JP3150606B2 - Method for controlling specific resistance of silicon carbide sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the specific resistance of a silicon carbide sintered body that can adjust the specific resistance of the silicon carbide sintered body to a desired value.

[0002]

2. Description of the Related Art Conventionally, a silicon carbide sintered body formed by molding silicon carbide powder into a predetermined shape and sintering the same has been manufactured for a long time. It is used in various industrial fields as a chemically stable high-temperature heating element. For this reason, improvement studies for the purpose of improving the performance of the silicon carbide heating element have been actively conducted. Among them, the following are related to the adjustment of the specific resistance value.

[0003] In other words, Japanese Patent Application Laid-Open No. Sho 52-110499 discloses a method of adding a third element component to lower the specific resistance value, for example, N, P, As when sintering silicon carbide powder. , Sb, Bi, etc., in a solid phase or a gas phase are disclosed. Also, Japanese Patent Application Laid-Open No.
No. 9090 discloses that α-SiC having a particle diameter of 1 μm or less
A method of molding a mixed powder containing β-SiC, boron, carbon, or the like, and sintering to a predetermined density in a vacuum or an inert atmosphere, or pressurizing subsequent to the sintering. A method of performing secondary sintering at a predetermined temperature in a nitrogen atmosphere is disclosed.

[0004]

However, in the method disclosed in Japanese Patent Application Laid-Open No. Sho 52-110499, it is difficult to homogenize the dispersion composition, so that industrialization is difficult. When a silicon carbide sintered body is used as a heating element for a vacuum device, there is a problem that these third element components volatilize from the surface of the heating element and become a contamination source. On the other hand, in the method disclosed in Japanese Patent Application Laid-Open No. 57-9090, the controllable range of the specific resistance value is as narrow as several Ω · cm to several tens Ω · cm by primary sintering alone, which is not practical. When the silicon carbide sintered body is used as a heating element because of its large resistance value, there is a problem in design that miniaturization is difficult. In addition, when performing two-stage sintering, introduction and holding of nitrogen gas are necessary, so that the production equipment is inevitably increased in size and complexity, and furthermore, a silicon carbide sintered body is used as a heating element for a vacuum device. In such a case, there is a problem that an additive component such as boron and carbon volatilizes from the surface of the heating element and becomes a contamination source. The present invention has been made in order to solve such problems of the conventional technology, and greatly expands the control range of the specific resistance of the silicon carbide sintered body, and can easily reduce the specific resistance. An object of the present invention is to provide a method for controlling the specific resistance of a silicon carbide sintered body.

[0005]

The object of the present invention is to provide an α-SiC powder having an average particle size of 0.1 μm or more and 10 μm or less and a β-SiC powder having an average particle size of 0.1 μm or more and 10 μm or less.
The SiC powder and the SiC ultrafine powder having an average particle diameter of less than 0.1 μm synthesized by a plasma CVD method in a gas phase are mixed at a desired ratio to obtain a SiC mixed powder, and the SiC mixed powder is heated and sintered. Can be solved by The content of the α-SiC powder in the SiC mixed powder is
It can be 20% by weight or less.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for controlling the specific resistance of a silicon carbide sintered body according to the present invention can be performed, for example, as follows. Using SiH ₄ and C ₂ H ₄ as raw material gases, SiC ultrafine powder synthesized in a gas phase by a plasma CVD method in an argon thermal plasma excited by a high frequency with a reaction system pressure controlled to 0.08 Torr, α -SiC powder and β-
SiC mixed powder obtained by mixing SiC powder at a desired ratio is mixed in a solvent such as methanol by a ball mill to form a slurry. Next, the slurry is spray-dried to produce granulated powder, and the granulated powder is subjected to a uniaxial pressing machine.
It is molded at a molding pressure of 20 MPa to obtain a molded body. This compact was packed in a graphite hot press container, and uniaxially pressed at 40 MPa.
Sintering is performed in an argon atmosphere at 1 atmosphere and 2300 ° C. for 4 hours to obtain a silicon carbide sintered body having a desired specific resistance.

The average particle size of the SiC ultrafine powder is 0.1
It is less than μm, usually 0.01 to 0.08 μm. In the ultrafine SiC powder synthesized by the plasma CVD method, the conditions for the gas phase synthesis by the plasma CVD method and the crystal phase are not particularly limited. Alternatively, a β-type (β-SiC ultrafine powder) obtained by introducing a raw material gas of a silicon halide and a hydrocarbon and performing a gas phase reaction while controlling the pressure of the reaction system within a range of less than 1 atm to 0.1 Torr. , Amorphous or SiC ultrafine powder comprising a mixed phase thereof improves the sinterability of the silicon carbide sintered body,
This is preferable because the mechanical properties are also improved. Especially β-SiC
The ultrafine powder has a small aspect ratio and excellent dispersibility, and is extremely excellent in electric conductivity. Therefore, the effect is large, and the specific resistance of the silicon carbide sintered body is reduced only by mixing a small amount with the SiC mixed powder. And it is preferable.

As the α-SiC powder and β-SiC powder, those generally produced by a silica reduction method, an Acheson method or the like can be used. However, when the purpose of use of the silicon carbide sintered body is a heating element for a heating device used in the production of semiconductors and the like, high purity is required. Must be used. Further, their average particle size is 0.1.
1 to 10 μm, more preferably 0.1 μm to 1 μm
When m, the sinterability of the silicon carbide sintered body is improved.

The SiC ultrafine powder is preferably the S
5% by weight or more in iC mixed powder, more preferably 5 to 50%
% By weight. If the amount is less than 5% by weight, the silicon carbide sintered body may not be sufficiently densified, and the mechanical strength may be reduced. If it exceeds 50% by weight, the cost increases. The α
It is preferable that the content of the -SiC powder be 20% by weight or less in the SiC mixed powder because the control range of the specific resistance of the silicon carbide sintered body is expanded. Usually, it is used in the range of 2 to 20% by weight. If the content exceeds 20% by weight, the effect of lowering the specific resistance of the silicon carbide sintered body is reduced, and the control range of the specific resistance is reduced. Therefore, when a silicon carbide sintered body is used as a heating element, there is a problem in design that miniaturization is difficult. The content of β-SiC powder is
It is the balance of ultrafine C powder and α-SiC powder, and is not particularly limited.

The method for mixing the above-mentioned ultrafine β-SiC powder, α-SiC powder and β-SiC powder, and the method for molding this mixed SiC powder are not particularly limited, and can be carried out by known methods. Further, at the time of molding, polyvinyl alcohol, polyvinylpyrrolidone or the like may be used as a molding binder, or if necessary, a dispersant such as a stearic acid salt may be added. In the heat sintering, not only the hot press sintering but also normal pressure sintering, H
Conventional methods such as IP sintering can be adopted, but pressure sintering such as hot press sintering is desirable in order to obtain a silicon carbide sintered body with higher density. The sintering temperature is usually 1900-24
It is about 00 ° C. The sintering atmosphere is not particularly limited, and any of a vacuum atmosphere, an inert gas atmosphere, and a reducing atmosphere can be employed.

Since the SiC ultrafine powder is excellent in dispersibility and electric conductivity, the specific resistance value of the silicon carbide sintered body can be reduced by mixing the SiC ultrafine powder, The specific resistance of the silicon carbide sintered body can be controlled. At this time, if the amount of the α-SiC powder is 20% by weight or less in the SiC mixed powder, the effect is large, and the control range of the specific resistance is greatly expanded. As a result, the SiC
By changing the ratio of the ultrafine powder, the α-SiC powder and the β-SiC powder, the specific resistance value of the silicon carbide sintered body is set to about 1.0 × 10 ^{−3 to} 1.0 × 10 ² Ω.・ Cm
Can be controlled over a wide range. However, although the specific resistance changes mainly depending on the ratio of the SiC ultrafine powder, α-SiC powder and β-SiC powder, it depends on conditions such as heating and sintering. In order to obtain a sintered body, it is necessary to experimentally determine the relationship between the specific resistance of the silicon carbide sintered body and these parameters.

Further, by using the ultrafine SiC powder, a high-purity and dense silicon carbide sintered body can be easily obtained without adding a sintering aid. Therefore, for example, even when a silicon carbide sintered body is used as a heating element for a vacuum device, unlike the conventional silicon carbide sintered body using a sintering aid such as boron and carbon, the sintering aid component is not used. It does not volatilize from the heating element surface and become a source of contamination. However, depending on the purpose of use of the silicon carbide sintered body, there is no problem even if the sintering aid such as boron or carbon is added as needed. Further, the SiC ultrafine powder has good dispersibility and a uniform dispersion composition can be easily obtained, so that it is easy to adapt this specific resistance control method to industrialization.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. (Examples 1 to 14, Comparative Examples 1 to 4) Si as a source gas
Using the H ₄ and C ₂ H _4, in an argon thermal plasma excited by the high frequency was controlled pressure of the reaction system to 0.08 Torr, the vapor phase synthesized SiC ultrafine powder by a plasma CVD method, alpha-SiC powder And β-SiC powder mixed in the ratio shown in Table 1 were mixed with a ball mill in a solvent such as methanol to form a slurry. Next, the slurry is spray-dried to form granulated powder, and the granulated powder is formed with a uniaxial press at a molding pressure of 20MPa.
Formed as a to obtain a disk-shaped molded body having a diameter of 210 mm and a thickness of 12 mm. This compact was packed in a graphite hot press container, uniaxially pressed at 40 MPa, 1 atm.
Sintering was performed at 300 ° C. for 4 hours to obtain a silicon carbide sintered body having a desired specific resistance. The raw materials used at this time are as follows. β-SiC ultrafine powder: (average particle diameter 0.06 μm; synthesized by gas phase by plasma CVD method) β-SiC powder: (average particle diameter 0.3 μm; manufactured by Ibiden) α-SiC powder: (average particle Diameter 0.3 μm; manufactured by Showa Denko KK) The specific resistance of the silicon carbide sintered body thus manufactured was measured by a four probe method, and the sintered density and the four-point bending strength were measured. The sintering density was 3.21 the theoretical density of silicon carbide.
The relative density was 6 g / cm ³ , and the four-point bending strength was 3
The measurement was performed in accordance with JIS-R1601 using a test piece having a 3 × 40 mm sample surface mirror-polished with a No. 600 grindstone. The results are shown in Table 1. The relationship between the specific resistance value and the amount of the α-SiC powder mixed is shown in the graph of FIG. The curves A, B, C, and D in FIG.
The mixing amount of the iC ultrafine powder was 0 (Comparative Examples 1-4),
3 (Examples 7 to 10), 5 (Examples 1 to 6), and 10 (Examples 11 to 14) show the results in the case of weight%.

[0014]

[Table 1]

From FIG. 1, it can be seen that the addition of the ultrafine β-SiC powder reduces the specific resistance of the silicon carbide sintered body, and the amount of the decrease increases as the content of the ultrafine β-SiC powder increases. It is clear. Also, it can be seen that this effect is large and the control range of the specific resistance is expanded particularly in the range where the α-SiC powder is 20% by weight or less. As a result, β
By adjusting the ratio of the -SiC ultrafine powder, α-SiC powder and β-SiC powder, about 1.0 × 10 ⁻³ to
It is clear that the specific resistance can be controlled in a wide range of 1.0 × 10 ² Ω · cm.

Further, from Table 1, it was found that Examples 1 to 4, 7, 8, 11, and
In No. 12, the specific resistance values are all lower than 1.0 Ω · cm. On the other hand, in the example in which the α-SiC powder was set to be more than 20% by weight, Example 13 (β-SiC ultrafine powder: 10% by weight;
C powder: 25% by weight), the specific resistance value is 1.0Ω · c.
The value is lower than m. That is, even when the content exceeds 20% by weight of the α-SiC powder, the specific resistance of the silicon carbide sintered body can be controlled to a low value by increasing the ratio of the β-SiC ultrafine powder.

Further, the examples in which the β-SiC ultrafine powder was mixed were all superior in the sintered density and the four-point bending strength as compared with the comparative example in which no β-SiC powder was mixed. β-S
In Examples 7 to 10 in which the ratio of the iC ultrafine powder was 3% by weight, the sintering density was slightly inferior to the other examples in which the ratio was 5% by weight or more. Density and 4
The point bending strength is clearly large, and β-
It is clear that the effect of increasing the strength of the silicon carbide sintered body can be obtained by the SiC ultrafine powder.

[0018]

As described above, in the present invention, ultrafine SiC powder, α-SiC powder and β-SiC powder are used.
By changing the ratio of the powder, the specific resistance value of the silicon carbide sintered body can be set to about 1.0 × 10 ^{−3 to} 1.0 × 10 ² Ω · c.
m can be controlled over a wide range. Further, by using the SiC ultrafine powder, a high-purity and dense silicon carbide sintered body can be easily obtained without adding a sintering aid. Therefore, for example, even when a silicon carbide sintered body is used as a heating element for a vacuum device, unlike the conventional silicon carbide sintered body using a sintering aid such as boron and carbon, the sintering aid component is not used. It does not volatilize from the heating element surface and become a source of contamination. Further, since the SiC ultrafine powder has good dispersibility and a uniform dispersion composition can be easily obtained, it is easy to industrially carry out the method for controlling the specific resistance of the silicon carbide sintered body.

[Brief description of the drawings]

FIG. 1 shows the specific resistance and α of a silicon carbide sintered body in an example.
4 is a graph showing a relationship with the content of SiC powder.

Claims (2)

(57) [Claims] An average particle diameter of 0.1 μm or more and 10 μm
Α-SiC powder below, β-SiC powder having an average particle diameter of 0.1 μm or more and 10 μm or less, and plasma CVD
Carbonized powder obtained by mixing at a desired ratio with ultrafine SiC powder having an average particle diameter of less than 0.1 μm synthesized by a gas phase method to obtain a SiC mixed powder, and heating and sintering the SiC mixed powder. A method for controlling the specific resistance of a silicon sintered body. 2. The α-SiC in the SiC mixed powder
2. The method according to claim 1, wherein the content of the powder is not more than 20% by weight.