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602 Chapter 4.9: Preparation and Cleaning of Vacuum Surfaces
3.
J.F. O'Hanlon, Contamination reduction in vacuum processing systems, J.
Vac.
Sci. Technoi,
A7(3) (1989) 2500.
4.
Y.T. Sasakim A survey of vacuum material cleaning procedures: A subcommittee report on the
American Vacuum Society Recommended Practices Committee, J. Vac. Sci. Technoi, A9(3)
(1991)2025.
5. B. S. Halliday, Cleaning materials and components for vacuum use, in Modem
Vacuum
Prac-
tice: Design, Operation, Perfonnance and Application of
Vacuum
Equipment, edited by G. F.
Weston, special issue of
Vacuum,
37(8/9), 1987.
6. L. E. Samuels, Mechanical grinding, abrasion and polishing, in Metals
Handbook,
9th ed.. Vol.
9: Metallography and
Microstructure,
(American Society for Metals, 1985), p. 33.
7. John F. Jumer, Electropolishing, in Metal
Finishing
Guidebook Directory 1994 (Elsevier, New
York, 1994), p. 383.
8. P.V Shigolev, Electrolytic and Chemical Polishing of Metals, (Freund Publishing, London,
1974).
9. U. Schafer and J. Beuers, Instructions and tips concerning chemical-mechanical polishing.
Metallography, 18 (1985) 319.
10.
R. Venkatachalam, S. Mohan, and S. Guruviah, Electropolishing of stainless steel from a low
concentration phosphoric acid electrolyte. Metal
Finish,
89(4) (1991) 47.
11.
J. A. Knapp, D. M. Follstaedt, and B. L. Doyle,
Nucl.
Instrum.
Method,
87-88 (1985) 38.
12.
A. Boschi, C. Ferro, G.Luzzi, and L. Papagno,
J. Vac.
Sci. Technoi, 16 (1979) 1037.
13.
H. C. Hseuh and X. Cui, "Outgassing and desorption of the stainless-steel beam tubes after
dif-
ferent degassing treatments,
J. Vac.
Sci Technoi, A7(3) (1989) 2418.
14.
N. Yoshimura, T. Sato, S. Adachi, and T. Kanazawa, Outgassing characteristics and microstruc-
ture of
an
electropolished stainless steel surface,
J. Vac.
Sci Technoi, A8(2) (1990) 924.
15.
J. R. Young, Outgassing characteristics of stainless steel and aluminum with different surface
treatments,
J. Vac.
Sci Technoi, 6(3) (1969) 398.
16.
R. W. Bonham and D. M. Holloway, Effects of specific surface treatments on type 304 stainless
steel,
J. Vac.
Sci Technoi, 14(2) (1977) 745.
17.
R. O. Adams, A review of
the
stainless steel surface, /
Vac.
Sci Technoi, Al (1983) 12.
18.
SEMATECH
Test Method for AES Analysis of
Surface
and Oxide Composition of Electro-
polished Stainless Steel Tubing for Gas Distribution System Components (Provisional)
SEMASPEC 91060573A-STD. Sematech, 2706 Montopolis Dr., Austin, TX 78741.
19.
SEMATECH
Test Method for ESC A Analysis of
Surface
Composition and Chemistiy of
Elec-
tropolished Stainless Steel
Tubing
for Gas Distribution System Components (Provisional) —
SEMASPEC 90120403A-STD. Sematech, 2706 Montopolis Dr., Austin, TX 78741.
20.
H. Tomari, H. Hamada, Y. Nakahara, K. Sugiyama, and T. Ohmi, Metal surface treatment for
semiconductor equipment: Oxygen passivation. Solid State
Technology,
34(2) (1991) SI.
21.
D. Verma, Surface passivation of AISI 400 series stainless steel components. Metal Finish,
86(2) (1988) 85.
22.
Earl C. Groshart, Pickling and acid dipping. Metal
Finishing
Guidebook Directory 1994 (Else-
vier, New York, 1994), p. 153.
23.
N. Kaufherr, A. Krauss, D. M.. Gruen, and R. Nielsen, Chemical cleaning of aluminum alloy
surfaces for use as vacuum material in synchrotron light sources, /
Vac.
Sci Technoi, A8(3)
(1990) 2849.
24.
R L. Oliphant, The cleanroom enigma,
Semicond
Internal, 15(10) (1992) 82.
25.
H. Ishimaru, Ultimate pressure of the order of 10"'^ in an aluminum vacuum chamber, J. Vac.
Sci Technoi, A7(3) (1989) 2439.
26.
H. Ishimaru, Developments and applications for all-aluminum alloy vacuum systems, MRS
Bull.,
15(7) (1990) 23.
27.
M. Suemitsu,
T.
Kaneko, and N. Miyamoto, Aluminum alloy ultrahigh vacuum chamber for mo-
lecular beam epitaxy, /
Vac.
Sci Technoi, A5(l) (1987) 37.
References
^03
28.
A. W. Brace, The Technology of Anodizing Ahimmum (Robert Draper Publishing, New York,
1968).
29.
David Thomas, Anodizing aluminum, in Metal Finishing Guidebook Directoiy 1988 (Elsevier,
New York, 1988), p. 451.
30.
J. K. G. Panitz and D. J. Sharp, The effect of different alloy surface compositions on barrier an-
odic film formation, J. Electrochem. Soc, 131(10) (1984) 2227.
31.
E. D. Erikson, T. G. Beat, D. D. Berger, and B. A. Fraizer, Vacuum outgassing of various mate-
rials,
J.
Vac.
ScL TechnoL, A2(2) (1984) 206.
32.
D. J. Santeler, Estimating the gas partial pressure due to diffusive outgassing, 7.
Vac.
Sci. Tech-
«o/.,A10(4)(1992) 1879.
33.
J. H. Tilley, Release agent for system cleaning, SVC 38th Annual Technical Conference Pro-
ceedings, SVC Publications, Albuquerque, NM, 1995, p. 457.
34.
J. Winter, Surface conditioning of fusion devices by carbonization: Hydrogen recycling and wall
pumping, J.
Vac.
Sci. Technol, A5(4) (1987) 2286.
35.
Ted Kostilnik, Mechanical cleaning systems, in Surface Engineering, ASM Handbook, Vol. 5
(ASM Publications, Materials Park, OH, 1994), p. 55.
36.
Robert C. Mulhall and Nicholas D. Nedas, Impact blasting with glass beads, in Metal Finishing
Guidebook and Directory (Elsevier, New York, 1994), p. 75.
37.
G. P Balcar and M. M. Woelfel, Specifying glass beads. Metal Finish, 83(12) (1985) 13.
38.
B. E. Durst, Non-chemical cleaning of fixtures and surfaces using plastic blast media, Society of
Vacuum Coaters 35th Annual Technical Conference Proceedings 1992 (SVC Publications, Al-
buquerque, NM, 1992), p. 271.
39.
Mark Hanna, Blast Finishing, Metal Finishing Guidebook and Directory (Metal Finishing,
1994),
p. 68.
40.
Stanley Hirsch and Charles Rosenstein, Stripping metallic coatings, in Metal Finishing Guide-
book and Directory (Elsevier, New York, 1995), p. 428.
41.
D. M. Mattox, Surface effects on the growth, adhesion and properties of reactively deposited
hard coatings.
Surf.
Coat. TechnoL, 81 (1996) 8.
42.
T. Spalvins, A review of recent advances in solid film lubricants, J.
Vac.
Sci. Technol. A5 (1987)
212.
43.
David B. Chalk, Classification and selection of cleaning processes, in Surface Engineering,
ASM Handbook, Vol. 5 (ASM Publications, Materials Park, OH, 1994), p. 3.
44.
V. B. Menon, Particle adhesion to surfaces: Theory of cleaning, Particle Control for Semicon-
ductor Manufacturing, edited by R. P. Donovan (Marcel Dekker, New York, 1990), p. 359.
45.
R. A. Bowling, An analysis of particle adhesion on semiconductor surfaces, J. Electrochem.
5oc.,
132 (1985) 2208.
46.
M. B. Renade, Adhesion and removal of fine particles on surfaces. Aerosol. Sci. TechnoL, 7(2)
(1987) 161.
47.
I. F. Stowers, Advances in cleaning metal and glass surfaces to micron-level cleanliness, J. Vac.
Sci. TechnoL, 15(2) (1978) 751.
48.
J. M. Bennett, L. Mattsson, M. P. Keane, and L. Karlsson, Test of strip coating material for pro-
tecting optics, AppL Optics, 28(5) (1989) 1018.
49.
E. J. Wegener, Glass cleaning utilizing a cerium oxide solution in a high volume production en-
vironment. Society of
Vacuum
Coaters 36th Annual Technical Conference Proceedings (SVC
Publications, Albuquerque, NM, 1993), p. 495.
50.
L. Layden and D. Wadlow, High velocity carbon dioxide snow for cleaning vacuum system sur-
faces,
J.
Vac.
ScL TechnoL, A8(5) (1990) 3881.
51.
S. P. Hotaling, Adapting military technology to civilian use: Contamination removal and collec-
tion techniques, Microcontamination, 11(5) (1993) 32.
52.
R. Sherman and W. Whitlock, The removal of hydrocarbons and silicone oil stains from silicon
wafers, J.
Vac.
ScL TechnoL, B8(3) (1990) 563.
604 Chapter 4.9: Preparation and Cleaning of Vacuum Surfaces
53.
Etching Composition and Processes (Chemical technology review 210), edited by M. J. Collie
(Noyes Publications, Park Ridge, NJ, 1990).
54.
Perrin Walker and William H. Tarn, Etchants for Metals and Metallic Compounds, CRC Hand-
book (CRC Press, Boca Raton, FL, 1990).
55.
Bibliography on Chemical Cleaning of
Metals
Vol.
I (52135) & Vol. 2 (52
J29),
(NACE (Na-
tional Association of Corrosion Engineers) Publications, Houston, TX).
56.
R. C. Sundahl, Relationship between part surface chemistry and adhesion of thin films, J. Vac.
Sci.
Technol.,
9 (1972) 181.
57.
G. J. Kominiak and D. M. Mattox, Reactive plasma cleaning of metals, Thin Solid Films, 40
(1977) 141.
58.
R. Hamilton, Volatile organic compound destruction using thermal processing, Solid State Tech-
nol.,34(9)(\99\)5i.
59.
P Taylor, M-Pyrol—A practical replacement solvent. Plat.
Surf.
Finish., 76 (1989) 42.
60.
V. Wang and A. N. Merchant Metal-cleaning alternatives for the 1990s, Metal Finish, 91(4)
(1993) 13.
61.
CD. D'Ruis, Aqueous
Cleaning
as
an
Alternative to CFC
&.
Chlorinated Solvent based Clean-
ing, (Noyes Publications, Park Ridge, NJ, 1991).
62.
G. M. Schneider, Physicochemical principles of extraction with supercritical gases, Angew.
Chem.
Int.
Ed.
Engl.
17 (1978) 716.
63.
E. Bok, D. Kelch, and K. S. Schumacher, Supercritical fluids for single wafer cleaning. Solid
State TechnoL, 35(6) (1992) 117.
64.
Gerald J. Cormier, Alkaline cleaning, ASM Handbook, vol. 5: Suiface Engineering (ASM Inter-
national, Materials Park, OH, 1994).
65.
V. L. Morris, Cleaning agents and techniques for concentrating solar collectors. Solar Energy
Materials, 3 (1979) 35.
66.
Werner Kern, ed.. Handbook of
Semiconductor
Wafer Cleaning Technology (Noyes Publica-
tions,
Park Ridge, NJ, 1993).
67.
L. Holland, The cleaning of
glass,
in
77?^
Properties of Glass Sutfaces (Wiley, New York, 1964),
chap.
5.
68.
Cleaning of substrate surfaces, in Coatings on Glass, H. K. Pulker (Elsevier, New York, 1984),
chap.
4.
69.
R. R. Sowell, R. E. Cuthrell, R. D. Bland, and D. M. Mattox, Surface cleaning by ultraviolet ra-
diation, /
Vac.
Sci.
TechnoL,
11 (1974) 474.
70.
J. R. Vig , UV/ozone cleaning of surfaces, J.
Vac.
Sci. TechnoL, A3(3) (1985) 1027.
71.
J. M. Frank, Vacuum processing equipment for quartz crystal oscillators, in Proc. 35th Annual
Frequency Control Symposium (IEEE Publications, New York, 1981), p. 40.
72.
H. Norstrom, M. Ostling, R. Buchta, and C. S. Petersson, Dry cleaning of contact holes, / Elec-
trochem. Soc, 132 (1985) 2285.
73.
R. Bouwman, J. B. van Mechelen, and A. A. Holscher, Surface cleaning by low temperature
bombardment with hydrogen an AES investigation on copper and Fe-Cr-Ni steel surfaces,
J.
Vac.
ScL
TechnoL,
15(1) (1978) 91.
74.
L. Holland, Wetting glass surfaces, in The Properties of Glass Surfaces, (Wiley, New York,
1964),
chap. 6.
75.
M.A. Baker, Plasma cleaning and the removal of carbon from metal surfaces. Thin Solid Films,
69(1980)359.
76.
H. F. Dylla, A review of the wall problem and conditioning techniques for TOKAMAKS,
/ NucL Mat., 93, 94 (1980) 61.
77.
H. Yamada, "Low temperature surface cleaning method using low-energy reactive ionized spe-
cies,
J. AppL Phys., 65(2) (1989) 775.
78.
R. P. H. Chang, C. C. Chang, and S. Darack, Hydrogen plasma etching of semiconductors and
their oxides, J.
Vac.
ScL TechnoL, 20(1) (1982) 45.
References 605
79.
M. K. Balazs, A summary of new methods for measuring contaminants in ultrapure water,
Microcontamination,
5(1) (1987) 35.
80.
Vicki L. Rupp and Ken Surprenant, Solvent cold cleaning and vapor degreasing, in ASM
Hand-
book,
5: Siuface Engineering (ASM International, Materials Park, OH, 1994), p. 21.
81.
B. Kanegsberg, Cleaning systems for low-flashpoint solvents. Precision Clean, 3(3) (1995) 21.
82.
Joseph Scapelli, Enclosed vapor degreasing systems, Metal Finishing Guidebook and Direc-
tory (Elsevier, New York, 1995), p. 144.
83.
Kenneth R. Allen, Ultrasonics —
A
Practical Approach, in Metal Finishing Guidebook and Di-
rectory (Elsevier, New York, 1995), p. 152.
84.
Jeff Hancock, Ultrasonic cleaning, in ASM Handbook, Vol. 5: Surface Engineering (ASM In-
ternational, Materials Park, OH, 1994), p. 44.
85.
F. J. Fuchs, Ultrasonic cleaning, in Metal Finishing Guidebook and
Directory^
(Elsevier, New
York, 1992).
86.
J. H. Schleckser, Process control ultrasonics. Society of
Vacuum
Coaters 35th Annual Technical
Conference Proceedings (1992) (SVC PubUcations, Albuquerque, NM, 1992), p. 15.
87.
J. Halbert, Using uhrasonic techniques for wet-process cleaning, Microcontamination, 6(11)
(1988)36.
88.
S.M. Goho, An Auger electron spectroscopy study of the oxidation and mechanical degrada-
tion of Ta thin film protective overlayers at microelectronic solid/liquid interfaces, J.
Vac.
Sci.
TechnoL,
A8(3) (1990) 3026.
89.
T. Ohmi, H. Mishima, T. Mizuniwa, and M. Abe, IPA vapor-drying technology: Developing
contamination-free cleaning and drying technologies, Microcontamination, 7(5) (1989) 25.
90.
A. E. Walter and C. F. McConnell, Direct displacement wet processing: How it affects wafer
surface phenomena, Microcontamination, 8(1) (1990) 35.
91.
B. Kanegsberg, Cleaning systems for low-flashpoint solvents. Precision Clean, 3(3) (1995) 21.
92.
Robert J. Good, Contact angle, wetting, and adhesion: a critical review, in Contact Angle, Wett-
ability and Adhesion, edited by K. L. Mittal (VSP Publishers, Utrecht, The Netherlands, 1993),
p.
3.
93.
A. K. Furr, CRC
Handbook
ofLoborotojy
Safety,
3rd ed. (1989).
94.
W. Mahn, Fundamentals of Laboratory Safety, (Van Nostrand Reinhold, New York, 1991).
95.
D. J. Young, How to use materials safety data sheets in PWB manufacturing, Electriconics,
32(5) (1986) 40.
96.
SEMATECH
Guide for
Contamination
Control in the Design, Assembly and Delivery of Semi-
conductor Manufacturing Equipment, #92051107A-STD (July 10, 1992). Sematech, 2706
Montopolis Dr., Austin, TX
78741.
97.
Bennie
W.
Goodwin, Cleanroom garments and fabrics, in Handbook of Contamination Control
in Microelectronics, edited by Donald L. Tolliver (Noyes Publications, 1988), chap. 3.
98.
Annual buyers guide: A guide to ultraclean suppliers and products. Micro (formally Micro-
contamination) Magazine (Canon Publishing, Santa Monica, CA).
99.
Handbook
of
Contamination
Control
in
Microelectronics, edited by Donald L. Tolliver (Noyes
Publications, 1988).
100.
Particle Control for
Semiconductor
Manufacturing,
edited by R. P. Donovan (Marcel Dekker,
New York, 1990).
101.
Compendium
of Standards, Practices, Methods etc. Relating to Contamination Control (lES-
C-CC-009-84-T) available from the Institute of Environmental Sciences.
102.
G. A. Harvey, James L. Raper, and D. C. Zellers, Measuring low-level nonvolatile residue con-
tamination on wipes, swabs and gloves, Microcontamination, 8(11) (1990) 43.
103.
The detection and control of organic contaminants on surfaces, Malcolm L. White, in Clean
surfaces: Their preparation and characterization for interfacial studies, edited by George
Goldfinger (Marcel Dekker, New York, 1970), p. 361.
606 Chapter 4.9: Preparation and Cleaning of Vacuum Surfaces
104.
J. J. Wu, D. W. Cooper, and R. J. Miller, Aerosol model of particle generation during pressure
reduction,/
Vac.
Sci.
Teclmol.
A8(3) (1990) 1961.
105.
D. Chen and S. Hackwood, Vacuum particle generation and the nucleation phenomena during
pumpdown, /
Vac.
Sci. Technoi, A8(2) (1990) 933.
106.
Christoph Steinbruchel, The Formation of particles in thin-film processing plasmas, in Physics
of
Thin
Films, Vol. 18: Plasma Sources for Thin Film Deposition and Etching, edited by
Maurice H. Francombe and John L. Vossen (Academic Press, San Diego, 1994).
107.
Plasma Etching: An Introduction, edited by Dennis M. Manos and Daniel L. Flamm (Aca-
demic Press, San Diego, 1989).
108.
H. Ishimaru, K. Itoh, T. Ishigaki, and S. Furutate, Fast pump-down UHV aluminum vacuum
system using super-dry nitrogen gas
flushing,
J.
Vac.
Sci.
TechnoL,
A10(3) (1992) 547.
109.
G. Comsa and R. David, Dynamical parameters of desorbing molecules.
Surf.
Sci. Reports, 5
(1985) 145.
110.
G. Carter, P.Bailey, and D. G. Armour, The precise deduction of desorption activation energy
distributions from thermal evolution spectra,
Vacuum,
34(8/9) (1984) 797.
111.
J. F. O'Hanlon, Thermal desorption measurement technique, J. Vac. Sci. TechnoL, A9(l)
(1991) 1.
112.
G. W. Fabel, S. M. Cox, and D. Lichtman, Photodesorption from 304 stainless steel.
Surf.
Sci.,
40(1973)571.
113.
P. Danielson, Understanding water vapor in vacuum systems, Microelectron
Manuf.
Test,
13(8)
(1990)24.
114.
R. P. Govier and G. M. McCracken, Gas discharge cleaning of vacuum surfaces, J.
Vac.
Sci.
Technol.,l{5) {1910) 552.
115.
Surface conditioning
of
vacuum
systems, edited by Robert A. Langley, Daniel L. Flamm, H. C.
Hseuh, Wen L. Hsu, and Thomas W. Rusch, AIP Conference Proceedings No. 199, American
Vacuum Society Series 8 (American Institute of Physics, 1990).
116.
R. Anderson, J. Behnke, M. Berman, H. Kobeissi, B. Ruling, J. Langan, S.-Y. Lynn, and
R. Morgan, Using COO to select nitride PECVD clean cycle, Semicond. Intemat., 16(11)
(1993)86.
117.
D. M. Mattox, R. E. Cuthrell, C. R. Peeples, and P L. Dreike, Design and performance of a
moveable-post-cathode magnetron sputtering system for making PBFA II accelerator sources.
Surf.
Coat.
TechnoL,
33 (1987) 425.
118.
V. S. Dharmadhikari, R. O. Lynch, W. Brennan, and W. Cronin, Physical vapor deposition
equipment evaluation and characterization using statistical methods, / Vac. ScL TechnoL,
A8(3)(1990) 1603.
CHAPTER 5.1
High-Vacuum-Based
Processes: Sputtering
Stephen M. Rossnagel
/.5.M.,
T,
J.
Watson Research
Center
Sputtering is a process by which an energetic particle strikes a surface with suffi-
cient energy that one or more of the surface atoms is ejected from the surface. The
incident particle could be an ion, an atom, an electron, an alpha particle, etc., al-
though for most practical purposes ions — typically inert gas ions —
are
used. The
sputter yield is defined as the ratio of the number of emitted atoms to the number
of incident particles:
Y = emitted (sputtered) atoms/incident particle
The sputtering process has four basic regimes, based on the incident energy. At
very low energies approaching the surface-binding energy, the yield is very low
(<10E~'^), and this is known as "near-threshold sputtering." There is some de-
bate over whether a true threshold exists for sputtering, although ion energies be-
low the binding energy are extremely unlikely to result in the removal of surface
atoms.
At moderate energies of perhaps 30 eV up to about 1000 eV, sputtering is char-
acterized by "knock on" effects in which the incident ion collides with a surface
atom, the two atoms then collide with additional atoms, and eventually this chain
of events may lead back to the surface, resulting in emission of a near-surface
atom or two. This regime is difficult to model or calculate because the exact point
of impact (between two atoms, directly on top of one atom, etc.) results in a
dif-
ferent chain of
collisions.
This requires a more Monte Carlo approach, using large
ISBN 0-12-325065-7 Copyright f) 1998 by Academic Press
^ -'•^ All rights of reproduction in any form reserved.
609
610
Chapter
5.1:
High-Vacuum-Based Processes: Sputtering
numbers of trial impacts. The sputter yields in this region are generally in the
range of 0.1-5 atoms per incident ion.
At ion energies of
1
to 50 keV or so, the incident ion has sufficient energy to
break essentially all the bonds in a semispherical region at the point of impact.
This "cascade" of collisions can be calculated with high accuracy by using statis-
tical mechanics and essentially treating the collision cascade volume as a sort of
gas.
This approach, first developed by Sigmund in the late 1960s has been very
successful at predicting sputter yields
[1,2].
Yields in this region are generally
two-five times higher than in the direct knock-on range, depending on the mate-
rial and the incident particle species.
The final, highest-energy regime is at energies in the 50keV to several MeV
range, where the incident particle travels well into the bulk of the sample before
slowing down and depositing its energy. This is more characteristic of implanta-
tion, and the sputter yield falls eventually to a very low level at the MeV range.
A graph of the sputter yield as a function of ion energy for Ar bombardment of
Si,
Zn, Ti, Cu, and Al is shown in Figure 1.
Sputter yields for many materials have been collected by numerous authors.
However, many inconsistencies appear in these published results. Reported yields
Fig.l.
10 ^
I
3
Q.
CO
0.1 h
0.01
10 100 1000 10,000 100,000
Ion Energy (eV)
The sputter yield for Ar-I- bombardment for Si, Zn, Ti, Cu and Al as a function of ion energy.
5.1.1 Sputtering and Deposition
611
Table
1
Sputter Yields as a Function of Ar Ion Energy
for Commonly Used Materials
Material
Ag
Al
Au
B
Be
C
Cd
Co
Cr
Cu
Fe
Ge
Hf
Mn
Mo
Nb
Ni
Pb
Pd
Pt
Re
Rh
Ru
Si
Sn
Ta
Ti
U
V
W
Zn
300 eV
1.7
.6
l.l
.2
.3
.1
5
.7
.8
1.5
.7
.6
.4
1.5
.3
.4
.7
2.5
1.5
.7
.4
.7
.7
.3
.6
.3
.3
.5
.4
.3
3.7
500 eV
2.5
.9
1.7
.6
.5
.3
6
1.1
1.9
.6
2
.5
.6
1.0
3.2
1.8
1
.6
1
1
.7
.9
.5
.5
.7
.7
.5
5
1000
eV
3.5
1.5
2.5
1.1
.9
.6
9
1.7
1.9
2.9
1.7
1.5
.9
3
.9
.9
1.7
4
2.5
1.6
1.0
1.7
1.7
1
1.4
.9
.7
1.1
1
.9
7
can change by a factor of at least 2X depending on the type of experiment, the
crystalline structure of the target, surface conditioning, chamber geometries, op-
erating pressures, etc. Table 1 shows approximate sputter yields.
5.1.1
SPUTTERING AND DEPOSITION
Sputter etching and sputter deposition arc differentiated simply by the observer's
point of view. If the sample is bombarded with energetic ions, it is being sputter
612
Chapter
S.l:
High-Vacuum-Based
Processes:
Sputtering
Fig.
2.
1.0 -
CO —
0
O
(d
Q. ^
o •i'-
0
Si
E
Z3
Z
0
r,
. I
' /
y
^-" *»
\
/
/
\
/
I /
^^'
iX
i/\
'i \ 0
' Evaporated at 1500 K
\
^1 1 1
Sputtered
s^^f^
\
\
\
\
1 1
1 1
\
^
8
10 12
Particle Velocity x 10 cm/sec
Velocity distributions of Cu atoms evaporated at 1500°K (solid line) and Cu atoms sputtered
from a Cu target with 600 eV Ar ions.
etched. If the sample is located near the surface that is being sputtered, then the
emitted, sputtered atoms can be deposited in the form of a thin film on the sur-
face.
Sputter etching is described in more detail in the following chapter (5.2), on
plasma etching. The remainder of this section focuses on sputter deposition.
Consistent with the fairly violent collision processes that are the basis of sput-
tering, the sputtered atoms generally are emitted from the surface with signifi-
cantly more kinetic energy than atoms evaporated from a hot source. An example
of the relative distribution of atom velocities for evaporation and sputtering is
shown in Figure 2. The sputtered atom distribution has roughly a 1/E^ distribu-
tion on the high-energy side of the peak, which extends to fairly high energies.
These high-energy sputtered atoms may actually cause secondary sputtering at the
sample surface,
a
concept known as "intrinsic resputtering"
[3].
The higher energy
for the sputtered atoms can significantly change the film microstructure, grain size,
stress,
etc., which are discussed later.
5.1.2
SPUTTER DEPOSITION TECHNOLOGIES
Sputter deposition has been around for nearly 150 years from the earliest days of
gas discharges and plasma physics. Currently, sputter deposition is practiced by
a number of high-vacuum technologies. The most commonly used is magnetron
sputtering, which is a form of a diode plasma. Another conmion technology is RF
5.1.2 Sputter Deposition Technologies
613
diode sputtering, which is used primarily for dielectrics. A third variant is to use
an ion beam and remove the sample or target from direct contact with
a
plasma.
The
most common technique used here is the Kaufman ion source, originally developed
for space engine applications (see Chapter 5.3, on ion-beam-based processes).
Historically, though, sputter deposition started with simple DC diodes, and it is
best to use these as a base to explore the other, more complicated variations.
5.1.2.1 DC Diodes
A DC diode is simply an anode and a cathode placed within a vacuum system.
Under suitable pressure and voltage conditions, a discharge can be formed be-
tween the two electrodes (Figure 3). The minimum voltage for the discharge is a
function of the pressure and the electrode spacing [4] (see Figure
4).
For purposes
of this description, two electrodes of a few cm^ in size, separated by 50 cm and in
a vacuum of 100 mtorr might require 600V to form a plasma.
Ions from the plasma are accelerated to the negative electrode (the cathode),
and electrons are collected at the anode. The discharge is sustained by secondary
electrons that are emitted from the cathode during ion bombardment. These sec-
ondary electrons are accelerated into the plasma, gaining enough energy to make
a few ions along the way, before they are collected at the anode. Because the sec-
ondary electron coefficient is typically on the order of 5%, each secondary elec-
tron needs to generate roughly 20 ion-electron pairs before it reaches the anode.
The cross section for electron impact ionization of the gas in the chamber is
fairly small and energy dependent [5]. Therefore in a DC diode it is usually nec-
essary to operate at fairly high pressures (0.2 to 2 torr) to have any reasonable ion
Fig.
3.
Cathode
Anode
Typical DC diode configuration.