JP2000143347A - Production of silicon carbide sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high purity, a high density and a high strength in excellent surface conditions and the electroconductivity with a slight dispersion by converting a silicon carbide powder, an organic substance or a carbon powder and a nitrogen source into a slurry form, forming the resultant slurry into a green compact, permeating metallic silicon through a carbon fiber assembly into pores in the green compact and filling the pores with silicon carbide. SOLUTION: A silicon carbide powder, an organic substance or a carbon powder composed of a carbon source and a nitrogen source are dispersed in a solvent to provide a slurrylike mixed powder, which is then cast into a forming mold and dried to afford a green compact. One end of a carbon fiber assembly is then brought into contact with the green compact in a vacuum/inert gas atmosphere and the other end is dipped in metallic silicon heated and melted at 1,450-1,700 deg.C to permeate the metallic silicon into pores of the green compact. The permeated silicon is reacted with free carbon in the green compact to produce silicon carbide. Thereby, the pores in the green compact are filled to produce a silicon carbide sintered compact.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-purity, high-density, high-strength, conductive, and conductive material useful as a component for semiconductor manufacturing equipment, a component for electronic information equipment, a vacuum device, and other structural components. The present invention relates to a method for producing a silicon carbide sintered body having a small variation in rate by a reaction sintering method.

[0002]

2. Description of the Related Art Conventionally, silicon carbide has been attracting attention as a material used in a high temperature range because of its good strength, heat resistance, thermal shock resistance, and abrasion resistance even at high temperatures exceeding 1000 ° C. It is used as a substitute for quartz as a jig for manufacturing semiconductors. One of the methods for producing the above-mentioned sintered body made of silicon carbide is a reaction sintering method. In this reaction sintering method, first, a silicon carbide powder and an organic substance or a carbon powder composed of a carbon source are dissolved and dispersed in a solvent to produce a slurry-like mixed powder. Next, the obtained mixed powder is subjected to a casting mold, an extrusion mold,
Pour into a press mold or the like and dry to obtain a green body. Next, the obtained green body is heated in a vacuum atmosphere or an inert gas atmosphere, immersed in molten metal silicon, and reacted with free carbon in the green body and silicon permeated into the green body by capillary action. This is a method of obtaining a silicon carbide sintered body. In this method, as shown in the schematic diagram of FIG. 2, the green body 10 is gripped by the clip 12 and at least the lower end of the green body 10 is immersed in the metal silicon 14 in a container 16 filled with heated and molten metal silicon 14. Lowering from the upper part, maintaining the state for a predetermined period of time, allowing the metallic silicon 14 to penetrate into the voids in the green body 10, and reacting the free carbon in the green body with the permeated silicon to form the silicon carbide sintered body. How to get. However, in this method, in a high temperature atmosphere,
The green body 10 is gripped and transported, and the metal silicon container 1
6 requires a heat-resistant device for immersion and pulling up, so that the entire device becomes complicated.
In order to hold the green body 10 above the container 16 filled with the molten metal silicon 14, the evaporated metal silicon 1
4 adheres to the surface of the green body 10 and precipitates, and phenomena such as formation of a metallic silicon film on the surface and inability of molten silicon to uniformly penetrate into the green body tend to occur. The silicon carbide sintered body could not obtain sufficient strength, for example, lacking uniformity and low bulk specific gravity.

Further, the present inventors have developed such a high density,
It was found that a sintered body having conductivity can be obtained by introducing nitrogen into a high-purity silicon carbide sintered body, and was filed earlier, but in practice, the variation in conductivity in the sintered body is reduced. Was desired.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-purity, high-density, high-strength, uniform property without requiring a complicated apparatus, having an excellent surface condition in appearance, and It is another object of the present invention to provide a method for producing a silicon carbide sintered body having less variation in conductivity.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a silicon carbide sintered body meeting this purpose can be manufactured by using a specific infiltration method, and has completed the present invention. did. That is, the method for producing silicon carbide of the present invention has the following configuration. [1] Silicon carbide powder, an organic substance or carbon powder comprising at least one carbon source, and at least one nitrogen source are dissolved and dispersed in a solvent to produce a slurry-like mixed powder. And a step of pouring the slurry-like mixed powder into a mold, drying the green body, and contacting one end of the carbon fiber aggregate with the green body under a vacuum atmosphere or an inert gas atmosphere. A step of immersing the other end of the carbon fiber aggregate in metallic silicon heated and melted at 1450 to 1700 ° C. to allow the metallic silicon to penetrate into pores in the green body via the carbon fiber aggregate by capillary action; Reacting the infiltrated silicon with the free carbon in the green body to generate silicon carbide to fill the pores in the green body. Production method.

[2] A silicon source containing at least one silicon compound, a carbon source containing at least one organic compound that generates carbon by heating, a nitrogen source containing at least one nitrogen compound, and a polymerization catalyst Or a cross-linking catalyst, and dissolving in a solvent, drying, and then calcining the obtained powder in a non-oxidizing atmosphere to produce a nitrogen-containing silicon carbide powder, and the nitrogen-containing silicon carbide Powder, an organic substance or carbon powder comprising at least one carbon source,
Is dissolved and dispersed in a solvent to produce a slurry-like mixed powder; a step of pouring the slurry-like mixed powder into a molding die and drying to produce a green body; Under an active gas atmosphere, one end of the carbon fiber aggregate is brought into contact with the green body, and the other end of the carbon fiber aggregate is
A step of immersing in metallic silicon heated and melted at 50 to 1700 ° C. to cause metallic silicon to penetrate into pores in the green body through a carbon fiber aggregate by a capillary phenomenon; Reacting the free carbon with the free carbon to form silicon carbide to fill pores in the green body, thereby producing a silicon carbide sintered body.

In the method of manufacturing a silicon carbide sintered body according to the present invention, when the heated and molten metallic silicon is infiltrated into the green body, the molten metallic silicon is passed through, for example, a string-like carbon fiber aggregate. Is transported by using the function of capillary action in the fine voids formed in the carbon fiber aggregate, and penetrates the pores in the green body, and one end of the carbon fiber aggregate is immersed in a molten metal silicon bath. However, since the infiltration can be carried out by means of contacting or wrapping the other end with the green body, uniform infiltration becomes possible and quality as compared with the conventional method of contacting or dipping the green body in the heated and molten metal silicon. It is considered that a sintered body that is uniform and has less variation in conductivity is obtained. Further, a lifting device for transporting the green body into contact with the metal silicon bath is not required, and the distance between the molten metal silicon bath and the green body can be separated to some extent. It is possible to effectively prevent a phenomenon in which metallic silicon is deposited on the body surface by cooling and is deposited by cooling, and an undesirable metallic silicon film is formed on the surface.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The method for producing a silicon carbide sintered body of the present invention includes a step of producing silicon carbide powder, a step of producing a slurry-like mixed powder from the silicon carbide powder, and a step of producing a green body from the mixed powder. The method includes a step of producing a silicon carbide sintered body from a green body and a step of introducing nitrogen at any timing, and is particularly characterized by a step of producing a silicon carbide sintered body from a green body. In the present invention, the green body refers to a silicon carbide molded body before reaction sintering having many pores and obtained by removing a solvent from a slurry-like mixed powder.

In the method for producing a silicon carbide sintered body of the present invention, nitrogen is introduced at the same time as adding a nitrogen source at the same time as adding a silicon source in the production process of the raw material silicon carbide powder, and A method of adding a carbon source to these raw material silicon carbide powders and adding a nitrogen source in the step of preparing a slurry. Here, the substance used as the nitrogen source is preferably a substance that generates nitrogen by heating. For example, a nitrogen-containing polymer compound (specifically, a polyimide resin or a polyamide resin) and a precursor thereof, hexamethylenetetramine, triethylamine And amines such as ammonia. Of these, hexamethylenetetramine is preferable from the viewpoint of handling. A phenol resin synthesized using hexamine as a catalyst and containing 2.0 mmol or more of nitrogen derived from the synthesis process per 1 g of the resin can also be suitably used as a nitrogen source. Only one nitrogen source may be used, or two or more nitrogen sources may be used in combination.

The step of producing the silicon carbide powder comprises the steps of: a silicon source containing at least one or more silicon compounds; a carbon source containing at least one or more organic compounds that generate carbon by heating; a polymerization or crosslinking catalyst; Is dissolved in a solvent, dried, and then the obtained powder is fired in a non-oxidizing atmosphere. During the production of this silicon carbide powder,
When a nitrogen source is added simultaneously with a silicon source, the silicon source, the carbon source and the catalyst are uniformly mixed and dissolved in a solvent together with the catalyst.
Thereafter, it may be carried out by a conventional method. When the nitrogen source is added at this timing, the amount of nitrogen is preferably 1 mmol or more per 1 g of the silicon source. And more preferably 700 μg to 1000 μg.

[0011] The step of producing a slurry-like mixed powder from the silicon carbide powder comprises dissolving and dispersing the silicon carbide powder and an organic substance or carbon powder comprising at least one or more carbon sources in a solvent. And a step of producing a slurry-like mixed powder. If a uniform and stable slurry-like mixed powder is prepared by sufficiently stirring and mixing at the time of dissolution and dispersion in a solvent, the green body obtained in the subsequent step of manufacturing the goon body has pores therein. It becomes uniformly dispersed. In order to prepare a uniform and stable slurry-like mixed powder, there may be mentioned means such as adjusting stirring and mixing conditions and adding a dispersing aid. When a nitrogen source is added in the step of producing the slurry-like mixed powder, the nitrogen source is added together with the silicon carbide powder, an organic substance comprising at least one or more carbon sources or carbon powder, and uniformly mixed. The nitrogen source is added at this timing, and the amount of nitrogen added is preferably 1 mmol or more per 1 g of silicon carbide powder. More preferably, the amount is 1500 μg to 2000 μg.

The silicon carbide powder, which is the raw material of the mixed powder,
From the viewpoint of the purity of the sintered body, it is preferable to use a high-purity product, but it is difficult to procure a high-purity commercially available raw material, and prior to the step of preparing these slurry-like mixed powders,
It is preferable to carry out a step of producing a high-purity silicon carbide powder. Here, a method for producing a high-purity silicon carbide powder will be described in detail. In the present invention, silicon carbide powder used as a raw material of the silicon carbide sintered body is α
Type, β type, amorphous or a mixture thereof. In order to obtain a high-purity silicon carbide sintered body,
It is preferable to use high-purity silicon carbide powder as the raw material silicon carbide powder.

[0013] The grade of the β-type silicon carbide powder is not particularly limited, and for example, generally commercially available β-type silicon carbide powder can be used.

The particle size of the silicon carbide powder is preferably small from the viewpoint of increasing the density, and specifically, 0.01%.
About 10 μm, more preferably 0.05 to 5 μm
It is. If the particle size is less than 0.01 μm, handling in processing steps such as measurement and mixing tends to be difficult, and
If it exceeds 0 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, which is not preferable.

The high-purity silicon carbide powder includes, for example, a silicon source containing at least one or more silicon compounds, at least one or more carbon sources containing an organic compound that generates carbon by heating, a polymerization or crosslinking catalyst, Is dissolved in a solvent and dried, and then the obtained powder is calcined in a non-oxidizing atmosphere.

A silicon source containing the silicon compound (hereinafter referred to as “silicon compound”)
As the silicon source), a liquid source and a solid source can be used in combination, but at least one type must be selected from liquid sources. 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, propoxysilane, butoxysilane and the like, and ethoxysilane is preferred from the viewpoint of handling. Examples of the tetraalkoxysilane polymer 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. Examples of solid materials that can be used in combination with these include silicon oxide. In the present invention, the silicon oxide includes, in addition to SiO, silica sol (colloidal ultrafine silica-containing liquid, containing OH groups and alkoxyl groups therein), silicon dioxide (silica gel, fine silica, quartz powder) and the like. These silicon sources may be used alone or in combination of two or more.

Among these silicon sources, from the viewpoint of good homogeneity and handling properties, tetraethoxysilane oligomers and mixtures of tetraethoxysilane oligomers with finely divided silica are preferred. In addition, a high-purity substance is used for these silicon sources, and the initial impurity content is preferably 20 ppm or less, more preferably 5 ppm or less.

As the carbon source containing an organic compound that produces carbon by heating (hereinafter, appropriately referred to as a carbon source), a liquid source and a liquid source and a solid source can be used in combination. Organic compounds that have a high carbon content and polymerize or crosslink by catalyst or heating, specifically, for example, monomers and prepolymers of resins such as phenolic resins, furan resins, polyimides, polyurethanes, and polyvinyl alcohol are preferable, and cellulose, Examples thereof include liquid substances such as sucrose, pitch, and tar, and a resol-type phenol resin is particularly preferable. These carbon sources may be used alone or in combination of two or more. The purity can be controlled and selected as appropriate depending on the purpose. In particular, when high-purity silicon carbide powder is required, it is desirable to use an organic compound containing no metal at 5 ppm or more.

The polymerization and crosslinking catalyst used in the production of high-purity silicon carbide powder can be appropriately selected according to the carbon source. When the carbon source is a phenol resin or a furan resin, toluene sulfonic acid, toluene carboxylic acid, acetic acid Oxalic acid, sulfuric acid and the like. Among these, toluenesulfonic acid is preferably used.

The ratio of carbon to silicon (hereinafter abbreviated as C / Si ratio) in the step of producing the high-purity silicon carbide powder, which is the raw material powder used in the present invention, is set to 1000 for the mixture.
It is defined by elemental analysis of a carbide intermediate obtained by carbonization at ° C. Stoichiometrically, when the C / Si ratio is 3.0, the free carbon in the generated silicon carbide should be 0%, but actually, the low C / Si ratio is caused by the volatilization of the simultaneously generated SiO gas. , Free carbon is generated. It is important to determine the composition in advance so that the amount of free carbon in the produced silicon carbide powder does not become an unsuitable amount for the production use of a sintered body or the like. Usually, in the case of 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, when firing at a low or high pressure in the atmosphere, the C / Si ratio for obtaining pure silicon carbide varies, and in this case, the C / Si ratio is not necessarily limited to the above range.

In the present invention, the silicon source and the carbon source containing the organic compound are dissolved in a solvent and dried to obtain a powder. The mixture may be cured to form a powder, if necessary. Examples of the curing method include a method of crosslinking by heating, a method of curing with a curing catalyst, and a method of electron beam or radiation. As a curing catalyst,
Although it can be appropriately selected according to the carbon source, in the case of a phenol resin or a furan resin, acids such as toluenesulfonic acid, toluenecarboxylic acid, acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, and maleic acid, and amines such as hexamine are used. Used. These mixed catalysts are dissolved or dispersed in a solvent and mixed. Examples of the solvent include lower alcohols (for example, ethyl alcohol and the like), ethyl ether, acetone and the like.

A silicon source and a carbon source containing an organic compound which generates carbon by heating are dissolved in a solvent, and the dried powder is heated and carbonized. This is performed at 800 ° C. to 1000 ° C. for 30 minutes to 12 minutes in a non-oxidizing atmosphere such as nitrogen or argon.
This is done by heating the powder for 0 minutes.

Further, the carbide is heated at 1350 ° C. to 2000 ° C. in a non-oxidizing atmosphere such as argon to produce silicon carbide. The firing temperature and time can be appropriately selected according to the desired properties such as the particle size, but firing at 1600 ° C. to 1900 ° C. is desirable for more efficient production.

When a silicon carbide 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-mentioned firing.

As a method for obtaining a silicon carbide powder having a higher purity than the above-mentioned method, a method for producing a raw material powder described in the method for producing a single crystal of Japanese Patent Application Laid-Open No. 9-48605 filed by the present applicant, A mixture obtained by using at least one selected from high-purity tetraalkoxysilane and a tetraalkoxysilane polymer as a silicon source, and using a high-purity organic compound that generates carbon by heating as a carbon source, and uniformly mixing these. Is heated and fired in a non-oxidizing atmosphere to obtain a silicon carbide powder, and the obtained silicon carbide powder is kept at a temperature of 1700 ° C. or more and less than 2000 ° C. ℃ ~ 2100 ℃
And a post-treatment step of performing heating at least once at a temperature of 5 to 20 minutes to obtain a silicon carbide powder having a content of each impurity element of 0.5 ppm or less by performing the two steps. And a method for producing a high-purity silicon carbide powder characterized by the following. Since the silicon carbide powder thus obtained is not uniform in size, it is processed by pulverization and classification so as to conform to the particle size.

Next, the step of producing a slurry-like mixed powder from silicon carbide powder will be described in more detail.
The step of producing a slurry-like mixed powder from silicon carbide powder comprises dissolving or dispersing silicon carbide powder, an organic substance or carbon powder comprising at least one or more carbon sources, and optionally a nitrogen source in a solvent. Thus, a slurry-like mixed powder is produced, and pores can be uniformly dispersed in the green body by sufficiently stirring and mixing when dissolving and dispersing in a solvent.

In the step of producing a slurry-like mixed powder from silicon carbide powder, examples of the organic substance comprising a carbon source used together with the silicon carbide powder include an organic compound which generates carbon by heating. The organic substance composed of a carbon source may be used alone, or two or more kinds may be used in combination. Further, it may be used in combination with a carbon powder described later.

Examples of the organic compound which forms carbon by heating include coal tar pitch, pitch tar, phenol resin, furan resin, epoxy resin, phenoxy resin, monosaccharides such as glucose, oligosaccharides such as sucrose, etc.
Various sugars such as polysaccharides such as cellulose and starch are exemplified. 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 resol-type phenol resin is preferable.

In the step of producing a slurry-like mixed powder from silicon carbide powder, the carbon powder used together with the silicon carbide powder includes pyrolytic carbon such as carbon black and acetylene black, graphite, activated carbon, and water dispersible powder. Carbon is mentioned, and carbon black is particularly preferred.

In a step of producing a slurry-like mixed powder from silicon carbide powder (hereinafter, appropriately referred to as a slurry preparation step), silicon carbide powder and an organic substance or carbon powder comprising a carbon source are dissolved in a solvent. Water may be used as a solvent to be dispersed and used for producing a slurry-like mixed powder, but for example, for a phenol resin which is a suitable organic compound that generates carbon by heating, a lower-grade solvent such as ethyl alcohol is used. Alcohols and ethyl ether,
Acetone is preferred. It goes without saying that it is preferable to use an organic substance composed of a carbon source, a carbon powder, and a solvent having a low impurity content, which are used in the slurry preparation step.

In the slurry preparation step using silicon carbide powder or the like, an organic binder may be added for the purpose of improving the dispersion stability of the powder. As an organic binder,
Peptizers, powder binders, and the like, and as the deflocculant, a nitrogen-based compound is preferable in terms of further increasing the effect of imparting conductivity; for example, ammonia and ammonium polyacrylate are preferably used. Used. As the powder binder, polyvinyl alcohol, urethane resin (for example, water-soluble polyurethane) or the like is preferably used. In addition, an antifoaming agent may be added. Examples of the antifoaming agent include a silicone antifoaming agent.

The amount of the organic substance composed of a carbon source mixed with the silicon carbide powder is 10% to 50% as the amount of carbon.
Is more preferable, and more preferably 15% to 40%.
When the content is less than 10%, when silicon is infiltrated and converted into SiC in a process of manufacturing a silicon carbide sintered body from a green body, carbon is insufficient, and Si which cannot be deposited in the reaction contains 5% in the pores.
% Or more, it becomes difficult to obtain conductivity. On the other hand, if it exceeds 50%, the thixotropy of the slurry tends to be large, and the moldability tends to be inferior.

In the present invention, the stirring and mixing in each step can be performed by a known stirring and mixing means, for example, a mixer, a planetary ball mill or the like. Stir and mix 10-3
It is preferably carried out for 0 hour, especially for 16 to 24 hours.

The step of producing a green body from the slurry-like mixed powder will be described in detail. In order to cast the slurry-like mixed powder into a mold, generally, casting is suitably used. The slurry-like mixed powder is poured into a mold at the time of casting, left to stand, and then demolded.
By removing the solvent by heating or air drying under a temperature condition of 0 ° C., a green body having a specified size can be obtained. Usually, heat drying is preferable, and drying is performed at 50 ° C to 8 ° C.
Perform at about 0 ° C. for 10 to 30 hours. The green body may be calcined at a temperature condition of 1200 to 2400 ° C. for a holding time of about 10 to 120 minutes to obtain a calcined green body before the metal silicon is continuously infiltrated. From the viewpoint of the permeability of metallic silicon in the subsequent process, it is preferable to use a calcined green body. However, if the target sintered body has a small volume and is a machine tool part, a calcining step is not necessarily required. do not do. In the case of producing a large-volume sintered body that is cut and used by electric discharge machining or the like, it is preferable to perform calcination from the viewpoint of production efficiency. In the calcination step, the solvent remaining in the voids of the green body is preferably used. This is considered to be because the metal silicon is completely removed, the permeability of the metal silicon by the capillary action is improved, and the voids in the green body having a large area can be filled with the metal silicon in a short time.

The step of producing a silicon carbide sintered body from a green body (including a calcined green body) will be described in more detail. The green body obtained as described above is impregnated with metallic silicon, and the silicon and silicon carbide generated by reacting the silicon with the free carbon present in the green body fill the pores in the green body with a high density. First, a step of infiltrating metal silicon heated and melted at 1450 to 1700 ° C. into pores in the green body in a vacuum atmosphere or an inert gas atmosphere is performed. FIG. 1 is a schematic view showing an example of a state in which a step of infiltrating molten metal silicon into pores in a green body is performed in a manufacturing method of the present invention. As shown in FIG.
The permeation of the metallic silicon 14 into the green body 12 is performed via the carbon fiber aggregate 18. One end of the carbon fiber assembly 18 is brought into contact with the green body 10, and the other end of the carbon fiber assembly 18 is placed at least at the lower end of the green body 10 in a container 16 filled with metallic silicon 14 heated and melted at 1450 to 1700 ° C. Is immersed in the metal silicon 14, the liquid metal silicon 14 penetrates into the voids of the carbon fiber aggregate 18 by capillary action, and further gradually penetrates through the pores in the green body 10. While maintaining that state for a predetermined time, the metal silicon 14 penetrates into the voids in the green body 10. Silicon 14 permeated into green body 10
Reacts with free carbon in the green body 10 to generate silicon carbide, and the silicon carbide fills pores in the green body, so that a high-density silicon carbide sintered body can be obtained. Since the reaction between silicon and free carbon occurs in a temperature range of about 1420 to 2000 ° C. as shown in the process of manufacturing silicon carbide powder, molten high-purity metallic silicon heated to 1450 to 1700 ° C. is contained in the green body. At the stage of infiltration into the carbon, the reaction with free carbon proceeds without any special operation.

Further, as shown in FIG. 3, the reactor may be separated into two chambers by a shielding wall 20 provided with an opening through which the carbon fiber aggregate 18 penetrates. Shielding wall 20
Is provided, the influence of the evaporated metal silicon on the silicon carbide sintered body to be manufactured can be further reduced.

High-purity metallic silicon is 1450-170
Melting is performed by heating to 0 ° C., preferably 1550 to 1650 ° C. If the melting temperature is lower than 1450 ° C., the viscosity of the high-purity metallic silicon increases, so that the high-purity metallic silicon does not penetrate into the green body due to the capillary phenomenon. If it exceeds 300, evaporation will be remarkable and the furnace body will be damaged. Here, the furnace atmosphere temperature is preferably in the range of 1450 to 1700 ° C. in order to maintain the infiltration of the molten metal silicon and promptly generate the silicon carbide generation reaction.
The time to supply the metallic silicon to the green body by immersing the carbon fiber aggregate in the molten metal silicon is the length, diameter, length of the carbon fibers constituting the carbon fiber aggregate, fiber diameter, Further, it is appropriately determined according to the size of the voids in the green body and the total volume of the voids, but is generally about 20 minutes to 3 hours.

Examples of the high-purity metallic silicon include powdered, granular, and massive metallic silicon, and from the viewpoint of easy melting, massive metallic silicon having a particle size of 2 to 5 mm is preferably used. In the present invention, high purity in high purity metal silicon means that the content of impurities is 1 pp.
means less than m.

The carbon fiber aggregate used for infiltrating metallic silicon is not particularly limited as long as fine voids through which molten metallic silicon can penetrate can be formed between carbon fibers by capillary action. Examples include bundled or cord-like aggregates such as twisted cords, elongated ones of randomly aggregated carbon fibers, and sheet-like aggregates of fibers entangled like non-woven fabric. it can. There is no particular limitation on the carbon fibers forming the aggregate, and the raw material is polyacrylonitrile (PAN).
System, rayon system, or pitch system, and the size is arbitrary. The size may be appropriately selected in consideration of the ease of forming the aggregate and the size of the formed void. As a preferable carbon fiber aggregate, a strand of about 1,500 to 12,000 denier (167 to 1,335 tex) is used for 2 to 2 strands.
3 yarns twisted under the conditions of a twist number of 85 to 220 (times / m), felt-like carbon fibers having a bulk density of 0.01 to 0.5 g / cm ³ and an apparent thickness of about 1.0 to 15.0 mm A string-shaped body formed by cutting the aggregate to a width of about 2 to 8 mm is exemplified. These are, for example, Crecus Liver /
It is available as yarn, Crecafelt (all trade names made by Kureha Chemical Co., Ltd.) and the like. In order to prevent impurities from being mixed during the permeation of the carbon fiber aggregate, it is preferable that the carbon fibers used here also contain as little impurities as possible.

The position where the fiber assembly is brought into contact with the green body is arbitrary, and can be selected according to the shape of the green body. For example, in the case of a cylindrical green body, the contact position may be the end face of the cylinder or the side face. And it may be at the end of the side surface or at the center, but from the viewpoint of permeation efficiency, it is preferable to make contact with the side surface. Also. As a contact method, a method of simply contacting the end of the aggregate to the surface of the green body, another dense body of the contacted fiber aggregate, for example, a method of pressing against the surface of the green body with a graphite block or the like, Examples include a method of winding a string-like carbon fiber aggregate to make contact therewith, and a method of pressing an end portion of the contacted fiber aggregate to the surface of the green body and a method of winding a string-like carbon fiber aggregate to make contact therewith. This is a preferred embodiment from the viewpoint of permeation efficiency.

By passing through the carbon fiber aggregate as described above, the metallic silicon penetrates into the green body at a uniform speed without being substantially affected by the evaporated silicon. The dispersed free carbon and the silicon gradually react with each other, and the generated silicon carbide fills the pores in the green body, whereby a high-density, high-strength, uniform silicon carbide sintered body can be obtained. The silicon carbide sintered body obtained by the above manufacturing method is sufficiently densified, and has a density of 2.9 g / cm ³ or more.

The total content of impurity elements in the silicon carbide sintered body obtained by the production method of the present invention is 10 ppm or less,
The content is preferably 5 ppm or less, but 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. Practically, 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 the silicon carbide sintered body under predetermined heating conditions using various practical devices by various means. According to the production method of the present invention, the total content of impurity elements contained in the silicon carbide sintered body can be reduced to 10 ppm or less. Here, the impurity element belongs to a group 1 to group 16 element in the periodic table of the revised edition of the 1989 IUPAC inorganic chemical nomenclature,
And atomic number 3 or more, and atomic numbers 6 to 8 and 1
Refers to elements other than element 4.

The silicon carbide sintered body obtained by the method of the present invention as described above is subjected to processing such as processing, polishing, and washing according to the purpose of use. The silicon carbide sintered body obtained by the production method of the present invention has high strength and uniform characteristics, and has a small variation in electric conductivity. Therefore, the silicon carbide sintered body is suitably used for semiconductor production parts, electronic information equipment parts, and the like. be able to.

In the production method of the present invention, as long as the heating conditions can be satisfied, there is no particular limitation on the production apparatus and the like, and a general-purpose heating furnace or reaction apparatus can be appropriately selected without adding any special apparatus. Can be used.

[0045]

EXAMPLES The present invention will be specifically described below with reference to examples, but is not limited to the examples unless it exceeds the gist of the present invention. (Example 1) As silicon carbide powder, a central particle diameter of 1.1 µm
m high-purity silicon carbide powder (impurity content 5 pp manufactured according to the manufacturing method described in JP-A-9-48605).
m or less of silicon carbide: containing 1.5% by weight of silica) 85
0g, carbon black (HTC-S
L: manufactured by Shinnichi Kagaku Co., Ltd.) 150 g, 5 g of hexamethylenetetramine as a nitrogen source, and 500 g of water in which 9 g of polyammonium ammonium acrylate was dissolved, and dispersed and mixed in a ball mill for 16 hours. 30 g of water-soluble polyurethane ("Yukote" manufactured by Sanyo Chemical) as
Silicone defoamer (“KM72A” manufactured by Shin-Etsu Chemical Co., Ltd.)
10 g was added, and the mixture was further dispersed and mixed by a ball mill for 10 minutes to produce a slurry-like mixed powder having a viscosity of 1.7 poise.

The slurry-like mixed powder is 150 m long.
m, cast into a cylindrical plaster mold with a diameter of 10 mm, 12
After drying at 50 ° C. for a time, it was calcined at 1600 ° C. in a vacuum atmosphere. The heating rate is 1 ° C./min up to 800 ° C., 160
The temperature was set to 5 ° C./min up to 0 ° C., and the holding time was set to 10 minutes.

The calcined body was measured for bulk density, porosity and bending strength by a three-point bending test according to the Archimedes' method by the following method.
The porosity was 34.3% and the bending strength was 13.3 MPa. Next, the green body 10 was arranged as shown in FIG. It was arranged in a crucible 16 made of graphite having a height of 200 mm. Inner diameter 60mm, height 50mm
A high-purity metallic silicon powder (particle size: 2 to 5 μm, manufactured by High-Purity Chemical Laboratory) is placed in a graphite crucible 17 and the other end of the carbon cord 18 is inserted into the container 17 so as to touch the silicon powder. did. Then, the temperature was raised to 1580 ° C. in an argon atmosphere and the temperature was maintained for 30 minutes to melt the metal silicon powder, and the carbon fiber aggregate 18 was formed by capillary action.
Then, the molten metal silicon 14 permeated into the green body 10 through the green body and the free carbon of the green body were reacted and sintered by reaction to obtain a silicon carbide sintered body.

Example 2 850 to 800 g of silicon carbide powder and 150 to 100 g of carbon black
A silicon carbide sintered body of Example 2 was produced in the same manner as in Example 1 except that a slurry having a viscosity of 1 poise was obtained and used.

(Comparative Example 1) Cord-like carbon fiber aggregate 18
Using the apparatus shown in FIG. 2, the green body 10 is gripped with the clip 12 and heated and melted.
Except that at least the lower end of the green body 10 was lowered from the top so as to be immersed in the metal silicon 14, and kept in that state for 30 minutes to allow the metal silicon 14 to permeate the green body 10. A silicon carbide sintered body of Comparative Example 1 was manufactured in the same manner as in Example 1.

<Evaluation> The obtained silicon carbide sintered bodies of Examples 1 and 2 and Comparative Example 1 were each measured for bulk density and porosity by the Archimedes method shown below, and for bending strength by a three-point bending test. And measurement of the variation in the resistance value.

(Method for Measuring Density and Porosity by Archimedes Method)
Performed according to SR1634. Table 1 shows the results.

(Three-point bending test) The three-point bending test of the silicon carbide sintered body was performed according to JIS R1601. However, the sample length was 60 mm and the span was 50 mm. Table 1 shows the results.

[0053]

[Table 1]

From Table 1, it can be seen that the silicon carbide sintered bodies of Examples 1 and 2 have the same bulk density and no large difference in comparison with the sintered body of Comparative Example 1 even though the same material is used. It was found that the porosity was rather low and the bending strength was excellent. In the sintered body of Comparative Example 1, the formation of a film having a metallic luster due to the metallic silicon deposited on the surface was observed, but the sintered bodies of Examples were all uniform and had excellent surface appearance. Condition.

(Measurement Method of Resistance Variation) A sample having a length of 60 mm, a width of 15 mm, and a thickness of 3 mm was prepared in a silicon carbide sintered body, and measurement points were set at 10 mm intervals in the length direction, and 5 points were determined. Volume resistivity of "Lorester A" manufactured by Mitsubishi Chemical Corporation
P "was measured by a four-terminal four-probe method. Table 2 below shows the measurement results and the results of calculating the standard deviation of the data.

[0056]

[Table 2]

As shown in Table 2, the silicon carbide sintered body of the example is
It was found that there was little variation in the volume resistivity depending on the measurement location, and that it had uniform conductivity. On the other hand, the sintered body of Comparative Example 1 was found to have a large variation in volume resistivity depending on the measurement location, even though the same material was used.

[0058]

As described above, according to the present invention, a complicated device is not required, the surface condition is excellent in appearance, high purity, high density, high strength and uniform characteristics are obtained. A method for producing a silicon carbide sintered body with less variation in conductivity can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a step of infiltrating metal silicon into pores in a green body via a carbon fiber polymer in a production method of the present invention.

FIG. 2 is a schematic view showing one embodiment of a step of infiltrating metal silicon into pores in a green body in a conventional reaction sintering method.

FIG. 3 is a schematic diagram showing an embodiment in which the step of infiltrating metallic silicon into pores in a green body via a carbon fiber polymer is performed using a two-chamber reaction furnace.

[Explanation of symbols]

 Reference Signs List 10 green body 14 molten metal silicon 16 metal silicon container (graphite crucible) 18 carbon fiber aggregate

Claims (2)

[Claims] 1. A slurry-like mixed powder is obtained by dissolving and dispersing a silicon carbide powder, an organic substance or carbon powder comprising at least one carbon source, and at least one nitrogen source in a solvent. A step of producing, a step of pouring the slurry-like mixed powder into a molding die and drying to produce a green body; and a step of forming one end of a carbon fiber aggregate into the green body under a vacuum atmosphere or an inert gas atmosphere. Contacting, immersing the other end of the carbon fiber aggregate in metallic silicon heated and melted at 1450-1700 ° C., and infiltrating metallic silicon into pores in the green body via the carbon fiber aggregate by capillary action. And the infiltrated silicon, free carbon in the green body,
Reacting to produce silicon carbide to fill pores in the green body, and a method for producing a silicon carbide sintered body. 2. A silicon source containing at least one silicon compound, a carbon source containing at least one organic compound that generates carbon by heating, a nitrogen source containing at least one nitrogen compound, a polymerization catalyst or A step of producing a nitrogen-containing silicon carbide powder by dissolving a cross-linking catalyst and a solvent in a solvent and drying, and then firing the obtained powder in a non-oxidizing atmosphere to produce a nitrogen-containing silicon carbide powder. And dissolving and dispersing an organic substance or carbon powder comprising at least one carbon source in a solvent to produce a slurry-like mixed powder; and forming the slurry-like mixed powder into a molding die. Pouring and drying to produce a green body; and contacting one end of the carbon fiber aggregate with the green body under a vacuum atmosphere or an inert gas atmosphere, and bringing the other end of the carbon fiber aggregate to 1450 to 1700 ° C. Addition A step of immersing in hot and molten metal silicon to infiltrate the metal silicon into the pores in the green body through the carbon fiber aggregate by a capillary phenomenon, and the infiltrated silicon and free carbon in the green body,
Reacting to produce silicon carbide to fill pores in the green body, and a method for producing a silicon carbide sintered body.