JPH0255285A - Method and appartus for producing quartz crucible - Google Patents

Abstract

PURPOSE: To obtain a quartz crucible having a high air bubble content in its outer peripheral side part by stopping a pressure reduction during the course of heating at the time of forming a quartz packing layer on the inner peripheral surface of a gas permeable mold, heating and melting the layer from the inner peripheral surface side and reducing the pressure from the outer periphery of the mold.

CONSTITUTION: A core 40 is inserted to the rotating gas permeable mold 21 and quartz powder is packed therebetween to form the quartz packing layer on the inside surface of the mold 21. The core 40 is pulled up and an electrode 50 is installed. The quartz packing layer is heated and melted by an arc discharge to form a thin molten layer. The gas in the quartz packing layer is sucked and discharged through the vent holes 24 of the mold 10 by activating a pressure reduction mechanism 30. The pressure reduction is stopped after about 120 seconds, and the arc discharge is maintained. The air leaks into the reduced pressure chamber 23 from the spacing between the mold 21 and a mold holder 22 to restore the atm. pressure in the chamber after the stop of the pressure reduction. The heating is continued thereafter as well. As a result, the quartz crucible having the higher air bubble content of the outer peripheral side part as compared with the inner peripheral side part is obtd.

COPYRIGHT: (C)1990,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for manufacturing a quartz crucible used in manufacturing silicon single crystals for semiconductors.

[Prior Art and Problems] When producing silicon single crystals from polycrystalline silicon, a quartz crucible is used to melt the polycrystalline silicon.

Several manufacturing methods are conventionally known for manufacturing quartz crucibles. According to that example, a rotatable hollow mold is filled with quartz powder as a raw material along the inner peripheral surface of the mold, and the centrifugal force is applied by heating and melting the quartz powder while rotating the mold. The molten or semi-molten quartz filling layer is expanded onto the inner peripheral surface of the mold and sintered into the shape of a crucible.

The quartz crucible manufactured by this method has the disadvantage that many air bubbles remain inside the wall. If there are many bubbles in the walls (peripheral wall and bottom wall), the strength of the crucible will decrease. Furthermore, when the crucible is heated, bubbles near the inner circumferential surface of the crucible expand thermally, causing the inner circumferential surface to partially peel off, and the peeled off quartz pieces mix into the molten silicon, increasing the single crystallization rate (silicon polycrystalline becomes single crystal). ) decreases.

Therefore, there is a need for a crucible with few internal air bubbles, and a known manufacturing method involves heating and melting quartz powder filled in a mold under reduced pressure (Japanese Patent Publication No. 59-34559).
According to this method, the air bubbles inside the quartz layer filled in the mold are removed by suction during melting, so a crucible with almost no air bubbles observed inside the wall can be obtained with the naked eye. However, in this manufacturing method, as the quartz filling layer is heated and melted inside the rotating mold during manufacturing, air bubbles, which have a much lower specific gravity than quartz, gradually move toward the rotating shaft side, that is, the inner periphery of the quartz filling layer. Microbubbles that move toward the surface and cannot be observed with the naked eye become unevenly distributed near the inner peripheral surface of the wall. The fine T's bubbles thermally expand when the crucible is heated, causing the same problem as described above.

[Objects and Structure of the Invention] An object of the present invention is to provide a method and apparatus for manufacturing a quartz crucible in which air bubbles remain on the outer peripheral side of the crucible wall, while fewer air bubbles are present near the inner peripheral surface of the wall.

According to the present invention, quartz powder is filled along the inner peripheral surface of a rotating gas permeable mold, the quartz powder filled layer is heated and melted from the inner peripheral surface side, and the outer periphery of the mold is In the manufacturing method, the internal gas of the quartz powder is sintered into the shape of a crucible under reduced pressure while being sucked and exhausted through the wall of a gas-permeable mold.

There is provided a method for manufacturing a quartz crucible in which the outer circumferential portion has a higher bubble content than the inner circumferential portion by stopping the depressurization in the middle of the heating and melting.

Further, according to the present invention, there is provided a rotatable gas permeable mold, a means for rotating the mold, a means for reducing the pressure around the outer periphery of the mold, and a removable core inserted into the inside of the mold and a removable core. In a quartz crucible manufacturing apparatus having a flexible heating means, the mold is removably fitted into a mold holder, the mold holder rotates while supporting the mold, and forms a decompression chamber around the outer periphery of the mold. An apparatus is provided which is characterized in that:

In the manufacturing method of the present invention, a rotatable mold that is bowl-shaped and has gas-permeable walls is used. A core is inserted into the hollow center of the mold, and the raw material quartz powder is supplied between the mold and the core while rotating the mold. The quartz powder is pressed against the inner peripheral surface of the mold by the action of the centrifugal force of the rotating mold, and is deposited along the inner peripheral surface to form a quartz filled layer. is installed, and the quartz filling layer is heated and melted from the inner peripheral surface side. The heating first forms a thin molten or semi-molten coating on the inner peripheral surface of the quartz filling layer. On the other hand, during the heating, the pressure of the mold is reduced, and the gas inside the quartz packed layer is sucked and exhausted through the gas-permeable inner circumferential surface. As the heating progresses, the quartz filled layer gradually melts and sinters from the inner peripheral surface to the vicinity of the outer surface. The steps described above from filling quartz powder to heating and melting under reduced pressure are common to conventional manufacturing methods.

The manufacturing method of the present invention is fundamentally different from conventional manufacturing methods in that the depressurization operation is stopped during heating and melting, and after the depressurization is stopped, the quartz packed bed is further heated from its inner peripheral surface. The air bubbles inside the crucible wall are drawn to the outer circumference side by the pressure reduction operation, and when the pressure reduction is stopped, the outer circumference side is sintered with the air bubbles remaining. Although microbubbles remain in the one-direction circumference side portion, relatively large bubbles are attracted to the grain side portion and do not exist in the inner circumference side portion, so that sintering is performed with few bubbles. As a result, a crucible is obtained in which the bubble content in the outer circumferential side of the crucible is higher than in the inner circumferential side.

Regarding the depressurization stop time, when heating and melting is performed for t minutes, it is preferable to stop the above-mentioned suction and exhaust 0.2 to 0.9 t minutes before the start of heating. If the vacuum is stopped before 0.2 minutes, a transparent layer with the melt thickness necessary for pulling single crystal silicon will not be formed.

If the vacuum is stopped after 0.9 t minutes, the molten layer will be sucked into the vacuum hole and a convex portion will be formed on the outer peripheral surface, which is not preferable. The above heating is completed leaving a thin unmolten peeling layer on the outer surface of the quartz filled layer, and after cooling and assimilation, the quartz filling layer is taken out from the mold.

An apparatus for carrying out the above manufacturing method includes a rotatable gas permeable mold, means for rotating the mold, and means for reducing pressure around the outer periphery of the mold.

A quartz crucible manufacturing apparatus having a removable core inserted into the inside of the mold and a removable heating means, the mold being removably fitted into a mold holder, the mold holder comprising: It is possible to use an apparatus that supports and rotates the mold and forms a decompression chamber around the outer periphery of the mold.

An example of a manufacturing apparatus according to the present invention is shown in FIG.

The manufacturing apparatus 10 includes a mold forming part 20 that can freely rotate once, a rotating means (not shown) for rotating the mold forming part 20, and a depressurizing means 3 connected to the mold forming part 20.
0. The mold forming portion 20 is formed from a mold 21 into which quartz powder is charged and a mold holder 22 that supports the mold 21. Both the mold 21 and the mold holder 22 are hollow, and have a cylindrical peripheral wall 21a.
, 22a and bottom walls 21b, 22b, which form an airtight vacuum chamber 23 and are removably fitted together. The mold 21 and mold holder 22 are rotated together by a rotating means. A plurality of ventilation holes 24 are bored in the mold 21, and the ventilation holes 24 are formed in the wall 21 of the mold 21.
It communicates with the decompression chamber 23 through c. mold 2
A fitting groove into which the upper end 22c of the mold holder 22 is inserted is provided on the outer periphery of the lower end of the mold holder 2.
It is preferable to form a convex portion 21d that closely contacts the upper inner circumferential surface of No.2. A hole 25 communicating with the pressure reducing mechanism 30 is provided in the bottom wall 22b of the mold holder 22. The pressure reducing mechanism 30 is composed of a piping system including a vacuum pump 31, a filter 32, and an electromagnetic valve 33.

A vertically movable core 40 and a vertically movable electrode 50 for producing a single discharge are disposed above the mold 21.

Conventional cores 40 and electrodes 50 can be used.

[Effects of the Invention] According to the manufacturing method of the present invention, a crucible can be obtained in which the bubble content in the vicinity of the inner peripheral surface of the wall is small and the bubble content in the outer circumference side is large. Even when the crucible according to the manufacturing method of the present invention is heated during use, the microscopic bubbles in the inner circumferential portion are absorbed into the outer circumferential portion with a large bubble content, and as a result,
Since the thermal expansion of the bubbles in the inner peripheral side portion is suppressed, there is no risk of partial peeling of the inner peripheral surface of the crucible. Therefore, compared to crucibles produced by conventional methods, single crystal allogenes are much better.

According to the manufacturing apparatus according to the present invention, after the depressurization is stopped, the atmosphere enters through the minute gap between the mold and the mold holder, and the inside of the decompression chamber immediately returns to atmospheric pressure, so that the suction of the quartz packed layer is quickly performed. This makes it easy to leave bubbles in the outer circumference. Furthermore, in the apparatus of the present invention, the mold and mold holder can be separated, so
When manufacturing crucibles with different diameters, only the mold can be replaced. In manufacturing equipment that has a pressure reduction mechanism,
Replacement of the parts connected to the pressure reducing mechanism is complicated;
There is a great practical advantage that the mold holder to which the decompression mechanism is connected can be used without replacement, as in the apparatus of the present invention.

[Example] A core 4 is placed in a mold 2 which rotates once using the device shown in Milo.
0 was inserted, and quartz powder was filled between them to form a quartz filling layer along the inner circumferential surface of the mold 21. Subsequently, the core 40 was pulled up, the electrode 50 was placed at the center inside the mold, and arc discharge was performed to heat and melt the quartz filling layer 5 from the inner peripheral surface side. After 45 seconds from the start of heating, a thin molten layer is formed on the inner circumferential surface of the quartz filled layer, and at this point, the vacuum pump 31 of the pressure reduction mechanism 30 is activated to blow the gas inside the quartz filled layer through the vent hole 24 of the mold 10. 6
The vacuum was evacuated at a pressure of 0.00 + i m Hg. The pressure reduction was stopped 120 seconds after the start of the pressure reduction, and the arc discharge was continued. After the decompression was stopped, air leaked through the gap between the mold 21 and the mold holder 22, and the decompression chamber 23 returned to atmospheric pressure, and the heating after the decompression was stopped was continued under atmospheric pressure. Arc discharge was terminated 15 minutes after the start of arc melting, and after cooling, a quartz crucible in which the quartz filling layer was melted and sintered was obtained.

Polycrystalline silicon was melted using the quartz crucible according to the manufacturing method of the present invention, and single-crystalline silicon was pulled. The single crystallization rate in this case is shown in the following table (No, 1.2). The following table also shows the single crystallization rate under the same conditions using a conventional quartz crucible as a comparative example (No. 3.4).

3o-pressure reduction mechanism, 40-Nakako, 50-electrode

Claims (3)

[Claims] (1) Fill quartz powder along the inner circumferential surface of a rotating gas-permeable mold, heat and melt the quartz powder filled layer from the inner circumferential side, and reduce pressure on the outer circumference of the mold during melting. In a manufacturing method in which the internal gas of quartz powder is sintered into the shape of a crucible while being sucked and exhausted through the wall of a gas-permeable mold, by stopping the depressurization midway through the heating and melting process, the outer periphery is smaller than the inner periphery. A method of manufacturing a quartz crucible with a high bubble content in the side portion. (2) When heating and melting is performed for t minutes, 0% from the start of heating.
The method according to claim 1, wherein the suction and exhaustion is stopped after 2 t minutes to 0.9 t minutes before, so that the bubble content in the outer circumference side portion is higher than that in the inner circumference side portion. (3) A rotatable gas permeable mold, a means for rotating the mold, a means for reducing the pressure around the outer periphery of the mold, a removable core inserted into the inside of the mold, and a removable heating means. A quartz crucible manufacturing apparatus having a mold is detachably fitted into a mold holder, the mold holder rotates while supporting the mold, and forms a decompression chamber around the outer periphery of the mold. Device.