JPH1059770A - Silicon carbide polycrystal material and corrosion resistant member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon carbide polycrystal material suitable for such use to be exposed to a highly corrosive material so that contamination due to a corrosive material such as particles produced from a polycrystal material and due to divergence of metal impurities caused by corrosion can be prevented. SOLUTION: This silicon carbide polycrystal material shows >=50% non- decomposition rate when the crystal is heated in a mixture acid of conc. hydrofluoric acid, conc. nitric acid and conc. sulfuric acid at 250 deg.C for 50 hours in a sealed container. It is preferable that the polycrystal material consists of aggregation of hexagonal particles having >=10μm average particle size and essentially comprising 3C crystalline phase. The material has the density between >=3.15g/cc and 33.21 g/cc and contains metal impurities by <=10ppm. The half- width of the highest peak in the X-ray diffraction chart of the polycrystal material is between >=0.20 deg. and <=0.30 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polycrystalline silicon carbide having high corrosion resistance and a method for producing the same.

[0002]

2. Description of the Related Art At present, it is known that a dense silicon carbide film is effective as a surface oxidation-resistant film of a ceramic member used in a high-temperature atmosphere such as a liner of a gas turbine component or a diesel engine component. I have. In some other applications, it is known that the surface of a ceramic member is covered with a dense silicon carbide thin film or silicon nitride thin film. As a method for forming such a ceramic thin film, a chemical vapor deposition method, an electrochemical vapor deposition method, a sputtering method, a thermal spraying method and the like are known. Among them, the so-called vapor phase method can be used to form a dense and high-quality thin film, and is currently widely used. Further, as a method for producing a silicon carbide polycrystal having a form other than a coating film, there are a sintering method and a reaction sintering method in which Si is injected into a SiC-C-based formed body.

[0003]

In recent years, the demand for corrosion resistance of such polycrystalline silicon carbide has become more severe. In particular, in recent years, it has been studied to form various members to be installed in a semiconductor manufacturing apparatus using nitride ceramics such as aluminum nitride and silicon nitride, and silicon carbide. However, in such applications, various members are exposed to an etching gas and a cleaning gas composed of a halogen-based corrosive gas.

The present inventor has attempted to form such a member by a sintered body of silicon carbide powder. However, the sintering aid usually remains in the silicon carbide sintered body, and the high-purity silicon carbide powder usually contains about 0.1% of metal impurities. Remains in the sintered body even after sintering. Then, it has been found that when a silicon carbide sintered body is actually placed and exposed in a halogen-based corrosive gas, such impurities and particles may scatter in the atmosphere and contaminate the semiconductor. Further, a reaction sintering method of heating while injecting Si into the SiC molded body was also examined, but there was a similar problem.

The present inventor has manufactured a sintered body obtained by a so-called recrystallization method. However, there is a possibility that the semiconductor may be contaminated by the influence of impurities in the sintered body or particles due to surface corrosion. was there. In particular, there has been a demand for preventing the generation of extremely small amounts of impurities and particles, which has not been a problem in the past, due to the recent progress in increasing the density of semiconductor patterns.

[0006] It is an object of the present invention to provide a silicon carbide polycrystal suitable for applications exposed to highly corrosive substances, and to provide corrosive substances such as particles generated from the silicon carbide polycrystal. Another object of the present invention is to prevent contamination due to divergence of metal impurities accompanying this.

[0007]

The polycrystalline silicon carbide according to the present invention is heated and heated in a closed vessel at 250 ° C. for 50 hours in a mixed acid consisting of concentrated hydrofluoric acid, concentrated nitric acid and concentrated sulfuric acid. The undecomposed ratio after pressing is 50% or more.

Further, the corrosion-resistant member of the present invention is a corrosion-resistant member exposed to a corrosive substance, wherein at least a surface portion in contact with the corrosive substance is made of the silicon carbide polycrystal. Features.

The inventor of the present invention has exposed silicon carbide polycrystals of various properties to highly corrosive substances and investigated contamination caused by emission of particles and impurity metal elements. The present inventors have found that it is effective to use a specific silicon carbide polycrystal described later, and have reached the present invention.

That is, conventionally, the corrosion resistance of polycrystalline silicon carbide to acids and alkalis has been investigated in various ways, and it has been used as a corrosion-resistant coating. However, members exposed to a high-temperature halogen-based corrosive gas or its plasma have a particularly high degree of corrosion, and even when the surface of the member is slightly corroded, the member is contained inside the silicon carbide polycrystal. The adverse effects of trace metal impurities easily occur. For this reason, the conventional corrosion resistance test method cannot be adopted,
In particular, it is practically impossible to select a silicon carbide polycrystal that eliminates the possibility of semiconductor contamination, so that a member that can be used effectively for a long period of time as a member for semiconductor production cannot be provided.

On the other hand, in the field of silicon carbide sintered body, as a method for analyzing impurities, a sample of silicon carbide sintered body is housed in a closed vessel together with a mixed acid consisting of concentrated hydrofluoric acid, concentrated nitric acid and concentrated sulfuric acid. There has been known a method of dissolving a sample by keeping the sample at 250 ° for a predetermined time and quantifying a metal component contained in the solution thus obtained. The present inventor has paid attention to this point, and the silicon carbide polycrystal obtained by the method described below does not dissolve even when performing a dissolution method for analyzing impurities of such a silicon carbide sintered body. , 50% of that
It was found that the above was retained without disassembly.

In addition, the sample is accommodated in a closed vessel together with a mixed acid consisting of concentrated hydrofluoric acid, concentrated nitric acid and concentrated sulfuric acid, and the undecomposed ratio is 50% even after being kept at 250 ° for 50 hours. % Or more, no corrosive substances such as particles are generated even when exposed to a highly corrosive cleaning gas such as a halogen-based corrosive gas or an etching gas. And no adverse effects due to impurity elements are found.

As described above, this method has been used for dissolving a silicon carbide sintered body to analyze an impurity metal, and is not a corrosion resistance test method. The inventor has succeeded in providing, for the first time, a corrosion-resistant silicon carbide polycrystal under these conditions by the method described below, and such a silicon carbide polycrystal has no precedent, and According to the present invention, a specific silicon carbide polycrystal selected by such a corrosion resistance test is unlikely to cause a problem of semiconductor contamination due to scattering of particles and impurity metals under conditions of exposure to a halogen-based corrosive gas. Was discovered by a person.

As the halogen-based corrosive gas, CF ₄ ,
Examples include NF ₃ , ClF ₃ , HF, HCl, and HBr. Among CF ₄ , NF ₃ and ClF ₃ , ClF ₃ has a particularly high degree of dissociation of F radicals, and has the strongest corrosiveness when compared under the same temperature and plasma power.

Next, a preferred method for producing a polycrystalline silicon carbide having the above characteristics will be described. The present inventor sought a method for forming a polycrystalline silicon carbide film, but in this process, focused on a sublimation method known as a method for manufacturing a single crystal. As a result of repeated experiments with various changes in the substrate and the like, a high-purity polycrystalline silicon carbide film was obtained by heating and vaporizing the silicon carbide raw material and depositing the vapor of the silicon carbide raw material on the substrate. Was found to be able to. Even when the thus obtained silicon carbide polycrystal was accommodated in the mixed acid and kept at a high temperature of 250 ° C., decomposition or dissolution proceeded very slowly, and a surprising result was obtained that corrosion was difficult.

The reason why such a result is obtained is not completely clear yet, but is presumed to be due to the following reason. That is, at the stage of vaporizing the silicon carbide raw material and depositing it on the substrate, it has an effect of purifying impurities in the silicon carbide raw material, and a raw material powder having a relatively high purity, particularly preferably a raw material having a purity of 99.5% or more By selecting the powder, it is possible to form a silicon carbide polycrystal of extremely high purity having a metal impurity content of 10 ppm or less.

However, even when a silicon carbide thin film is formed by a so-called chemical vapor deposition method, an extremely high purity silicon carbide thin film having a metal impurity content of 10 ppm or less can be formed. However, as mentioned above, 2
It was found that when kept at 50 ° C., almost 100% decomposition occurred. Therefore, it is understood that the high purity of silicon carbide is not a decisive factor.

On the other hand, a sample of a normal pressure sintered body or a sintered body obtained by reaction sintering can be easily maintained at 250 ° C. in a mixed acid even if it has a density close to the theoretical density. Thus, chemical analysis of the metal element, which is an impurity, is possible. This is probably because the metal component is distributed at the grain boundaries and erosion by the mixed acid proceeds along the grain boundaries. Therefore, it is also important that the purity of the silicon carbide polycrystal is high.

Here, when the silicon carbide polycrystal is formed by the sublimation method, the reason why it is resistant to mixed acid is probably that the temperature at the time of volumetric deposition on the substrate is higher in the case of the sublimation method. , To about 2000 ° C., it is considered to affect the crystallinity in the deposited film and the degree and shape of the growth of crystal grains.

The present inventors have more specifically studied these points and found that the silicon carbide polycrystal has an average particle size of 10 μm.
It has been found that it is particularly preferable to be composed of an aggregate of the hexagonal columnar particles described above. This average particle size is usually 6
μm or less. Further, an aggregate of hexagonal columnar particles mainly composed of a 3C crystal phase is preferable.

Here, the crystal type of the polycrystalline silicon carbide will be described. Looking at the atomic structure of SiC, Si and C
The tetrahedrons formed in the above form layers in a plane, and the layers are stacked. Many polymorphs are known for SiC, but important polymorphs as industrial materials are 2H, 3H
C, 4H, 6H and 15R. These notations are in accordance with Ramsdell's notation. H, C, and R represent hexagonal, cubic, and rhombohedral, respectively. Each number is the number of stacks in the unit cell. Cubic (3C) silicon carbide is called β-type silicon carbide, and non-equiaxed crystals other than cubic are called α-type silicon carbide.

The density of the silicon carbide polycrystal is 3.15 g / c.
It is particularly preferable that it is not less than c and not more than 3.21 g / cc.

Further, as to the crystallinity of the silicon carbide polycrystal, it is particularly preferable that the half width of the strongest peak in the X-ray diffraction chart of the silicon carbide polycrystal is 0.30 ° or less. This is greater than 0.20 °, typically 0.24 °
That is all.

A method for measuring the half width will be described. A sample of the polycrystalline silicon carbide is pulverized to obtain a powder having an average particle size of 30 μm or less, and this powder is set in a sample holder. X
In the line diffractometer, copper is used as the tube, the goniometer radius is 185 mm, the DS slit is 1 °,
SS slit 1 °, RS slit 0.3mm,
A graphite single crystal monochromator was installed on the diffraction side.

The half width is an index indicating the crystallinity of the polycrystalline silicon carbide. Generally, the smaller the half width,
It can be determined that the crystallinity of the silicon carbide polycrystal is good.
Since this value itself varies depending on the reference crystal and the like used in the X-ray measurement device, the measurement conditions were selected as described above.

Hereinafter, more specific embodiments will be described. FIG. 1 is a cross-sectional view schematically showing an example of an apparatus for producing a silicon carbide polycrystal of the present invention. The inner space 3 of the crucible 1 is divided into two by a partition wall 5.
In this embodiment, the space 3a above the partition 5 is used as a raw material chamber, and the space 3b below the partition 5 is used as a film formation chamber. The partition 5 divides the raw material chamber 3a and the film forming chamber 3b. The partition walls 5 need to be capable of passing the vapor of the raw material, and are provided with vent holes for this purpose.
Alternatively, it must be porous enough to allow the passage of steam.

The raw material chamber 3a is closed by a lid 6, and the silicon carbide raw material 2 is accommodated in the raw material chamber 3a.
The base 7 is fixed to the lower end of the film forming chamber 3b. The lid 6 and the base 7 serve to prevent the vapor in the raw material chamber 3a and the film forming chamber 3b from leaking outside.

In the crucible 1, the temperature of the raw material chamber 3a is relatively high, and the temperature of the film forming chamber 3b on the base 7 is relatively low. As shown by arrow A, the vapor from raw material 2
And moves to the film forming chamber on the low temperature side, and the silicon carbide film 4 is formed on the surface of the base 7. However, in the present invention, by continuing this process for a long time,
A bulk material having a thickness of about 5 to 50 mm can also be formed.

The ceramic raw material 2 is preferably a powder from the viewpoint of ease of sublimation, but is not limited to a powder. The use of a powder compact is preferable because the weight of the raw material powder that can be filled in the raw material chamber 3a can be increased and the raw material can be easily handled.

The substrate 7 can be made of various materials, but is preferably made of polycrystalline ceramics in order to produce a high-quality silicon carbide polycrystal. As the material of the substrate, for example, SiC, Si ₃ N ₄ , AlN, Al ₂
Examples include O ₃ , ZrO ₂ , SiO ₂ , MgO, C, Si, and composites thereof.

[0031] Either the low temperature part or the high temperature part of the furnace may be up. However, as shown in FIG. 1, when the high temperature portion (the portion where the ceramic raw material is present) rises, the heat rises from the lower side to the upper side. This is preferable because it is easy to maintain the temperature difference between the high temperature portion and the high temperature portion. Also, so that the hot and cold parts are horizontal,
It may be arranged.

As a method for heating the raw material, various methods can be applied, but a resistance heating method and a high-frequency heating method that can relatively easily generate a high temperature state are preferable. In the case of the high-frequency heating method, the reaction needs to be performed at a pressure higher than the pressure at which high-frequency discharge does not occur. In order to improve the crystallinity and deposition rate of the polycrystalline silicon carbide, the pressure is preferably set to 10 Torr or less, more preferably 0.5 Torr or less. When deposition is performed under such a low pressure, it is preferable to heat the raw material by a resistance heating method.

In order to form a silicon carbide polycrystal having uniform crystallinity and a silicon carbide polycrystal having a uniform thickness, it is necessary to keep the temperature of the substrate uniform. From this point, the temperature distribution in the base is preferably within ± 20 ° C., and more preferably within ± 5 ° C.

According to this method, a ceramic member having a silicon carbide polycrystal formed on a substrate can be provided. After forming the silicon carbide polycrystal on the mold, the mold is removed, whereby a member made of the silicon carbide polycrystal can be manufactured.

[0035] The corrosion-resistant member of the present invention may be formed entirely of the silicon carbide polycrystal.
At least the surface portion on the side in contact with the corrosive substance may be formed of the silicon carbide polycrystal.

The corrosion-resistant member of the present invention can be applied to various products. Such products include ceramic parts used in high-temperature atmospheres such as gas turbines. Specifically, in a combustor, a stationary blade, a moving blade, a heat exchanger, and a combustion gas passage component for a gas turbine, the corrosion-resistant member made of the silicon carbide polycrystalline film that covers the surface of the substrate is used. be able to. Also in these cases, the silicon carbide polycrystal of the present invention hardly undergoes deterioration in strength due to oxidation or corrosion, and is durable for a long time.

The corrosion-resistant member of the present invention can be applied to an electromagnetic wave transmitting body. Examples thereof include an electromagnetic wave transmission window, a high-frequency electrode device, a tube for generating high-frequency plasma, and a dome for generating high-frequency plasma. Further, the silicon carbide polycrystal of the present invention can be applied to a susceptor for installing a semiconductor wafer.
Examples of such a susceptor include a ceramic electrostatic chuck, a ceramic heater, and a high-frequency electrode device. In addition, it can be used as a base material of each semiconductor manufacturing apparatus such as a dummy wafer, a shadow ring, a lift pin for supporting a semiconductor wafer, and a shower plate.

[0038]

EXAMPLES Hereinafter, more specific experimental results will be described. The silicon carbide polycrystals of the respective comparative examples and the present invention examples were produced according to the production methods described below, and the following experimental results were obtained.

Comparative Example 1 (Production of sample) Purity: 99.5% by weight, average particle size: 0.6 μm
100 parts by weight of silicon carbide powder having an average particle size of 1.5 μm.
2.0 parts by weight of B ₄ C powder having an average particle size of 0.02 μm.
m of carbon powder and 1.5 parts by weight. 5 kg of this compound was put into a 20-liter medium stirring type pulverizer together with 7.5 kg of silicon carbide boulders and 6 liters of water, mixed for 20 hours, and pulverized to obtain a slurry. Next, this slurry was dried using a spray drier to produce a granulated powder having an average particle size of 50 μm.
This granulated powder is filled in a rubber mold, and a pressure of 2.5 ton /
It was isostatically pressed in cm ² . The molded body was fired at 2100 ° C. for 1 hour in an argon atmosphere at 1 atm to obtain a sintered body of Comparative Example 1.

(Test Result) The density of the sintered body was 3.12.
g / cc, the average particle size was 6 μm, and the content of metal impurities was 800 ppm. This sintered body was subjected to a gas phase decomposition corrosion resistance test. Specifically, a 0.3 g sample from the sintered body was collected in a Teflon container for pressure decomposition having a capacity of 100 cc, and concentrated hydrofluoric acid 8 ml and concentrated nitric acid 6 m
1 and 5 ml of concentrated sulfuric acid, and a pressure decomposition vessel was set.
The pressure decomposition container was heated in a dryer at 250 ° C. for 50 hours. Then, the pressure decomposition container was cooled, the contents of the container were filtered under reduced pressure through a 0.5 μm Teflon filter, the unfiltered residue was washed with warm water, dried at 110 ° C. for 1 hour, cooled to room temperature, and weighed. Was measured. The percentage (undecomposed rate) of the weight before decomposition and the weight of the residue after decomposition was calculated to be less than 0.5% by weight.

(Comparative Example 2) According to the same procedure as in Comparative Example 1, the molded article was obtained. The molded body was fired at 2100 ° C. for 1 hour under an atmosphere of argon at 1 atm, and further heated for 2 hours by a hot isostatic press (HIP) device.
ton / cm ² of argon gas pressure, 2000 ° C.
For 2 hours to obtain a HIP sintered body of Comparative Example 2.

The sintered body had a density of 3.20 g / cc, an average particle size of 6 μm, and a metal impurity content of
It was 800 ppm. About this sintered body, Comparative Example 1
When a gas phase decomposition corrosion resistance test was performed in the same manner as in the above, the undecomposed rate was less than 0.5% by weight.

In Comparative Example 1, B ₄ C was used as a sintering aid, and a metal impurity component contained in the silicon carbide powder used as a raw material at a ratio of 0.5% by weight or less. Is considered to have been decomposed under the conditions described above. In Comparative Example 2, the density was 3.20 g.
/ Cc HIP sintered body was manufactured, but the same result was obtained with such a dense sintered body.

Comparative Example 3 Purity 99.5%, Average Particle Size 3
μm silicon carbide powder, 45 parts by weight, purity 99.5%,
Silicon carbide powder having an average particle size of 80 μm and 55 parts by weight were mixed. 11. Water is added to 100 parts by weight of the mixed powder.
5 parts by weight and 0.1 part by weight of water glass were added, and the mixture was poured into a gypsum mold and dried to obtain a molded body. This molded body is brought into contact with molten Si,
Heat treatment was performed at 2000 ° C. for 1 hour in a vacuum to impregnate with Si to obtain a reaction sintered body of Comparative Example 3.

The density of the sintered body was 3.00 g / cc. This reaction sintered body was subjected to a gas phase decomposition corrosion resistance test in the same manner as in Comparative Example 1, and the undecomposed rate was 0.5.
%. This is still 0.5% by weight in the raw material
It is presumed that the metal impurities contained in the following proportions act, and that corrosion is progressing from Si impregnated between the particles of the sintered body.

Comparative Example 4 Purity 99.5%, average particle size 3
μm silicon carbide powder, 45 parts by weight, purity 99.5%,
Silicon carbide powder having an average particle size of 80 μm and 55 parts by weight were mixed. 11. Water is added to 100 parts by weight of the mixed powder.
5 parts by weight and 0.1 part by weight of water glass were added, and the mixture was poured into a gypsum mold and dried to obtain a molded body. The obtained compact was fired at 2400 ° C. for 1 hour in an argon atmosphere at 1 atm to obtain a recrystallized sintered body of Comparative Example 4.

The density of the sintered body is 2.80 g / cc, the average particle size is 4 μm, and the content of metal impurities is
It was 180 ppm. About this sintered body, Comparative Example 1
When a gas phase decomposition corrosion resistance test was performed in the same manner as in the above, the undecomposed rate was 22%. Thus, it is noted that the undecomposed ratio is significantly increased as compared with Comparative Examples 1, 2, and 3.

(Comparative Example 5) Using carbon as a base material,
Using a VD apparatus, a silicon carbide film was formed on the surface of the substrate. Specifically, the base material was inserted into a reaction vessel having a capacity of 7000 cm ³ , and the base material was maintained at a temperature of 1350 ° C., and SiCl ₄ , CH _4, and H ₂ were each placed in a reaction vessel at a temperature of 1.350 ° C.
It flowed at a flow rate of 5, 1.5 or 8.0 liter / min for 5 hours to form a silicon carbide film on the surface of the substrate. At this time, the pressure in the reaction vessel was controlled at 250 mbar. Thus, a polycrystalline silicon carbide of Comparative Example 5 was obtained.

The density of the silicon carbide polycrystal was 3.21 g.
/ Cc, the particle size is 3 to 6 μm, and the purity is 99.
999% or more. About this sintered body, Comparative Example 1
When a gas phase decomposition corrosion resistance test was performed in the same manner as in the above, the undecomposed ratio was less than 0.5%. As described above, it has been found that the decomposition of the CVD film proceeds rapidly under corrosive conditions having an extremely intense decomposition force such as pressurization and heating under a mixed acid.

The X-ray diffraction chart of this silicon carbide polycrystal was measured according to the method described above. This X-ray chart is shown as chart E in FIG. The strongest peak is a peak corresponding to the (111) plane of the crystal phase 3C, and its half width was 0.35 °.

(Example 1 of the Present Invention) Using the film forming apparatus shown in FIG. 2, a silicon carbide film 4 was formed on a substrate 7 made of carbon (C).
Was formed. However, in FIG. 2, the same members as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The crucible 1 has a cylindrical shape, and the material of the crucible is made of high-density carbon (C). The size of the base 7 was a disk shape having a diameter of 100 mm and a thickness of 5 mm. 100 kg of silicon carbide powder having an average particle size of 0.6 μm
Uniaxial pressing was performed with a load of f / cm ² to obtain a disk-shaped molded body having a diameter of 30 mm and a thickness of 5 mm. The molded body 2 was filled in the raw material chamber 3a in the crucible 1. The crucible 1 filled with the raw material 2 was set in a vacuum heating furnace shown in FIG. However,
8 is a hearth and 9 is a furnace wall. As the raw material 2, α-SiC powder having an average particle size of 0.5 μm and a purity of 99.5% was used.

The resistance heater 10 was set in the furnace, and the inside of the heater 10 was heated to 2200 ° C. The heating temperature must be 2000 ° C. or higher at which sublimation of SiC starts, and is preferably 2200 to 2400 ° C. At this time,
The atmosphere in the furnace was argon and the pressure was 0.01 Torr
And Since the temperature control is performed near the raw material chamber 3a, the temperature of the raw material chamber 3a is 2200 ° C.,
The temperature of the film forming chamber 3b without the heater 10 is slightly lower than that of the raw material chamber. The temperature of the substrate 7 in contact with the hearth 8 is lower than that in the film forming chamber 3b because heat escapes from the substrate 7 to the hearth. In this embodiment, the difference between the temperature of the raw material chamber and the temperature of the substrate was set to 50 ° C. The difference between the temperature of the raw material chamber and the temperature of the base is preferably 20 ° C. or more and 500 ° C. or less.

When the temperature inside the crucible 1 was raised to the polycrystal growth temperature, the crucible 1 was filled with an argon atmosphere so that unstable crystal nuclei would not grow on the substrate 7. After reaching a predetermined growth temperature, the pressure in the crucible 1 was reduced to start the growth of polycrystal.

As a result, a dense polycrystalline silicon carbide film 4 having a thickness of about 1 mm was deposited on the base 7. The surface of this film 4 was smooth and transparent. This was designated as polycrystalline silicon carbide of Example 1 of the present invention.

The density of the silicon carbide polycrystal is 3.19 g.
/ Cc, the average particle size is 200 μm, and the purity is 9
9.999% or more. A gas phase decomposition corrosion resistance test was performed on this sintered body in the same manner as in Comparative Example 1.
The undecomposed rate was 76%.

An X-ray diffraction chart of this polycrystalline silicon carbide was measured according to the method described above. The X-ray chart is shown as a top chart C in FIG. 3 and a chart C in FIG. In FIG. 3, below the top chart C, a chart of peak data indicating the intensity of each peak of the chart C is shown. The bottom row shows the peak data (JCPDS-29-1129 card) corresponding to crystal phase 3C. As can be seen from FIG. 3, chart C is almost crystalline phase 3C.
As a result, a weak peak was observed in only a part of the peak corresponding to the crystal phase 6H. The strongest peak A is a peak corresponding to the (111) plane of the crystal phase 3C, and its half width was 0.28 °.

As described above, the progress rate of decomposition of the silicon carbide polycrystal of Example 1 of the present invention is extremely low even under corrosive conditions having extremely severe decomposition power, such as pressure and heating under mixed acid. I understand. These corrosive conditions are:
As described above, such durability is surprising considering that it was conventionally known as a test method for decomposing silicon carbide and analyzing its metal component. this is,
It is thought to be due to the extremely high purity, the crystallinity determined from the half width of the X-ray diffraction peak, the large hexagonal columnar particles having a particle size of 10 μm or more, and the high relative density.

(Example 2 of the present invention)
The polycrystalline silicon carbide of Inventive Example 2 was produced. However, in Example 1 of the present invention, raw material 2 had an average particle size of 0.5 μm.
m, β-SiC powder having a purity of 99.5% was used. As a result, a dense polycrystalline silicon carbide film 4 having a thickness of about 1 mm was deposited on the base 7. The surface of this film 4 was smooth and transparent.

The density of the polycrystalline silicon carbide is 3.19 g.
/ Cc, the average particle size is 150 μm, and the purity is 9
9.999% or more. A gas phase decomposition corrosion resistance test was performed on this sintered body in the same manner as in Comparative Example 1.
The undecomposed rate was 83%.

The X-ray diffraction chart of this polycrystalline silicon carbide was measured according to the method described above. This X-ray chart is shown as the top chart D in FIG. FIG.
, Below the top chart D, a chart of peak data indicating the intensity of each peak of the chart D is shown. At the bottom, the peak data corresponding to the crystal phase 3C (JCPD
S-29-1129). As can be seen from FIG. 3, the chart D is almost due to the crystalline phase 3C, but a weak peak was observed in a very small portion that corresponds to the crystalline phase 6H. This strongest peak is in crystalline phase 3
The peak B corresponding to the (111) plane of C had a half width of 0.26 °. This peak was even steeper than that of Example 1 of the present invention.

[Test of Corrosion Resistance to Halogen Corrosive Gas] Approximately 1 mg of each sample was collected from each of the polycrystalline silicon carbides according to Comparative Example 5, Inventive Example 1, and Inventive Example 2. Plasma was generated at 450 ° C. against NF ₃ (0.1 torr) and each sample was exposed for 20 hours. When the ratio of the weight before exposure to the weight after exposure was measured for each sample, it was 99.88% in Comparative Example 5, 99.97% in Example 1 of the present invention, and 99.97% in Example 1 of the present invention. Was 99.98%.

[0063]

As described above, the silicon carbide polycrystal of the present invention suppresses the generation of corrosive substances such as particles even when exposed to a corrosive substance having extremely high corrosiveness. And contamination by metal impurities can be prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing an example of an apparatus that can be used for producing a silicon carbide polycrystal of the present invention.

FIG. 2 is a cross-sectional view schematically showing one example of an apparatus that can be used for producing the silicon carbide polycrystal of the present invention.

FIG. 3 is a chart showing an X-ray diffraction chart C, a peak data of the chart C, and a peak data corresponding to the crystal phase 3C of a sample obtained from the polycrystalline silicon carbide of Example 1 of the present invention.

FIG. 4 is a chart showing an X-ray diffraction chart D, a peak data of the chart D, and a peak data corresponding to the crystal phase 3C of a sample obtained from the polycrystalline silicon carbide of Example 2 of the present invention.

FIG. 5 is a chart showing an X-ray diffraction chart C of a sample obtained from the polycrystalline silicon carbide of Example 1 of the present invention and an X-ray diffraction chart E of a sample obtained from the polycrystalline silicon carbide of Comparative Example 5. .

[Explanation of symbols]

1 Crucible 3 Internal space of crucible 1 5 Partition wall
3a Raw material chamber 3b Film forming chamber 6 Lid 7 Base 8 Hearth floor 9 Furnace wall 10 Heater B, F Peak corresponding to (111) plane of crystal phase 3C C Sample of silicon carbide polycrystal obtained in Example 1 of the present invention X-ray diffraction chart D X-ray diffraction chart of a sample obtained from the polycrystalline silicon carbide of Example 2 of the present invention
E X-ray diffraction chart of sample obtained from polycrystalline silicon carbide of Comparative Example 5

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Keiichiro Watanabe 2-56 Suda-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Inside Nihon Insulator Co., Ltd.

Claims (6)

[Claims] An undecomposed rate of 50% or more after heating at 250 ° C. for 50 hours in a mixed acid comprising concentrated hydrofluoric acid, concentrated nitric acid and concentrated sulfuric acid in a closed vessel. A silicon carbide polycrystal. 2. The polycrystalline silicon carbide has an average particle size of 10%.
The polycrystalline silicon carbide according to claim 1, wherein the polycrystalline silicon carbide is an aggregate of hexagonal columnar particles having a size of not less than μm. 3. The silicon carbide polycrystal has a density of 3.15 g.
3. The polycrystalline silicon carbide according to claim 1, wherein the content is not less than / cc and not more than 3.21 g / cc. 4. The polycrystalline silicon carbide according to claim 1, wherein a content of metal impurities contained in said polycrystalline silicon carbide is 10 ppm or less. Crystal. 5. The X-ray diffraction chart of said polycrystalline silicon carbide, wherein the half width of the strongest peak is 0.20 ° or more and 0.3 or more.
The silicon carbide polycrystal according to claim 1, wherein the angle is 0 ° or less. 6. A corrosion-resistant member exposed to a corrosive substance, wherein at least a surface portion in contact with the corrosive substance has a silicon carbide multi-layer structure according to any one of claims 1 to 5. A corrosion-resistant member comprising a crystalline body.