U.S. patent application number 10/608674 was filed with the patent office on 2004-03-25 for corrosion and erosion resistant thin film diamond coating and applications therefor.
This patent application is currently assigned to Saint-Gobain Ceramics & Plastics. Invention is credited to Windischmann, Henry.
Application Number | 20040058155 10/608674 |
Document ID | / |
Family ID | 22637263 |
Filed Date | 2004-03-25 |
United States Patent
Application |
20040058155 |
Kind Code |
A1 |
Windischmann, Henry |
March 25, 2004 |
Corrosion and erosion resistant thin film diamond coating and
applications therefor
Abstract
A thin film diamond coating is formed relatively slowly with a
relatively low methane concentration and is identified by its Raman
spectrographic characteristics. The thin film diamond, preferably 5
to 40 microns thick, provides substantially greater corrosion and
erosion resistance in a corrosive environment than other thin film
diamond coatings. It is believed that such thin film diamond
coating is provided with enhanced chemical resistance due to its
purity and quality.
Inventors: |
Windischmann, Henry;
(Northboro, MA) |
Correspondence
Address: |
David P. Gordon
GORDON & JACOBSON, P.C.
65 Woods End Road
Stamford
CT
06905-2701
US
|
Assignee: |
Saint-Gobain Ceramics &
Plastics
|
Family ID: |
22637263 |
Appl. No.: |
10/608674 |
Filed: |
June 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10608674 |
Jun 27, 2003 |
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09724045 |
Nov 28, 2000 |
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6605352 |
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60174727 |
Jan 6, 2000 |
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Current U.S.
Class: |
428/408 ;
118/715; 118/726; 427/249.1; 427/249.8; 428/336 |
Current CPC
Class: |
C02F 1/46109 20130101;
C02F 2001/46138 20130101; Y10T 428/265 20150115; C23C 16/276
20130101; C23C 16/4404 20130101; Y10T 428/26 20150115; Y10T 428/30
20150115 |
Class at
Publication: |
428/408 ;
118/715; 118/726; 427/249.1; 427/249.8; 428/336 |
International
Class: |
C23C 016/26; B32B
009/00; C23C 016/00 |
Claims
1. A protective coating for use on a surface of an article in a
corrosive environment, consisting of: a polycrystalline diamond
film material made by chemical vapor deposition having a thermal
conductivity greater than 1000 W/mK and a Raman Full Width at Half
Maximum of less than 10 cm.sup.-1, said diamond film material
having a thickness not greater than 150 microns.
2. A protective coating according to claim 1, wherein: said diamond
film material has a thickness between 5 and 40 microns.
3. A protective coating according to claim 1, wherein: said diamond
film material is transparent to infrared radiation.
4. A protective coating according to claim 1, wherein: said diamond
film material has a Raman Full Width at Half Maximum of less than 5
cm.sup.-1.
5. A protective coating according to claim 1, further comprising: a
dopant added to said polycrystalline diamond film material to
increase its electrical conductivity.
6. A protective coating according to claim 5, wherein: said dopant
is boron.
7. An apparatus for processing a semiconductor wafer, comprising:
a) a processing chamber having an inner surface; and b) a mandrel
within said chamber and adapted to receive and hold the
semiconductor wafer, at least one of said inner surface and said
mandrel including a protective coating comprising a polycrystalline
diamond film material made by chemical vapor deposition having a
thermal conductivity greater than 1000 W/mK and a Raman Full Width
at Half Maximum of less than 10 cm.sup.-1, said diamond film
material having a thickness not greater than 100 microns.
8. A apparatus according to claim 7, wherein: said processing
chamber includes a heat source and at least one window which is
substantially transparent to heat from said heat source, at least a
portion of said window being provided with said protective
coating.
9. A processing chamber according to claim 7, wherein: said mandrel
is adapted to rotate about an axis within said chamber.
10. A processing chamber according to claim 7, wherein: said
protective coating has a Raman Full Width at Half Maximum of less
than 5 cm.sup.-1.
11. An electrode, comprising: a) an electrically conductive body;
b) a polycrystalline diamond film coating on said body, said
coating having been made by chemical vapor deposition and having a
thermal conductivity greater than 1000 W/mK and a Raman Full Width
at Half Maximum of less than 10 cm.sup.-1, said diamond coating
having a thickness not greater than 40 microns; and c) a dopant in
said diamond coating for increasing its electrical
conductivity.
12. An electrode according to claim 11, wherein: said
polycrystalline diamond film has a Raman Full Width at Half Maximum
of less than 5 cm.sup.-1.
13. A method of growing a thin film diamond coating which resists
corrosion and erosion, said method comprising: a) positioning a
substrate element on a deposition mandrel in a processing chamber
of a chemical vapor deposition (CVD) system b) growing a diamond
coating on said substrate to a thickness of between 5 and 150
microns, the diamond coating having a Raman Full Width at Half
Maximum of less than 10 cm.sup.-1, and c) removing said substrate
from said processing chamber.
14. A method according to claim 13, wherein: said substrate is
maintained at a temperature of greater than 700.degree. C.
15. A method according to claim 13, wherein: said diamond coating
is grown at a rate of between 0.5 and 6.0 microns per hour.
16. A method according to claim 13, wherein: said diamond coating
has a thermal conductivity greater than 1000 W/mK.
17. A method according to claim 13, wherein: said diamond coating
has a Raman Full Width at Half Maximum of less than 10
cm.sup.-1.
18. A method according to claim 13, wherein: said diamond coating
has a Raman Full Width at Half Maximum of less than 5 cm.sup.-1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of the copending
provisional application 60/174727 filed Jan. 6, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates broadly to thin film diamond
coatings. More particularly, this invention relates to the use of a
thin film diamond coating as a protectant against corrosion and
erosion in semiconductor processing chambers.
[0004] 2. State of the Art
[0005] One step in the manufacture of semiconductor chips is
processing a wafer in a semiconductor processing chamber to deposit
layers on the wafer. The process of depositing layers on a
semiconductor wafer substrate usually involves a chemical vapor
deposition (CVD) or physical vapor deposition (PVD)process in which
the wafer is placed on a graphite mandrel (which may also be
designed as a susceptor for microwave or other radiation) in a
thermal reactor chamber. The mandrel is typically coated with
silicon carbide (SiC) to protect the graphite against corrosion. As
used herein, the term "corrosion" refers to physical and/or
chemical degradation. The wafer is held within a stream of a
reactant gas flowing across the surface of the wafer. The thermal
reactor may be heated to a high temperature by external lamps which
pass infra-red radiation into the reactor chamber through heating
ports. The heating ports are typically positioned both above and
below the mandrel, and are covered by quartz windows which are
transparent to the infra-red radiation. The mandrel positions and
rotates the wafer during the deposition process, and a pyrometer
aimed at the back of the mandrel is generally used to detect the
temperature of the mandrel, and thereby the wafer, during
processing and to serve as an input to a controller for the power
to the external lamps.
[0006] During the process, the interior surfaces of the chamber and
surfaces of components within the chamber are subject to coating by
a deposition film. For example, during a high temperature nitride
process, silicon nitride ceramic film is deposited on the walls of
the chamber as well as the mandrel. As the deposition film on the
chamber walls and mandrel thickens, it is prone to flaking, which
introduces undesirable particulates into the chamber as well as
alters the radiation emissivity of the mandrel. As the emissivity
of the mandrel changes, the accuracy of a pyrometer coupled to the
mandrel to monitor the temperature of the mandrel is compromised.
As a result, the precision of controlling the temperature of the
mandrel and consequently the precision of depositing the deposition
film on the mandrel becomes limited.
[0007] Therefore, an in-situ etching process is periodically used
to remove the ceramic film from the chamber walls, the mandrel, and
other coated surfaces. Typically, a halogen gas or plasma, e.g.,
NF.sub.3, is used as the etchant. It is not uncommon for portions
of a protective coating on the mandrel to also be etched away
during this process, and once the protective coating is removed
from the surface of the mandrel, the mandrel itself is subject to
corrosive attack by the etchant. Other surfaces of the system are
similarly effected. Attack by the etchant affects the emissivity of
the mandrel which, discussed above, reduces quality control over
the semiconductor wafer. Moreover, such etching reduces the
structural integrity of the etched system components.
[0008] It is known that a thick film CVD diamond, e.g., 200-300
microns thick, is an effective protective coating against both
mechanical and chemical degradation. However, as a practical matter
the cost of such thick diamond films prohibits their use in this
application.
[0009] U.S. Pat. No. 5,916,370 to Chang discloses using relatively
thin diamond films, e.g. 7-15 microns thick, to protect against
corrosion and erosion in semiconductor processing chambers.
However, thin diamond films are generally not nearly as effective a
protective coating as are thick diamond coatings. The processing
chamber corrosion is a particularly challenging problem and attacks
even materials coated with the diamond film described in Chang.
[0010] Similar problems exist for materials in other environments
subject to highly corrosive fluids.
SUMMARY OF THE INVENTION
[0011] In accordance with the present invention, a novel
combination of a member coated with a thin film diamond coating
formed by a particular process has been determined to be as
effective in resisting corrosion as is a typical CVD diamond thick
film. The thin film diamond coating is formed relatively slowly
with a relatively low methane concentration and is identified by
its Raman spectrographic characteristics. The thin film diamond,
preferably 5 to 40 microns thick, has substantially similar Raman
characteristics to the thick film diamond disclosed in U.S. Pat.
No. 5,736,252 to Bigelow et al., which is hereby incorporated by
reference herein in its entirety. While the Bigelow et al. patent
identified that the thick free standing diamond film described
therein had particular favorable thermal conductivity and optical
transparency, it was not recognized that a thin film diamond grown
in the described manner and having the resulting particular Raman
spectrographic characteristics would provide substantially greater
corrosion resistance in a corrosive environment and greater erosion
resistance in a mechanically degrading environment than other thin
film diamond coatings. It is believed that such a thin film diamond
coating is provided with enhanced chemical resistance and
mechanical integrity due to its purity and quality. In particular,
the process minimizes grain boundaries where impurities tend to
concentrate and which present an opportunity for free chemical
bonds to be available at the surface. Exposed grain boundaries are
therefore generally more susceptible to chemical activity and
mechanical breakdown than exposed bare crystalline surfaces.
[0012] According to one embodiment of the invention, the
particularly specified thin film diamond coating is coated onto
exposed surfaces within a semiconductor processing chamber. The
exposed surfaces of the processing chamber are thereby provided
with a protective coating which resists mechanical and chemical
degradation, and which is particularly resistive to chemical attack
at a variety of temperatures.
[0013] According to another embodiment of the invention, in an
environment in which various fluids containing corrosive
environmentally harmfuil constituents are to be detoxified by
electrolytic means, electrodes are coated with the specified
diamond coating. The electrodes may be made conductive by adding to
the diamond of the coating an electrical charge carrier dopant,
e.g. boron, to increase its electrical conductivity. The dopant may
be a donor or acceptor type.
[0014] Additional objects and advantages of the invention will
become apparent to those skilled in the art upon reference to the
detailed description taken in conjunction with the provided
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic view of a chemical vapor deposition
(CVD) system for coating a diamond film on a substrate;
[0016] FIG. 2 is a section view of a semiconductor processing
chamber coated with a protective diamond coating in accordance with
a first exemplar application of the invention; and
[0017] FIG. 3 is a section view of an electrode coated with the
protective diamond coating in accordance with a second exemplar
application of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] In accord with the invention, a thin film diamond coating
(that is, a diamond film coating typically having a thickness of
between 5 and 150 microns (micrometers) and preferably having a
thickness of less than 40 microns is provided which has the Raman
spectrographic characteristics of the thick film diamond coating
disclosed in U.S. Pat. No. 5,736,252, previously incorporated by
reference. More particularly, the thermal conductivity matches that
of free-standing thick film (i.e., is greater than 1000 W/mK), has
a Raman Full Width at Half Maximum (FWHM) of less than 10
cm.sup.-1, and preferably less than 5 cm.sup.-1, which is an
indicator of diamond coating purity and quality, and optical
absorption and transparency.
[0019] The thin film diamond coating may be coated upon substrates
and various component surfaces using a chemical vapor deposition
(CVD) system, e.g., d.c. arc jet, hot wire, or microwave energy CVD
system. Referring to FIG. 1, with respect to a d.c. arc jet CVD
system, for example, a CVD system 100 includes a hollow, tubular
cathode 102 located near the top end of a hollow barrel 104 in a
metal jacket member 106. The jacket member 106 has an annular space
108 suitable for holding a fluid coolant. The barrel 104 and jacket
member 106 are surrounded by a fluid-cooled magnetic coil assembly
110. Longitudinally spaced at the end of the barrel 104 opposite
that of the cathode 102 is an anode 112. The anode 112 has a
central opening (not shown) aligned with the axis. of the barrel
104 and leading to a nozzle 114. The nozzle 114 opens into an
evacuated deposition chamber 116 which has a preferably
liquid-cooled mandrel 117 on which a deposition substrate 118 is
spaced fro the end of the nozzle 114. A first gas injection tube
120 located at the anode 112 injects gas into the central opening
of the anode 112. A second gas injection tube 122 is located
between the anode 112 and the nozzle 114.
[0020] In the operation of the system 100, hydrogen gas is injected
through the first injection tube 120 at a predetermined rate.
Between the anode 112 and the nozzle 114, more hydrogen gas, mixed
with methane or another hydrocarbon, is injected through the second
injection tube 122. The concentration of methane is based on the
total percentage of methane injected as a volume percent of the
total gas injected through both injection tubes 120, 122. A direct
current arc is struck between the cathode 102 and the anode 112.
The enthalpy of the gas in the barrel 104 is then adjusted by
control of the arc power to result in the desired temperature of
the substrate 118, which is heated by the gas impinging from the
nozzle 114. At this enthalpy, the hydrogen becomes dissociated into
a plasma of hydrogen atoms. The magnetic coil assembly 110 around
the barrel 104 generates a solenoidal magnetic field which has the
effect of swirling the arc about the anode 112 to reduce anode
erosion.
[0021] The activated gas travels through the nozzle 114, enters the
evacuated deposition chamber 116, and impinges on the substrate 118
to form a diamond film. As the methane enters the activated gas
through the second injection tube 122, it also becomes partially
dissociated into activated, unstable hydrocarbon radical species.
At the substrate 118, the hydrogen acts as a facilitating gas for
the deposition of the carbon atoms from the activated hydrocarbon
radicals as diamond crystallites bonded to each other. The diamond
crystallites consist of carbon atoms bonded chemically to each
other by what is generally referred to as "sp3" bonds in a film
upon the substrate 118.
[0022] The advantageous characteristics of the protective thin film
diamond coating are primarily achieved by forming the diamond in a
very low methane concentration environment and at a very slow rate
of growth. Preferred methane concentrations are below approximately
0.07 percent, and the diamond coating is preferably deposited on a
substrate kept at a temperature at or below 900.degree. C. The
diamond film is preferably grown at a rate of between 0.5 and 6.0
microns per hour to a thin film thickness of approximately 5 to 40
microns.
[0023] The particulars of CVD systems and their operation are well
known in the art, and parameters other than the particular low
methane concentration, e.g., enthalpy, vacuum level, and substrate
temperature, are determinable by those skilled in the art without
the necessity of undue experimentation.
[0024] The resulting thin film diamond is optically and infrared
transparent, thermally conductive, and, most importantly, corrosion
and erosion resistant. Previously, the optical transparency and
thermal conductivity of thick film diamonds grown in the described
manner had been recognized. However, there had been no prior
recognition of the superior corrosion and erosion resistance
provided by a diamond film as described herein. In addition, there
had been no prior suggestion that a thin film diamond coating would
have such similar favorable optical and thermal characteristics or
superior corrosion and erosion resistance. It is believed that the
thin film diamond coating is provided with enhanced chemical and
mechanical properties due to its purity and quality. In particular,
the grain boundaries which tend to concentrate impurities and
present an opportunity for free surface bonds to be available, and
which are therefore generally more susceptible to chemical activity
and mechanical breakdown than exposed bare crystalline surfaces,
are minimized.
[0025] Therefore, the thin film diamond coating is suitable for use
in the corrosive environment of a semiconductor wafer processing
chamber. Referring to FIG. 2, a semiconductor processing chamber
200 includes a main body 212 having inner surfaces 214 and defining
a gas inlet port 216 and a gas exhaust port 218. Upper and lower
quartz windows 220, 222, each transparent to infrared radiation,
are held about the main body 212 by an upper clamp ring 224 and a
lower clamp ring 226. An inner chamber 228 is formed between the
inner surfaces 214 of the main body 212 and the upper and lower
quartz windows 220, 222 and facilitates the flow of a process gas
over the surface of a semiconductor wafer, which is supported and
positioned as described below.
[0026] Process gas is injected into the inner chamber 228 through
the gas inlet port 216, which is connected to a gas source (not
shown). Residual process gas and various waste products are removed
from the inner chamber 228 through the exhaust port 218. Upper
heating sources 230 are mounted above upper window 220 and lower
heating sources 232 are mounted below lower window 222 to provide
infra-red radiant heat into the inner chamber 228 through the
respective upper and lower windows 220, 222.
[0027] A rotatable mandrel (or susceptor) 240 is provided within
the inner chamber 228 for supporting the semiconductor wafer. The
mandrel 240 includes a body 242 having a recess (seating surface)
244 or other means for retaining a wafer within the mandrel. The
body 242 of mandrel 240 is preferably made of graphite; however,
the body 242 may be made of other materials such as silicon
carbide, silicon nitride, aluminum nitride, and other ceramics. The
body 242 may also be comprised of a metal material having a
protective coating.
[0028] The rotatable mandrel 240 is coupled to a mounting fixture
246 that supports the mandrel within the inner chamber 228. In this
manner, a semiconductor wafer (not shown) supported on the mandrel
240 may be rotated during processing to permit a more uniform
heating and deposition. Preferably, the mandrel 240 also includes a
plurality of through-holes 248 for receiving at least three loading
pins 250. Loading pins 250 are mounted to a support shaft 252 which
provides vertical movement to raise and lower the pins 250. Such
pins are used to raise a semiconductor wafer above the seating
surface 244 while the wafer is being loaded or unloaded from the
processing chamber.
[0029] An annular pre-heat ring 254 positioned on the main body 212
of the processing chamber encircles the mandrel 240. The pre-heat
ring 254 is typically made of silicon carbide-coated graphite or
quartz, depending upon the particular type of processing chamber
being used.
[0030] The exposed surfaces within the processing chamber are
coated with an optically transparent, thermally conductive and
corrosion and erosion resistant thin film diamond coating 256. More
particularly, the exposed surfaces include, but are not limited to,
the inner surfaces 214 of the main body 212, the inner surfaces of
the upper lower quartz windows 220, 222, the mandrel body 242, the
mandrel support shaft 246,. and the loading pins 250. It will be
appreciated that the quartz windows 220, 222 may also be coated,
since the diamond coating utilized is infrared transparent.
[0031] Therefore, when an etchant is injected into the processing
chamber for purposes of wafer etching or chamber etch-cleaning, the
etchant removes the undesirable buildup, yet is unable to penetrate
the thin film diamond coating on the surfaces of the components of
the processing chamber and expose the underlying component
material. As such, the processing chamber retains its
integrity.
[0032] The thin film diamond coating may additionally be used in
other environments, particularly in highly corrosive environments.
For example, referring to FIG. 3, in an environment in which
various fluids containing corrosive environmentally harmful
constituents are to be detoxified by electrolytic means, the
protective coating may be provided on an electrode 300. The
electrode 300 includes a conductive body 302 which is provided with
a thin film diamond coating 304 of the type identified above. The
diamond coating 304 is made conductive by doping the diamond
coating with a charge carrier donor or acceptor, e.g. boron.
[0033] There have been described and illustrated herein a
protective coating, and several applications for the use thereof.
While a particular embodiment of the invention has been described,
it is not intended that the invention be limited thereto, as it is
intended that the invention be as broad in scope as the art will
allow and that the specification be read likewise. While the thin
film diamond coating is preferably between 5 and 40 microns thick,
it will be appreciated that the coating may be less than 5 microns,
e.g., 0.5 to 5 microns, or greater than 40 microns, e.g., up to 150
microns thick. However, it is preferred that coatings no thicker
than 100 microns be used, as such coatings begin to function as
thick films and are therefore unduly costly to manufacture and may
suffer a reduction in their adhesion to the underlaying surface. In
addition, while the methane concentration and substrate deposition
temperature have been considered a key parameter, it is understood
that other hydrocarbons may be substituted for methane and, when a
substitute is used, its concentration is likewise kept within the
same concentration limit as methane in terms of the resulting
concentration of activated species of carbon radicals. Specifically
referring to the use of the protective coating on the interior
surfaces of a processing chamber, while a rotatable mandrel has
been disclosed, it will be appreciated that the mandrel may be
fixedly mounted. In addition, while particular surfaces of the
processing chamber have been described as being provided with a
diamond coating according to the invention, it will be understood
that not all such surfaces and elements need be coated, and that
other surfaces may likewise be coated. For example, and not by way
of limitation, due to costs, it may be desirable to coat with
diamond solely the mandrel or the quartz windows. Also, while it
has been described to use the thin film diamond coating in a
semiconductor wafer processing chamber, it will be appreciated that
other deposition and etching environments may also be protectively
coated in a like manner. In addition, with respect to the electrode
application, it will be appreciated that other conductive elements,
alloys, and composites may be used as the doping material.
Furthermore, it will therefore be appreciated that the thin film
diamond coating described herein may be provided on other articles
for protection in corrosive and erosive environments, such as in
combustion chambers, process monitoring windows, and the like. It
will therefore be appreciated by those skilled in the art that yet
other modifications could be made to the provided invention without
deviating from its spirit and scope as claimed.
* * * * *