JP2002201070A - Silicon carbide sintered compact and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wetting property of silicon carbide sintered compact mixed with boron or carbon as sintering assistant, to formed films or various kinds of adhesives. SOLUTION: The silicon carbide sintered compact having pores with mean diameter of 5-40 μm, the mean crystal grain diameter of which is 5-40 μm, and the relative density of which is 90-99.5%, is formed with fine ruggedness by eliminating grain boundary layer on surface part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide sintered body used for coating a surface of a sintered body chemically or physically and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION In 1974, Prochazka of the United States
Has announced that adding a small amount of boron and carbon as a sintering aid to β-SiC with a submicron particle size will result in a dense sintered body.
It has been widely and commonly used as a material capable of overcoming high stress loading conditions.

[0003] Generally, as the densification progresses, the strength,
Since the mechanical and thermal material properties such as hardness and thermal conductivity are increased, a method for manufacturing a denser silicon carbide sintered body has been studied.
It has been devised. The present inventor has also obtained a silicon carbide sintered body having a thermal conductivity of 190 W / mK or more by densifying the silicon carbide sintered body.

Similarly, for the purpose of improving the sinterability and the fracture toughness of the sintered body, a sintering aid such as aluminum oxide or the like which generates a liquid layer component around the crystal grain boundaries in the sintering process is used. Silicon carbide to be added has also been devised.

On the other hand, porous silicon carbide having a high porosity has been studied in order to improve the sliding characteristics when a silicon carbide sintered body is used as a sliding member.

[0006] Often, these ceramic structural materials are coated with a film formed by CVD, PVD or the like. In addition, other objects may be bonded to the ceramic structural member using various kinds of adhesives such as organic and inorganic materials.

The problem here is the wettability between the ceramic sintered body and the resulting film and various adhesives. To improve this, the crystal grain boundary is covered as a vitreous matrix. The surface of the ceramic sintered body existing in the above is etched by a chemical treatment or the like to form fine irregularities on the surface, and a method of improving wettability is often used (Hiroshi Suzuki High Temperature Ceramic Material Nikkan Kogyo Shimbun) Company
reference).

For example, an alumina sintered body and a silicon carbide sintered body to which aluminum oxide is added as a sintering aid are present in a form in which crystal grain boundaries are covered as a vitreous matrix. Because the vitreous matrix at the grain boundaries is selectively etched,
As a result, fine irregularities around the crystal grain size are likely to occur on the surface of the sintered body, and the generated film and various adhesives enter the irregularities, so that the formed product film and various adhesives become wedges and become wedges. Adhesion between the sintered body and various kinds of adhesives and the like, that is, an anchor effect is generated.

The anchor effect is based on the mechanism that the wettability of the formed film and various adhesives is improved.

[0010]

However, a silicon carbide sintered body to which boron or carbon is added as a sintering aid has a problem that the formed film and various adhesives have poor wettability as compared with other sintered bodies. There is.

That is, as shown in FIG. 1, a silicon carbide sintered body in which boron or carbon is added to a sintering aid is a solid layer sintering that does not generate a liquid layer component in the sintering process. Since there is no vitreous matrix around the crystal grain boundaries, even if chemical etching is performed, the effect is thin, there is not much fine unevenness, the anchor effect is not enough, and the wettability is not much improved. It cannot be done.

Another method is to use a relative density of 90%.
Although there is a method using less than porous silicon carbide, this sintered body has many pores on its surface, so that the resulting film and the adhesive have good wettability. The mechanical properties were significantly inferior to the dense body.

For example, a lap plate, which is a polishing jig of a semiconductor manufacturing apparatus, fixes a silicon wafer, which is a material to be polished, with wax. In order to provide additional performance, a film may be formed on the surface by a method such as CVD or PVD.

In this silicon carbide wrap plate, from the viewpoints of thermal conductivity, wear resistance, etc., boron,
The use of a silicon carbide sintered body to which carbon is added is expected, but the adhesion strength of the generated film is low for the above-described reasons. Therefore, a generated film for coating the surface or a wax used for bonding a silicon wafer. However, there is a problem that the flakes are easily peeled.

[0015]

SUMMARY OF THE INVENTION In view of such problems of the prior art, the present inventor has set a comparatively high density in a silicon carbide sintered body in which boron or carbon is added to a sintering aid. The present invention has devised a method of manufacturing a silicon carbide sintered body in which fine irregularities are formed on the surface by chemical means such as etching and the adhesion of an adhesive or a formed film is high due to the anchor effect.

That is, according to the present invention, the sintered body has an average diameter of 5 to 40.
It has pores of μm, an average crystal particle diameter of 5 to 40 μm, a relative density of 90 to 99.5%, and has fine irregularities formed by removing a crystal grain boundary layer on the surface. Further, the crystal grain boundary layer on the surface portion is removed by a chemical means.

Further, as a method for producing the same, a carbon source containing silicon carbide as a main component, not more than 2.0% by weight,
A starting material containing a boron source of not more than 5% by weight is formed into a predetermined shape, a temperature rising rate gradient from room temperature to 1500 to 1950 ° C. is 20 to 200 ° C. per hour, and the maximum firing temperature is 20.
After firing at 00 to 2200 ° C., the grain boundary layer on the surface of the sintered body was removed by a chemical method, for example, using a mixed molten salt of potassium nitrate and sodium hydroxide.

Since the sintered body obtained in this manner has voids around the crystal grains which have grown relatively large while being relatively dense, after the etching treatment is performed, finely divided particles which are appropriately dispersed are obtained. A sintered body base material surface having irregularities can be obtained.

As a result, since the wettability is very good and the anchor effect is high, very high adhesion to the resulting film and the adhesive can be obtained.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The silicon carbide sintered body of the present invention has pores having an average diameter of 5 to 40 μm and an average crystal particle diameter of 5 to 40 μm.
40 μm, relative density is 90 to 99.5%, and irregularities are formed by removing the grain boundary layer on the surface. Thereby, the wedge effect due to the unevenness difference between the pore-free portion and the pore portion is enhanced, and a case where a coating film is generated on the surface of the sintered body by a chemical or physical method,
The wettability when applying an inorganic adhesive or the like increases.

Here, the average grain size and the average pore size are 5 μm.
When it is less than m, the wedge effect is low and the adhesion of the film is low. Conversely, the average crystal grain size and the average pore size are 40 μm
When it exceeds, the resulting porous body has a relative density of less than 90%, so that the densification is not sufficient and the mechanical properties and thermal properties are poor. When the relative density exceeds 99.5%, the wedge effect is low and the adhesion of the film is low.

As described above, the silicon carbide sintered body of the present invention is a relatively dense sintered body having a relative density of 90 to 99.5%, and the average grain boundary layer is removed by a chemical method. Diameter 5
In this case, pores as large as ４０40 μm are made to exist.

For the measurement of the crystal grain size and the pore size, see SE
Observation of a surface photograph by M (scanning electron microscope) or image analysis such as Luzex based on the SEM photograph.

Here, the crystal grain size and the average diameter of the pores are defined as the observation of a surface photograph by SEM or the SEM
It indicates the converted value on the assumption that it is a sphere by image analysis of a photograph.

On the other hand, to measure the relative density, the density of the sintered body was measured by the Archimedes method, and the theoretical density was 3.21 g / c.
calculated by dividing by m ^3.

The removal of the crystal grain boundary layer on the surface is preferably performed by chemical means such as etching.

As a specific example of the method, a mixed molten salt of potassium nitrate and sodium hydroxide is used for removing the grain boundary layer.

FIG. 2 shows a photograph of the ground surface of the sintered silicon carbide body after sintering, and FIG. 3 shows a photograph of the surface after removing the grain boundary layer of the sintered surface by etching. Shown in In these figures, the black portions indicate depressions, that is, pores.

That is, the grain boundary layer present at the crystal grain boundaries on the surface of the sintered body is removed by etching using a mixed molten salt of potassium nitrate and sodium hydroxide, as shown in FIG. In this case, more pores having a diameter of about 5 to 40 μm can be generated. For example, the number of pores having a diameter of 5 to 40 μm is about 5 in FIG. 1 which is a conventional example. Grinding after sintering when chemical means such as etching of the sintered body obtained by the present invention is not used. In FIG. 2 showing the front surface, the number is about three, whereas in FIG. 3, which is the embodiment of the present invention, 40 or more can be confirmed.

Therefore, the silicon carbide sintered body of the present invention shown in FIG. 3 forms a coating film on the surface of the sintered body by a chemical or physical method, as compared with the sintered body shown in FIG. The wettability in the case or when applying an organic or inorganic adhesive or the like can be increased.

Next, a method for producing the silicon carbide sintered body of the present invention will be described.

In the present invention, first, by controlling the amount of boron or carbon added as a sintering aid, the growth of crystal grains is promoted in the sintering process, but the densification is slightly suppressed. The composition was as follows.

Although the role of boron and carbon is extremely important in the sintering mechanism of silicon carbide, many studies have been made on the amount of boron and carbon.

In particular, most studies have been made on the densification of silicon carbide, and the optimum amounts of boron and carbon for the densification have been considerably studied and found.

That is, by appropriately adding the amounts of boron and carbon, densification can be promoted while suppressing the growth of crystal grains. The present investigator also verified experimentally the compounding amount that makes the most compact by arbitrarily changing the added amount of boron and carbon.

However, according to the present invention, the crystal grains are grown to some extent before the densification is completed, and the grown crystal grains hinder further densification at the densification stage. Although pores were densified, pores were present around crystal grains that grew greatly after sintering.

In particular, boron is an optimum addition amount of 0.2.
０．４0.4% by weight, and the addition of carbon is an optimum amount of 2.0
It has been found that the above-mentioned effect is achieved by reducing the amount of carbon added to less than about% by weight. When the addition of carbon is more than the optimum amount of about 2.0% by weight, the densification is gently suppressed, whereas when the addition is less than about 2.0% by weight, the density is sharply reduced.

Specifically, silicon carbide is used as a main component and 0.1.
By sintering the sintered body as a starting material having a carbon source of 5 to 2.0% by weight or less and a boron source of 0.2 to 0.4% by weight or less, mechanical and thermal properties are sufficiently maintained. In addition, excessive densification is suppressed and grain growth is promoted, and the above-described silicon carbide sintered body of the present invention can be manufactured.

Here, when the carbon source exceeds 2.0% by weight and the boron source exceeds 0.4% by weight, the densification is suppressed, but the surface diffusion of the silicon carbide particles is suppressed too much and the grain growth is inhibited. I do. Therefore, the amount of carbon added is preferably 0.5
To 2.0% by weight or less, and the boron addition amount is preferably 0.2 to 0.4% by weight.

The content percentages of the carbon source and the boron source in the starting materials are the conversion amounts of carbon or boron alone, as determined by weight measurement of the added amounts and X-ray diffraction of the raw material powder.

Secondly, in the production method of the present invention, by promoting the grain growth of the sintered body crystal before the sintered body shows the shrinkage behavior in the firing process, the sintered body is made to have a shrinkage behavior after the shrinkage behavior starts. Also suppresses densification in a form that is hindered by large grown crystals.

For this purpose, firing may be carried out with a very gentle temperature gradient in the temperature range in which densification is performed, and preferably with a step-shaped interval of a heat-retention time. When sintering, from room temperature to 1500
Ramp rate up to 1950 ° C.
00 ° C and the maximum firing temperature is 2000 to 2200 ° C.

Conventionally, when sintering a silicon carbide sintered body, a rate of temperature increase from 300 to 1500 to 1800 to 1950 ° C. is used in order to suppress excessive growth of crystals and obtain a denser sintered body. By making the gradient 200 ° C. or more per hour, a method of preventing grain growth and densifying without being hindered by grown crystal grains has been used.

However, in the present invention, when sintering, by making the temperature rising rate gradient from room temperature to 1500 to 1950 ° C. gentle at 20 to 200 ° C. per hour, the densification by volume diffusion is rapidly performed. Sufficient sintering energy was given in the temperature range before the occurrence to promote grain growth, and densification was suppressed to some extent by being hindered by the grown crystal grains.

When the maximum firing temperature is lower than 2000 ° C., the mechanical and thermal properties are reduced, and the maximum firing temperature is lower than 220 ° C.
When the temperature exceeds 0 ° C., the crystal grains grow too much due to the secondary recrystallization, and very large plate-like crystals are generated. The temperature was 2000-2200 ° C. This suppresses excessive densification without significantly impairing the mechanical and thermal properties, promotes grain growth, and has good wettability of the resulting film, adhesive, etc., as shown in FIG. A sintered body can be manufactured.

The temperature in the furnace is measured using a thermocouple or an optical pyrometer.

The silicon carbide sintered body of the present invention obtained in this manner and having good wettability such as a formed film and an adhesive is a semiconductor S
It can be used for a wrap plate used when manufacturing an i-wafer. Resin film, PV
D, The wettability can be improved when a metal / ceramic generation film is formed by CVD, or when a Si wafer is similarly fixed to a lap plate with wax. Alternatively, if the silicon carbide sintered body of the present invention is used for a chamber member used in an etching step of a semiconductor manufacturing apparatus, PVD is applied to the inner surface of the chamber member for the purpose of preventing the reaction products attached to the inner surface from dropping and improving corrosion resistance. Also, the present invention is effective when a ceramic forming film is formed by CVD.
In addition, it is expected to be effective in applications such as fixing by bonding metal and ceramic, and various metallizations to ceramic.

[0049]

Embodiments of the present invention will be described below in detail. Note that the present embodiment is an example, and the present invention is not limited to this. (Experimental example 1) Boron carbide was added as a boron source so that the added amount in terms of boron alone was 0.33% by weight.
The addition amount of carbon, including the amount of carbon contained in boron carbide, was changed in the range of 0.5, 1.0, 2.0, and 4.0% by weight. A molded body was prepared, and the maximum firing temperature was set to 2000, 20 respectively.
The temperature was changed to 25, 2050, 2100, and 2200 ° C. to be fired. It should be noted that calcination is performed by preventing Ar
Firing in an atmosphere, the furnace pressure is slightly more positive than atmospheric pressure,
That is, it was set to 0.5 kgf / cm ² . Further, as a firing temperature profile, a temperature gradient at a temperature rise of 1500 to 1950 ° C. was set to 50 ° per hour, and one hour of heat retention time was provided for each 50 °. As a result of measuring the density of the obtained sintered body, as shown in Table 1 and FIG. 4, the amount of added carbon was 2. at any maximum firing temperature regardless of the maximum firing temperature.
0% by weight was the most compact.

In this state, since the sintered body has small pores as shown in FIG. 1, the anchor effect is low, and a coating film on the surface of the sintered body by a chemical or physical method, or an organic or inorganic material is used. Low wettability of adhesive etc.

On the other hand, by reducing the amount of carbon added to less than 2.0% by weight, the densification is rapidly suppressed, and a sintered body having large pores can be obtained.

More specifically, the amount of carbon added is desirably 0.5 to 2.0% by weight, preferably 1.0 to 2.0% by weight in view of the density. This is because, as can be seen from Table 1 and FIG.
In the above, the density of the sintered body is from 2.732 g / cm ³ to 3.1.
It is 85 g / cm ^3, which is from 85% to 99% of the theoretical density, because it satisfies mechanical and thermal properties as a dense silicon carbide body.

Further, the effects of the amounts of boron and carbon added and the temperature profile of firing, the change of the pore diameter on the surface of the sintered body depending on whether or not the grain boundary layer was removed by etching, and the change of the anchor effect were compared and verified. did. As a comparative example, a sintered body obtained by the conventional manufacturing method shown in FIG. 1 and a sintered body shown in FIG. 2 in which the amount of carbon added was 1.0% and the maximum firing temperature was 2000 ° C. × 1 hour and etching was not performed. Was prepared as an example of the present invention, as shown in FIG. With these three types, a coating film was actually formed by CVD on a sintered body of φ60 × 5t molded body, and the adhesion was verified.

In the embodiment of the present invention, a mixed molten salt of potassium nitrate and sodium hydroxide was used for etching.

As a result, as shown in Table 2, the diameter was 5 to 4 mm.
The number of pores of 0 μm is about 5 in FIG.
In FIG. 2 where etching is not performed, the number is about three, whereas in FIG. 3 which is the embodiment of the present invention, 40 or more can be confirmed.

Further, as shown in Table 2, the sintered body of the comparative example shown in FIG. 1 peeled off almost completely without adhering over the entire area of the surface of the sintered body, and peeling was observed at several places in FIG. Was done. On the other hand, in the example of the present invention in which the silicon carbide sintered body was etched as shown in FIG. 3, the coating film was completely adhered over the entire area of the sintered body surface.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

According to the present invention, pores having an average diameter of 5 to 40 .mu.m, an average crystal particle diameter of 5 to 40 .mu.m, a relative density of 90 to 99.5%, and a crystal grain boundary layer on the surface are formed. By removing the silicon carbide sintered body having fine irregularities and performing etching, an anchor effect due to a difference in irregularity between a portion having no pores and a pore portion is enhanced, and a chemical or physical method for the surface of the sintered body is performed. , And the wettability of an organic or inorganic adhesive or the like can be increased.

Further, according to the present invention, when a starting material having silicon carbide as a main component and having a carbon source of 2.0% by weight or less and a boron source of 0.4% by weight or less is used,
The heating rate gradient from room temperature to 1500 to 1950 ° C is 20 to 200 ° C per hour, and the maximum firing temperature is 2000 to 2
After the temperature is set to 200 ° C., the grain boundary layer existing on the crystal grain boundaries on the surface of the sintered body is removed by chemical etching using a mixed molten salt of potassium nitrate and sodium hydroxide, thereby providing mechanical and thermal While maintaining sufficient properties, excessive densification is suppressed, grain growth is promoted, and a silicon carbide sintered body having good wettability such as a formed film and an adhesive can be manufactured.

[Brief description of the drawings]

FIG. 1 is an SEM photograph of the surface of a conventional silicon carbide sintered body.

FIG. 2 shows SE on a ground surface of a silicon carbide sintered body of the present invention.
It is an M photograph.

FIG. 3 is an SEM photograph of the sintered body of FIG. 2 obtained by etching a ground surface of the sintered body.

FIG. 4 is a graph showing the relationship between the amount of carbon added and the density in the silicon carbide sintered body of the present invention.

Claims (3)

[Claims] The present invention has pores having an average diameter of 5 to 40 μm, an average crystal particle diameter of 5 to 40 μm, and a relative density of 90 to 99.5.
%, And having fine irregularities with the crystal grain boundary layer removed on the surface. 2. The silicon carbide-based sintered body according to claim 1, wherein the crystal grain boundary layer on the surface is removed by a chemical means. 3. A starting material containing silicon carbide as a main component and containing not more than 2.0% by weight of a carbon source and from 0.2 to 0.4% by weight of a boron source is formed into a predetermined shape, and is heated from room temperature to 1500.
Ramp rate up to 1950 ° C.
A method for producing a silicon carbide-based sintered body, characterized in that after firing at 00 ° C. and a maximum firing temperature of 2000 to 2200 ° C., a grain boundary layer on the surface of the sintered body is removed using a chemical method. .