JP2707351B2 - Carbon crucible for silicon single crystal production - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a carbon crucible for producing a silicon single crystal used for pulling a silicon single crystal.

2. Description of the Related Art Silicon single crystals are widely manufactured using the Czochralski method. In this method, a silicon single crystal is pulled from molten silicon in a heated crucible.
The crucible is usually composed of a quartz crucible and a carbon crucible disposed outside the quartz crucible. The carbon crucible has a role to support the quartz crucible.

In order to improve the temperature controllability of the molten silicon in the crucible, attempts have been made to reduce the thickness of the side surface of the carbon crucible.

Problems to be Solved by the Invention As described above, the temperature controllability of molten silicon can be improved by reducing the thickness of the carbon crucible and reducing the heat capacity of the crucible. Further, power consumption can be reduced.

However, when the carbon crucible is used a plurality of times, silicon is impregnated non-uniformly therein. For this reason, the coefficient of thermal expansion of the crucible is not uniform, and cracks are easily generated in a crucible having a small thickness. Cracks often occur during cooling after completion of silicon single crystal growth.

As described above, if the thickness of the carbon crucible is uniformly reduced, the strength is reduced, cracks are easily generated, and the life of the crucible is shortened. As described above, there is a limit in a method of uniformly reducing the thickness as a whole, which is not practical.

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides a carbon crucible for producing a silicon single crystal, which can improve the temperature controllability of molten silicon and can obtain a practical useful life. The purpose is.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention provides a plurality of recesses on the outer surface so as to be separated from each other, and the width of each recess is increased in any direction. 4 times or less and more than 0 times, the distance between adjacent recesses is 3 mm or more, and the thickness at the bottom of the recess is 1/2 or more of the crucible wall thickness and less than 1 time. The present invention provides a carbon crucible for producing a silicon single crystal characterized by the following.

Function In the carbon crucible for producing a silicon single crystal of the present invention, it is desirable that a number of recesses provided on the outer surface be provided on the side surface of the carbon crucible by dimple processing by an NC processing machine.

The thickness of the crucible at the bottom of the recess, that is, the distance from the bottom surface to the inner surface of the crucible is 1 / th of the thickness of the crucible.
Set to 2 or more. If this is less than 1/2, cracks are likely to occur because the steel cannot withstand the thermal stress generated in the cooling process after the completion of the single crystal growth. In addition, the temperature distribution of the molten silicon in the crucible may be disturbed, which may adversely affect the crystal characteristics and lower the single crystallization ratio. In order to form a recess, the thickness at the bottom of the recess must be less than one time the thickness of the crucible.

The width of the recess is less than four times the thickness of the crucible in any direction. The distance between adjacent recesses is set to 3 mm or more. Contrary to these limiting conditions, the strength of the crucible becomes insufficient and the life is shortened. Also, in order to form a recess, the width of the recess must be greater than 0 times in any direction.

By providing a number of recesses on the outer surface of the crucible in a form separated from each other, the heat capacity of the crucible is reduced and the thermal responsiveness is improved while maintaining the mechanical strength. Therefore, the temperature of the molten silicon can be easily and accurately controlled.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The crucible 8 shown in FIG. 1 comprises a quartz crucible 12 and a carbon crucible 10 disposed outside the quartz crucible 12. The crucible 8 is provided in a single crystal pulling apparatus having a heater, a heat retaining cylinder, and the like, but FIG. 1 shows only the crucible 8 for simplicity. Crucible 8 contains molten silicon 13,
From there, the silicon single crystal 14 is pulled.

The outer surface, particularly the side surface, of the carbon crucible 10 is provided with a number of recesses 11. As a result, a net-like thick portion 9 is formed on the crucible surface.

The recesses 11 are disk-shaped and are evenly arranged as shown in FIG. The distance W between the adjacent recesses 11 is set to, for example, 10 mm. The distance 1 is set to, for example, 43.3 mm.

As shown in FIG. 3, it is configured to have a concave spherical shape, and has, for example, a width a = 40 mm and a curvature R = 45 mm. The thickness d of the crucible at the bottom of the recess is 1 / th of the thickness D of the thick portion 9.
Set to a value of 2 or more. For example, D = 17.5mm, d = 11.9mm
Set to.

Using five carbon crucibles 10 shown in FIG. 1, 10 lots of silicon single crystals were manufactured. As a comparative example, an experiment was conducted under the same conditions using a conventional carbon crucible having the same size, a side wall thickness of 20 mm, and no recess. The results of the experiment were as shown in Table 1. According to the embodiment of the present invention, the molten silicon temperature controllability is high,
It was also found that the power consumption was small and the working time could be reduced.

These crucibles were used repeatedly, and the number of times of use until cracks were generated was measured. The average service life of the carbon crucible according to the present invention is 42.8 times (45, 42, 40, 46, 41 each).
Times), and the average of the conventional product was 37.7 times.

Thus, it was revealed that the carbon crucible according to the present invention has a longer life than conventional products.

Next, another embodiment of the present invention will be briefly described with reference to FIG.

In the modification shown in FIG. 4, the recess 21 has a rectangular shape. Accordingly, a thick portion 19 running vertically and horizontally is formed on the surface of the carbon crucible.

According to the carbon crucible for producing a silicon single crystal of the present invention, the following effects can be obtained.

(1) By providing a recess on the outer surface of the crucible to reduce the heat capacity, the thermal responsiveness is improved, and the temperature control of the silicon melt becomes easy. Therefore, the quality of single crystal silicon can be improved. Further, the power consumption of the heater can be reduced.

(2) The surface area of the crucible can be increased by the recess, and the melting time of silicon and the cooling time after the completion of the growth of the single crystal can be shortened.

(3) By providing the recess, the strength of the crucible can be maintained and the service life can be prolonged, rather than making the thickness of the side surface of the carbon crucible uniform.

(4) If a large number of groove-shaped recesses are provided, the connection of the thick portions (original thickness) is substantially deteriorated, and the mechanical strength as a whole is substantially reduced. For this reason, after the pulling of the single crystal, when the quartz crucible shrinks while being partially fused to the graphite crucible, a crack may be generated along the groove. In the present invention, by forming the concave portion of a predetermined shape, the thick portion has a mesh-like connection having a width of 3 mm or more at intervals of at least four times the thickness as a whole, so that the overall strength does not decrease, and Problems can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a carbon crucible for producing a silicon single crystal according to the present invention, FIG. 2 is an enlarged plan view of the outer surface of its side,
FIG. 3 is an enlarged sectional view, and FIG. 4 is a plan view showing another embodiment. 8 Crucible 10,30 Carbon crucible 12 Quartz crucible 11,21 Concave 31 Groove 13 Fused silicon 14 Silicon single crystal

Claims (1)

(57) [Claims] A plurality of recesses are provided on an outer surface so as to be separated from each other, and the width of each recess is not more than 4 times and more than 0 times the thickness of a crucible in any direction, and the adjacent recesses are provided. A carbon crucible for producing a silicon single crystal, characterized in that the distance between the places is 3 mm or more and the thickness at the bottom of the recess is at least 1/2 and less than 1 time of the thickness of the crucible.