U.S. patent application number 10/737785 was filed with the patent office on 2004-07-01 for high dielectric strength member.
Invention is credited to Maeda, Takao, Shima, Satoshi.
Application Number | 20040126625 10/737785 |
Document ID | / |
Family ID | 32652744 |
Filed Date | 2004-07-01 |
United States Patent
Application |
20040126625 |
Kind Code |
A1 |
Maeda, Takao ; et
al. |
July 1, 2004 |
High dielectric strength member
Abstract
A sprayed member is obtained by plasma spraying an oxide
containing a rare earth element having atomic number 64 to 71 onto
a substrate to form a spray coating. The sprayed member exhibits a
high dielectric strength without a need for sealing treatment and
is useful as dielectric rolls, heating substrates, electrostatic
chucks, susceptors and the like.
Inventors: |
Maeda, Takao; (Takefu-shi,
JP) ; Shima, Satoshi; (Takefu-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
32652744 |
Appl. No.: |
10/737785 |
Filed: |
December 18, 2003 |
Current U.S.
Class: |
428/702 |
Current CPC
Class: |
C23C 4/11 20160101; C23C
24/04 20130101; H02H 1/00 20130101 |
Class at
Publication: |
428/702 |
International
Class: |
B32B 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2002 |
JP |
2002-379389 |
Claims
1. A high dielectric strength member comprising a substrate and a
high dielectric strength coating formed thereon in the form of a
sprayed coating of an oxide containing a rare earth element having
atomic number 64 to 71.
2. The high dielectric strength member of claim 1 wherein the
sprayed coating has not been subjected to sealing treatment.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to members having high dielectric
strength spray coatings for use as sprayed members required to have
a high dielectric strength, such as insulating coated members,
spray coated heaters, semiconductor manufacturing susceptors and
electrostatic chucks.
[0003] 2. Background Art
[0004] Conventional insulating ceramic coated members relying on
the thermal spraying process include dielectric rolls for corona
discharge treatment, heating substrates and electrostatic chucks
for semiconductor manufacturing apparatus.
[0005] For example, dielectric rolls for corona discharge treatment
are required to have a dielectric strength of at least 5 kV when
ceramic coatings have a thickness of at least 300 .mu.m. While
currently available alumina sprayed coatings have a dielectric
strength of approximately 10 kV/mm, ceramic coatings are made as
thick as 500 .mu.m to 3 mm in order to clear the requirement. Such
thick ceramic coatings tend to craze or separate from supports. See
JP-A 11-279302.
[0006] Also used as heating substrates are alumina spray coated
members. They fail to maintain dielectric strength if the thickness
of sprayed coating is less than 100 .mu.m, and are prone to crack
if the thickness of sprayed coating is more than 500 .mu.m. Then
sprayed coatings desirably have a thickness in the range of 100 to
500 .mu.m. To enhance dielectric strength, pores in sprayed
coatings must be sealed (see JP-A 2002-289329).
[0007] The processes of manufacturing semiconductor wafers and flat
panel display substrates involve many substrate-processing steps
like etching, deposition and exposure, for which electrostatic
chucks, heaters, susceptors and the like are used in the processing
chamber. In these steps, workpieces are often treated with a plasma
of corrosive halide gas. Since those members serving as processing
jigs in such an environment are attacked by corrosive species, use
is typically made of ceramic material members and metal material
members having ceramics sprayed thereon. Currently, ceramic sprayed
members are often used because wafers become of a larger size and
complex members combined with metal members such as heaters can be
easily fabricated and because of a low cost.
[0008] Typical of ceramic sprayed members are alumina sprayed
members. They are used as electrostatic chucks or the like. Because
of their properties, however, alumina sprayed members need sealing
treatment in order to provide a high dielectric strength. Organic
materials are used in the sealing treatment. Such organic fills are
susceptible to etching in a halogen plasma environment, becoming a
cause of generating particles.
[0009] Since the recent halogen plasma process has a high
selectivity and uses a high density plasma in order to form narrow
and deep channels by etching, there arises a problem that even the
alumina sprayed members are less resistant to the halogen
plasma.
[0010] Attention is now drawn to Group IIIa compounds as the
material having improved erosion resistance in a halogen plasma
environment. Of these compounds, yttrium-containing oxides and
fluorides are known to be resistant to halogen plasma erosion.
Members having such oxides and fluorides sprayed thereon are
disclosed in JP-A 2001-164354 and JP-A 2001-226773. However,
sprayed coatings of alumina and yttria are still insufficient in
dielectric strength, and must be made thick or subjected to sealing
treatment.
SUMMARY OF THE INVENTION
[0011] An object of the invention is to provide a high dielectric
strength member bearing a sprayed coating which has halogen plasma
resistance and improved dielectric strength properties.
[0012] It has been found that a member having a sprayed coating of
an oxide of an atomic number 64 to 71 rare earth element formed on
a substrate exhibits a high dielectric strength without a need for
sealing treatment on the sprayed coating and possesses halogen
plasma resistance.
[0013] Accordingly, the present invention provides a high
dielectric strength member comprising a substrate and a high
dielectric strength coating formed thereon in the form of a sprayed
coating of an oxide containing a rare earth element having atomic
number 64 to 71.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The high dielectric strength member of the invention is
arrived at by forming on a substrate a sprayed coating of an oxide
containing a rare earth element having atomic number 64 to 71. The
sprayed coating has a high dielectric strength without a need for
sealing treatment.
[0015] The substrate may be selected from among ceramics, metals
and composites thereof depending on a particular application,
though not critical. Exemplary ceramic materials include shaped
bodies composed mainly of quartz, alumina, magnesia and yttria, and
complex oxides thereof, shaped bodies composed mainly of silicon
nitride, aluminum nitride and boron nitride, and shaped bodies
composed mainly of silicon carbide and boron carbide. Exemplary
carbon materials include carbon fibers and sintered carbon bodies.
Exemplary metal materials include those based on iron, aluminum,
magnesium, copper, silicon and nickel, alloys thereof, for example,
stainless alloys, aluminum alloys, anodized aluminum alloys,
magnesium alloys and copper alloys, and single crystal silicon.
Also included in the composite category are metal materials covered
with ceramic coatings and aluminum alloys subjected to anodizing
treatment or surface treatment, typically plating.
[0016] The sprayed coating contains an oxide of a rare earth
element having atomic number 64 to 71, i.e., Gd, Tb, Dy, Ho, Er,
Tm, Yb and Lu. It is most preferred that the sprayed coating
consist solely of the rare earth oxide although the advantages of
the invention are achievable with a sprayed coating containing at
least 45% by weight, especially at least 50% by weight of the rare
earth oxide. The oxides other than the rare earth oxide in the
sprayed coating include Al.sub.2O.sub.3, Y.sub.2O.sub.3 and oxides
of other rare earth elements.
[0017] Useful spraying techniques include flame spraying, high
velocity oxy-fuel (HVOF) spraying, detonation spraying, plasma
spraying, water stabilized plasma spraying, induction (RF) plasma
spraying, electromagnetic acceleration plasma spraying, cold
spraying, and laser spraying. The spraying technique is not
particularly limited although the plasma spraying featuring a high
spray output is preferred.
[0018] Depending on the operating atmosphere, the spraying is
divided into atmospheric spraying and low pressure or vacuum
spraying wherein spraying is effected in a chamber kept at a low
pressure or vacuum. Internal pores may be reduced in order to form
a more densified coating, and the low pressure spraying is
recommended in this regard. However, the low pressure or vacuum
spraying technique requires a low pressure or vacuum chamber in
order to perform a spraying operation. This imposes spatial or time
limits to the spraying operation. Then the present invention favors
the atmospheric spraying technique which can be practiced without a
need for a special pressure vessel.
[0019] The plasma spraying system generally includes a plasma gun,
a power supply, a powder feeder, and a gas controller. The plasma
output is determined by the power supplied to the plasma gun and
the feed rates of argon gas, nitrogen gas, hydrogen gas, helium gas
or the like. The feed rate of powder is controlled by the powder
feeder.
[0020] In the plasma spraying technique, a coating is formed by
operating a plasma gun to create a plasma, feeding a powder into
the plasma for melting particles, and instantaneously impinging
molten particles against a substrate. In order to obtain a
satisfactory coating, it is requisite that spraying particles be
melted fully and moved at a high flight velocity. In order that
particles be melted, the residence time of particles within the
plasma should be longer, which is equivalent to a lower velocity as
long as a limited space is concerned, and is thus contradictory to
the high velocity requirement. Increasing the input to the gun
leads to increases in both the temperature and flow velocity of a
plasma jet. However, the melting of particles is determined by the
latent heat of fusion, particle size, specific gravity of material
and gas temperature, and the flight velocity is determined by the
particle size, specific gravity and jet velocity. It is then
believed that the input power must be optimized for each type of
powder material.
[0021] For the manufacture of a sprayed member having higher
dielectric strength, with the above-described spraying conditions
taken into account, it is important to use a material having a
higher specific gravity as the coating. Namely, by forming a
sprayed coating of an oxide having a higher specific gravity than
alumina which has traditionally been used in dielectric strength
sprayed members, a sprayed member having higher dielectric strength
than the alumina-sprayed member is obtainable. In general,
compounds of elements of greater atomic numbers often have a higher
specific gravity. Of these, rare earth compounds are known to have
halogen plasma resistance. However, it is unknown that such rare
earth compounds have high dielectric strength. The inventor has
discovered that sprayed coatings of oxides of elements having
atomic number 64 to 71 have high dielectric strength as well.
[0022] Although the thickness of a sprayed coating is not critical,
the preferred thickness is from 100 .mu.m to less than 500 .mu.m,
more preferably from 100 .mu.m to 450 .mu.m, even more preferably
from 100 .mu.m to 400 .mu.m. Too thin a coating may undergo
breakdown due to the low dielectric strength at that thickness. Too
thick a coating is liable to craze and separate from the
substrate.
[0023] No particular limits are imposed to the dielectric strength
(kV/mm) of the sprayed coating. The preferred dielectric strength
is at least 15 kV/mm, more preferably at least 17 kV/mm as the
lower limit and up to 50 kV/mm as the upper limit.
[0024] Herein, the dielectric strength can be measured according to
JIS C2110, for example, using a specimen in which oxide is plasma
sprayed on a metal substrate. The sprayed coating on the specimen
may have a thickness of about 100 to 500 .mu.m. Specifically, an
aluminum substrate of 100 mm.times.100 mm.times.5 mm is used, one
surface is blasted prior to spraying, and an oxide containing an
element having atomic number 64 to 71 is plasma sprayed to form a
sprayed coating of about 200 .mu.m thick. The coated substrate is
sandwiched between electrodes according to JIS C2110, and voltage
is applied thereacross and increased at a rate of 200 V/sec. The
voltage at which dielectric breakdown occurs is the breakdown
voltage of the coating.
[0025] The voltage which is lower by 0.5 kV than the breakdown
voltage is a preset voltage. If no dielectric breakdown occurs when
the voltage is increased at a rate of 200 V/sec up to the preset
voltage and maintained at the preset voltage for 20 seconds, that
voltage is the dielectric strength (kV) of the entire sprayed
coating. The thus measured dielectric strength (kV) of the entire
sprayed coating is normalized as a voltage per the sprayed coating
thickness of 1 mm. The normalized value is the dielectric strength
(kV/mm).
EXAMPLE
[0026] Examples of the invention are given below by way of
illustration and not by way of limitation.
Examples 1-7
[0027] Sprayed coatings of 200 .mu.m thick were formed on aluminum
substrates of 100 mm.times.100 mm.times.5 mm by spraying powders of
oxides of atomic number 64 to 71 rare earth elements under spraying
conditions: a plasma power of 35 kW, an argon gas flow rate of 40
l/min, a hydrogen gas flow rate of 5 l/min, and a powder feed rate
of 20 g/min. Without sealing treatment, the sprayed coatings were
subjected to a dielectric strength test.
[0028] The dielectric strength test was performed according to JIS
C2110. While the voltage was increased at a rate of 200 V/sec, the
voltage at which dielectric breakdown occurred was first measured.
The voltage which was lower by 0.5 kV than the breakdown voltage
was then assumed to be a preset voltage. If no dielectric breakdown
occurred when the voltage was increased at a rate of 200 V/sec up
to the preset voltage and maintained at the preset voltage for 20
seconds, that voltage was the dielectric strength (kV) of the
entire sprayed coating. The thus measured dielectric strength (kV)
of the entire sprayed coating was divided by the thickness (200
.mu.m) of the sprayed coating, obtaining a dielectric strength
(kV/mm). The results are shown in Table 1.
Comparative Example 1
[0029] As in Example 1, Y.sub.2O.sub.3 powder having an average
particle size of 35 .mu.m was sprayed, and a dielectric strength
test performed.
Comparative Example 2
[0030] As in Example 1, Al.sub.2O.sub.3 powder having an average
particle size of 30 .mu.m was sprayed, and a dielectric strength
test performed.
[0031] The results are shown in Table 1.
1 TABLE 1 Dielectric Atomic Specific strength number Oxide gravity
(kV/mm) Example 1 64 Gd.sub.2O.sub.3 7.62 19 Example 2 65
Tb.sub.2O.sub.3 7.81 22 Example 3 66 Dy.sub.2O.sub.3 7.41 26
Example 4 67 Ho.sub.2O.sub.3 8.36 19 Example 5 68 Er.sub.2O.sub.3
8.65 26 Example 6 70 Yb.sub.2O.sub.3 9.17 28 Example 7 71
Lu.sub.2O.sub.3 9.84 25 Comparative Example 1 39 Y.sub.2O.sub.3
5.03 12 Comparative Example 2 13 Al.sub.2O.sub.3 3.99 10
[0032] There have been described spray coated members having a high
dielectric strength. They are useful as dielectric rolls, heating
substrates, electrostatic chucks and susceptors for semiconductor
manufacturing apparatus and the like.
[0033] Japanese Patent Application No. 2002-379389 is incorporated
herein by reference.
[0034] Reasonable modifications and variations are possible from
the foregoing disclosure without departing from either the spirit
or scope of the present invention as defined by the claims.
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