U.S. patent number RE30,401 [Application Number 05/922,719] was granted by the patent office on 1980-09-09 for gasless ion plating.
This patent grant is currently assigned to Illinois Tool Works Inc.. Invention is credited to Gerald W. White.
United States Patent |
RE30,401 |
White |
September 9, 1980 |
Gasless ion plating
Abstract
A gasless ion plating process wherein plating material is
melted, vaporized, and then subjected to an ionization environment
in a low pressure chamber with a "virtual cathode" consisting of a
plasma of ionized atoms of evaporant material created by
evaporating in an RF field. It is a gasless ion plating process
wherein the system ambient pressure prior to plating material
evaporation may be much lower than that required to sustain a glow
discharge, however, with vapor pressure of evaporant material added
to the environment base pressure being such as to result in a
plasma of ionized atoms of the plating material developing as the
vaporized material approaches the RF cathode.
Inventors: |
White; Gerald W. (Dallas,
TX) |
Assignee: |
Illinois Tool Works Inc.
(Chicago, IL)
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Family
ID: |
25447500 |
Appl.
No.: |
05/922,719 |
Filed: |
July 7, 1978 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
569679 |
Apr 21, 1975 |
04039416 |
Aug 2, 1977 |
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Current U.S.
Class: |
427/524;
118/50.1; 118/620; 118/726; 204/298.05; 427/523; 427/553;
427/562 |
Current CPC
Class: |
C23C
14/32 (20130101) |
Current International
Class: |
C23C
14/32 (20060101); C23C 015/00 (); C23C
013/12 () |
Field of
Search: |
;204/192N,298
;118/49.1,49.5,50.1,620 ;427/38,39,45,50 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
D M. Mattox, "Fundamentals of Ion Plating," J. Vac. Sci. Technol.,
vol. 10, pp. 47-52 (1973). .
L. Leder, "Fundamental Parameters of Ion Plating," Metal Finishing,
pp. 41-45 (1974). .
Berry et al., "Thin Film Technology," Van Nostrand Reinhold, N.Y.,
pp. 156-157, 142-144 (1968). .
S. Aisenberg et al., "Physics of Ion Plating & Ion Beam
Deposition," J. Vac. Sci. Technol., vol. 10, pp. 104-107
(1973)..
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Primary Examiner: Weisstuch; Aaron
Attorney, Agent or Firm: Buckman; Thomas W.
Claims
I claim:
1. A process for ion plating a substrate supported within a chamber
with a plating material and in the absence of any inert gas
inputted to said chamber, comprising the steps of: evacuating said
chamber, vaporizing plating material in the evacuated chamber,
developing a direct current negative bias on said substrate, and
applying a radio frequency field from a .[.first.]. radio frequency
source to the vaporized plating material within said chamber.
2. The ion plating process of claim 1, wherein said substrate is
conductive, and said step of developing a direct current negative
bias on said substrate comprises the application of a direct
current negative bias source to said substrate. .[.3. The ion
plating process of claim 2, further including the application of a
further radio frequency signal
source to said substrate..]. 4. The process of claim .[.3.].
.Iadd.1 .Iaddend.wherein said radio frequency field applied within
said chamber is at a frequency within the range of approximately
.[.10 to 800 kilohertz, and said further radio frequency signal
applied to the substrate is in the
range of approximately.]. 2 to 40 megahertz. 5. The process of
claim 1, wherein the substrate is to be cleaned prior to plating,
further comprising the preliminary steps of: evacuating said
chamber; introducing an inert gas into said chamber; and applying a
radio frequency field to an
area within said chamber. 6. The process of claim 1, wherein the
step of vaporizing is a result of the step of applying the radio
frequency field.
. A process for plating a substrate supported within a chamber with
a plating material comprising the steps of: evacuating said
chamber; vaporizing said plating material in the evacuated chamber;
developing a direct current negative bias on said substrate;
forming and maintaining an ionized plasma from the vaporized
plating material in the absence of any inert gas inputted to said
chamber; and applying a radio frequency field within said chamber
to ion plate said material from said plasma onto said substrate.
.[.8. The process of claim 7, wherein the steps of vaporizing
plating material, forming an ionized plasma, and applying a radio
frequency field, are performed concurrently from a single radio
frequency power supply..]. .[.9. Apparatus for plating a conductive
substrate with a plating material, including: a chamber adapted to
hold said substrate and said plating material; means for evacuating
said chamber; means for vaporizing said plating material in the
evacuated chamber; means for applying radio frequency power to the
vaporized plating material to form and maintain an ionized plasma
therefrom in the absence of any inert gas inputted to said chamber;
a radio frequency bias source means connected to said substrate;
and means for applying a direct current negative bias to said
substrate..]. .[.10. The apparatus of claim 9, further including
connection of said radio frequency bias source means through a
radio frequency coupling capacitive means to said substrate..].
.[.11. The apparatus of claim 10, wherein said means for applying a
direct current negative bias to said substrate includes a direct
current source having a negative terminal connection through RF
choke means to said substrate and a positive terminal connection to
a voltage potential reference source of the system..]. .[.12. The
apparatus of claim 9, wherein said radio frequency power is at a
frequency of about 450 kilohertz, and including means for applying
a further radio frequency bias source means at a frequency of about
13.5 megahertz to said substrate..]. .[.13. The apparatus of claim
9, wherein the vaporizing means is a conventional resistance heat
element device..]. .[.14. The apparatus of claim 13, wherein said
vaporizing means is a filament device..]. .[.15. The apparatus of
claim 13, wherein said vaporizing means is a boat..]. .Iadd. 16. A
process for ion plating a substrate within a chamber with a plating
material source inside of said chamber comprising the steps of
evacuating said chamber, vaporizing said plating material,
effecting a D.C. negative electrical potential to the substrate
relative to the source of plating material and other portions of
the chamber by applying a D.C. bias to the substrate, applying an
RF signal to the substrate creating an RF field at the substrate
wherein the RF field creates an ionized plasma from the vaporized
plating material in the immediate vicinity of the substrate with
the ionized plating material thus accelerated onto the substrate
surface as a result of the negative electrical potential, for
particular advantage in plating a conductive substrate.
.Iaddend..Iadd. 17. Apparatus for plating a substrate with a
plating material including a chamber adapted to hold said substrate
and said plating material, means for evacuating said chamber, means
for vaporizing said plating material in the evacuated chamber, RF
source means connected within the chamber to apply radio frequency
signal power at said substrate creating an RF field at said
substrate, said RF field creating means to ionize the plating
material forming a plasma substantially surrounding the substrate,
and external source means for inducing a D.C. negative bias on the
substrate relative to the rest of the chamber. .Iaddend..Iadd. 18.
The apparatus of claim 17, particularly adapted to plate a
conductive substrate wherein the means for inducing a D.C. negative
bias on the substrate includes a D.C. bias source connected to the
substrate. .Iaddend. .Iadd. 19. The apparatus of claim 17, wherein
the means for vaporizing the plating material comprises a further
RF source means which operates at a frequency of about 450
kilohertz. .Iaddend..Iadd. 20. The apparatus of claim 17, wherein
the means for vaporizing the plating material is a resistance heat
element device. .Iaddend..Iadd. 21. The apparatus of claim 20,
wherein the means for vaporizing the plating material is a filament
device. .Iaddend..Iadd. 22. The apparatus of claim 20, wherein the
means for vaporizing the plating material is a boat device.
.Iaddend..Iadd. 23. The apparatus of claim 17, including the
connection of said RF source means through a radio frequency
coupling capacitive means to said substrate. .Iaddend..Iadd. 24.
The apparatus of claim 23, wherein said means for creating a DC
negative potential to the substrate includes a direct current
source having a negative terminal connection through RF choke means
to said substrate and a positive terminal connection to a voltage
potential reference source of the system. .Iaddend. .Iadd. 25. A
process for ion plating a substrate supported within a chamber with
a plating material comprising the steps of: evacuating said
chamber; vaporizing plating material in the evacuated chamber at a
pressure prior to evaporation lower than necessary to sustain a
glow discharge, effecting a DC negative bias on said substrate, and
applying a radio frequency field at the substrate to the vaporized
plating material immediately adjacent the substrate within said
chamber. .Iaddend. .Iadd. 26. A process for plating a substrate
supported within a chamber with a plating material comprising the
steps of: evacuating said chamber, vaporizing said plating material
in the evacuated chamber, developing a DC negative bias on said
substrate, forming and maintaining an ionized plasma from the
vaporized plating material in the absence of any inert gas inputted
to said chamber; and applying a radio frequency field within said
chamber to ion plate said material from said plasma onto said
substrate. .Iaddend. .Iadd. 27. The process of claim 26, wherein
the system ambient pressure prior to the plating material
evaporation is lower than that necessary to sustain a glow
discharge. .Iaddend. .Iadd. 28. Apparatus for plating a substrate
with a plating material, including: a chamber adapted to hold said
substrate and said plating material; means for evacuating said
chamber; means for vaporizing said plating material in the
evacuated chamber; means for applying radio frequency power to the
vaporized plating material to form and maintain an ionized plasma
therefrom in the absence of any inert gas inputted to said chamber;
a radio frequency bias source means adapted to be connected to said
substrate; and means for applying a DC negative bias to said
substrate. .Iaddend.
Description
This invention relates in general to high particulate energy level
ion plating deposition of plating material, and in particular, to
gasless ion plating. Various high-rate ion plating sources
advantageously suited to applicant's gasless ion plating process
are disclosed in applicant's co-pending application entitled, "High
Rate Ion Plating Source," Application Ser. No. 551,703, filed Feb.
21, 1975, .Iadd.now U.S. Pat. No. 4,016,389, .Iaddend.in addition
to electron gun, filament and boat type sources, among other known
sources.
In the application of protective coatings to substrates, vacuum
evaporation systems, sputtering, and classical ion plating have
been used in the past with varying degrees of success. Vacuum
evaporation provides high deposition rates, but has the
disadvantage of being a "line-of-sight" process. Three-dimensional
uniformity is very difficult to achieve and requires expensive
tooling--and such deposited coating results in poorly bonded
columnar grains. Further, since there is no particle acceleration
involved in the vapor deposition, adhesion can frequently be a
problem. To some extent, sputtering overcomes the "line-of-sight"
problem, and offers a wide variety of materials, film
stoichiometry, and generally better adhesion, than does vapor
deposition. There are, however, serious problems with slow
deposition rates and three-dimensional uniformity. An often
overlooked problem with sputtering is the decreased energy of the
deposited atom. Sputtering is a secondary process. An ion of inert
gas is born in a plasma, at a space charge depression of typically
+80 to +100 volts. Only after an inelastic collision with the
target, is an atom of target material released for useful coating.
The neutral atom must then migrate back across the dark space,
through the plasma, onto the substrate. In the process, numerous
collisions deplete the atom's energy. Thus, in its journey to the
substrate, the inert gas that heretofore has been considered
essential for maintaining the plasma and removing the target
material, becomes a hindrance to the liberated atom of coating
material. Additionally, a considerable amount of this inert gas
becomes included in the deposited film. Classical ion plating-as
described, for example, in Mattox, U.S. Pat. No.
3,329,601--provides some of the advantages of the previous two
methods, but is entirely dependent upon an inert gas that is
introduced into the system to maintain the plasma. The classical
ion plating system ionizes only about 20% of the evaporated
material. Further, the full effect of the gas upon the coating
and/or substrate is unknown.
It is therefore a principal object of this invention to provide an
improved plating system.
Another object is to provide a plating system with high deposition
rates.
A further object is to provide a plating system not subject to
degradation caused by inert gases.
A still further object is to provide a plating system which coats
small internal diameters and irregularly shaped cavities of a
substrate.
Still another object of this invention is to provide a plating
process for plating a wide variety of materials, both conductive
and non-conductive.
Features of this invention useful in accomplishing the above
objects include a plating system utilizing a high rate ion source,
operable in a vacuum. The ion source is instrumental in converting
the plating material to the form of a plasma forming a "virtual"
cathode in the region of the substrate.
A specific embodiment representing what is presently regarded as
the best mode of carrying out the invention is illustrated in the
accompanying drawing:
In the drawing:
FIG. 1 represents a partially broken away and sectional view of a
gasless ion plating system constructed in accordance with the
principles of this invention; and,
FIG. 2, an illustrative representation of the operation voltage to
a conductive substrate, for plating thereof.
Referring to the drawing:
A high rate ion plating source 10 that functions as a material
vaporizing and ion generation source, for controlled environment
material ion plating, is supported by feedthrough ring 11, with the
power feed conduits 12 and 13 and combination ground connection and
support bracket 14. Such a source is disclosed, for example, in my
co-pending application entitled, "High Rate Ion Plating Source,"
application Ser. No. 551,703, filed Feb. 21, 1975.Iadd., now U.S.
Pat. No. 4,016,389.Iaddend.. It is expressly understood that any
other source may be utilized without departing from the principles
of this invention. Feedthrough ring 11, along with bell jar 15 and
base 16 supporting feedthrough ring 11, together, provide a closed,
controlled-environment, enclosure. Substrate items 17, to be ion
plated, are suspended by clamps 18 from the mounting arm 19 of
mounting post 20, anchored in base 16. Evacuation line 21, with
valve 22, is connected to opening 23 in base 16 for enclosure by an
evacuation pump (not shown), connected through line 21, with the
controlled environment bell jar enclosure. A gas supply line 24
with a metering control valve 25 is connected through opening 26 in
base 16 for feeding a gas from a single gas source (not shown), or
selected gases from a plurality of gas sources that valve-control
feed the line 24. Radio frequency power supply 27 feeds power
through hollow, tubular, copper lines 28 and 29, and on through
conduits 12 and 13, to ion source 10. .Iadd.As noted above, the
vaporizing source 10, shown as an RF source in FIGS. 1 and 2, may
be other known vaporizing sources without departing from the
principles of this invention. For example, conventional resistance
heat element sources including filament devices and boat devices
could be ulitized. .Iaddend.
In operation, the system represented in FIG. 1 is first evacuated
through evacuation line 21. Ratio frequency power is supplied to
ion source 10 from supply 27 to create a plasma of evaporated and
ionized deposition material, as described in the aforementioned
application. If substrate 17 is an insulator, the well known DC
self-bias effect that occurs when an insulator is placed in a radio
frequency field, causes a negative self-bias to occur on the
surface of the substrate 17. When plating a conductive substrate,
it is necessary to induce a bias on the substrate from an external
source. This is accomplished as shown in FIG. 2, where radio
frequency power supply 30 is connected to substrate 31 through
capacitor 32, and DC supply 33 provides a negative bias to
substrate 31 through RF choke coil 34. In a typical plating
operation, radio frequency power supply 27 was operated at a
frequency of 450 kilohertz, and radio .Iadd.frequency
.Iaddend.power supply 30 supplied on RF signal of 13.5 megahertz.
These frequencies are only illustrative, and may be adjustably
varied to apply to specific applications .Iadd.for example, power
supply 27 can be operated at a range of frequencies of
approximately 10 to 800 kilohertz while power supply 30 may be
operated in a range of frequencies of approximately 2-40
megahertz.Iaddend.. As shown in FIG. 2, ion source 10 vaporizes
plating material that then forms an ionized plasma 35, due to the
action of the radio frequency field. Plasma 35, with its uniform
density of ions and accompanying dark space, tends to follow the
geometry of a negatively charged substrate 31, forming a "virtual
cathode" for sputtering. The quality of the plasma allows for full,
three-dimensional, coverage for even the most irregular
surfaces--including the inside of small-diameter holes.
Classical ion plating requires that an inert gas (usually Argon) be
bled into the chamber to maintain the plasma. Using a high rate ion
source, such as manufactured by Endurex Corporation, Dallas, Tex.,
and described in the aforementioned co-pending patent application,
the plasma is made up of the evaporant, itself, and no gas needs to
be bled into the system .Iadd.in such a high rate system, with the
vaporizing means being an RF source, such a high rate source could
vaporize the plating material while simultaneously ionizing the
evaporant.Iaddend.. With this system, approximately 75% of the
evaporant is ionized. With the system shown in FIG. 2, the radio
frequency and direct current bias on substrate 31 helps shape the
plasma "virtual" cathode in optimizing the deposition of metal
plating materials and dielectric materials. The dark space is
formed, substantially as in radio frequency sputtering, except that
primary ions of the coating material, with high sticking
probability--instead of Argon-sputtering ions--are accelerated
across the dark space.
If it is desired to clean the substrate prior to plating, Argon gas
may be admitted into the chamber through gas supply line 24,
.Iadd.a radio frequency field applied to the appropriate area in
the chamber as in typical sputter cleaning operations, .Iaddend.and
back sputtering can then be performed. Further, other gases could
be admitted for controlled thermochemical, metalurgical, and/or
physical process purposes, in intermediate plating process steps
prior to, between, or after, gasless ion plating, in various
compound ion plating processes.
With the above-described system, a wide variety of materials can be
plated, including even paper, plastic, and textiles; and the
materials may be either conductive or non-conductive. To prevent
damage to temperature-sensitive substrates, a heat shield may be
placed between the high temperature ion source and the substrate.
The ionized plating material plasma moves around the shield to
plate on the substrate.
Whereas this invention is herein illustrated and described with
respect to several embodiments hereof, it should be realized that
various changes may be made without departing from essential
contributions to the art made by the teachings hereof.
* * * * *