JPH06226722A - Casting mold and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the thermal shock resistance of a casting mold by a method wherein high purity silicon dioxide porous body is heat-treated so as to control the porosity and pore diameter of the porous body to specified values. CONSTITUTION:A silicon dioxide porous body 12 consisting of a mold 10 is provided by VAD method in advance and then worked roughly into a roughly worked body 13, which is then heat-treated into a roughly worked body after heat treatment 14 and finally precision-work it into a casting mold 10. The resultant purity silicon dioxide porous body is made of minute particles having the average particle diameter of 0.01-10mum and controlled by heat treatment so as to realize the porosity of 30-70vol.%, the pore diameter of 1.0-30mum and high purity such as the impurity content of 1ppm or less. By heating the casting mold 10 made of the above-mentioned porous body at 1,100 deg.C, silicon dioxide particles are softened, resulting in producing partial sintering, enhancing the bonding force between particles and improving the strength of the casting mold. Accordingly, the excellent casting moldability and thermal shock resistance. Further, no metallic pollution and the like is recognized in cast moldings.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting mold and a method for manufacturing the same, and more particularly to a jig for semiconductor manufacturing, for example, a heat-resistant heat treatment for a process tube, a wafer boat, etc. used for thermal diffusion treatment of a silicon wafer. The present invention relates to a casting mold suitable for molding a high-purity silicon carbide composite material useful for a tool and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a plaster mold has been used as a casting mold for molding ceramics, for example, by casting slurry into a mold for molding. Gypsum molds are widely used because they are easy to manufacture, have high water absorption, and are relatively inexpensive.
However, since gypsum is made of a hydrate of calcium sulfate, there is a problem that Ca elutes and pollutes the ceramic molded body when pouring a slurry of, for example, high-purity ceramics for semiconductors. In addition, gypsum has a problem that strength and wear resistance are low and durability is poor.

On the other hand, in the pressure cast molding method and the like, a mold in which silica sand or the like is used as an aggregate and they are hardened with a thermoplastic resin is used, but since the resin is an elastic body, there is a problem that the dimensional accuracy is poor. is there. Further, the resin also contains metal impurities, which may contaminate the obtained ceramic molded body.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a casting mold which does not contaminate a molded body and is particularly useful for molding a silicon carbide material for semiconductor manufacturing, and a method for manufacturing the same. It is in.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have recognized that it is important to develop a material having excellent purity and capable of rapid heating / cooling as a means for achieving the above object. ,
As a result of examining various materials, usually, among the high-purity silicon dioxide used in the production of optical fiber, it was found that those having specific physical properties are particularly promising, and further studies were conducted to the present invention. I arrived.

That is, the gist of the present invention is to
It is composed of a high-purity silicon dioxide porous body and has a porosity of
It is a casting mold characterized by 30 to 70 vol.% And a pore diameter of 1.0 to 30 μm.

Furthermore, the present invention is characterized in that the high-purity silicon dioxide porous body is heat-treated at 1100 to 1400 ° C. to control the porosity and the pore diameter of the porous body, and the casting having the above-mentioned characteristics is obtained. It is a manufacturing method of a mold.

[0008]

The present invention will be further described with reference to the accompanying drawings. FIG. 1 is a schematic perspective view showing an example of a casting mold according to the present invention. In the illustrated example, it is a split mold, but the porous body 12 constituting the mold 10 is VAD in advance.
Which is formed by a method or the like, and is appropriately processed into a predetermined shape to form the mold 10. The molding die 10 thus obtained is subjected to a heat treatment described later to adjust the porosity and the pore diameter, and then used for casting a silicon carbide slurry or the like.

FIG. 2 is a flow chart of the manufacturing process of the casting mold according to the present invention, in which a porous body is synthesized (example: VAD method),
It consists of each step of rough processing, heat treatment, and precision processing.In the figure, the shape of the porous body is also shown. Reference numeral 11 is an oxyhydrogen burner that oxidizes silicon tetrachloride, and 12 is a synthetic quartz porous body (soot).
, 13 is a rough processed body, 14 is a rough processed body after heat treatment, and 10 is a casting mold obtained after precision processing.

According to the present invention, the porous silicon dioxide body constituting the casting mold is generally manufactured by MOCV as a method for producing ultrahigh-purity silicon dioxide (synthetic quartz glass) by a vapor phase method.
Techniques generally called soot method such as D method and VAD method have been developed and put to practical use for the purpose of manufacturing optical fibers, but even in the present invention, high purity silicon dioxide is manufactured by this method and formed into a predetermined shape. It may be molded.

For example, in the VAD method, silicon chloride particles such as silicon tetrachloride are vaporized and oxidized in an oxyhydrogen flame or the like to synthesize and deposit silicon dioxide particles. In the present invention, the casting mold may be manufactured by substantially the same operation.

The porous synthetic quartz glass thus obtained is formed of silicon dioxide fine particles having an average particle diameter of 0.01 to 10 μm, a porosity of 40 to 80% and a pore diameter of 2 to 30 μm.
Highly pure with a total impurity content of 1 ppm or less.

Therefore, according to the present invention, the porous synthetic quartz glass thus obtained is subjected to heat treatment or the like to adjust the porosity and the pore diameter and processed into a predetermined shape to form a casting mold. To do.

According to the present invention, the casting mold is composed of a high-purity silicon dioxide porous body, and when used for molding a high-purity silicon carbide material used for heat treatment such as a Si wafer, it contaminates the wafer. There is no problem of mixing metal impurities.

According to the present invention, the porosity of the casting mold is 30 to
It is 70 vol.%. When the porosity exceeds 70 vol.%, The strength of the casting mold is low and it cannot be processed into the required shape. Also, 30 vol.
If it is less than%, sufficient water absorption cannot be obtained, and cast molding becomes difficult.

The pore diameter of the porous synthetic quartz glass is 1.0 to 30.
μm. If it exceeds 30 μm, the ceramic particles in the slurry will penetrate into the inside of the porous body and a molded product having a predetermined shape cannot be obtained, and the releasability will deteriorate. On the other hand, if it is less than 1.0 μm, the diffusion rate of water decreases and it takes a long time to dry. The pore diameter of the casting mold is preferably 5 to 30 μm.

The synthetic quartz glass porous body has an average particle size of 0.
It is made of 01-10 μm silicon dioxide particles and has a porosity of 40-
80%, pore size is 1 to 30 μm. This porous body 1100 ~
When heated at 1400 ° C., the silicon dioxide particles are softened to cause partial sintering, the bonding force between the silicon dioxide particles is increased, and the strength of the porous body is improved. Further, the shrinkage of the porous body progresses to reduce the porosity, and finally the fine quartz glass is formed. However, the porosity and the pore diameter of the porous body are controlled by adjusting the temperature, time, etc. of the heat treatment. It is possible.

FIG. 3 shows the processing temperature and processing time dependence of the porosity of high-purity silicon dioxide used in the present invention. If the treatment temperature is lower than 1100 ° C, the shrinkage of the porous body hardly progresses, and the treatment time becomes extremely long, which is not realistic. Further, when the temperature exceeds 1400 ° C., the shrinkage rapidly progresses, so that it is necessary to increase the temperature raising / lowering rate and the temperature distribution of the porous silica expands, which makes control difficult and is not practical.

Further, since the coefficient of thermal expansion of quartz glass is very small, there is no risk of cracks or the like even if it is subjected to rapid heating / quenching. Therefore, the work such as drying the casting mold should be done at 100 ° C.
It can be easily performed at the above temperature.

As described above, according to the present invention, since the molded body is excellent in purity and does not contaminate the molded body and can withstand rapid cooling and rapid heat, it is particularly useful for molding silicon carbide based materials for semiconductor production. A mold can be obtained.

[0021]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 According to the process chart shown in FIG. 2, the bulk density was about 0.4 g / cm ³ and the specific surface area was about 12 synthesized by the VAD method.
A synthetic quartz glass porous body having m ² / g and an average particle size of about 0.2 μm was roughly processed, heat-treated at 1200 ° C. for 1 hour, and precisely processed into a predetermined shape by a diamond mill to obtain a casting mold.

Next, a high-purity silicon carbide powder having an impurity content of 1 ppm or less was slurried and cast-molded. Table 1 shows the density, porosity, thermal shock resistance, and cast formability of the obtained casting mold, and Table 2 shows the metal impurity concentration of the cast body obtained by the cast molding.

Example 2 Synthesized by the VAD method in the same manner as in Example 1, the bulk density is about 0.4 g / cm ³ , and the specific surface area is about.
A synthetic quartz glass porous body having a particle size of 12 m ² / g and an average particle size of about 0.2 μm was rough-processed, heat-treated at 1400 ° C. for 30 minutes, and precisely processed into a predetermined shape by a diamond mill to obtain a casting mold.

Next, a high-purity silicon carbide powder having an impurity content of 1 ppm or less was slurried and cast-molded. Table 1 shows the density, porosity, thermal shock resistance, and cast formability of the obtained casting mold, and Table 2 shows the metal impurity concentration of the cast body obtained by the cast molding.

Comparative Example 1 A bulk density of about 0.4 g / cm ² , which was synthesized by the VAD method according to the process chart shown in FIG.
After roughly processing a synthetic quartz glass porous body with a specific surface area of about 12 m ² / g and an average particle size of about 0.2 μm, in this example it is heat-treated at 1450 ° C. for 20 minutes and then precision-processed into a predetermined shape with a diamond mill. A casting mold was obtained.

Next, a high-purity silicon carbide powder having an impurity content of 1 ppm or less was slurried and cast-molded. Table 1 shows the density, porosity, thermal shock resistance, and cast formability of the obtained casting mold, and Table 2 shows the metal impurity concentration of the cast body obtained by the cast molding.

(Comparative Example 2) A high-purity silicon carbide powder having an impurity content of 1 ppm or less was slurried and cast-molded using an ordinary plaster mold. Table 1 shows the density and porosity of the casting mold, the thermal shock resistance, and the casting formability, and Table 2 shows the metal impurity concentration of the cast body.

[0028]

[Table 1]

[0029]

[Table 2]

Here, the thermal shock resistance is as follows:
Judging by the presence or absence of cracks in the test of putting in water,
The cast formability is a property judged by a test for cracking or peeling when the mold is left for a whole day and night and then released from the mold. As can be seen from these results, according to the present invention, both the cast moldability and the thermal shock resistance are excellent, and no contamination of the cast molded product with metal impurities is observed.

[0031]

As described above in detail, according to the present invention, a silicon carbide-based material for semiconductor manufacturing, which has excellent purity, does not contaminate a molded body, and can be rapidly heated and cooled, is particularly useful. A casting mold useful for molding can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an example of a casting mold according to the present invention.

FIG. 2 is a manufacturing process diagram of a casting mold according to the present invention.

FIG. 3 is a graph showing the processing temperature and time dependence of the porosity of a casting mold (high-purity silicon dioxide porous body).

Claims (2)

[Claims] 1. A casting mold comprising a high-purity silicon dioxide porous body having a porosity of 30 to 70 vol.% And a pore diameter of 1.0 to 30 μm. 2. A high-purity silicon dioxide porous body at 1100-1400 ° C.
The method for producing a casting mold according to claim 1, wherein the porosity and the pore diameter of the porous body are controlled by heat-treating at 2.