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32-1
32Cathodic Arc PlasmaDeposition32.1 Introduction ......................................................................32-1
32.2 Cathodic Arc Plasma Deposition Process .......................32-132.3 Cathodic Arc Sources........................................................32-3
32.4 Cathodic Arc Emission Characteristics ...........................32-3
32.5 Microdroplets ....................................................................32-4
32.6 Recent Developments........................................................32-5
References.....................................................................................32-7
32.1 Introduction
The cathodic arc plasma deposition (CAPD) method1,2 of thin film deposition belongs to a family of ion
plating processes that includes evaporative ion plating3,4 and sputter ion plating.5,6 However, the CAPD
process involves deposition species that are highly ionized and posses higher ion energies than other ion
plating processes. All the ion plating processes have been developed to take advantage of the special
process development features and to meet particular requirements for coatings, such as good adhesion,
wear resistance, corrosion resistance, and decorative properties.
The cathodic arc technique, having proved to be extremely successful in cutting tool applications, is
now finding much wider ranging applications in the deposition of erosion resistance, corrosion resistance,
decorative coatings, and architectural and solar coatings.
32.2 Cathodic Arc Plasma Deposition Process
In the CAPD process, material is evaporated by the action of one or more vacuum arcs, the source
chamber, a cathode and an arc power supply, an arc ignitor, an anode, and substrate bias power supply.
Arcs are sustained by voltages in the range of 15 to 50 V, depending on the source material; typical arc
currents in the range of 30 to 400 A are employed. When high currents are used, an arc spot splits into
multiple spots on the cathode surface, the number depending on the cathode material. This is illustrated
spots move randomly on the surface of the cathode, typically at speeds of the order of tens of meters persecond. The arc spot motion and speed can be further influenced by external means such as magnetic
fields, gas pressures during coatings, and electrostatic fields.
Materials removal from the source occurs as a series of rapid flash evaporation events as the arc spot
migrates over the cathode surface. Arc spots, which are sustained as a result of the material plasma
generated by the arc itself, can be controlled with appropriate boundary shields and/or magnetic fields.
H. RandhawaVac-Tec Systems, Inc.
2006 by Taylor & Francis Group, LLC
material being the cathode in the arc circuit (Figure 32.1). The basic coating system consists of a vacuum
in Figure 32.2 for a titanium source. In this case, an average arc current/arc spot is about 75 A. The arc
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32-2 Coatings Technology Handbook, Third Edition
FIGURE 32.1 Schematic of a cathode arc deposition system.
FIGURE 32.2 Number of arc spots on the titanium cathode arc source as a function of arc current.
GasInlet
ArcSupply
ArcSupply
()
()
()
(+)
(+)
(+)
To Anode
To Anode
ArcSource
To Pump
Substrate
??
??
??
??
Bias
Supply
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Cathodic Arc Plasma Deposition 32-3
CAPD is markedly different from the physical vapor deposition process. Some of its characteristic
features are as follows:
1. The material plasma is generated by one or more arc spots.
2. A high percentage (30 to 100%) of evaporation material is ionized.
3. The ions exist in multiple charge states (e.g., in case of Ti, Ti+, Ti2+, Ti3+, etc.).4. The ions possess very high kinetic energies (10 to 100 eV).
These characteristics of CAPD result in deposits that are of superior quality in comparison to other
plasma processes. Some of these advantages are as follows:
1. Good quality films over a wide range of deposition conditions (e.g., stoichiometric reached films
with enhanced adhesion and film density can be obtained over a wide range of reactive gas pressures
and evaporation rates)
2. High deposition rates for metals, alloys, and compounds with excellent coating uniformity
3. Low substrate temperature
4. Retention of alloy composition from source to deposit
5. Ease of producing reacted compound films
32.3 Cathodic Arc Sources
of a typical large area source. The arc source comprises a cathode (source material), an anode, an arc
ignitor, and a means of arc confinement.
The method of arc confinement is a key factor in arc source design and configuration. Cathodes using
magnetic fields or boundary shields are limited to small sizes of the order of a few inches in diameter.This limits the uniformity attained from such sources. It is generally necessary to use a multitude of such
sources to obtain a reasonable coating quality. Arc sources employing confinement passive boarders
range of sizes. Such cathode sources provide good uniformity over a wide range of substrate sizes in
various industrial applications. Typical thickness uniformity observed using an 8 in. 24 in. titanium
cathode at a source to substrate distance of 10 in. was approximately 10% over a flat area measuring 5
in. 20 in. Furthermore, the target utilization of such arc sources exceeds 70% much higher in
comparison to the magnetron sputtering source (N 40%).
32.4 Cathodic Arc Emission Characteristics
The cathodic arc results in a plasma discharge within the material vapor released from the cathode surface.
The arc spot is typically a few micrometers in size and carries current densities as high as 10 A/m2. This
high current density causes flash evaporation of the source material, and the resulting evaporant consists
of electrons, ions, neutral vapor atoms, and microdroplets. Emissions from the cathode spots are illus-
the cathode spots split into a number of spots. The average current carried per spot depends on the
nature of the cathode material. The extreme physical conditions present within cathode spots are listed
It is likely that almost 100% of the material may be ionized within the cathode spot region. These ions
are ejected in a direction almost perpendicular to the cathode surface. The microdroplets, however, have
been postulated to leave the cathode surface at angles up to about 30 above the cathode plane. The
microdroplet emission is a result of extreme temperatures and forces that are present within emission
results for copper, chromium, and tantalum.
2006 by Taylor & Francis Group, LLC
inTable 32.1.
A schematic cross section of a cathodic arc source is shown as an inset in Figure 32.1, in a photograph
(Figure 32.3) with predetermined electronic characteristics may be built much larger and over a wide
trated in Figure 32.4. The electrons are accelerated toward the cloud of positive ions. The emissions from
craters. The microdroplet emission is greater for metals with low boiling points. Figure 32.5 shows such
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32-4 Coatings Technology Handbook, Third Edition
32.5 Microdroplets
Microdroplets are emitted as one of the products of the flash evaporation events. In an uncontrolled
situation, very high microdroplet densities may be produced and deposited onto the substrates. The
microdroplets are found to be metal-rich in composition in the case of reacted compound films. Micro-droplet size and density can be controlled in the arc deposition process. Parameters and source design
are the key factors that influence the density and size of the microdroplets.
As previously reported, microdroplet density and size vary with the material. Zirconium nitride films,
deposited under the same conditions as titanium nitride, exhibit a much lower density of much smaller
microdroplets (N 0.1 to 0.2 m). It is believed that the smaller microdroplets result from the higher
melting point and low vapor pressure of zirconium coupled with the higher arc spot velocity observed
on a zirconium cathode surface. The higher arc spot velocity results in a low mean residence time of the
arc spot on a given localized area; thus, it minimizes localized overheating and, hence, the size and density
of the microdroplets.The arc motion of a conventional arc source was studied using a very high speed photographic
technique. The arc speed was measured to be approximately 8 m/sec. The application of suitable external
magnetic fields was found to enhance the arc speed to 17 m/sec. A corresponding reduction in macro-
particles was observed. The source design as well as the operating gas pressure during deposition had an
effect on the microdroplet emission. A new arc source using these modified microdroplets could be totally
illuminated. This is illustrated for films of titanium and zirconium nitrides and titanium dioxide, as
FIGURE 32.3 Typical large-area cathodic arc source.
2006 by Taylor & Francis Group, LLC
shown in Figure 32.6.
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Cathodic Arc Plasma Deposition 32-5
32.6 Recent Developments
A major interest in the cathodic arc process until recently has been in the deposition of hard coatings
for tribology, wear, and decorative applications. Deposition, characterization, and performance evalua-
tions of nitrites, carbides, and carbonitrites of several materials [Ti, Zr, Hf, (TiAl), (TiZr)(Ti6Al4V),
etc.] using the cathodic arc deposition process have been investigated in detail and will not be discussed
here. Some of the most recent developments involve deposition of oxides and multicomponent materials
for architectural glass, solar reduction applications, barrier films, and so on. Thin films of tin, zirconium
nitride, titanium dioxide, zirconium dioxide, oxide of copper, and other metallic materials have been
investigated for these applications. Films of TiO2 and ZrO2 were deposited in a reactive mode using an
oxygengas mixture. ZrO2 and TiO2 films with very low absorption (
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32-6 Coatings Technology Handbook, Third Edition
FIGURE 32.5 Microdroplet emission from metals having different melting points.
FIGURE 32.6 Scanning electron micrographs showing surface topography of various films using modified arc
technology.
Cu
Ta
Cr
1.50 kv 30 kv 002
30 kv 0141.00 kv
TiN ZrN
TiO2
1.50 kv 30 kv 003
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Cathodic Arc Plasma Deposition 32-7
TiN and ZrN films deposited by cathodic arc have also been investigated for architectural glass coatings.
The deposition rates and stoichiometry control were found to be superior to magnetron sputtering. A
deposition rate as high as 10 times that of magnetron sputtering for production scale was demonstrated.
Multicomponent films consisting of Inconel and NiCrAlY alloys have also been successfully depos-
ited at rates as high as 1 mm/min. The film composition as analyzed by spectroscopic techniques (e.g.,
ESCA and AES) was found to be within 10 to 15% of the source material. This makes cathodic arc an
excellent choice for multicomponent materials.
The cathodic arc deposition process has proved to be capable of fulfilling the most exacting demands
in applications as diverse as tool coatings, decorative coatings, architectural glass coatings, and turbine
engine coatings. Developments are continuing to broaden the range of various potential applications of
the cathodic arc.
References
1. H. Randhawa and P. C. Johnson, A review, Surf. Coat. Technol., 31, 303 (1987).2. J. L. Vossen and W. Kem, Eds., Thin Film Processes. New York: Academic Press, 1978.
3. J. A. Thornton, in Deposition Technologies for Films and Coatings. R. F. Bunshah, Ed. Park Ridge,
NJ: Noyes Publications, 1982.
4. W. M. Mullarie, U.S. Patent No. 4,430,184 (1984).
5. H. Randhawa and P. C. Johnson, Surf. Coat. Technol., 33, 53 (1987).
6. H. Randhawa, presented at ASM International Strategic Machining and Materials Conference,
Orlando, FL, 1987.
2006 b T l & F i G LLC
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