Surface modified quartz glass crucible and its modification process

Abstract

A surface modified quartz glass crucible and a process for modifying the crucible includes a layer of a metal oxide on the whole or a part of the inside and / or outside of the crucible, and baking it. At least an inside surface of the crucible is coated with a said metal oxide of magnesium, calcium, strontium or barium. The coated layer of the crucible does not abrade easily and provides a high dislocation free ratio of silicon single crystals pulled by using the crucible.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a surface modified quartz glass crucible and its modification process, in which the crucible is used in the process of pulling up silicon single crystal used for a semiconductor, etc., from molten silicon.[0003] 2. Discussion of the Background[0004] As one of the causes that a dislocation is formed in a silicon single crystal during pulling up of the crystal, it has been known that cristobalite formed on the inside surface of the quartz glass crucible is released into the molten silicon. It is also known that a process in which an alkaline earth metal is coated on the inside surface of the crucible as a crystallization accelerator to form cristobalite layer on the inside surface of the crucible at an early sage of the pulling up (e.g. U.S. Pat. No. 5,976,247 or Japanese Pat. No. 3100836), is a counter measure to this problem. In these inventions, a barium hydroxide solution etc. is coated on the surface of the q...

AI Technical Summary

Benefits of technology

[0025] The surface modified quartz glass crucible of the present invention has a coated layer of metal oxide on the whole or a part of the inside and / or outside surface of the crucible. This metal oxide acts as a crystallization accelerator to the surface glass layer of the crucible at the high temperature in the process of pulling up the silicon single crystal. Therefore, when the crucible is used for pulling up the silicon single crystal, a uniform cristobalite layer is formed on the inside surface of the crucible at any early stage of pulling up, and as a result a high dislocation free ratio of pulled crystal can be obtained. Moreover, the strength of the crucible under the high temperature is increased by the uniform cristobalite layer formed on the inside or outside surface of the crucible.

[0026] Moreover, since the coated layer is an integrated structure to the surface of the crucible by baking, it is very stable and has high durability. Therefore, there is no abrasion when contacted with instruments or persons and no problem that the adhesion state of the metal oxide in the coated layer becomes non-uniform. In addition, the dislocation free ratio of silicon can be increased, since the uniform cristobalite layer is formed on the surface of the crucible during pulling up the single crystal even if the coating layer is comparatively thin. On the other hand, regarding a conventional quartz crucible having an adhered barium carbonate powder on its surface, since the adhesion strength of the barium carbonate powder is very weak, the powder can be washed away easily by water washing. Therefore, it is impossible to wash the crucible even if impurities are adhered on the surface of the crucible. While regarding the surface modified quartz glass crucible of the present invention, since the coated layer is baked on the surface of the crucible, it is not washed away during water washing. So that the impurities on the surface of the crucible can be removed easily to prevent the contamination of the silicon single crystal by such impurities to as great an extent as possible.

Problems solved by technology

However, the alkaline earth metals beryllium, magnesium, calcium, and strontium, have a large segregation coefficient, so that there is a fatal problem that these metals can be easily included in the single crystal silicon to significantly reduce its semiconductor properties.

Moreover, although barium has a small segregation coefficient, there is also a problem that handling is difficult since its toxicity is high.

However, there are the following problems in the above-described strategy.

Moreover there is also a possibility that the worker's health its injured because the barium carbonate powder is scattered.

In addition, (B) the adhesion amount of barium carbonate becomes excessive easily.

Therefore it is impossible to wash the crucible after the adhesion of the barium carbonate powder, even if some soils adhere on the surface of the crucible.

However, the surface modified layer baked on the surface of the crucible cannot be formed by heat-treatment at such low temperature, so that the problem, i.e., the surface layer is abraded easily, cannot be solved.

Therefore, it is impossible to wash the crucible even if impurities are adhered on the surface of the crucible.

In addition, when the amount of the metal oxide is less than said range, the desired effect cannot be obtained, and when the amount of the metal oxide is more than said range, the crystallized layer is abraded and dislocations are more likely to occur.

When the baking temperature is too low, the coated layer cannot be baked on the surface of the crucible.

Moreover, when the baking temperature is more than 1200.degree. C., the crucible is devitrified.