JP2614583B2 - Cristobalite sintered body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cristobalay sintered body and a method for producing the same. More specifically, the present invention relates to a cristobalite sintered body obtained by sintering a molded body of amorphous silica particles, which can be used as a material for manufacturing jigs for semiconductor manufacturing or a heat-resistant structural material, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, materials for manufacturing jigs for semiconductor manufacturing,
Alternatively, quartz glass, which is a material having both heat resistance and high purity, has been widely used as a heat resistant structural material. In general, quartz glass products are produced with higher purity than other high temperature heat-resistant materials, but when used repeatedly in a temperature range exceeding the glass transition temperature range (about 1100 ° C.), the mechanical strength becomes high. And there is a problem that the material is gradually deformed due to a decrease in viscosity to cause crushing and twisting. Further, when used in a temperature range exceeding 1250 ° C., recrystallization proceeds, devitrification occurs, and there are problems such as peeling and cracking due to a difference in expansion coefficient.

[0003] Various inventions have been proposed for the purpose of improving such problems relating to the mechanical strength of quartz glass in a high-temperature region. 1) A quartz glass tube whose outer surface is covered with a cristobalite layer. (Japanese Patent Publication No. 47-1477, Japanese Patent Publication No. 47-18
No. 83, etc.) 2) A quartz glass member in which cristobalite crystals are formed on the outer surface layer. (3) A method of obtaining a crystalline quartz sintered body by sintering a mixed compact of crystalline quartz powder and amorphous quartz powder without vitrification. (JP-A-62-28361, etc.).

[0004]

In general, quartz glass obtained by converting cristobalite into cristobalite has an α of cristobalite.
-Β transition point (transition point: 250 to 300 ° C; α: low-temperature type,
(Specific gravity 2.34, β: high temperature type, specific gravity 2.18), cracks, cracks, etc. occur due to the change in specific gravity, and the mechanical strength decreases.

The above prior art has the following problems. The quartz glass tube of 1) has an outer surface covered with a cristobalite layer. Further, the quartz glass member of 2) has a large number of strain nuclei that can grow into cristobalite crystals at a high temperature in the glass layer. It is to form cristobalite crystals in the surface layer, thereby reducing bending, deformation and warpage in the heat treatment process of semiconductor wafers, which are useful as quartz glass furnace tubes and bell jars used in the semiconductor industry. The present invention relates to a quartz glass member that can be formed.

However, such a quartz glass member has only a part thereof made of cristobalite.
There is a limit in improving the heat resistance of the obtained member, and there is a limit in the field where it can be used. In addition, when these members are used at a high temperature of 1250 ° C. or higher, cristobalite crystals continuously grow and become devitrified, so that there is a problem that they cannot be used for a long time in a temperature region of 1250 ° C. or higher.

In view of the recent trend toward ultra-high purification of jigs and reagents for semiconductor production, strain nucleating agents (for example, zinc, magnesium, calcium, zirconium,
Tin, boron, aluminum, phosphorus, antimony, etc.)
The use of a method requires the use of a jig containing impurities in the semiconductor manufacturing process, which goes against the demand for high purity.

In the method 3), a mixed compact of 100 parts by weight of crystalline quartz powder and 1 to 100 parts by weight of amorphous quartz powder is sintered at a temperature of 1400 ° C. or more and a melting point of the crystalline quartz powder or less. It is a method for providing a crystalline quartz sintered body that is dense, has excellent mechanical strength, and can withstand a long-time use at a high temperature exceeding 1100 ° C.

According to this method, a crystalline quartz sintered body that can withstand long-term use in a temperature range exceeding 1100 ° C. can be produced. However, the crystalline quartz powder is sintered using amorphous quartz powder as a binder. As a result, an essentially heterogeneous sintered body is obtained. A jig for manufacturing a semiconductor is generally washed with hydrofluoric acid and used repeatedly. The sintered body obtained by this method is non-homogeneous with a mixture of crystalline quartz powder and amorphous quartz powder,
There is a problem that the dissolution rate of the amorphous quartz powder portion in hydrofluoric acid is high, and the durability is inferior to that of ordinary quartz glass.

An object of the present invention is to sinter an amorphous silica particle molded article obtained by molding amorphous silica particles to obtain a material for manufacturing jigs for semiconductor production or a heat-resistant structural material. An object of the present invention is to provide a suitable cristobalite sintered body having excellent mechanical strength in a high temperature range.

[0011]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems in the conventional method, and as a result, obtained amorphous silica particles having a specific particle size range by molding. By subjecting the formed compact to heat treatment under specific conditions, it was found that a cristobalite sintered body having excellent mechanical strength in a high temperature region could be obtained directly from amorphous silica particles, and the present invention was completed. did.

The first invention of the present invention has a gist of "a cristobalite sintered body obtained by sintering a molded body of amorphous silica particles".

[0013] The second invention of the present invention is directed to a method of forming amorphous silica particles having an average particle diameter in the range of 0.1 to 10 µm, and heating the obtained amorphous silica particle molded body. A method for producing a cristobalite sintered body, wherein the temperature is maintained in a range of 1300 to 1712 ° C. for a period of 1 to 50 hours. ”

Hereinafter, the present invention will be described in detail. According to the present invention, the cristobalite sintered body obtained by converting a formed body of amorphous silica particles into cristobalite surprisingly shows almost no cracks or cracks even if the α-β transition of cristobalite is repeated. And excellent mechanical strength can be maintained.

Although this mechanism is not clear, in the case of quartz glass, the vitreous material is converted into cristobalite.
While the stress due to the specific gravity difference of the α-β transition of cristobalite cannot be absorbed, in the present invention, the compact of amorphous silica particles is sintered to be cristobalite, so that the α-β transition The stress due to the specific gravity difference can be absorbed by each silica particle unit constituting the sintered body,
It is estimated that the effect of the generated stress does not affect the entire sintered body.

As the silica particles as the raw material in the present invention, it is preferable to use amorphous silica particles. It is not preferable to use crystalline silica particles because there is a problem in moldability at the time of molding.

The purity of the raw silica particles is not particularly limited.
When a high-purity cristobalite is used as a semiconductor jig, a high-purity cristobalite sintered body can be obtained by using raw silica particles having a low impurity content. The amorphous silica particles having a low impurity content are described in, for example, JP-A-62-3011 and JP-A-62-3012.
No. 6,086,283 or JP-A-62-283810, the fine particles obtained by extruding an aqueous solution of an alkali metal silicate from pores into a water-miscible organic medium or an acid solution. The fibrous coagulate can be obtained by treating with an acid-containing liquid to extract and remove impurities. As the alkali metal silicate, sodium salt, potassium salt, lithium salt and the like of silicic acid can be used. Amorphous silica particles obtained using silicon tetrachloride or silicate alkoxide as a raw material can also be used.

In the present invention, as a molding method for obtaining an amorphous silica particle molded body, an appropriate molding method of a wet method or a dry method is appropriately selected in accordance with the shape of a desired cristobalite sintered body. can do. Examples of the wet molding method include a slurry casting method, and examples of the dry molding method include a cold isostatic pressing method (rubber pressing method) and a mold pressing method.

The amorphous silica particles used in the present invention include:
Its average particle size is 0.1-10 μm, preferably 0.2-5 μm
m, more preferably in the range of 0.3 to 2 μm. It is not preferable to use silica particles having an average particle diameter of more than 10 μm, because the compactness of the obtained amorphous silica particle molded product is reduced, and the time required for sintering becomes longer.
On the other hand, when silica particles having an average particle size of less than 0.1 μm are used, the obtained amorphous silica particle molded product has low strength and it is difficult to maintain the shape.

When the dry molding method is used, the moldability is improved by using silica particles having an average particle diameter in the above-mentioned range or an amorphous silica particle aggregate obtained by granulating the silica particles. , A compact of amorphous silica particles having improved compactness can be obtained.

When the particle size of the silica particles is adjusted, a conventional pulverizer such as a pot mill, a tube mill,
A rolling ball mill such as a conical ball mill or a compartment mill, a vibration ball mill, a tower type pulverizer, a medium stirring mill or a roll mill such as a stirred bed mill can be used, and preferably a rolling ball mill or a vibration ball mill is used. .

The amorphous silica particle molded body obtained by molding the amorphous silica particles is dried, if necessary, and then heated and maintained at a temperature of 1300 to 1712 ° C. for 1 to 50 hours. Thus, sintering is performed and cristobalite is produced to produce a cristobalite sintered body.

The sintering temperature is preferably in the range of 1300 to 1712 ° C., and if it is lower than 1300 ° C., the cristobalite conversion rate of the amorphous silica particles is very low, and the cristobalite conversion requires a long time, and is not efficient. on the other hand,
When the temperature exceeds 1712 ° C., the melting point of cristobalite becomes 17
Since the temperature is 13 ° C., cristobalite is melted into amorphous quartz glass, which is not preferable.

The equipment used for performing the sintering process includes:
As long as the silica particles can be maintained in a predetermined temperature range, a bogie furnace, a box furnace, a tunnel furnace, a vacuum furnace, or the like can be used. The heating source is optional, and electric heating or combustion gas is an economical heat source. In addition, plasma heating and an image furnace can be used.

The atmosphere for the sintering may be any of an air atmosphere, a reducing atmosphere such as argon and helium, and a vacuum atmosphere under reduced pressure. It is economical to fire in an air atmosphere.

The sintering time is preferably in the range of 1 to 50 hours, and is selected according to the sintering temperature.

[0027]

The present invention will be specifically described below with reference to examples. It should be noted that the present invention is not limited to only these examples unless it exceeds the gist. Example-1 Amorphous silica particles as a raw material were prepared by the following method. After filtering JIS No. 3 sodium silicate, it was extruded into a sulfuric acid coagulation bath through a nozzle (pore diameter: 400 μm, number of holes: 100) to obtain a transparent fibrous gel. The resulting fibrous gel is immersed in sulfuric acid at 100 ° C. for 1 hour with stirring, deoxidized with Nutsche, and washed and filtered twice with ion-exchanged water. It was dehydrated to obtain wet silica.

The obtained wet silica is dried by heating at 150 ° C. for 15 hours, and has a water content of 0.8%, an average particle size of 250 μm, and a specific surface area.
Amorphous dried silica particles of 800 m ² / g (by BET method) were obtained. The content of impurities per SiO _{2 of the} dried silica particles is Na: 0.4 ppm, Fe: 0.3 ppm, Ti: 0.2 ppm,
Al: 0.5 ppm.

The dried silica particles were calcined at 1250 ° C. for 4 hours. The obtained calcined silica particles were amorphous, and their average particle size and impurity content were not changed, but the specific surface area was 0.2 m ² / g.

A quartz glass ball (5 mmφ) was prepared by mixing 200 g of the calcined silica particles with 300 g of ion-exchanged pure water.
Using 2 kg as a grinding medium, charge in a ball mill (rolling type, quartz glass pot: volume 3 liters), and rotate at 80 r.
The mixture was pulverized at pm for 24 hours to obtain an amorphous fine particle silica slurry. The silica particles in the obtained slurry are amorphous and have an average particle size of 1.6 μm, and SiO ₂ (dry weight basis)
The content of impurities per unit was not different from that of the dried silica particles.

The amorphous fine-particle silica slurry is supplied to a rotary disk type spray-drying granulator at a rate of 2.5 liters / hour, and hot air at an inlet temperature of 150 ° C. is supplied to perform dry granulation. An amorphous silica fine particle aggregate having a size of about 90 μm was obtained.

This amorphous silica fine particle aggregate was filled in a rubber press, and molded by applying a pressure of 700 kg / cm ^2.
A molded article of amorphous silica particles of 0 mm × 80 mm × 30 mm (hereinafter referred to as a green molded article) was obtained. The obtained green molded body was heated at a temperature of 1500 ° C. for 2 hours in a box furnace in an air atmosphere and sintered to obtain a cristobalite sintered body of 164 mm × 66 mm × 24 mm. This sintered body was confirmed to be cristobalite by an X-ray diffraction test. Also, SiO
The impurity content per ₂ (dry weight basis) was not different from that of the dried silica particles.

The mechanical strength of the sintered body in a high temperature range was evaluated based on the result of viscosity measurement by a beam bending method. The test conditions are as follows.・ Testing equipment: Beam bending test equipment, manufactured by Tokyo Kogyo Co., Ltd. ・ Specimen size: 50mm × 5mm × 3mm, ・ Holding of the specimen: Double-ended method ・ Test load: Temperature, ° C load, g 1100 200 1200 30 1300 20

The cristobalite sintered body obtained by the above treatment was subjected to a beam bending test at each temperature of 1100 ° C., 1200 ° C. and 1300 ° C. In any of the tests, no bending was caused by plastic deformation, and the viscosity value was not increased. Could not be measured.

Example-2. The amorphous silica fine particle aggregate used in Example-1 was filled in a mold press, and molded by applying a pressure of 1 ton / cm ² to obtain a diameter.
A cylindrical green compact having a thickness of 30 mm and a thickness of 10 mm was obtained. This green compact was heat-treated under the same conditions as in Example 1,
A cylindrical cristobalite sintered body having a diameter of 25 mm and a thickness of 8 mm was obtained. About the obtained cristobalite sintered body,
Beam bending tests were performed at 1100 ° C, 1200 ° C, and 1300 ° C. In any of the tests, no bending was caused by plastic deformation, and the viscosity value could not be measured.

Example 3 The amorphous fine particle silica slurry obtained in Example 1 was filled in a casting mold and held at a pressure of 4.5 kg / cm ² for 60 minutes to form a mold having a diameter of 100 mm. A disk-shaped green molded article having a thickness of 25 mm and a moisture content (150 ° C., weight loss rate) of 22% was obtained. After drying this green molded body in a dryer at a temperature of 15 ° C. and a relative humidity of 95% for 50 hours, the obtained dried molded body was subjected to a heat treatment under the same conditions as in Example 1 to a diameter of 80 mm. Thus, a white cristobalite sintered body having a thickness of 19 mm was obtained. The obtained cristobalite sintered body was subjected to a temperature of 11
Beam bending tests were performed at 00 ° C, 1200 ° C, and 1300 ° C. In any of the tests, no bending was caused by plastic deformation, and the viscosity value could not be measured.

Example 4 A cristobalite sintered body was obtained in the same manner as in Example 1 except that the firing conditions of the green compact were 1350 ° C. and 20 hours. This sintered body was confirmed to be cristobalite by an X-ray diffraction test. Further, the content of impurities per SiO ₂ (on a dry weight basis) was not different from that of the dried silica particles. The obtained cristobalite sintered body was subjected to a beam bending test at temperatures of 1100 ° C., 1200 ° C., and 1300 ° C. In any of the tests, no bending due to plastic deformation occurred, and the viscosity value could not be measured.

Comparative Example-1 The green compact obtained in Example-1 was subjected to a melting treatment while maintaining the temperature at 1500 to 1750 ° C to obtain a transparent quartz glass of 162 mm x 64 mm x 23 mm. As the heating furnace, a vacuum furnace using a carbon material was used for both the heater and the furnace material. The obtained quartz glass was subjected to beam bending tests at temperatures of 1100 ° C., 1200 ° C. and 1300 ° C., and it was plastically deformed to bend. The viscosity values measured in the tests at each of the above temperatures are as follows:
They were 14.2, 13.0 and 11.4 (g / cm · sec, poise), respectively.

Comparative Example 2 Temperature of Commercially Available Transparent Quartz Glass (Shin-Etsu Quartz Co., Ltd.)
When beam bending tests were performed at 1100 ° C, 1200 ° C, and 1300 ° C, plastic deformation and bending occurred in all of the tests. The viscosity values measured in the tests at the above temperatures were 14.1, 12.8 and 11.6 (g / cm ·
sec, poise).

[0040]

According to the present invention, a cristobalite sintered body having excellent mechanical strength in a high temperature range can be obtained directly from amorphous silica particles. Furthermore, by appropriately selecting the amorphous silica particles to be used, the content of impurities such as alkali metals is extremely low, and a high-purity cristobalite sintered body can be obtained. Alternatively, it can be suitably used as a heat-resistant structural material.

Continuation of the front page (72) Inventor Akifumi Okawa 3-1-19-1 Eyo, Hachinohe City, Aomori Prefecture Nitto Chemical Industry Co., Ltd. Examiner in the Hachinohe Works Kenshi Yoneda (56) References JP-A-61-183164 (JP, A )

Claims (1)

(57) [Claims] An amorphous silica particle having an average particle diameter in the range of 0.1 to 10 μm is formed, and the obtained amorphous silica particle molded body is heated at a temperature of 1300 to 1712 ° C. A method for producing a cristobalite sintered body, wherein the sintered body is maintained for 1 to 50 hours.