U.S. patent application number 11/175237 was filed with the patent office on 2006-01-12 for protective coating on a substrate and method of making thereof.
This patent application is currently assigned to General Electric Company. Invention is credited to Toshiki Ebata, Yuji Morikawa.
Application Number | 20060008676 11/175237 |
Document ID | / |
Family ID | 35542147 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060008676 |
Kind Code |
A1 |
Ebata; Toshiki ; et
al. |
January 12, 2006 |
Protective coating on a substrate and method of making thereof
Abstract
Disclosed herein is a protective coating having a compressive
stress of less than 280 Mpa, for devices to be used in a corrosive
environment such as halogen containing gases or halogen plasma
atmosphere, e.g., wafer supporting device for use in semi-conductor
processing assemblies such as electrostatic chucks, heaters, etc.
The protective coating in one embodiment is crack-free, with a
compressive stress of less than 250 Mpa. It is deposited onto at
least one surface of the device via an ion-plating process, in
which the Ar flow is kept below 5 sccm, and one embodiment, at 0
sccm, for a crack-free protective layer.
Inventors: |
Ebata; Toshiki; (Osaka,
JP) ; Morikawa; Yuji; (Ako-Gun, JP) |
Correspondence
Address: |
GEAM - QUARTZ;IP LEGAL
ONE PLASTICS AVENUE
PITTSFIELD
MA
01201-3697
US
|
Assignee: |
General Electric Company
|
Family ID: |
35542147 |
Appl. No.: |
11/175237 |
Filed: |
July 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60586059 |
Jul 7, 2004 |
|
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|
Current U.S.
Class: |
428/698 ;
427/532 |
Current CPC
Class: |
C04B 41/52 20130101;
C23C 14/22 20130101; C04B 41/52 20130101; C04B 41/009 20130101;
C04B 41/89 20130101; C04B 41/009 20130101; C04B 41/5031 20130101;
C23C 14/0617 20130101; C04B 41/009 20130101; H01L 21/68757
20130101; C04B 41/52 20130101; C04B 41/5063 20130101; C23C 16/4581
20130101; C04B 41/4529 20130101; C04B 35/583 20130101; C04B 41/4529
20130101; C04B 41/5064 20130101; C04B 41/52 20130101; C04B 41/522
20130101; C04B 41/4529 20130101; C04B 41/5031 20130101; C04B
41/4531 20130101; C04B 41/4531 20130101; C04B 35/522 20130101; C04B
41/522 20130101; C04B 41/4529 20130101; C04B 41/5057 20130101; C04B
41/5063 20130101; C04B 41/87 20130101; C23C 16/4404 20130101; C04B
41/5031 20130101; Y10T 428/30 20150115; C04B 41/52 20130101; C23C
16/513 20130101; C23C 16/303 20130101; C04B 41/5063 20130101 |
Class at
Publication: |
428/698 ;
427/532 |
International
Class: |
B05D 3/00 20060101
B05D003/00; B32B 19/00 20060101 B32B019/00 |
Claims
1. A protective layer for coating at least a surface of an article
for use in a halogen-containing gas and/or plasma environment,
wherein said at least a surface comprises one of pyrolytic boron
nitride, graphite, pyrolytic graphite, and combinations thereof,
wherein the protective layer has a compressive stress of less than
280 Mpa.
2. The protective layer of claim 1, wherein the protective layer
has a compressive stress of less than 250 Mpa.
3. The protective layer of claim 1, wherein the protective layer
comprises one of aluminum nitride, aluminum oxynitride, and
combinations thereof.
4. The protective layer of claim 1, wherein the protective layer is
deposited onto said at least a surface of an article via an ion
plating method.
5. The protective layer of claim 4, wherein the protective layer is
deposited onto said at least a surface of an article via an ion
plating method.
6. The protective layer of claim 5, wherein ion plating method
includes Argon as a non-reactive gas.
7. The protective layer of claim 6, wherein the Argon flow rate is
kept below a rate of 10 sccm.
8. The protective layer of claim 7, wherein the Argon flow rate is
kept below a rate of 5 sccm.
9. The protective layer of claim 1, wherein at least a surface
comprises pyrolytic boron nitride.
10. The protective layer of claim 1, wherein the protective layer
comprises aluminum nitride.
11. The protective layer of claim 1, wherein the protective layer
has a thickness in the range between 3 .mu.m to 200 .mu.m.
12. The protective coating layer of claim 1, wherein the protective
layer is substantially crack-free.
13. The protective coating layer of claim 1, wherein the layer has
an etch resistance rate of less than 50 Angstroms per minute upon
exposure to a halogen-containing gas and/or plasma environment.
14. The protective coating layer of claim 13, wherein the layer has
an etch resistance rate of less than 40 Angstroms per minute upon
exposure to a fluorine-containing gas and/or plasma
environment.
15. An article comprising a protective coating layer on at least
one of its surfaces, said coating layer comprises at least one of
aluminum nitride, aluminum oxynitride or combinations thereof, and
wherein the coating layer is substantially crack free when said
article is exposed to fluorine containing gases and/or plasma.
16. The article of claim 13, wherein the protective coating layer
has a compressive stress of less than 280 Mpa.
17. A method for modifying the in-film stress in a protective
coating layer of an article for use in a halogen-containing gas
and/or plasma environment, said method comprising: depositing a
protective coating layer on at least one surface of the article,
said coating layer comprising at least one of aluminum nitride,
carbon and/or oxygen doped aluminum nitride, aluminum oxynitride or
combinations thereof, said at least one surface comprises at least
one of pyrolytic boron nitride, pyrolytic graphite and/or carbon
doped boron nitride, and combinations thereof; wherein said
protective coating layer is substantially crack free upon exposure
to said halogen-containing gas and/or plasma environment.
18. The method of claim 17, wherein the deposited coating layer has
a compressive stress of less than 280 Mpa.
19. The method of claim 17, wherein the protective coating layer is
deposited on said at least one surface via an ion plating
method.
20. The method of claim 19, wherein the ion plating method includes
Ar as a non-reactive gas, and wherein the Ar gas flow rate is
maintained at an average of less than 10 sccm.
21. The method of claim 17, wherein the protective coating layer
has an adhesion strength which exceeds the cohesive strength of the
surface protected by said coating layer.
22. The method of claim 17, wherein said at least one surface of
the article is first protected by depositing at least a layer of
pyrolytic boron nitride, pyrolytic graphite and/or carbon doped
boron nitride on said surface.
23. An article manufactured the method of claim 28.
24. The protective layer of claim 1, wherein the layer is a
multilayer.
25. The protective layer of claim 1, wherein the protective coating
layer has an adhesion strength which exceeds the cohesive strength
of the surface protected by said coating layer.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/586,059, filed Jul. 7, 2004.
BACKGROUND
[0002] In the semi-conductor industry, equipment is typically
exposed to a corrosive environment such as ammonia, hydrogen and
halogens at elevated temperatures. Examples of such equipment
include substrates, liners, evaporators, crucibles, heating
elements, electrostatic chucks, wafer carriers, susceptors, and the
like. With respect to the manufacture of computer integrated
circuits (e.g., computer chips), a device called electrostatic
chuck (ESC) is typically used to support the substrates such as
wafer etc., in the process wherein layers of materials are
selectively deposited and removed from the wafers.
[0003] During wafer coating, some of the materials that are applied
to the wafer or chip also deposit on the equipment in the
deposition chamber. This requires periodic cleaning of the
equipment, which is commonly done using high-energy gas plasma.
Aggressive cleaning agents generally use a halogen-bearing gas such
as nitrogen trifluoride (NF.sub.3) to produce fluorine plasma,
which cleans the chamber but may simultaneously attack the
components of the equipment causing erosion. This erosion limits
the life of the components and the equipment. It is therefore
desirable to extend the service life of components and equipment by
the use of a durable protective coating.
[0004] Japanese Published Patent Application No. JP62-123094A2
discloses susceptors employing a coating layer of AlN formed by a
thermal chemical vapor deposition ("CVD") method, on a substrate of
high purity carbon based material. Japanese Published Patent
Application No. H06-061335 discloses an electrostatic chuck having
a protective coating layer comprising AlN, Al2O3, AlON, deposited
by methods including sputtering, ion plating and CVD methods to
protective the underlying PBN layer. PBN does not have
anti-corrosive property with respect to halogen gas and halogen
plasma. In the protective coating layers of the prior art, there
exhibits cracking on the coating thus typically resulting in an
etch rate of exceeding 5,000 Angstroms per minute (/min). Peeling
is also experienced in the protective coating layers of the prior
art.
[0005] Stresses in films are measured using techniques known in the
art, e.g., as described in "Mechanical Properties of Thin Films,"
by W. D. Nix, Metallurgical Transactions A, 20A, 2217 (1989); "The
Mechanical Properties of Thin Condensed Films" by R. W. Hoffman,
Physics of Thin Films, Vol 3, Academic Press, New York, 1966; and
P. H Townsend et al., J. Appl. Phys. 62, 4438 (1987), for
multi-layered structures. For AlN coating films, the residual
(mechanical) stress is the sum of the stress due to the CTE
mismatch between AlN and the substrate, and the intrinsic stress of
the AlN as deposited. The total mechanical or residual stress of a
film can be summarized by the following formula (1):
Stress(residual)s=Stress s.sub.T(thermal)+Stress s.sub.i
(intrinsic) (1).
[0006] In the equation, s.sub.i is intrinsic stress, which is a
fundamental result of the conditions and method of film growth and
is to a large degree a reflection of the film structure and the
presence of impurities. The term s.sub.T refers to the thermal
stress in the film due to the CTE mismatch between the film and the
substrate. Thermal stress s.sub.T is dependent on various factors,
including the CTE of the substrate, the CTE of the protective film,
the processing temperature (T.sub.dep) and the reference
temperature (T.sub.ref), which can be the room temperature or the
temperature of the device under operating condition(s) of
interest.
[0007] For AlN coatings on pBN substrates, since PBN is a material
with low thermal heat expansion coefficient as compared to
materials comprising the protective layer such as aluminum nitride,
aluminum oxynitride, and the like, etc., there is a strong tensile
stress formed in a protective layer that is formed at high
temperature and then cooled at room temperature. Because of this
reason, cracks and peeling are expected in the protective layer
formed in the processes of the prior art.
[0008] There remains a need for protective coating layers of
equipment used in corrosive environment, e.g., wafer supporting
device such as ESCs, susceptors, heater, etc. to strongly adhere to
the underlying substrate. There is also a need for protective
coating layers for substrates including pBN, graphite, or
combinations thereof, to have excellent anti-corrosion property in
halogen gas/halogen plasma environments.
SUMMARY
[0009] This disclosure relates to a protective coating on a
substrate and method of making thereof. In one embodiment, the
invention relates to a protective layer for coating at least a
surface of a device for use in a halogen-containing gas and/or
plasma environment, the protective coating layer having compressive
stress of less than 280 Mpa, wherein said surface comprising one of
pyrolytic boron nitride, graphite, pyrolytic graphite, and
combinations thereof.
[0010] The invention further relates to a protective layer for
coating at least a surface of a device for use in a
halogen-containing gas and/or plasma environment, wherein the
protective coating is under a compressive stress of greater than or
equal to about 50 kilograms per square centimeter when disposed
upon the substrate, and wherein the coating is deposited on the
surface of the device by means of a reactive ion plating method at
an Ar flow rate of <6 sccm. In one embodiment of the invention,
the Ar flow rate is kept at 0 sccm.
[0011] Lastly, the invention relates to articles comprising the
aforementioned protective coating, and articles manufactured by the
aforementioned method of making the protective coating.
BREIF DESCRIPTION OF THE FIGURES
[0012] FIG. 1 illustrates a cross-section view of one embodiment of
an article employing the protective coating of this invention, an
electrostatic chuck.
[0013] FIG. 2 shows three pictures of AlN coatings. Figure (a) is a
scanning electron microscopy (SEM) image showing an AlN protective
layer (a) that is formed via a thermal CVD method. Figure (b) is a
SEM image showing an AlN layer (b) that is via an ion-plating
method, wherein the Ar flow is kept at about 15 sccm. Figure (c) is
a SEM image showing an AlN layer (c) formed via the ion-plating
method, with the Ar flow is kept at 05.
[0014] FIG. 3 is a graph illustrating the relationship between the
compressive stress of the AlN protective layer and the Ar flow rate
in the ion-plating process.
[0015] FIG. 4 contains two diagrams showing the behavior of the
protective layer under tensile stress (a) and compressive
stress.
[0016] FIG. 5 is a bar chart comparing the etching rates of AlN
layer formed via the ion-plating method of one embodiment of the
invention, versus protective layers formed by other methods,
including pBN and sintered AlN surfaces.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0017] As used herein, the terms "first," "second," and the like do
not denote any order or importance, but rather are used to
distinguish one element from another, and the terms "the", "a" and
"an" do not denote a limitation of quantity, but rather denote the
presence of at least one of the referenced item. Furthermore, all
ranges disclosed herein are inclusive of the endpoints and are
independently combinable.
[0018] As used herein, approximating language may be applied to
modify any quantitative representation that may vary without
resulting in a change in the basic function to which it is related.
Accordingly, a value modified by a term or terms, such as "about"
and "substantially," may not to be limited to the precise value
specified, in some cases. In at least some instances, the
approximating language may correspond to the precision of an
instrument for measuring the value.
[0019] As used herein, "substrate" or "substrates" may be used
interchangeably with "surface" or "surfaces."
[0020] As used herein, "protective coating" layer may be used
interchangeably with "coating layer" or "coating film," or
"protective layer," or "protective coating layer."
[0021] As used herein, "crack free" or "substantially crack free"
means that no cracks can be observed by optical microscopy or SEM
with 10 k magnification. Cracks also include holes, perforations,
pores, or lines.
[0022] Adhesion means the bonding of two different materials, and
cohesion means a mass that resists separation. As used herein,
having an excellent adhesion or having a layer that free from
peeling, or a coating layer that doesn't peel, means that the
adhesive strength of the coating layer exceeds the cohesive
strength of underlying layer or layers. The stress at T.sub.ref can
be lowered by having T.sub.dep closer to T.sub.ref, or to adjust
the intrinsic stress for a given fixed Delta CTE where: [0023]
Stress s.sub.T (thermal) is proportional to
((CTE.sub.substrate-CTE.sub.film)*(T.sub.dep-T.sub.ref)).
[0024] As known in the art, the in-film or mechanical stress is a
force in the plane of a coating film such as AlN, acting per unit
area of the film cross section. The mechanical stress may be
compressive or tensile in character. The compressive stress
prevents the formation of cracks thereby increasing the useful life
of the article.
[0025] In one embodiment, the invention relates to articles
comprising protective coatings that can be advantageously used in
harsh semiconductor manufacturing environments that contain
ammonia, hydrogen and halogens at elevated temperatures. These
coated articles are advantageously used as electrostatic chucks,
heater elements and wafer carriers during the manufacture of
integrated circuits, semiconductors, silicon wafers, chemical
compound semiconductor wafers, liquid crystalline display devices
and their glass substrates, or the like.
[0026] Coating Characteristics The protective coating comprises at
least one of AlN, AlON, or combinations thereof. In one embodiment,
the protective coating layer is a single layer of AlN, AlON, or
combinations thereof. In another embodiment, it is a multi-layer of
multiple coatings of the same material, e.g., AlN, AlON, etc., or
multiple different layers of AlN, AlON, etc., coated in
succession.
[0027] In one embodiment, the protective coatings are deposited
upon substrates comprising boron nitride (BN), pyrolytic boron
nitride (PBN), or carbon doped pyrolytic boron nitride (C-PBN),
graphite, pyrolytic graphite (pG), or combinations thereof.
[0028] The protective coatings are also advantageously in a state
of compressive stress when disposed upon the substrates, thus
facilitating the retention of dimensional stability and mechanical
strength as well as a reduction in the number of cracks. The
protective coatings also have a substantially reduced number of
cracks when compared with other protective coatings manufactured by
processes such as thermal chemical vapor deposition. In one
embodiment, the protective coating has excellent adhesion to the
substrate and is crack free. The reduced number of cracks as well
as the morphology of the coating minimizes any etching of the
substrate during the periodic cleaning of the equipment.
[0029] When applied to a substrate, the protective coating layer of
the invention significantly increases the life cycle of the
article. The life cycle is the amount of time that the article can
be subjected to a cleansing environment before it has to be
replaced as a result of the etching away of the protective coating.
Examples of suitable cleansing environments include halogen-based
plasmas, halogen-based radicals generated from remote plasma
source, halogen-based species decomposed by heating, halogen-based
gases, oxygen plasmas, oxygen-based plasmas, or the like. An
example of a halogen-based plasma is a nitrogen trifluoride
(NF.sub.3) plasma. Fluorinated hydrocarbons such as, for example,
carbon tetrafluoride (CF.sub.4) can be used either alone or in
combination with oxygen. The article may also be subjected to a
reactive ion-etching environment and should be capable of offering
resistance to etching in such an environment as well.
[0030] In one embodiment, the protective coating increases the life
cycle of the article by a time period of greater than or equal to
about 5 hours over articles that have unprotected PBN as a
substrate. In one embodiment, the protective coating increases the
life cycle of the article by a time period of greater than or equal
to about 10 hours over similar articles that have unprotected PBN.
In yet another embodiment, the protective coating increases the
life cycle of the article by a time period of greater than or equal
to about 50 hours over similar articles that have unprotected PBN.
In yet another embodiment, the protective coating increases the
life cycle of the article by a time period of greater than or equal
to about 100 hours over similar articles that have unprotected
PBN.
[0031] The thickness of the protective coating may be varied
depending upon the application and upon the cleaning conditions.
Protective coatings having thickness of about 1 to about 5 .mu.m,
generally permit good thermal contact between the wafer and the
electrostatic chuck, but do not last as long as coatings having
greater thicknesses. Coatings having thicknesses of greater than 5
.mu.m, however, have longer life cycles than coatings having
thickness of less than 5 .mu.m. In one embodiment, the coating has
a thickness of greater than or equal to about 2 micrometers
(.mu.m). In another embodiment, the protective coating thickness is
greater than or equal to about 10 .mu.m. In a third embodiment, the
thickness is greater than or equal to about 50 .mu.m. In yet
another embodiment, the thickness is greater than or equal to about
75 .mu.m.
[0032] As known in the art, compressive stress in protective
coating films or layers prevents the formation of cracks thereby
increasing the useful life of the article. The protective coatings
of the present invention are generally under compressive stress
when deposited upon substrates comprising PBN, PG or C-PBN.
[0033] In one embodiment, the protective film has a compressive
stress of less than 300 MPa. In a second embodiment, the film has a
compressive stress of less than 280 MPa. In a third embodiment, the
film has a compressive stress of less than 250 MPa.
[0034] The compressive stress permits the protective coating to
withstand thermal cycling without cracking. The protective coatings
have very few cracks and this feature provides significant
resistance against etching. In one embodiment, the initial
protective coating may have cracks that occupy a volume of less
than 10% of the total volume of the coating. In another embodiment,
the initial protective coating may have cracks that occupy a volume
of less than 5% of the total volume of the coating. In yet another
embodiment, the protective coating may be completely crack free
when it is initially manufactured.
[0035] The protective coating is characterized as being
etch-resistant, or having a low-etch rate in an environment
comprising halogens or when exposed to plasma etching, reactive ion
etching, plasma cleaning and gas cleaning. The etch rate for the
protective coating is much lower than coatings of a similar
chemical composition that are sintered. The etch rate of the
protective coating is also less than the etch rate for the PBN
substrate. This low etch rate provides protection for the PBN
thereby extending the life of the article. In one embodiment, the
etch rate is less than 100 Angstroms per minute (/min). In a second
embodiment, the etch rate is less than 50/min. In a third
embodiment; it is less than or equal to about 40 Angstroms per
minute (/min) in a cleansing environment that comprises halogens or
when exposed to a reactive ion etching environment.
[0036] Process of depositing the protective coating--IP the
protective coating is deposited using ion plating (IP). In ion
plating, aluminum is ionized using a radio frequency (RF)
discharge. Ionization and plasma is mainly sustained by the
formation of nitrogen ions from nitrogen. Ionization is brought by
plasma discharge, which can be sustained not only by RF coils but
also by using a capacitive coupling plasma or an inductive coupling
plasma. The chamber in which the deposition occurs is generally
maintained under vacuum conditions. Nitrogen gas is introduced into
the chamber and becomes ionized by RF discharge. The substrate is
generally placed on or near a cathode to direct the ionized gases.
The substrate is placed in an argon/nitrogen plasma, together with
the aluminum metal, which vaporizes on heating and becomes partly
ionized (acquires charged atoms) as it diffuses through the
discharging region to form the protective coating.
[0037] The temperature in the chamber during ion plating is
maintained at less than or equal to about 400.degree. C. The
deposition rate during ion plating is greater than or equal to
about 0.1 .mu.m/hour. In one embodiment, the deposition rate is
greater than or equal to about 0.15 .mu.m/hour. In another
embodiment, the deposition rate is greater than or equal to about
0.20 .mu.m/hour. In yet another embodiment, the deposition rate is
greater than or equal to about 0.25 .mu.m/hour.
[0038] In an ion plating method, an inert/non-reactive gas such as
Argon can be introduced into the vacuum reactor. Applicants have
found that by controlling the Ar flow amount in the reactor, the
anti-corrosive property of the protective coating layer can be
controlled, for an anti-corrosive protective layer with no
cracks/minimal or no peeling (strong adhesion strength between the
coating layer and the pBN/pG substrate).
[0039] In one embodiment of the ion-plating process, when the Ar
flow is reduced to 10 sccm, there is some evidence of peeling along
the entire protective layer. When the Ar flow is reduced to 5 sccm,
peeling is observed in one some part of the protective layer. In
one embodiment wherein the Ar flow is kept below 6 sccm, the
protective coating layer displayers a compressive stress of less
than 280 Mpa and little if no peeling. In another embodiment, the
Ar flow rate is kept at 0 sccm for a crack-free protective layer
that also adheres to the substrate (without peeling), and with a
compressive stress of less than 250 Mpa.
[0040] Applications of the Invention The protective coatings can be
advantageously used for semi-conductor processing components such
as substrates, liners, evaporators, crucibles, heating elements,
wafer carriers, electrostatic chucks, susceptors, or the like. The
protective coating enhances the life of the aforementioned
semi-conductor processing components when these components are
exposed to ammonia, hydrogen, halogens such as fluorine, chlorine,
nitrogen trifluoride, or the like, at temperatures of greater than
or equal to about 200.degree. C.
[0041] FIG. 1 illustrates the cross section of an article employing
the protective coating of the invention. The article can be a
heating element, an electrostatic chuck or a wafer carrier that can
be used for locating and/or heating the silicon wafers during the
deposition of surface layers on the wafer. In one embodiment, the
article 8 is an electrostatic chuck. The article comprises a
graphite core 1 of about 10 mm. The core can also be made from PBN,
hot pressed BN, or composites. Disposed upon the graphite core is a
pyrolytic boron nitride (BN) layer 2 of about 300 .mu.m. In one
embodiment, the pBN layer 2 is can be deposited by thermal chemical
vapor deposition (thermal CVD), hot pressing, sintering, or plasma
enhanced chemical vapor deposition (PECVD).
[0042] Disposed upon the BN layer 2 is a layer of pyrolytic
graphite (PG). The PG layer is deposited upon the BN layer 2 by
chemical vapor deposition (CVD) or other processes known in the
prior art. The PG layer is machined into a desired configuration,
forming chuck electrode(s) 3 at the top surface and heater
electrode (4) at the bottom surface of the article. The machined PG
layer 3 and 4, together with the first pBN layer 2 and the graphite
substrate 1, form the substrate body 5 of the article. A pyrolytic
boron nitride (PBN) coating 6 is disposed upon the body of the
article such that it substantially covers the body of the article.
The pBN coating layer 6 is formed in a thermal CVD furnace at
1850.degree. C., under reduced pressure with 3 moles of ammonia and
2.4 moles of methane gas with respect to 1 mole of boron
trichloride. A carbon-doped PBN insulation layer 6 of a thickness
of 100 about .mu.m is formed on the entire surface of substrate 5,
having an electrical resistivity of 2.8.times.10.sup.12
.OMEGA.-cm.
[0043] This PBN coating 6 resists oxidation, provides electrical
insulation, chemical and mechanical protection and minimizes the
opportunity for carbon contamination of the wafers. It also has
very high thermal conductivity in the a-b direction, thereby
minimizing any thermal non-uniformity on the top of the heater. The
protective coating AlN 7 is then disposed upon the PBN coating
6.
[0044] In one embodiment to provide the electrostatic chuck
protection to be usable even in a corrosive environment such as
halogen gases and/or halogen plasma atmosphere, the AlN coating
layer 7 is applied onto the electrostatic chuck 8 in a reactive ion
plating process, wherein the Ar flow rates are kept at 0 sccm (no
Ar), 5 sccm, 10 sccm, and 15 sccm respectively. In the ion plating
process, nitrogen reacts with aluminum at about 400.degree. C.
forming as the AlN protective layer 7 of the invention with
anti-corrosive property with respect to halogen gas and halogen
plasma.
[0045] As a comparative example on a comparative electrostatic
chuck, instead of using an AlN protective coating via ion-plating
method, an AlN protective layer is formed using a thermal CVD
method at 950.degree. C. FIGS. 2 (a)-2(c) are SEM (Scanning
Electron Microscope) images, comparing the AlN protective layers of
the invention with the prior art AlN coating via thermal CVD.
[0046] FIG. 2 (a) shows cracks in the AlN layer formed by a thermal
CVD process, confirming that it is not practical to employ this
coating in a corrosive environment. FIG. 2 (c) is an SEM showing an
AlN coating formed by the ion-plating method, wherein the Ar flow
rate is reduced to 0, thus forming a crack-free AlN layer and
without forming. FIG. 2 (b) is an SEM showing that when the Ar flow
is reduced to 15 sccm, the AlN layer remains crack-free although
there is some showing of peeling.
[0047] FIG. 3 is a graph illustrating the relationship between the
compressive stress of the AlN protective layer and the Ar flow rate
in the ion-plating process. In one embodiment wherein the AlN
protective layer 7 thickness of 0.5 .mu.m is formed, with the
Young's Modulus value is 130 GPa and the Poisson ratio is measured
as 0.28 by the deflection method, the compressive stress is
measured to be 248 Mpa when the Ar flow amount is reduced to 0
sccm. The compressive stress is measured to be 267 Mpa when the Ar
flow rate is kept at 5 sccm. When the Ar flow is set at 10 sccm,
the compressive stress is 344 Mpa. Finally, when the Ar flow rate
is 15 sccm, the compressive stress is 360 Mpa. A
[0048] It should be note that the AlN protective layer formed by
the thermal CVD method whose SEM is shown in FIG. 2 (a), the
compressive stress cannot be measured since all samples show
evidence of cracks.
[0049] FIG. 4 contains two diagrams showing the behavior of the
protective layer under tensile stress (a) and compressive stress.
As illustrated in the prior art AlN coating via thermal CVD and
with the occurrence of cracks, the thermal heat expansion
coefficient of pBN is small comparing to materials comprising the
protective layer such as aluminum nitride, aluminum oxynitride, and
the like, etc. Since there is a strong tensile stress due to the
difference in thermal expansion coefficients and this residual
tensile stress exceeds the tensile strength of the protective layer
itself, the protective layer is ruptured thus causing cracks. This
is illustrated in FIG. 4 (a). In the AlN protective layer formed
via an ion-plating method and as illustrated in FIG. 4 (b),
compressive stress is formed and thus minimizing or eliminating the
occurrence of cracks.
[0050] FIG. 5 is a graph comparing the anti-corrosion property of
the AlN coating layer of the invention as formed via the
ion-plating process, with other protective surfaces. The
anti-corrosion property is illustrated as the etch rate under a NF3
plasma atmosphere, the lower the rate, the higher the
anti-corrosion property. In the Figure, etch rates measured in an
AlN protective layer formed by the ion-plating method wherein the
Ar flow is 0 sccm is compared with the etch rates as measured in
sintered AlN, thermal CVD pBN, and Si wafer. The etch rates of the
ion-plated AlN of the present invention is at 4.8 .ANG./minute, as
compared to rates in sintered AlN of 33 .ANG./min., 455
.ANG./minute in Si wafer, and >10,000 .ANG./minute in pBN.
* * * * *