U.S. patent application number 17/192216 was filed with the patent office on 2021-06-24 for sprayed coating, method for manufacturing sprayed coating, sprayed member and spraying material.
This patent application is currently assigned to Shin-Etsu Chemical Co., Ltd.. The applicant listed for this patent is Shin-Etsu Chemical Co., Ltd.. Invention is credited to Noriaki Hamaya, Ryo Iwasaki, Hajime Nakano, Yasushi Takai.
Application Number | 20210189542 17/192216 |
Document ID | / |
Family ID | 1000005434479 |
Filed Date | 2021-06-24 |
United States Patent
Application |
20210189542 |
Kind Code |
A1 |
Iwasaki; Ryo ; et
al. |
June 24, 2021 |
SPRAYED COATING, METHOD FOR MANUFACTURING SPRAYED COATING, SPRAYED
MEMBER AND SPRAYING MATERIAL
Abstract
A sprayed coating having a multilayer structure including a
lower layer made a sprayed coating containing a rare earth oxide,
and a surface layer made of another sprayed coating containing a
rare earth fluoride and/or a rare earth oxyfluoride, the
multilayered sprayed coating having a volume resistivity at
23.degree. C. and a volume resistivity at 200.degree. C., the
volume resistivity at 23.degree. C. being 1.times.10.sup.9 to
1.times.10.sup.12 .OMEGA.cm, and a temperature index of the volume
resistivities defined by the ratio of the volume resistivity at
200.degree. C. to the volume resistivity at 23.degree. C. being 0.1
to 10.
Inventors: |
Iwasaki; Ryo; (Echizen-shi,
JP) ; Hamaya; Noriaki; (Echizen-shi, JP) ;
Takai; Yasushi; (Echizen-shi, JP) ; Nakano;
Hajime; (Echizen-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shin-Etsu Chemical Co., Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Shin-Etsu Chemical Co.,
Ltd.
Tokyo
JP
|
Family ID: |
1000005434479 |
Appl. No.: |
17/192216 |
Filed: |
March 4, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16539165 |
Aug 13, 2019 |
10968507 |
|
|
17192216 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 4/134 20160101;
C23C 4/11 20160101 |
International
Class: |
C23C 4/11 20060101
C23C004/11; C23C 4/134 20060101 C23C004/134 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 15, 2018 |
JP |
2018-152883 |
Claims
1. A method for manufacturing an RF.sub.3 powder by firing an
ammonium fluoride double salt under nitrogen atmosphere, and then
pulverizing, R being at least one element selected from rare earth
elements inclusive of Y and Sc.
2. The method for manufacturing an RF.sub.3 powder of claim 1,
wherein a firing temperature under the nitrogen atmosphere is at
least 825.degree. C.
3. The method for manufacturing an RF.sub.3 powder of claim 1,
wherein the ammonium fluoride double salt is
R.sub.3(NH.sub.4)F.sub.10, R being at least one element selected
from rare earth elements inclusive of Y and Sc.
4. The method for manufacturing an RF.sub.3 powder of claim 1,
wherein the RF.sub.3 powder has a particle hardness of 7 to 12 GPa
as measured by nanoindentation method.
5. The method for manufacturing an RF.sub.3 powder of claim 1,
wherein the RF.sub.3 powder has an average of value of roundnesses
(an average roundness) of at least 0.9 represented by the following
expression (1): (Roundness)=(Circumferential length of an assumed
circle having the equivalent area in planar view to an area of an
observed particle)/(Circumferential length of the observed particle
in planar view).
6. The method for manufacturing an RF.sub.3 powder of claim 1,
wherein the RF.sub.3 powder has an average particle size (volume
basis D.sub.50) of 2 to 6 .mu.m.
7. The method for manufacturing an RF.sub.3 powder of claim 1,
wherein the RF.sub.3 powder has a BET specific surface area of up
to 2 m.sup.2/g.
8. The method for manufacturing an RF.sub.3 powder of claim 1,
wherein the RF.sub.3 powder has a total pore volume of up to 0.5
cm.sup.3/g measured in the range of a diameter of up to 10 .mu.m by
mercury porosimetry.
9. The method of claim 1 for manufacturing an RF.sub.3 powder,
wherein a method for the pulverizing is a jet mill pulverizing.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/539,165 filed on Aug. 13, 2019, which
claims priority under 35 U.S.C. .sctn. 119(a) on Patent Application
No. 2018-152883 filed in Japan on Aug. 15, 2018, the entire
disclosure of each of the foregoing is herein incorporated by
reference.
TECHNICAL FIELD
[0002] This invention relates to a sprayed coating suitable for
such as an erosion-resistant coating formed on electrostatic
chucks, or parts or members in a plasma etching apparatus for a
semiconductor manufacturing process. This invention also relates to
a method for manufacturing the sprayed coating, a sprayed member
formed the sprayed coating, and a spraying material suitably used
for forming the sprayed coating.
BACKGROUND ART
[0003] An electrostatic chuck use for a lower electrode in a
semiconductor manufacturing apparatus is generally categorized to
two types of a Coulomb force type electrostatic chuck and a
Johnson-Rahbek force type electrostatic chuck, in accordance with
the difference between materials. For a Coulomb force type
electrostatic chuck, a sintered ceramic such as aluminum oxide and
aluminum nitride with high purity is commonly utilized such that a
dielectric layer portion has a volume resistivity of over
1.times.10.sup.15 .OMEGA.cm. Thus, this type has an issue of high
production cost. Further, a Coulomb force type electrostatic chuck
must be applied a high voltage of about 2,000 to 3,000 V for
ensuring sufficient adsorption power because charge transfer is
scarcely occurred in the Coulomb force type electrostatic
chuck.
[0004] For a Johnson-Rahbek force type electrostatic chuck, a
sintered ceramic such as aluminum oxide and aluminum nitride in
which an additive such a metal oxide is doped is commonly utilized
such that a dielectric layer portion has a volume resistivity of
about 1.times.10.sup.9 to 1.times.10.sup.12 .OMEGA.cm. This type
also has an issue of high production cost. Further, in a
Johnson-Rahbek force type electrostatic chuck, it is required that
the material has a low temperature dependency since the adsorption
property depends to volume resistivity.
[0005] In addition, a processing object (semiconductor) is treated
under high corrosive halogen series gas atmosphere in a plasma
etching apparatus. Fluorine series gas and chlorine series gas are
utilized as the gas for the treatment. Examples of the fluorine
series gas include SF.sub.6, CF.sub.4, CHF.sub.3, ClF.sub.3, HF and
NF.sub.3, and examples of the chlorine series gas include Cl.sub.2,
BCl.sub.3, HCl, CCl.sub.4 and SiCl.sub.4.
[0006] On the surface of parts or members of which a plasma etching
apparatus is composed, an erosion-resistant coating is generally
formed by atmospheric plasma spraying (APS) which supplies rare
earth compound as a raw material in form of particulate. Further,
in case that a reaction product deposited or attached on the
surface of the member by halogen series gas plasma is removed by a
cleaning solution, Patent Document 1 proposes to suppress, by a
coating having a multilayer structure, a dissolving amount of a
substrate caused by infiltration of an acid generated from a
reaction of the reaction product and the cleaning solution. As
another matter, an average particle size of the spraying particles
is preferably at least 10 .mu.m to spray in form of particulate. If
the size is less than the range, flowability of the particles may
become low, resulting a supply tube being clogged with the sprayed
material, or the particle introduced in a flame may vaporize,
resulting deterioration of process yield (Patent Document 2).
Accordingly, a sprayed coating obtained by thermal spraying with
particles having a large average particle size results in many
cracks and a large porosity because the splat diameter of the
particle is large. Thus, a dense coating cannot be obtained, and
particles generates adversely from the coating in etching process.
For example, when a yttrium fluoride series sprayed coating which
has a good erosion resistance to halogen series gas plasma is
formed by APS, initial generation of particles are suppressed in
comparison with a yttrium oxide sprayed coating formed by APS.
However, the yttrium fluoride series sprayed coating has a Vickers
hardness of 350 to 470 and a porosity of approx. 2% (in Patent
Document 3) which do not necessarily mean enough properties.
[0007] Particularly, integration of a semiconductor is in progress,
recently, and will be expected to reach to a width of wiring of up
to 10 nm. The above yttrium series coating is easy to drop yttrium
series particles from the surface of the yttrium series coating of
the parts when the integrated semiconductor devices is processed by
etching, and the released particles are dropped readily on a wafer
and prevent the etching treatment. These particles may cause
deterioration of process yield in manufacturing semiconductor
devices. Thus, it is required that an erosion-resistant coating
formed on a member which constitutes a chamber exposed to a plasma
has a further high erosion resistibility.
[0008] Recently, a suspension plasma spraying (SPS) is investigated
to solve the above-described problems. In SPS, spraying particles
are not sprayed as a particulate form but are sprayed as a slurry
form in which the spraying particles are dispersed in a dispersion
medium. When thermal spraying is conducted with a slurry form, fine
particles having a particle size of up to 10 .mu.m that is
difficult to apply for thermal splaying with a particulate form can
be introduced to a flame of thermal spraying. Thus, the obtained
sprayed coating is very dense since splat diameter of the sprayed
coating becomes very small.
[0009] For example, a thermal spraying method using a slurry in
which yttrium oxide particles are dispersed in a medium is known as
a method in which particles are splayed in a slurry form. The
method can prepare a dense sprayed coating having a Vickers
hardness of at least 500 and a porosity of up to 1% (Patent
Document 4). However, even if the sprayed coating is dense, the
yttrium oxide has a problem such that a sprayed coating of yttrium
oxide can be progressively halogenated at its surface by chemical
reaction of yttrium oxide and halogen series gas plasma, and many
yttrium series particles are generated as unfavorable particles
source.
[0010] To deal with the problem, a sprayed coating obtained from a
slurry in which yttrium fluoride or yttrium oxyfluoride spraying
particles are dispersed in a medium is proposed, however, a dense
sprayed coating that can satisfy current needs has not been formed
in this method (Patent Documents 5 and 6).
CITATION LIST
[0011] Patent Document 1: JP-B 4985928 [0012] Patent Document 2:
JP-A 2017-186678 [0013] Patent Document 3: JP-A 2017-190475 [0014]
Patent Document 4: JP-B 5987097 [0015] Patent Document 5: JP-A
2017-61734 [0016] Patent Document 6: JP-A 2017-78205
DISCLOSURE OF INVENTION
[0017] An object of the invention is to provide a method that can
prepare a dense sprayed coating suitable for an electrostatic chuck
in a plasma etching apparatus that is hard to generate particles by
halogen series gas plasma that and has a low temperature dependency
of volume resistivity, and a sprayed coating suitable for an
erosion-resistant coating formed on parts or members in a plasma
etching apparatus. Further, another object of the invention is to
provide a method of manufacturing the sprayed coating, a sprayed
member in which the sprayed coating is formed, and a spraying
material suitably used for forming a sprayed coating.
[0018] The inventors have found that a sprayed coating having a
multilayer structure including a lower layer made of a sprayed
coating containing a rare earth oxide, and a surface layer made of
another sprayed coating containing a rare earth fluoride and/or a
rare earth oxyfluoride formed on the lower layer has a low
temperature dependency of volume resistivity and superior electric
characteristics, in particular, has a good volume resistivity at
23.degree. C. being 1.times.10.sup.9 to 1.times.10.sup.12
.OMEGA.cm, and a temperature index of the volume resistivities
defined by a ratio of the volume resistivity at 200.degree. C. to
the volume resistivity at 23.degree. C. being 0.1 to 10 by
adjusting thicknesses of each layers, porosity, hardness and/or
surface roughness. Further, thicknesses of the surface and lower
layers, hardness of the coating, porosity of the coating, and
surface roughness of the coating are repeatedly investigated, then,
the invention has been accomplished.
[0019] In one aspect, the invention provides a sprayed coating
having a multilayer structure including a lower layer made of a
sprayed coating containing a rare earth oxide, and a surface layer
made of another sprayed coating containing a rare earth fluoride
and/or a rare earth oxyfluoride, wherein the sprayed coating having
the multilayer structure has a volume resistivity at 23.degree. C.
and a volume resistivity at 200.degree. C., the volume resistivity
at 23.degree. C. being 1.times.10.sup.9 to 1.times.10.sup.12
.OMEGA.cm, and a temperature index of the volume resistivities
defined by the ratio of the volume resistivity at 200.degree. C. to
the volume resistivity at 23.degree. C. being 0.1 to 10.
[0020] Preferably, the surface layer contains RF.sub.3, or RF.sub.3
and at least one selected from the group consisting of
R.sub.5O.sub.4F.sub.7, R.sub.7O.sub.6F.sub.9 and ROF, wherein R is
at least one selected from rare earth elements inclusive of Y and
Sc, and each R may be the same or different.
[0021] Preferably, the lower layer contains R.sub.2O.sub.3, or
R.sub.2O.sub.3 and at least one selected from the group consisting
of RF.sub.3, R.sub.5O.sub.4F.sub.7, R.sub.7O.sub.6F.sub.9 and ROF,
wherein R is at least one selected from rare earth elements
inclusive of Y and Sc, and each R may be the same or different.
[0022] Preferably, the lower layer has a multilayer structure
consisting of at least two sub-layers of sprayed coatings, and at
least one of the sub-layer consists of a sprayed coating containing
a rare earth oxide.
[0023] Preferably, the lower layer has a thickness of 50 to 300
.mu.m, and the surface layer has a thickness of 10 to 200
.mu.m.
[0024] Preferably, the surface layer has a Vickers hardness of at
least 500, a porosity of up to 1%, and/or a centerline average
roughness Ra of 0.1 to 6 .mu.m.
[0025] In another aspect, the invention provides a sprayed member
including a metal substrate, a ceramic substrate or a carbon
substrate, and the sprayed coating formed thereon.
[0026] Preferably, the metal substrate is composed of an aluminum
alloy, an anodized aluminum alloy or a stainless steel, the ceramic
substrate is composed of alumina, zirconia, quartz glass, silicon
carbide or silicon nitride.
[0027] In another aspect, the invention provides a method for
manufacturing the sprayed coating including the steps of:
[0028] thermal spraying a rare earth oxide powder on a substrate to
form the lower layer by atmospheric plasma spraying, and thermal
spraying a slurry including an organic solvent and a rare earth
fluoride powder dispersed therein on the lower layer to form the
surface layer by suspension plasma spraying.
[0029] Preferably, the slurry further includes a rare earth oxide
powder, and a weight ratio of fluoride powder/oxide powder is 99/1
to 90/10.
[0030] In another aspect, the invention provides a method for
manufacturing the sprayed coating including the steps of:
[0031] thermal spraying a rare earth oxide powder on a substrate to
form the lower layer by atmospheric plasma spraying, and thermal
spraying a powder containing rare earth fluoride and a rare earth
oxide to the lower layer to form the surface layer by atmospheric
plasma spraying.
[0032] In another aspect, the invention provides a spraying
material in a form of a slurry including an organic solvent and a
rare earth compound powder dispersed therein, the rare earth
compound powder including an RF.sub.3 powder, and R being at least
one selected from rare earth elements inclusive of Y and Sc.
[0033] Preferably, the RF.sub.3 powder has a BET specific surface
area of up to 2 m.sup.2/g, and a volume basis average particle size
D.sub.50 of 2 to 6 .mu.m.
[0034] Preferably, the RF.sub.3 powder has an average value of
roundnesses of at least 0.9, the roundness being defined by the
following expression (1):
(Roundness)=(Circumferential length of an assumed circle having the
equivalent area in planar view to an area of an observed
particle)/(Circumferential length of the observed particle in
planar view) (1)
[0035] Preferably, the RF.sub.3 powder has a particle hardness of 7
to 12 GPa as measured by nanoindentation method.
[0036] Preferably, the RF.sub.3 powder has a total volume of pores
having a diameter of up to 10 .mu.m in the range of up to 0.5
cm.sup.3/g as measured by mercury porosimetry.
[0037] Preferably, the spraying material further including an
R.sub.2O.sub.3 powder, R being at least one selected from rare
earth elements inclusive of Y and Sc, and a weight ratio of
RF.sub.3 powder/R.sub.2O.sub.3 powder is 99/1 to 90/10.
Advantageous Effects of Invention
[0038] According to the inventive sprayed coating having a
multilayer structure including a lower layer containing a rare
earth oxide and a surface layer containing a rare earth fluoride
and/or a rare earth oxyfluoride, the sprayed coating has a small
variation of volume resistivities from a room temperature to
200.degree. C., and good electric characteristics having a low
temperature dependency, and exerts superior erosion-resistance in a
treatment under halogen series gas atmosphere or halogen series gas
plasma atmosphere. Further, the sprayed coating can accomplish
reduced generation of particles that are dropped from a reaction
product or a coating as much as possible. Moreover, the sprayed
coating can be readily obtained by the method and spraying material
of the invention.
BRIEF DESCRIPTION OF DRAWINGS
[0039] FIG. 1 is a photographic image for analysis of the
cross-section surface in the sprayed coating manufactured in
Example 3 in which the surface layer was formed with adding a small
amount of yttrium oxide fine particles.
[0040] FIG. 2 is a photographic image for analysis of the
cross-section surface in the sprayed coating manufactured by the
same method of Example 3 without adding yttrium oxide fine
particles.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0041] A sprayed coating of the invention has a multilayer
structure including a lower layer made of a sprayed coating
containing a rare earth oxide, and a surface layer made of another
sprayed coating containing a rare earth fluoride and/or a rare
earth oxyfluoride (a rare earth fluoride series coating). In the
present invention, the rare earth element includes Sc, Y and
lanthanoid (La: atomic number 57 to Lu: atomic number 71). The rare
earth element is used alone or a combination of two or more
elements.
[0042] The sprayed coating containing a rare earth fluoride and/or
a rare earth oxyfluoride for forming the surface layer may be a
sprayed coating containing RF.sub.3, or a sprayed coating
containing RF.sub.3, and at least one selected from the group
consisting of R.sub.5O.sub.4F.sub.7, R.sub.7O.sub.6F.sub.9 and ROF,
wherein, R is, independently, at least one element selected from
rare earth elements inclusive of Y and Sc, and R may be the same or
different. In this case, the rare earth fluoride and/or the rare
earth oxyfluoride preferably has a crystal structure including
RF.sub.3, and at least one selected from the group consisting of
R.sub.5O.sub.4F.sub.7, R.sub.7O.sub.6F.sub.9 and ROF in view of
erosion-resistance to halogen series gas atmosphere or halogen
series gas plasma atmosphere, however, not limited thereto.
[0043] In particular, as the rare earth element, Sc, Y, La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are exemplified.
Among them, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are preferable,
however, not limited thereto.
[0044] The surface layer preferably has a thickness of 10 to 200
.mu.m, more preferably 50 to 150 .mu.m, even more preferably 80 to
120 .mu.m, however, not limited thereto. If the thickness of the
surface layer is less than 10 .mu.m, the surface layer may not
exert a sufficient erosion-resistance to halogen series gas plasma.
On the other hand, if the thickness is more than 200 .mu.m, the
surface layer may be adversely peeled from the lower layer.
[0045] The surface layer preferably has a Vickers hardness of at
least 500, more preferably 500 to 700. If the Vickers hardness is
less than 500, the sprayed coating may readily generate particles
from its surface by halogen series gas plasma in some cases. On the
other hand, if the Vickers hardness is more than 700, the coating
of the surface layer may be adversely peeled from the coating of
the lower layer.
[0046] To control generation of particles by halogen series gas
plasma and to improve erosion-resistance, the sprayed coating
forming the surface layer preferably a dense coating having a
porosity of preferably up to 1%, more preferably up to 0.5%,
however, not limited thereto. A method for measuring the porosity
includes, for example, as described in Examples and Comparative
Examples, taking cress-section photo images by an electron
microscope, quantifying the porosity of the total area of the image
in a plurality of views (10 views in Examples and Comparative
Examples), determining an average of the porosities of the
plurality of views expressed by percentage as the porosity.
[0047] As described above, a surface layer formed of a hard and
dense sprayed coating having a Vickers hardness of at least 500,
more preferably 500 to 700 and a porosity of less than 1% can
effectively control generation of particles and interfusion of
halogen series corrosive gases when the sprayed coating is used in
halogen series gas atmosphere or halogen series gas plasma
atmosphere.
[0048] The coating forming the surface layer preferably has a
centerline average roughness Ra (defined in JIS B 0601) of 0.1 to 6
.mu.m, more preferably 0.1 to 5.5 .mu.m, even more preferably 0.1
to 5 .mu.m, however, not limited thereto. If the centerline average
roughness Ra is more than 6 .mu.m, generation of particles by s
halogen series gas plasma is adversely accelerated. On the other
hand, if the centerline average roughness Ra is less than 0.1
.mu.m, the sprayed coating may be adversely damaged by excessive
machining for adjusting the thickness, or particles are
inexpediently dropped from the coating.
[0049] The surface layer of a sprayed coating containing a rare
earth fluoride is formed on a lower layer which is described below.
As a method for forming the surface layer, for example, suspension
plasma spraying (SPS) method using a slurry including a rare earth
fluoride powder, or atmospheric plasma spraying (APS) method using
a rare earth fluoride powder is applied. In particular, SPS method
is preferably applied to form the surface layer since the method
can easily form a dense sprayed coating having a Vickers hardness
and a porosity in the preferably ranges described above.
[0050] As a slurry for use in suspension plasma spraying (SPS)
method for forming the surface layer, a slurry including an organic
solvent as a dispersion medium and a rare earth compound powder
including a rare earth fluoride powder (a RF.sub.3 powder, wherein
R is at least one element selected from rare earth elements
inclusive of Y and Sc) dispersed therein is preferably used. In
this case, the organic solvent includes, e.g., alcohols, ethers,
esters and ketones, however, not limited thereto. Among them,
ethanol, methanol, 1-propanol, 2-propanol, ethyl cellosolve,
dimethyl diglycol, glycol ether, ethyl cellosolve acetate, butyl
cellosolve acetate glycol ester, isophorone or acetone is more
preferably used. A content of the RF.sub.3 powder in the slurry is
preferably 10 to 45 wt %, more preferably 20 to 35 wt %, however
not limited thereto. Further, the dispersion medium of which the
slurry is composed may contain a small amount of water other than
the organic solvent (e.g., up to 10 wt %, preferably up to 5 wt %,
to the amount of the organic solvent). More preferably, the
dispersion medium of which the slurry is composed consists
essentially of an organic solvent alone, however, an impurity may
be contained therein in relevant amount.
[0051] The RF.sub.3 powder dispersed in the slurry preferably has a
BET specific surface area of up to 2 m.sup.2/g, more preferably up
to 1.5 m.sup.2/g, even more preferably up to 1 m.sup.2/g, most
preferably up to 0.8 m.sup.2/g, and preferably at least 0.1
m.sup.2/g. The RF.sub.3 powder dispersed in the slurry preferably
has a volume basis average particle size D.sub.50 of 2 to 6 .mu.m,
more preferably 2.5 to 5 .mu.m. The RF.sub.3 powder dispersed in
the slurry preferably has a particle hardness of 7 to 12 GPa, more
preferably 7.5 to 11.5 GPa, as measured by nanoindentation method.
The RF.sub.3 powder dispersed in the slurry preferably has a total
volume of pores having a diameter of up to 10 .mu.m in the range of
up to 0.5 cm.sup.3/g, more preferably up to 0.4 cm.sup.3/g, as
measured by mercury porosimetry. The RF.sub.3 powder dispersed in
the slurry preferably has an average value of roundnesses (average
roundness) of at least 0.9, defined by the following expression
(1):
(Roundness)=(Circumferential length of an assumed circle having the
equivalent area in planar view to an area of an observed
particle)/(Circumferential length of the observed particle in
planar view) (1)
Notably, for example, when a spraying particle has a perfect
circular shape in planar view, the average roundness is 1 (one),
and when a spraying particle has a square shape in planar view, the
average roundness is 0.886. Accordingly, the average roundness
increases as the shape in planar view of the spraying particle
approaches to perfect circular shape, and the average roundness
decreases as the shape in planar view of the spraying particle
becomes more complicated shape. However, the RF.sub.3 powder is not
limited to the above-described features.
[0052] The dense surface layer having a Vickers hardness of at
least 500, particularly 500 to 700 and a porosity of up to 1% can
be formed by preparing a slurry with a RF.sub.3 powder satisfying
the BET specific surface area, the average particle size D.sub.50,
the average roundness, the particle hardness and/or the volume of
pores, and forming the surface layer by suspension plasma spraying
(SPS) method.
[0053] The slurry may include fine particles composed of one or
more materials selected from the group consisting of inorganic
compounds, polymers, nonmetals, metalloids and nonferrous metals,
as an additive in the range of up to 10 wt %. Thermal
characteristics, electrical characteristics, and mechanical
characteristics of the sprayed coating (surface layer) can be
controlled by the addition of an extremely small amount of the fine
particles.
[0054] As the inorganic compound, a compound including one or more
selected from the group consisting of oxides, nitrides, carbides,
haloids, hydroxides, carbonates, ammonium salts, oxalates,
nitrates, sulfates and hydrochloride salts, of rare earth elements,
boron, aluminum, gallium, indium, beryllium, magnesium, calcium,
strontium, barium, titanium, zirconium, hafnium, silicon,
germanium, tin, lead, phosphorus or sulfur is exemplified, however
no limited thereto.
[0055] As the polymer, polysilanes, polycarbosilanes,
polysiloxanes, polyborosiloxanes, polysilazanes,
polyorganoborosilazanes, polycarbosilazanes, polycarbonates, and
the like are exemplified, however no limited thereto.
[0056] As the nonmetal and metalloid, carbon, boron, silicon,
germanium, phosphorus, sulfur, and the like are exemplified,
however no limited thereto.
[0057] As the nonferrous metal, rare earth elements, aluminum,
gallium, indium, beryllium, magnesium, calcium, strontium, barium,
titanium, zirconium, hafnium, tin, lead, and the like are
exemplified, however no limited thereto. The nonferrous metal may
be an alloy of the metal.
[0058] The slurry may be added with a small amount of an oxide
powder of rare earth element (a R.sub.2O.sub.3 powder, wherein R is
at least one element selected from rare earth elements inclusive of
Y and Sc) in the range of 99/1 to 90/10 (weight ratio) being
defined as the ratio of the RF.sub.3 powder to the R.sub.2O.sub.3
powder, however not limited thereto. In this case, the rare earth
element of the R.sub.2O.sub.3 powder is preferably the same rare
earth element of the RF.sub.3 powder. The added R.sub.2O.sub.3
powder preferably has a BET specific surface area of 30 to 80
m.sup.2/g, more preferably 40 to 60 m.sup.2/g, and preferably has a
volume basis average particle size D.sub.50 of 10 to 500 nm, more
preferably 50 to 300 nm, however not limited thereto, and such fine
particles is suitably as the R.sub.2O.sub.3 powder. Generation of
lateral cracks in the surface layer can be effectively controlled
by adding a small amount of such a powder of R.sub.2O.sub.3 fine
particles to the slurry, as shown in Example 3 described below.
[0059] In addition, the slurry is suitably used as a spraying
material for forming the surface layer of the multilayered sprayed
coating of the invention, however, the slurry is not limited to
this application. The slurry may be used as a slurry for forming a
single layered sprayed coating or a sprayed coating of which a
multilayered coating other than the invention is composed.
[0060] The surface layer of which the sprayed coating of the
invention is composed may be formed, as described above, by
atmospheric plasma splaying with a rare earth fluoride powder. In
this case, a powder containing a fluoride and an oxide of rare
earth element can be provided to atmospheric plasma splaying by,
for example, mixing a predetermined amount of a rare earth fluoride
powder (a RF.sub.3 powder) with a predetermined amount of a rare
earth oxide powder (a R.sub.2O.sub.3 powder), and optionally
granulating the mixture. However, the powder is not limited
thereto. A sprayed coating containing RF.sub.3, and at least one
selected from the group consisting of R.sub.5O.sub.4F.sub.7,
R.sub.7O.sub.6F.sub.9 and ROF, wherein R is at least one selected
from rare earth elements inclusive of Y and Sc, and each R may be
the same or different, can be obtained by the method. In this case,
a content of the added rare earth oxide may be preferably 1 to 50
wt %, more preferably 5 to 30 wt % of the total amount of the
spraying powder. The powder containing a fluoride and an oxide of
rare earth element preferably has a volume basis average particle
size D.sub.50 of 15 to 45 .mu.m, more preferably 20 to 40
.mu.m.
[0061] The spraying conditions such as plasma gases, spray gun
output, spraying distance, and the like may be set in accordance
with material and/or size (spraying area) of a substrate, and/or
type and/or thickness of a sprayed coating in any cases of
suspension plasma spraying and atmospheric plasma spraying.
[0062] The sprayed coating of the invention has a multilayer
structure in which the surface layer is formed on the lower layer
composed of a sprayed coating containing a rare earth oxide.
[0063] The sprayed coating containing a rare earth oxide of which
the lower layer is composed may be a sprayed coating containing
R.sub.2O.sub.3, or a sprayed coating containing R.sub.2O.sub.3, and
at least one selected from the group consisting of RF.sub.3,
R.sub.5O.sub.4F.sub.7, R.sub.7O.sub.6F.sub.9 and ROF, wherein R is
at least one selected from rare earth elements inclusive of Y and
Sc, and each R may be the same or different.
[0064] In this case, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy,
Ho, Er, Tm, Yb and Lu are exemplified as the rare earth element R,
however, not limited thereto. Among them, as same as the surface
layer, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are preferable.
[0065] The lower layer preferably has a thickness of 50 to 300
.mu.m, more preferably 70 to 200 .mu.m, even more preferably 80 to
150 .mu.m, however not limited thereto. If the thickness of the
lower layer is less than 50 .mu.m, an elution amount of the
substrate caused by an acid may be increase. On the other hand, if
the thickness is more than 200 .mu.m, the lower layer may be
adversely peeled from the substrate.
[0066] Since the surface roughness of sprayed coating forming the
lower exerts an influence on the surface roughness of the surface
layer, a small surface roughness is advantageous for the lower
layer. The coating forming the lower layer preferably has a
centerline average roughness Ra (defined in JIS B 0601) of 0.1 to
10 .mu.m, more preferably 0.1 to 6 .mu.m, however, not limited
thereto. After forming the sprayed coating of the lower layer by
atmospheric plasma spraying, the surface roughness may be adjusted
to the above range by, for example, conducting optionally
mechanical polishing (surface grinding, inner cylinder finishing,
mirror finishing, and the like), blast treatment using micro beads,
or hand polishing using a diamond pad,
[0067] Further, as the same reason for the surface layer, the
coating forming the lower layer preferably has a porosity of up to
5%, more preferably up to 3%, however, not limited thereto. The
porosity can be attained by the following method, however, not
limited thereto.
[0068] For example, a lower layer made of a dense sprayed coating
composed of a rare earth oxide having a porosity of up to 5% can be
formed by atmospheric plasma spraying, explosion spraying, and the
like with a powder of single particles or a granulated spraying
powder, as a raw material for the rare earth oxide, that has a
volume basis average particle size D.sub.50 of 0.5 to 50 .mu.m,
more preferably 1 to 30 .mu.m, with melting the particles
sufficiently. Since the powder of single particles which is used
for a spraying material is fine particles having a smaller particle
size and consisting of particles filled with the content, in
comparison with a general granulated spraying powder, the method
can form a lower layer that includes a splat having a small
diameter and control generation of cracks. According to the effect,
a sprayed coating having a porosity of up to 5% and a small
centerline average roughness Ra can be obtained. The powder of
single particles, herein, means a powder having a spherical shape,
a powder having an angular shape, a pulverized powder, and the
like, and the particle is solidly filled with the content.
[0069] The lower layer may have a multilayer structure in which at
least two sprayed coatings are laminated. In this case, at least
one sub-layer which constitutes the multilayer structure is the
above-described sprayed coating containing a rare earth oxide for
the lower layer. Further, in this case, a sprayed coating
containing a rare earth fluoride is exemplified as other layer
laminated with the sprayed coating containing a rare earth oxide,
however not limited thereto. In particular, as described below in
Example 6, a double layer structure including a Y.sub.2O.sub.3
sprayed coating and a YF.sub.3 sprayed coating laminated thereon
may be obtained by forming a sprayed coating of a rare earth oxide
by atmospheric plasma spraying of a yttrium oxide powder on the
surface of a substrate, and forming a sprayed coating of a rare
earth fluoride by atmospheric plasma spraying of a yttrium fluoride
powder thereon.
[0070] As a method for forming the lower layer, atmospheric plasma
spraying is preferably applied, as described in Examples below,
however, not limited thereto.
[0071] The sprayed coating of the invention is a coating having a
multilayer structure including the lower layer formed on the
surface of a substrate, and the surface layer laminated on the
lower layer. The sprayed coating exerts superior electric
characteristics by the multilayer structure. In particular, the
sprayed coating has a volume resistivity at 23.degree. C. being
1.times.10.sup.9 to 1.times.10.sup.12 .OMEGA.cm which is good
electrical resistant ability, and variation of the volume
resistivity in the temperature range from 23 to 200.degree. C. of
the sprayed coating is very small. In particular, a sprayed coating
having a temperature index of the volume resistivities defined by
the ratio of the volume resistivity at 200.degree. C. to the volume
resistivity at 23.degree. C. being 0.1 to 10 can be provided, and
the sprayed coating is extremely stable in electric
characteristics.
[0072] In the invention, since the sprayed coating has a multilayer
structure including a lower layer and a surface layer, the
temperature index of volume resistivities can be arbitrarily
controlled with variation of thicknesses of the lower and/or
surface layers, or variation of oxygen content of rare earth
fluoride series coating of the surface layer. For example, a
material having a small variation of the volume resistivity between
a room temperature and the high temperature of 200.degree. C. is
required for an electrostatic chuck used in a plasma etching
apparatus. The invention can provide a material satisfying the
requirement.
[0073] Further, the sprayed coating of the invention, as described
in Examples below, has a stable surface resistivity enough, and a
sufficiently high dielectric breakdown strength, thus, a good
dielectric breakdown voltage value that is applicable to material
of an electrostatic chuck is attained by the sprayed coating.
[0074] The sprayed coating of the invention is suitable for an
erosion-resistant coating that is formed on an electrostatic chuck,
or a part or a member in a plasma etching apparatus for use in
semiconductor manufacturing process, however, not limited thereto.
The sprayed coating is applicable for a substrate having e.g., a
flat plate shape or a cylindrical shape, and composed of a
heat-resistant material, for example, a metal such as an aluminum
alloy, an alumite-treated aluminum alloy and a stainless steel, a
ceramic such as alumina, zirconia, quartz glass, silicon carbide
and silicon nitride, carbon, and the like.
EXAMPLES
[0075] Examples of the invention are given below by way of
illustration and not by way of limitation.
Example 1
[0076] An A5052 aluminum alloy substrate having the surface size of
100 mm square and 5 mm thick was degreased at the surface by
acetone, and one surface of the substrate was subjected to
roughening treatment with an abrasive corundum. A yttrium oxide
sprayed coating of 100 .mu.m thick was formed as a lower layer on
the substrate by using an atmospheric plasma spraying apparatus
with a yttrium oxide powder (granulated particles) having an
average particle size (D.sub.50) of 20 .mu.m. As spraying
conditions, argon gas and hydrogen gas were used as plasma gases,
and output of 30 kW, and spraying distance of 120 mm were applied.
The porosity of the lower layer was determined by image analysis
method as explained below, and was 2.0%.
[0077] Further, a slurry was prepared such that 30 wt % of yttrium
fluoride particles having a BET specific surface area of 0.7
m.sup.2/g and an average particle size (D.sub.50) of 3.3 .mu.m was
dispersed in ethanol. A yttrium fluoride series sprayed coating of
150 .mu.m thick was formed as a surface layer on the lower layer
disposed on the substrate by using a suspension plasma spraying
apparatus with the slurry. The outermost surface portion of the
surface layer was machined by grinding to remove 50 .mu.m-thick
from the surface, and the surface was polished to a mirror surface
having a surface roughness Ra of 0.1 .mu.m. Then, a sample piece of
an erosion-resistant coating having a double layer structure and a
total thickness of 200 .mu.m was prepared. The porosity of the
surface layer was determined by image analysis method as explained
below, and was 0.4%.
[Measurement of Porosity]
[0078] The sample piece was embedded into resin, cross-section
surface was polished to mirror surface (surface roughness Ra: 0.1
.mu.m). Then, electron microscopic pictures of the cross-section
surface were taken (at 200 times magnification). The photographic
images were taken at ten view fields (photographed area: 0.017
mm.sup.2 per view field) of the cross-section surface. After the
image was processed by utilizing image processing software
"Photoshop" (produced by Adobe Systems Co., Ltd.), the porosity was
quantified by utilizing image analysis software "Section Image"
(produced by Scion Corporation), and the porosity was computed as
the ratio of the total area of pore portions to the total area of
the observed area. The porosity was evaluated as an average of ten
view fields.
Example 2
[0079] An A5052 aluminum alloy substrate having the surface size of
100 mm square and 5 mm thick was degreased at the surface by
acetone, and one surface of the substrate was subjected to
roughening treatment with an abrasive corundum. An erbium oxide
sprayed coating of 100 .mu.m thick was formed as a lower layer on
the substrate by using an atmospheric plasma spraying apparatus
with an erbium oxide powder (granulated particles) having an
average particle size (D.sub.50) of 20 .mu.m. As spraying
conditions, argon gas and hydrogen gas were used as plasma gases,
and output of 30 kW and spraying distance of 120 mm were applied.
The porosity of the lower layer was determined by image analysis
method as the same in Example 1, and was 3.2%.
[0080] Further, a slurry was prepared such that 30 wt % of erbium
fluoride particles having a BET specific surface area of 1.5
m.sup.2/g and an average particle size (D.sub.50) of 2.3 .mu.m was
dispersed in ethanol. An erbium fluoride series sprayed coating of
100 .mu.m thick was formed as a surface layer on the lower layer
composed of erbium oxide sprayed coating disposed on the substrate
by using a suspension plasma spraying apparatus with the slurry. As
spraying conditions, argon gas, nitrogen gas and hydrogen gas were
used as plasma gases, and output of 100 kW, and spraying distance
of 75 mm were applied. Then, a sample piece of an erosion-resistant
coating having a double layer structure and a total thickness of
200 .mu.m was prepared. The porosity of the surface layer was
determined by image analysis method as the same in Example 1, and
was 0.8%.
Example 3
[0081] An A5052 aluminum alloy substrate having the surface size of
100 mm square and 5 mm thick was degreased at the surface by
acetone, and one surface of the substrate was subjected to
roughening treatment with an abrasive corundum. A yttrium oxide
sprayed coating of 100 .mu.m thick was formed as a lower layer on
the substrate by using an atmospheric plasma spraying apparatus
with a yttrium oxide powder (granulated particles) having an
average particle size (D.sub.50) of 20 .mu.m. As spraying
conditions, argon gas and hydrogen gas were used as plasma gases,
and output of 30 kW, and spraying distance of 120 mm were applied.
The porosity of the lower layer was determined by image analysis
method as the same in Example 1, and was 2.9%.
[0082] Further, a slurry was prepared such that 30 wt % of a
mixture of yttrium fluoride particles having a BET specific surface
area of 1.0 m.sup.2/g and an average particle size (D.sub.50) of
3.7 .mu.m, and yttrium oxide fine particles having a BET specific
surface area of 48.3 m.sup.2/g and an average particle size
(D.sub.50) of 200 nm that contains them in the weight ratio of
yttrium fluoride/yttrium oxide=99/1 was dispersed in ethanol. In
this case, the content of the yttrium oxide fine particles in the
slurry is 0.3 wt %. A yttrium fluoride series sprayed coating of
100 .mu.m thick was formed as a surface layer on the lower layer
composed of yttrium oxide sprayed coating disposed on the substrate
by using a suspension plasma spraying apparatus with the slurry. As
spraying conditions, argon gas, nitrogen gas and hydrogen gas were
used as plasma gases, and output of 100 kW, and spraying distance
of 75 mm were applied. Then, a sample piece of an erosion-resistant
coating having a double layer structure and a total thickness of
200 .mu.m was prepared. The porosity of the surface layer was
determined by image analysis method as the same in Example 1, and
was 0.2%.
Example 4
[0083] An A5052 aluminum alloy substrate having the surface size of
100 mm square and 5 mm thick was degreased at the surface by
acetone, and one surface of the substrate was subjected to
roughening treatment with an abrasive corundum. A yttrium oxide
sprayed coating of 180 .mu.m thick was formed as a lower layer on
the substrate by using an atmospheric plasma spraying apparatus
with a yttrium oxide powder (granulated particles) having an
average particle size (D.sub.50) of 30 .mu.m. As spraying
conditions, argon gas and hydrogen gas were used as plasma gases,
and output of 30 kW and spraying distance of 120 mm were applied.
The porosity of the lower layer was determined by image analysis
method as the same in Example 1, and was 3.5%. The surface
roughness Ra of the resulting coating was 5.6 .mu.m. Next, the
outermost surface portion of the yttrium oxide sprayed coating was
machined by using a surface grinding machine, and the grinded
surface was polished to a mirror surface having a surface roughness
Ra of 0.1 .mu.m. The thickness of the coating was adjusted to 100
.mu.m.
[0084] Further, a slurry was prepared such that 30 wt % of yttrium
fluoride particles having a BET specific surface area of 0.6
m.sup.2/g and an average particle size (D.sub.50) of 4.6 .mu.m was
dispersed in ethanol. A yttrium fluoride series sprayed coating of
100 .mu.m thick was formed as a surface layer on the lower layer
composed of yttrium oxide sprayed coating disposed on the substrate
by using a suspension plasma spraying apparatus with the slurry. As
spraying conditions, argon gas, nitrogen gas and hydrogen gas were
used as plasma gases, and output of 100 kW, and spraying distance
of 75 mm were applied. Then, a sample piece of an erosion-resistant
coating having a double layer structure and a total thickness of
200 .mu.m was prepared. The porosity of the surface layer was
determined by image analysis method as the same in Example 1, and
was 0.9%.
Example 5
[0085] An A5052 aluminum alloy substrate having the surface size of
100 mm square and 5 mm thick was degreased at the surface by
acetone, and one surface of the substrate was subjected to
roughening treatment with an abrasive corundum. A yttrium oxide
sprayed coating of 100 .mu.m thick was formed as a lower layer on
the substrate by using an atmospheric plasma spraying apparatus
with a yttrium oxide powder (granulated particles) having an
average particle size (D.sub.50) of 18 .mu.m. As spraying
conditions, argon gas and hydrogen gas were used as plasma gases,
and output of 30 kW, and spraying distance of 120 mm were applied.
The porosity of the lower layer was determined by image analysis
method as the same in Example 1, and was 2.9%.
[0086] Further, a yttrium fluoride series sprayed coating of 100
.mu.m thick was formed as a surface layer on the lower layer
disposed on the substrate by using an atmospheric plasma spraying
apparatus with granulated particles containing 90 wt % of yttrium
fluoride and 10 wt % of yttrium oxide, and having an average
particle size (D.sub.50) of 30 .mu.m. As spraying conditions, argon
gas and hydrogen gas were used as plasma gases, and output of 35 kW
and spraying distance of 120 mm were applied. Then, a sample piece
of an erosion-resistant coating having a double layer structure and
a total thickness of 200 .mu.m was prepared. The porosity of the
surface layer was determined by image analysis method as the same
in Example 1, and was 2.3%.
Example 6
[0087] An A5052 aluminum alloy substrate having the surface size of
100 mm square and 5 mm thick was degreased at the surface by
acetone, and one surface of the substrate was subjected to
roughening treatment with an abrasive corundum. A yttrium oxide
sprayed coating of 50 .mu.m thick was formed as a first layer on
the substrate by using an atmospheric plasma spraying apparatus
with a yttrium oxide powder (granulated particles) having an
average particle size (D.sub.50) of 20 .mu.m. As spraying
conditions, argon gas and hydrogen gas were used as plasma gases,
and output of 30 kW, and spraying distance of 120 mm were applied.
Next, a yttrium fluoride series sprayed coating of 50 .mu.m thick
was formed as a second layer on the first layer by using an
atmospheric plasma spraying apparatus with granulated particles
containing 90 wt % of yttrium fluoride and 10 wt % of yttrium oxide
and having an average particle size (D.sub.50) of 30 .mu.m. As
spraying conditions, argon gas and hydrogen gas were used as plasma
gases, and output of 35 kW, and spraying distance of 120 mm were
applied. Herein, a combined coating having a multilayer structure
that consists of first and second layers was formed as a lower
layer. The porosity of the lower layer was determined by image
analysis method as the same in Example 1, and was 2.9%.
[0088] Further, a slurry was prepared such that 30 wt % of a
mixture of yttrium fluoride particles having a BET specific surface
area of 0.5 m.sup.2/g and an average particle size (D.sub.50) of
5.7 .mu.m, and silicon carbide fine particles having an average
particle size (D.sub.50) of 2 .mu.m that contains them in the
weight ratio of yttrium fluoride/silicon carbide=95:5 was dispersed
in ethanol. In this case, the content of the silicon carbide fine
particles in the slurry is 1.5 wt %. A yttrium fluoride series
sprayed coating of 150 .mu.m thick was formed as a surface layer on
the lower layer of the coating having a multilayer structure by
using a suspension plasma spraying apparatus with the slurry. As
spraying conditions, argon gas, nitrogen gas and hydrogen gas were
used as plasma gases, and output of 100 kW, and spraying distance
of 75 mm were applied. Then, a sample piece of an erosion-resistant
coating having a triple layer structure and a total thickness of
250 .mu.m was prepared. The porosity of the surface layer was
determined by image analysis method as the same in Example 1, and
was 0.3%.
Example 7
[0089] An A5052 aluminum alloy substrate having the surface size of
100 mm square and 5 mm thick was degreased at the surface by
acetone, and one surface of the substrate was subjected to
roughening treatment with an abrasive corundum. A gadolinium oxide
sprayed coating of 300 .mu.m thick was formed as a lower layer on
the substrate by using an atmospheric plasma spraying apparatus
with a gadolinium oxide powder (granulated particles) having an
average particle size (D.sub.50) of 15 .mu.m. As spraying
conditions, argon gas and hydrogen gas were used as plasma gases,
and output of 30 kW, and spraying distance of 120 mm were applied.
The porosity of the lower layer was determined by image analysis
method as the same in Example 1, and was 2.2%.
[0090] Further, a slurry was prepared such that 30 wt % of a
mixture of gadolinium fluoride particles having a BET specific
surface area of 0.3 m.sup.2/g and an average particle size
(D.sub.50) of 5.9 .mu.m, and silicon carbide fine particles having
an average particle size (D.sub.50) of 2 .mu.m that contains them
in the weight ratio of gadolinium fluoride/silicon carbide=90:10
was dispersed in ethanol. In this case, the content of the silicon
carbide fine particles in the slurry is 3 wt %. A gadolinium
fluoride series sprayed coating of 50 .mu.m thick was formed as a
surface layer by using a suspension plasma spraying apparatus with
the slurry. As spraying conditions, argon gas, nitrogen gas and
hydrogen gas were used as plasma gases, and output of 100 kW, and
spraying distance of 75 mm were applied. Then, a sample piece of an
erosion-resistant coating having a double layer structure and a
total thickness of 350 .mu.m was prepared. The porosity of the
surface layer was determined by image analysis method as the same
in Example 1, and was 0.1%.
Comparative Example 1
[0091] An A5052 aluminum alloy substrate having the surface size of
100 mm square and 5 mm thick was degreased at the surface by
acetone, and one surface of the substrate was subjected to
roughening treatment with an abrasive corundum. An alumina sprayed
coating of 200 .mu.m thick was formed on the substrate by using an
atmospheric plasma spraying apparatus with an alumina powder
(Sumicorundum AA-18) having an average particle size (D.sub.50) of
18 .mu.m. As spraying conditions, argon gas and hydrogen gas were
used as plasma gases, and output of 30 kW, and spraying distance of
120 mm were applied. Then, a sample piece of an erosion-resistant
coating composed of an alumina sprayed coating was prepared. The
porosity of the alumina sprayed coating was determined by image
analysis method as the same in Example 1, and was 3.5%.
Comparative Example 2
[0092] An A5052 aluminum alloy substrate having the surface size of
100 mm square and 5 mm thick was degreased at the surface by
acetone, and one surface of the substrate was subjected to
roughening treatment with an abrasive corundum. A yttrium oxide
sprayed coating of 200 .mu.m thick was formed on the substrate by
using an atmospheric plasma spraying apparatus with a yttrium oxide
powder (granulated particles) having an average particle size
(D.sub.50) of 30 .mu.m. As spraying conditions, argon gas and
hydrogen gas were used as plasma gases, and output of 30 kW and
spraying distance of 120 mm were applied. Then, a sample piece of
an erosion-resistant coating composed of an yttrium oxide sprayed
coating was prepared. The porosity of the alumina sprayed coating
was determined by image analysis method as the same in Example 1,
and was 1.8%.
Comparative Example 3
[0093] An A5052 aluminum alloy substrate having the surface size of
100 mm square and 5 mm thick was degreased at the surface by
acetone, and one surface of the substrate was subjected to
roughening treatment with an abrasive corundum. A slurry was
prepared such that 30 wt % of yttrium fluoride particles having a
BET specific surface area of 2.8 m.sup.2/g and an average particle
size (D.sub.50) of 1.6 .mu.m was dispersed in pure water containing
10 wt % of ethanol. A yttrium fluoride series sprayed coating of
100 .mu.m thick was formed by using a suspension plasma spraying
apparatus with the slurry. As spraying conditions, argon gas,
nitrogen gas and hydrogen gas were used as plasma gases, and output
of 100 kW, and spraying distance of 75 mm were applied. Then, a
sample piece of an erosion-resistant coating consisting of a single
layer was prepared. The porosity of the yttrium fluoride sprayed
coating was determined by image analysis method as the same in
Example 1, and was 3.5%.
[0094] With respect to the erosion-resistant coating of the sample
pieces of Examples 1 to 7 and Comparative Example 1 to 3, crystal
phase, Vickers hardness, amount of particles generated, erosion
resistivity to plasma, thickness, centerline average roughness
(surface roughness) Ra, and concentrations of rare earth element
(R), oxygen (O) and nitrogen (N) were measured in each of the
sprayed coating by the following respective methods. The results
are shown in Table 1.
[0095] [Measurement of Crystal Phase]
[0096] The crystal phase contained in the erosion resistant coating
of the obtained sample piece was identified by X-ray diffractometer
"X'Pert Pro/MPD", manufactured by Malvern Panalytical Ltd.
[0097] [Measurement of Thickness]
[0098] The thickness of the obtained sample piece was measured by
Eddy-current Coating Thickness Tester, LH-300J, manufactured by
Kett Electric Laboratory.
[0099] [Measurement of Vickers Hardness]
[0100] The surface of coating was polished to mirror surface
(surface roughness Ra=0.1 .mu.m), and the Vickers hardness of the
obtained sample piece was measured at the surface of the coating by
a micro Vickers hardness tester, AVK-C1, manufactured by Mitutoyo
Corporation (loading: 300 gf (2.94 N), loading time: 10 min). The
Vickers hardness was evaluated as an average of five points.
[0101] [Test for Evaluation of Particle Generation]
[0102] The obtained sample piece was cleared by ultrasonic cleaning
(power: 200W, cleaning time: 30 min), then dried, and the sample
piece was immersed into 20 cc of pure water, and further cleaned by
ultrasonic cleaning. After the cleaning, the sample piece was
removed from the treated water, and 2 cc of 5.3N nitric acid
aqueous solution was added into the treated water to solve
R.sub.2O.sub.3 fine particles included in the treated water, then
R.sub.2O.sub.3 was quantified by inductively-coupled plasma
emission spectrometry.
[0103] [Test for Evaluation of Erosion-Resistance]
[0104] The surface of the obtained sample piece was polished to a
mirror surface having a surface roughness Ra of 0.1 .mu.m, and a
part of the surface was cover with a masking tape to form a portion
covered with the masking tape, and a portion for exposure. The
sample piece was set in a reactive plasma etching apparatus, then,
a test for erosion-resistance to plasma was conducted under the
conditions of plasma output of 440 W, gas species of CF.sub.3 and
O.sub.2(20 vol %), flow rate of 20 sccm, gas pressure of 5 Pa, and
test time of 8 hours. The height of the step formed between the
covered portion and the exposed portion due to erosion was measured
by surface profile measuring system "Dektak3030". The result was
evaluated as an average of four measured points.
[0105] [Measurement of Centerline Average Roughness (Surface
Roughness) Ra]
[0106] The roughness Ra of the obtained sprayed coating was
measured by surface texture measuring instrument, HANDYSURF E-35A,
manufactured by Tokyo Seimitsu Co., Ltd.
[0107] [Measurement of Constituent Elements]
[0108] The obtained sprayed coating was peeled from the substrate
on which the sprayed coating disposed, and the surface layer of the
coating was provided to measurement of constituent elements. R
concentration was measured by EDTA titration method, O
concentration was measured by inert gas fusion infrared absorption
spectrophotometry, and F concentration was NaOH fusion IC
method.
TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 3 4 5 6 7 1
2 3 Surface Layer Spraying Method for SPS SPS SPS SPS APS SPS SPS
APS APS SPS Surface Layer Crystal Phase YF.sub.3 ErF.sub.3 YF.sub.3
YF.sub.3 YF.sub.3 YF.sub.3 GdF.sub.3 Al.sub.2O.sub.3 Y.sub.2O.sub.3
YF.sub.3 YOF ErOF Y.sub.5O.sub.4F.sub.7 YOF Y.sub.5O.sub.4F.sub.7
YOF Gd.sub.5O.sub.4F.sub.7 Y.sub.5O.sub.4F.sub.7 YOF Coating
Thickness 100 100 100 100 100 150 50 200 200 100 (.mu.m) Vickers
Hardness 590 560 530 510 360 530 520 800 450 390 Porosity (%) 0.4
0.8 0.2 0.9 2.3 0.3 0.1 3.5 1.8 3.5 Amount of R Particles 1.8 0.9
0.2 0.4 5.2 0.8 1.1 -- 7.3 9.4 (.mu.g/cm.sup.2) Erosion Resistivity
2.5 2.9 3.3 2.8 4.3 3.8 3.9 7.7 1.9 3.5 (Average Height of Step)
(.mu.m) Surface Roughness 0.1 4.7 4.5 1.4 4.3 0.9 2.4 3.9 4.9 11.8
Ra (.mu.m) Concentration of R 64.7 64.5 64.2 63.3 65.5 61.5 68.6 --
78.7 63.4 (wt %) Concentration of O 3.7 4.6 3.7 3.0 5.8 3.5 2.5
47.0 21.3 3.2 (wt %) Concentration of F 30.4 30.1 31.6 33.0 26.5
28.9 18.9 -- -- 31.4 (wt %) Lower Layer Spraying Method for APS APS
APS APS APS APS APS -- -- -- Lower Layer Crystal Phase
Y.sub.2O.sub.3 Er.sub.2O.sub.3 Y.sub.2O.sub.3 Y.sub.2O.sub.3
Y.sub.2O.sub.3 YF.sub.3 Gd.sub.2O.sub.3 -- -- -- Y.sub.2O.sub.3
Coating Thickness 100 100 100 100 100 50 300 -- -- -- (.mu.m) 50
Surface Roughness 5.8 3.1 4.0 0.1 4.5 4.8 4.2 -- -- -- Ra (.mu.m)
Porosity (%) 2.0 3.2 2.9 3.5 2.9 2.9 2.2 -- -- --
[0109] Further, electric performances of each of the
erosion-resistant coatings of Examples 1 to 7 and Comparative
Examples 1 to 3 were investigated by the following methods. Three
test pieces (N=3) were prepared for the test of electric
performances, and a volume resistivity, a surface resistivity and a
dielectric breakdown voltage at room temperature (23.degree. C.)
and 200.degree. C. were investigated in each of the three pieces,
respectively. The results are shown in Tables 2 to 4.
[0110] [Method for Measuring Volume Resistivity]
[0111] Volume resistances at room temperature (23.degree. C.) and
200.degree. C. were measured by ultrahigh resistance/minimal
current digital meter "Type 8340A" (manufactured by ADC
Corporation) in conformity with Standard Test Method (ASTM
D257:2007), and a volume resistivity was computed based on the
thickness. The result was evaluated as an average of three test
pieces (N=3). The "temperature index" in Table 2 means a value
calculated by the expression: (Volume resistivity at 200.degree.
C.)/(Volume resistivity at 23.degree. C.). When the temperature
index is closer to 1 (one), volume resistivity of the
erosion-resistant coating is maintained regardless of temperature
variation, and such a temperature index means that the
erosion-resistant has resistance to temperature variation.
[0112] [Method for Measuring Surface Specific Resistance]
[0113] Surface resistances at room temperature (23.degree. C.) and
200.degree. C. were measured by ultrahigh resistance/minimal
current digital meter "Type 8340A" (manufactured by ADC
Corporation) in conformity with Standard Test Method (ASTM
D257:2007), and a surface resistivity was computed. The result was
evaluated as an average of three test pieces (N=.sup.3).
[0114] [Method for Measuring Dielectric Breakdown Voltage]
[0115] Dielectric breakdown voltages at room temperature
(23.degree. C.) and 200.degree. C. were measured by dielectric
breakdown tester "Type HAT-300-100RHO" (manufactured by Yamasaki
Sangyo Kabushiki Kaisha) in conformity with Standard Test Method
(ASTM D149:2009), and a dielectric breakdown strength was computed
based on the thickness. The result was evaluated as an average of
three test pieces (N=3).
TABLE-US-00002 TABLE 2 [Volume Resistivity] Volume Resistivity
(.OMEGA. cm) Temperature at 23.degree. C. at 200.degree. C. Index
Example 1 1.45 .times. 10.sup.10 8.97 .times. 10.sup.10 6.2 Example
2 1.01 .times. 10.sup.11 3.23 .times. 10.sup.11 3.2 Example 3 1.35
.times. 10.sup.11 2.83 .times. 10.sup.11 2.1 Example 4 2.10 .times.
10.sup.11 1.20 .times. 10.sup.11 0.6 Example 5 5.37 .times.
10.sup.9 1.23 .times. 10.sup.9 0.2 Example 6 1.00 .times. 10.sup.12
1.03 .times. 10.sup.11 0.1 Example 7 1.82 .times. 10.sup.11 1.83
.times. 10.sup.12 10.0 Comparative Example 1 1.37 .times. 10.sup.9
2.20 .times. 10.sup.14 160975.6 Comparative Example 2 2.40 .times.
10.sup.10 1.16 .times. 10.sup.13 483.3 Comparative Example 3 2.70
.times. 10.sup.11 2.06 .times. 10.sup.9 0.008
TABLE-US-00003 TABLE 3 [Surface Specific Resistance] Surface
Resistivity (.OMEGA.) at 23.degree. C. at 200.degree. C. Example 1
4.49 .times. 10.sup.12 6.57 .times. 10.sup.10 Example 2 5.00
.times. 10.sup.14 4.23 .times. 10.sup.12 Example 3 1.02 .times.
10.sup.14 9.95 .times. 10.sup.11 Example 4 1.79 .times. 10.sup.15
4.73 .times. 10.sup.9 Example 5 5.77 .times. 10.sup.12 1.18 .times.
10.sup.14 Example 6 3.73 .times. 10.sup.14 6.63 .times. 10.sup.9
Example 7 7.00 .times. 10.sup.13 5.53 .times. 10.sup.9 Comparative
Example 1 7.70 .times. 10.sup.11 1.97 .times. 10.sup.15 Comparative
Example 2 4.87 .times. 10.sup.12 2.33 .times. 10.sup.15 Comparative
Example 3 4.93 .times. 10.sup.15 2.00 .times. 10.sup.14
TABLE-US-00004 TABLE 4 [Dielectric Breakdown Voltage] Dielectric
Breakdown Strength (kV/mm) at 23.degree. C. at 200.degree. C.
Example 1 12.0 17.2 Example 2 15.4 9.7 Example 3 17.5 14.3 Example
4 20.3 15.5 Example 5 20.6 15.0 Example 6 18.0 15.0 Example 7 17.9
14.9 Comparative Example 1 24.7 13.5 Comparative Example 2 17.4
14.4 Comparative Example 3 17.9 10.3
[0116] As shown in Tables 1 and 2, the erosion-resistant coating of
the invention having a multilayer structure that consists of a rare
earth oxide coating, and a rare earth fluoride series coating
formed thereon has a temperature index of 0.1 to 10. It is
confirmed that variation of the volume resistivity in the
temperature range from 23 to 200.degree. C. is almost maintained.
That is to say, in the erosion-resistant coating of the invention,
variation of the volume resistivity between 23.degree. C. and
200.degree. C. is very small, thus, the invention can provide an
erosion-resistant coating being stable in electric performances.
The temperature index of volume resistivities can be arbitrarily
controlled by variation of thicknesses of the lower and surface
layers, and/or variation of oxygen content of rare earth fluoride
series coating of the surface layer. For Example, a material having
a small variation of the volume resistivity between a room
temperature and the high temperature of 200.degree. C. is required
for an electrostatic chuck used in a plasma etching apparatus. It
is confirmed that the invention is a material satisfying the
requirement from the results. The erosion-resistant coating of the
invention has a stable and sufficient surface resistivity to
temperature variation, as shown in Table 3. Further, the
erosion-resistant coatings in Examples 1 to 7 of the invention have
a sufficiently high dielectric breakdown strength as shown in Table
4. It is confirmed the erosion-resistant coating has a dielectric
breakdown voltage applicable for a material of an electrostatic
chuck.
[0117] As shown in Table 1, the surface layer which constituents
the sprayed coating of each of Example 1-4, 6 and 7 was obtained by
suspension plasma slurry (SPS) method with a slurry including an
organic solvent (ethanol) only as a dispersion medium, and includes
crystal phases consisting of a rare earth fluoride and a rare earth
oxyfluoride. These have a higher Vickers hardness in comparison
with Comparative Example 3 in which mostly of the dispersion medium
is water, and are dense coatings having a low porosity. It is
confirmed generation of particles is reduced in the invention and
the sprayed coating has an excellent erosion-resistance.
[0118] Next, in Example 3, the surface layer of the sprayed coating
was formed by suspension slurry spraying with a slurry including
yttrium fluoride particles in which yttrium oxide fine particles
(D.sub.50: 50 nm) were added. The effect of the addition of the
yttrium oxide fine particles was confirmed by observing and
comparing a cross-section surface of the surface layer in the
sprayed coating of Example 3, with a cross-section surface of a
sprayed coating that was formed by the same method except for
excluding addition of the yttrium oxide fine particle, though an
electron microscope. The results are shown in FIGS. 1 and 2. As
shown in FIGS. 1 and 2, it is confirmed that generation of lateral
cracks in a cross-section surface of the surface layer of the
sprayed coating was effectively suppressed in the coating of the
surface layer obtained with a slurry which was added a small amount
of the yttrium oxide fine particles in comparison with the coating
obtained with a slurry which was added no yttrium oxide fine
particles.
[0119] [Preparation of Rare Earth Fluoride Particles for Forming a
Surface Layer in Examples 1-4, 6 and 7]
[0120] The rare earth fluoride particles for forming a surface
layer in Examples 1-4, 6 and 7 were prepared by the following
method. First, a solution including a rare earth nitrate was heated
to 50.degree. C., and a solution of ammonium fluoride was added
into the solution including a rare earth nitrate, then the solution
was mixed with stirring at 50.degree. C. for 30 min. As a result, a
white precipitate was crystallized. After that, the precipitate was
filtrated, washed with water, and dried. The resulting precipitate
was identified, by of X-ray diffraction analysis, as an ammonium
fluoride double salt in form of R.sub.3(NH.sub.4)F.sub.10, wherein
R is a rare earth element (i.e., Y in Examples 1, 3, 4 and 6, Er in
Example 2, or Gd in Example 7). Further, the double salt was fired
under nitrogen atmosphere at 900.degree. C. in Examples 6 and 7, at
875.degree. C. in Example 4, at 850.degree. C. in Examples 1 and 3,
or at 825.degree. C. in Example 2. The fired product was pulverized
by a jet mill, then, the rare earth fluoride particles were
obtained.
[0121] [Preparation of Yttrium Fluoride Particles for Forming a
Surface Layer in Comparative Example 3]
[0122] The yttrium fluoride particles for forming a surface layer
in Comparative Example 3 were prepared by the following method.
First, a yttrium oxide powder and an ammonium hydrogenfluoride
powder were mixed. The mixture was fired under nitrogen atmosphere
at 650.degree. C. for 2 hours, then, yttrium fluoride was obtained.
The obtained yttrium fluoride was pulverized by a jet mill, and
sifted by air classification, then, rare earth fluoride particles
were obtained.
[0123] With respect to the rare earth compound powder (yttrium
fluoride particles, erbium fluoride particles or gadolinium
fluoride) prepared by the above-described method, and used for
preparing the slurry for thermal spraying (spraying material) in
each of Examples 1-4, 6 and 7 and Comparative Example 3, BET
specific surface area, average particle size D.sub.50, average
roundness, particle hardness and pore volume were measured by the
following respective methods. The results are shown in Table 5.
[0124] [Measurement of BET Specific Surface Area]
[0125] The BET specific surface area of the obtained rare earth
compound powder was measured by Full Automatic BET Specific Surface
Area Analyzer, Macsorb HM model-1208, manufactured by Mountech Co.,
Ltd.
[0126] [Measurement of Average Particle Size D.sub.50]
[0127] Particle size distribution of the rare earth compound powder
was measured by laser diffraction method and the average particle
size D.sub.50 was evaluated in volume basis. For the measurement, a
laser diffraction/scattering type particle size distribution
measuring apparatus "Microtrac MT3300EX II", manufactured by
MicrotracBEL Corp., was used. The obtained slurry (in Example 1 to
4, 6 or 7 or Comparative Example 3) was added into 30 ml of pure
water, irradiated with ultrasonic (40 W, 1 min), and then provided
to evaluation as a sample. The obtained powder (in Example 5 or
Comparative Example 1 or 2) was added into 30 ml of pure water, and
then directly provided to evaluation as a sample. The sample was
dropped into the circulation system of the measuring apparatus so
as to be adjusted to Concentration Index DV (Diffraction Volume) of
0.01 to 0.09 that adopts to the specification of the measuring
apparatus, and the measurement was subjected.
[0128] [Measurement of Average Roundness]
[0129] An average roundness is an evaluated value for circularity
of spraying particles defined by the expression:
(Roundness)=(Circumferential length of an assumed circle having the
equivalent area in planar view to an area of an observed
particle)/(Circumferential length of the observed particle in
planar view).
The average roundness of the obtained rare earth compound powder
was measured by "FPIA-3000S", manufactured by Sysmex Corporation.
In particular, a flat sample flow of a sample of slurry was formed
by a sheath fluid, and a still image of particles was taken under
strobe illumination by a flat sheath flow method using Flow
particle image analyzer "FPIA-3000S". The average roundness was
measured by analyzing each of the sampled particles by image
analysis technique. Specifically, 20 mg of a sample powder was
added into a beaker, a particle sheath, as an aqueous solution of
dispersing agent (manufactured by Sysmex Corporation) was added
into the beaker to fix the volume of the mixture to 20 ml, then,
the slurry was dispersed by ultrasonic (100W) for 2 min. The
measurement was conducted with the obtained slurry for the
measurement.
[0130] [Measurement of Particle Hardness]
[0131] The particle hardness of the obtained rare earth compound
powder was measured by nanoindentation method. "ENT-2100",
manufactured by Elionix Inc. was utilized for as an analysis
apparatus.
[0132] The nanoindentation method is a technique that measures
mechanical properties such as hardness of material, elastic modulus
(physical property value indicating difficulty of plastic
deformation) and yield stress (stress at which a substance starts
plastic deformation), on nanometer scale. The diamond indenter is
pressed into a sample powder placed on a stage, load (pressing
strength) and deformation (pressing depth) are measured, and
mechanical properties are calculated from the obtained
load-deformation curve. The measuring apparatus includes a diamond
indenter, a transducer and a controller for detecting control and
measurement values of the diamond indenter, and a computer for
operation.
[0133] [Measurement of Pore Volume]
[0134] The pore volume of the rare earth compound powder was
measured by mercury porosimetry with Mercury Porosimeter, AutoPore
III, manufactured by Micromeritics Instrument Corporation, and from
the obtained cumulative pore volume distribution relative to the
pore diameter, total volume of pores having a diameter of up to 10
.mu.m was computed.
TABLE-US-00005 TABLE 5 Example Comparative Example 1 2 3 4 5 6 7 1
2 3 Raw Material Powder YF.sub.3 ErF.sub.3 YF.sub.3 YF.sub.3
YF.sub.3 + YF.sub.3 GdF.sub.3 Al.sub.2O.sub.3 Y.sub.2O.sub.3
YF.sub.3 Y.sub.2O.sub.3 Dispersion Medium Ethanol -- Ethanol -- --
Pure Water + Ethanol Additive (Fine Particles) -- -- Y.sub.2O.sub.3
-- -- SiC SiC -- -- -- BET Specific Surface 0.7 1.5 1.0 0.6 -- 0.5
0.3 -- -- 2.8 Area (m.sup.2/g) Average Particle Size 3.3 2.3 3.7
4.6 30 5.7 5.9 18 30 1.6 D.sub.50 (.mu.m) Average Roundness 0.93
0.91 0.93 0.90 -- 0.92 0.92 -- -- 0.84 Particle Hardness (GPa) 9.12
9.40 9.90 8.23 -- 7.58 11.34 -- -- 6.32 Volume of Pore Having 0.31
0.27 0.26 0.23 -- 0.19 0.14 -- -- 0.56 Diameter of up to 10 .mu.m
(cm.sup.3/g)
[0135] As shown in Table 5, in case that the surface layer formed
by SPS method, it is confirmed that a dense sprayed coating having
a very high hardness and being superior in erosion-resistance, as
shown in Table 1, was obtained by the SPS method with a slurry
including a rare earth compound powder dispersed in an organic
solvent. In this case, use of a rare earth fluoride powder having a
BET surface area of up to 2 m.sup.2/g and an average particle size
D.sub.50 of 2 to 6 .mu.m, and further having an average roundness
of at least 0.9, a particle hardness of 7 to 12 GPa, and a total
volume of pore having a diameter of up to 10 .mu.m of up to 0.5
cm.sup.3/g, as the rare earth compound powder, is more preferably
for forming the advantageous sprayed coating. On the other hand, in
case that the surface layer formed by APS method, it is confirmed
that a sprayed coating having a very small variation of the volume
resistivity, stable electrical characteristics, and a sufficient
high dielectric breakdown voltage was obtained.
[0136] Japanese Patent Application No. 2018-152883 is incorporated
herein by reference.
[0137] Although some preferred embodiments have been described,
many modifications and variations may be made thereto in light of
the above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
* * * * *