Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
2002-06-06
2004-03-30
Norton, Nadine (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
C117S019000, C117S020000, C117S013000, C065S033100, C065S030100
Reexamination Certificate
active
06712901
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a surface modification process of a quartz glass crucible and to a surface modified quartz glass crucible which is used in the process of pulling up silicon single crystal used for a semiconductor etc. from molten silicon.
DISCUSSION OF THE BACKGROUND
As one of the causes that a dislocation is formed in silicon single crystal in the pulling method, it has been known that cristobalite formed on the inside surface of the quartz glass crucible is released into the molten silicon. As a countermeasure to this, a process is known in which an alkaline earth metal is coated on an inside surface of the crucible to act as a crystallization promoter. The metal forms a cristobalite layer on the inside surface of the crucible at an early stage of pulling up (e.g. U.S. Pat. No. 5,976,247, Japanese Patent No. 3,100,836). In these inventions, a barium hydroxide solution is coated on the surface of the quartz glass crucible and the coated barium hydroxide reacts with carbon dioxide in air to form barium carbonate on the surface of the crucible. The barium carbonate is weakly adhered on the surface of the crucible by drying and is used as a crystallization promoter.
However, quartz glass crucibles surface-treated by conventional methods have the following problems and improvements are desired. That is, (A) since the barium carbonate powder on the quartz glass crucible is not fixed with any binder, the adhesion strength of the powder is very weak so that the powder is easily abraded and falls off when contacted by persons and instruments. Such abrasion occurs in the production process of the crucibles, such as product inspection, conveyance, and insertion to a carrying case, etc. It also occurs in the user's process, where the quartz glass crucible is set on a carbon susceptor in the crystal puller. As a result, its adhesion state becomes non-uniform and spot-like. Furthermore, there is also a possibility that worker health is negatively affected because barium carbonate powder is scattered when the carrying case is opened. (B) Since the adhesion strength of powder is very weak, nucleation efficiency as a crystallization promoter is low, and so the amount of barium carbonate required becomes excessive. (C) If the crucible is washed, the barium carbonate powder adhered on the surface of the crucible is washed away. It is then impossible to wash the crucible after the adhesion of the barium carbonate powder, even if some contaminants adhere on the surface of the crucible.
SUMMARY OF THE INVENTION
The present invention solves the problems of the conventional quartz glass crucible and provides a surface modified quartz glass crucible having a transparent coated layer which is not abraded upon contact with handling instruments or persons, has sufficient durability, and also provides its surface modification process.
That is, the present invention relates to the following surface modification process of the quartz glass crucible.
[1] A surface modification process of a quartz glass crucible, the process comprising, coating a mixed solution, (hereinafter referred to as the silica sol liquid), containing a metal salt and a partial hydrolyzate of alkoxysilane oligomer on the surface of the crucible, baking said coated solution to form a transparent coated layer containing a crystallization promoter derived from the metal salt in the silica matrix.
The surface modification process of the present invention includes the following processes.
[2] The surface modification process of a quartz glass crucible, wherein the metal salt is a metal organic acid salt or a metal carbonate of one or more kinds of magnesium, calcium, strontium, or barium.
[3] The surface modification process of a quartz glass crucible, the process comprising, coating the silica sol liquid on the whole or a part of the inside and/or outside of the surface of the quartz glass crucible, and baking said coated silica sol liquid.
[4] The surface modification process of the quartz glass crucible, wherein the silica sol liquid has 0.01 to 15 weight % of metal content, which is calculated as an oxide, and 0.5 to 30 weight % of silicon concentration, which is calculated as SiO
2
, is used.
[5] The surface modification process of the quartz glass crucible, the process also comprising, drying the silica sol liquid, and baking said dried liquid at 350 to 1200° C. for 10 to 120 minutes.
In addition, the present invention also relates to the following quartz glass crucible.
[6] A quartz glass crucible, having a transparent coated layer, in which the crystallization promoter is dispersed in the silica matrix, on the whole or a part of the inside and/or outside surface of the crucible.
The quartz glass crucible of the present invention includes the following crucibles.
[7] The quartz glass crucible, wherein the crucible is made by, coating the silica sol liquid containing the metal salt and the partial hydrolyzate of alkoxysilane oligomer on the surface of the crucible, and baking the coated silica sol liquid to form a transparent coated layer containing the crystallization promoter derived from the metal salt in the silica matrix.
[8] The quartz glass crucible, wherein the crucible is made by coating the silica sol liquid containing a metal organic acid salt or a metal carbonate of one or more kinds of magnesium, calcium, strontium, or barium, on the surface of the crucible, and baking coated silica sol liquid to form the transparent coated layer containing the metal oxide or the metal carbonate as the crystallization promoter.
[9] The quartz glass crucible used as the crucible for silicon single crystal production.
The surface modified quartz glass crucible of the present invention has a hard and transparent coated layer, in which the metal oxide or the metal carbonate is dispersed in a silica matrix, on the whole or a part of the inside and/or outside surface of the crucible. In addition, the metal oxide or metal carbonate acts as a crystallization promoter to the surface glass layer of the crucible at the high temperature of pulling up the silicon single crystal. Therefore, when the crucible is used for the production of silicon single crystal, a uniform cristobalite layer is formed on the inside surface of the crucible at an early stage of pulling up, and as a result a high dislocation free ratio of the pulled crystal can be obtained. Moreover, the strength of the crucible under a high temperature is increased by the uniform cristobalite layer formed on the inside or outside surface of the crucible.
Moreover, since the coated layer is baked on the surface of the crucible, 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 to non-uniform. In addition, even if the coating layer is comparatively thin, the surface of the crucible is crystallized uniformly during pulling up the single crystal and the dislocation free ratio of silicon can be increased. On the other hand, regarding the conventional quartz glass crucible having the adhered barium carbonate powder on its surface, since the adhesion strength of the barium carbonate powder is very weak, it can be washed away easily by acid washing. Therefore, it is impossible to wash the crucible even if some contaminants 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 by acid washing. Contaminants on the surface of the crucible can be removed easily by acid washing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereafter, the present invention is explained concretely according to the preferred embodiment.
The surface modification process for producing the quartz glass crucible of the present invention is a formatio
Tsuji Yoshiyuki
Tsujimoto Toshio
Japan Super Quartz Corporation
Norton Nadine
Song Matt
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