U.S. patent application number 09/927244 was filed with the patent office on 2003-02-13 for corrosion resistant coating for semiconductor processing chamber.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Dam, Chuong Quang, Kaushal, Tony S..
Application Number | 20030029563 09/927244 |
Document ID | / |
Family ID | 25454456 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030029563 |
Kind Code |
A1 |
Kaushal, Tony S. ; et
al. |
February 13, 2003 |
Corrosion resistant coating for semiconductor processing
chamber
Abstract
Resistance to corrosion in a plasma environment is imparted to
components of a semiconductor processing tool by forming a rare
earth-containing coating over component surfaces. The
plasma-resistant coating may be formed by sputtering rare
earth-containing material onto a parent material surface.
Subsequent reaction between these deposited materials and the
plasma environment creates a plasma-resistant coating. The coating
may adhere to the parent material through an intervening adhesion
layer, such as a graded subsurface rare earth layer resulting from
acceleration of rare earth ions toward the parent material at
changed energies prior to formation of the coating.
Inventors: |
Kaushal, Tony S.;
(Cupertino, CA) ; Dam, Chuong Quang; (San Jose,
CA) |
Correspondence
Address: |
APPLIED MATERIALS, INC.
2881 SCOTT BLVD. M/S 2061
SANTA CLARA
CA
95050
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
25454456 |
Appl. No.: |
09/927244 |
Filed: |
August 10, 2001 |
Current U.S.
Class: |
156/345.1 |
Current CPC
Class: |
C23C 16/4404 20130101;
H01J 37/32477 20130101 |
Class at
Publication: |
156/345.1 |
International
Class: |
C23F 001/02 |
Claims
What is claimed is:
1. A substrate processing chamber having at least one component
bearing a rare earth-containing coating bound to a parent material
by an intervening adhesion layer, such that the component exhibits
resistance to etching in a plasma environment.
2. The substrate processing chamber of claim 1 wherein said rare
earth-containing coating is selected from the group of Yttrium
fluoride, Yttrium oxides, Yttrium-containing oxides of Aluminum,
Erbium oxides, and Neodymium oxides.
3. The substrate processing chamber of claim 1 wherein the
component is selected from the group comprising a chamber liner, a
chamber dome, a chamber wall, a cover plate, a gas manifold, a
faceplate, a substrate support, and a substrate support/heater.
4. The substrate processing chamber of claim 1 wherein the adhesion
layer comprises a graded subsurface layer of rare earth material
formed in the surface of the parent material.
5. The substrate processing chamber of claim 4 wherein the adhesion
layer comprises a subsurface rare earth layer resulting from a
changed energy of bombardment during introduction of rare earth
material into the parent material through an IBAD process.
6. The substrate processing chamber of claim 4 wherein the adhesion
layer comprises a subsurface rare earth layer resulting from a
changed implantation energy during introduction of rare earth
material into the parent material through a MEPIIID process.
7. The substrate processing chamber of claim 1 wherein the parent
material comprises aluminum nitride or aluminum oxide.
8. A method for treating a parent material for corrosion resistance
to plasma comprising: forming an adhesion layer over a parent
material; and forming a rare earth-containing coating over the
adhesion layer.
9. The method of claim 8 wherein the rare earth-containing coating
is formed by deposition of rare earth-containing material.
10. The method of claim 9 wherein rare-earth ions are introduced by
conducting reactive sputter deposition in an oxygen-containing
ambient.
11. The method of claim 8 wherein the adhesion layer is formed by
introducing rare earth metals into the parent material at varying
energies to form a graded implant layer.
12. The method of claim 11 wherein the adhesion layer is formed by
an ion bombardment assisted deposition (IBAD) technique employing
bombardment of a deposited rare earth layer with inert Argon ions
at changed energies.
13. The method of claim 11 wherein the adhesion layer is formed by
accelerating rare-earth ions at the parent material at changed
energies of implantation.
14. The method of claim 13 wherein rare-earth ions are accelerated
using a MEPIIID ion implanter.
15. The method of claim 8 wherein the rare-earth containing coating
is formed by exposing a rare earth present on a surface of the
parent material to a fluorine ambient.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to equipment used in the
manufacture of semiconductor devices. More specifically, the
present invention relates to formation of a plasma-resistant
coating on the surfaces of selected components of semiconductor
manufacturing equipment.
[0002] With the development of high density plasma sources and 300
mm-wafer-size reactors, and the growing importance of certain high
temperature processing steps, wear on chamber materials may impact
tool performance and productivity. Specifically, interaction
between corrosive plasmas and reactor materials become of critical
importance to development of future product lines of semiconductor
manufacturing equipment. Very harsh environments (e.g., NF.sub.3,
C.sub.2F.sub.6, C.sub.3F.sub.3, ClF.sub.3, CF.sub.4, SiH.sub.4,
TEOS, WF.sub.6, NH.sub.3, HBr, etc.) can be found in plasma etchers
and plasma-enhanced deposition reactors. Constituents from many of
these environments may react with and corrode parent anodized
materials such as aluminum oxide.
[0003] Because of their favorable physical characteristics, ceramic
materials are commonly used in today's semiconductor manufacturing
equipment to meet the high process performance standards demanded
by integrated circuit manufacturers. Specifically, ceramic
materials exhibit high resistance to corrosion, which helps to
increase process kit lifetimes and lowers the cost of consumables
as compared to other materials such as aluminum or quartz. Example
of components that can be advantageously manufactured from ceramic
materials include chamber domes for inductively coupled reactors,
edge rings used to mask the edge of a substrate support in certain
processing chambers, and chamber liners that protect walls of the
chamber from direct exposure to plasma formed within the chamber
and improve plasma confinement by reducing coupling of a plasma
with conductive chamber walls. In some instances, the chamber walls
themselves may also be manufactured from ceramic materials. Ceramic
materials are also used for critical components such as high
temperature heaters and electrostatic chucks.
[0004] Ideally, critical and/or high value ceramic parts of a
semiconductor processing tool employed in production should have a
lifetime of at least one year. Depending on the particular tool,
this can correspond to processing of 50,000 wafers or more without
changing any parts on the tool (i.e., a zero consumable situation),
while at the same time maintaining high process performance
standards. For example, to meet the requirements of some
manufacturers, less than 20 particles of size of greater than 0.2
.mu.m should be added to the wafer during the processing of the
wafer in the chamber.
[0005] However, unwanted particle generation is an issue for high
temperature applications where processing temperatures exceed
550.degree. C. For example, in highly corrosive fluorine and
chlorine environments, Al.sub.2O.sub.3 and AlN ceramic materials
may corrode to form unwanted AlO:F, AlF.sub.x, or AlCl.sub.x films
at the component surface. These AlO:F, AlF.sub.x, or AlCl.sub.x
films have relatively high vapor pressures and relatively low
sublimation temperatures. For example, the sublimation temperature
of aluminum chloride (AlCl.sub.x) is approximately 350.degree. C.
and the sublimation temperature of aluminum fluoride (AlF.sub.x) is
approximately 600.degree. C. If a ceramic component is employed at
a temperature exceeding the sublimation temperature, the outer
surface of the component may be consumed by the process of
formation of AlO:F, AlF.sub.x or AlCl.sub.x. This consumption of
material can degrade the chamber component and/or introduce
particles into the process.
[0006] In light of the above, improvement in the corrosion
resistance of various substrate processing chamber parts and
components is desirable.
SUMMARY OF THE INVENTION
[0007] The present invention provides a method for improving the
corrosion resistance of components of semiconductor tools by
creating high temperature halogen corrosion resistant surface
coatings. Specifically, coatings of rare earth-containing materials
are formed over the surfaces of ceramic tool components. These rare
earth-containing materials are stable in plasma environments at
high temperatures and may be formed onto the chamber components by
sputter deposition. To promote adhesion of the coating to the
parent material, an adhesion layer may be first formed on the
ceramic material by accelerating rare earth ions into the surface
of the ceramic material at changed energies to form an implant
layer prior to formation of the surface coating.
[0008] An embodiment of a substrate processing chamber in
accordance with the present invention includes at least one
component bearing a rare earth-containing coating bound to a parent
material by an intervening adhesion layer, such that the component
exhibits resistance to etching in a plasma environment.
[0009] An embodiment of a method for treating a parent material for
resistance to plasma etching comprises forming an adhesion layer
over a parent material, and forming a rare earth-containing coating
over the adhesion layer.
[0010] These and other embodiments of the present invention, as
well as its advantages and features, are described in more detail
in conjunction with the text below and attached figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A is a simplified cross-sectional view of a high
density plasma chemical vapor deposition chamber;
[0012] FIG. 1B is a simplified cross-sectional view of a
capacitively coupled plasma enhanced chemical vapor deposition
chamber;
[0013] FIG. 2A is a cross-sectional view of a coated member in
accordance with a first embodiment of the present invention;
[0014] FIG. 2B is a cross-sectional view of a coated member in
accordance with a second embodiment of the present invention;
[0015] FIG. 3 is a simplified schematic view of a Metal Plasma
Immersion Ion Implantation and Deposition (MEPIIID) technique;
[0016] FIG. 4 is a graph illustrating the concentration of rare
earth ions at various depths in a ceramic component treated with
MEPIIID;
[0017] FIG. 5 is a simplified cross-sectional view of an exemplary
metal vapor vacuum arc implanter used in the MEPIIID technique;
[0018] FIG. 6 is a simplified schematic view of an Ion Bombardment
Assisted Deposition (IBAD) technique;
[0019] FIG. 7A shows a magnified (2000.times.) view of the top
surface of a first grade of an AlN coupon following exposure to a
fluorine ambient at high temperature.
[0020] FIG. 7B shows a further magnified (7500.times.) view of the
top surface of the AlN coupon of FIG. 7A.
[0021] FIG. 7C shows a magnified (2000.times.) view of the top
surface of a second grade of an AlN coupon following exposure to a
fluorine ambient at high temperature.
[0022] FIG. 7D shows a further magnified (7500.times.) view of the
top surface of the AlN coupon of FIG. 7C.
[0023] FIG. 8A shows a magnified (2000.times.) view of the top
surface of a first grade of an AlN coupon coated with yttrium oxide
by reactive sputtering in accordance with an alternative embodiment
of the present invention.
[0024] FIG. 8B shows a further magnified (7500.times.) view of the
top surface of the AlN coupon of FIG. 8A.
[0025] FIG. 8C shows a magnified (2000.times.) view of the top
surface of the AlN coupon of FIGS. 8A-B following exposure to a
fluorine ambient at high temperature.
[0026] FIG. 8D shows a magnified (7500.times.) view of the top
surface of the AlN coupon of FIG. 8C.
[0027] FIG. 8E shows a magnified (2000.times.) view of the top
surface of a second grade of an AlN coupon coated with yttrium
oxide by reactive sputtering in accordance with an alternative
embodiment of the present invention.
[0028] FIG. 8F shows a further magnified (7500.times.) view of the
top surface of the coated AlN coupon of FIG. 8E.
[0029] FIG. 8G shows a magnified (2000.times.) view of the top
surface of an AlN coupon coated with in accordance with one
embodiment of the present invention, following exposure to a
fluorine ambient at high temperature.
[0030] FIG. 8H shows a further magnified (7500.times.) view of the
top surface of the AlN coupon of FIG. 8G.
[0031] FIG. 9A shows a magnified (2000.times.) view of the top
surface of an AlN coupon implanted with yttrium in accordance with
one embodiment of the present invention.
[0032] FIG. 9B shows a further magnified (7500.times.) view of the
top surface of the implanted AlN coupon of FIG. 9A.
[0033] FIG. 9C shows a further magnified (9000.times.) view of the
fractured AlN coupon of FIGS. 9A-9B.
[0034] FIG. 9D shows a magnified (2000.times.) view of the surface
of the implanted AlN coupon of FIGS. 9A-9C following exposure to a
fluorine ambient at high temperature.
[0035] FIG. 9E shows a further magnified (7500.times.) view of the
surface of the implanted AlN coupon of FIG. 9D.
[0036] FIG. 10A shows a magnified (3300.times.) view of a fractured
AlN coupon implanted with yttrium oxide following exposure to a
fluorine ambient at high temperature.
[0037] FIG. 10B shows a further magnified (7500.times.) view of the
fractured AlN coupon of FIG. 10A.
[0038] FIG. 11 shows the results of Energy Dispersive Spectroscopy
(EDS) of the surface of the AlN coupon of FIGS. 10A-10B coated in
accordance with an embodiment of the present invention, following
exposure to a fluorine ambient at high temperature.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0039] According to the present invention, ceramic components of
semiconductor fabrication tools, including but not limited to
electrostatic chucks, gas nozzles, chamber domes, heated pedestals,
gas distribution manifolds, chamber walls and chamber liners, may
be coated with a rare earth-containing material and adhesion layer
in order to improve corrosion resistance. Environments for which
the coated components can be advantageously used include, but are
not limited to, highly corrosive plasma etching environments, and
high temperature deposition environments that feature corrosive
gases.
[0040] I. Exemplary Substrate Processing Chambers
[0041] FIGS. 1A and 1B are simplified cross-sectional views of
exemplary substrate processing chambers in which ceramic components
made according to the method of the present invention may be
employed. FIG. 1A is a simplified cross-sectional view of a high
density plasma chemical vapor deposition (HDP-CVD) chamber 10 such
as an Ultima HDP-CVD substrate processing chamber manufactured by
Applied Materials, the assignee of the present invention. In FIG.
1A, substrate processing chamber 10 includes a vacuum chamber 12 in
which a substrate support/heater 14 is housed. Substrate
support/heater 14 includes an electrostatic chuck 15 that securely
clamps substrate 16 to substrate support/heater 14 during substrate
processing.
[0042] When substrate support/heater 14 is in a processing position
(indicated by dotted line 18), deposition and carrier gases are
flowed into chamber 10 via gas injection nozzles 20. Nozzles 20
receive gases through gas supply lines, which are not shown.
Chamber 10 can be cleaned by the introduction of fluorine radicals
or other etchant radicals that are dissociated in a remote
microwave plasma chamber (not shown) and delivered to chamber 10
through a gas feed port 22. Unreacted gases and reaction byproducts
are exhausted from the chamber 10 by a pump 24 through an exhaust
port on the bottom of the chamber. Pump 24 can be isolated from
chamber 10 by a gate valve 26.
[0043] The rate at which deposition, carrier and clean gases are
supplied to chamber 10 is controlled by a mass flow controllers and
valves (not shown), which are in turn controlled by computer
processor (not shown). Similarly, the rate at which gases are
exhausted from the chamber is controlled by a throttle valve 28 and
gate valve 26, which are also controlled by the computer
processor.
[0044] A plasma can be formed from gases introduced into chamber 10
by application of RF energy to independently controlled top coil 30
and side coil 32. Coils 30 and 32 are mounted on a chamber dome 34,
which defines the upper boundary of vacuum chamber 12. The lower
boundary of vacuum chamber 12 is defined by chamber walls 36.
Substrates can be loaded into chamber 10 and onto chuck 15 through
an opening 38 in chamber wall 36.
[0045] According to the present invention, any or all of
electrostatic chuck 15, gas nozzles 20, and chamber dome 34 of
substrate support/heater 14 may be fabricated from material
implanted with rare-earth ions.
[0046] FIG. 1B is a simplified cross-sectional view of a
capacitively-coupled plasma enhanced chemical vapor deposition
chamber (PECVD) 50 such as the CxZ CVD substrate processing chamber
manufactured by Applied Materials, the assignee of the present
invention. In FIG. 1B, substrate processing chamber 50 includes a
vacuum chamber 52 in which a heated pedestal 54 and a gas
distribution manifold 56 are housed. During processing, a substrate
58 (e.g., a semiconductor wafer) is positioned on a flat or
slightly convex surface 54A of pedestal 54. The pedestal can be
controllably moved between a substrate loading position (depicted
in FIG. 1B) and a substrate processing position (indicated by
dashed line 60 in FIG. 1B), which is closely adjacent to manifold
56.
[0047] Deposition, carrier and cleaning gases are introduced into
chamber 52 through perforated holes 56A of a gas distribution
faceplate portion of manifold 56. More specifically, gases input
from external gas sources (not shown) flow into the chamber through
the inlet 62 of manifold 56, through a conventional perforated
blocker plate 64 and then through holes 56A of the gas distribution
faceplate. Gases are exhausted from chamber 52 through an annular,
slot-shaped orifice 70 surrounding the reaction region and then
into an annulate exhaust plenum 72. Exhaust plenum 72 and
slot-shaped orifice 70 are defined by ceramic chamber liners 74 and
76 and by the bottom of chamber lid 57.
[0048] The rate at which deposition, carrier and clean gases are
supplied to chamber 50 is controlled by mass flow controllers and
valves (not shown), which are in turn controlled by computer
processor (not shown). Similarly, the rate at which gases are
exhausted from the chamber is controlled by a throttle valve (not
shown and also controlled by the computer processor) connected to
exhaust port 66, which is fluidly-coupled to exhaust plenum 72.
[0049] The deposition process in chamber 50 can be either a thermal
or a plasma-enhanced process. In a plasma-enhanced process, an RF
power supply (not shown) provides electrical energy between the gas
distribution faceplate and an electrode 68A within pedestal 54 so
as to excite the process gas mixture to form a plasma within the
generally cylindrical region between the faceplate and pedestal.
This is in contrast to an inductive coupling of RF power into the
gas, as is provided in the chamber configuration shown in FIG. 1A.
In either a thermal or a plasma process, substrate 58 can be heated
by a heating element 68B within pedestal 54.
[0050] According to the present invention, any or all of pedestal
54, heating element 68B gas distribution manifold 56, and chamber
liners 74 and 76 may be constructed from a ceramic material
implanted with rare-earth ions according to the present invention.
The embodiments of FIGS. 1A and 1B are for exemplary purposes only,
however. A person of skill in the art will recognize that other
types of ceramic parts in these and other types of substrate
processing chambers in which highly corrosive environments are
contained (e.g., reactive ion etchers, electron cyclotron resonance
plasma chambers, etc.) may benefit from the teaching of the present
invention.
[0051] II. Coating Formation
[0052] In accordance with embodiments of the present invention,
parent materials of components of semiconductor fabrication
apparatuses are protected against corrosion by a surface coating
containing a rare earth metal, the coating exhibiting low
reactivity to a halogen gas environment at elevated temperatures.
For purposes of this patent application, yttrium is considered a
rare earth metal.
[0053] Surface coatings in accordance with embodiments of the
present invention maintain adhesion to the parent material at high
operating temperatures (up to 1000.degree. C.). The surface
coatings may include yttrium fluoride, yttrium oxides,
yttrium-containing oxides of Aluminum (YAlO.sub.3,
Y.sub.3Al.sub.5O.sub.12, Y.sub.4Al.sub.2O.sub.9), Erbium oxides,
Neodymium oxide, and other rare earth oxides.
[0054] The high operating temperatures of many plasma processes can
create problems arising from a lack of adhesion between a parent
material and an overlying coating. Accordingly, it is useful to
form an adhesion layer between the coating and parent material.
[0055] This is illustrated in FIG. 2A, which is a cross-sectional
view of coated member 215 in accordance with an embodiment of the
present invention. As shown in FIG. 2A, adhesion layer 212 overlies
parent material 214, and coating 216 is formed over adhesion layer
212. Parent material 214 may comprise AlN, Al.sub.2O.sub.3, or some
other material. In accordance with one embodiment of the present
invention, rare earth-containing coating 216 may be deposited over
adhesion layer 212 by sputtering techniques. Sputtering may take
place in a particular ambient, for example by reactive sputtering
of a target of the rare earth material in an oxygen ambient to
create a rare earth oxide coating.
[0056] Adhesion layer 212 may exhibit a coefficient of thermal
expansion intermediate that of parent material 214 and coating 216,
such that coating 216 adheres to parent material 214 over a wide
temperature range. The adhesion layer may be formed over the
substrate by deposition prior to formation of the coating.
[0057] In alternative embodiments in accordance with the present
invention, the adhesion layer may be formed by accelerating rare
earth ions toward the parent material at changed energies prior to
formation of the surface coating. For example, adhesion layer 212
of structure 215 of FIG. 2A may result from ion-implantation, with
reduction over time in the energy of implantation of rare earth
metals into parent material 214 creating implanted adhesion layer
212. Implanted adhesion layer 212 may be graded, with the rare
earth metal concentration gradient determined by duration of
implantation at particular energy levels.
[0058] Acceleration of rare-earth ions to a depth into the target
parent material may be accomplished using a variety of techniques.
In one implantation approach, rare earth ions are introduced into
the parent material utilizing metal plasma ion immersion
implantation and deposition (MEPIIID). FIG. 3 shows a simplified
schematic view of the MEPIIID technique.
[0059] As shown in FIG. 3, single or dual-source MEPIIID source 300
is used to implant and deposit a layer of rare-earth ions over the
component 300 being treated. With this technique, component 302 is
inserted into plasma 304 after plasma 304 has been deflected with
magnetic filter 304. Sheath edge 311 represents a concentrated
plasma zone near biased target component 302, where most reactions
and rearrangements of materials occur.
[0060] The treated component 302 is then subjected to implantation
by biasing component 302 with a negative voltage utilizing
electrode 307 in communication with power supply 306. When target
component 302 is unbiased, it is subject to the initial deposition
phase of the treatment process. When target component 302 is
negatively biased (e.g., at -50 keV), ions 310 from plasma 304 are
accelerated toward target component 302 at high velocities so that
target component 302 is subjected to ion implantation to a depth
into the material. The magnitude of the negative bias of the target
material, and hence the energy of bombardment, is then reduced to
produce a gradient of concentration of rare earth material to a
depth in the material.
[0061] A more detailed description of a single-source MEPIIID
system is set forth in U.S. Pat. No. 5,476,691 issued to Ian Brown
et al., hereby incorporated by reference in its entirety. In a
technique employing a dual-source MEPIIID implanter, the treatment
process is similar except that plasmas from two separate plasma
guns are brought together through independent magnetic channels, in
order to deposit a thin film over the parent component.
[0062] The MEPIIID approach to implantation of rare earth metals
requires that the component be subject to an electrical bias.
However, such biasing is not possible with parent materials that
are poor conductors. This issue can be resolved if an electrode is
embedded within the component, the embedded electrode capable of
being biased during the implantation step. Such is the case for
heaters and electrostatic chucks.
[0063] FIG. 4 is a graph that shows the concentration of rare-earth
ions and aluminum nitride at various depths of an aluminum nitride
component treated with a MEPIIID technique. As can be seen in FIG.
4 the upper surface of the treated component comprises a layer M of
rare-earth material formed from the deposition phases of the
treatment process. Beneath layer M, the concentration of rare-earth
ions decreases with depth until point N, where the concentration of
rare-earth ions reaches background levels (essentially zero).
[0064] Because of this profile of implanted material, a graded
interface is obtained between the coated surface and the bulk of
the parent material. An interface of this type provides a gradual
transition of surface properties such as physical and chemical
properties, and results in improved adhesion as compared to more
abrupt, stepped profile distributions. Such a graded interface also
eliminates limitations of adhesion due to thermal mismatch--often a
limiting factor of corrosion resistant coatings having an abrupt
interface.
[0065] In components having an abrupt transition between coating
and parent material, the protective coating deposited over chamber
materials may crack in response to environmental stresses. For
example, during high temperature thermal cycles the temperature
change during and/or between various cycles can be as high
700.degree. C. for ceramic heater applications. Another example of
an environmental stress that may induce cracking of a coating are
the mechanical stresses associated with wafer handling.
[0066] Once a crack in a coating is initiated, in a corrosive
environment aggressive and corrosive free radicals may penetrate
the film coating and erode the underlying wall material. This
penetration may cause film delamination and particulate
contamination.
[0067] By contrast, corrosion-resistant coatings in accordance with
embodiments of the present invention may serve as a barrier to the
diffusion of reactive species into the parent material. In this
respect, implanted structures may have superior performance and
versatility as compared with structures formed by plasma spray,
CVD, laser ablation or PVD deposition techniques.
[0068] FIG. 5 is a simplified cross-sectional view of an exemplary
MEPIIID.TM. ion implanter 500 useful to implant ceramic components
with rare-earth metals according to this embodiment of the present
invention. Implanter 500 includes a cathode 502 of the desired
metal atoms or alloy to be implanted, an anode 504, a plasma
extractor 506, a trigger 508, a cavity 510, and an insulative
bushing 512 all surrounded by an outer frame 514.
[0069] The vacuum arc is a plasma discharge that takes place
between cathode 502 and the grounded anode 504. The plasma is
generated at a number of tiny points on the surface of the cathode,
called cathode spots and having a dimension of few microns. The arc
is concentrated to an extremely high current density, in the order
of 10.sup.8-10.sup.12 .ANG./cm.sup.2. The metal ions are extracted
from the plasma using perforated extraction grids 506 which are
polarized at appropriate conditions to accelerate the extracted
ions toward the ceramic component target. Such MEPIIID.TM. ion
sources are efficient and do not require a background gas--the
plasma generation process is neither an evaporative nor a
sputtering process. A more detailed description of a MEPIIID.TM.
ion implanter similar to the one shown in FIG. 5 is given in U.S.
Pat. No. 5,013,578 issued to Ian Brown et al. The '578 patent is
hereby incorporated by reference in its entirety.
[0070] In the past, MEPIIID.TM. implanters have typically been used
for metal surface treatment in the automotive industry (e.g.,
piston surface treatment) and the tooling industry for increased
hardness. However, one limitation of such commercially available
implanters is their anisotropy, e.g., the limitation to implant
flat surfaces only. This is perfectly acceptable to implant the
exposed face of flat ceramic heaters or electrostatic chucks, but
it is a limitation in treating complex-shaped ceramic parts.
[0071] Manufacturability of a commercially feasible MEPIIID.TM.
implanter based on a design similar to that shown in FIG. 5 has
been established, however, in which large-area or complex-shaped
parts could be treated in an industrial scale, high dose implanter.
A description of such implanter is set forth by Ian Brown in Brown,
et al., "Metal Ion Implantation for Large Scale Surface
Modification," J. Vac. Sci. Tech., A 11(4), July 1993, which is
hereby incorporated by reference in its entirety.
[0072] While the MEPIIID technique is described above in
conjunction with formation of an adhesion layer for a rare-earth
containing coating in accordance with one embodiment of the present
invention, the present invention is not limited to use of any
particular fabrication technique. For example, an alternative
embodiment for forming a corrosion-resistant coating in accordance
with embodiments of the present invention utilizes Ion Bombardment
Assisted Deposition (IBAD) to accelerate rare earth metals into the
parent material.
[0073] Specifically, FIG. 6 shows rare earth metal 601 such as
Yttrium sputtered onto the surface of parent material 604 while ion
gun 600 accelerates ion beam 602 of inert Argon ions at high
(.about.10-12 keV) energies against coated target parent material
604. As a result of the high energy of ion bombardment, deposited
metal 601 is driven to a depth within parent material 604. Over
time, the energy of the ion beam is then reduced to a lower level
(.about.0.5 keV), such that deposited rare earth remains on the
surface as a coating rather than being driven into the parent
material. In this manner a graded adhesion layer may be formed,
with the concentration of rare earth metals in the adhesion layer
determined by the duration of bombardment at a particular reduced
energy level.
[0074] As a result of deposition of rare earth metal under these
conditions, graded subsurface rare earth layer 612 lies between
coating 608 and parent material 604, promoting adhesion between
coating 608 and parent material 604. Performing such deposition in
an oxygen ambient can cause the rare earth metal to react with
oxygen to form rare earth oxide coating 608 over parent material
604.
[0075] Having fully described several embodiments in accordance
with the present invention, many other equivalent or alternative
embodiments of the present invention will be apparent to those
skilled in the art. For example, in accordance with an alternative
embodiment of the present invention, a coating and/or adhesion
layer may be formed by a chemical vapor deposition (CVD) process
rather than a physical vapor deposition process.
[0076] Moreover, in accordance with yet another alternative
embodiment of the present invention, a plasma resistant coating may
take the form of a multi-layer structure. This is shown in FIG. 2B,
which depicts a cross-sectional view of a coated member 219 in
accordance with yet another alternative embodiment in accordance
with the present invention. In FIG. 2B, coating 220 overlies
adhesion layer 222 which in turn overlies parent material 224.
Coating 220 itself is comprised of successive layers 220a-220b.
Such successive layers may create complementary diffusion barriers,
i.e. a yttrium-containing coating layer may serve to inhibit
unwanted diffusion of fluorine, while a complementary
nitrogen-containing coating layer may serve to inhibit unwanted
diffusion of oxygen. Multiple layers of the coating could be formed
by successive deposition steps, successive ion implantation steps,
or ion implantation in conjunction with deposition.
[0077] In certain embodiments, one or both of layers 220a-220b may
function as a barrier to inhibit unwanted diffusion of specific
chemical species from the chamber environment into the parent
material during plasma exposure. For example, a layer of yttrium
fluoride could serve to inhibit unwanted diffusion of fluorine
through the coating. Similarly, a nitride-containing layer could
serve to inhibit unwanted diffusion of oxygen through the
coating.
[0078] Alternatively, or in conjunction with a barrier diffusion
layer, a multilayer coating in accordance with the present
invention may include layers having a different thermal modulus,
such that thermal conditions possibly inducing unwanted cracking in
one layer of the coating will not produce similar cracking in
another layer, thereby ensuring the integrity of the coating as a
whole.
[0079] III. Experimental Results
[0080] In order to illustrate the corrosion resistance imparted by
embodiments of the present invention, various samples of coated and
uncoated AlN parent materials were subjected to a highly corrosive
environment in the form of NF.sub.3 gas at 500.degree. C. for 200
hours. Two grades of AlN were tested, and the coatings were formed
with an approximate thickness of 1 .mu.m. A first grade of AlN
having a purity of approximately 95% is most commonly used and
exhibits high thermal conductivity characteristics favored in
heater applications. A second grade of AlN having a purity of
approximately 99.9% is less commonly used and exhibits lower
thermal conductivity as compared with the first grade of AlN, but
has smaller grain size allowing strong adhesion to overlying
coatings. The various experimental conditions are summarized below
in TABLE A.
1TABLE A FIG. Grade of AlN Coating Adhesion NO. Parent Material
Material Layer (Y) View Mag. Conditions 7A 1.sup.st None None Top
2000X Corrosion Test 7B 1.sup.st None None Top 7500X Corrosion Test
7C 2.sup.nd None None Top 2000X Corrosion Test 7D 2.sup.nd None
None Top 7500X Corrosion Test 8A 1.sup.st YO Sputtering Top 2000X
Pre-Corrosion Test 8B 1.sup.st YO Sputtering Top 7500X
Pre-Corrosion Test 8C 1.sup.st YO Sputtering Top 2000X Corrosion
Test 8D 1.sup.st YO Sputtering Top 7500X Corrosion Test 8E 2.sup.nd
YO Sputtering Top 2000X Pre-Corrosion Test 8F 2.sup.nd YO
Sputtering Top 7500X Pre-Corrosion Test 8G 2.sup.nd YO Sputtering
Top 2000X Corrosion Test 8H 2.sup.nd YO Sputtering Top 7500X
Corrosion Test 9A 1.sup.st Y MEPIIID Top 2000X Pre-Corrosion Test
9B 1.sup.st Y MEPIIID Top 7500X Pre-Corrosion Test 9C 1.sup.st Y
MEPIIID Fracture 9000X Pre-Corrosion Test 9D 1.sup.st Y MEPIIID Top
2000X Corrosion Test 9E 1.sup.st Y MEPIIID Top 7500X Corrosion Test
10A 1.sup.st YO MEPIIID Fracture 3300X Corrosion Test 10B 1.sup.st
YO MEPIIID Fracture 7500X Corrosion Test Corrosion Test = 200 hrs.
in NF.sub.3 ambient at 500.degree. C.
[0081] In a first experiment, uncoated coupons of the two grades of
AlN parent material were exposed to the corrosive conditions. FIG.
7A shows a magnified (2000.times.) view of the top surface of a
coupon of the first grade of AlN following exposure to a fluorine
ambient at high temperature. FIG. 7B shows a further magnified
(7500.times.) view of the top surface of the AlN coupon of FIG.
7A.
[0082] FIG. 7C shows a magnified (2000.times.) view of the top
surface of coupon of the second grade of AlN following exposure to
a fluorine ambient at high temperature. FIG. 7D shows a magnified
(7500.times.) view of the top surface of the AlN coupon of FIG.
7C.
[0083] As expected, FIGS. 7A-7D reveal formation of AlF.sub.3
crystals on the surfaces of both grades of AlN parent material in
the presence of a corrosive fluorine ambient. Formation of this
AlF.sub.3 material reflects corrosion of the parent AlN
material.
[0084] In a second experiment, a yttrium adhesion layer was formed
by sputter deposition over coupons of the first and second grade of
AlN, with later portions of the deposition process taking place on
an oxygen ambient to create the surface YO coating. FIG. 8A shows a
magnified (2000.times.) view of the top surface of the first grade
AlN coupon sputtered with yttrium oxide in accordance with one
alternative embodiment of the present invention. FIG. 8B shows a
further magnified (7500.times.) view of the top surface of the AlN
coupon of FIG. 8A. FIG. 8C shows a magnified (2000.times.) view of
the top surface of the AlN coupon of FIGS. 8A-B following exposure
to a fluorine ambient at high temperature. FIG. 8D shows a
magnified (7500.times.) view of the top surface of the AlN coupon
of FIG. 8C.
[0085] FIG. 8E shows a magnified (2000.times.) view of the top
surface of a second grade AlN coupon coated with yttrium oxide in
accordance with the embodiment of the present invention just
described. FIG. 8F shows a further magnified (7500.times.) view of
the top surface of the coated AlN coupon of FIG. 8E.
[0086] FIG. 8G shows a magnified (2000.times.) view of the top
surface of the AlN coupon of FIG. 8E coated with in accordance with
one embodiment of the present invention, following exposure to a
fluorine ambient at high temperature. FIG. 8H shows a further
magnified (7500.times.) view of the top surface of the AlN coupon
of FIG. 8G.
[0087] FIGS. 8A-8H show that the yttrium oxide coating deposited by
reactive sputtering converted to dense, even coverage of yttrium
fluoride (YF) in the presence of fluorine and high
temperatures.
[0088] In a third experiment, coupons of the first grade of AlN
were ion implanted with yttrium using MEPIIID to form an adhesion
layer, and then the energy of implantation was reduced to produce a
coating of yttrium on the coupon surface. FIG. 9A shows a magnified
(2000.times.) view of the top surface of an AlN coupon implanted
with Y using MEPIIID in accordance with one embodiment of the
present invention. FIG. 9B shows a further magnified (7500.times.)
view of the top surface of the implanted AlN coupon of FIG. 9A.
FIG. 9C shows a further magnified (9000.times.) view of the
fractured AlN coupon of FIGS. 9A-9B.
[0089] FIG. 9D shows a magnified (2000.times.) view of the surface
of the AlN coupon of FIGS. 9A-9C following exposure to a fluorine
ambient at high temperature. FIG. 9E shows a further magnified
(7500.times.) view of the surface of this exposed coupon.
[0090] FIGS. 9A-9E show that the yttrium coating over the graded
adhesion layer resulting from a reduced energy of implantation by
MEPIIID was converted by reaction with fluorine to dense, even
coverage of yttrium fluoride (YF). Because of its low vapor
pressure and high sublimation temperature, this yttrium fluoride
coating is expected to be much more stable than AlF.sub.3.
[0091] In a fourth experiment, the coupons of the first grade of
AlN were implanted using MEPIID to form the adhesion layer, with
latter stages of the implant process at reduced implant energies
occurring in an oxygen ambient to create a YO surface coating.
FIGS. 10A and 10B show formation utilizing MEPIIID of a yttrium
oxide coating on an AlN coupon, followed by exposure to a fluorine
ambient at high temperature. FIG. 10A shows a magnified
(3300.times.) view of a fractured coated AlN coupon following
exposure to a fluorine ambient at high temperature. FIG. 10B shows
a further magnified (7500.times.) view of the AlN coupon of FIG.
10A.
[0092] FIGS. 10A-10B show that upon exposure to fluorine plasma,
the yttrium oxide coating converted to dense, even coverage of
yttrium fluoride (YF). In addition, good adhesion of the YF coating
to the parent material was observed. Specifically, upon fracture of
the coated coupon as shown in FIGS. 10A-10B, the YF coating at the
fracture point remained in place, whereas an AlF.sub.3 coating
would be expected to flake off at the fracture point.
[0093] The identity of the YF coating on the AlN coupon of FIGS.
10A-B subject to MEPIIID implantation is further evidenced by FIG.
11, which shows the results of Electron Dispersive Spectroscopy
(EDS) of the surface of the coupon of FIGS. 10A-10B. EDS shows the
coupon coating to be made up almost entirely of YF.
[0094] While the above experimental results illustrate formation of
coatings imparting resistance to corrosion to fluorine-based
plasmas, the present invention is not limited to this particular
application. Resistance to corrosion in other types of plasma
environments, including but not limited to chlorine-based plasmas,
may also be imparted to chamber components by coatings in
accordance with other embodiments of the present invention.
[0095] Moreover, while the above description focuses upon the
formation of coatings and adhesion layers including yttrium, the
present invention is not limited to use of this particular rare
earth element. Coatings and adhesion layers in accordance with
embodiments of the present invention may be formed utilizing a
variety of rare earth metals, including but not limited to Sc, La,
Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
[0096] Having fully described several embodiments of the present
invention, many other equivalent or alternative embodiments of the
present invention will be apparent to those skilled in the art.
These equivalents and alternatives are intended to be included
within the scope of the present invention and the following
claims.
* * * * *