JPH0465361A - Silicon carbide heater and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a silicon carbide heater excellent in anti-oxidation property, corrosion resistance and thermal conductivity by sintering a mixture composed of the general silicon carbide powder having a specified particle size and the silicon carbide powder manufactured by vapor-phase reaction having a specified particle size and manufacturing the electric heater with this sintered body. CONSTITUTION:This silicon carbide heater is sintered without addition of a sintering auxiliary and composed of the silicon carbide sintered body having >=2.8 kg/cm<2> density of the sintered body and <=10OMEGA cm of the electric specific resistance at room temperature. The silicon carbide heater is obtained by a process as follows. That is, a first silicon carbide powder 0.1-10 mum of particle size, a second silicon carbide powder having 0.1 mum of a mean particle size obtained by the vapor-phase reaction by introducing a gaseous raw material composed of silane compounds or silicon halide and hydrocarbons into plasmas in non-oxidative atmosphere and controlling the pressure of a reaction system is in the range of 1 atm to 0.1 Torr are mixed, then the mixture is heated and sintered to manufacture the silicon carbide sintered body and this sintered body is used as the electric heater.

Description

Detailed Description of the Invention "Industrial Field of Application The present invention is a highly pure and dense carbonized material that has excellent oxidation resistance, corrosion resistance, and heat resistance, and is suitable for use in an oxidizing atmosphere and a vacuum atmosphere. The present invention relates to a silicon carbide heater made of a silicon sintered body and a method for manufacturing the same.

"Prior Art" Heaters that can generally be used in an oxidizing atmosphere include metals such as iron-chromium-aluminum alloys and nickel-chromium alloys. However, heaters made of these metals have been dissatisfied with the fact that they can only be used up to about 1100° C. due to corrosion or melting due to oxidation.

As for ceramics, porous silicon carbide, molybdenum silicide, etc. have been put into practical use, and the upper limit of the usable temperature for these heaters is 1600°C for porous silicon carbide.
Molybdenum silicide exhibits a temperature of about 1800° C., which is higher than that of the metals mentioned above.

However, since heaters made of porous silicon carbide contain about 20% by volume of pores, they oxidize quickly in high-temperature air, and electrically insulating silicon dioxide is generated not only on the surface but also inside. However, there are problems in that the performance as a heater deteriorates significantly, such as localized abnormal heat generation and a decrease in mechanical strength. On the other hand, molybdenum silicide begins to soften at 1,300°C, so when used at high temperatures, ie, 1,300°C or higher, its mechanical strength and thermal shock resistance decrease, resulting in a shortened lifespan as a heater.

Furthermore, carbon has been commonly used as a heater that can be used in an inert atmosphere or a vacuum atmosphere. However, carbon has extremely poor oxidation resistance at high temperatures, so it easily reacts with moisture and oxygen that evaporates from heated samples, etc., producing monomorphic carbon and carbon dioxide, which is emitted. There is a problem in that it cannot be used in heating devices for semiconductors or superconducting materials that do not like contamination.

As described above, conventional heaters used in an oxidizing atmosphere or a vacuum atmosphere have various problems with respect to oxidation resistance, corrosion resistance, heat resistance, etc.

Therefore, as a heater material, it originally has oxidation resistance, corrosion resistance,
Techniques that utilize dense silicon carbide, which has excellent heat resistance, have been provided in the past. Broadly speaking, such technologies can be classified as shown below.

(a) Silicon carbide with titanium carbon, zirconium carbide, molybdenum boride, zirconium boride, molybdenum silicide,
A silicon carbide sintered body to which one or more of tantalum silicide, titanium nitride, zirconium nitride, carbon, etc. is added and the electric resistivity value is adjusted by continuously contacting a conductive substance in the sintered body can be used as a heater. Technology used.

(b) By adding one or more types of compounds such as aluminum oxide, aluminum nitride, aluminum carbide, titanium oxide, etc. to silicon carbide and reacting these compounds with each other, or by reacting the compound and silicon carbide, conductivity can be achieved. f: A technology in which a sintered silicon carbide body is used as a heater by forming a chemical compound or a composite phase at the grain boundaries of silicon carbide to adjust the electrical resistivity.

(c) A technique in which a dense silicon carbide film is coated on a conventional heater such as porous silicon carbide or carbon by a CVD method or a PVD method, and this is used as a heater.

"Problems to be Solved by the Invention" However, the heater manufactured by the above technique has the following disadvantages.

What the above technologies (a) and (b) have in common is that one or more types of conductive substances or compounds are added, or because these substances are different from silicon carbide. It is very difficult to uniformly disperse it in a sintered body, and furthermore, the conductive path in the sintered body is easily broken, and when used as a heater, variations in heat generation characteristics occur. Furthermore, when these substances are added, there is a serious problem in that any of the inherent properties of silicon carbide, such as high M oxidation resistance, high corrosion resistance, high thermal conductivity, and high temperature high strength, deteriorate. Furthermore, in heaters made of these silicon carbide sintered bodies, additive substances often have inferior corrosion resistance and heat resistance than silicon carbide, so when heat is generated to high temperatures, the additive substances may evaporate or decompose. It easily gasifies and is released, making it unsuitable for use in processes for manufacturing semiconductors and superconducting materials, which are sensitive to external contamination.

On the other hand, in the heater manufactured using the technology (c), the thermal expansion coefficient of porous silicon carbide or carbon, which is the resistance heating element, and the dense repurchased silicon film, which acts as a protective film against oxidation and corrosion. Since the values are often different, the film peels off during repeated heating and cooling, shortening the life of the heater.

In addition, this dense silicon carbide has a high electrical resistivity value, so
The electrodes of the heater cannot be coated, so oxidation and corrosion are likely to occur from the exposed parts.

The present invention has been made in view of this technical background.
The aim is to obtain a highly pure and dense silicon carbide sintered body without adding any sintering aids, thereby achieving the excellent toughness resistance, corrosion resistance, heat resistance, etc. inherent to silicon carbide. It is an object of the present invention to provide a silicon carbide heater which has excellent electrical conductivity and has an electrical resistivity value of 10 cm or less at room temperature, and a method for manufacturing the same.

1. Means for Solving Problem 1" As a result of intensive research to achieve the above object, the present inventors discovered that a first silicon carbide powder having an average particle diameter of 0.1 to 10 μm and a non-oxidizing atmosphere It was synthesized by introducing a raw material gas consisting of a silane compound or silicon halide and a hydrocarbon into the plasma of the plasma, and conducting a gas phase reaction while controlling the pressure of the reaction system in the range of less than 1 atm to 0.1 jorr. A silicon carbide sintered body is obtained by mixing the powder with a second silicon carbide powder having an average particle size of 0.1 μm or less, heating and sintering this, and this sintered body can be used as a heater, or simply as a non-oxidized Introducing a raw material gas consisting of a silane compound or a silicon halide and a hydrocarbon into a plasma in a neutral atmosphere,
Ultrafine silicon carbide powder with an average particle diameter of 0.1 μm or less synthesized by gas phase reaction while controlling the pressure of the reaction system in the range of less than 1 atm to 0°1 torr is calorically heated and sintered. By obtaining a silicon carbide sintered body by using this sintered body and using this sintered body as a heater, the sintered body density can be increased to 2.8 g / We have discovered that it is possible to obtain a silicon carbide heater made of a silicon carbide sintered body with a resistivity of 1Ωcm or more and an electrical resistivity of 1Ωcm or less at room temperature, and have solved the above problems! child .

Hereinafter, the silicon carbide heater of the present invention will be explained in detail based on its manufacturing method.

First, a first silicon carbide powder having an average particle diameter of 0.1 to 10 μm and a second silicon carbide powder having an average particle diameter of 0.1 μm or less are prepared. Here, the first silicon carbide powder may be one that is commonly used, such as silica reduction method,
Those manufactured by a method such as the Acheson method are used. However, when manufacturing heaters for heating devices used in the manufacturing process of semiconductors and superconducting materials, high purity is required, so it is necessary to use high-purity powder that has been subjected to rigorous treatment. As the first crystal phase of silicon carbide,
It may be amorphous 1, α type, β type, or a mixed phase of these. Further, it is desirable that the average particle diameter of the silicon carbide powder is 0.1 to 1 μm, since this improves sinterability.

In addition, as the second silicon carbide powder, a raw material gas of a silane compound or a silicon halide and a hydrocarbon is introduced into plasma in a non-oxidizing atmosphere, and the pressure of the reaction system is adjusted from less than 1 atmosphere to 0, I Lorr. The product obtained by controlling the gas phase reaction is used. For example, when synthesis is performed by introducing a raw material gas consisting of monosilane and methane into argon plasma excited by radio frequency, β-type ultrafine powder with an average particle diameter of 0.02 μm and a small aspect ratio can be synthesized. Depending on the conditions, a mixed phase of 1iα type and β type can be obtained. The ultrafine powder obtained in this way has very good sinterability, so it can be made into a highly pure and dense powder by simply mixing it with the first silicon carbide powder without adding any sintering aid. It becomes possible to obtain a silicon carbide sintered body.

Next, the first silicon carbide powder and the second silicon carbide powder are mixed to form a mixture. Here, when mixing the first silicon carbide powder and the second silicon carbide powder, the blending amount of the second silicon carbide powder is 0.5 to 50% by weight of the whole.
It is said that it is suitable to set it as the range of. That is, if the blending amount of the second silicon carbide powder is less than 0.5% by weight, the effect of blending this silicon carbide powder on densification will not be sufficiently exhibited, and if the blending amount is less than 50% by weight. This is because the density of the sintered body is almost flat and the effect cannot be obtained. In addition, when manufacturing heaters used in heating furnaces and vapor deposition equipment used in the manufacture of semiconductors and superconducting materials, high purity is required, so only the second silicon carbide powder is used. Preferably, a sintered body is produced. That is, since the second silicon carbide powder is synthesized using a high-purity gas as a raw material, the amount of impurities it contains is extremely small at several ppm or less, and the purity is high.

Thereafter, the mixture or the second silicon carbide powder is molded into a desired shape using a heater, and the resulting molded body is
The silicon carbide heater is obtained by heating in a temperature range of 800° C. to 2400° C. and sintering without adding a sintering aid. In molding the silicon carbide powder, conventionally known methods such as press molding, extrusion molding, and injection molding 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, sintering methods include normal pressure sintering, atmospheric pressure sintering, hot press sintering, or hot isostatic sintering (HI
Conventional methods such as P) can be employed, or it is desirable to employ a pressure sintering method such as hot pressing in order to obtain a silicon carbide heater with higher density and excellent conductivity. The sintering temperature is also not particularly limited, but is 19
If the heating temperature is lower than 00°C, insufficient sintering will occur, and 2
At heating temperatures higher than 300°C, silicon carbide tends to evaporate, and the strength and toughness of the sintered body may decrease due to particle growth.
It is preferred to sinter at a temperature range of °C.

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

The silicon carbide heater thus obtained has a sintered body density of 2-8 g/cm3 or more (theoretical density is 3°21
x/cm3, which is about 87% or more of the theoretical density). And the sintered body density is 2.81/cm”
Because of the above, the bonding strength between silicon carbide particles is sufficient, and the pores are small and few in number, resulting in excellent oxidation resistance and corrosion resistance, and thus stable heater performance. Furthermore, since it has high mechanical strength at high temperatures, it is possible to reduce the weight by making the wall thinner, and the durability is further improved compared to conventional products.

In addition, this silicon carbide heater has an electrical resistivity value of 10 CIl+ or less at room temperature, so it can be made smaller when used as a resistance heating heater, and the electrical resistivity value does not change much due to temperature. Therefore, it has the advantage that it is easy to control the current to keep the heater surface temperature constant.

In addition, as mentioned above, the silicon carbide heater here is dense with a sintered body density of 2.8 g/cm or more, and since no sintering aid is added, sintering agents exist at the grain boundaries. A fine and uniform structure with few impurities can be obtained, and therefore a high thermal conductivity of 15QW/1Il- or more can be obtained.

Therefore, this silicon carbide heater has excellent heat uniformity.
! Not only that, but the thermal response is also fast.

As described above, the silicon carbide heater of the present invention has a high purity, and in particular, if it is produced based on the manufacturing method described in claim 4, the content of impurities other than free carbon and free silica can be reduced to 1.
00 ppm or less. Therefore, even when such high-purity heaters are used at high temperatures and under reduced pressure, there is almost no gas generation due to evaporation or decomposition of impurities from the heater, making them ideal for the production of semiconductors and superconducting materials. It can also be used in fields where a high purity atmosphere is required, such as in manufacturing processes.

First of all, silicon carbide heaters are highly pure and dense, so they have the inherent high oxidation resistance, high corrosion resistance, high thermal conductivity, and high strength at high temperatures that are inherent to silicon carbide.
As a result, wear due to oxidation, corrosion, decomposition, etc. is extremely reduced even when used in an oxidizing atmosphere or a vacuum atmosphere, thereby extending the life of the heater and making it possible to reduce the weight by making the heater body thinner. In addition, heater properties such as thermal uniformity and thermal response are improved, and the heater is excellent in heat resistance even in high-temperature atmospheres, eliminating deformation of the heater and making it sufficiently resistant to thermal shock. Furthermore, it can be fully used in processes where contamination is averse, such as in the field of manufacturing semiconductors and superconducting materials.

Secondly, the electrical resistivity value at room temperature is low and there is little variation due to temperature, which makes it possible to downsize the heater.
;The heater temperature can be easily controlled by the current value. Furthermore, since the structure of the sintered body is uniform, electrical discharge machining can be performed better than ever before, and micro-machining and three-dimensional machining can be carried out freely.

[Example code] Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example 1) As the first silicon carbide powder, the average particle diameter was 0.7 μm, B
β-type silicon carbide powder with an ET specific surface width of 13 m 2 /g was used. When we investigated the amount of metal impurities contained in this powder, we found that
10 ppm sodium, 5 ppm potassium, 55
ppm iron, 171 ppm aluminum, 22p
Contains pm calcium, nickel, chromium,
The copper content was less than IpP ■.

Next, this first silicon carbide powder was subjected to vapor phase synthesis using silicon tetrachloride and ethylene as raw material gases by plasma CVD method, with an average particle diameter of 0.01 μm and a specific surface area of 96 m2/
g of ultrafine amorphous silicon carbide powder (second silicon carbide powder) was added in an amount of 5% by weight, and this was dispersed in methanol,
Further, the mixture was mixed in a ball mill for 12 hours.

Next, this mixture was dried and filled into a graphite mold with an inner diameter of 160 mm, and heated in a hot press machine under an argon atmosphere at a press pressure of 400 kg/cm2 and a sintering temperature of 2.
Sintering was performed at 200°C for 90 minutes.

When the density of the obtained silicon carbide sintered body was examined, it was found to be 3.1.
g/c was. In addition, the three-point bending strength of this sintered body at room temperature was measured in accordance with JIS R-1fi01, and the result was 64,3 kg/mm2, and the three-point bending strength at 1500°C was 68.5 kg/mm". Also, when the electrical resistivity value at room temperature was measured using the four-probe method, it was 0.68.5 kg/mm".
A result of 0.05Ω・cm was obtained, and when the thermal conductivity at room temperature was measured using the laser flash method, it was 197W.
/w-. In addition, when the amount of impurities contained in the sintered body was investigated by arc emission analysis, it was found that iron was 32 PPTnS.
Aluminum s s ppm, calcium power 5 ppm
ffl, copper was 3 pp+a, and sodium, potassium, chromium, and nickel were all less than 1 pp+n. Furthermore, the surface of the sintered body was etched with potassium ferrocyanide at a concentration of 10%, and the surface of the sintered body was etched using a scanning electron microscope (SE).
Examine the microstructure of the sintered body using M)! Second, it was found that the size of the bores was 1 μm or less, the number of bores was small, and the structure was extremely homogeneous and dense.

Next, this disc-shaped silicon carbide sintered body with a diameter of 160+ am and a thickness of 10 mm was removed by wire electrical discharge machining to remove a part of its outer periphery and a part of the inside, and to form a six-dimensional structure as shown in Figs. A disk-shaped silicon carbide heater 1 was provided that protruded in the direction, and a molybdenum electrode 2 was further attached. Note that wire electrical discharge machining was performed using a transistor pulse circuit type electrical discharge machine. Further, a brass wire with an outer diameter of 2 mm was used as the discharge wire, and the machining conditions were a machining voltage of 50 V, a pulse width of 1.2 μsec, and a pause time of 20 μsec.

When electrical discharge machining was performed in this manner and the surface roughness of the electrical discharge machined surface was measured, Rmax was 2.5 μm, confirming that the silicon carbide sintered body had good electrical discharge machinability.

Then, when this silicon carbide heater was attached to an oxidation heating furnace and a current of 15A was passed while keeping the applied voltage constant,
The surface of the heater is heated at a rate of approximately 2°C/1n, and
After 5 minutes, the temperature reaches the set temperature of 1000°C. Next, when heating was continued for 5 hours, almost no wear on the heater was observed, and no abnormality was observed even after this heating test was repeated 10 times.

In addition, when this silicon carbide heater was placed in a vacuum heating furnace and a similar heating test was conducted under a vacuum of 1 ton and 10-'torr, there was almost no wear on the heater, and no gas was generated. It was also long.

From the above results, it was confirmed that the silicon carbide heater of the present invention has good heating characteristics and excellent durability even when used in an oxidizing atmosphere and a vacuum atmosphere.

(5j! Examples 2 to 4) Same silicon carbide powder as Example 1 (first silicon carbide powder)
Plasma C using monosilane and methane as raw material gases
Average particle size 0.02 μm, B synthesized in vapor phase by VD method
ET specific surface area value 70+++2/! 5 to 50% by weight of second base silicon carbide ultrafine powder (second silicon carbide powder) was added and sintered under the same conditions as in Example 1 to produce a silicon carbide sintered body.

The sintered body density, 3-point bending strength at room temperature, 3-point bending strength at 1500°C, electrical specific resistance value at room temperature, and thermal conductivity at room temperature of the obtained silicon carbide sintered body were determined as in Example 1. Each was investigated using the same method, and the results are shown in Table 1 together with the measurement results of Example 1.

From the results shown in Table 1, the effects of the present invention can be sufficiently obtained even if ultrafine silicon carbide powder synthesized from different raw material gases is used or the amount of ultrafine silicon carbide powder added is changed. was confirmed.

In addition, the amount of impurities contained in these sintered bodies was determined according to Example 1.
As a result of examination using the same method as above, the total amount of impurities in all sintered bodies was 2 Q Oppm or less.

Blank space below (Example 5) Plasma CVD using monosilane and methane as raw material gases
Average particle size 0.03 μm synthesized in vapor phase by method, BET
Ultrafine β-type silicon carbide powder having a specific surface area of 58 Io27 g was dispersed in methanol and further mixed in a ball mill for 12 hours.

Next, this mixture was dried and granulated to obtain a powder, which was sintered under the same conditions as in Example 1 to produce a silicon carbide sintered body.

When the density of the obtained silicon carbide sintered body was investigated, it was found that 3-1
Hot with g/cm3! :. In addition, the three-point bending strength at room temperature, the three-point bending strength at 1500'C, the electrical resistivity at room temperature, and the thermal conductivity at room temperature of this silicon carbide sintered body were measured using the same method as in Example 1. The results are also listed in Table 1.

Furthermore, impurity analysis of this silicon carbide sintered body was conducted using the same analytical method as in Example 1, and it was found that sodium content was 5 ppm.
1 Iron is 8 ppm, aluminum is 10 ppm.

It contained 2 ppm of chromium, and less than 1 ppm of potassium, calcium, nickel, and copper.

From the above results, it was confirmed that the silicon carbide sintered body made only from ultrafine silicon carbide powder has higher strength and purity, and it was found that it can be used as a heater that can be used even under severe conditions.

"Effect of the invention" As explained above, claims 1 and 2 of the present invention
The silicon carbide heater according to the invention described in Claims 3 and 4
It is obtained by the manufacturing method of the invention described in .

According to the manufacturing method according to claims 3 and 4,
Since dense sintering can be performed without the addition of sintering aids, it is possible to obtain a sintered body of extremely high purity and high density, thereby achieving high oxidation resistance and high corrosion resistance, which are the inherent properties of silicon carbide. , it is possible to manufacture a silicon carbide heater that has both high thermal conductivity and high temperature and high strength, and also has a low electrical resistivity value.

As a result, the silicon carbide heaters according to claims 1 and 2 have almost no wear even when used in an oxidizing atmosphere, and have excellent durability. In addition, because it is dense and highly pure, even when used under reduced pressure or vacuum, there is almost no generation of contaminant gas due to evaporation of impurities from the heater, so there is no contamination caused by the production of semiconductors or superconducting materials. Even if it is used in the process where it is most disliked, it will not deteriorate the product properties. Furthermore, since the heat dissipation property is good, the heater properties such as heat uniformity and thermal response are excellent.

Furthermore, the silicon carbide heater of the present invention has significantly higher mechanical strength at high temperatures than conventional heaters, which reduces the heater's deformation and damage due to thermal shock, and allows for weight reduction through thinner walls. This makes handling easier. In addition, it has a low electrical resistivity value and little fluctuation due to temperature, making it possible to use small heaters.
The heating device using this can be made compact,
Furthermore, since the heater temperature can be easily controlled by the current value, the control system of the heating device can be simplified.

Furthermore, since it has good electrical discharge machinability, it can be manufactured with sufficient accuracy even into three-dimensional complex shapes, and therefore its range of use is wide. As a result, the silicon carbide heater can be used in an oxidation heating furnace, an atmosphere heating furnace, a vacuum heating furnace,
It can be used as a heater for vapor deposition equipment, CVD equipment, etc., and has great industrial effects.

[Brief explanation of drawings]

1 and 2 are diagrams showing one embodiment of the present invention, in which FIG. 1 is a plan view of a silicon carbide heater, and FIG. 2 is a plan view of a silicon carbide heater.
It is a view taken along the line ■-■ in the figure. 1...Silicon carbide heater 2...Molybdenum electrode part.

Claims (4)

[Claims] (1) Sintered without the addition of sintering aids, with a sintered body density of 2.8 g/cm^3 or more, and an electrical resistivity value of 1 at room temperature.
A silicon carbide heater made of a silicon carbide sintered body of Ω・cm or less. (2) The silicon carbide heater according to claim 1, which has a thermal conductivity of 150 W/m·K or more at room temperature. (3) A first silicon carbide powder with an average particle size of 0.1 to 10 μm and a raw material gas consisting of a silane compound or a silicon halide and a hydrocarbon are introduced into plasma in a non-oxidizing atmosphere, and the reaction system is A second silicon carbide powder with an average particle size of 0.1 μm or less synthesized by gas phase reaction while controlling the pressure in the range of less than 1 atmosphere to 0.1 torr is mixed, and this is heated and sintered. A method for manufacturing a silicon carbide heater, characterized in that a silicon carbide sintered body is obtained by this process, and the sintered body is used as a heater. (4) 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 atm to 0.1 torr. A silicon carbide sintered body is obtained by heating and sintering ultrafine silicon carbide powder having an average particle diameter of 0.1 μm or less, which is synthesized by heating, and this sintered body is used as a heater. A method for manufacturing a silicon carbide heater.