JPH042662A - High-purity silicon carbide sintered material and production thereof - Google Patents

Abstract

PURPOSE:To obtain high-density sintered material of silicon carbide, containing a sintering auxiliary by introducing a raw material gas comprising a silane compound, etc., into plasma in a nonoxidizing atmosphere to synthesize fine powder of silicon carbide and sintering the fine powder. CONSTITUTION:A raw material gas comprising a silane compound or a silicon halide and a hydrocarbon is introduced into plasma in a nonoxidizing atmosphere. Then the raw material gas is subjected to gas-phase reaction while controlling the reaction system in a range of <1atm. to 0.1Torr. Fine powder of silicon carbide thus synthesized, having <=0.1mum average particle diameter is heated and sintered to give the objective sintered composition. The reason why high-density sintered material of silicon carbide is obtained by the above- mentioned method is considered that the fine powder of silicon carbide used has <=0.1mum average particle diameter and superfine and, because of the clean surface of the fine powder, the fine powder has high sintering activity.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a silicon carbide sintered body and a method for manufacturing the same, and more specifically to the use of highly active ultrafine silicon carbide powder synthesized by plasma CVD method. This invention relates to a highly pure and high-density silicon carbide sintered body that can be obtained without adding a sintering aid, and a method for producing the same.

"Conventional technology" Silicon carbide is chemically extremely stable and has excellent mechanical properties and oxidation resistance at high temperatures, so its sintered bodies are used in chemical pump parts, heat exchanger parts, and gas turbine parts. It is expected to be applied to engine parts, etc. In addition, recently in the semiconductor field, as the heat treatment temperature for silicon has increased, there has been a shift from conventional quartz jigs to silicon carbide jigs, which have better creep resistance at higher temperatures. In addition, its application as a functional material to high-temperature semiconductor devices, blue light-emitting devices, etc. is being considered.

By the way, silicon carbide is a difficult-to-sinter material with strong covalent bonds, so to obtain a high-density sintered body, powder with an average particle size of submicron or more produced by the Acheson method or silica reduction method is used. Ni, B.

C, Al1. It was necessary to add one or more of elements such as Be, Ti, and Fe as a sintering aid in an amount of at least % by weight.

However, these sintering aids have a lower melting point than silicon carbide,
It has low strength and precipitates as impurities at the grain boundaries and triple points of the sintered body, so the high temperature and high strength that silicon carbide originally has,
This was a cause of deterioration of excellent performance such as high corrosion resistance. In addition, in the semiconductor field where high purity is required,
When these impurities mix into the silicon of the product due to thermal diffusion, the electrical characteristics deteriorate, making it inconvenient that it cannot be used in such fields.

In order to eliminate these drawbacks, it is necessary to reduce the content of the sintering aid as much as possible, or preferably to produce a high-density silicon carbide sintered body containing no sintering aid at all. As a method for manufacturing such a high-density silicon carbide sintered body, for example, a raw material powder containing no sintering aid,
There is a method of sintering while applying pressure of several GPa.

"Problem to be solved by the invention" However, in the method of JP-A-63-8263,
Because it requires an ultra-high pressure of several GPa during sintering, it is not suitable as an industrial manufacturing method because only a poor quality sintered body can be obtained due to equipment limitations, and the manufacturing cost is therefore high. Ta.

It is also known that silicon carbide sintered bodies that do not contain sintering aids can be produced by vapor deposition methods such as PVD and CVD, but the sintered bodies obtained by these vapor deposition methods are This method has disadvantages in that it can only be obtained with a maximum thickness of several centimeters, which limits its uses and increases manufacturing costs.

The present invention has been made to solve the problems in the conventional method of manufacturing sintered silicon carbide, and its purpose is to:
It has excellent high-temperature strength, corrosion resistance, oxidation resistance, and high purity, and is used in a wide range of applications from high-temperature structural parts such as gas turbines to high-purity parts such as semiconductor manufacturing equipment. It is an object of the present invention to provide a high-density silicon carbide sintered body containing substantially no sintering aid and a method for producing the same.

"Means for Solving the Problems" In the high-purity silicon carbide sintered body of the invention according to claim 1 of the present invention, a raw material consisting of a 7-ranium compound or a silicon halide and a hydrocarbon is placed in plasma in a non-oxidizing atmosphere. Introduce the residue and reduce the pressure of the reaction system from less than 1 atm to Q, l t
It is obtained by heating and sintering ultrafine silicon carbide powder with an average particle size of 0.1μ or less, which is synthesized by a gas phase reaction while controlling it within the range of This was the solution to the above problem.

In addition, in the method for producing a high-purity silicon carbide sintered body of the invention according to claim 2, a raw material gas consisting of a 7-ran compound or a silicon halide and a hydrocarbon is introduced into plasma in a non-oxidizing atmosphere, and a reaction system from less than 1 atm to Q, l
The above problem was solved by heating and sintering ultrafine silicon carbide powder having an average particle size of 0.1 μm or less, which was synthesized by a gas phase reaction while controlling the torr range.

Hereinafter, the present invention will be explained in detail based on the method for manufacturing a high-purity silicon carbide sintered body according to claim 2.

As a result of intensive research to achieve the above object, the present inventors have developed ultrafine silicon carbide powder with an average particle size of 0.1 μm or less synthesized by performing a gas phase reaction in a pressure-controlled plasma. Based on this knowledge, we have discovered that it is possible to obtain a high-density, high-purity sintered silicon carbide without adding a sintering aid by heating and sintering in an active gas, reducing gas, or vacuum atmosphere. The present invention was completed.

The ultrafine silicon carbide powder used to obtain the sintered body of the present invention must have an average particle size of 0.1 μm or less. Methods for obtaining such ultrafine silicon carbide powder with a particle size of 0.1 μm or less include: (1) heating organic silicon such as polymethyl carbosilane at a temperature of 1500'C or more; (2) SiH, 5iCI2. and hydrocarbon, or CH
Gas-phase reaction method that heats sS iCQ3 etc. at a temperature of 1000°C to 1800°C, ■ S in the tail flame part of arc plasma or high frequency induction thermal plasma
r Plasma CVD method in which H4, 5iCQ and hydrocarbons are introduced and reacted in the gas phase, ■ Laser CVD method in which a mixed gas such as SiH, C, H4, etc. is irradiated with CO and laser and reacted in the gas phase. Traditionally known.

However, the silicon carbide ultrafine powder obtained by these methods contains many coarse particles with a particle size of 1 μm or more, so the particle size distribution is wide, the inside of the particle tends to have a hollow structure, and the particle shape is distorted. This was often disadvantageous in terms of ease of sintering. Therefore, the ultrafine powder obtained by these methods could not be densified without a sintering aid unless a special method such as sintering under ultra-high pressure was used.

In contrast, in the present invention, as ultrafine silicon carbide powder with a particle size of 0.1 μm or less, silane compounds or silicon halide and hydrocarbons are mixed in plasma in a non-oxidizing atmosphere created by non-polar discharge of high frequency induction method. Introducing raw material gas,
A compound synthesized by a gas phase reaction while controlling the pressure of the reaction system in a range from less than 1 atm to more than Q,1 torr is used. For example, when silicon tetrachloride and ethylene are synthesized by introducing a raw material gas into argon plasma excited by radio frequency, an amorphous ultrafine particle with an average particle size of about 0.01 to 0.03μ and a small aspect ratio is produced. A powder is obtained.

In addition, when synthesized in the same manner using monosilane and ethylene as the raw material gas, the average particle size was 0.00.
A β-type ultrafine powder with a small aspect ratio of about 5 to 0.03 μm can be obtained, and depending on the synthesis conditions, a mixed phase of α-type and β-type can be obtained.

In this way, the pressure of the reaction system is changed from less than 1 atm to Q
, several thousand degrees by controlling in the range of l torr.
Since it is possible to introduce raw material gas into plasma, which is in an ultra-high temperature state of C or higher, it is possible to stably precipitate silicon carbide from the ion, atomic, etc. state, and therefore it is possible to synthesize it using this method. The crystal growth of the ultrafine silicon carbide powder produced is well controlled by the rapid temperature gradient, so the individual particles are ultrafine, the particle size distribution is extremely narrow, and the particle shape has an aspect ratio of 1. It has a nearly spherical shape, high surface activity, and excellent sinterability.

In addition, since the obtained powder is an ultra-fine powder, there is no need for a pulverization process to make it fine, so there is no contamination of impurities due to abrasion from the pulverizing media, and the advantage is that high purity can be obtained. There is.

This ultrafine powder has crystal phases such as α phase, β phase, amorphous phase,
Alternatively, it may be a mixed phase thereof. The crystallinity can be easily controlled by adjusting the conditions of the plasma CVD method, such as the precipitation temperature and speed of ultrafine powder.

In the manufacturing method of the present invention, a high-density and high-purity silicon carbide sintered body can be manufactured using high-purity ultrafine silicon carbide powder without adding substantially any sintering aid. The most important feature is that a sintering aid may be added to this ultrafine powder for applications where high purity characteristics are not required and only compactness is required. For example, the conventionally known AI21
It goes without saying that a high-density sintered body can be obtained by adding Be, T I + Fe, Ba, B, etc. as sintering aids and sintering.

The reason why a high-density silicon carbide sintered body can be obtained by the manufacturing method of the present invention is that the average particle size of the ultrafine silicon carbide powder used is 0.1 μm.
It is presumed that this is due to the fact that it has a high sintering activation power because it is ultrafine, less than m, and its surface is clean.

In addition, in molding the ultrafine powder silicon carbide obtained in this way, press molding method, CIP molding method, slip casting molding method, tape molding method, calendar roll molding method, extrusion molding method, injection molding method, etc. Conventionally known methods can be employed. In this case, polyvinyl alcohol, polyvinylpyrrolidone, or the like can be used as the molding binder, and a dispersant such as stearate may be added as necessary.

In addition, for sintering, conventional methods such as normal pressure sintering, atmosphere pressure sintering, hot press sintering, or hot isostatic pressing (HIP) can be used. In order to obtain a silicon carbide sintered body with higher density and higher strength, it is preferable to employ pressure sintering such as hot pressing. The sintering temperature is also not particularly limited, but 1
If the heating temperature is lower than 800°C, insufficient sintering will occur, and if the heating temperature is higher than 24°C, evaporation of silicon carbide will easily occur, and the strength and toughness of the sintered body may decrease due to particle growth. From, 1800°C to 240
It is preferred to sinter at a temperature range of 0'C.

Further, as the atmosphere during sintering, any of an inert gas atmosphere, a reducing gas atmosphere, and a vacuum atmosphere can be employed.

The density of the obtained silicon carbide sintered body is preferably 85% or more of the theoretical density, and when the density is 85% or more of the theoretical density, the sintered body has the original characteristics of silicon carbide. For example, it exhibits high strength at high temperatures, excellent corrosion resistance, oxidation resistance, and abrasion resistance. It goes without saying that if a sintered body is manufactured under normal conditions based on the manufacturing method of the present invention, the density of the obtained sintered body will be 85% or more of the theoretical density.

The silicon carbide sintered body thus obtained has an average particle size of 0.1 μm obtained by plasma CVD method.
Because it is sintered using ultrafine silicon carbide powder with high sintering activity, and without containing an impurity sintering aid (or with only a trace amount of sintering aid), its density is low. For example, it has a high density of 85% or more of the theoretical density, and therefore exhibits the original properties of silicon carbide, such as high temperature high strength, excellent corrosion resistance, oxidation resistance, and wear resistance. It can be applied to a wide range of fields such as turbine parts, engine parts, and mold parts for molding optical disks. Further, since the amount of impurities contained in the ultrafine silicon carbide powder used as a raw material is extremely small, and therefore has extremely high purity, it is also useful in the semiconductor field.

"Example" EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example 1) SjH,1,5SLPM and CH,1,8S were placed in Ar thermal plasma excited by a radio frequency of about 4 MHz.
LPM (C/Si [molar ratio]=1..2) was introduced, and a gas phase reaction was carried out while controlling the pressure of the reaction system at 260 torr to obtain ultrafine silicon carbide powder.

When the obtained fine powder was examined using a transmission electron microscope, it was found that the average particle size was 0 as shown in the drawing (transmission electron micrograph).
．． It was 03μ shoulder. Further, when the crystal phase of this ultrafine silicon carbide powder was examined using a powder X-ray diffraction apparatus, it was confirmed that it was a β phase. Furthermore, the amount of metal impurities contained was measured by ICP emission spectrometry, and the results are shown in Table 1.

Table 1 From the results shown in Table 1, it was found that the obtained ultrafine silicon carbide powder did not contain any elements that could be used as sintering aids, and had extremely high purity.

Next, 100 parts by weight of this ultrafine silicon carbide powder was placed in a container, and 2 parts by weight of polyvinylpyrrolidone as a molding binder and an appropriate amount of methyl alcohol as a solvent were added thereto, and mixed in a planetary ball mill for 12 hours. , dried, crushed, and formed into a disk shape using a conventional single-screw pressing machine.

The weight and dimensions of the obtained molded body were measured to determine the density of the molded body, and the relative density was found to be 50.1%.

Here, relative density refers to theoretical density 3.21g/cx3 as 1
This is the value calculated assuming that the value is 00%. (The same applies hereafter) Furthermore, this molded body was placed in a hot press container made of graphite, and heated at a temperature increase rate of 50° C./min while pressurizing at 40 MPa in an Ar atmosphere of 1 atm.
After reaching C, this temperature was maintained for 30 minutes for sintering, and then allowed to cool.

After cooling, the density of the sample taken out was measured by the Archimedes method, and the relative density was 95.6%.

In addition, from the obtained sintered body, 3X4X
When a 4Qiz bending strength test piece was prepared and a three-point bending test was performed with a span of 30zm, the three-point bending strength at room temperature was 90,7 kg/Ijl'', and in the air
3-point bending strength at 500°C is 97.4kg/111″
Met. Furthermore, when the hardness of this test piece was examined using a Vickers hardness tester, the Vickers hardness was 2600.
It was HV.

(Examples 2 to 6) SiH in Ar thermal plasma under the same conditions as in Example 1.

1.5SLPM and CH, 1,95SLPM (C
/ Si [molar ratio]=1.3) was introduced, and a gas phase reaction was carried out while controlling the pressure of the reaction system at 21 Q torr to obtain ultrafine silicon carbide powder.

When the obtained fine powder was examined with a transmission electron microscope, it was found that the average particle size was 0.02 μm, and the crystal phase was
When examined using a ray diffraction device, it was found to be a mixed phase of β and α phases.

Next, 100 parts by weight of this ultrafine silicon carbide powder was placed in a container, and 2 parts by weight of polyvinylpyrrolidone as a molding binder and an appropriate amount of ethyl alcohol as a solvent were added thereto, and mixed in the same manner as in Example 1. It was dried, crushed and molded.

The obtained molded bodies were sintered under different conditions as shown in Table 2, and the relative density, three-point bending strength, and Vickers hardness of the produced sintered bodies (Examples 2 to 6) were measured according to Example 1.
The results are also listed in Table 2.

From the results shown in Table 2 below, it was confirmed that all of Examples (1 to 6) had a relative density of 85% or more, and were sintered with high density. Furthermore, the results revealed that the silicon carbide sintered body obtained by the method of the present invention has extremely high purity.

Further, the amount of trace metal impurities contained in the sintered body of Example 2 shown in Table 2 was measured by arc emission spectrometry, and the results are shown in Table 3.

Table 3 (-: not detected) From the results shown in Table 3, it was found that the sintered body of Example 2 did not contain any impurity elements and was extremely pure. .

(Comparative Example 1) 100 parts by weight of commercially available β-type silicon carbide powder with an average particle size of 0.3 μm was placed in a container, and 2 parts by weight of polyvinylpyrrolidone was added as a molding binder, and an appropriate amount of methyl alcohol was added as a solvent. In addition, the mixture was mixed, dried, crushed, and molded in the same manner as in Example 1.

The relative density of the obtained molded body was 56.7%.

Furthermore, this molded body was placed in a hot press container made of graphite, and heated at a temperature increase rate of 50'C/min while pressurized at 40 MPa in an atmosphere of Arl atmospheric pressure.
After reaching 00°C, it was held at this temperature for 30 minutes for sintering, and then allowed to cool. (Same conditions as Example 1) The relative density, three-point bending strength, and Vickers hardness of the obtained sintered body were tested in the same manner as in Example 1. The results are also listed in Table 2.

(Comparative Examples 2 and 3) The molded bodies obtained by the same method as Comparative Example 1 were sintered under the conditions shown in Table 2, and the obtained sintered bodies (Comparative Examples 2 and 3) were sintered under the conditions shown in Table 2.
), the relative density, three-point bending strength, and Vickers hardness were examined in the same manner as in Example 1, and the results are also listed in Table 2.

From the results shown in Table 2, it was found that the obtained sintered bodies all had low relative densities.

(Comparative Example 4) Commercially available β-type silicon carbide powder with an average particle size of 0.3μ 100
Pour part by weight into a container, and add 1 part of the average particle size as a sintering aid.
μm boron carbide powder 0.5 parts by weight and average particle size 0.03
Adding 2.5 parts by weight of carbon black powder of μ degree,
Further, 2 parts by weight of polyvinylpyrrolidone as a molding binder and an appropriate amount of methyl alcohol as a solvent were added, and the mixture was mixed, dried, crushed, and molded in the same manner as in Example 1.

The relative density of the obtained molded body was 537%.

Furthermore, this compact was sintered under the same conditions as in Example 1, and the relative density, three-point bending strength, and Vickers hardness of the obtained sintered body were examined in the same manner as in Example 1. 2
Also listed in the table.

In addition, in Comparative Example 4, as shown in Table 2, the three-point bending strength at high temperatures was lower than the strength at room temperature, so boron carbide added as a sintering aid, It is presumed that carbon exists in part of the grain boundaries.

(Comparative Example 5) Commercially available α-type silicon carbide powder with an average particle size of 0.5 μm 100
Pour part by weight into a container, and add sintering agent with an average particle size of 0 to this as a sintering aid.
．． Add 2 parts by weight of 2 μm alumina powder, further add 2 parts by weight of polyvinylpyrrolidone as a molding binder, and add an appropriate amount of methyl alcohol as a solvent,
The mixture was mixed, dried, crushed, and molded in the same manner as in Example 1.

The relative density of the obtained molded body was 54.9%.

Furthermore, this compact was sintered under the same conditions as in Example 1, and the relative density, three-point bending strength, and Vickers hardness of the obtained sintered body were examined in the same manner as in Example 1. 2
Also listed in the table.

In addition, as shown in Table 2, the three-point bending strength of Comparative Example 5 significantly decreases under high bulk, so alumina, a low melting point substance added as a sintering aid, It is presumed that it exists in some parts of the world.

"Effects of the Invention" As explained above, the high purity silicon carbide sintered body of the invention according to claim 1 of the present invention consists of a silane compound or a silicon halide and a hydrocarbon in plasma in a non-oxidizing atmosphere. Ultrafine silicon carbide powder with an average particle size of 0.1 μm or less is synthesized by introducing a raw material gas and performing a gas phase reaction while controlling the pressure of the reaction system in the range of less than 1 atmosphere to Q, l torr. , is obtained by heating and sintering without adding a sintering aid, and the manufacturing method of the invention according to claim 2 is a method capable of manufacturing the above-mentioned high-purity silicon carbide. Therefore, according to this high-purity silicon carbide sintered body and its manufacturing method, the following excellent effects can be obtained.

■The high-purity silicon carbide sintered body according to claim 1 has a high density and does not contain any sintering aids, so it does not contain impurities in the grains and has no impurities in the grain boundaries or triple points. It also has high purity and no structural defects, with no impurities precipitated. Therefore, this sintered body has excellent mechanical properties such as high-temperature strength.

(2) Since ultrafine powder with an average particle size of 0.1 μm or less is used as the starting material, a sintered body with a fine structure can be obtained, resulting in high strength and high hardness.

■When not using a sintering aid, conventional methods required special methods such as sintering under ultra-high pressure to obtain a high-density sintered body; It is possible to easily obtain high-density, high-purity silicon carbide sintered bodies using industrial methods such as hot pressing and pressureless sintering. This is much more advantageous than before. In addition, since pressureless sintering is possible, it is possible to reduce the manufacturing cost of the sintered body, expand shapeability, and improve operability through continuous operation.

(2) Since no sintering aid is added, the mixing process in producing the sintered body can be shortened, and production costs can therefore be reduced compared to conventional methods.

(2) Since it does not contain any sintering aids and produces a highly pure sintered body with an extremely low amount of metal impurities, it can be used in the semiconductor field, which has traditionally been difficult to use.

[Brief explanation of drawings]

The drawing is an electron micrograph showing the particle structure of ultrafine β-type silicon carbide powder, which is used as a raw material for the sintered body of the present invention. ,1,5SLPM and CH41,8SLP
M (C/Si [molar ratio] 12) was introduced, and the pressure of the reaction system was set to 260 to? ? This figure shows ultrafine silicon carbide powder obtained by a controlled gas phase reaction.

Claims (6)

[Claims] (1) A raw material gas consisting of a silane compound or silicon halide and a hydrocarbon is introduced into plasma in a non-oxidizing atmosphere, and a gas phase reaction is performed while controlling the pressure of the reaction system in the range of less than 1 atm to 0.1 torr. Ultrafine silicon carbide powder with an average particle size of 0.1 μm or less synthesized by
A high-purity silicon carbide sintered body obtained by heating and sintering without the addition of sintering aids. (2) Introducing a raw material gas consisting of a silane compound or silicon halide and hydrocarbon into plasma in a non-oxidizing atmosphere, and performing a gas phase reaction while controlling the pressure of the reaction system in the range of less than 1 atmosphere to 0.1 torr. A method for producing a high-purity silicon carbide sintered body, which comprises heating and sintering ultrafine silicon carbide powder having an average particle size of 0.1 μm or less. (3) The high purity silicon carbide sintered body according to claim 1, wherein the density of the sintered body is 85% or more of the theoretical density. (4) The method for producing a high-purity silicon carbide sintered body according to claim 2, wherein the density of the high-purity silicon carbide sintered body is 85% or more of the theoretical density. (5) The high-purity silicon carbide sintered body according to claim 1, wherein the sintering atmosphere during sintering is an inert atmosphere, a reducing atmosphere, or a vacuum atmosphere. (6) The method for producing a high-purity silicon carbide sintered body according to claim 2, wherein the sintering atmosphere during sintering is an inert atmosphere, a reducing atmosphere, or a vacuum atmosphere. .