Glass manufacturing – Processes – Sol-gel or liquid phase route utilized
Patent
1997-11-26
2000-10-17
Silverman, Stanley S.
Glass manufacturing
Processes
Sol-gel or liquid phase route utilized
65 173, 65DIG8, 556466, C03B 800, C03B 1901
Patent
active
061314099
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a high purity synthetic quartz powder and a shaped product of quartz glass, and a high purity tetraalkoxysilane useful as their starting material and a method for its production.
BACKGROUND ART
In recent years, for glass products used in the field of optical communication or in the semiconductor industry or the like, a very strict control is carried out with respect to their minor impurities and fine bubbles in the products. For example, in a case where the glass product is a crucible for pulling up a silicon single crystal, if it contains minor impurities, the minor impurities eluted from the crucible will be entrapped in the silicon single crystal and deteriorate the performance of the semiconductor. Especially, Group III-V elements such as phosphorus and boron substantially influence the semiconductor properties, and a special attention is paid to them. Further, in the case of a quartz jig to be used at a high temperature, Group III-V elements contained in the shaped product of quartz will diffuse and contaminate a silicon wafer, whereby the desired semiconductor properties can hardly be obtained. Further, if the crucible contains fine bubbles, there will be a problem such that they not only cause disturbance of the liquid surface during pulling up of a silicon single crystal and formation of crystal defects, but also deteriorate the durability of the crucible.
Such high quality glass is produced mainly by e.g. (1) a method of purifying natural quartz, (2) a method in which a fume generated by decomposition of silicon tetrachloride in an oxyhydrogen flame is deposited and grown on a substrate, or (3) a method in which a silica gel obtained by e.g. hydrolysis and gelation of e.g. a silicon alkoxide, is baked and a synthetic quartz powder thereby obtained is employed.
However, the method (1) has a problem that there is a limit in reducing the content of minor impurities, and the method (2) has a problem that the production cost is extremely high. On the other hand, in the method (3) wherein a silica gel, particularly a silica gel derived from a silicon alkoxide, is employed, it is possible to obtain a synthetic quartz powder having relatively low content of minor impurities, but the desired level is not necessarily satisfied. Further, by this method (3), fine bubbles are likely to form in the shaped product as the final product, thus leading to the above-mentioned problem caused by fine bubbles.
DISCLOSURE OF THE INVENTION
In view of the above-mentioned circumstances, the present inventors have conducted an extensive research on a method for producing a synthetic quartz powder or its molded product, wherein, as compared with conventional products, the content of minor impurities is low, particularly the content of phosphorus and boron is low, and formation of fine bubbles is very little, by using a silica gel obtained by hydrolysis and gelation of a silicon alkoxide. As a result, they have found that the main cause of these problems resides in a specific compound in the starting material silicon alkoxide, further that minor impurities are entrained from the reaction mixture and from the apparatus, that phosphorus in the starting material alkoxide, which is the main cause of the problems, can be substantially reduced under a specific distillation condition, and that phosphorus and boron in the staring material alkoxide have an interrelation with the content of the specific compound in the alkoxide; and they have arrived at the present invention.
Namely, the present invention resides in a method for producing a high purity synthetic quartz powder, characterized by using a tetraalkoxysilane having a trialkoxyalkylsilane content of at most 0.3 wt %, and converting it to a synthetic quartz by a sol-gel method; etc.
Now, the present invention will be described in detail.
The crude tetraalkoxysilane to be used in the present invention, can be obtained by reacting metallic silicon with an aliphatic alcohol, as shown by the following formula (1):
As the aliph
REFERENCES:
patent: 5902893 (1999-05-01), Laxman
Kato Hanako
Katsuki Takanobu
Katsuro Yoshio
Takazawa Akihiro
Utsunomiya Akira
Mitsubishi Chemical Corporation
Ruller Jacqueline A
Silverman Stanley S.
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