JPH09286691A - Production of quarts glass crucible - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a quartz glass crucible capable of preventing formation of an aggregate of fine bubbles to the crucible and industrially useful. SOLUTION: In the production method of the quartz glass crucible, after forming a packed layer of silicon dioxide powder along an inner peripheral surface of a mold whose upper part is open, a graphite electrode is set at the inside of the mold after preheating at >=800 deg.C under an inert gas atmosphere, and the packed layer is heat melted by arc discharge while rotating the mold to form the quartz glass crucible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a quartz glass crucible used for manufacturing a silicon single crystal.

[0002]

2. Description of the Related Art Conventionally, a quartz glass crucible for producing a silicon single crystal is prepared by filling and forming silicon dioxide powder on the inner peripheral surface of an upper opening mold and setting a graphite electrode in the mold through the upper opening of the mold. The silicon dioxide powder is heated and melted by the arc discharge generated between the electrodes while the mold is rotated to form the powder.

[0003]

In the quartz glass crucible produced by the above method, the silicon dioxide vaporized during heating contacts the upper portion of the electrode exposed to a lower temperature atmosphere and condenses. It falls into the crucible and a micro-bubble aggregate is generated at the place where it falls. When the aggregate of microbubbles is present near the inner surface of the crucible, the microbubbles expand and become open bubbles during the production of the silicon single crystal, and at that time, the fragments of quartz glass whose surface is peeled off are melted. It was mixed in silicon and caused problems such as phase transition in crystals. In order to solve this problem, conventionally, the vaporized component of silicon dioxide was removed from the molten atmosphere by controlling the air flow in the mold during energization or by forcibly exhausting the atmosphere in the mold. The satisfactory effect was not obtained.

As a result of intensive studies on the above points, the present inventors found that most of the above-mentioned microbubble aggregates were generated.
It was clarified that the silicon dioxide evaporated in the initial stage of energization of the graphite electrode is cooled and agglomerated at the upper part of the graphite electrode in the initial low temperature state and formed by dropping. It has been found that the above problem can be solved by preheating the electrode in a predetermined temperature range. Therefore, it is an object of the present invention to provide an industrially useful method for producing a quartz glass crucible that can prevent the formation of microbubble aggregates in the crucible.

[0005]

In order to solve the above-mentioned problems, in the method for manufacturing a quartz glass crucible of the present invention, a graphite electrode serving as a heat source when melting silicon dioxide previously filled in a mold having an open upper part Is preheated to 800 ° C. or higher in an inert gas atmosphere, then set in a mold and energized. The preheating temperature of the graphite electrode is 800 ° C or higher, preferably 1000 ° C or higher. If the temperature is lower than 800 ° C, a sufficient effect cannot be obtained,
Further, the upper limit is preferably 2000 to 3000 ° C. in consideration of the influence on peripheral devices.

The graphite electrode is preheated while waiting for the raw material filling step and the like, and is performed by a dedicated heating device. As such a heating device, it is preferable that the heating device is formed of a heat-resistant heat retaining body such as graphite or ceramic formed so as to cover the graphite electrode, and the heating body is provided inside the heat retaining body. Must be performed under an inert gas atmosphere. This makes it possible to prevent the electrodes and the heating device from being consumed by oxidation. The heating element may be made of metal such as Nichrome wire or Kanthal wire, or graphite. Further, as the inert gas used at the time of heating, for example, nitrogen gas, argon gas and the like can be mentioned, but in terms of easy handling and low cost,
Nitrogen gas is preferred.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A method for manufacturing a quartz glass crucible of the present invention will be described with reference to FIGS. FIG. 1 is a schematic sectional view showing a manufacturing method of the present invention, and FIG. 2 is a perspective view showing an example of a graphite electrode preheating device used in the manufacturing method of the present invention. As shown in FIG. 1, the method for producing a quartz glass crucible of the present invention is a mold 1 having an upper opening.
Forming a silicon dioxide powder filling layer 2 along the inner peripheral surface of
After setting the graphite electrode 3 preheated to 800 ° C. in the mold 1 using the preheating device shown in FIG. 2, the graphite electrode 3 is energized while the mold 1 is rotated, and the electrode 3,
The filling layer 2 is heated and melted by an arc discharge generated between 3 to form a quartz glass crucible. Graphite electrode 3
In the above, since the whole is heated in advance to a high temperature state, silicon dioxide evaporated in the initial stage of melting of the filling layer 2 does not aggregate even if it touches the graphite electrode.

As shown in FIG. 2, the preheating device 4 used for preheating the graphite electrode is composed of a graphite heat retaining body 5 and is formed in a cylindrical split mold so as to cover the graphite electrode 3. . In addition, a heating body 6 made of a nichrome wire is attached to the inner wall surface inside thereof, and an inlet 7 for an inert gas such as nitrogen is formed on the upper surface thereof. Graphite electrode 3 placed in preheater 4
Is heated to 800 ° C. or higher by the heating body 6 in an atmosphere of an inert gas such as nitrogen gas sent from the inlet 7.
Although the preheating device in FIG. 2 has a cylindrical shape,
It may be formed by appropriately changing it according to the graphite electrode used.

According to the method for producing a quartz glass crucible of the present invention, in the initial stage of energizing the graphite electrode,
Evaporation components of silicon dioxide from the filling layer filled / formed on the inner surface of the mold are exhausted to the outside of the upper opening mold without condensing / accumulating on the graphite electrode, so that minute amounts near the inner surface of the glass Foam aggregates can be significantly reduced. Therefore, not only the yield of the quartz glass crucible but also the productivity can be improved without mixing fine bubbles in the silicon melt and the ingot during the production of the silicon single crystal.

[0010]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. [Example 1] Before heating and melting the silicon dioxide filling layer in the mold, a graphite electrode was placed in the preheating device shown in Fig. 2 which was previously heated to about 1,000 ° C, and the nitrogen flow rate was 1 m ³ / mi.
n atmosphere for 10 minutes. The surface of the taken out graphite electrode was about 800 ° C. this,
Immediately after setting in the upper opening mold 1 as shown in FIG. 1, while rotating the mold 1, the graphite electrodes 3, 3 were energized and discharged to fill and mold the silicon dioxide powder packed layer on the inner peripheral surface of the mold. 2 was heated and melted at 2,000 ° C. to produce a quartz glass crucible having a diameter of 22 inches. The number of microbubble aggregates formed on the inner surface of the obtained quartz glass crucible was measured, and the results are shown in Table 1. Here, the microbubble aggregate is 1
It means that 10 or more bubbles having a diameter of 1 mm or more are aggregated per cm ² .

[Comparative Example 1] For comparison, a graphite electrode was preheated to 600 ° C. under the same conditions as in Example 1, using the apparatus shown in FIG. A silicon dioxide powder packed layer filled and molded in the same mold as in Example 1 was heated and melted to mold a quartz glass crucible.
The frequency of occurrence of microbubble aggregates generated on the inner surface of this quartz glass crucible was measured, and the results are shown in Table 1.

[Comparative Example 2] As in Example 1, the apparatus shown in FIG. 2 was used to heat and melt a silicon dioxide powder filling layer filled and molded in the same mold as in Example 1 without preheating to obtain quartz. A glass crucible was molded. The frequency of occurrence of microbubble aggregates generated on the inner surface of the obtained quartz glass crucible was measured, and the results are shown in Table 1.

[0013]

[Table 1] The numerical values showing the frequency of occurrence of the microbubble aggregates of Example 1, Comparative Example 1 and Comparative Example 2 in the table are relative values with Comparative Example 2 as 100. As is clear from Table 1, when the graphite electrode is preheated to 800 ° C. in advance, the number of microbubble aggregates generated is extremely smaller than in Comparative Examples 1 and 2.

[0014]

Since the quartz glass crucible produced by the method of the present invention has very few fine bubble aggregates formed inside, the quartz glass crucible reduces the inclusion of quartz glass fragments in the silicon melt even in the production of a single crystal. Therefore, productivity can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a manufacturing method of the present invention.

FIG. 2 is a perspective view showing an example of a graphite electrode preheating device used in the manufacturing method of the present invention.

[Explanation of symbols]

 1 type 5 heat retaining body 2 silicon dioxide powder packed layer 6 heating body 3 graphite electrode 7 inlet 4 heating device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Matsumura 2-13-60 Kitafu, Takefu City, Fukui Prefecture Shin-Etsuishi Ei Takefu Factory Co., Ltd.

Claims (1)

[Claims] 1. A filling layer of silicon dioxide powder is formed along an inner peripheral surface of a mold having an open top, a graphite electrode is set inside the mold, and the filling layer is formed by arc discharge while rotating the mold. In manufacturing a quartz glass crucible by heating and melting, the graphite electrode is preheated at a temperature of 800 ° C. or more in an inert gas atmosphere, and then set in a mold to generate electricity by heating. Crucible manufacturing method.