U.S. patent application number 09/407998 was filed with the patent office on 2002-04-11 for structural body and method of producing the same.
Invention is credited to KATO, NAOTAKA, NISHIOKA, MASAO.
Application Number | 20020041983 09/407998 |
Document ID | / |
Family ID | 17751872 |
Filed Date | 2002-04-11 |
United States Patent
Application |
20020041983 |
Kind Code |
A1 |
NISHIOKA, MASAO ; et
al. |
April 11, 2002 |
STRUCTURAL BODY AND METHOD OF PRODUCING THE SAME
Abstract
A structural body has an aluminum nitride sintered body, a
silicon carbide film formed on a surface of the sintered body, and
an intermediate layer generated between the sintered body and the
silicon carbide film. The intermediate layer is mainly made of a
silicon nitride. Preferably, the intermediate layer includes
smaller than 5 wt % of carbon and smaller than 5 wt % of aluminum,
and a thickness of the intermediate layer is greater than 0.2
.mu.m.
Inventors: |
NISHIOKA, MASAO; (TOKONAME,
JP) ; KATO, NAOTAKA; (OWARIASAHI, JP) |
Correspondence
Address: |
PARKHURST & WENDELL LLP
1421 PRINCESTREET SUITE 210
ALEXANDRIA
VA
223142805
|
Family ID: |
17751872 |
Appl. No.: |
09/407998 |
Filed: |
September 29, 1999 |
Current U.S.
Class: |
428/698 |
Current CPC
Class: |
C04B 41/89 20130101;
H01L 21/67103 20130101; Y10T 428/265 20150115; C04B 41/52 20130101;
C04B 41/009 20130101; C04B 41/52 20130101; C04B 41/4531 20130101;
C04B 41/4556 20130101; C04B 41/5066 20130101; C04B 41/52 20130101;
C04B 41/4531 20130101; C04B 41/5059 20130101; C04B 41/009 20130101;
C04B 35/581 20130101 |
Class at
Publication: |
428/698 |
International
Class: |
B32B 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 1998 |
JP |
10-290105 |
Claims
What is claimed is:
1. A structural body comprising an aluminum nitride sintered body,
a silicon carbide film formed on a surface of said aluminum nitride
sintered body, and an intermediate layer generated between said
aluminum nitride sintered body and said silicon carbide film, said
intermediate layer being mainly made of silicon nitride.
2. The structural body according to claim 1, wherein smaller than 5
wt % of carbon and smaller than 5 wt % of aluminum are included in
said intermediate layer.
3. The structural body according to claim 1, wherein a thickness of
said intermediate layer is greater than 0.2 .mu.m.
4. The structural body according to claim 1, wherein a purity of
said aluminum nitride sintered body is greater than 94%.
5. The structural body according to claim 1, wherein a resistance
heater is embedded in said aluminum nitride sintered body.
6. The structural body according to claim 1, further comprising a
power supply means for supplying a power to said silicon carbide
film, wherein said silicon carbide film functions as a resistance
heater when a power is supplied to said silicon carbide film.
7. A method of producing the structural body set forth in one of
claims 1-6, comprising the steps of, when a silicon carbide film is
formed to said aluminum nitride sintered body by means of a
chemical vapor deposition method; flowing hydrogen at a film
forming temperature; flowing a gas for a first silicon generation
compound including at least silicon, chlorine and hydrogen; and
flowing a gas for a second silicon generation compound and a carbon
generation compound.
8. The method according to claim 7, wherein said first silicon
generation compound is a silicon generation compound made of at
least one material selected from a group of SiCl.sub.4, SiHCl.sub.3
and SiH.sub.2Cl.sub.2.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a structural body and a
method of producing the same having an excellent heat cycle
resistivity.
[0003] 2. Description of Related Art
[0004] Generally, an electrostatic chuck is used for chucking a
semiconductor wafer and retaining it in the steps of film forming
such as transfer, exposure, thermal CVD (Chemical Vapor Deposition
method), plasma CVD, and sputtering of the semiconductor wafer,
fine working, washing, etching, dicing and so on. As a substrate of
the electrostatic chuck mentioned above, and as a substrate of the
heater, dense ceramics having a high density are used recently.
Especially in an apparatus for producing semiconductors, halogen
corrosive gasses such as ClF.sub.3 and so on are widely used as
etching gas and cleaning gas. Moreover, in order to heat and cool
the semiconductor wafer rapidly while it is retained, it is desired
that the substrate of the electrostatic chuck has a high heat
conductivity. Further, it is desired that the substrate of the
electrostatic chuck has a thermal shock resistivity so as to be
fractured due to a rapid temperature variation.
[0005] Dense aluminum nitride has a high corrosive resistivity with
respect to the halogen corrosive gas as mentioned above. Moreover,
the dense aluminum nitride is known as a material having a high
heat conductivity such as a volume resistivity of greater than
10.sup.8 ohm-cm. In addition, the dense aluminum nitride is known
as a substance having a high thermal shock resistivity. Therefore,
it is thought to be preferred that the substrate of the
electrostatic chuck or the heater used for producing semiconductors
is formed by an aluminum nitride sintered body.
[0006] As a member having corrosive resistivity exposed to a
corrosive gas in the apparatus for producing semiconductors
mentioned above, the inventors studied a corrosion resistive member
in which a silicon carbide film was formed on a surface of the
aluminum nitride substrate by means of chemical vapor deposition
method. When such a corrosion resistive member was subjected to a
heat cycle was applied to the corrosion resistive member. In this
case, it was found that cracks or abruptions were liable to be
generated according to an increase of heat cycle numbers. If cracks
were generated in the corrosion resistive member, AlN substrate was
eroded by the corrosive gas, so that the silicon carbide film was
peeled off.
SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a
structural body in which a silicon carbide film is formed on an
aluminum nitride sintered body, which does not generate cracks or
abruptions of the silicon carbide film when a heat cycle is applied
to the structural body.
[0008] According to the invention, a structural body comprises an
aluminum nitride sintered body, a silicon carbide film formed on a
surface of said aluminum nitride sintered body, and an intermediate
layer generated between said aluminum nitride sintered body and
said silicon carbide film, said intermediate layer being mainly
made of silicon nitride.
[0009] Moreover, according to the invention, a method of producing
the structural body mentioned above, comprises the steps of flowing
hydrogen at a film forming temperature; flowing a gas for a first
silicon generation compound including at least silicon, chlorine
and hydrogen; and flowing a gas for a second silicon generation
compound and a carbon generation compound; thereby forming said
silicon carbide film to said aluminum nitride sintered body by
means of a chemical vapor deposition method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a cross sectional view showing one embodiment of a
chemical vapor deposition apparatus for forming a silicon carbide
film;
[0011] FIG. 2 is a schematic view illustrating one embodiment of a
test apparatus for heat cycle test;
[0012] FIG. 3 depicts an analyzing result of especially carbon,
nitrogen, aluminum by using X-ray microanalyzer for a boundary
portion between an aluminum nitride sintered body and the silicon
carbide film;
[0013] FIG. 4 shows an analyzing result of especially silicon and
chlorine by using X-ray for the boundary portion between the
aluminum nitride sintered body and the silicon carbide film;
[0014] FIG. 5 is a photograph taken by a scanning electron
microscope showing a boundary of a structural body according to one
embodiment of the invention between the silicon carbide film and
the aluminum nitride sintered body;
[0015] FIG. 6 is a photograph taken by a scanning electron
microscope illustrating a boundary of a structural body according
to another embodiment of the invention between the silicon carbide
film and the aluminum nitride sintered body;
[0016] FIG. 7 is a photograph taken by a scanning electron
microscope depicting a boundary of a structural body according to a
comparative embodiment between the silicon carbide film and the
aluminum nitride sintered body;
[0017] FIG. 8 is a plan view showing one embodiment of a heater in
which the silicon carbide film is used as a resistance heating
element;
[0018] FIG. 9 is a perspective view illustrating the heater shown
in FIG. 8;
[0019] FIG. 10 is an enlarged cross sectional view of the heater
shown in FIG. 8;
[0020] FIG. 11a is a plan view depicting one embodiment of a
ceramic heater 31 according to one embodiment of the invention and
FIG. 11b is a schematic cross sectional view showing the heater
shown in FIG. 11a; and
[0021] FIGS. 12a, 12b and 12c are cross sectional views
respectively illustrating a net-like microstructure which can be
used in the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] The inventors performed a number of screenings in such a
manner that various chemical vapor deposition methods were
examined, and in such a manner that a microstructure and a heat
cycle test of a corrosion resistive member, in which a silicon
carbide film was formed on an aluminum nitride sintered body
actually, were also examined in detail. During this screening
operations, the inventors found that, if the silicon carbide film
was generated under a particular condition mentioned below, an
intermediate layer made of mainly silicon nitride was sometimes
generated on a boundary between the sintered body and the silicon
carbide film, and in this case, a heat cycle resistivity was
extraordinarily improved. The present invention was achieved by
these findings.
[0023] In this embodiment, it is necessary that a main ingredient
of the intermediate layer is silicon nitride, and it is preferred
that an amount of silicon nitride is greater than 90 wt %. In the
intermediate layer, aluminum originated from aluminum nitride
sintered body and carbon originated from silicon carbide may be
included. In this case, it is preferred that an amount of aluminum
is smaller than 5 wt % and an amount of carbon is smaller than 5 wt
%. Moreover, as mentioned below, in the case that use is made of a
chloride gas when the silicon carbide film is generated, chlorine
is included sometimes as impurities, but it is preferred that an
amount of chlorine is smaller than 1 wt %.
[0024] A reason that the silicon carbide film is not peeled off
from the sintered body due to a generation of the intermediate
layer is not clear, but it is estimated as follows.
[0025] That is to say, a thermal stress occurs due to a difference
of thermal expansion coefficient between the sintered body and the
silicon carbide film. Since a thermal expansion coefficient of the
silicon carbide film is smaller than that of the sintered body, a
compression stress is generated in the silicon carbide film and a
tensile stress is generated in the sintered body. If the silicon
carbide film is arranged on the sintered body only in a physical
manner without being connected, the silicon carbide film is peeled
off from the sintered body due to these stresses. However, if the
intermediate layer according to the invention is generated, the
intermediate layer has a chemical bonding force and thus it is
likely to be firmly connected to both of the sintered body and the
silicon carbide film.
[0026] In order to prevent an abruption of the silicon carbide
film, it is preferred to set a thickness of the intermediate layer
to larger than 0.2 .mu.m more preferably larger than 2 .mu.m.
Moreover, in upper limitation of a thickness of the intermediate
layer is not generally set. However, it is difficult to make a
thickness of the intermediate layer greater than a predetermined
value due to an actual producing process. From this view point, it
is preferred to set a thickness of the intermediate layer to
smaller than 20 .mu.m and more preferably to smaller than 10 .mu.m
from the view point of heat cycle resistivity.
[0027] A method of producing the intermediate layer is not limited,
but it is preferred to use the following methods. That is to say, a
method of producing the structural body, comprises the steps of,
when a silicon carbide film is formed to the aluminum nitride
sintered body by means of a chemical vapor deposition method;
flowing hydrogen at a film forming temperature; flowing a gas for a
first silicon generation compound including at least silicon,
chlorine and hydrogen; and flowing a gas for a second silicon
generation compound and a carbon generation compound. As the first
silicon generation compound, it is preferred to use at least one
compound selected from the group of SiCl.sub.4, SiHCl.sub.3, and
SiH.sub.2Cl.sub.2. As the second silicon generation compound, it is
preferred to use at least one compound selected from the group of
SiCl.sub.4, SiHCl.sub.3, SiH.sub.2Cl.sub.2 and SiH.sub.4. As the
carbon generation compound, it is especially preferred to use at
least one compound selected from the group of CH.sub.4,
C.sub.2H.sub.6 and C.sub.3H.sub.8. It is preferred that the first
silicon generation compound is the same as the second silicon
generation compound, but they may be different with each other.
[0028] As mentioned above, during the chemical vapor deposition
step, a gas for the first silicon generation compound including at
least hydrogen is introduced prior to a gas for the carbon
generation compound at a high temperature. Therefore, a silicon
chloride is acted with hydrogen and resolved to generate hydrogen
chloride. The thus generated hydrogen chloride gas functions to
corrode and activate a surface of the aluminum nitride. Here,
silicon atoms are bonded to generate silicon nitride, carbon
introduced after that become further reactable with silicon, and
the thus generated silicon carbide is likely to be firmly connected
to silicon nitride as a substrate. An introducing period of the
first silicon generation compound including chlorine such as
silicon tetrachloride i s determined suitably according to a film
generation temperature so as to generate the intermediate layer
having a desired thickness. It is preferred that the film
generation temperature is set to 1350-1500.degree. C. more
preferably 1400-1450.degree. C.
[0029] Heat cycle resistivity of the sintered body and the silicon
carbide film was further improved, by making a purity of aluminum
nitride of the aluminum sintered body to greater than 90% more
preferably greater than 94%. This is because affects of oxides in
the sintered body can be reduced. Moreover, a relative density of
the sintered body is preferably set to greater than 94% from the
view points of strength and heat conductivity.
[0030] As a corrosive substance, it is especially important to use
a reactive plasma gas used in the apparatus for producing
semiconductors. As such a reactive plasma gas, there are Cl.sub.2,
BCl.sub.3,ClF.sub.3, HCl, HBr and so on, and all of them have a
strong corrosive property. Among them, the structural body
according to the invention shows an extraordinarily high corrosion
resistivity with respect to chloride gas. Particularly, in a high
temperature region of 600-1000.degree. C., it is preferred to use
the structural body according to the invention as a corrosion
resistive member exposed especially to chloride gas.
[0031] The structural body according to the invention can be
applied to various kinds of products. As such a product, the
structural body according to the invention can be preferably
applied to an electromagnetic radiation transmission member. For
example, there are electromagnetic radiation transmission window,
high frequency electrode apparatus, tube for generating high
frequency plasma, dome for generating high frequency plasma.
Moreover, the structural body according to the invention can be
applied to a suscepter for setting a semiconductor wafer. Ads such
a suscepter, there are ceramic electrostatic chuck, ceramics
heater, high frequency electrode apparatus. Further, the structural
body according to the invention can be used for a substrate of the
semiconductor producing apparatus such as shower plate, lift pin
used for supporting semiconductor wafer, shadow ring, and dummy
wafer.
[0032] In the case that the structural body according to the
invention is applied to the member which is set in plasma, there is
an advantage such that a charge-up level of a surface of the
structural body in plasma can be reduced by means of the silicon
carbide film. Especially in the case that the structural body
according to the invention is applied to the suscepter set in
plasma, it is possible to reduce charge generation on a surface of
the suscepter since the surface of the suscepter is covered with
the silicon carbide film having a semi-conductive property.
[0033] Moreover, in another embodiment of the present invention,
the structural body according to the invention can be applied to
the electrostatic chuck.
[0034] Generally, the electrostatic chuck was produced by embedding
a metal electrode in the substrate made of an aluminum nitride
sintered body. In the method mentioned above, it is difficult to
maintain a spacing between the electrode and a chucking surface of
the sintered body at a constant level, and thus there is a drawback
such that an electrostatic chucking force is liable to be varied in
the chucking surface. Moreover, since it is necessary to protect
the metal electrode from corrosive atmospheres, it is necessary to
increase a total thickness of the substrate. Therefore, there is a
tendency such that a heat capacity of the electrostatic chuck
becomes larger. If the heat capacity becomes larger, it takes an
additional time for heating and cooling operations.
[0035] Contrary to this, the electrostatic chuck can be obtained by
forming the silicon carbide film on one surface of aluminum nitride
sintered body according to the invention, wherein the silicon
carbide film is used as the electrostatic chuck electrode and the
sintered body is used as a dielectric layer. In this case, it is
easy to maintain a thickness of the sintered body at a constant
level by means of a mechanical working, a chucking force is not
varied in the chucking surface. Moreover, the silicon carbide film
has a high durability with respect to corrosive atmospheres and is
easy to make a thickness of the sintered body thinner as compared
with the metal electrode. In addition, if the sintered body is made
thinner, the silicon carbide film has no problem as compared with
the metal embedded electrode. Therefore, it is possible to make a
total heat capacity of the electrostatic chuck smaller.
[0036] Hereinafter, experimental results will be shown in
detail.
Experiment 1
[0037] A silicon carbide film was formed on an aluminum nitride
sintered body by using a chemical vapor deposition (CVD) apparatus
shown schematically in FIG. 1. A substrate 1 was set in a furnace.
The substrate 1 was supported by a supporting member 5. In this
apparatus, a raw material supply tube 8 having a front shape of
character T was set. The raw material supply tube 8 comprises a
base portion 8b and a blowing portion 8a extended breadthwise. A
predetermined number of gas discharge outlets 9 were arranged at a
surface 8c opposed to a substrate of the blowing portion 8a. A
numeral 6 was an inner cylindrical member and a numeral 7 was an
external heater.
[0038] A spacing between the surface 8c of the raw material supply
tube 8 and the substrate 1 was set to 100 mm-300 mm. A gas was fed
from the gas discharge outlets 9 while the raw material supply tube
8 was rotated. A raw material gas for CVD was fed from the gas
discharge outlets 9, flowed in a space 10, encountered to a surface
of the substrate 1, flowed along a surface of the substrate 1, and
was fed through gas discharge holes 3 formed in the supporting
member 5.
[0039] Since use was made of the raw material supply tube 8 having
the shape mentioned above and a gas was discharged while the raw
material supply tube 8 was rotated, a thickness of the silicon
carbide film which covered overall surface of the substrate 1 could
be maintained at a constant level.
[0040] In this apparatus, at a film generation temperature,
hydrogen was flowed in the furnace, silicon tetrachloride was
supplied after that and then silicon tetrachloride and methane were
supplied in addition. After the CVD process, the silicon carbide
film was subjected to a grinding operation, so that a product
having a predetermined could be obtained.
[0041] A structural body was produced according to the method
mentioned above by using the apparatus shown in FIG. 1. As the
substrate 1, use was made of a discoid aluminum nitride sintered
body having a diameter of 250 mm and a thickness of 20 mm. A purity
of aluminum nitride in the sintered body was 99.5% and a remainder
was made of yttria. Respective raw material gases was introduced
according to respective conditions shown in Table 1, so as to form
a silicon carbide film. A pressure during a film formation was 120
Torr. A thickness of the silicon carbide film was 100 .mu.m at a
center portion of the film. In a comparative example 1, argon was
only flowed in the furnace during a temperature ascending operation
up to 1425.degree. C., and hydrogen, silicon tetrachloride, methane
were flowed at 1425.degree. C. In examples 1, 2, 3 according to the
invention, argon was only flowed in the furnace during a
temperature ascending operation up to respective film forming
temperatures, hydrogen was only flowed for 10 minutes at respective
film forming temperatures after that, then hydrogen and silicon
tetrachloride were flowed for 1 minute, and then methane was flowed
in addition.
[0042] With respect to respective structural bodies thus prepared,
a heat cycle test at a temperature range between room temperature
and 900.degree. C. was performed. In this case, use was made of a
heat cycle test apparatus shown schematically in FIG. 2. Sample
pieces each having a rectangular shape of 4 mm.times.3 mm.times.50
mm were cut out from respective structural bodies. In this case,
the silicon carbide film was arranged on a plane defined by 4
mm.times.50 mm. The thus prepared sample piece 14 was supported by
a chuck member 15 made of Inconel in a space 19 maintained at room
temperature. A portion between a resistance heating furnace 11 and
a cylinder 17 was covered with a closed vessel 16, and an argon gas
under atmosphere pressure was flowed in the closed vessel 16. An
outer wall of the resistance heating furnace 11 was covered with a
metal plate in a highly hermetic manner.
[0043] The sample piece 14 was inserted into a furnace inner space
13 of the resistance heating furnace 11 by driving the air pressure
cylinder 17. A numeral 12 was a resistance heater. A temperature of
the furnace inner space 13 was maintained at 900.degree. C. The
sample piece 14 was maintained for 1 minute in the furnace inner
space 13, and then it was pulled out from the furnace inner space
13 by driving the air pressure cylinder 17. An argon gas was blown
from a nozzle 18 having a diameter of 2 mm at a rate of 2
litter/minute and the sample piece 14 was cooled down for 1 minute.
A temperature of the sample piece 14 when it was completely pulled
out from the furnace inner space 13 was lower than 30.degree. C. An
argon gas blown from the nozzle 18 was discharged into an
atmosphere through a check valve arranged to the closed vessel 16.
By using the test apparatus as mentioned above, a heat cycle
resistive property of the sample piece was examined while an
oxidation of the aluminum nitride in an argon atmosphere was
prevented. These results are shown in Table 1.
1 TABLE 1 raw material gas introducing method unit: liter/minute
temperature predetermined results of heat cycle test ascending time
10 min. 1 min. time 10 100 1000 10000 5000 comparative Ar 7.5 7.5
0/5 -- -- -- -- example 1 H.sub.2 17.5 film forming SiCl.sub.4 5.2
temperature CH.sub.4 4 1425.degree. C. example 1 Ar 7.5 7.5 7.5 7.5
5/5 5/5 5/5 5/5 5/5 film forming H.sub.2 17.5 17.5 17.5 temperature
SiCl.sub.4 5.2 5.2 1425.degree. C. CH.sub.4 4 example 2 Ar 7.5 7.5
7.5 7.5 5/5 5/5 5/5 3/5 0/5 film forming H.sub.2 17.5 17.5 17.5
temperature SiCl.sub.4 5.2 5.2 1400.degree. C. CH.sub.4 4 example 3
Ar 7.5 7.5 7.5 7.5 5/5 5/5 5/5 5/5 5/5 film forming H.sub.2 17.5
17.5 17.5 temperature SiCl.sub.4 5.2 5.2 1450.degree. C. CH.sub.4
4
[0044] In the comparative example 1, all the five sample pieces
show a result such that the film was peeled off from the substrate
by at best 10 heat cycles. In the examples 1 and 3, there was no
abruption of the film even after 50000 heat cycles. In the example
2, three sample pieces among five sample pieces show no abruption
of the film after 10000 heat cycles.
[0045] From the sample piece of the example 1, specimens for
microscope observation were cut out, and the thus cut out specimens
were further cut out at an angle of 20.degree. with respect to a
boundary between aluminum nitride and silicon carbide. Then, the
20.degree. cut out surface of the specimen was ground and the thus
ground cut out surface was observed by scanning electron
microscope. The result is shown in FIG. 5. In FIG. 5, a lower side
was the sintered body and an upper side was the silicon carbide
film. Moreover, the intermediate layer having a thickness of about
7 .mu.m was observed between the sintered body and the silicon
carbide film. The intermediate layer was analyzed by using EPMA
(X-ray micro-analyzer). The results are shown in FIGS. 3 and 4. A
composition of the intermediate layer was 60 wt % of silicon, 35 wt
% of nitrogen, 1 wt % of carbon, 2 wt % of aluminum and 0.04 wt %
of chlorine. Moreover, the intermediate layer was measured by using
micro-focus X-ray. As a result, it was confirmed that there was a
silicon nitride crystal corresponding to JCPDS card No. 33-1160 in
the intermediate layer.
[0046] FIG. 6 shows an observation result of the specimen according
to the example 2. The intermediate layer having a thickness of 0.2
.mu.m was generated. Moreover, FIG. 7 shows an observation result
of the specimen according to the comparative example 1. No
intermediate layer was generated, and the silicon carbide film was
peeled off from the aluminum nitride sintered body.
Experiment 2
[0047] As is the same as the experiment 1, respective specimens
shown in Table 2 were prepared, and the heat cycle test was
performed with respect to the thus prepared specimens. In this
experiment 2, use was made of propane instead of methane used in
the experiment 1. Microstructures of the specimen according to the
comparative example 2 was same as those of the specimen according
to the comparative example 1, and microstructures of the specimens
according to the examples 4, 5, 6 were same as those of the
specimens according to the examples 1, 2, 3. In this experiment 2,
a thickness of the intermediate layer of the example 4 was 8 .mu.m,
that of the example 5 was 2 .mu.m and that of the example 6 was 12
.mu.m. Moreover, a composition of the intermediate layer of the
example 4 was silicon nitride as a main ingredient, 3 wt % of
aluminum and 4 wt % of carbon, that of the example 5 was silicon
nitride as a main ingredient, 4 wt % of aluminum and 3 wt % of
carbon, and that of the example 6 was silicon nitride as a main
ingredient, 2 wt % of aluminum and 2 wt % of carbon.
2 TABLE 2 raw material gas introducing method unit: liter/minute
temperature predetermined results of heat cycle test ascending time
10 min. 1 min. time 10 100 1000 10000 5000 comparative Ar 7.5 7.5
0/5 -- -- -- -- example 2 H.sub.2 17.5 film forming SiCl.sub.4 5.2
temperature C.sub.3H.sub.8 1.3 1425.degree. C. example 4 Ar 7.5 7.5
7.5 7.5 5/5 5/5 5/5 5/5 5/5 film forming H.sub.2 17.5 17.5 17.5
temperature SiCl.sub.4 5.2 5.2 1425.degree. C. C.sub.3H.sub.8 1.3
example 5 Ar 7.5 7.5 7.5 7.5 5/5 5/5 2/5 1/5 0/5 film forming
H.sub.2 17.5 17.5 17.5 temperature SiCl.sub.4 5.2 5.2 1400.degree.
C. C.sub.3H.sub.8 1.3 example 6 Ar 7.5 7.5 7.5 7.5 5/5 5/5 5/5 5/5
5/5 film forming H.sub.2 17.5 17.5 17.5 temperature SiCl.sub.4 5.2
5.2 1450.degree. C. C.sub.3H.sub.8 1.3
Experiment 3
[0048] As is the same as the experiment 1, respective specimens
shown in Table 3 were prepared, and the heat cycle test was
performed with respect to the thus prepared specimens. In this
experiment 3, use was made of silane trichloride instead of silicon
tetrachloride used in the experiment 1. Microstructures of the
specimen according to the comparative example 3 was same as those
of the specimen according to the comparative example 1, and
microstructures of the specimens according to the examples 7, 8, 9
were same as those of the specimens according to the examples 1, 2,
3. In this experiment 3, a thickness of the intermediate layer of
the example 7 was 7 .mu.m, that of the example 8 was 1 .mu.m and
that of the example 9 was 10 .mu.m. Moreover, a composition of the
intermediate layer of the example 7 was silicon nitride as a main
ingredient, 2 wt % of aluminum and 3 wt % of carbon, that of the
example 8 was silicon nitride as a main ingredient, 1.5 wt % of
aluminum and 3 wt % of carbon, and that of the example 9 was
silicon nitride as a main ingredient, 2 wt % of aluminum and 2 wt %
of carbon.
3 TABLE 3 raw material gas introducing method unit: liter/minute
temperature predetermined results of heat cycle test ascending time
10 min. 1 min. time 10 100 1000 10000 5000 comparative Ar 7.5 7.5
0/5 -- -- -- -- example 3 H.sub.2 17.5 film forming SiHCl.sub.3 5.2
temperature CH.sub.4 4 1425.degree. C. example 7 Ar 7.5 7.5 7.5 7.5
5/5 5/5 5/5 5/5 5/5 film forming H.sub.2 17.5 17.5 17.5 temperature
SiHCl.sub.3 5.2 5.2 1425.degree. C. C.sub.4 4 example 8 Ar 7.5 7.5
7.5 7.5 5/5 5/5 3/5 2/5 0/5 film forming H.sub.2 17.5 17.5 17.5
temperature SiHCl.sub.3 5.2 5.2 1400.degree. C. C.sub.4 4 example 9
Ar 7.5 7.5 7.5 7.5 5/5 5/5 5/5 5/5 5/5 film forming H.sub.2 17.5
17.5 17.5 temperature SiHCl.sub.3 5.2 5.2 1450.degree. C. C.sub.4
4
Experiment 4
[0049] As is the same as the experiment 1, respective specimens
were prepared, and the heat cycle test was performed with respect
to the thus prepared specimens. In this experiment 4, film forming
temperature, precedent introducing time of silicon tetrachloride
and precedent introducing flow amount of silicon tetrachloride were
varied as shown in Table 4. These results are shown in Table 4.
4TABLE 4 SiCl.sub.4 SiCl.sub.4 precedent thickness heat film
precedent introducing of cycle forming introducing flow
intermediate resistive temperature time amount layer number
(.degree. C.) (minute) (litter/minute) (.mu.m) (number) 1400 0 0 0
100 1350 3 5.2 0.5 1000 1375 3 5.2 0.2 1000 1400 1 5.2 0.2 1000
1400 3 5.2 2 10000 1425 1 5.2 7 50000 1425 3 5.2 10 50000 1450 1
5.2 12 50000 1450 3 5.2 12 50000 1500 1 5.2 4 50000 1500 1 5.2 2
50000
[0050] In this experiment 4, compositions of the intermediate
layers according to respective specimens shown in Table 3 were
silicon nitride as a main ingredient, 1-3 wt % of aluminum, 1-3 wt
% of carbon and 0.02-0.3 wt % of chlorine. From these results, it
was confirmed that a thickness of the intermediate layer was
preferable if it was greater than 0.2 .mu.m, more preferable if it
was greater than 2 .mu.m and further more preferable if it was
greater than 4 .mu.m.
Experiment 5
[0051] In the experiment 5, a purity of aluminum nitride in the
sintered body was varied as shown in Table 5. Compositions other
than aluminum nitride in the sintered body were sintering agents
mainly composed of yttrium, ytterbium, oxygen, magnesium, carbon
and so on and inevitable impurities. As can be understood from the
results shown in Table 5, a purity of aluminum nitride was
preferable if it was greater than 90% and more preferable if it was
greater than 94%.
5 TABLE 5 purity of aluminum heat cycle resistive nitride (%)
number (number) 85 90 10000 94 50000 99 50000 99.5 50000
Experiment 6
[0052] As is the same as the experiment 1, specimens were prepared.
In this experiment 6, use was made of a discoid substrate having a
thickness of 2 mm and a diameter of 200 mm, which was made of the
aluminum nitride sintered body having a purity of 99.5%. On the
substrate mentioned above, the silicon carbide film having a
thickness of 50 .mu.m was formed according to the condition of the
example 1 in the experiment 1. A thickness of the intermediate
layer was 8 .mu.m. Compositions other than silicon nitride in the
intermediate layer were 2 wt % of aluminum, 1 wt % of carbon and
0.05 wt % of chlorine.
[0053] The thus prepared specimen was exposed in chlorine plasma at
825.degree. C. In this case, a flow amount of chlorine gas was
300SCCM, a pressure was 0.1 Torr, an alternate current power was
800 watt and an exposed time was 2 hours. As a result, the silicon
carbon film was not corroded at all.
[0054] Hereinafter, the embodiment, in which the structural body
according to the invention is applied to the heater especially to
the heater to which corrosive gas is exposed, will be
explained.
[0055] At first, the heater, in which the silicon carbide film
itself is used as a resistance heating element, will be
explained.
[0056] In the case that a metal resistance heating element is
embedded in a substrate made of an aluminum nitride sintered body,
it is necessary to arrange portions of the resistance heating
element with a spacing so as to prevent a contact between these
portions in the substrate. Therefore, when the heater is viewed
from a heating surface side, a temperature of the heating surface
positioned just on the resistance heating element becomes high, but
a temperature of the heating surface positioned on a portion in
which the resistance heating element is not embedded becomes low,
so that a temperature variation on the heating surface is
generated. Moreover, since a heat capacity of the heater becomes
larger, it is difficult to perform abrupt heating and cooling
operations, and thus a precise temperature control cannot be
performed. However, in the case that the resistance heating element
is formed by patterning the silicon carbide film, since there is no
limitations as that of the heater in which the metal resistance
heating element is embedded in the sintered body, it is possible to
eliminate the temperature variation on the heating surface
mentioned above by making a spacing of the pattern of the silicon
carbide film sufficiently smaller. Moreover, in this case, it is
possible to perform the abrupt heating and cooling operations.
[0057] Further, in the case that a pattern made of a metal film is
formed on a surface of the sintered body and the pattern generates
heat, there is a case such that the metal film is gradually peeled
off due to a difference of thermal expansion coefficient between
the metal film and the sintered body when a heat cycle is applied,
or, such that a resistance value is varied partially due to an
oxidation of the metal film. However, if the silicon carbide film
pattern according to the invention is used as the resistance
heating element, the resistance heating element is not varied on a
surface of the substance even after applying a long term heat
cycle.
[0058] The inventors produced a heater having a shape as shown in
FIGS. 8-10. FIG. 8 is a plan view of a heater 21, FIG. 9 is a
perspective view of the heater 21 and FIG. 10 is a partially cross
sectional view of the heater 21.
[0059] A plate-like substrate 22 having a dimension of 300
mm.times.300 mm.times.3 mm and made of an aluminum nitride sintered
body having a purity of 99.5% was prepared. A silicon carbide film
having a thickness of about 100 .mu.m was formed on one surface of
the substrate 22 according to the method shown in the experiment 1.
An intermediate layer having a thickness of 7 .mu.m was generated
at a boundary between the silicon carbide film and the substrate. A
main ingredient of the intermediate layer was silicon nitride, and,
2 wt % of aluminum, 1 wt % of carbon, 0.05 wt % of chlorine were
included therein.
[0060] As shown by the planar pattern illustrated in FIGS. 8 and 9,
recesses 24 each having a depth of about 200 .mu.m and a width of 1
mm were formed by using a diamond cutter and a resistance heating
clement pattern 23 was formed. The pattern 23 comprised linear
portions 23c and connection portions 23d for connecting ends of
respective linear portions 23c. A width of the linear portion 23c
was 1 mm. Aluminum nitride was exposed at a bottom of the recess
24. Platinum wires 26 were connected to both ends 23a and 23b of
the pattern 23 respectively and a power was supplied to the
resistance heating element pattern 23 through the platinum wires 26
so as to generate heat. After a power supply was started, a
temperature of a surface of the substrate 22 to which no pattern 23
was formed was measured by using a radiation. As a result, a
temperature difference in a region positioned within 8 mm from
respective corner portions of the substrate was within 0.4.degree.
C., and a temperature was increased uniformly in this region. In
addition, since a resolution of the radiation thermometer was 0.5
mm, a substantial temperature distribution was not detected on the
heater surface.
[0061] Then, the thus prepared heater was subjected to a heat cycle
test in argon atmosphere including 5% of hydrogen. One heat cycle
was as follows: a temperature of the heater was ascended to
500.degree. C. for 0.5 hour, maintained at 500.degree. C. for 0.1
hour and descended to room temperature for 0.5 hour. After 100 heat
cycles, a temperature distribution was measured on the heater
surface by using the radiation thermometer. As a result, an average
temperature difference was within .+-.0.2.degree. C. and a
temperature distribution was within .+-.0.4.degree. C., as compared
with the heater before the heat cycle test.
[0062] In an apparatus for producing semiconductors, a heater in
which a metal resistance heating element was embedded in an
aluminum nitride sintered body was known. However, a heater was not
known which was used preferably under a condition such that a heat
cycle between room temperature and a high temperature region such
as 600-1100.degree. C. was applied and it was exposed in a
corrosive gas especially chlorine corrosive gas. Such a heater was
strongly required.
[0063] According to the invention, a heater which solved all the
disadvantages mentioned above could be achieved by embedding a
resistance heating element in an aluminum nitride sintered body,
covering overall surface of the sintered body, and forming an
intermediate layer at a boundary between the sintered body and the
silicon carbon film.
[0064] That is to say, the silicon carbide film formed by a
chemical vapor deposition method has an extraordinarily high
corrosion resistivity with respect to a chlorine corrosive gas in a
high temperature region especially in a high temperature region of
600-1100.degree. C. In addition, since the silicon carbide film is
integrated with the aluminum nitride sintered body, in which a
resistance heating element is embedded, through the intermediate
layer, the structural body having a strong heat cycle resistivity
can be achieved. This reason is assumed as follows.
[0065] That is to say, in the case that the structural body
according to the invention is used as a suscepter and a heat from
an external heat source (for example infrared lamp) is applied to
the suscepter, a heat from the external heat source is first
introduced to the silicon carbide film by means of a heat
radiation, and then conducted to the aluminum nitride sintered body
through the intermediate layer. In this case, all the silicon
carbide film is heated rapidly at first and a temperature is
extraordinarily increased. Since a thermal expansion coefficient of
the silicon carbide film is greater than that of the aluminum
nitride sintered body, if both of the silicon carbide film and the
aluminum nitride sintered body are heated, the silicon carbide film
is expanded largely as compared with the aluminum nitride sintered
body and thus a compression stress is applied to the silicon
carbide film. In addition, since a temperature of the silicon
carbide film is first increased rapidly due to a heat radiation for
the silicon carbide film, an excess compression stress is liable to
be applied to the silicon carbide film. Therefore, even if taking
into consideration of a buffer function of the intermediate layer
according to the invention, an abruptions of the film is liable to
be generated after the heat cycle is applied.
[0066] On the other hand, in this case that the silicon carbide
film is integrated through the intermediate layer, with the
aluminum nitride sintered body, in which the resistance heating
element is embedded, a heat from the resistance heating element is
conducted through the sintered body by means of a heat conduction
and reaches to the silicon carbide film through the intermediate
layer. In this case, since a heat capacity of the sintered body is
greater than that of the silicon carbide film and the silicon
carbide film is thin, when a heat is conducted from the sintered
body to the silicon carbide film through the intermediate layer
during a temperature ascending step, a temperature difference
between the silicon carbide film and an outermost region of the
sintered body is small, and a temperature of the silicon carbide
film is lower than that of the sintered body. In addition, since a
thermal expansion coefficient of the sintered body is smaller than
that of the silicon carbide film, a difference on a thermal
expansion between the sintered body and the silicon carbide layer
becomes smaller and smaller. Therefore, a stress applied near the
boundary between an outermost region of the sintered body and the
silicon carbide film during a heating step can be largely relieved
and further it is dispersed by the intermediate layer.
[0067] As the resistance heating element which is embedded in the
aluminum nitride sintered body, metal wire having a coil spring
shape, metal foil and metal plate are preferably used, and they are
known in a heater filed.
[0068] In this embodiment, it is preferred to use a heater in which
the resistance heating element is embedded in the aluminum nitride
sintered body, at least a part of the resistance heating element is
made of a conductive net-like member and an aluminum nitride is
filled in a net of the net-like member. The heater having the
construction mentioned above shows an extraordinary durability with
respect to a heat cycle especially between a high temperature
region on a low temperature region such as a room temperature
region.
[0069] Materials of the net-like member are not limited, but it is
preferred to use a metal having a high melting point when a
temperature becomes greater than 600.degree. C. during use. As the
metal having a high melting point, use is made of tungsten,
molybdenum, platinum, rhenium, hafnium and an alloy thereof.
[0070] As a configuration of the net-like member, it is preferred
to use the net-like member formed by fibers or wires. In this case,
if a cross section of the fiber or the wire is circular, it is
possible to reduce a stress concentration due to thermal
expansion.
[0071] In a preferred embodiment, the net-like member should be cut
into a slender string like a picture drawn with a single stroke of
the brush. In this case, since a current is flowed toward a
longitudinal direction of the net-like member formed by the slender
strips, an unevenness of temperature distribution due to a current
concentration is not liable to be generated as compared with the
circular net-like member.
[0072] FIG. 11a is a plan view showing a ceramics heater 31
according to another embodiment of the invention and FIG. 11b is a
cross sectional view cut along Xb-Xb line in FIG. 11a. In the
ceramics heater 31, a net-like member 34 is embedded in a substrate
32 having for example discoid shape.
[0073] At a center portion of the substrate 32, a terminal 33A
which continues to a rear surface 32b is embedded, and at a
peripheral portion of the substrate 32, a terminal 33B which
continues to the rear surface 32b is embedded. The terminal 33A and
the terminal 33B are connected through the net-like member 34. A
numeral 32a is a heating surface. The substrate 32 comprises an
aluminum nitride sintered body 36 having a discoid shape and a
silicon carbide film 35 which covers a surface of the sintered body
36.
[0074] The net-like member 34 is formed by a net having a
configuration shown in for example FIGS. 12a-12c. It should be
noted that a fine net configuration of the net-like member 34 is
not shown in FIGS. 11a and 11b due to a size limitation. The
net-like member 34 has a convoluted shape in a major plane between
the terminals 33A and 33B. The terminals 33A and 33B are connected
to a power supply cable not shown.
[0075] FIGS. 12a-12c are cross sectional views respectively showing
one embodiment of the net-like member. In a net-like member 46
shown in FIG. 12a, longitudinal wires 46b and transversal wires 46a
are knitted in a three-dimensional manner, and both of the
longitudinal wires and the transversal wires waves. In a net-like
member 47 shown in FIG. 12b, transversal wires 47a are straight and
longitudinal wires 47b are bent. In a net-like member 48 shown in
FIG. 12c, longitudinal wires 48b and transversal wires 48a are
knitted in a three-dimensional manner, and both of the longitudinal
wires and the transversal wires waves. Moreover, the net-like
member 48 is worked by a rolling mill, and thus outer surfaces of
the longitudinal wires and transversal wires are aligned along
one-dotted chain lines A and B.
[0076] Hereinafter, an experiment result of the heater in which the
resistance heating element is embedded in the sintered body will be
explained.
[0077] Aluminum nitride powders obtained by a reduction nitriding
method were used as raw material powders. In aluminum nitride
powders, contents of Si, Fe, Ca, Mg, K, Na, Cr, Mn, Ni, Cu, Zn, W,
B, Y were respectively smaller than 100 ppm, and the other metal
components except for aluminum were not detected. A preliminarily
formed body having a discoid shape was produced by forming the raw
material powders by applying one directional stress thereto. A
resistance heating element made of molybdenum having a coil spring
shape was embedded in the preliminarily formed body. The
preliminarily formed body was sintered by a hot press method under
a pressure of 200 kgf/cm.sup.2 at 1900.degree. C. to obtain an
aluminum nitride sintered body. The sintered body had a diameter of
250 mm and a thickness of 20 mm.
[0078] A silicon carbide film having a thickens of 50 .mu.m was
formed on a surface of the sintered body according to the condition
of the example 1 in the experiment 1. A thickness of the
intermediate layer was 7 .mu.m. A chemical composition other than
silicon nitride in the intermediate layer was 2 wt % of aluminum, 1
wt % of carbon and 0.04 wt % of chlorine. A silicon wafer was set
on the heater according to this embodiment. As a comparative
example {circle over (1)}, a heater {circle over (1)}, in which no
silicon carbide film was formed in the sintered body, was produced.
As a comparative example {circle over (2)}, a heater {circle over
(2)}, in which the silicon carbide film having a thickness of 50
.mu.m was formed according to the condition of the comparative
example 1 in the experiment 1, was produced.
[0079] Respective heaters were exposed in a chlorine plasma. In
this case, a flow amount of a chlorine gas was 300SCCM, a pressure
was 0.1 Torr, an alternating current power was 800 W, and an
exposing time was 2 hours. A power was supplied to the resistance
heating element of the heater and a temperature of the silicon
wafer was maintained at 800.degree. C. As a results, the silicon
carbide film was not corroded at all in the example according to
the invention {circle over (1)}. However, the substrate was
corroded heavily in the comparative example. Moreover, a
contamination level of Al with respect to the silicon wafer was as
follows. In the heater according to the comparative example {circle
over (1)}, a contamination level was 10.sup.15 atm/cm.sup.2. On the
other hand, in the heater according to the invention, a
contamination level was 10.sup.10 atm/cm.sup.2. Since the
contamination level of 10.sup.10 atm/cm.sup.2 was the same as that
of the silicon wafer before processing, a plasma heating process
could be performed under a condition of substantially no silicon
wafer contamination in the heater according to the invention.
[0080] Further, since the silicon carbide film has a conductive
property, it was possible to prevent a particle adhesion due to an
electrostatic potential which was a problem in the aluminum nitride
sintered body having an insulation property. Especially, it was
possible to prevent a generation of electrostatic potential
completely by connecting the silicon carbide film to the
ground.
[0081] With respect to the heater according to the invention and
the heater according to the comparative example {circle over (2)},
the heat cycle test was performed as is the same as the experiment
1. As a result, in the heater according to the invention, the
silicon carbide film was not peeled off even after 10000 heat
cycles. However, in the heater according to the comparative example
{circle over (2)}, the silicon carbide film was peeled off after 20
heat cycles.
[0082] As is clearly understood from the above explanations,
according to the invention, in the structural body in which the
silicon carbide film is formed on a surface of the aluminum nitride
sintered body, the silicon carbide film is firmly connected to the
sintered body, it is possible to prevent abruption of the silicon
carbide film when the heat cycle is applied to the structural
body.
* * * * *