JP2000154063A - Production of silicon carbide sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve processability by forming a sintered body in a hot-press sintering process and then heat treating the sintered body in an inert atmosphere in a specified temp. range. SOLUTION: The silicon carbide sintered body obtd. in a hot-press sintering process is heat treated in an inert atmosphere in the temp. range from 1.00 Ts to 0.70 Ts ( deg.C), wherein Ts is the sintering temp. in the sintering process. To obtain the silicon carbide sintered body, silicon carbide powder is mixed with a nonmetal sintering assistant, heated and sintered. As for the sintering assistant, org. compds. which produce carbon by heating, or silicon carbide powder coated with the org. compds. are preferably used. As for the org. compds., especially a resol-type phenol resin is preferable. The amt. of the sintering assistant added is preferably 2 to 5 wt.%. The obtd. sintered body is made dense enough as >=2.9 g/cm3 density, and preferably it contains <=10% free carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a silicon carbide sintered body, and more particularly to a method for producing a silicon carbide sintered body having improved workability and hardly causing chipping or chipping during processing. .

[0002]

2. Description of the Related Art Silicon carbide sintered bodies are used or planned to be used in various fields by making use of heat resistance, thermal shock resistance, abrasion resistance or corrosion resistance. Normally, methods for producing silicon carbide include press molding, cast molding, extrusion molding, injection molding, and the like. Among these, press molding involves molding and then sintering at normal pressure to obtain a ceramic or pressurizing as it is There is a hot press sintering method in which the temperature is raised and sintered. The sintered body obtained by the above manufacturing method,
Depending on the purpose, processing such as slicing, cutting, and polishing is performed, and the final product is obtained. However, silicon carbide is a hard material next to diamond, and its toughness value falls in a small category among ceramics, and is also known as a difficult-to-work material. Therefore, there is a problem that chipping or cracking occurs during processing, and when a thin plate is processed, there is a problem that the thin plate is warped after a lapse of time, and particularly in a sintered body obtained by a hot press sintering method. There are many trends.

[0003] The high hardness, which is an inherent advantage of silicon carbide, results in a large amount of labor required in the forming and processing steps, and such poor processing efficiency leads to an increase in manufacturing costs and a great obstacle to mass production. Has become. Metallic materials exhibiting large ductility are less likely to cause chipping and cracking, and the current state of production is efficient and inexpensive. If this can be achieved, the manufacturing cost will be much lower than before, and mass production or a dramatic expansion of applications is expected.

[0004]

As described above, silicon carbide sintered bodies are difficult to process, and there is a need for a sintered body that is easy to process. That is, an object of the present invention is to provide a silicon carbide sintered body having excellent workability, which does not cause defects such as chipping in slicing processing, cracks in punching, and warpage after processing, and which can easily produce a silicon carbide sintered body having excellent workability. An object of the present invention is to provide a method for manufacturing a sintered body.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the workability is improved by performing post-treatment by predetermined heating on a silicon carbide sintered body. Was completed. That is, the method for producing a silicon carbide sintered body of the present invention is as follows: when the sintering temperature in the hot press sintering step is Ts, the silicon carbide sintered body obtained through the hot press sintering step is 1. 00 Ts ° C-0.70T
a heat treatment in an inert atmosphere in a temperature range of s ° C. In a preferred embodiment, the production of the sintered body includes a step of sintering a mixture of the silicon carbide powder and the nonmetallic sintering aid.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. In the method for producing a silicon carbide sintered body of the present invention,
As a manufacturing step of the sintered body prior to the heating step, the silicon carbide sintered body described in Japanese Patent Application No. 9-41048 previously proposed by the present applicant can be applied. Hereinafter, the method for producing a silicon carbide sintered body of the present invention will be sequentially described according to the steps. Examples of the silicon carbide powder used as a raw material of the sintered body include α-type, β-type, amorphous, and mixtures thereof, and β-type silicon carbide powder is particularly preferably used. There is no particular limitation on the grade of the β-type silicon carbide powder, and, for example, generally commercially available β-type silicon carbide powder can be used. The particle size of the silicon carbide is preferably small from the viewpoint of high density,
It is about 10 μm, more preferably 0.05 to 2 μm. If the particle size is less than 0.01 μm, it is difficult to handle in processing steps such as measurement and mixing, and if it exceeds 10 μm, the specific surface area is small, that is, the contact area with the adjacent powder is small, and it is difficult to increase the density. Is not preferred.

In particular, when a high-purity silicon carbide sintered body is desired, it is preferable to use a high-purity silicon carbide powder as a raw material silicon carbide powder. High-purity silicon carbide powder includes, for example, a silicon source containing at least one or more liquid silicon compounds, a carbon source containing at least one or more liquid organic compounds that generate carbon by heating, and a polymerization or crosslinking catalyst. And a solid product obtained by homogeneously mixing and baking in a non-oxidizing atmosphere. Here, a silicon source containing a liquid silicon compound, for example, a liquid silicon compound can be used in combination with a solid silicon compound. As the silicon compound (hereinafter, appropriately referred to as a silicon source) used as a raw material of the high-purity silicon carbide powder, a liquid compound and a solid compound can be used in combination, but at least one is selected from liquid compounds. Must-have. As the liquid, a polymer of alkoxysilane (mono-, di-, tri-, tetra-) and tetraalkoxysilane is used. Among alkoxysilanes, tetraalkoxysilane is suitably used, and specific examples thereof include methoxysilane, ethoxysilane, proxy silane, and butoxysilane. However, ethoxysilane is preferable from the viewpoint of handling. Further, as a polymer of tetraalkoxysilane,
Examples thereof include a low molecular weight polymer (oligomer) having a degree of polymerization of about 2 to 15 and a liquid silicate polymer having a higher degree of polymerization. As a solid material that can be used in combination therewith, silicon oxide can be mentioned. In the present invention, the silicon oxide includes, in addition to SiO, silica sol (colloidal ultrafine silica-containing liquid, containing an OH group or an alkoxyl group therein), silicon dioxide (silica sol, fine silica, quartz powder) and the like. Among these silicon sources, from the viewpoint of good homogeneity and handling properties, tetraxysilane oligomers and mixtures of tetraxysilane oligomers with fine powder silica are preferred. In addition, these silicon sources use high-purity substances, and the initial impurity content is 20 ppm.
Or less, more preferably 5 ppm or less.

The organic compound used for producing high-purity silicon carbide powder, which produces carbon by heating, may be a liquid compound or a combination of a liquid compound and a solid compound. Organic compounds having a high rate and polymerizing or cross-linking by a catalyst or heating, specifically, for example, a monomer or prepolymer of a resin such as a phenol resin, a furan resin, a polyimide, a polyurethane, or a polyvinyl alcohol are preferable, In addition, liquid substances such as cellulose, sucrose, pitch, and tar are also used, and a resol type phenol resin is particularly preferable. In addition, the purity can be appropriately controlled and selected depending on the purpose. In particular, when high-purity silicon carbide powder is required, it is preferable to use an organic compound containing no more than 5 ppm of each metal element.

In the present invention, the ratio of carbon to silicon (hereinafter referred to as "the ratio of
(Abbreviated as C / Si ratio) is defined by elemental analysis of a carbide intermediate obtained by carbonizing the mixture at 1000 ° C. Stoichiometrically, the free carbon in the generated silicon carbide should be 0% when the C / Si is 3.0, but in practice, the low C / S
Free carbon is generated at the i ratio. It is important to determine the blending in advance so that the amount of free carbon in the produced silicon carbide powder does not become an amount unsuitable for production use such as a sintered body. Usually, in baking at 1600 ° C. or higher at around 1 atm, free carbon can be suppressed by setting the C / Si ratio to 2.0 to 2.5, and this range can be suitably used. When the C / Si ratio is 2.5 or more, the amount of free carbon increases remarkably. However, since this free carbon has an effect of suppressing grain growth, it may be appropriately selected according to the purpose of forming particles.

However, in the case of firing at a low or high pressure in the atmosphere, the firing is not necessarily limited to the range of the C / Si ratio. In addition, since the action at the time of sintering of free carbon is very weak as compared with that of carbon derived from the nonmetallic sintering aid coated on the surface of the silicon carbide powder used in the present invention, Basically it can be ignored. Also,
In the present invention, in order to obtain a solid in which a silicon source and an organic compound that generates carbon by heating are homogeneously mixed, a mixture of the silicon source and the organic compound is cured to be a solid, if necessary. Will be As a curing method, a method of crosslinking by heating, a method of curing with a curing catalyst,
Examples include a method using an electron beam or radiation. The curing catalyst can be appropriately selected according to the carbon source, but in the case of a phenol resin or a furan resin, an acid such as toluenesulfonic acid, toluenecarboxylic acid, acetic acid, oxalic acid, hydrochloric acid, or sulfuric acid, or an amine such as hexamine. And the like. The solid material mixture is heated and carbonized as necessary. This is done by heating the solid in a non-oxidizing atmosphere such as nitrogen or argon at 800-1000 ° C. for 30 to 120 minutes. Further, the carbide is placed in a non-oxidizing atmosphere such as argon.
By heating at 50 ° C. or more and 2000 ° C. or less, silicon carbide is generated. The firing temperature and time can be appropriately selected according to the desired properties such as the particle size, but firing at 1600 to 1900 ° C. is desirable for more efficient production. Also,
When a powder of higher purity is required, impurities can be further removed by performing a heat treatment at 2000 to 2100 ° C. for 5 to 20 minutes during the above-described firing.

Particularly, a method for obtaining a high-purity silicon carbide powder is disclosed in Japanese Patent Application Laid-Open No. 9-4860 filed by the present applicant.
No. 5, the production method of the raw material powder described in the production method of a single crystal, that is, a high purity tetraalkoxysilane, one or more selected from tetraalkoxysilane polymer as a silicon source, by heating A high purity organic compound that produces carbon is used as a carbon source, and a mixture obtained by mixing these homogeneously is heated and fired in a non-oxidizing atmosphere to obtain a silicon carbide powder, and a silicon carbide production step is obtained. A silicon carbide powder, comprising a post-treatment step of holding at a temperature of 1700 ° C. or more and less than 2000 ° C., and performing at least one heat treatment at a temperature of 2000 ° C. to 2100 ° C. for 5 to 20 minutes while maintaining the temperature Producing a silicon carbide powder having a content of each impurity element of 0.5 ppm or less by performing the first two steps. It is also possible to use the law and the like.

In order to produce the silicon carbide sintered body according to the present invention, the above-mentioned silicon carbide powder and a nonmetallic sintering aid are mixed and subjected to a heating and sintering step. As the metal-based sintering aid, a substance that generates carbon by heating, a so-called carbon source, is used. Specifically, an organic compound itself that generates carbon by heating or these organic compounds are used. Silicon carbide powder coated on the surface (particle size: about 0.01 to 1 micron) may be mentioned, and the former is preferred from the viewpoint of effects. The carbon term used for the auxiliaries is
It is the same as that used in the step of obtaining the silicon carbide powder earlier, specifically, a coal tar pitch, a pitch tar, a phenol resin, a furan resin, an epoxy resin, a phenoxy resin having a high residual carbon ratio. And various sugars such as monosaccharides such as glucose and glucose, oligosaccharides such as sucrose, and polysaccharides such as cellulose and starch. These are preferably those that are liquid at room temperature, those that dissolve in a solvent, those that are softened by heating such as thermoplastic or heat-meltable, or those that become liquid, for the purpose of being homogeneously mixed with silicon carbide powder. Among them, a phenol resin having high strength of the obtained molded body, particularly a resole type phenol resin is preferable.

In the present invention, the solvent used for obtaining a mixture of the silicon carbide powder and the nonmetallic sintering aid includes:
A suitable compound is selected for a compound used as a nonmetallic sintering aid. Specifically, for a phenol resin which is an organic compound that generates carbon by heating, ethyl alcohol or the like is used. Lower alcohols and ethyl ether,
Acetone or the like can be selected. In addition, it is preferable to use a nonmetallic sintering aid and a solvent having a low impurity content from the viewpoint of the purity of the obtained powder.

If the amount of the nonmetallic sintering aid mixed with the silicon carbide powder is too small, the density of the sintered body will not increase,
If it is too large, the amount of free carbon contained in the sintered body increases, which may hinder joining and densification. Therefore, although it depends on the type of nonmetallic auxiliary used, it is generally 10% by weight. Hereinafter, it is preferable to adjust the addition amount so as to be preferably 2 to 5% by weight. This amount can be determined by previously quantifying the amount of surface silica (silicon oxide) of the silicon carbide powder using hydrofluoric acid, and calculating the amount stoichiometrically sufficient for its reduction from the following reaction formula. . The amount of carbon added here is a value obtained by taking into account the ratio of silica produced in the nonmetallic sintering aid, which is quantified by the above method, to carbon. SiO ₂ + 3C → SiC + 2CO

The mixing of the silicon carbide powder and the non-metallic sintering aid can be performed by a known mixing means, for example, a mixer, a planetary ball mill or the like. Mixing is 10-3
It is preferably carried out for 0 hour, especially for 16 to 24 hours. After thorough mixing, a temperature compatible with the physical properties of the solvent, for example, 5
The solvent is removed at a temperature of 0 to 60 ° C, the mixture is evaporated to dryness, and then sieved to obtain a raw material powder of the mixture. In addition,
From the viewpoint of high purity, the material of the ball mill container and the balls needs to be a synthetic resin containing as little metal as possible.
In drying, a granulator such as a spray dryer may be used.

Next, the process proceeds to a sintering step. In the sintering step, the powder obtained in the above step is subjected to a temperature of 2000 to 2400 ° C.
This is a hot-press sintering step in which the mold is placed in a molding die under a non-oxidizing atmosphere at a pressure of 300 to 700 kgf / cm ² and hot-pressed. The molding die used here, from the viewpoint of the purity of the obtained sintered body, use a graphite material for part or all of the mold so that the molded body does not directly contact the metal part of the mold. Alternatively, it is preferable to interpose a Teflon sheet or the like in the mold. When the pressure in the hot pressing in the present invention may be pressurized under conditions of 300 to 700 kgf / cm ^2, setting the particular 400 kgf / cm ² or more pressure conditions, hot pressing parts used here,
For example, it is necessary to select a die, a punch, and the like having good pressure resistance.

Next, the sintering step will be described in detail. Prior to the hot pressing step for producing a sintered body, heating and heating are carried out under the following conditions to sufficiently remove impurities and to remove non-metallic substances. After the carbonization of the system sintering aid is completely performed, it is preferable to perform hot pressing under the above conditions. Specifically, it is preferable to perform the following two-stage heating process. First, the inside of the furnace is gently heated from room temperature to 700 ° C. under vacuum. Here, when it is difficult to control the temperature of the high-temperature furnace, 7
The temperature may be continuously raised to 00 ° C., but preferably, the inside of the furnace is kept at 10 ⁻⁴ torr, the temperature is gradually raised from room temperature to 200 ° C., and the temperature is maintained for a certain time.
Thereafter, the temperature is further gently increased and heated to 700 ° C. Further, it is kept at a temperature of about 700 ° C. for a certain time. In the first temperature raising step, the adsorbed moisture and the organic solvent are desorbed, and further, the nonmetallic sintering aid is carbonized by thermal decomposition. A suitable range of time for maintaining the temperature at about 200 ° C. or about 700 ° C. is selected depending on the size of the sintered body. Whether or not the holding time is sufficient can be determined based on the point at which the decrease in the degree of vacuum is reduced to some extent. If rapid heating is performed at this stage, it is not preferable because impurities are not removed or the nonmetallic sintering aid is not sufficiently carbonized, which may cause cracks or voids in the molded body.

As an example, for a sample of about 5 to 10, the temperature is gently raised from room temperature to 200 ° C. at 10 ⁻⁴ torr, kept at that temperature for about 30 minutes, and then further gently raised. The temperature is maintained and heated to 700 ° C., and the time from room temperature to 700 ° C. is about 6 to 10 hours, preferably about 8 hours. Further, it is preferable to maintain the temperature at about 700 ° C. for 2 to 5 hours. In a vacuum, the temperature is further increased from 700 ° C. to 1500 ° C. for about 6 to 9 hours under the above conditions, and
Hold for 1-5 hours at a temperature of ° C. It is considered that a reduction reaction of silicon dioxide and silicon oxide is performed in this step. It is important to complete the reduction reaction sufficiently to remove oxygen bonded to silicon, and the holding time at a temperature of 1500 ° C. is sufficient to complete the generation of carbon monoxide as a by-product of the reduction reaction. , Ie, the temperature before the reduction reaction starts, since the decrease in the degree of vacuum is small.
It is necessary to perform the process until the degree of vacuum at around 00 ° C. is restored. By the reduction reaction in the second temperature raising step, silicon dioxide which adheres to the surface of the silicon carbide powder, inhibits densification, and causes large grain growth is removed. Since the gas containing SiO and CO generated during this reduction reaction is accompanied by impurity elements, it is preferable to constantly discharge and remove these generated gases from the reaction furnace by a vacuum pump from the viewpoint of high purity, Further, it is preferable to sufficiently maintain the temperature.

After these temperature raising steps are completed, it is preferable to perform high-pressure hot pressing. Temperature 1500
When the temperature rises above ℃, sintering starts.
300-700kgf / c to suppress abnormal grain growth
up to about m ² starts pressurization as a guide. Thereafter, an inert gas is introduced to make the inside of the furnace a non-oxidizing atmosphere. As the inert gas, nitrogen or argon is used, but is non-reactive even at a high temperature.
It is desirable to use argon gas because it is difficult for impurities to remain in the sintered body.

After the furnace is set in a non-oxidizing atmosphere, the temperature is set to 2
000-2400 ° C, pressure 300-700kgf / cm
Heat and pressurize to ² As for the pressure at the time of pressing, if the raw material powder has a small particle size, a suitable sintered body can be obtained even if the pressure at the time of pressing is relatively small. Also here 15
The temperature rise from 00 ° C. to the maximum temperature of 2000 to 2400 ° C. is performed over 2 to 4 hours, while sintering is performed between 1850 and 19
It proceeds rapidly at 00 ° C. Furthermore, at this maximum temperature,
Hold for 3 hours to complete sintering. Where the maximum temperature is 20
If the temperature is lower than 00 ° C., the densification becomes insufficient, and 2400
If the temperature exceeds ℃, the powder or the raw material of the molded product is undesirably sublimated (decomposed). Also, if the pressing condition is 500
If it is less than kgf / cm ² , the densification becomes insufficient,
If it exceeds 700 kgf / cm ² , it may cause breakage of a mold such as a graphite mold, which is not preferable in terms of production efficiency.

Also in this sintering step, from the viewpoint of maintaining the purity of the obtained sintered body, it is preferable to use a high-purity graphite material for the graphite mold and the heat insulating material of the heating furnace used here. High-purity treated products are used,
Specifically, it is desirable that the baking is sufficiently performed in advance at a temperature of 2500 ° C. or more and no impurities are generated at the sintering temperature. Furthermore, it is preferable to use high purity with little impurities for the inert gas to be used.

In the production method of the present invention, a silicon carbide sintered body having excellent characteristics can be obtained by performing the hot press sintering step, but the viewpoint of increasing the density of the finally obtained sintered body is obtained. Therefore, a forming step may be performed prior to the sintering step. Hereinafter, a forming step which can be performed prior to the sintering step will be described. Here, the molding step means that the raw material powder obtained by homogeneously mixing the silicon carbide powder and the non-metallic sintering aid is placed in a molding die, and in a temperature range of 80 to 300 ° C. And heating and pressurizing for 5 to 60 minutes to prepare a molded body in advance. Here, the filling of the raw material powder into the mold should be performed as tightly as possible.
It is preferable from the viewpoint of increasing the density of the final sintered body. When this molding step is performed, a bulky powder can be made compact in advance when filling a sample for hot pressing. Therefore, by repeating this molding step, the thick molding step is repeated to increase the thickness. It becomes easier to manufacture a molded article.

The heating temperature in the optional forming step is 80 to 30 depending on the characteristics of the nonmetallic sintering aid.
0 ° C, preferably in the range of 120 to 140 ° C, pressure of 60 to
Within the range of 100 kgf / cm ² , the density of the filled raw material powder is 1.5 g / cm ³ or more, preferably 1.9 g.
/ Cm ³ or more and press
After holding for 60 minutes, preferably for 20 to 40 minutes, a molded body made of the raw material powder is obtained. Here, the density of the compact is 1.8 g / cm for powder having an average particle diameter of about 1 μm.
³ or more, average particle diameter is more preferably in the 0.5μm about powder is density of 1.5 g / cm ³ or more. For each particle size, the density is 1.5 g / cm ³ or 1.
If it is less than 8 g / cm ³ , it will be difficult to increase the density of the finally obtained sintered body.

The molded body is subjected to the following sintering process.
Cutting can be performed so as to be compatible with a hot press mold used in advance. This molded body is subjected to the above-mentioned temperature
It is placed in a molding die under a non-oxidizing atmosphere at 2400 ° C. under a pressure of 300 to 700 kgf / cm ² , and is subjected to a hot pressing step, that is, a firing step to obtain a silicon carbide sintered body of high density and high purity. Things. The silicon carbide sintered body produced as described above has a sufficiently high density, and the density is 2.
9 g / cm ³ or more. The density of the obtained sintered body is 2.
If it is less than 9 g / cm ³ , the mechanical properties such as bending strength and breaking strength and the electrical properties are reduced, and the number of particles is increased, and the contamination is undesirably deteriorated.
More preferably, the density of the silicon carbide sintered body is 3.0 g / cm ³ or more. When the obtained sintered body is porous, heat resistance, oxidation resistance, chemical resistance and mechanical strength are inferior.

In the silicon carbide sintered body obtained by the production method of the present invention, the total of carbon atoms derived from silicon carbide and carbon atoms derived from the nonmetallic sintering aid contained in the silicon carbide sintered body is Exceeds 30% by weight and 40% by weight
The following is preferred. When the sintered body contains no impurities, the content of carbon atoms in the sintered body is theoretically 3
0% by weight (C / SiC). That is, when the proportion of impurities contained in the sintered body is increased, the content of carbon atoms in the sintered body is not more than 30% by weight, which is not preferable. On the other hand, if the content exceeds 40% by weight, the carbon content increases, the density of the obtained sintered body decreases, and various properties such as the strength and oxidation resistance of the sintered body deteriorate, which is not preferable. Further, the content of free carbon is preferably 10% or less from the viewpoint of being suitable for use in manufacturing sintered bodies and the like.

In the production of the silicon carbide sintered body according to the present invention, there is no particular limitation on a production apparatus or the like as long as the above heating conditions can be satisfied. Known heating furnaces and reaction devices can be appropriately selected and used.

Since the sintered body obtained through the hot press sintering step is difficult to process, the sintered body is further subjected to a heat treatment in an inert atmosphere in order to facilitate the workability. I do. In the hot press sintering process, the powders compressed by the press are pressed against each other, and the particles are fused and sintered by diffusion energy. In this process,
Many non-oxide ceramics achieve high densification, but on the other hand, distortion occurs inside the sintered body due to the change in volume and crystal structure. This strain is stored as a stress and remains as an internal stress. When an external stress is applied at the time of working due to the internal stress, it is considered that chipping or chipping occurs even by applying a slight stress. In the production method of the present invention, the above-mentioned problem at the time of processing has been solved by performing a step of heating this sintered body in an inert atmosphere after the hot press sintering step. . The mechanism by which the heat treatment step improves workability is not clear, but it is presumed that the heat treatment releases the residual stress by the application of thermal energy. In addition, by high temperature treatment,
It is also conceivable that the crystal grains inside the sintered body cause grain boundary slip, thereby eliminating the distortion.

The processing conditions in the heat treatment step include:
It is preferably performed in an inert atmosphere from the viewpoint of preventing oxidation, and is preferably performed in an argon or helium atmosphere. The processing temperature is preferably equal to or slightly lower than the sintering temperature. Specifically, when the sintering temperature is Ts, the sintering temperature is preferably in the range of 1.00 Ts ° C. to 0.70 Ts ° C. When the heating temperature exceeds 1.00Ts ° C,
Exceeding the sintering temperature and being exposed to an atmosphere having a temperature higher than the thermal history of the formed sintered body, the sintering reaction will proceed further. On the other hand, since the pressure is released, the dimensions cannot be maintained, and the dimensional accuracy is affected by the high-temperature heating. In addition, these phenomena further increase the grain growth of silicon carbide, causing a serious problem that pores and pores are generated in the sintered body. On the other hand, when the heating temperature is 0.70
If the temperature is lower than Ts ° C., the effect of the heat treatment, that is, the effect of improving workability becomes insufficient.

Such a heat treatment also has an effect of promoting high purity in the production of a high-purity product such as a semiconductor member, for example. There is also an advantage that no special equipment such as a furnace is required and the heating can be performed in a general heating furnace.

The total amount of impurities in the silicon carbide sintered body obtained by the production method of the present invention is 5 ppm or less, preferably 3 ppm or less.
Although the content is not more than 1 ppm, more preferably not more than 1 ppm, from the viewpoint of application to the semiconductor industry, the content of impurities by these chemical analyzes has only a meaning as a reference value. In practice, the evaluation differs depending on whether the impurities are uniformly distributed or locally unevenly distributed. Therefore, those skilled in the art generally evaluate the extent to which impurities contaminate semiconductor products under various predetermined heating conditions using practical equipment by various means. The liquid silicon compound, the nonmetallic sintering aid, and the polymerization or cross-linking catalyst were heated and carbonized in a non-oxidizing atmosphere, and then further solidified in a non-oxidizing atmosphere. According to the production method including the sintering step of sintering, the total content of impurities other than silicon, carbon, oxygen, and nitrogen contained in the silicon carbide sintered body can be reduced to 5 ppm or less.

The silicon carbide powder used as the raw material powder of the silicon carbide sintered body used in the method of the present invention, a silicon source for producing the raw material powder, a nonmetallic sintering aid, and a non-oxidizing atmosphere The purity of the inert gas used in the process is preferably such that the content of each impurity element is 1 ppm or less, but is not necessarily limited to this as long as it is within the allowable range of purification in the heating and sintering steps. is not. Here, the impurity element is an element having an atomic number of 3 or more in the periodic table of the revised edition of the 1989 IUPAK inorganic chemical nomenclature, and an element having an atomic number of 6 to 8 and 14 (that is, carbon,
Nitrogen, oxygen, and silicon).

Regarding other preferable physical properties of the silicon carbide according to the present invention, for example, the bending strength at room temperature is 550 to 800 kgf / mm ² and the Young's modulus is 3.5 × 10 ^4.
~ 4.5 × 10 ⁴ , Vickers hardness is 2000kgf /
mm ² or more, Poisson's ratio is 0.14 to 0.21, coefficient of thermal expansion is 3.8 × 10 ^{-6 to} 4.2 × 10 ^-6 1 / ° C., thermal conductivity is 150 W / m · K or more, specific heat Is 0.15 to 0.1
8 cal / g · ° C, thermal shock resistance 500-700 ° T
C., the specific resistance is preferably 1 Ω · cm.

[0033]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

(Example 1) [Production of raw material powder] High-purity silicon carbide powder (average particle size of 0.
8 μm: silicon carbide with an impurity content of 5 ppm or less, produced according to the production method described in the above-mentioned JP-A-9-48605: containing 1.5% by weight of silica) 8800 g and high purity with a water content of 20% 1200 g of liquid resole type phenol resin (residual carbon ratio after thermal decomposition is 50%)
The material dissolved in 6000 g was stirred by a ball mill for 18 hours and mixed well. After that, the ethanol is evaporated to dryness with an atomizer type spray dryer, granulated,
A homogeneous silicon carbide granule was obtained. [Production of Sintered Body] The silicon carbide powder obtained as described above was subjected to a hot press sintering step to produce a sintered body. Hot pressing conditions The above powder 470 was placed in a graphite mold having an inner diameter of 270 mm.
0 g was put in a graphite punch and set in a hot press. Under a vacuum condition of 10 ^-5 to 10 ^-4 torr,
The temperature was raised from room temperature to 1200 ° C. over 4 hours and maintained at that temperature for 1 hour, and then raised to 1400 ° C. over 3 hours and maintained at that temperature for 4 hours. 500kgf /
pressurized with a pressure of cm ^2, under an argon atmosphere 2350 ° C.
Until 4 hours, and kept at that temperature for 3 hours to obtain a sintered body. The obtained sintered body has a thickness of 25 mm and a density of 3.
It was 15 g / cm ³ .

[Heat Treatment Step] The silicon carbide sintered body obtained above was further subjected to a heat treatment under the following conditions. The sintered body was placed in a graphite container and set in a heating furnace. After the vacuum condition was set to 10 ^-2 to 10 ^-3 torr, argon gas was charged into the heating furnace to maintain the pressure at 0.02 kg / cm ² . Next, the temperature is raised to a predetermined temperature of 2250 ° C. at a temperature rising rate of 100 ° C./hr, and the temperature is maintained for 3 hours.
, And the sintered body was taken out of the heating furnace.

(Example 2) A sintered body was obtained in the same manner as in Example 1 except that the maximum temperature of hot pressing in the production of the sintered body was 2300 ° C. This sintered body had a thickness of 25.5 mm and a density of 3.09. The obtained silicon carbide sintered body was subjected to a heat treatment under the same conditions as in Example 1. (Example 3) A sintered body was obtained in the same manner as in Example 1 except that the heating temperature in the heat treatment step was 1850 ° C.

(Comparative Example 1) A sintered body was obtained in the same manner as in Example 1 except that the heating temperature in the heat treatment step was 2370 ° C. Comparative Example 2 A sintered body was obtained in the same manner as in Example 1 except that the heating temperature in the heat treatment step was 1600 ° C. (Comparative Example 3) A sintered body obtained by the same hot press sintering process as in Example 1 but not subjected to heat treatment was used as a sintered body of Comparative Example 3.

[Evaluation of workability of sintered body]
The silicon carbide sintered bodies obtained in Comparative Examples 1 to 3 were ground under the following conditions, and their workability and the state of pores inside the sintered bodies were observed. Both surfaces of the obtained sintered body were ground by 1 mm with a surface grinder and evaluated by the following method. 1. Evaluation of flatness A flat plate sliced to a thickness of about 1.3 mm by wire discharge was ground to a thickness of 1 mm by inversion four times using a surface grinder, and the flatness was measured by a three-dimensional measuring device. For example, the allowable value of the flatness of a dummy wafer used in semiconductor manufacturing is
It is said to be 0.1 mm or less, and the smaller the value, the better the flatness.

2. Evaluation of Centering Workability A centering process of 200 mm in diameter was performed by wire discharge on a flat plate sliced to a diameter of 270 mm and a thickness of about 1.3 mm. When a circular hole was formed by hollowing, the result was evaluated as ○, and when chipping occurred during processing, the result was evaluated as ×. 3. Pore observation The surface of the sintered body was ground and polished to a surface roughness of 0.05 mm, and pores (pores) of 1 μm or more were observed with a Nomarski microscope (× 1000).

The results of the evaluation are shown in Table 1 below together with the heating conditions.

[0041]

[Table 1]

As is apparent from Table 1, it was found that the silicon carbide sintered body obtained by the production method of the present invention had excellent workability. In addition, after the sample ground to a thickness of 1 mm used in the evaluation of the flatness in Examples 1 to 3 was left at room temperature one month later, the flatness was evaluated in the same manner, and almost no change was observed. On the other hand, in Comparative Example 1 in which the heating temperature was too high, generation of pores was observed in the sintered body, and Comparative Example 2 in which the heating temperature was too low and Comparative Example 3 in which the heat treatment was not performed were all inferior in workability. there were.

[0043]

According to the method for manufacturing a silicon carbide sintered body of the present invention, carbonization excellent in workability, which does not cause defects such as chipping in slicing, cracking in punching, and warping after processing. A silicon sintered body can be easily manufactured.

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Claims (7)

[Claims] 1. When the sintering temperature in the hot press sintering step is Ts, the silicon carbide sintered body obtained through the hot press sintering step is 1.00 Ts ° C. to 0.70 Ts.
A method for producing a silicon carbide sintered body, comprising a step of performing a heat treatment in an inert atmosphere at a temperature range of ° C. 2. The silicon carbide sintered body according to claim 1, wherein the hot press sintering step includes a step of sintering a mixture of silicon carbide powder and a nonmetallic sintering aid. Manufacturing method. 3. The method for producing a silicon carbide sintered body according to claim 2, wherein the nonmetallic sintering aid covers the surface of the silicon carbide powder. 4. The silicon carbide sintered body obtained by the hot press sintering step has a density of 2.9 g / cm ³ or more and a free carbon content of 10% or less. 4. The method for producing a silicon carbide sintered body according to any one of items 3 to 3. 5. The production of a silicon carbide sintered body according to claim 2, wherein the non-metallic sintering aid is an organic compound that generates carbon by heating. Method. 6. The method for producing a silicon carbide sintered body according to claim 5, wherein the organic compound that generates carbon by heating is a resol-type phenol. 7. The silicon carbide sintered body obtained by the hot press sintering step, wherein the total content of elements other than silicon, carbon, oxygen and nitrogen is less than 5 ppm. 7. The method for producing a silicon carbide sintered body according to any one of items 1 to 6.