JPH0535105B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a silicon carbide sintered body suitable mainly for heating furnace structural parts, and in particular, the present invention relates to a method for producing a silicon carbide sintered body suitable for a member for a diffusion furnace for manufacturing semiconductors. This invention relates to a method for producing a solid. [Prior Art] In general, materials with good thermal conductivity, high strength even at high temperatures, and high spalling resistance are effective for the structural parts of a heating furnace, especially the soaking tube. In particular, it is important that the soaking tubes of diffusion furnaces for semiconductor manufacturing have extremely high _purity because high-purity silicon wafers are loaded inside them. ,
Since it is cleaned with HF-HNO ₃ -CH ₃ COOH aqueous solution or HCl gas, it is important that the material has excellent corrosion resistance against these chemicals. As such a material, silicon carbide sintered body is the most promising material. Conventional methods for manufacturing silicon carbide sintered bodies include JP-A No. 45-38061, JP-A No. 57-501578, and JP-A No. 57-501578.
No. 54-16521 JP-A-56-109872 JP-A-56-
No. 114871 There is a method disclosed in JP-A-55-67573. These methods generally involve premixing silicon carbide powder (100 parts by weight), carbon powder (20 to 50 parts by weight), and pyrolytic carbon (10 to 20 parts by weight) to form a porous silicon carbide compact;
After being carbonized at 1200°C, it is then brought into contact with molten silicon and reacted at a high temperature of 1400°C or higher. However, in these methods, the bond between the reaction-produced silicon carbide and the pre-mixed silicon carbide particles is poor, and the free silicon remaining in the sintered body melts at temperatures above 1400°C. It had a drawback that the strength of the sintered body was significantly reduced to 20 Kgf/mm ² or less. On the other hand, as another manufacturing method, JP-A-51-85374
There is a method disclosed in Japanese Patent Publication No. 48-37404.
According to these methods, a high-density silicon carbide molded body is produced in advance by mixing and molding silicon carbide coarse particles mainly in the range of 40 to 200 μm and silicon carbide powder of 10 μm or less, and then impregnated with porous silicon. It is something to do. Therefore, since these sintered bodies are composed of extremely large silicon carbide crystals, they not only have a low strength of about 30 Kgf/mm ² in general, but also have a low strength at temperatures of 1400°C or higher due to the low strength between silicon carbide crystals. Strength increases to 15kg at high temperatures
It had the disadvantage that it was significantly lower than f/mm ² . [Problems to be Solved by the Invention] The present invention solves the above-mentioned drawback that the strength decreases at high temperatures, and makes it possible to obtain a high-density silicon carbide sintered body whose strength hardly decreases even at high temperatures. A manufacturing method is provided. [Means for solving the problem] As a result of various studies on silicon carbide sintered bodies, the present inventor found that the content of free carbon and free silica contained in the starting material silicon carbide powder By controlling the amounts of free carbon and free silica to below a certain amount, we have discovered that the strength of the primary sintered body of silicon carbide is significantly affected. succeeded in manufacturing. Next, in order to increase the density of this high-strength porous material, the amount of free carbon that must be impregnated must have an appropriate range and carbonization temperature to achieve high strength, and then the appropriate temperature and temperature must be maintained for the reaction with free silicon. Knowing that time was running out, they succeeded in obtaining a high-density silicon carbide sintered body with high strength and no decrease in high-temperature strength, which is the object of the present invention, and completed the present invention. The present invention will be explained in detail below. The present invention provides a method for producing a silicon carbide sintered body having a density of at least 3.0 g/cm ³ and an average diameter of silicon carbide crystals of 10 μm or less, comprising: (a) a free carbon content of 10% by weight or less; The free silica content is 5% by weight or less and the average particle size is
A step of molding silicon carbide powder of 10 μm or less into a green body of a desired shape; (b) charging the green body into a heat-resistant container;
(c) After impregnating the primary sintered body with a carbonaceous material,
A step of heating the carbonaceous material to a temperature of 900 to 2,200°C to carbonize the carbonaceous material to form a carbon/silicon carbide composite; (d) Heat the carbon/silicon carbide composite obtained in the above step (c) to a temperature of 1,500 to 2,200°C. A method for producing a silicon carbide sintered body, comprising the steps of contacting with molten silicon maintained at It is. In step (a) of the present invention, it is necessary that the powder be mainly silicon carbide powder with an average particle size of 10 μm or less. The reason for this is that when the diameter is larger than 10 μm, atoms move and evaporate between silicon carbide crystals during primary sintering.
This is because condensation is difficult to occur and the bond strength between silicon carbide crystals tends to be low. In order to increase the strength between silicon carbide crystals, the average particle size must be increased.
More preferably, the thickness is 3 μm or less. Further, it is preferable that the content of β-type silicon carbide in the silicon carbide powder is at least 60% by weight, and the remainder is α-type crystal or amorphous silicon carbide. The reason for this is that the β-type crystal is a low-temperature synthesis type crystal, recrystallization occurs at a relatively low temperature, and a silicon carbide crystal having high bonding strength can be obtained. Among them, the content of β-type silicon carbide is
More preferably, it is 80% by weight or more. The free carbon content in the silicon carbide powder used in step (a) must be 10% by weight or less. The reason for this is that free carbon originally has the effect of suppressing the growth of silicon carbide crystals, and if a large amount of free carbon exists between silicon carbide crystals, silicon carbide crystals with high bond strength cannot be obtained. can be,
Among these, it is more preferable that the content of free carbon is 5% by weight or less. On the other hand, the content of free silica contained in the silicon carbide raw material used in step (a) needs to be 5% by weight or less. The reason for this is that some free silica reacts with free carbon to form silicon carbide crystals, but most of it volatilizes, covers the surface of silicon carbide crystals, and forms a glass-like bond between silicon carbide crystals. This is to significantly reduce the bonding between silicon carbide crystals, and the content of free silica is preferably 2% by weight or less. Next, the formed body obtained in step (a) is primarily sintered at a temperature of 1500 to 2200° C. in step (b). The reason for this is that even if sintered at a temperature lower than 1500° C., bonding of silicon carbide crystals is difficult to occur, making it difficult to form a silicon carbide sintered body with high strength. On the other hand, when primary sintering is performed at a temperature higher than 2200°C, a portion of the silicon carbide crystals transforms into α-type silicon carbide and becomes large crystals, making it difficult to form silicon carbide crystals with a size of 10 μm or less. Moreover, it is difficult to obtain a sintered body with high strength. Among these, it is more preferable to perform primary sintering at a temperature of 1700°C to 2100°C. The porous silicon carbide sintered body obtained in step (b) has a porosity of 30 to 60 vol% and an extremely high strength of 10 to 30 Kgf/mm ² . Next, in step (c), it is necessary to impregnate the primary sintered body obtained in step (b) with a carbonaceous material. Examples of the carbonaceous substance include various organic substances such as furfural resin, phenolic resin, lignin sulfonate, polyvinyl alcohol, cornstarch, molasses, coal tar pitch, and alginates, and pyrolytic carbon such as carbon black and acetylene black. can be used to advantage. As for the impregnation method, the usual method of vacuum impregnation or pressure impregnation with a dispersion liquid or unpolymerized material can be used. Next, in step (d), the impregnated body created in step (c) is
It is necessary to carbonize between 900 and 2200°C.
The reason for setting such a temperature range for carbonization is that the carbon impregnated in the above step becomes extremely small particles during thermal decomposition at temperatures lower than 900°C and is highly reactive with molten silicon, but has a low bulk density. This is because it tends to block the pores of the primary sintered body and prevent molten silicon from penetrating into the porous body.On the other hand, when the temperature is higher than 2200℃, it tends to block the pores of the primary sintered body and prevent the penetration of molten silicon into the porous body. This is because a porous body having high strength cannot be obtained. Among them, 1200-2100
It is more preferable to set it at ℃. According to the present invention, the carbon obtained by the above (c)
The amount of carbon contained in the silicon carbide composite is 0.6 to 0.6 to the pore volume of the primary sintered body obtained in step (b).
Preferably, it is present in a proportion of 1.3 g/cm ³ . The reason for this is that if the ratio of carbon to the pore volume of the primary sintered body is less than 0.6 g/ ^cm3 , a large amount of free silicon will remain in the sintered body obtained in step (d), making it difficult to obtain high density. If the amount is more than 1.3 g/cm ³ , on the contrary, a large amount of free carbon remains, making it difficult to obtain a sintered body with high density and high strength. It goes without saying that step (c) can be repeated multiple times in order to obtain such a free carbon content. Next, in step (d), the carbon/silicon carbide composite obtained in step (c) is maintained at 1500 to 2200°C to fill the pores of the carbon/silicon carbide composite with silicon, and then heated for 1 to 15 hours. It is necessary to maintain it. The reason for setting this temperature range is that if the temperature is lower than 1500°C, the impregnated free carbon and silicon will not react sufficiently, and the silicon carbide produced by the reaction with the silicon carbide crystals primary sintered in step (b) will This is because the crystals tend not to bond sufficiently and cannot have high strength, and if the temperature is higher than 2200℃,
This is because the silicon carbide crystals tend to become coarse particles and the strength decreases, especially in the range of 1900 to 2100.
It is more preferable that the temperature is ℃. On the other hand, the reason why the temperature is maintained for 1 to 15 hours is that if the temperature is less than 1 hour, the reaction will not be sufficient and the bonds between silicon carbide crystals tend to be weak. This is because silicon crystals become coarser. The silicon carbide sintered body produced by these steps (a) to (d) is a sintered body having an average grain size of silicon carbide crystals of 10 μm or less and a high density of at least 3.0 g/m ² . , bending strength at room temperature is 40~80Kg
f/mm ² , and even at high temperatures of 1500℃, it is 30 to 50Kgf/mm ²
It is possible to produce a sintered body with high strength. Examples of the present invention will be described below. Example 1 The silicon carbide powder used as a starting material consisted of 95% by weight β-type crystals, 0.29% by weight free carbon,
It mainly contained 0.17% by weight free silica, 0.3 ppm iron, 3 ppm aluminum, and had an average particle size of 0.28 μm. 5 parts by weight of polyvinyl alcohol and 300 parts by weight of water are blended with 100 parts by weight of the silicon carbide powder,
The mixture was mixed in a ball mill for 5 hours and then dried. An appropriate amount of this dry mixture was collected, granulated, and then molded using a metal mold at a pressure of 3000 kg/cm ² . The dimensions of this generated feature are 250mm x 250mm x 30mm
The density was 2.0 g/cm ³ (porosity 38 vol%). The formed body was placed in a graphite crucible and fired in a Tammann type firing furnace in an atmosphere of mainly argon gas at 1 atm. The temperature was raised to 2000°C at a rate of 450°C/hour and maintained at the maximum temperature of 2000°C for 1 hour. The average bending strength of this sintered body is 18.5Kg/
It showed an extremely high value of mm ² . Next, this sintered body is coated with phenyl resin (carbonization rate
40wt%) was vacuum impregnated, dried, and then carbonized at 1900°C in an inert atmosphere. By repeating the same operation again, the amount of free carbon present in the pores of the primary sintered body was 0.84 g/cm ³ . This impregnated body was immersed in molten silicon at 2050°C and held for about 3 hours. The density of the obtained sintered body was 3.16 g/cm ³ and the sintered body was composed of silicon carbide crystals with an average grain size of 3 μm. The bending strength of this sintered body is 62 at room temperature.
Kgf/mm ² and was as high as 48 Kgf/mm ² at 1500°C. Examples 2 to 9/Comparative Examples 1 to 12 In the same manner as in Example 1, when the average particle size of the starting material was changed (Example 2, Comparative Example 1), when the amount of free carbon was changed (Example 3) , Comparative Example 2), when the free silica content was changed (Example 4, Comparative Example 3),
When the firing temperature of the primary sintered body was changed (Example 5,
Comparative Examples 4 and 5), when the carbonization temperature was changed (Example 6, Comparative Example 6), and when the amount of carbon impregnation was changed (Example 7, Comparative Examples 7 and 8), silicon was removed in step (e). When the impregnation temperature was changed (Example 8, Comparative Example

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〔Effect of the invention〕

As described above, the silicon carbide sintered body of the present invention is made of fine silicon carbide crystals, has high bending strength from room temperature to high temperature, and has high density. This sintered body has a high density of 3.0 g/cm2 or ^more even without the conventional sintering aids such as boron and alumina, so it can be used for diffusion for semiconductor manufacturing, which is extremely sensitive to impurities. It is an extremely useful material for structural parts such as furnace soaking tubes, paddles, and boat-shaped jigs, as well as for sliding parts such as corrosion-resistant jigs, wear-resistant parts, and mechanical seals.

Claims (1)

[Claims] 1. A method for producing a silicon carbide sintered body having a density of at least 3.0 g/cm ³ and an average diameter of silicon carbide crystals of 10 μm or less, comprising the following steps (a) to (d): A method for producing a silicon carbide sintered body, characterized by: (a) The free carbon content is 10% by weight or less, the free silica content is 5% by weight or less, and the average particle size is
A step of molding silicon carbide powder of 10 μm or less into a green body of a desired shape; (b) charging the green body into a heat-resistant container;
(c) After impregnating the primary sintered body with a carbonaceous material,
A step of heating the carbonaceous material to a temperature of 900 to 2,200°C to carbonize the carbonaceous material to form a carbon/silicon carbide composite; (d) Heat the carbon/silicon carbide composite obtained in the above step (c) to a temperature of 1,500 to 2,200°C. After filling the pores of the carbon-silicon carbide composite with silicon,
Holding process for ~15 hours. 2. The silicon carbide powder contains at least 60% by weight.
The manufacturing method according to claim 1, wherein is β-type silicon carbide. 3. Carbon contained in the carbon/silicon carbide composite obtained in step (c) is present at a ratio of 0.3 to 1.3 g/cm ³ based on the pore volume of the primary sintered body obtained in step (b). A manufacturing method according to claim 1. 4 The silicon carbide powder, carbonaceous material, and molten silicon each have an alkali metal content of 5 ppm.
or less, the alkaline earth metal content is 20 ppm or less, the copper content is 5 ppm or less, the iron content is 20 ppm or less, the aluminum content is 100 ppm or less, and the alkali metal, alkaline earth metal, copper, iron, The manufacturing method according to claim 1, wherein the total aluminum content is 200 ppm or less.