JP2722785B2 - High purity silica powder - Google Patents

Description

The present invention relates to high-purity silica powder. More specifically, the present invention relates to a high-purity silica powder synthesized by hydrolysis of silicon tetrachloride, which has a low OH group content and is suitable as a raw material for a silicon single crystal pulling crucible.

[Conventional technology and problems]

BACKGROUND ART A quartz crucible for pulling a silicon single crystal has conventionally been manufactured by pulverizing natural quartz and arc-melting using quartz powder produced. However, with the recent commercialization of VLSI, various kinds of high-purity electronic materials have been demanded. Not only impurities in silicon itself, but also impurities in single crystals from quartz crucibles used for pulling single crystals At present, there is a demand for a single crystal pulling crucible having high purity.

The characteristics of refined natural quartz that has been conventionally used in the production of crucibles for pulling silicon single crystals are as follows: Granularity +48 mesh less than 1.0% +80 mesh 50.0% or more +200 mesh 99.0% or more bulk density 1.35 to 1.45 OH group 70 to 100 ppm crystal It has no problem in the production of crucibles for these properties, but natural quartz contains, for example, aluminum (8.0 pp).
m), iron (0.5 ppm), sodium (0.8 ppm), boron (<0.1 ppm), lithium (0.2 ppm), potassium (0.2 pp)
m), the content of impurities such as titanium (1.3 ppm) is large, and there is a limit in the removal thereof, and it is difficult to obtain a high-purity product having a purity higher than the above.

Therefore, as a substitute for natural quartz, research and development of high-purity synthetic quartz has been conducted, and the hydrolysis method of silicon tetrachloride has been taken up. Various methods for producing synthetic silica powder by hydrolysis of silicon tetrachloride have been proposed in the past.For synthetic silica powder for producing high-purity crucibles, however, impurities content, particle size, bulk density, OH group content, crystal It is known that there are strict restrictions on the properties and the like, and if these restrictions are not met, crucible molding is difficult.

Synthetic quartz has a high purity of each other and a large content of OH groups.
Contains 300 to 1200 ppm. If there are many OH groups, the viscosity at high temperatures will be low, and it will be difficult to maintain the shape of the crucible when pulling a silicon single crystal at 1500 ° C. or higher. Also
OH groups are very undesirable because they are highly reactive with the silicon melt, elute from the crucible body, increase the oxygen concentration in the silicon single crystal, and induce defects.

Under such circumstances, a device for reducing the number of OH groups in synthetic quartz for crucible production has been proposed. For example, a method has been disclosed in which a gel-like silica synthesized by a sol-gel method is heated to crystallize into α-cristobalite (Japanese Patent Application Laid-Open No. 2-9783). However, this method uses a metal alkoxide as a starting material, and has a problem that the synthesis of the starting material requires cost and trouble. No attempt has been made to reduce the number of OH groups in the synthetic silica powder obtained by hydrolyzing silicon tetrachloride.

The present invention has been made in view of the above circumstances, and has as its object to provide a high-purity silica powder in which the OH group content of a synthetic silica powder obtained by hydrolysis of silicon tetrachloride is suppressed to 100 ppm or less.

[Means for Solving the Problem / Configuration of the Invention]

That is, the present invention provides a high-purity silica powder having an OH group concentration of 100 ppm or less, wherein the synthetic silica powder produced by hydrolyzing silicon tetrachloride is calcined at a temperature of 1,400 ° C. or more. .

The high-purity silica powder of the present invention is a synthetic silica powder obtained by drying and calcining silicon dioxide synthesized by hydrolyzing silicon tetrachloride. Further, in the present invention, the firing temperature is a temperature of 1400 ° C. or more. Conventionally, synthetic silica powder produced by the hydrolysis method of silicon tetrachloride is 1400
It is baked at less than ℃ and has an OH group content of 300 to 1200 ppm, which is not suitable as a raw material for producing a quartz crucible for pulling a silicon single crystal. As mentioned above,
Silica with many OH groups has low viscosity at high temperature,
When used as a crucible for pulling a silicon single crystal at a temperature of 00 ° C. or higher, it is difficult to maintain the shape due to deformation of the crucible, and OH groups react with the silicon melt to reduce the oxygen concentration in the silicon. Melting the defects in the obtained silicon single crystal.

The OH group content of the silica powder of the present invention is 100 ppm or less. Its characteristics are: Bulk density 1.2-1.27 OH group 30-55ppm Crystalline cristobalite Impurity content Al, Fe, Ne, B, Li, K, Ti, Zr, 0.1ppm or less for all Particle size distribution +48 mesh Less than 1.0% +80 mesh 50% or more +200 mesh 99% or more, which is a silica powder suitable as a raw material of a quartz crucible for pulling a silicon single crystal.

In the present invention, the temperature at which the hydrolysis product of silicon tetrachloride is fired is a temperature exceeding 1,400 ° C. 1,400
Since those baked at a temperature of not more than 100 ° C. do not have OH groups of not more than 100 ppm, they are not suitable as raw materials for a quartz crucible for pulling a silicon single crystal having few defects.

[Specific disclosure of the invention]

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

Examples 1 and 2 Synthetic silica obtained by the silicon tetrachloride hydrolysis method was calcined at 1,420 ° C. and 1,450 ° C. for 50 hours to obtain silica powder. The impurities contained in the silica powder (Table 1), the bulk density (Table 2), and the OH group concentration (Table 3) were measured.

Comparative Examples 1 and 2 The silica powder obtained by calcining the synthetic silica used in the examples at 1,300 ° C. and 1,200 ° C. for 50 hours was measured according to the examples. The results are shown in Tables 1 to 4.

Comparative Examples 3 and 4 The silica powder obtained by purifying natural quartz (Comparative Example 3) and a commercially available silica powder (Comparative Example 4) were measured in accordance with the examples, and the results are shown in Tables 1 to 4. did.

FIG. 1 shows the result of measurement of 10 mg of a synthetic silica powder after drying the product of the hydrolysis of silicon tetrachloride using a natural balance. As can be seen in this figure, a significant weight loss is observed at temperatures above 1200 ° C. FIGS. 2 (A), (B) and (C) are X-ray diffraction diagrams of synthetic silica calcined at 1200 ° C., 1300 ° C. and 1420 ° C. for 50 hours, respectively. Silica calcined at a temperature of 1400 ° C. or more completely shows cristobalite crystallization peak. These results indicate that the change starting at around 1200 ° C. reaches 1400 ° C. and is complete and at this temperature complete cristobalite crystals.

〔The invention's effect〕

The crucible produced using the synthetic silica powder of the present invention is a high-purity silica having an OH group content of 100 ppm or less as compared with a conventional natural quartz crucible, so that a pulled silicon single crystal can maintain high purity. The high-purity silica of the present invention is a CCD
Demand is expected to increase for power transistors and power transistors.

[Brief description of the drawings]

FIG. 1 is a chart of the results of thermobalance measurement of the synthetic silica powder obtained by the silicon tetrachloride hydrolysis method, FIG. 2 (A) shows the synthetic silica powder at 1,200 ° C., and FIG. (C)
FIG. 3 is an X-ray diffraction diagram of a sample fired at 1420 ° C. for 50 hours.

Claims (1)

(57) [Claims] 1. A high-purity silica powder having an OH group concentration of 100 ppm or less, characterized in that a synthetic silica powder produced by hydrolyzing silicon tetrachloride is calcined at a temperature of 1,400 ° C. or more.