JP2003081689A - Synthetic quartz crucible and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress vibration of the liquid surface caused in the vicinity of a melt line when a silicon single crystal is pulled and to produce a crucible providing a good DF (dislocation-free) rate even when it is used for pulling the crystal for a long time. SOLUTION: In a synthetic quartz glass crucible for pulling the single crystal, the etching amount in the vicinity of the melt line in silicon melting is made different from that at the part below the melt line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic quartz crucible, and more particularly to a crucible having a low liquid level vibration and a high DF conversion rate.

[0002]

2. Description of the Related Art Recently, with the increase in diameter and the reduction in defects of silicon single crystals, pulling at high temperature for a long time has been carried out, and synthetic quartz crucibles have come to be used. As this synthetic quartz crucible, a synthetic quartz glass lined with natural quartz glass is used. This is because synthetic quartz is less likely to devitrify. The first patent for this synthetic quartz crucible was German Patent 4528163, but this patent only describes a method for producing the synthetic crucible. In 1990, development aimed at commercialization was carried out, but adoption was postponed due to liquid level vibration and cost. However, in 1995, it was gradually adopted from the viewpoint of recharging and low COP, and now about 70% of crucibles of 22 inches or more are synthetic quartz crucibles.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a synthetic quartz crucible which has a small liquid surface vibration and a good DF ratio even when used for a long time. In order to use a quartz crucible for a long time, it is necessary to raise the purity and prevent devitrification, but when using an ultra-high purity synthetic quartz crucible, vigorous liquid surface vibration occurs and the seed crystal cannot be squeezed. There is. Therefore, the operability was remarkably deteriorated.

[0004]

[Means for Solving the Problems] As a result of diligent research, the present inventors have clarified the mechanism of liquid level vibration and the mechanism of DF conversion rate, and found that the two satisfy both in the design of the quartz crucible. It is a thing.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION It is a well known fact that a synthetic quartz crucible has a good DF ratio because it is hard to devitrify. However, when a synthetic quartz crucible is used, the liquid surface vibrates and the phenomenon that seeding cannot be performed occurs. This is DF
Crucibles with a high rate of conversion occur remarkably. The present inventor has noticed that the liquid level vibration and the DF conversion rate are the opposite phenomena, and has found that it is related to the devitrification of quartz glass. When the devitrification rate balances with the melting loss rate of quartz within a certain range, the liquid surface vibration stops. Here, the devitrification of the quartz crucible is determined by the structure of the quartz glass itself and impurities. And the devitrification rate is determined by devitrification nucleation and growth. For example, natural quartz easily forms crystal nuclei because its structure is close to that of crystals,
The devitrification speed becomes faster. Therefore, the liquid level vibration is unlikely to occur, but the devitrification rate is high, and therefore the DF ratio deteriorates when used for a long time. The opposite phenomenon occurs in synthetic quartz. As a method for solving this contradictory problem, the present inventor controls the devitrification rate by making the surface impurity concentration near the melt line worse than the portion below it, and the liquid level vibration is small, and the DF conversion rate is low. It was the inventor of a good crucible. For example, the portion up to 30 mm below the melt line from the upper end of the crucible is etched with hydrofluoric acid to 2 μm to 4 μm, and the lower portion is etched from 6 μm to 12 μm to change the purity of the crucible surface layer. The inner surface of the crucible is usually contaminated, and the more etching, the better the purity. The part 30 mm below the melt line from the top of the crucible forms crystal nuclei early and devitrifies, and the reaction with the silicon melt is reduced, and the liquid surface vibration is reduced. Since the portion underneath has good purity, devitrification is less likely to occur and the DF conversion rate is improved.

[0006]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

[0007]

Example 1 A 24-inch synthetic quartz crucible was prepared by a conventional method, and a portion 30 mm below the melt line was etched with 12% hydrofluoric acid to 4 μm, and a lower portion thereof was etched with 10 μm. Using this crucible, an 8 "silicon single crystal was pulled. The results are shown in Table 1.

[0008]

Example 2 A 24-inch synthetic quartz crucible was prepared by a conventional method, heat-treated at 1200 ° C. for 10 hours, and then melted from the melt line at 30 ° C.
Etching up to 4 mm with 12% hydrofluoric acid to the bottom of the
It was etched by 0 μm. Using this crucible, an 8 "silicon single crystal was pulled. The results are shown in Table 1.

Comparative Example 1 A 24-inch synthetic quartz crucible was prepared by a conventional method, and the entire crucible was etched with 12% hydrofluoric acid to 4 μm. Using this crucible, an 8 "silicon single crystal was pulled. The results are shown in Table 1.

Comparative Example 2 A 24-inch synthetic quartz crucible was prepared by a conventional method, and the entire crucible was etched with 12% hydrofluoric acid to 6 μm. Using this crucible, an 8 "silicon single crystal was pulled. The results are shown in Table 1.

Comparative Example 3 A 24-inch synthetic quartz crucible was prepared by a conventional method, and the entire crucible was etched with 12% hydrofluoric acid for 11 μm. Using this crucible, an 8 "silicon single crystal was pulled. The results are shown in Table 1.

[0009]

[Table 1]

[0010]

The crucible of the present invention provides a crucible useful for improving operability and yield in pulling a large-diameter silicon single crystal.

Claims (2)

[Claims] 1. A synthetic quartz crucible characterized in that the purity near the melt line when silicon is melted in the quartz crucible is worse than the purity in the lower part. 2. A method for producing a synthetic quartz crucible, characterized in that the purity of the portion near the melt line and the portion below the melt line when the silicon is dissolved is changed by changing the etching amount of the quartz crucible with acid.