JPS62283871A - Manufacture of silicon carbide sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method of manufacturing a silicon carbide sintered body mainly suitable for heating furnace structural parts. The present invention relates to a method for manufacturing a silicon carbide sintered body suitable as a member for a diffusion furnace for manufacturing.

(Prior Art) In general, it is effective to use materials that have good thermal conductivity, high strength even at high temperatures, and high spalling resistance for the structural convex 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. -HN Ox
CHy COO1 (Since it is cleaned with an aqueous solution or 80M gas, it is important that the material is highly tactile to 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-45
There are methods disclosed in JP-A-38061, JP-A-57-501578, JP-A-54-16521, JP-A-56-109872, JP-A-56-114871, and JP-A-55-67573. These methods generally use silicon carbide powder (100 fi parts), carbon powder (20 to 5
0ffi parts) and pyrolytic carbon (10 to 20 parts by weight) are mixed in advance to form a porous silicon carbide molded body, and carbonized at 600 to 120 °C, then 1
It contacts and reacts with molten silicon at a high temperature of 400°C or higher.

However, in these methods, the bond between the silicon carbide produced in one reaction and the silicon carbide particles mixed in advance is poor, and the free silicon remaining in the sintered body is 400%
When the temperature exceeds .degree. C., it melts and the strength of the sintered body decreases significantly to 20 Kgf/recommended 2 or less.

On the other hand, as another manufacturing method, there are methods disclosed in JP-A-51-85374 and JP-A-41-374 (No. 14).
A high-density silicon carbide molded body is prepared in advance by mixing and molding silicon carbide coarse particles in the range of 10 m or less and silicon carbide powder, and then the pores are impregnated with silicon. Therefore, since these sintered bodies are composed of extremely large silicon carbide crystals, generally 1
Not only does it have a low strength of about 0 kgf/m2,
Since the strength between silicon carbide crystals is low, it has the disadvantage that when the temperature reaches a high temperature of 1400°C or higher, the strength decreases significantly to less than is kgf/ms+''.

[The problem that the invention attempts to solve]

The present invention solves the above-mentioned drawback that the strength decreases at high temperatures, and provides a manufacturing method capable of obtaining a high-density silicon carbide sintered body whose strength hardly decreases even at high temperatures.

[Means for solving problems]

The present inventor has conducted various research on silicon carbide sintered bodies. As a result of repeated efforts, we newly discovered that the content of free carbon and free silica contained in the starting material silicon carbide powder significantly affects the strength of the primary sintered body of porous silicon carbide,
7F to reduce the amount of free a carbon and free silica to below a certain amount.
We succeeded in producing a high-strength porous silicon carbide sintered body by using JLIL. Next, in order to increase the density of this high-strength porous body, the amount of M released carbon that should be impregnated has an appropriate range and carbonization temperature in order to achieve high strength;
Next, they discovered that there is an appropriate temperature and holding time for the reaction with free silicon, and succeeded in obtaining a high-density silicon carbide sintered body that has high strength and does not lose high-temperature strength, which is the objective of the present invention. 1. 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' and an average diameter of silicon carbide crystals of 10 lumen or less, comprising: (a) a free carbon content of 10 wt. % or less, the free silica content is 5% by weight or less, and the average particle size is 0 gm or less. Step of molding silicon carbide powder into a green body of a desired shape: (b) The green body is placed in a heat-resistant container. charged to 150
(c) After impregnating the primary sintered body with a carbonaceous material, 9
Step of heating to a temperature of 00 to 2200°C to carbonize the carbonaceous material to form a carbon/silicon carbide composite: (d) the above (
c) The carbon/silicon carbide composite obtained in step
A silicon carbide sintered body comprising the step of contacting with molten silicon maintained at ~2200°C to infiltrate the molten silicon into the pores of the carbon/silicon carbide composite, and then holding the body for 1 to 15 hours. This is a manufacturing method.

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 lm or less. The reason is that if it is larger than 104 m, it is difficult for atoms to move between silicon carbide crystals and for evaporation-condensation to occur during primary sintering.
This is because the bond strength between silicon carbide crystals tends to be low, and in order to increase the strength between silicon carbide crystals,
It is more preferable that the average particle size is 3 Bm 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 with high bonding strength can be obtained. Among these, it is more preferable that the content of β-type silicon carbide 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 suppresses the growth of silicon carbide crystals, and if a large amount of free carbon exists between silicon carbide crystals, silicon carbide crystals with high bonding strength cannot be obtained. Among them, the content of free carbon is 5% by weight.
It is more preferable that it is the following.

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, 22
When primary sintering is performed at a temperature higher than 00°C, a part of the silicon carbide crystals transforms into α-type silicon carbide and becomes large crystals, so it is difficult to form silicon carbide crystals with a size of 1 [1Bm 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 Iji silicon carbide sintered body obtained in this step (b) has a porosity of 30 to 60 VO1% and a weight of 10 to 30 kgf.
/■m2 is an extremely strong sintered body.

Next, in step (C), it is necessary to impregnate the primary sintered body obtained in step (b) with a carbonaceous material.

Examples of this carbonaceous material include furfural resin,
Phenolic resin, lignin sulfonic acid group, polyvinyl alcohol, cornstarch, honey, coal tar pitch,
Various organic substances such as alginates or pyrolytic carbons such as carbon black and acetylene black can be advantageously used.

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), it is necessary to carbonize the impregnated body created in step (C) at a temperature of 900 to 2200°C. The reason why the carbonization temperature range is set in this way is that the carbon impregnated in the above process becomes extremely small particles during thermal decomposition at temperatures lower than 900°C, and although it is highly reactive like molten silicon, it 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"C, 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 it becomes impossible to obtain a porous body with high strength.

More preferably, the temperature is between 1200°C and 2100°C.

According to the present invention, the carbon obtained by the step (c)
The amount of carbon contained in the silicon carbide composite is 0.6 to 11% relative to the pore volume of the primary sintered body obtained in step (b).
Preferably, it is present in a ratio of g/ctn'.

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/cm'', a large amount of free silicon will remain in the sintered body obtained in step (d), resulting in a high density. This is because if it exceeds 1-:l g /crrf, a large amount of free carbon remains, making it difficult to obtain a high-density and high-strength sintered body.

In addition, in order to obtain such a tolerable amount of free carbon, (c
) It goes without saying that the process can be repeated multiple times.

Next, in step (d), the carbon/silicon carbide composite obtained in step (C) is maintained at 1,500 to 2,200°C, and after filling the pores of the carbon/silicon carbide composite with silicon, a t-tS time is obtained. It is necessary to maintain it. The reason for setting the temperature range is that the temperature is lower than 1500°C.
The impregnated free Il carbon and silicon do not react sufficiently, and the silicon carbide crystals produced by the reaction with the silicon carbide crystals pre-sintered in step (b) do not combine sufficiently, making it impossible to have high strength. This is because there is a tendency, 2200
When the temperature is higher than ℃, silicon carbide crystals become coarse particles.

This is because the strength tends to decrease, especially 190
On the other hand, the temperature is more preferably 0 to 2100°C.

The reason why the temperature is maintained for 1 to 15 hours is that if it is less than 1 hour, the reaction will not be sufficient and the bonds between silicon carbide crystals will tend to be weak, whereas if it is longer than 15 hours, the silicon carbide crystals will This is because coarsening occurs.

The silicon carbide sintered body produced by the steps (a) to (d) is a sintered body having an average grain size of silicon carbide crystals of less than 10 m and a high density of at least 3.0 g/g. , the bending strength at room temperature is 40 to 80 kgf/mm
2, and 30 to 50 kgf even at high temperatures of 1500°C
It is possible to produce a sintered body with a high strength of /l 2.

Examples of the present invention will be described below.

Example 1 Silicon carbide powder used as a starting material was 95% by weight or β
Consisting of type crystals, 0.29% by weight free GL carbon.

Q, 17 wt i% free silica, Q, 'lPPm iron,
Mainly contains aluminum of lPP-, 0.28g
It had an average particle size of m.

5 parts by weight of polyvinyl alcohol and 300 parts by weight of wood were blended with 100 parts by weight of the silicon carbide powder, mixed in a ball mill for 5 hours, and then dried.

An appropriate amount of this dry mixture was taken, granulated, and then molded using a metal mold at a pressure of 30,110 kg/cm'.

The dimensions of this generated shape are 250mm x 25Gmmx
: l [] mm, density is 2.0 g/cm'' (porosity 38
vo1%).

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. In the heating process, the temperature was raised to 2000°C at a rate of 450°C/hour, and the maximum temperature of 2000°C was maintained for 1 hour. The average bending strength of this sintered body was 18.5 kg/12, which was an extremely high value.

Next, phenyl resin (carbonization rate 40vt) was applied to this sintered body.
%), dried and carbonized in an inert atmosphere at 1900'c. By repeating the same operation again, the free a present in the pores of the primary sintered body is
The carbon content was 0.84 g/crn'.

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 3.15 g/crn',
It was a sintered body made of silicon carbide crystals with an average grain size of 3 JLm. The bending strength of this sintered body is 62kgf at room temperature.
/v++”, 48 kgf/ at 1500℃
It had a high am2.

Examples 2 to 9/Comparative Examples 1 to 12 When the average particle size of the starting materials was changed in the same manner as in Example 1 (Example 2, Comparative Example 1), free l! When the carbon content was changed (Example 3, Comparative Example 2), When the MIS silica content was changed (Example 4, Comparative Example 3), When the firing humidity of the primary sintered body was changed (Example 5) , Comparative Example 4.5), when the carbonization temperature was changed (Example 6, Comparative Example 6), when the amount of carbon impregnation was changed (Example 7, Comparative Examples 7 and 8), when the process (
Characteristics of the reaction sintered bodies obtained when the silicon impregnation temperature was changed in e) (Example 8, Comparative Example 9.10) and the holding time was changed (Example 9, Comparative Example 11.12) are summarized in Tables 1 and 2.

(Effects of the Invention) As described above, the silicon carbide sintered body of the present invention is made of fine silicon carbide compacts, has high bending strength from room temperature to high temperature, and has high density. It is the body.

This sintered body does not contain conventional sintering aids such as boron or alumina. Because it has a high density of Og/crri'' or higher, it can be used for structural parts such as soaking tubes, paddles, and boat-shaped jigs for diffusion furnaces used in semiconductor manufacturing, which are extremely sensitive to impurities, or for corrosion-resistant jigs. It is an extremely useful material for sliding parts such as tools, 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, which comprises the following (a) to (d): A method for manufacturing a silicon carbide sintered body, comprising the steps of: (a) A step of molding silicon carbide powder having a free carbon content of 10% by weight or less, a free silica content of 5% by weight or less, and an average particle size of 10 μm or less into a desired shape; (b) ) The formed body was placed in a heat-resistant container, and
A step of firing within a temperature range of 0 to 2200°C to form a porous primary sintered body; (c) After impregnating the primary sintered body with a carbonaceous material,
(d) step of heating to a temperature of 0 to 2200°C to carbonize the carbonaceous material to form a carbon/silicon carbide composite; (d) the step of (c)
) The carbon/silicon carbide composite obtained in step 1500~
A step of maintaining the temperature at 2200°C and filling the pores of the carbon/silicon carbide composite with silicon, and then holding it for 1 to 15 hours. 2. The silicon carbide powder contains at least 60% by weight of β.
The manufacturing method according to claim 1, which is silicon carbide. 3. Carbon contained in the carbon/silicon carbide composite obtained in step (c) above is 0.3 to 1.3 g/cm^3 relative to the pore volume of the primary sintered body obtained in step (b).
2. The manufacturing method according to claim 1, wherein: 4. The silicon carbide powder, carbonaceous material, and molten silicon each have an alkali metal content of 5 ppm or less, an alkaline earth metal content of 20 PPm or less, and a copper content of 5 P.
Pm or less, iron content is 20 ppm or less, aluminum content is 100 ppm or less, and the total content of the alkali metal, alkaline earth metal, copper, iron, and aluminum is 200 ppm or less. The manufacturing method according to item 1.