JPH0733528A - Composite sintered ceramic, its production and semiconductor production jig made therefrom - Google Patents

Abstract

PURPOSE:To decrease the amount of cationic metal other than Si and improve the purity, density and strength of a composite sintered ceramic by heat-treating a formed article composed of specific SiC powder in nitrogen atmosphere, thereby nitriding a part of SiC to form Si3N4 and C. CONSTITUTION:The composite sintered ceramic material containing Si3N4 and free carbon uniformly distributed in the sintered material and having a cationic metal content of <=100ppm excluding Si and a relative density of >=70% is produced by adding an organic binder to SiC powder having an average particle diameter of 0.5-10mum and containing <=200ppm of cationic metal other than Si, forming the mixture to a desired form, heat-treating the formed article to decompose and remove the binder and leave a formed article having a porosity of 30-56%, calcining the article, as necessary in a vacuum of <=10Torr at 1600-2100 deg.C for 0.5-12hr and heat-treating at 1500-1950 deg.C in an atmosphere having nitrogen partial pressure of 10-1,000atm to effect the nitridation of a part of SiC to form Si3N4 and C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic composite sintered body suitable for a high-purity jig for semiconductor production and a method for producing the same.

[0002]

2. Description of the Related Art A high-purity silicon carbide sintered body has been attracting attention as a material for a jig used in manufacturing a semiconductor element or the like, and its practical application is being promoted. Generally, a high-purity silicon carbide sintered body is obtained by densifying boron, which is known as a sintering aid for silicon carbide, an oxide of a Group 3a element of the periodic table, Al ₂ O ₃ or the like, without any addition. Yes, usually
It is produced by the reaction sintering method.

The reaction sintering method is a method in which carbon powder is added to high-purity silicon carbide powder and molded, and then this molded body is heated to 1200 ° C.
After heat treatment at the following temperature to prepare a porous body, the porous body is brought into contact with molten metallic silicon to allow the metallic silicon to permeate into the porous body by a capillary phenomenon, and then 1450 to 170.
A sintered body composed of only silicon carbide or silicon carbide and metallic silicon is obtained by reacting and sintering at about 0 ° C. to silicify carbon powder to generate silicon carbide in voids of a porous body. is there.

[0004]

However, according to the above-mentioned reaction sintering method, there is a problem that the corrosion resistance is remarkably lowered and the strength is deteriorated at a high temperature because an excessive amount of metallic silicon is contained. Moreover, although a jig for semiconductor manufacturing is required to have durability against a heat cycle, there is a problem that cracks are generated due to the heat cycle because the conventional sintered body is non-uniform.

Further, since the strength of the porous body composed of silicon carbide and carbon is very weak, there is a problem that cracks are generated in the sintered body due to generation of silicon carbide due to an exothermic reaction during the silicidation treatment of carbon.

[0006]

As a result of repeated studies on the above problems, the present inventors have noticed that nitriding silicon carbide produces silicon nitride and carbon. By nitriding the formed body, free carbon is uniformly generated together with generation of silicon nitride, and further, high density and high strength can be achieved by generation of silicon nitride, and the amount of cation metal other than Si can be increased. The inventors have found that a small amount of high-purity sintered body can be obtained, and have reached the present invention.

That is, the ceramic composite sintered body of the present invention is
A sintered body composed of silicon carbide, silicon nitride and free carbon, wherein the silicon nitride and the free carbon are substantially uniformly present in the sintered body and the amount of cation metal other than Si is 100 ppm or less. And a relative density of 70% or more, a skeleton having a three-dimensional network structure is formed from a composite of silicon carbide and silicon nitride. As a manufacturing method of such a ceramic composite sintered body, other than Si By heat-treating a compact made of silicon carbide powder having a cation metal content of 200 ppm or less in a nitrogen atmosphere to nitrid a part of the silicon carbide to generate silicon nitride and carbon. Amount less than 100ppm, relative density 7
After obtaining a sintered body of 0% or more or calcining the molded body, the molded body is heat-treated in a nitrogen atmosphere to nitride part of the silicon carbide to generate silicon nitride and carbon. It is characterized by obtaining a sintered body having a cation metal content other than Si of 50 ppm or less and a relative density of 70% or more. Thereby, the above-mentioned ceramic composite sintered body is used for a jig for semiconductor production.

The present invention will be described below with reference to examples.
Usually, in a silicon nitride sintered body or a silicon carbide sintered body, various sintering aids are required to achieve a certain degree of densification. However, in order to achieve high density and high purity of the sintered body, it is necessary to avoid adding the sintering aid as much as possible.

The present invention achieves densification by the nitriding reaction of silicon carbide without adding any sintering aid. According to this nitriding reaction of silicon carbide, silicon nitride and free carbon are generated, and at the same time, the density can be increased. By controlling the nitriding conditions at this time, a sintered body of silicon carbide, silicon nitride and free carbon is obtained.
Further, by such a reaction, a skeleton having a three-dimensional network structure in which silicon carbide and silicon nitride are intricately entangled with each other is formed in the sintered body. Therefore, in the sintered body of the present invention, since no sintering aid is added, the amount of cation metal other than Si is 100 ppm.
Hereinafter, a high density body is obtained, in which the relative density is controlled to 80 ppm or less and the relative density is 70% or more, particularly 80% or more.

In the present invention, the amount of the cation metal other than Si is controlled within the above range in order to suppress the influence on the element as much as possible when it is used in a jig or the like for manufacturing a semiconductor element. Was set to the above range in order to impart the mechanical strength required for the jig.

Next, the method for producing the sintered body of the present invention will be described. First, silicon carbide powder is used as a starting material. The silicon carbide powder to be used may be either α-type or β-type, and its particle size is preferably an average particle size of 0.5 to 10 μm in order to promote the subsequent nitriding reaction. The amount of metal impurities other than Si in the raw material powder needs to be as small as possible, and the amount of cation metal needs to be 200 ppm or less, particularly 150 ppm or less. This is because the amount of impurities in the raw material is 200p
If it exceeds pm, purification in the manufacturing process becomes insufficient,
This is because a high-purity final sintered body cannot be obtained.

The above-mentioned silicon carbide powder is formed into a desired shape by adding an organic binder and a dispersant, if desired, based on well-known molding methods such as press molding, extrusion molding, injection molding, casting molding, cold isostatic molding and the like. To mold. Then, the organic binder is decomposed and removed from the molded body by heat treatment.
The porosity of the molded body at this time is about 30 to 56%.

Next, the molded body is nitrided. The nitriding treatment is 1500 to 1000 in a nitrogen partial pressure of 10 to 1000 atm.
It is performed at a temperature of 1950 ° C. By this nitriding treatment, silicon carbide in the molded body reacts with nitrogen to generate silicon nitride and carbon, and the silicon carbide particles are firmly bonded by the generated silicon nitride to form a skeleton having a three-dimensional network structure. Further, the volume expansion at the time of conversion of silicon carbide into silicon nitride also progresses the densification as a whole to form a sintered body having a porosity of about 10 to 30% (relative density of 70 to 90%). Since the nitriding reaction at this time occurs in the entire molded body, silicon nitride and carbon are uniformly generated in the molded body. However, in producing silicon nitride and carbon, a concentration difference may occur between the surface portion and the inside. Therefore, the nitrogen partial pressure during nitriding treatment is preferably 10 to 500 atm and the nitriding temperature is 1550 to 195.
It is recommended to set it to 0 ° C.

In the sintered body after the nitriding treatment as described above,
Although silicon carbide, silicon nitride and free carbon are present, according to the present invention, it is desirable to control the nitriding time so that the amount of silicon nitride is 28% by weight or more and the amount of free carbon is 7% by weight or more. This is because if the nitriding is insufficient and the carbon content is less than 7% by weight, the density of the sintered body cannot be increased and a high density body cannot be obtained. By nitriding silicon carbide, the generated free carbon does not exceed 21% by weight. Further, according to the nitriding treatment, the amount of cation impurities in the molded body can be reduced, and can be reduced to 100 ppm or less by controlling the nitriding conditions.

Further, according to the present invention, in the above manufacturing process, the green body before nitriding is heated to 1600 to 2100 ° C., particularly 1
By performing the calcination treatment at 700 to 2000 ° C. under a reduced pressure of 10 torr or less, the amount of cationic impurities in the molded body can be further reduced, and the calcination treatment tends to improve the purity as the treatment time increases. , Practically 0.5-12
Time is appropriate. According to this calcination treatment, the amount of cation metal in the molded body can be significantly reduced as compared with that before the treatment. The amount of cationic impurities in the starting material is 200 ppm
When the amount is less than 50, the amount of cation metal in the final sintered body is 50
By controlling the calcination conditions and the nitriding conditions as below ppm, and further as in Examples described later, it is possible to reduce to below 10 ppm.

As another method for high purification, although not as effective as the above-mentioned calcination treatment, impurities existing on the surface of the molded body by immersing the sintered body after the nitriding treatment in aqua regia or the like. Purity can also be increased by dissolving and removing the components and then washing with pure water or exposing the molded body to a high temperature atmosphere of 800 to 1200 ° C. consisting of hydrochloric acid gas and a small amount of water vapor.

[0017]

The ceramic composite sintered body of the present invention does not contain auxiliary components at all, and does not contain free silicon, etc., and has a three-dimensional network structure skeleton made of a composite of silicon carbide and silicon nitride. Therefore, it has higher strength than the conventional silicon carbide sintered body by the reaction sintering method. Moreover, since densification is achieved without adding any auxiliaries or the like, and the amount of cation metal impurities is very small, it is necessary to avoid mixing of impurities especially in jigs for semiconductor device manufacturing. It can be applied to various manufacturing jigs and parts.

By calcining the green body before nitriding, the amount of cation impurities in the green body can be significantly reduced, the purity in the sintered body can be increased, and a semiconductor manufacturing treatment can be performed. It is especially useful for application as a ingredient. Further, the sintered body after nitriding has high strength of the skeleton itself because the silicon carbide crystal particles are formed by the three-dimensional network skeleton bonded by silicon nitride.

Further, in the conventional reaction sintering method, it is necessary to use high-purity silicon carbide powder, but according to the method of the present invention, since high purification can be achieved in the manufacturing process, the starting raw material is exceptionally high. The raw material cost can be reduced because it is not necessary to use a high-purity raw material.

[0020]

【Example】

Example 1 α-type silicon carbide powder (average particle size 0.5 μm, metal impurity amount 180 ppm) was thoroughly mixed with pure water as a solvent using a rubber lining pot and urethane balls, and PVA was added as a molding binder and dried. Granulation was performed.

The obtained granulated powder was die-pressed at a pressure of 1000 kg / cm ² to obtain a molded product having an outer diameter of 60 mm and a thickness of 20 mm, and the molded product was heated in vacuum to decompose and remove the binder. When the relative density of the molded body at this time was measured by the Archimedes method, it was 60%.

Next, this molded body was nitrided under the conditions shown in Table 1. The relative density of the obtained sintered body was measured by the Archimedes method, and the crystal phase was identified by X-ray diffraction measurement. Further, the sample cut out from the surface portion of the sintered body and the inside of the sintered body was crushed, and the total carbon amount, the total nitrogen amount and the free carbon amount were measured by a nitrogen-oxygen simultaneous analyzer (manufactured by LECO), and nitrogen was silicon nitride. The bonded carbon present as silicon carbide was determined by the difference between the total carbon content and the free carbon content, and the silicon carbide, silicon nitride and free carbon content were quantified. The amount of impurities was measured by ICP emission spectroscopy.

Further, as an evaluation of mechanical properties of the sintered body,
Four-point bending strength was measured based on JISR1601.
In addition, as a heat cycle test, the presence or absence of cracks was observed after carrying out in and out from room temperature to 1500 ° C. 10 times in an N ₂ atmosphere. The measurement results are shown in Table 1.

[0024]

[Table 1]

According to Table 1, the N ₂ pressure during the nitriding treatment is 10
The nitriding did not occur in the sample No. 1 lower than atm and the nitriding temperature lower than 1500 ° C. Further, in the sample No. 10 and the sample No. 11 where the N ₂ pressure is high, which is the condition for nitriding, the nitriding proceeds from the surface to the inside, but the difference in carbon amount between the inside and the outside occurred. As a result, cracks are generated in the heat cycle. From the viewpoint of repeated characteristics, the nitriding conditions are N ₂ pressure of 10 to 500 atm and nitriding temperature of 1550 to.
It can be seen that it is desirable to set the temperature to 1950 ° C. and suppress the difference between the inside and outside of the carbon amount within 20%.

Example 2 The molded body obtained in the same manner as in Example 1 was subjected to calcination treatment and nitriding treatment under the conditions shown in Table 2. In addition,
Sample Nos. 12 to 17 are obtained by changing the calcination conditions while keeping the nitriding conditions constant, and Samples No. 18 to 27 are samples No. 1 to 1 in Table 1.
A calcination treatment step of 1800 ° C. for 8 hours is added to the No. 10 condition. The characteristics of each of the obtained sintered bodies were evaluated in the same manner as in Example 1.

[0027]

[Table 2]

In Table 2, according to the samples No. 12 to 17, the effect of removing impurities is not remarkable in the sample No. 12 in which the calcination temperature is lower than 1600 ° C., and the decomposition of silicon carbide occurs above 2300 ° C. occured. In addition, sample No. 18-27
In comparison with the samples No. 1 to 10 in Table 1 regarding the amount of cation impurities in the final sintered body, it can be seen that the amount of cation impurities is significantly reduced by the calcination treatment.

Comparative Example 1 90 parts by weight of the silicon carbide powder used in Example 1 and 10 parts by weight of carbon powder (average particle size 2 μm) were mixed in a vibrating mill using a methanol solvent, and P was used as a molding binder.
VA was added and dry granulation was performed. The granules were molded with a die press at a molding pressure of 1000 kg / cm ² and an outer diameter of 40 m.
A disk-shaped molded product having a thickness of m and a thickness of 5 mm was obtained.

This molded body was treated under nitrogen at 5 atm at 1800 ° C. for 1 hour to form a porous body having a porosity of 48%. The porous body was brought into contact with molten metallic silicon at 1600 ° C. under vacuum to fill the voids of the porous body with metallic silicon and to carbonize the carbon. As a result, carbon disappeared, and formation of β-type silicon carbide was newly confirmed.

The bulk specific gravity of this sintered body is 2.82 g / c.
m ³ , the open porosity was 8%, and the bending strength was 20 kg / mm ² , and the density was low and the strength was low as compared with Examples 1 to 3 of the present invention. Furthermore, although metallic silicon was adhered to the surface of this sintered body, it adhered very firmly,
It could not be removed without polishing. Further, when the amount of cationic impurities was measured, it was 168 ppm,
It was found that the amount of impurities in the raw material was directly reflected and was not reduced in the manufacturing process.

Comparative Example 2 22% by weight of silicon carbide powder (average particle size 0.5 μm), 62% by weight of silicon nitride powder (average particle size 0.6 μm), and 16% by weight of carbon powder were mixed in a vibrating mill using methanol as a solvent. Then, PVA was added as a molding binder, and dry granulation was performed. Molding pressure of these granules is 1000kg using a die press.
A disk-shaped molded body having an outer diameter of 60 mm and a thickness of 20 mm was obtained at a pressure of / cm ² . The amount of cation impurities in this compact is 173 pp
It was m.

This compact was fired at 1800 ° C. for 1 hour in nitrogen atmosphere of 5 atmospheres. With this firing, sufficient densification was not possible, and the density of the obtained sintered body was 60% in relative density,
Its strength was as low as 70 MPa. Further, the amount of cationic impurities was as large as 170 ppm, and the amount of impurities in the starting material could not be reduced.

[0034]

As described above in detail, according to the present invention, high density can be achieved without adding any auxiliary agent, and in comparison with the conventional silicon carbide sintered body by the reaction sintering method. It has high strength and can achieve high purification.
As a result, the present invention can be applied to various manufacturing jigs, parts, etc. that need to avoid mixing of impurities such as jigs for manufacturing semiconductor elements.

Claims (4)

[Claims] 1. A sintered body composed of silicon carbide, silicon nitride and free carbon, wherein the silicon nitride and the free carbon are substantially uniformly present in the sintered body and a cation metal other than Si. An amount of 100 ppm or less, and a relative density of 70% or more, a ceramic composite sintered body. 2. The amount of cation metal other than Si is 200 ppm.
A molded body made of the following silicon carbide powder is heat-treated in a nitrogen atmosphere to nitride part of the silicon carbide to generate silicon nitride and carbon. The amount of cation metal other than Si is 100 ppm or less, and the relative density is Of 70% or more is obtained, a method for producing a ceramic composite sintered body. 3. The amount of cation metal other than Si is 200 ppm.
After calcination treatment of the following formed body made of silicon carbide powder,
A sintered body having a content of cation metals other than Si of 50 ppm or less and a relative density of 70% or more by heat-treating the formed body in a nitrogen atmosphere to nitride part of the silicon carbide to generate silicon nitride and carbon. A method for producing a ceramic composite sintered body, which comprises: 4. A sintered body composed of silicon carbide, silicon nitride and free carbon, wherein the silicon nitride and the free carbon are substantially uniformly present in the sintered body and a cation metal other than Si. A jig for semiconductor production, which comprises a ceramic composite sintered body having an amount of 100 ppm or less and a relative density of 70% or more.