JP3023435B2 - High purity silicon carbide sintered body and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a silicon carbide sintered body and a method for producing the same, and more particularly to a method using a highly active silicon carbide fine powder synthesized by a plasma CVD method. , A high-purity and high-density silicon carbide sintered body obtained without adding a sintering aid,
It relates to the manufacturing method.

"Prior art" Since silicon carbide is extremely stable chemically and has excellent mechanical properties and oxidation resistance at high temperatures, its sintered body is used for chemical pump parts, heat exchanger parts, gas turbine parts. It is expected to be applied to engine parts and the like. In recent years, in the field of semiconductors, with the rise in the heat treatment temperature of silicon, the conventional quartz jig has been switched to a silicon jig having excellent creep resistance at a higher temperature. In addition, as a functional material, application to a high-temperature semiconductor element, a blue light-emitting element, and the like is being studied.

By the way, since silicon carbide is a hardly sinterable substance having a strong covalent bond, in order to obtain a high-density sintered body, powder having an average particle size of submicron or more manufactured by Acheson method or silica reduction method is used. In addition, it was necessary to add one or more of elements such as B, C, Al, Be, Ti, Fe, etc. as a sintering aid by several weight% or more.

However, these sintering aids have a lower melting point and lower strength than silicon carbide, and precipitate as impurities at the grain boundaries and triple points of the sintered body. However, this is a cause of deteriorating excellent performance such as high contact resistance. Further, in the semiconductor field where high purity is required, there is a disadvantage that such impurities cannot be used in such a field because the impurities are mixed into the silicon of the product by thermal diffusion to lower the electrical characteristics.

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

[Problem to be Solved by the Invention] However, in the method of Japanese Patent Application Laid-Open No. 63-8263, since a super-high pressure of several GPa is required during sintering, only a small sintered body can be obtained due to limitations of the apparatus. Therefore, the production cost is high, so that it is not suitable as an industrial production method.

Further, it is known that a silicon carbide sintered body containing no sintering aid can be produced by a vapor deposition method such as a PVD method or a CVD method. A thickness of only about several centimeters is obtained at the maximum, which limits the applications and increases the manufacturing cost.

The present invention has been made in order to solve the problems in the conventional method for manufacturing a silicon carbide sintered body, and the object of the present invention is to provide high-temperature strength, corrosion resistance, excellent oxidation resistance, and high purity. A high-density silicon carbide sintered body substantially free of any sintering aid for use over a wide range from high-temperature structural parts such as gas turbines to high-purity parts such as semiconductor manufacturing equipment. And a method of manufacturing the same.

[Means for Solving the Problems] In the high-purity silicon carbide sintered body according to claim 1 of the present invention, a raw material gas comprising a silane compound or a silicon halide and a hydrocarbon in a plasma in a non-oxidizing atmosphere. , A silicon carbide ultra-fine powder having an average particle size of 0.1 μm or less synthesized by 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, to obtain a sintering aid. A silicon carbide sintered body obtained by heating and sintering without addition and containing no metal impurities at the triple point is a means for solving the above problem.

In the method for producing a high-purity silicon carbide sintered body according to the second aspect of the present invention, a raw material gas comprising a silane compound or silicon halide and a hydrocarbon is introduced into plasma in a non-oxidizing atmosphere to form a reaction system. By heating and sintering ultra-fine silicon carbide powder with an average particle size of 0.1 μm or less synthesized by performing a gas phase reaction while controlling the pressure within the range of less than 1 atm to 0.1 torr, metal impurities are added to the triple point. The object of the present invention is to obtain a silicon carbide sintered body containing no.

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

The present inventors have conducted intensive studies to achieve the above object,
Heating and sintering 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 in an inert gas, reducing gas or vacuum atmosphere As a result, it was determined that a high-purity high-purity silicon carbide sintered body could be obtained without adding a sintering aid, and the present invention was completed based on this finding.

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. As a method for obtaining such silicon carbide ultrafine powder having a particle size of 0.1 μm or less, organosilicon such as polymethylcarbosilane is heated to 1500 ° C.
Heating at the above temperature, 100% of SiH ₄ , SiCl ₄ and hydrocarbon, or CH ₃ SiCl ₃
Gas phase reaction method of heating at a temperature of 0 ° C to 1800 ° C. For tail flame of arc plasma or high frequency induction thermal plasma
A plasma CVD method in which SiH ₄ , SiCl ₄ and hydrocarbons are introduced to cause a gas phase reaction, and a laser CVD method in which a gas mixture of SiH ₄ and C ₂ H ₄ is irradiated with a CO ₂ laser to cause a gas phase reaction, and the like. Conventionally known.

However, since the silicon carbide ultrafine powder obtained by these methods contains many coarse particles having a particle size of 1 μm or more, the particle size distribution is wide, the inside of the particles tends to have a hollow structure, and the particle shape is irregular. There were many disadvantages from the viewpoint of the sinterability. Therefore, the ultrafine powder obtained by these methods cannot be densified without a sintering aid unless a special method such as sintering under ultrahigh pressure is used.

On the other hand, in the present invention, as a silicon carbide ultrafine powder having a particle size of 0.1 μm or less, a silane compound or a silicon halide and a hydrocarbon are contained in plasma in a non-oxidizing atmosphere created by a non-polar discharge of a high frequency induction method. Introduce raw material gas,
The reaction system is prepared by 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 or more. For example, when a raw material gas is introduced from silicon tetrachloride and ethylene into an argon plasma excited by high frequency and synthesized, an amorphous ultrafine powder having an average particle size of about 0.01 to 0.03 μm and a small aspect ratio is obtained. . Also, when the same synthesis is performed using a material gas consisting of monosilane and ethylene as a raw material gas, β-type fine powder having an average particle diameter of about 0.005 to 0.03 μm and a small aspect ratio is obtained. A mixed phase with the mold is obtained.

Then, as described above, the pressure of the reaction system is reduced from less than 1 atm to 0.
By controlling the pressure within the range of 1 torr, it becomes possible to introduce the source gas into the plasma at an ultra-high temperature of several thousand degrees Celsius or more, so that silicon carbide can be stably precipitated from the state of ions, atoms, etc. Therefore, since the crystal growth of the ultrafine silicon carbide powder synthesized by this method is sufficiently controlled by a sharp temperature gradient, the individual particles are ultrafine and the particle size distribution is extremely high. It is narrow and the particle shape is spherical with an aspect ratio close to 1, resulting in high surface activity and excellent sinterability.

In addition, since the obtained powder is an ultrafine powder, there is no need for a pulverizing step for miniaturizing the powder, and therefore, there is no contamination due to abrasion from the pulverizing medium, and a high-purity powder can be obtained. There is.

The ultrafine powder may have any of an α phase, a β phase, an amorphous phase, or a mixed phase thereof. The crystallinity can be easily controlled by adjusting the conditions of the plasma CVD method, for example, adjusting the deposition temperature and speed of the ultrafine powder.

In the production method of the present invention, it is possible to produce a high-density and high-purity silicon carbide sintered body using a high-purity silicon carbide fine powder without adding any sintering aid at all. However, in applications where high purity properties are not required and only denseness is required, a sintering aid may be added to this ultrafine powder. For example, conventionally known Al, Be, Ti, F
Needless to say, a high-density sintered body can be obtained by adding e, Ba, B or the like as a sintering aid and sintering.

The high density silicon carbide sintered body can be obtained by the production method of the present invention because the average particle size of the silicon carbide ultrafine powder used is 0.1 μm.
m or less, and the surface is clean, which is presumed to be due to high sintering activity.

In addition, in forming the ultrafine powdered silicon carbide thus obtained, press molding, CIP molding, slip casting, tape molding, calender roll molding, extrusion molding, injection molding, etc. A conventionally known method can be adopted. In this case, polyvinyl alcohol, polyvinyl pyrrolidone, or the like can be used as the molding binder, and a dispersant such as a stearate may be added as necessary.

In sintering, normal pressure sintering is used as the sintering method.
Conventional methods such as atmospheric pressure sintering, hot press sintering, and hot isostatic sintering (HIP) can be used, but in order to obtain a higher density and higher strength silicon carbide sintered body, It is preferable to employ pressure sintering such as hot pressing. The sintering temperature is not particularly limited, but is 1800 ° C.
At a lower heating temperature, insufficient sintering occurs, and at a heating temperature higher than 2400 ° C., silicon carbide is liable to evaporate, and the strength and toughness of the sintered body may decrease due to the growth of particles. Sintering in the temperature range of 温度 2400 ° C. is preferred.

The atmosphere during sintering is an inert gas atmosphere,
Either a reducing gas atmosphere or a vacuum atmosphere can be employed.

The density of the obtained silicon carbide sintered body is preferably 85% or more of the logic density. When the density becomes 85% or more of the theoretical density, the sintered body has the original characteristics of silicon carbide, For example, they exhibit sufficient high-temperature high-strength, excellent touch resistance, oxidation resistance, and abrasion resistance. If a sintered body is manufactured under ordinary conditions based on the manufacturing method of the present invention, the density of the obtained sintered body is, of course, 85% or more of the theoretical density.

In the silicon carbide sintered body thus obtained,
Uses ultra-fine silicon carbide powder with an average particle size of 0.1 μm or less and high sintering activity, obtained by plasma CVD, without sintering aids as impurities (or with only a trace amount of sintering aids). ) Since it is sintered, its density becomes higher than 85% of the theoretical density, for example, so that the original properties of silicon carbide, such as high temperature and high strength,
Since it exhibits excellent contact resistance, oxidation resistance, and wear resistance, it can be applied to a wide range of fields such as gas turbine parts, engine parts, and mold parts for optical disk molding. Further, since the amount of impurities contained in the ultrafine silicon carbide powder used as a raw material is extremely small and thus extremely high in purity, it is useful in the field of semiconductors.

"Example" Hereinafter, the present invention will be described more specifically with reference to examples.

(Example 1) SiH ₄ 1.5SLPM and CH ₄ 1.8SLPM (C / Si [molar ratio]) were introduced into Ar thermal plasma excited by a high frequency of about 4 MHz.
= 1.2), and a gas phase reaction was performed while controlling the pressure of the reaction system to 260 torr to obtain ultrafine silicon carbide powder.

When the obtained fine powder was examined with a transmission electron microscope,
As shown in the drawing (transmission electron micrograph)
It was 0.03 μm. Further, when the crystal phase of this ultrafine silicon carbide powder was examined with a powder X-ray diffractometer, it was confirmed that it was a β phase. Further, the amount of contained metal impurities was measured by ICP emission spectroscopy, and the results are shown in Table 1.

From the results shown in Table 1, the obtained ultrafine silicon carbide powder contains almost no element that can serve as a sintering aid.
It turned out to be of very high purity.

Next, 100 parts by weight of the silicon carbide ultrafine 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 for 12 hours in a planetary ball mill. The mixture was dried, crushed, and formed into a disk by a conventional uniaxial press.

When the weight and size of the obtained molded body were measured to determine the molded body density, the relative density was 50.1%. Here, the relative density is a value calculated and calculated based on a theoretical density of 3.21 g / cm ³ as 100%. (The same applies hereinafter.) Further, the molded body is placed in a graphite hot press container, and pressurized at 40 MPa in an atmosphere of Ar1 atm.
in at a temperature rise rate of 2200 ° C
After sintering for about one minute, it was allowed to cool.

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

Also, from the obtained sintered body, 3 × 4 × 4
A flexural strength test piece of 0 mm was prepared and subjected to a three-point bending test at a span of 30 mm.The three-point bending strength at room temperature was 90.7 kg / m.
m ² and a three-point bending strength of 97.4 in air at 1500 ° C.
kg / mm ² . Further, when the hardness of this test piece was examined with a Vickers hardness meter, the Vickers hardness was 26.
00HV.

(Examples 2 to 6) SiH ₄ 1.5SLPM in Ar thermal plasma under the same conditions as in Example 1
CH ₄ 1.95 SLPM (C / Si [molar ratio] = 1.3) was introduced, and a gas phase reaction was performed while controlling the pressure of the reaction system at 210 torr to obtain ultrafine silicon carbide powder.

When the obtained fine powder was examined with a transmission electron microscope,
The average particle size was 0.02 μm, and the crystal phase was examined by a powder X-ray diffractometer. As a result, it was found that the mixed phase was a mixed phase of β phase and α phase.

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

The obtained compact was sintered under different conditions as shown in Table 2 and the relative density, three-point bending strength and Vickers hardness of the produced sintered body (Examples 2 to 6) were determined in Example 1 respectively. And the results are shown in Table 2.

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

In addition, the amount of trace metal impurities contained in the sintered body of Example 2 shown in Table 2 was measured by arc emission spectroscopy,
Table 3 shows the results.

From the results shown in Table 3, it was found that the sintered body of Example 2 contained almost no element as an impurity and was extremely high in purity.

(Comparative Example 1) 100 parts by weight of a commercially available β-type silicon carbide powder having an average particle diameter of 0.3 µm was placed in a container, and 2 parts by weight of polyvinylpyrrolidone as a forming binder and an appropriate amount of methyl alcohol as a solvent were added thereto. Mixing, drying, crushing, and molding were performed in the same manner as in Example 1.

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

Further, the molded body was placed in a graphite hot press container, and pressed at 40 MPa in an atmosphere of Ar1 atm.
in at a temperature rise rate of 2200 ° C
After sintering for about one minute, it was allowed to cool. (Same conditions as in Example 1) 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, and the results are also shown in Table 2.

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

From the results shown in Table 2, it was found that each of the obtained sintered bodies had a low relative density.

(Comparative Example 4) 100 parts by weight of a commercially available β-type silicon carbide powder having an average particle diameter of 0.3 µm was placed in a container, and an average particle diameter of 1 µm was added thereto as a sintering aid.
Of boron black powder and 2.5 parts by weight of carbon black powder having an average particle size of 0.03 μm, 2 parts by weight of polyvinylpyrrolidone as a molding binder, and an appropriate amount of methyl alcohol as a solvent. Mixing, drying, crushing, and molding were performed in the same manner as described above.

 The relative density of the obtained molded body was 53.7%.

Further, the molded body 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, and the results were obtained. Also shown in Table 2.

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

(Comparative Example 5) 100 parts by weight of a commercially available α-type silicon carbide powder having an average particle diameter of 0.5 μm was placed in a container, and the average particle diameter was 0.2 μm as a sintering aid.
m, 2 parts by weight of alumina powder, 2 parts by weight of polyvinylpyrrolidone as a molding binder, and an appropriate amount of methyl alcohol as a solvent were added, followed by mixing, drying, crushing and molding in the same manner as in Example 1.

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

Further, the molded body 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, and the results were obtained. Also shown in Table 2.

In the case of Comparative Example 5, the three-point bending strength was remarkably reduced at a high temperature as shown in Table 2; therefore, alumina, which is a low-melting substance added as a sintering aid, was used at the grain boundary. It is presumed that it exists in a part of the data.

[Effect of the Invention] As described above, the high-purity silicon carbide sintered body of the present invention according to claim 1 of the present invention is characterized in that a silane compound or a silicon halide and a hydrocarbon are mixed in a plasma in a non-oxidizing atmosphere. The raw material gas is introduced and the reaction system pressure is controlled in the range of less than 1 atm to 0.1 torr in a gas phase to produce ultrafine silicon carbide powder having an average particle size of 0.1 μm or less. It is obtained by heating and sintering without the addition of a binder, and the production method of the invention according to claim 2 is a method capable of producing the 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 aid, so that it does not contain impurities in the grains, and furthermore, its grain boundaries and triple points are also present. It is high purity and free from structural defects, in which no impurities are deposited. Therefore, this sintered body has excellent mechanical properties such as high-temperature strength.

Since an ultrafine powder having an average particle size of 0.1 μm or less is used as a starting material, a sintered body having a fine structure can be obtained, which has high strength and high hardness.

Unless a sintering aid is used, a special method such as sintering under ultra-high pressure was required to obtain a high-density sintered body. High-density, high-purity sintered silicon carbide can be easily obtained by industrial methods such as hot pressing or atmospheric sintering. This is significantly more advantageous than. Further, since normal pressure sintering is possible, it is possible to reduce the production cost of the sintered body, expand the shape imparting property, and improve the operability by continuous operation.

Since no sintering aid is added, the mixing process can be shortened in the production of a sintered body, and thus the production cost can be reduced as compared with the conventional case.

Since a high-purity sintered body containing no sintering aid and having a very small amount of metal impurities can be obtained, it can be used in the semiconductor field, which has been conventionally difficult to use.

[Brief description of the drawings]

The drawing is an electron micrograph showing the particle structure of the β-type silicon carbide ultrafine powder, which is a raw material for a sintered body of the present invention, wherein the frequency is about 4 MHz. ₄ 1.5SLPM and CH ₄ 1.8SLPM (C / Si [molar ratio] = 1.
2) shows an ultrafine silicon carbide powder obtained by performing a gas phase reaction while controlling the pressure of the reaction system to 260 torr by introducing the above (2).

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor 131, Fukusaku-ku, Fushimi-ku, Kyoto-shi, Kyoto, Japan -204 (72) Inventor Hiromi Noguchi 1-38.2 Hijimachi, Kokubunji-shi, Tokyo 6th Kamiyama Mansion 318 (56) References JP-A-2-199064 (JP, A) JP-A-2-204363 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/565

Claims (6)

(57) [Claims] A raw material gas comprising a silane compound or a silicon halide and a hydrocarbon is introduced into a plasma in a non-oxidizing atmosphere, and the pressure of the reaction system is controlled within a range from less than 1 atm to 0.1 torr. It is obtained by heating and sintering ultrafine silicon carbide powder having an average particle size of 0.1 μm or less synthesized by reacting without adding a sintering aid, and including no metal impurities at the triple point. Characterized high-purity silicon carbide sintered body. 2. A raw material gas comprising a silane compound or a silicon halide and a hydrocarbon is introduced into a plasma in a non-oxidizing atmosphere, and the pressure of the reaction system is controlled within a range from less than 1 atm to 0.1 torr. Heating and sintering ultrafine silicon carbide powder having an average particle diameter of 0.1 μm or less synthesized by reacting to obtain a silicon carbide sintered body containing no metal impurities at the triple point. A method for producing a high-purity silicon carbide sintered body. 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 for 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 for sintering is an inert atmosphere, a reducing atmosphere or a vacuum atmosphere. Production method.