 23 0 Pow 46 0 Current 2 R10 Length1 R18 Length2 Pow This means that l m losing almost 10 watts of power initially through my wires when I start it up That is about 20 of my power lost through heat to the room Lets see how much I lose when I
24. coming increasingly important within physics due to its several applications The ideal vacuum is a space devoid of all particles All vacuum systems aren t created equal and like many things in physics actual vacuum systems fall short of the ideal The base pressure a system maintains determines the quality of its vacuum These levels aren t strictly defined but are generally described as rough low medium high or ultra high see Table 1 1 The most obvious factors determining the type of vacuum achieved are the equipment used and the system configuration Before delving into the details of vacuum design and its importance in developing thin films it will be beneficial to review a brief history of how vacuum systems were first developed One of the first contributors to vacuum technology was Otto von Guericke Von Guericke developed the first vacuum pump sometime in the 1650 s 2 With his pump he was able to study some of the most basic properties of vacuums Von Guericke believed that his pump pulled the air out of a container which is actually incorrect Vacuum pumps cannot pull the gases out of a container rather they Vacuum Type Low Medium High Pressure Range Torr e Ultra High E 10 en mE Extreme High O Outer Space 1075 Table 1 1 Vacuum quality pressure ranges create a difference in pressure which causes the gas in the high pressure area to move to the low pressure area Essentially a vacuum pump
25. ct a temporary O ring for use with the 25 OD CF Flange of the vacuum chamber Only Viton A cord with a cross section of 0 108 in should be used in the construction of this O ring e First as with any process involving a vacuum system you should put on powder free gloves e Take the old O ring and cut it once so that it forms one long cord e Tape the old O ring to a flat surface in a straight line You may find the straight edge of a meter stick to be helpful in placing the cord in a straight line e Place the new cord stock next to the old O ring with one end of the cord stock flush to one end of the old O ring and tape it down if needed e Next using the razor blade and a squaring tool cut the cord stock perpendicular to the cord so that it is the same length as the old O ring e Then perpendicularly cut a small amount of cord stock about 1mm off the other end of the newly cut Viton cord e At this point in order to ensure a better bond between the cyanoacrylate and the Viton both ends should be cleaned with isopropyl alcohol and allowed 15 20 minutes to dry e Once the alcohol has evaporated off of the Viton you will then place a small drop of cyanoacrylate on one end of the newly cut cord stock and the hold the ends together gently until the cyanoacrylate holds e Gently place the new O ring in a safe location and let it cure for an hour or two before using This method will produce a stable O ring capa
26. e cracking patterns used to determine the gas composition of the chamber see figure 1 1 A substantially low pressure is required to prevent film oxidation and reduce the contaminant density A pressure of 10 Torr is sufficient but lower pressures would help reduce the density of contaminants in the film At 107 Torr the mean free path of gas in the chamber is approximately 8 meters which without the unit of measurement is often referred to as the Knudsen number The mean free path can Figure 1 1 RGA cracking patterns be calculated using the following eguation kgT l nP eu where kg is the Boltzman constant T is the temperature in Kelvin d is the diameter of the molecule in meters and P is the pressure in Pascals As the mean free path of the gas particles increases so does the Knudsen number When the Knudsen number is close to or greater than one gas particles obey principles of free molecular flow more than viscous flow The Langmuire Knudsen equation is founded on the assumption that the molecules follow a molecular flow regime The Langmuire Knudsen equation is M 1 Rm Ci 2 cos sin 9 3 T P 1 2 mol K s Torr where Rm is the rate per unit area of the source Cm 1 85 x 107 a constant M is the gram molecular mass of the deposition material T is the temperature of Figure 1 2 Langmuire Knudsen angle dependence the deposition material 0 is the angle between the normal of the source
27. e the partial pressure Pp 10 15993 T 12 409 0 999 10g10 T 3 52 10 6 T Calculate the uncertainty in the partial pressure SIf y 10 x then dy dx 10 x 1n 10 Pp sqrt T u 2 Pp 1og 10 2 end Knudsen m function R R u Knudsen T T u Pp Pp u P P u This function calculates the deposition rate and its uncertainty using the angular independent form of the Langmuire Knudsen relation Cm 1 85 10 2 a constant term M 26 9815386 gram molecular mass of Al courtesy of Wolfram Alpha 54 r 16 3 Ssource substrate distance in cm r u 0 5 Suncertainty in r Calculate R R Cm sqrt M T 1 r 2 Pp P Calculate the cd ae in R R u sqrt r ed R ES mA ss es Sn CE 2 ie M 2 xu 2 1 2 T term P o PEE Me M p 1 x M SP term s u 2 Cn sqrt M T 1 r 2 SPp term end Experimental m function Rex Rex ul Experimental Pre Post Time This function calculates th xperimental deposition rates This is done assuming the uncertainty in the deposition time to be constant and accounting for slide outgassing by a constant adjustment factor in weight A 2 68 film surface area measure through scale projection method cm 2 A u 0 08 uncertainty in film surface area out 0 0012 outgassing mass adjustment Time u 1 5 a generous uncertainty of 1 5 seconds M u 0 0007 Sun
28. eeded to eventually evacuate the system and thereby reducing the overall contribution to the total pressure from water vapor 21 Length 72 in Power density 4 3 Watts in Note has a high chemical resistance Table 3 1 Silicon Heat Tape Specifications Placing the heat tape flat against the chamber walls during installation provides the best thermal transfer and can prevent hot spots on the tape during use In addition the tape should not overlap itself at any point The installer should be mindful of the proximity of the tape to specific chamber components to prevent damage to sensitive equipment When installing the user should make note to only use high temperature tape to adhere the silicon to the chamber During use a variable transformer in conjunction with the tape will help to control the bakeout temperature of the chamber Correct operation of the heat tape leads to lower base pressures and faster pump down times 3 1 2 Type C Thermocouple Thermocouples are capable of providing accurate temperature measurements both in and out of vacuum A special feedthrough is required in order to use a thermocouple within a vacuum There are several classifications of thermocouples that cover different temperature ranges and have varying accuracies A type C thermocouple is used with the BYU Idaho vacuum system as it is capable of measuring temperatures up to 2300 C By comparing the measured voltage across two differ
29. ent metals to that of a reference voltage a thermocouple can determine the temperature For this process to determine an accurate temperature a cold junction is often required We use this thermocouple in conjunction with power loss calculations to help evaluate consistency of our temperature calculations The approximation provided by the thermocouple will assist future students in determining the melting point of the Al Within the chamber the hot junction is 22 Temperature Range 0 2300 C Positive wire W 5 Re Negative wire W 26 Re Note Made for use in high and ultra high vacuums Table 3 2 Type C thermocouple specifications placed about an inch from the W filament so a correct temperature is read 3 1 3 Quartz Crystal Microbalance The quartz crystal microbalance QCM is one of the more costly purchases made for my research The purpose of the QCM is to measure the deposition rate of material onto the substrate A QCM operates on the piezoelectric principle During use the crystal resonates to a frequency generated by an oscillating circuit Most cut crystals are tuned to resonate to a 6 MHz frequency but as mass is added to the crystal during the deposition process the frequency of oscillation increases as explained by the Saurbrey equation 2 Af Am A Palla 3 1 where A f is the change in frequency m the change in mass A the crystal area fo g cm s the resonant freque
30. eybold Vacuum 2007 39 Appendix A Materials Guide for Thermal Evaporation Adapted from Kurt J Lesker Co Key of Symbols influenced by composition Cr plated rod or stip All metals alumina coated Ex excellent G good F fair P poor S sublimes D decomposes C carbon Gr graphite Q quartz Incl Inconel VC vitreous carbon SS stainless steel Temp C for Given Vap r Press Torr Thermal Sources Comments 10 6 10 4 Boat Coil Basket Formula MP Sublime 1 Symbol C Decompose g cm s and wets Stranded W is best Aluminum 2 au 640 282 Wire feed and flash Difficult from dual sources Sam 2 apusi 640 28 100 _ Wire feed and fash Difficult from dual sources Antimony Sb 630 S 6 68 279 345 425 p o Mo Ta Toxic Evaporates well Barium Ba 725 as sas 627 735 w w Wets witout toying reacts wit ceramics Beryllium Be 1278 1 85 710 878 1000 W Ta W W Wets W Mo Ta Powder and oxides toxic Evaporates easily Bismuth Bi 271 9 80 330 410 520 Mo w w Toxic vapor Resistivity high No shorting of baskets Ta Boron 8 2300 234 1278 1548 1797 C explodes with rapid cooling Forms carbide with container Cadmium Cd 321 864 64 120 180 Mo I Bad for vacuum systems Low sticking coefficient Ta Cadmium Antimonide Cd Sb2 456 L 6 92
31. generates a vacuum by creating pressure differences which creates a flow of gas that exits the chamber at a rate faster than the rate at which gas enters the chamber Aside from Von Guericke there were several other contributors to what is now considered modern vacuum technology Many of these individuals lived before or during the same time as Otto von Guericke Evangelista Torricelli the man who the unit of pressure Torr is named after was one of the first to recognize a sustained vacuum while observing mercury in a long tube He noted his discovery but never actually published his findings because he was more interested in mathematics Hendrik Lorentz Blaise Pascal Christiaan Huygens and others all played crucial roles in defining and developing the fundamental principles upon which modern vacuum systems run Modern vacuum technology is constantly adapting to be used in a broader range of applications in a plethora of disciplines within physics and engineering such as vacuum packaging welding and electron microscopes Even though vacuum technology has developed rapidly since the 1600 s what most would define as modern vacuum technology isn t that old Scientists and engineers developed most of the technology that we use today during and after World War II During the period of development after World War II people began to revisit thin films and explore the possibilities of their uses in industry particularly in the semiconductor
32. i a 0 53 Metal reacts in air _ 1300 Ta W Extremely high rates possible w e 4g 13 55 68 42 olybde Mo 2610 i ee er Films smooth hard Careful degas required E D HE O aaa Nichrome IV Ni Cr 8 50 1217 W Ta Alloys with refractory metals CI E 1 89 AA W Alloys with refractory metals Forms smooth adherent films Eun hec e tae ME rs Niobium Tin Nb3Sn Co evaporate from two sources J Palladium Pa se e W Alloys with refractory metals Rapid evaporation suggested Parylene CsHs Vapor depositable plastic F Film low in nickel mem 5 1 3 Material reacts violently in air n 2 14 HA HE W Alloys with metals Films soft poor adhesion z pi zx Polonium Po mM Radioactive Potassium K Metal reacts rapidly in air Preheat gently to outgas Praseodymium Pr a ei l Rhenium Re E 2053 1928 2207 sn X Fine wire will self evaporate Rhodium Rh 1240 1277 1472 w W E beam gun preferred Rubidium Rb 37 111 Ruthenium Ru 2919 m Us 2260 Samarium Sm EE 5 EN RE Senium Se 1541 Alloys with tantalum Alloys with tungsten use heavy tungsten boat SiO produced Silicon Si 1410 1147 Re ET 4x 10 Torr E best Silver Ag 10 50 847 1105 Ta Mo DC RF Sodium Na Ed EN o 192 Ta yA Preheat gently to outgas Metal reacts quickly in air n 4 22 Bo s E 1410 8 90 p pc P I Tantalum m De za Forms good films Technetium KEN Baffled
33. ing bolts were used this flange wouldn t be a big problem In order to moderate the side effects of using a large Viton gasket it must fit snuggly around the flange Determining the true size of the O ring that best fits the flange is very difficult because small changes in the cut length make the difference between whether it fits snuggly or not The equation for calculating the cut length of an O ring is OD ID Lan 2 1 where OD stands for the outer diameter and ID for the inner diameter which is calculated using D ODIO 2 2 where C is the cross sectional diameter of the cord These equations have been extremely helpful in determining the appropriate dimensions needed to manufacture an O ring 11 Figure 2 3 O ring over compression failure a reference photo 6 b actual O ring In addition to engineering an O ring diagnosing the failure of one is also very important In April 2012 the initial O ring broke due to over compression resulting from too much pressure and high temperatures due to baking A stable fix to this obstacle is still in development After several failed attempts to purchase the correctly sized O ring from manufacturers a temporary solution was achieved with a razor blade and some cyanoacrylate adhesive super glue The details of how we constructed the new O ring is in appendix D Minimizing the over compression and preventing the breaking of the cyanoacrylate bond of a temporary O ring is do
34. l rates A few alternative approximations still exist that may improve results This may lead to practical application in calibrating the QCM and use with films of other materials Analyzing the magnitude of uncertainties of variables in an experiment can be quite revealing of what needs improvement Such is the case with the deposition rates and the variable with the largest uncertainty is the temperature We believe the large uncertainty in the temperature to be related to the significant amount of power that is lost by the load cables Preliminary calculations suggest that the actual voltage across the W basket used to heat the crucible is significantly less than previously believed Incorporating the loss of 36 power during transmission may improve the accuracy and precision of the calculated temperature These projects are just a few of many that would be valuable for future students wanting to work with the BYU Idaho vacuum and deposition systems Excellent opportunities for research still exist for students Unlike the deposition system the vacuum system has limited room for further development without conducting a complete overhaul However this doesn t limit the possibilities for research in any way 37 Bibliography 1 John L Vossen and Werner Kern Thin Film Processes II Boston Academic Press 1991 2 James M Lafferty Vacuum from art to exact science Physics Today 34 11 211 231 1981 3 D M Mattox
35. may crack if the power went out 3 2 1 Pumping to Low Vacuum 1 Turn on the pressure gauge controller and verify that the chamber is pressurized 26 Close all vent or leak valves that connect the chamber or pumps to the atmosphere For the large flange make sure that the Viton O ring fits snuggly in its groove before closing the chamber lid Open the gate valve between the chamber and diffusion pump and the ball valve connecting the roughing pump to the diffusion pump Turn on the roughing pump Wait until the pressure controller for the chamber reads 107 Torr 3 2 2 Pumping to High Vacuum 1 wA 3 4 5 Make sure that the thermocouple gauge for the chamber reads 8 x 107 Torr Turn on the water cooling for the diffusion pump Plug in the diffusion pump and wait until the heating element reaches 170 C Wait another five minutes for the diffusion pump to reach approximately 1075 Torr Turn on the ion gauge and RGA as necessary Procedure for Removing Slides de 10 After turning off the power supply and giving the crucible time to cool proceed with the following steps If the ion gauge or RGA are on turn them off Firmly close the gate valve between the chamber and diffusion pump Confirm that the valve between the chamber and the roughing pump is also closed Vent the chamber Open the chamber retrieve replace the slide place the Viton O ring on the flange and
36. mbols used in vacuum technology extract from DIN 28401 continuation 52 Measurement and gauges General symbol for vacuum Vacuum measurement vacuum gauge head Vacuum gauge operating and display unit for vacuum gauge head Vacuum gauge recording Vacuum gauge with analog measured value display Vacuum gauge with digital measured value display Measurement of throughput Appendix F MATLAB Code for Analyzing Data Rates m function Rates clear clc SUsing the Vapor m Knudsen m and Temperature m files this function calculates the appropriate reduced Chi squared values for the data set SThe column order should be as follows pre weight post weight pressure pressure uncertainty current voltage and time elapsed Data xlsread E Film Calculations RateData xlsx N size Data 1 2 9 Separating the data Pre Data 1 Post Data 2 P Data 3 133 322368 Sconverting from Torr to Pa Pu Data 4 133 322368 C Data 5 V Data 6 m Time Data 7 Calculating theoretical values amp uncertainties T T u Temperature C V Pp Pp u Vapor T T u R R Knudsen T T u Pp Pp u P P u Calculating actual values amp uncertainties Rex Rex u Experimental Pre Post Time Chi sum sum R Rex 2 Rex u 2 Chi reduced Chi N
37. n a mineral glass substrate Methods for measuring thickness are also discussed and investigated in an attempt to determine the experimen tally produced film thickness A detailed explanation of the development and operation of the vacuum system in which the Al films were grown is given as well as future improvements that could be made ill ACKNOWLEDGEMENTS To my loving wife amp family who have supported me the whole way and to David Oliphant who has guided me on this project Table of Contents Page Ru csi eund recor an o dor dosnt dogs e eroe DC 111 E ooo e iv LEA A e A AE aa vii CAMS AT ak PR TN A viii 1 heu xt diea OE D db WL Goede ln dO poet Wo aor d 1 2 Review of Theory 4 2 Experimental Design amp Setup 9 21 Vacuum System Design 2 1 1 Recent Developments 2 1 2 UsingaVitonGasketi 10 2 1 3 Vacuum Conditioningi 12 en 14 2 2 1 The Original Experiment 14 ZEE 15 CAREER Oe OS 17 ARI 18 21 AAA 21 E ah A FOR A A 21 PTT 22 Henri ok domum deo Be de dus 23 TC WAA ee 24 AE eee ee eee E ee 25 3 1 6 Power Supplies 32 Vacuum Procedures 3 2 1 Pumping to Low Vacuum 3 2 2 Pumping to High Vacuum 3 3 Deposition Procedure 4 Thin Film Deposition Rates 4 1 Initial Ra
38. ncy p 2 6482 the density of quartz y 2 947 x 10 the shear modulus of quartz for the crystal Positioning the sensor head on the same spherical wave front as the substrate enables the QCM to provide a reasonable approximation for the rate of deposition To correctly position the sensor head the water cooling lines that support the sensor were bent using a tube bending tool to an angle slightly past 90 C see figure 3 1 In this position the QCM software can be calibrated to provide real time graphs of the rate of deposition and film thickness As of the moment the QCM still needs calibration before it will provide accurate results The calibration of the QCM is a project that future students might be 23 Figure 3 1 Quartz Crystal Microbalance Positioning interested in completing Calibration should be completed prior to collecting data 3 1 4 Residual Gas Analyzer The purpose of a residual gas analyzer RGA is to analyze the gas composition within the vacuum chamber A quick review of how to use the RGA will help prolong its life as all of the repairs for this piece of equipment are costly The RGA should not be operated if the base pressure of the chamber reads a pressure higher than 107 Torr Exposing the hot filament to the atmosphere oxidizes and ruins the filament Second the RGA repeller cage which looks like a miniature Faraday cage covering the filament tends to short with the chamber walls When the repeller cage
39. ne by monitoring baking temperatures via an infrared thermometer Exercising caution in avoiding the temperature limits usually 80 C specified by the manufacturer of the cyanoacrylate will prevent other more serious problems that would ensue if the seal broke 2 1 3 Vacuum Conditioning Vacuum conditioning and upkeep aids in achieving consistent results from in vacuum experiments A vacuum system left alone at atmospheric pressure will require a several days of conditioning prior to use for research due to water vapor build up 7 We condition our vacuum chamber using two techniques The first 12 commonly known as baking reduces outgassing through heating the chamber walls and components The second technique is to backfill the chamber with a dry gas such as argon nitrogen etc which has a molecular scrubbing effect The procedure for conditioning the chamber is found in appendix D Water vapor is the most detrimental molecule in most vacuum systems Because water molecules adsorb easily onto clean surfaces it is difficult to remove them from vacuum systems 7 Removing many of the monolayers of water from the stainless steel walls takes anywhere from several hours to days Accelerating desorption of water molecules is achieved by providing additional energy via heat tape on the outside of the chamber An RGA can characterize desorption of water monolayers during baking see figure 2 5 Note how the partial pressure due t
40. o water vapor gradually decreases over time If this same process was repeated without baking desorption of water would occur more slowly Baking via heating tape is a low cost solution for conditioning a vacuum There are alternatives that are more effective such UV radiation and sputtering with an inert gas 7 In addition to baking the practice of backfilling or refilling a vacuum with a dry gas is another common technique used to clean systems Argon is probably the most common gas used because of its large atomic size which makes it better for sputtering off unwanted molecules from chamber walls However dry nitrogen is a more cost effective alternative that also works fairly well Molecular scrubbing works by adding molecules in this case nitrogen gas which then collide with adsorbed molecules knocking them off so they will be pumped out This is best done near the crossover pressure of the roughing pump and requires the use of a leak vale to precisely control the backfilling of dry nitrogen The crossover pressure is the pressure at which the pump can no longer keep up with the gas load it is under Carrying out both conditioning processes simultaneously yields better results 13 Figure 2 4 RGA P vs T graph than they would separately Implementing additional conditioning methods would show only minimal improvement until a better process for transfering material into and out of the chamber is developed so that the
41. orr and T is the temperature There are of course many other methods capable of deriving the necessary quantities At the time of the initial experiment these were the best approximations available to us but with the addition of a type C thermocouple new vacuum feedthrough and power supply our capability to derive the temperature more accurately has improved Feasible alternatives to approximating the crucible temperature solely by using a blackbody approximation include incorporating power loss transmission calculations and the use of a thermocouple Understanding the fundamentals of vacuum theory can prevent many of the complications that diminish the accuracy and precision of collected data Recognizing the sources of leaks in a vacuum system is one item that is of particular interest for experimentalists A variety of sources lead to unwanted gas added to the chamber by leaks Vacuum leaks are often due to the pressure gradient that exists within a vacuum which creates a surplus of interesting and inimical problems Thus vacuum leaks should be addressed prior to experimentation At a standard temperature and pressure almost everything absorbs water vapor and other gases One factor that affects how much water vapor is absorbed by a material is the humidity Inside a vacuum these materials release the gases they absorbed because the same forces that helped trap gasses in them have diminished As a result preparing materials prior to use in
42. r supply is definitely the 60 amp supply both in features and power output As with any piece of complex equipment it would be wise to study the user manual prior to use Also when using any power supply make sure to use the proper gauge 25 Power Output 750 Watts Maz Current 60 Amps Max Voltage 12 5 Volts Features OVP UVP Foldback amp over temperature protection Table 3 3 Genesys 60 12 5 power supply details for the load cables for the intended power transmission Connecting several load cables in parallel works in a pinch to prevent the wires from overheating Over voltage protection OVP and under voltage protection UVP are features of the Genesys 60 12 5 power supply that allow the user to set a maximum or minimum output voltage respectively Foldback protection is an overload protection feature that lowers the output voltage and current to below normal levels in the event of a short circuit 3 2 Vacuum Procedures As a forewarning neglecting to follow the outlined procedure for use of the vacuum chamber may damage pumps gauges or the chamber itself In almost all cases it is beneficial to leave the chamber in a low vacuum state There is no limit to how long the chamber may remain at low vacuum as the lower pressure helps prevent the sorbtion of water onto the stainless steel walls Leaving the oil diffusion pump on at all times is impractical as the oil takes approximately two hours to cool and
43. shorts with the chamber the software reads noise around 107 Torr Carefully bending the repeller cage may fix the problem If this doesn t work you can check the resistance across the supply and return pins to test if the filament itself is bad 24 For additional resources and details regarding troubleshooting see appendix C 3 1 5 Crucibles Baskets amp Boats Thermal deposition is achievable via a number of tools Boats baskets wires etc provide different ways to heat the deposition material The table in appendix A describes the best tools to use for heating different materials As previously discussed the first baskets frequently broke during use So we switched to a stranded tungsten basked setup Using a wire basket and crucible combination facilitates an easy transition to making films with other materials To avoid cross contamination each element should have its own crucible Knowing the temperature limits of the crucible material will help to prevent breaking or damaging the crucible due to thermal stress Appendix C also provides useful information regarding the properties of the common materials used for crucibles Lastly figure 3 2 contains an illustration of the current W basket Figure 3 2 Crucible amp basket combination 3 1 6 Power Supplies Each power supply that we have used has its own pros and cons We have used or just recently purchased 20 40 and 60 amp power supplies The most capable powe
44. shut the chamber Close the vent valve to the chamber Close the ball valve between the diffusion and roughing pumps This step should be done as quick as possible to prevent the diffusion pump from pressurizing which can result in cracked oil Open the valve between the chamber and the roughing pump Pump down to 107 Torr 21 11 12 13 Open the gate valve and the ball valve Close the valve between the chamber and roughing pump Turn on any gauges as necessary 3 3 Deposition Procedure The deposition process is still under development Some factors such as slide outgassing have been investigated but the effects aren t fully known It is best to clean the slides with methanol or isopropyl alcohol and then let cleaning agent evaporate fully prior to placement in the chamber Recording more data will help future students to better tune this process and improve control over film characteristics Ove oem ak 10 Weigh the glass slide after cleaning and prior to placing it in the chamber While the chamber is open place a few Al pellets in the BN crucible Also position the shield at 55 to cover the substrate After reaching a high vacuum connect the power supply to the feedthrough Turn on the power supply and turn the voltage control all the way up so the power output is dependent on the current control knob Slowly increase the current output This is done by increasing the output by 3
45. side the chamber and considering their impact on the data is an important step in the experimental process All materials will experience some outgassing within a vacuum chamber A judicious selection of materials will reduce the effects of outgassing or leaking of gas from materials that are used For this reason conditioning of the vacuum chamber and if possible all the materials used in the chamber is also an important step of experimentation Chemical cleaning or pre exposure to vacuum pressures are both ways to condition materials for use in vacuum More technical processes such as those used in developing semiconductors have prescribed standard methods for cleaning materials prior to use in vacuum Chapter 2 Experimental Design amp Setup 2 1 Vacuum System Design 2 1 1 Recent Developments BYU Idaho purchased the vacuum chamber pressure gauges roughing pump and residual gas analyzer but received the oil diffusion pump and gate valve as a donation from another university The important details about almost all of the equipment are known However we don t know the material or manufacturer of the O ring used with the chamber Within the past year improvements to the vacuum system have helped to achieve lower pressures more consistently Initially the BYU Idaho vacuum chamber operated with only a couple thermocouple pressure gauges ion pressure gauge oil diffusion pump backed by a rotary vane roughing pump viewport
46. slide than was at first believed 32 Time Interval Days 3 sse ul a3uey a3eJany Figure 4 2 Average change in slide mass over time The initial time interval is the difference between the initial and post outgassing weights The error bars also provide the high and low deviation from the mean change in mass 33 n v je neqeudiv ai epis T IT 6 9 Aeq 8 Z Aeq S Aeg 8 9 eq v ea 3 s Aed e eq 8 v Aea x z Aeq 8 Aea x T Aeg 3 z Aea y 3 sse ul a3ueyo mO 3 T ed m se33nO Jeniul y Figure 4 3 Change in slide mass between consecutive days 34 Chapter 5 Future Experiments amp Summary Fully automating the deposition system is still a long ways down the road This means there is an ample supply of projects left for future students Developing the system will expand the research opportunities for future students enabling them to conduct experiments requiring the use of films Since we are now able to consistently produce films students may want to work on improving film quality and deposition rate calculations In addition it may interest some students to look into alternative deposition methods 5 1 Improving Film Quality There are two sides to improving film quality The first is the ability to recognize and characterize a films
47. source Film structure doubtful wawa Toxic Wets without alloying n 1 002 Terbium ra Ta Thallium 1106 470 W Ta W__ Very toxic Wets freely Thorium 11 70 1430 1660 1925 us W Toxic radioactive E UE NE MEE Tin w Wets molybdenum Use tantalum liner in E beam guns Titanium m ra 2E 19 Alloys with refractory metals evolves gas on first heating Tungst 3410 ga pu 2407 Forms volatile oxides Films hard and adherent umm EVI A BEH IOE3bE3E3 W Fims oxidize Wets molybdenum E beam evaporated films preferred n 1890 303 Yttrium 1522 447 d Aa w ligh tantalum solubility tate le te I Emme names Zinc Antimonide aol re eee l Zirconium 6 49 1477 1702 E Alloys with tungsten lt gt Films oxidize readily Zirconium Silicide ZrSi 100 4 88 41 Appendix B Vapor pressure curves M EEE m mm M n pu i 1 i M 1 HiH E ims i i Sii i sii i EM E E a E 3 dz us 2H d i a ie i i E 1 E im ity i QUIL 1500 2000 EET 200 300 400 500 600 800 1000 VAPOR PRESSURE CURVES OF THE ELEMENTS Temperature Degrees Centigrade NATTY UT 400 500 600 700 800900 1000 8 8 o e g MN n 1 28 o DH ww MMOL NI IYNSSIYA HOdVA i E 98 42 50 100 200 300 400 500 600 800 1000 o E ji i i bei TANIA y 5 A eT 8H ww YYOL NI 3N0SS3Hd HOdVA 43 5
48. te Calculations 4 2 Effects of Slide ODutgassing a Future Experiments amp Summary 5 1 Improving Film Quality 5 2 Improved Deposition Rates Bibliograph Appendix Appendix B Appendix C gt qe gt ol fol t 2 t O O O 5 e B ea S E x Es nj Ej J a vi 29 29 3l 35 35 36 38 40 42 45 49 50 53 List of Figures A A A A RE ee AA A 5 lavada seer 6 A 7 AN ee OR eee es Be 10 ide do hk re ai sg de WAG eh aa ae AWA a 11 EI ha a ee 12 24 RGA PAST graph cs s e ss a e As 14 2 5 Various boats and baskets J 15 ee ee ee ee A a 16 Sp a a D ee SoS UD Bote a E 17 to Wd ae II 18 ie Pde Soke ee me RA re eee Ge 19 Fo dried se oe hae as ad e GS 20 3 1 Quartz Crystal Microbalance Positioning 24 3 2 Crucible amp basket combination 20 Ex it He de d oh RR eal 30 4 2 Average change in slide massovertime 33 aera ences 34 vii List of Tables 1 1 Vacuum quality pressure ranges ee ee Dee CU oe 2 3 1 Silicon Heat Tape Specifications 22 3 2 Type C thermocouple specifications 23 3 3 Genesys 60 12 5 power supply details 26 vili Chapter 1 Introduction 1 1 A Brief History of Thin Film amp Vacuum Technology Vacuum technology is be
49. te the temperature of a wire with a known current running through it This approximation serves two purposes first it explains why the wire baskets began to melt and second it provides a more accurate calculation of the temperature for calculating the deposition rate Hence we adopted a crucible and stranded tungsten basket combination Although the tungsten wire won t melt until about 2300 C the crucibles will often break well before that temperature see figure 2 7 For Al deposition a boron nitride BN crucible works best because of its high thermal conductivity and thermal resistance and its low thermal expansion 9 A BN crucible can sustain temperatures up to roughly 1800 C without breaking Vapor pressure curves which can be found in appendix B show that the Al will begin to evaporate prior to 1800 C in the 10 to 1078 Torr range 17 2 2 3 Power Supplies amp Feedthroughs Upgrading the heating element meant we also needed to find a more suitable power supply The previous power supplies could only provide 20 and 40 amps which was not enough to heat the new filament design to an adequate temperature Joule heating requires large currents and or high voltages to accelerate the electrons traveling through a conductor Applying a high current is analogous to a large river of electrons moving through the structure and high voltages are similar to a strong accelerating force to the electrons Energy is transferred to the lattice s
50. than its pre deposition weight we realized that the mineral glass must have been outgassing So we devised an experiment to quantify the slide outgassing Determining how much a material outgasses is simple After cleaning each slide individually and letting the methanol evaporate off they were weighed and placed inside the vacuum chamber To maintain a controlled environment all of the slides were placed side by side inside 3l the vacuum for the same length of time After several hours the slides were removed and weighed Weighing each slide daily for several days after the experiment provided additional insight about the environmental effects on the slide s weight Figures 4 2 and 4 3 show the change in each slides weight over the course of several days The average change in slide mass between pre and post outgassing was 0 0012 grams This is the same value used to adjust for the weight lost during the film deposition process Adjusting the weight due to outgassing effects improves the accuracy of calculated rates Producing thicker films in the future would negate most of the effects from outgassing as the difference in slide mass would be more significant with a thicker layer of Al deposited on them Further inquiry into the causes that influence the weight of a slide on a given day would be helpful as well The data suggests that environmental factors such as humidity and room temperature may play a more crucial role in the weight of a
51. tructure of the conductor as moving electrons collide with other atoms Increasing the number of collisions or increasing the energy transferred per collision results in a greater macroscopic temperature change To reach our desired temperature we purchased a power supply with a power output of 750 watts 60 amps and 12 5 volts During the research of power supplies we reassessed the equipment that was being used and looked for improvements The high voltage feedthrough we were using wasn t suited use with high current To avoid future complications we also purchased a high current feedthrough with solid oxygen free copper OFE leads to help reduce the power loss through the feedthrough pins Additionally work was done to design a new support system for connecting the tungsten filament to the copper leads The new configuration can be seen in figure 2 8 and the previous design in figure 2 9 2 2 4 Substrate Holder Design Another feature of the new design is a substrate holder that won t chip the edges of the substrates A substrate is the surface on which films are grown In theory the substrate consists of any type of material However the application usually determines the material that is used i e silicon for semiconductors As the float glass substrates were wedged between the threads of two screws positioned above 18 Figure 2 8 New crucible holder configuration Figure 2 9 Old crucible configuration 19
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