Martin P.M. Handbook of Deposition Technologies for Films and Coatings, Third Edition: Science, Applications and Technology
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Surface Preparation for Film and Coating Deposition Processes 131
3.7 Some Surface Modification Processes
3.7.1 Ex Situ Surface Modification
3.7.1.1 Surface Morphology
Basecoats: polymer
Polymer basecoats such as the UV curing epoxies are used not only to flowcoat and smooth a
surface but also to seal in materials that can outgas or outdiffuse from a polymer substrate.
Surface chemistry
There are several ways to treat polymer surfaces and increase their surface energy or modify
the functional groups on the surface to make them more amenable to adhesive bonding to
another polymer or to a metal. These treatments include flame treatments, corona
(atmospheric) treatments, and plasma treatments. In vacuum coating technology, flame or
corona treatments are the most common external treatments, while plasma treatments are the
most common for in situ treatment in the deposition system [24].
Surface hardness
In addition to changing the surface morphology and chemistry, the hardness of the
near-surface region can be changed by diffusion. Diffusion hardening can be done by
high-temperature pack cementation or by plasma-enhanced gaseous diffusion (e.g. ionitriding)
[25–27]. Table 3.2 gives some typical values of hardness and thicknesses (case depth) formed
by high-temperature diffusion [2].
Surface barrier layers
Float glass is generally a soda lime glass and is a common substrate material. A problem with
float glass in some cases is the diffusion of sodium out of the glass and into the film during
Table 3.2: Hardening of surfaces by diffusion [2]
Treatment
Substrate Microhardness Case thickness
(kg/mm
2
)
Carburizing Steel: low C, medium C, C–Mn 650–950 50–3000
Cr–Mo, Ni–Mo, Ni–Cr–Mo
Nitriding (ion) Steel: Al, Cr, Mo, V, or W 90–1300 25–750
Austenitic stainless
Carbonitride Steel: low C, medium C, Cr 550–950 25–750
Cr–Mo, Ni–Cr–Mo
Boriding Steel: Mo, Cr, Ti, cast Fe 1600–2000 25–500
Cobalt-based alloys
Nickel-based alloys
132 Chapter 3
processing. To avoid this problem a barrier layer of silica can be deposited by spray pyrolysis
on the air side of the glass on the float glass line.
Basecoats: inorganic
An example of an inorganic basecoat to increase the functionality of a coating is the use of a
diamond-like carbon (DLC) basecoat to increase the scratch resistance of a decorative coating
on a soft substrate [28].
3.7.2 In Situ Surface Modification
There are several techniques to modify surface in the deposition system. They include:
Plasma immersion ion implantation deposition (PIIID), where a metallic cathode is
immersed in a plasma and pulsed momentarily to a high voltage (50–100 kV) [29, 30].
Ions are accelerated from the plasma and before there is an arc the pulse is terminated.
When using nitrogen and a high part temperature this process is similar to ionitriding
Plasma anodization is a method of growing a very coherent oxide layer on the surface
of some metal compounds and silicon [31, 32]
A plasma may be used to change the functional groups on the surface of a polymer to
change the surface energy and make the surface more acidic or more basic. This can
change the contact angle on the treated surface, as shown in Figure 3.12
Polymer evaporation and flow coating. The deposition of a film of liquid polymer on
the substrate surface is similar to flow coating and can be used to reduce the number of
surface defects in vacuum web coating [33, 34].
Plasma treatment by nitrogen plasmas (N
2
or NH
3
) can produce functional groups such as
imine (C=N), amide (N–C=O) or amine C–N) groups [35, 36], which can aid in
Figure 3.12: Contact angle. [From SVC Education Guides to Vacuum Coating Processing (2009) –
Surface Preparation: Surface Energy, Wetting Agents, and Surfactants, with permission.]
Surface Preparation for Film and Coating Deposition Processes 133
metal–polymer adhesion. Oxygen-containing plasmas are used to produce covalent bonds
(C–O–C), where the oxygen can bond to oxygen-active metals [37].
References
[1] D.M. Mattox, Surface preparation for vacuum surfaces and vacuum coating, Chap. 21, in: 50 Years of Vacuum
Coating Technology and the Growth of the Society of Vacuum Coaters, SVC (2007) 151.
[2] D.M. Mattox, Surface effects on the growth, adhesion and properties of reactively deposited hard coatings,
Surf. Coat. Technol. 81 (1996) 8.
[3] E.J. Wegener, Glass cleaning utilizing cerium oxide solution in a high volume production environment, in:
36th Annual Technical Conference Proceedings of the Society of Vacuum Coaters (1993) 495.
[4] R.E. Cuthrell, Influence of hydrogen on the deformation and fracture of the near surface region of solids:
proposed origin of the Rebinder–Westwood effect, J. Mater. Sci. 14 (1979) 612.
[5] J.M. Fowkes, D.W. Wright, J.A. Manson, T.B. Lloyd, D.O. Tischer, B.A. Shaw, Enhanced mechanical
properties of polymer composites by modification of the surface acidity or basicity of fillers, in: D.M. Mattox,
J.E.E.E. Baglin, R.J. Gottschall, C.D. Battich (Eds.), Adhesion in Solids, MRS Symposium Proceedings,
Vol. 119 (1988) 223.
[6] ASTM-D-2989 Acidity/Alkalinity of Hydrogenated Organic Solvents.
[7] K. Mittal (Ed.), Contact Angle, Wettability, and Adhesion, Vol. 5, Brill Academic Publishers (2008).
[8] R.R. Sowell, R.E. Cuthrell, R.D. Bland, D.M. Mattox, Surface cleaning by ultraviolet radiation, J. Vac. Sci.
Technol. 11 (1974) 474.
[9] J.R. Vig, UV/ozone cleaning of surfaces, J. Vac. Sci. Technol. A 3(3) (1985) 1027.
[10] G.J. Kominiak, D.M. Mattox, Reactive plasma cleaning of metals, Thin Solid Films 40 (1977) 141.
[11] H.F. Dylla, A review of the wall problem and conditioning techniques for TOKAMACKS, J. Nucl. Mater.
93-94 (1980) 61.
[12] F.J. Fuchs, New ultrasonic technology improves cleaning and prevents surface damage due to cavitation
erosion effects, in: 45th Annual Technical Conference Proceedings of the Society of Vacuum Coaters (2002)
64.
[13] R.R. Young, Sonoluminescence, CRC Press (2005).
[14] V.B. Menon, Particle adhesion to surfaces: theory of cleaning, in: R.P. Donovan (Ed.), Particle Control for
Semiconductor Manufacturing, Marcel Dekker (1990) 359.
[15] S. Hamilton, Yield Improvement in Metallizing Lines by Using Contact Cleaning Technology, in: 51st Annual
Technical Conference Proceedings of the Society of Vacuam Coaters (2008) 778.
[16] A.K. Furr, CRC Handbook of Laboratory Safety, 5th ed., CRC Press (2000).
[17] P. Patnaik, A Comprehensive Guide to the Hazardous Properties of Chemical Substances, 3rd ed., John Wiley
and Sons (2007).
[18] L. Holland, The cleaning of glass, Chap. 5, in: The Properties of Glass Surfaces, Wiley (1964).
[19] D.M. Mattox, R.R. Sowell, Kr
85
Autoradiography for nondestructive/noncontaminating surface porosity
measurements, in: Proc. 7th International Vacuum Congress and 3rd International Conference on Solid
Surfaces (1977) 2659.
[20] R.E. Cuthrell, D.W. Tipping, Rev. Sci. Instrum. 47 (1976) 595.
[21] W.J. Whitfield, Ultra-Clean Room USP 3158457 (Filed May 14, 1962, Issued Nov. 1964).
[22] W.J. Whitfield, A new approach to clean room design, Sandia Corp. Technical Report No. SC-4673 (RR),
(1962).
[23] D.M. Mattox, Particle bombardment effects on thin film deposition: a review, J. Vac. Sci. Technol. A 7(3)
(1989) 1105.
[24] R.A. Wolf, Which surface activation system should i use for optimizing adhesion to polymers? in: 50th
Annual Technical Conference Proceedings, Society of Vacuum Coaters (2007) 704.
[25] S. Guruvenket, L. Duanjie, A. Revah, J. Szpunar, L. Martinu, J.E. Klemberg-Sapieha, Tribological properties
of duplex treated 410 martensitic stainless steel, in: 51st Annual Technical Conference Proceedings of the
Society of Vacuum Coaters (2008) 712.
134 Chapter 3
[26] R.F. Bunshah (Ed.), Handbook of Hard Coatings, Noyes Publications (2001).
[27] A. Raveh, I. Zukerman, R.Z. Shneck, R. Avni, I. Fried, Thermal stability of TiAlBN and TiN/TiCN coatings,
High Temp. Mater. Process. 10(3) (2006) 445.
[28] P. Peeters, J. Sold
´
an, J. Landsbergen, R. Tietema, T. Krug, DLC base coat as part of decorative coating for
scratch resistant support on soft substrates, in: 51st Annual Technical Conference Proceedings of the Society
of Vacuum Coaters (2008) 735.
[29] J.R. Conrad, R.A. Dodd, S. Han, M. Madapura, J. Scheuer, K. Sridharan, F.J. Worzala, Ion beam assisted
coating and surface modification with plasma source ion implantation, J. Vac. Sci. Technol. A 8(4) (1990)
3146.
[30] A. Anders (Ed.), Handbook of Plasma Immersion Ion Implantation and Deposition, John Wiley and Sons
(2000).
[31] D.W. Hess, Plasma-assisted oxidation, anodization, and nitridation of silicon IBM, J. Res. Dev. 43(1/2) (1999)
127.
[32] A. Raveh, M. Gelbstein, G. Moshe, M. Weiss, J.E. Klemberg-Sapieha, L. Martinu, Wear-corrosion study of
tantalum-oxide layers produced by plasma anodization using inductively coupled plasma, in: 51st Annual
Technical Conference Proceedings of the Society of Vacuum Coaters (2008) 739.
[33] C.A. Bishop, Polymer web surface cleanliness, in: 45th Annual Technical Conference Proceedings, Society of
Vacuum Coaters (2002) 476.
[34] P.M. Martin, J.D. Affinito, M.E. Gross, C.A. Coronado, W.D. Bennett, D.C. Stewart, Multilayer coatings on
flexible substrates, in: 38th Annual Technical Conference Proceedings of the Society of Vacuum Coaters
(1995) 163.
[35] L.J. Gerenser, Surface chemistry for treated polymers, in: D.A. Glocker, S.I. Shah (Eds.), Handbook of Thin
Film Process Technology, Vol. 2, IoP Publishing (2002) Section E3.1.
[36] M.R. Wertheimer, L. Martinu, E.M. Liston, Plasma sources for polymer surface treatment, in: D.A. Glocker,
S.I. Shah (Eds.), Handbook of Thin Film Process Technology, Vol. 2, IoP Publishing (2002) Section E3.0.
[37] J.M. Burkstrand, Electron spectroscopic study of oxygen-plasma-treated polymer surfaces, J. Vac. Sci.
Technol. 15 (1978) 223.
CHAPTER 4
Evaporation: Processes, Bulk
Microstructures, and Mechanical Properties
S. Ismat Shah, G. Hassnain Jaffari, Emre Yassitepe and Bakhtyar Ali
University of Delaware
4.1 Introduction 136
4.2 Scope 138
4.3 PVD Processes 138
4.3.1 Preamble 138
4.3.2 PVD Processes 139
4.3.3 Advantages and Limitations 149
4.4 Theory and Mechanisms 151
4.4.1 Vacuum Evaporation 151
4.5 Evaporation Process and Apparatus 155
4.5.1 The System 155
4.6 Evaporation Sources 157
4.6.1 General Considerations 157
4.6.2 Resistance-Heated Sources 158
4.6.3 Sublimation Sources 163
4.6.4 Evaporation Source Materials 165
4.6.5 Induction-Heated Sources 167
4.6.6 Electron Beam-Heated Sources 167
4.6.7 Arc Evaporation 174
4.7 Deposition Rate Monitors and Process Control 177
4.7.1 Monitoring of the Vapor Stream 177
4.7.2 Monitoring of Deposited Mass 178
4.7.3 Monitoring of Specific Film Properties 180
4.7.4 Evaporation Process Control 180
4.8 Deposition of Various Materials 182
4.8.1 Deposition of Metals and Elemental Semiconductors 182
4.8.2 Deposition of Alloys 182
4.8.3 Deposition of Intermetallic Compounds 187
4.8.4 Deposition of Refractory Compounds 188
4.8.5 Materials Synthesized by Evaporation-Based Processes 207
4.8.6 Deposition of Nanocomposite Materials 208
Copyright © 2010 Peter M. Martin. Published by Elsevier Inc.
All rights reserved.
135
136 Chapter 4
4.9 Microstructure of PVD Condensates 208
4.9.1 Microstructure Evolution 208
4.9.2 Texture 222
4.9.3 Residual Stresses 223
4.9.4 Defects 224
4.10 Physical Properties of Thin Films 228
4.11 Mechanical and Related Properties 228
4.11.1 Mechanical Properties 228
4.11.2 Magnetic Properties 244
4.1 Introduction
Physical vapor deposition (PVD) technology consists of the techniques of evaporation, ion
plating and sputtering. It is used to deposit films and coatings or self-supported shapes such as
sheet, foil, and tubing. The thickness of the deposits can vary from angstroms to millimeters.
The wide variety of applications of these techniques ranges from decorative to utilitarian over
significant segments of the engineering, chemical, nuclear, microelectronics and related
industries. Their use has been increasing at a very rapid rate since modern technology
demands multiple, and often conflicting, sets of properties from engineering materials, e.g.
combinations of two or more of the following: high-temperature strength, impact strength,
specific optical, electrical or magnetic properties, wear resistance, ability to be fabricated into
complex shapes, biocompatibility, cost, etc. A single or monolithic material cannot meet
such demands in high-technology applications. The solution is, therefore, a composite
material, i.e. a core material and a coating each having the requisite properties to fulfill the
specifications.
PVD technology is very versatile, enabling one to deposit virtually every type of inorganic
material – metals, alloys, compounds and mixtures thereof, as well as some organic materials.
The deposition rates can be varied from 10 to 750,000
˚
A (10
−3
to 75 m) per minute, the
higher rates having come about in the past 20 years with the advent of electron beam
(e-beam)-heated sources. For zinc and aluminum, deposition rates as high as 25 m/s have
been reported using e-beam evaporation sources.
The thickness limits for thin and thick films are somewhat arbitrary. A thickness of 10,000
˚
A
(1 m) is often accepted as the boundary between thin and thick films. A recent viewpoint is
that a film can be considered thin or thick depending on whether it exhibits surface-like or
bulk-like properties.
Evaporation 137
Historically, the first evaporated thin films were probably prepared by Faraday [1] in 1857
when he exploded metal wires in a vacuum. The deposition of thin metal films in vacuum by
Joule heating was discovered in 1887 by Nahrwold [2] and was used by Kundt [3] in 1888 to
measure refractive indices of such films. In the ensuing period, the work was primarily of
academic interest concerned with optical phenomena associated with thin layers of metals,
research into kinetics and diffusion of gases, and gas metal reactions [4, 5]. The application of
these technologies on an industrial scale had to await the development of vacuum techniques
and therefore dates to the post-World War II era, i.e. 1946 and onwards. This proceeded at an
exponential pace in thin films and is covered in an excellent review by Glang [6] on evaporated
films and in other chapters of the Handbook of Thin Film Technology [7], as well as in the
classic text by Holland [8]. A more recent reference on the Science and Technology of Surface
Coatings [9] includes material on PVD techniques as well as the other techniques for surface
coatings. The work on mechanical properties of thin films has been reported in several review
articles [10–15].
The work on the production of full-density coatings or self-supported shapes by
high-deposition rate PVD processes started around 1961 independently at two places in the
USA. Bunshah and Juntz at the Lawrence Livermore Laboratories of the University of
California produced very high-purity beryllium foil [16–21] and titanium sheets [22], and
studied the variation of impurity content, microstructure, and mechanical properties with
deposition conditions, thus demonstrating that the microstructure and properties of PVD
deposits can be varied and controlled. At about the same time, Smith and Hunt were working
at Temescal Metallurgical Corporation in Berkeley on the deposition of a number of metals,
alloys and compounds, and reported their findings in 1964 [23, 24].
In the years between 1962 and 1969, there was considerable effort on the part of various steel
companies to produce Al and Zn coatings on steel using the high-rate physical vapor
deposition (HRPVD) techniques on a production scale [25, 26]. In 1969, Airco Temescal
Corporation decided to manufacture Ti–6Al–4V alloy foil in pilot production quantities for
use in honeycomb structures on the supersonic transport (SST) aircraft. The project was
eminently successful but the SST died. The results of this work were published in 1970 [27].
To give some idea of the production capability, 1200 feet/run of Ti–6Al–4V foil, 12 inches
wide and 0.002 inches thick was produced at the rate of 2–3 feet/min. The stated cost at that
time was about one-fifth of the cost for similar material produced by rolling (i.e. $60/lb for
HRPVD vs $300/lb for rolled material). It is very difficult to roll this alloy because it
work-hardens very rapidly and therefore needs many annealing cycles to be reduced to thin
gauge [28]. The work on thick films and bulk deposits has matured later than the work on thin
films and reviews on it have been given by Bunshah [29, 30] and by Paton et al. [31] who
summarized the work done at the Paton Electric Welding Institute up to 1973. In addition, the
Soviet literature in the 1960s has numerous references to the extensive work on thin and thick
138 Chapter 4
films by Palatnick and co-workers of the Kharkov Polytechnic Institute (see Appendix). Note
should also be made of a recent book in German on e-beam technology by Schiller et al., in
which many of the PVD aspects are treated [32].
4.2 Scope
The scope of this chapter will be to review the evaporation technologies, theory and
mechanisms, processes, deposition of various types of materials, the evolution of the
microstructure and its relationship to the properties of the deposits, preparation of high-purity
metals, current and future applications, and finally cost analysis as far as possible.
4.3 PVD Processes
4.3.1 Preamble
In general, deposition processes may principally be divided into two types: (1) those involving
droplet transfer such as plasma spraying, arc spraying, wire-explosion spraying, and
detonation gun coating, and (2) those involving an atom-by-atom transfer mode such as the
PVD processes of evaporation, ion plating and sputtering, chemical vapor deposition (CVD),
and electrodeposition. The chief disadvantage of the droplet transfer process is the porosity in
the final deposit, which affects the properties.
There are three steps in the formation of any deposit:
1. Synthesis of the material to be deposited:
(a) transition from a condensed phase (solid or liquid) to the vapor phase
(b) for deposition of compounds, a reaction between the components of the compound,
some of which may be introduced into the chamber as a gas or vapor.
2. Transport of the vapors between the source and substrate.
3. Condensation of vapors (and gases) followed by film nucleation and growth.
There are significant differences between the various atom transfer processes. In CVD and
electrodeposition processes, all of the three steps mentioned above take place simultaneously
at the substrate and cannot be independently controlled. Thus, if a choice is made for a process
parameter such as substrate temperature (which governs deposition rate in CVD), one is stuck
with the resultant microstructure and properties. On the other hand, in the PVD processes,
these steps (particularly steps 1 and 3) can be independently controlled and one can therefore
have a much greater degree of flexibility in controlling the structure and properties, and
deposition rate. This is a very important consideration.
Evaporation 139
4.3.2 PVD Processes
There are three PVD processes, namely evaporation, ion plating, and sputtering. Ion plating is
a hybrid process. In the evaporation process, vapors are produced from a material located in a
source which is heated by direct resistance, radiation, eddy currents, e-beam, laser beam, or an
arc discharge. The process is usually carried out in vacuum (typically 10
−5
–10
−6
torr) so that
the evaporated atoms undergo an essentially collisionless line-of-sight transport prior to
condensation on the substrate. The substrate is usually at ground potential (i.e. not biased).
4.3.2.1 Electron Beam Evaporation
Figure 4.1 is a schematic of a vacuum evaporation system illustrating e-beam heating. It may
be noticed that the deposit thickness is greatest directly above the center-line of the source and
decreases away from it [33, 34]. This problem is overcome by imparting a complex motion to
substrates (e.g. in a planetary or rotating substrate holder) so as to even out the vapor flux on
all parts of the substrate; or by introducing a gas at a pressure of 5–200 m into the chamber so
that the vapor species undergo multiple collisions during transport from the source to
substrate, thus producing a reasonably uniform (± 10%) thickness of coating on the substrate.
The latter technique is called gas-scattering evaporation or pressure plating [35, 36].
Figure 4.1: Vacuum-evaporation process using electron beam heating.
140 Chapter 4
Figure 4.2: Ion-plating process.
4.3.2.2 Ion-Plating Process
In the ion-plating process, the material is vaporized in a manner similar to that in the
evaporation process but passes through a gaseous glow discharge on its way to the substrate,
thus ionizing some of the vaporized atoms (Figure 4.2). The glow discharge is produced by
biasing the substrate to a high negative potential (−2to−5 kV) and admitting a gas, usually
argon, at a pressure of 5–200 mtorr into the chamber. In this simple mode, which is known as
diode ion-plating, the substrate is bombarded by high-energy gas ions which sputter off the
material present on the surface. This results in a constant cleaning of the substrate (i.e. a
removal of surface impurities by sputtering), which is desirable for producing better adhesion
and lower impurity content. This ion bombardment also causes a modification in the
microstructure and residual stresses in the deposit. However, it produces the undesirable
effects of decreasing the deposition rates since some of the deposit is sputtered off, as well as
causing a considerable (and often undesired for microelectronic applications) heating of the
substrate by the intense gas ion bombardment. The latter problem can be alleviated by using
the supported discharge ion-plating process [37, 38] where the substrate is no longer at the
high negative potential; the electrons necessary for supporting the discharge come from an
auxiliary heating tungsten filament. The high gas pressure during deposition causes a
reasonably uniform deposition of all surfaces owing to gas-scattering, as discussed above.