Thin Film Deposition& Vacuum Technology

THIN FILM DEPOSITION & 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 c Stefan Lofgran
All Rights Reserved

Brigham Young University–Idaho
Department Approvalof a senior thesis submitted by
Stefan Cannon LofgranThis thesis has been reviewed by the research committee, senior thesis coordinator and department chair and has been found to be satisfactory.

DateDavid Oliphant, Advisor

Date

Ryan Nielson, Committee Member

Date

Stephen McNeil, Senior Thesis CoordinatorABSTRACTTHIN FILM DEPOSITION & 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, semiconductors, and solar cells. Closely related to the study of thin films is the development 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 evaporation via resistive or Joule heating as a means for growing thin aluminum(Al) films on a mineral glass substrate. Methods for measuring thickness arealso discussed and investigated in an attempt to determine the experimentally produced film thickness. A detailed explanation of the development andoperation of the vacuum system in which the Al films were grown is given as
well as future improvements that could be made.

iii

ACKNOWLEDGEMENTS

To my loving wife & family who have supported me thewhole way, and to David Oliphant who has guided me on
this project.

iv

Table of Contents
Page
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iii
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iv
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
1 Introduction
1.1 A Brief History of Thin Film &Vacuum Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Review of Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

2 Experimental Design & Setup
2.1 Vacuum System Design . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.1 Recent Developments . . . . . . . . . . . . . . . . . . . . . . .
2.1.2 Using a Viton Gasket . . . . . . . . . . . . . . . . . . . . . . .
2.1.3 Vacuum Conditioning . . . . . . . . . . . . . . . . . . . . . . .
2.2 Deposition System Design . . . . . . . . . . . . . . . . . . . . . . . .
2.2.1 The Original Experiment . . . . . . . . . . . . . . . . . . . . .
2.2.2 New Crucibles & Improved Temperature Calculations . . . . .
2.2.3 Power Supplies & Feedthroughs . . . . . . . . . . . . . . . . .
2.2.4 Substrate Holder Design . . . . . . . . . . . . . . . . . . . . .

9
9
9
10
12
14
14
15
17
18

3 Procedures & Documentation
3.1 Equipment Documentation . . . . . . . . . . . . . . . . . . . . . . . .
3.1.1 Silicon Heating Tape . . . . . . . . . . . . . . . . . . . . . . .
3.1.2 Type C Thermocouple . . . . . . . . . . . . . . . . . . . . . .
3.1.3 Quartz Crystal Microbalance . . . . . . . . . . . . . . . . . .
3.1.4 Residual Gas Analyzer . . . . . . . . . . . . . . . . . . . . . .
3.1.5 Crucibles, Baskets, & Boats . . . . . . . . . . . . . . . . . . .

21
21
21
22
23
24
25

v

1
4

3.1.6 Power Supplies . . . . . . . . . . . . . . . . . . . . . . . . . .
Vacuum Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.1 Pumping to Low Vacuum . . . . . . . . . . . . . . . . . . . .
3.2.2 Pumping to High Vacuum . . . . . . . . . . . . . . . . . . . .
Deposition Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . .

25
26
26
27
28

4 Thin Film Deposition Rates
4.1 Initial Rate Calculations . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Effects of Slide Outgassing . . . . . . . . . . . . . . . . . . . . . . . .

29
29
31

5 Future Experiments & Summary
5.1 Improving Film Quality . . . . . . . . . . . . . . . . . . . . . . . . .
5.2 Improved Deposition Rates . . . . . . . . . . . . . . . . . . . . . . . .

35
35
36

Bibliography

38

Appendix A

40

Appendix B

42

Appendix C

45

Appendix D

49

Appendix E

50

Appendix F

53

3.2

3.3

vi

List of Figures
1.1
1.2
1.3

RGA cracking patterns . . . . . . . . . . . . . . . . . . . . . . . . . .
Langmuire-Knudsen angle dependence . . . . . . . . . . . . . . . . .
Initial deposition system configuration . . . . . . . . . . . . . . . . .

567

2.1 BYU-Idaho Vacuum system . . . . . . . . . . . . . . . . . . . . . . .
2.2 25” OD CF Flange . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 O-ring over compression failure . . . . . . . . . . . . . . . . . . . . .
2.4 RGA P vs T graph . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5 Various boats and baskets [1] . . . . . . . . . . . . . . . . . . . . . .
2.6 Broken tungsten baskets . . . . . . . . . . . . . . . . . . . . . . . . .
2.7 Broken quartz crucibles . . . . . . . . . . . . . . . . . . . . . . . . . .
2.8 New crucible holder configuration . . . . . . . . . . . . . . . . . . . .
2.9 Old crucible configuration . . . . . . . . . . . . . . . . . . . . . . . .
2.10 Substrate holder design . . . . . . . . . . . . . . . . . . . . . . . . . .

10
11
12
14
15
16
17
18
19
20

3.1
3.2

Quartz Crystal Microbalance Positioning . . . . . . . . . . . . . . . .
Crucible & basket combination . . . . . . . . . . . . . . . . . . . . .

24
25

4.1
4.2
4.3

Filmed slide projection . . . . . . . . . . . . . . . . . . . . . . . . . .
Average change in slide mass over time . . . . . . . . . . . . . . . . .
Change in slide mass between consecutive days . . . . . . . . . . . . .

30
33
34

vii

List of Tables
1.1

Vacuum quality pressure ranges . . . . . . . . . . . . . . . . . . . . .

2

3.1
3.2
3.3

Silicon Heat Tape Specifications . . . . . . . . . . . . . . . . . . . . .
Type C thermocouple specifications . . . . . . . . . . . . . . . . . . .
Genesys 60-12.5 power supply details . . . . . . . . . . . . . . . . . .

22
23
26

viii

Chapter 1
Introduction
1.1

A Brief History of Thin Film &Vacuum Technology

Vacuum technology is becoming 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 thequality 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 mostobvious factors determining the type of vacuum achieved are the equipment used
and the system configuration. Before delving into the details of vacuum design andits importance in developing thin films it will be beneficial to review a brief historyof 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 they1

Table 1.1: Vacuum quality pressure ranges
create a difference in pressure which causes the gas in the high-pressure area tomove to the low-pressure area. Essentially, a vacuum pump generates a vacuum bycreating 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 theunit 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 neveractually 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 asmodern vacuum technology isn’t that old. Scientists and engineers developed mostof the technology that we use today during and after World War II. During the2period of development after World War II people began to revisit thin films andexplore the possibilities of their uses in industry, particularly in the semiconductor
industry.

One of the most important applications of vacuum systems is the development ofthin films. Physical vapor deposition (PVD) is just one method of producing thinfilms. Michael Faraday pioneered the first PVD process in the early 1800’s [1].
Many sub processes fall under the description of PVD including electron beam,
sputtering, thermal, and plasma arc deposition methods. At BYU-Idaho themethod 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 andclarify the PVD processes that were known by that time. Since Powell, Oxley, andBlocher’s publication scientists have devised many new methods for growing films.
Recent developments in the past few decades have produced methods capable ofgrowing alloy films and processes suitable for large scale production in order tobetter meet the demands of consumers.

Today’s society overlooks the importance of vacuum coatings in products theyuse. 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 industries also use thinfilm technology most of which is for cosmetic purposes, such as mirrors and toys.

3

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 indetermining a film’s quality. Uniformity is an issue that was not addressed during
the development of the BYU-Idaho deposition system. Getting the system tofunction properly is a prerequisite to tasks concerning the film uniformity. The
purity of the material prior to deposition is the largest factor in determining thefilms purity. The second biggest factor is most likely the gas composition andpressure of the system in which the film was developed. Vacuum technicians knowthat 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 candetermine 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 produce cracking patterns used todetermine the gas composition of the chamber (see figure 1.1).

A substantially low pressure is required to prevent film oxidation and reduce thecontaminant density. A pressure of 10−5 Torr is sufficient, but lower pressures would
help reduce the density of contaminants in the film. At 10−5 Torr the mean freepath of gas in the chamber is approximately 8 meters, which without the unit ofmeasurement is often referred to as the Knudsen number. The mean free path can

4Figure 1.1: RGA cracking patterns
be calculated using the following equation
kB T
,
l=√
2πd2 P(1.1)

where kB is the Boltzman constant, T is the temperature in Kelvin, d is thediameter 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 freemolecular flow more than viscous flow. The Langmuire-Knudsen equation isfounded on the assumption that the molecules follow a molecular flow regime. The
Langmuire-Knudsen equation isr
Rm = CmM
1cos θ sin φ 2 (Pe (T ) − P ),
T
r

(1.2)

mol·K
where Rm is the rate per unit area of the source, Cm = 1.85 × 10−2 s·T
a constant,orr

M is the gram-molecular mass of the deposition material, T is the temperature of5

Figure 1.2: Langmuire-Knudsen angle dependence
the deposition material, θ is the angle between the normal of the source and thesubstrate, φ is the angle normal to the surface of the substrate and crucible, r is the
distance between the crucible and substrate, and P and Pe are the system pressureand evaporant partial pressure in Torr respectively. Another assumption of theLangmuire-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 basepressure of the vacuum will also reduce the number of particles “picked” up as theyflow towards the substrate to be deposited.

The Langmuire-Knudsen equation necessitates the use of other methods andequations to calculate an accurate deposition rate. Among these is Stefan-Boltzman
equation for blackbody radiation:

P = IV = σAT 4 ,(1.3)

where P is the electrical power through the crucible, I is the current, V is thevoltage, σ is the Stefan-Boltzman constant,  is the emissivity, A is the surface area
6

Figure 1.3: Initial deposition system configurationof the black body, and T is the temperature. Solving for T we find

T =[

IV 1
]4 .
σA

(1.4)

I also used an experimentally derived equation for determining the partial pressureof liquid Al[5] given bylog P = −15993
+ 12.409 − 0.999 log T − 3.52 × 10−6 T,
T

(1.5)

where P is the pressure in Torr and T is the temperature. There are, of course,many other methods capable of deriving the necessary quantities. At the time of theinitial experiment, these were the best approximations available to us, but with theaddition of a type C thermocouple, new vacuum feedthrough, and power supply; ourcapability 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 theuse of a thermocouple.

7

Understanding the fundamentals of vacuum theory can prevent many of thecomplications that diminish the accuracy and precision of collected data.
Recognizing the sources of leaks in a vacuum system is one item that is of particularinterest for experimentalists. A variety of sources lead to unwanted gas added to thechamber 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 thehumidity. 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 inside 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 ofgas, 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 areboth ways to condition materials for use in vacuum. More technical processes suchas those used in developing semiconductors have prescribed standard methods forcleaning materials prior to use in vacuum.

8Chapter 2
Experimental Design & Setup
2.1

Vacuum System Design

2.1.1

Recent Developments

BYU-Idaho purchased the vacuum chamber, pressure gauges, roughing pump, andresidual gas analyzer; but received the oil diffusion pump and gate valve as adonation from another university. The important details about almost all of theequipment 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, 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.
9

Figure 2.1: BYU-Idaho Vacuum system
The goal that drives development of the vacuum system is that of achieving thelowest base pressure possible. It is far more difficult to achieve an ultra-highvacuum than it is to reach a low vacuum. Fortunately, the oil diffusion pump that isused has a very high throughput rate of about 2,000 L/s. This makes it possible toachieve pressures as low as 10−8 Torr with the current pump configuration. Despite
this advantage, other elements of the system do more to limit the achievablepressure 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 andout 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 securing 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 theflange 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 lengthof an O-ring is
L = π(OD + ID
),
2

(2.1)

where OD stands for the outer diameter and ID for the inner diameter which is
calculated using:
ID = OD − 2 × (Cs ),(2.2)

where Cs 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

b.

a.

Figure 2.3: O-ring over compression failurea. 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 thisobstacle is still in development. After several failed attempts to purchase thecorrectly sized O-ring from manufacturers a temporary solution was achieved with arazor blade and some cyanoacrylate adhesive (super glue). The details of how weconstructed the new O-ring is in appendix D. Minimizing the over-compression andpreventing the breaking of the cyanoacrylate bond of a temporary O-ring is done bymonitoring 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 fromvacuum systems [7]. Removing many of the monolayers of water from the stainlesssteel walls takes anywhere from several hours to days. Accelerating desorption ofwater molecules is achieved by providing additional energy via heat tape on theoutside of the chamber. An RGA can characterize desorption of water monolayers
during baking (see figure 2.5). Note how the partial pressure due to 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 drygas, is another common technique used to clean systems. Argon is probably themost 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 amore cost effective alternative that also works fairly well. Molecular “scrubbing”
works by adding molecules, in this case nitrogen gas, which then collide withadsorbed 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 aleak vale to precisely control the backfilling of dry nitrogen. The crossover pressureis the pressure at which the pump can no longer keep up with the gas load it isunder. Carrying out both conditioning processes simultaneously yields better results
13

Figure 2.4: RGA P vs T graphthan they would separately. Implementing additional conditioning methods would
show only minimal improvement until a better process for transfering material intoand out of the chamber is developed so that the 25” flange can remain sealed. The
best practice for keeping a vacuum clean is to avoid putting anything in it thatwould 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 isunderstandable 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 [1]wire wrapped around a tungsten wire. Unfortunately, during the flashing thetungsten sublimated and created a nonhomogeneous film on the glass substrateinstead of the nickel-silver. Research done by Phillip Scott helped improve thisprocess 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 depositionmaterial. 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 & Improved Temperature Calculations

Because of these improvements, and a need for more uniform films for anotherresearch 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. We tried tungsten baskets and alumina coated tungsten
baskets, as suggest by the tables in appendix A, and both kept melting (see figure2.6). 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 werebreaking because of the wire’s small diameter. Joule proposed that the heat lost by awire filament with a known resistance and current passing through it is proportional
to I 2 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 thatP = I 2 R.

(2.3)

Incorporating the definition of resistance, which is R ≡ ρ Alcs , where ρ is theresistivity of the material, l is the length, and Acs is the cross sectional area, we end
up withP = I 2ρ

l
.
Acs

(2.4)

Using this equation, in conjunction with values found in the CRC Handbook for theemissivity of tungsten [8] and the Stefan-Boltzman law,

P = σAs T 4 ,

16

(2.5)

Figure 2.7: Broken quartz crucibles
where σ is the Stefan-Boltzman constant,  is the emissivity, As is the surface areaof the black body, and T is the temperature; yields

T =[I 2 lρ 1]4 .
As Acs σ(2.6)

This equation can then be used to approximate the temperature of a wire with aknown current running through it. This approximation serves two purposes, first it
explains why the wire baskets began to melt, and second it provides a moreaccurate calculation of the temperature for calculating the deposition rate. Hence,
we adopted a crucible and stranded tungsten basket combination. Although thetungsten wire won’t melt until about 2300◦ C the crucibles will often break wellbefore that temperature (see figure 2.7). For Al deposition, a boron nitride (BN)crucible works best because of its high thermal conductivity, and thermal resistanceand its low thermal expansion [9]. A BN crucible can sustain temperatures up toroughly 1800◦ C without breaking. Vapor pressure curves, which can be found inappendix B, show that the Al will begin to evaporate prior to 1800◦ C in the 10−5 to10−8 Torr range.

172.2.3

Power Supplies & 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 riverof electrons moving through the structure and high voltages are similar to a strong
accelerating force to the electrons. Energy is transferred to the lattice structure of
the conductor as moving electrons ”collide” with other atoms. Increasing thenumber of ”collisions” or increasing the energy transferred per collision results in agreater macroscopic temperature change. To reach our desired temperature, wepurchased 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 wereusing wasn’t suited use with high current. To avoid future complications, we alsopurchased a high current feedthrough with solid oxygen free copper (OFE) leads tohelp reduce the power loss through the feedthrough pins. Additionally, work wasdone to design a new support system for connecting the tungsten filament to thecopper 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 edgesof the substrates. A substrate is the surface on which films are grown. In theory, thesubstrate 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

Figure 2.10: Substrate holder design
the deposition source they often chipped and damaged the slides. The remedy tothis problem was to design a new holding system, seen in figure 2.10, and switch thesubstrate from float glass slides to round mineral watch glass. A lathe was used tocraft the designed holder from Al; and it was secured in place inside the vacuum
using 4 21 inch steel bolts mounted seated on a 6 inch blank flange on the top of thechamber.

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 explanationof each individual piece of equipment is given in the next chapter.

20

Chapter 3
Procedures & 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 ofheating the chamber to 120◦ C, the heat tape is primarily designed to reduce thewater vapor content of the vacuum chamber. Heating the chamber walls with thetape gives the sorbed, or adhered, water on the stainless steel the energy needed toeventually evacuate the system and thereby reducing the overall contribution to thetotal pressure from water vapor.

21

Length72 inPower density
4.3 W atts/in2
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, avariable 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 basepressures and faster pump down times.

3.1.2

Type C Thermocouple

Thermocouples are capable of providing accurate temperature measurements bothin and out of vacuum. A special feedthrough is required in order to use athermocouple 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 ofmeasuring temperatures up to 2300◦ C. By comparing the measured voltage across
two different metals to that of a reference voltage a thermocouple can determine thetemperature. 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 indetermining the melting point of the Al. Within the chamber, the hot junction is22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 madefor my research. The purpose of the QCM is to measure the deposition rate ofmaterial onto the substrate. A QCM operates on the piezoelectric principle. Duringuse, 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:[10]2f 2∆f = − √ 0 ∆m,
A ρ q µq

(3.1)

where ∆f is the change in frequency, δm the change in mass, A the crystal area, f0g
the resonant frequency, ρq = 2.648 cmg 3 the density of quartz, µq = 2.947 × 1011 cm·s
2

the shear modulus of quartz for the crystal. Positioning the sensor head on thesame spherical wave front as the substrate enables the QCM to provide a reasonableapproximation for the rate of deposition. To correctly position the sensor head, thewater cooling lines that support the sensor were bent, using a tube bending tool, toan angle slightly past 90◦ C (see figure 3.1). In this position, the QCM software canbe 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 be23

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 10−5 Torr. Exposing the hot filament to the atmosphere oxidizes and ruins thefilament. 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 shorts with the chamber the software reads noise around 10−9 Torr. Carefully
bending the repeller cage may fix the problem. If this doesn’t work, you can checkthe 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, & 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 crosscontamination, each element should have its own crucible. Knowing thetemperature 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 & 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
power 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
Max Current
60 AmpsMax Voltage
12.5 Volts
Features: OVP, UVP, Foldback & 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 theevent 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 isbeneficial to leave the chamber in a low vacuum state. There is no limit to how longthe chamber may remain at low vacuum as the lower pressure helps prevent thesorbtion 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 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 ispressurized.

26

2. Close all vent or leak valves that connect the chamber or pumps to theatmosphere. For the large flange make sure that the Viton O-ring fits snuggly
in its groove before closing the chamber lid.
3. Open the gate valve between the chamber and diffusion pump, and the ballvalve connecting the roughing pump to the diffusion pump.
4. Turn on the roughing pump.
5. Wait until the pressure controller for the chamber reads ∼ 10−3 Torr.

3.2.2

Pumping to High Vacuum

1. Make sure that the thermocouple gauge for the chamber reads ∼ 8 × 10−3 Torr.
2. Turn on the water cooling for the diffusion pump.
3. Plug in the diffusion pump, and wait until the heating element reaches 170◦ C.
4. Wait another five minutes for the diffusion pump to reach approximately 10−5
Torr.
5. Turn on the ion gauge and RGA as necessary.
Procedure for Removing Slides
1. After turning off the power supply and giving the crucible time to cool
proceed with the following steps.
2. If the ion gauge or RGA are on, turn them off.
3. Firmly close the gate valve between the chamber and diffusion pump.
4. Confirm that the valve between the chamber and the roughing pump is also
closed.
5. Vent the chamber.
6. Open the chamber, retrieve/replace the slide, place the Viton O-ring on theflange, and shut the chamber.
7. Close the vent valve to the chamber.
8. Close the ball valve between the diffusion and roughing pumps. This stepshould be done as quick as possible to prevent the diffusion pump frompressurizing, which can result in cracked oil.
9. Open the valve between the chamber and the roughing pump.
10. Pump down to ∼ 10−3 Torr.
27

11. Open the gate valve and the ball valve.
12. Close the valve between the chamber and roughing pump.
13. 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.
1. Weigh the glass slide after cleaning and prior to placing it in the chamber.
2. While the chamber is open place a few Al pellets in the BN crucible.
3. Also, position the shield at 55◦ to cover the substrate.
4. After reaching a high vacuum connect the power supply to the feedthrough.
5. Turn on the power supply and turn the voltage control all the way up so thepower output is dependent on the current control knob.
6. Slowly increase the current output. This is done by increasing the output by
3-5 amps and then waiting a few minutes for the crucible to reach a thermal
equilibrium with the W basket.
7. At the desired power output & temperature turn the mechanical feedthroughclockwise to move the shield out of the way.
8. During deposition record the time elapsed, power supply settings, and thechamber pressure before and during the deposition process.
9. When done, decrease the current output in the same manner that you
increased it (you can decrement the current in larger amounts) and eventuallyturn off the power supply.
10. Lastly, immediately after opening the chamber measure mass of the slide.

28

Chapter 4Thin 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 averagerate 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 purchaseof 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 ofgrams per square centimeter seconds. The experimental rate should look like

Rexp =

m
.
At

(4.1)

The mass m in the equation is the change in mass, or the mass of Al deposited, ofthe slide. Measuring the slide pre and post deposition is an easy task, but the scale
used needs to 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, wewere able to approximate the deposition area via a scale and the number of filmedsquares on the grid paper. Figure 4.1 shows a copy of the grid paper where the29Figure 4.1: Filmed slide projection
shaded squares represent the filmed area.

Assuming no angular dependence in the Langmuire-Knudsen equation further
simplifies the theoretical model to look liker
Rm = Cm

M 1(Pe (T ) − P ).
T r2

(4.2)

This justification is acceptable given the crucible is positioned directly beneath andsufficiently far from the substrate[11]. An appropriate distance should meet therequirement that the mean free path of molecules in the chamber be much greaterthan the distance between the crucible and substrate. Black body temperatureapproximations include an emissivity factor relating to the fraction of power that isemitted as radiation. For initial calculations we used an emissivity 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 thedeposition 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 amathematical mess. MATLAB code for analyzing the data and determining the χ2ν
value is in appendix F. This code accounts for the effects of slide outgassing while invacuum by adding an empirically calculated amount as well as a coefficient for theblack 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 χ2 value was around 3.3 × 107 . This alludes to the inadequacy of the tested
model in calculating the deposition rate of Al vapor. Despite the results theexperiment was useful in determining several areas of improvement for thedeposition system and the process used for calculating rates.

4.2

Effects of Slide Outgassing

After measuring a post-deposition slide mass that was less 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
31

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 theaccuracy 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 moresignificant with a thicker layer of Al deposited on them. Further inquiry into thecauses 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 slide than was at firstbelieved.

32

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 meanchange in mass.

33

Figure 4.3: Change in slide mass between consecutive days
34

Chapter 5
Future Experiments & Summary

Fully automating the deposition system is still a long ways down the road. Thismeans there is an ample supply of projects left for future students. Developing thesystem will expand the research opportunities for future students enabling them toconduct experiments requiring the use of films. Since we are now able toconsistently produce films, students may want to work on improving film qualityand 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 quality. This is known as film tribology. The other sideemphasizes 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, andhomogeneity can be determined. Some of the tribology methods are also an effective35

at determining film thickness after deposition. Students wanting to learn more
about film tribology would find the Handbook of Hard Coatings helpful in theirresearch[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. Typicalsubstrate preparation often involves chemical etching and cleaning prior todeposition 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 theoretical 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 ofvariables in an experiment can be quite revealing of what needs improvement. Suchis 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 of36

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, thevacuum system has limited room for further development without conducting acomplete 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. Foundations of Vacuum Coating Technology. William Andrew
Publishing/Noyes, 2003.
[4] John F. O’Hanlon. A User’s Guide to Vacuum Technology. John Wiley ’&’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 andcalibration. PDF. URL: http://www.thinksrs.com/downloads/PDFs/
ApplicationNotes/QCMTheoryapp.pdf.
[11] M. A. Herman, H. Sitter, and W. Richter. Epitaxy: Physical Principles andTechnical 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 Leybold Vacuum, 2007.

39

Appendix A
Materials Guide for Thermal Evaporation
Adapted from Kurt J.Lesker Co. [13]

40

41

Appendix B
Vapor pressure curves

42

43

44

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$10.00Note(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. The in vacuum microdot cable was purchased separately. All parts can bepurchased directly from the company.
Description
Part No.
6 Mhz Gold Coated Sensor Crystals 10pk
500-117
Vacuum Feedthrough500-017
Single Head Sensor
500-042
Oscillator & Transducer (STM-2)
500-408
30” Microdot Cable
500-024
10” Vacuum Microdot Cable
500-023

Cost$67.00$491.00$375.00$620.00$80.00N/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 withour 30” microdot cable. Preliminary findings have yielded no significant results
because the power supply couldn’t heat the material to a temperature that asubstantial deposition rate could be detected. Additionally, the water cooling forthe 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 thetechnical details can be found at ishttp : //www.us.tdk − lambda.com/hp/producth tml/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 isresistant to many 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
1” x 96” Silicone Heat TapeHigh Temperature Tape

Part No.
Cost
BS0101080L $173.65
PSAT36A$16.00Notes: 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 around125◦ C.

Mineral Glass Slides
Several companies sell mineral glass slides, but they don’t often refer to them asslides. 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 andpurchase 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 & more detailed documentation can be found at
www.thinksrs.com.
Description
Part No.
200 amu RGA
RGA200ThO2Ir Replacement Filament
O100RF
Replacement Ionizer Kit
O100RI
46

Cost$4750.00$200.00$450.00

For additional help diagnosing problems see
http : //www.thinksrs.com/support/RGAsup.htm. Also, the RGA pin diagramfrom ThinkSRS’ website is available below.

RGA Pin Diagram

Crucibles & 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
EVC1BN$34.00Notes: 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. Equivalent leakvalves are sold by Kurt J. Lesker and other companies, but the cost is significantly
greater than those sold on Ebay.
Description
Varian Leak Valve

Part No.
N/A

48

Cost
$80.00Appendix D
Equipment Troubleshooting & Repair
O-ring Construction Procedure
This step-by-step process describes the procedure used to construct 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 thisO-ring.
• First, as with any process involving a vacuum system, you should put on
powder-free gloves.
• Take the old O-ring and cut it once so that it forms one long cord.
• Tape the old O-ring to a flat surface in a straight line. You may find thestraight edge of a meter stick to be helpful in placing the cord in a straightline.
• 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.
• 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.
• Then perpendicularly cut a small amount of cord stock (about 1mm) off theother end of the newly cut Viton cord.
• 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.
• 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 theends together gently until the cyanoacrylate holds.
• 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 capable 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 [14]

50

51

52

Appendix F
MATLAB Code for Analyzing Data
Rates.mfunction [] = Rates()
clear; clc;
%Using the Vapor.m, Knudsen.m, and Temperature.m files this function%calculates the appropriate reduced Chi-squared values for the data
%set.
%The 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);%Separating the data
Pre = Data(:,1);
Post = Data(:,2);
P = Data(:,3).*133.322368; %converting from Torr to Pa
P_u = Data(:,4).*133.322368;
C = Data(:,5);V = Data(:,6);Time = Data(:,7);%Calculating theoretical values & uncertainties[T,T_u] = Temperature(C,V);[Pp,Pp_u] = Vapor(T,T_u);[R,R_u] = Knudsen(T,T_u,Pp,Pp_u,P,P_u);%Calculating actual values & uncertainties[Rex,Rex_u] = Experimental(Pre,Post,Time);
Chi = sum(sum((R-Rex).^2)./(Rex_u.^2))
Chi_reduced = Chi/(N-1)
end

	
  

Temperature.mfunction [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%heating and Ohm's law for resistors.
%This function assumes an uncertainty in the voltage and current of 0.1%A/V respectively
sig = 5.67*10^(-8); %Stefan-Boltzmann constant

	
  

53

	
  

eps = 0.41; %emissivity of W between ~1700-2500 degree C
eps_u = 0.05; %the rough uncertainty of the emissivity
A = 0.00005141; %crucible surface area
A_u = 0.00000025; %uncertainty in the surface area
C_u = 0.1; %uncertainty in current
V_u = 0.1; %uncertainty in voltage%There is a constant term in the partial derivative of T
dT_cons = (1/4)*(C.*V./(sig*eps*A)).^(-3/4);%Calculating T
T = (C.*V./(sig*eps*A)).^(1/4);%Calculating the uncertainty in T
T_u = sqrt( (C_u^2)*(dT_cons.*(V/(sig*eps*A))).^2 +... %current 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 +...
%emissivity(A_u^2)*(dT_cons.*(-C.*V/(sig*eps*A^2))).^2); %area term
end

	
  
	
  

Vapor.mfunction [Pp, Pp_u] = Vapor(T, T_u)
%This function is designed to calculate the experimental vapor pressure%and its associated uncertainties due to heated Al at a given%temperature as given by Wake Forest University's lab report.
%Calculate the partial pressure
Pp = 10.^((-15993./T) + 12.409 - 0.999*log10(T) - 3.52*10^(-6)*T);%Calculate the uncertainty in the partial pressure%If y = 10^x, then%dy/dx = (10^x)*(ln 10)
Pp_u = sqrt((T_u.^2).*((Pp*log(10)).^2));
end

	
  
	
  

Knudsen.mfunction [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)

	
  

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r = 16.3; %source-substrate distance in cm
r_u = 0.5; %uncertainty in r
%Calculate R
R = Cm*sqrt(M./T).*(1/(r.^2)).*(Pp - P);%Calculate the uncertainty in R
R_u = sqrt( (r_u^2)*(R.*(-2./r)).^2 +... %distance term
(T_u.^2).*((1-2)*(M./(T.^2)).*(M./T).^(-1)).^2 +... %T term
(P_u.^2).*(-Cm*sqrt(M./T).*(1/(r^2))).^2+... %P term
(Pp_u.^2).*(Cm*sqrt(M./T).*(1/(r^2))).^2); %Pp term
end

	
  
	
  

Experimental.mfunction [Rex,Rex_u] = Experimental(Pre,Post,Time)%This function calculates the experimental 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 areaout = 0.0012; %outgassing mass adjustment
Time_u = 1.5; %a generous uncertainty of 1.5 seconds
M_u = 0.0007; %uncertainty in the difference of mass measurement%Calculating the difference in mass pre & post deposition
M = (Post + out) - Pre;
%Experimental rate calculation
Rex = M./(A.*Time);%Experimental rate uncertainties
Rex_u = sqrt( (M_u^2)*(1./(A*Time)).^2 +... %mass term(Time_u^2)*(-1*(M./(A*Time.^2))).^2 +... %time term
(A_u^2)*(-1*(M./(A^2*Time))).^2); %area term
end

	
  
	
  
	
  
	
  

	
  

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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 thematerial 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 & 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)%/PowThis means that I'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 howmuch I lose when I 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 (forthis case I'll assume that the 18 gauge wire is hot ~75 degrees Celsius & the 10 gauge
wire is still ~50 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)%/PowThis 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;

	
  

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