Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus – For crystallization from liquid or supercritical state
Reexamination Certificate
2001-11-14
2004-09-28
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Apparatus
For crystallization from liquid or supercritical state
C117S013000, C117S213000, C117S200000, C117S900000
Reexamination Certificate
active
06797061
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a quartz glass crucible effectively used for pulling up a silicon single crystal and a production method therefor.
BACKGROUND ART
In company with recent demands for a silicon single crystal with defects at a low level and a large diameter, high purification of quartz glass crucible for pulling up such a silicon single crystal has been desired and as raw materials therefor, a high purity synthetic quartz glass powder obtained by means of a sol-gel method, synthetic cristobalite powder or purified natural quartz powder has been employed.
A so-called arc rotation melting method has generally been adopted in production of quartz glass crucibles, wherein a raw materials as described above is supplied into a rotating mold to form a powder layer along the inner surface thereof, the powder layer is molten by heating with arc that is applied from the inside of the mold, and after melting of the powder layer the arc is ceased and the molten powder layer is left to be eventually cooled to room temperature while the mold is continued to be rotated. In production of a quartz glass crucible by means of the method, the quartz glass crucible is required to be formed with an inner surface layer having as few bubbles as possible in order to improve a single crystallization ratio of silicon crystal produced in pulling up.
However, even a quartz glass crucible thus produced has had inconvenience that in the course of pulling up a crystal or crystals using such a quartz glass crucible under a reduced pressure, the crucible is transformed in such a manner that bubbles generate and grow in the transparent layer and the inner surface comes to assume an irregular topographic feature including recesses and projections, so that a single crystallization ratio of the pulled up crystal or crystals becomes decreased.
To cope with such a problem, the present applicant has proposed a quartz glass crucible in which fine bubbles in the transparent layer are suppressed from expansion when in usage under reduced pressure by means of doping hydrogen in the transparent layer and a production method therefor (Japanese Patent Laid-open Publication No. 5-124889). The proposed production method has faults that a hydrogen atmosphere treatment furnace for the hydrogen doping becomes large in scale for treating a large size crucible, which leads to high cost, and a special safety measure is necessary to be taken for explosion of hydrogen gas due to its inflammability.
Furthermore, the present applicant has proposed a production method in which an inner surface of a crucible still in the making is cooled in a hydrogen containing atmosphere after application of the arc is ceased and thereby, there are eliminated the faults associated with the above-described production method (Japanese Patent Laid-open Publication No. 7-330358). This method, however, is not yet an established one, since it stands in need of the treatment in a hydrogen containing atmosphere and also makes an apparatus and a process more complex.
The present inventors, taking the above described circumstances into consideration, have conducted studies about behavior of fine bubbles residing in the inner surface layer of a quartz glass crucible after pulling up a silicon crystal using the quartz glass crucible. The present inventors have obtained findings that, in a silicon single crystal pulling up process, even if no bubbles are virtually recognized in a layer 1 mm deep of the inner surface of a quartz glass crucible before use in the process, bubbles 0.5 mm or more in diameter are recognized in the transparent layer when the inner surface of the quartz glass crucible is observed after it is used in a silicon single crystal pulling up process and in the case, a single crystallization ratio is low. This has been estimated because bubbles burst, chips of quartz glass generated by the burst of bubbles float on the surface of a silicon melt and move up to a silicon crystal under growth.
The present inventors have investigated into the following methods in order to find a good measure to prevent bubble generation and growth in the transparent layer of a quartz glass crucible.
(1) Quartz glass crucibles were produced while changing some of conventional heat melting conditions in the arc rotation melting method, silicon single crystals were pulled up using the quartz glass crucibles, and the transparent layers of the quartz glass crucibles after the pulling up were examined with the findings obtained that bubble expansion in the transparent layers were decreased as compared with cases of quartz glass crucibles produced by means of conventional methods.
(2) Quartz glass crucibles were produced while using quartz powder having a low gas content, a low OH group concentration and/or a fine particle size as raw materials for a transparent layer of the inner surface under the same heat melting conditions as conventional conditions in the arc rotation melting method, silicon single crystals were pulled up using the quartz glass crucibles, and the transparent layers of the quartz glass crucibles after the pulling up were examined with the findings obtained that bubble expansion in the transparent layers were decreased as compared with cases of quartz glass crucibles produced using conventional quartz powder as raw materials.
In transparent layers of the inner surfaces of quartz glass crucibles produced by means of the above described two methods (1) and (2), the maximum diameters and total sectional areas of bubbles present, and gas contents in the transparent layers of the inner surfaces of quartz glass crucibles before use were reduced, and the maximum diameters and total sectional areas of bubbles recognized in the transparent layers of the quartz glass crucibles after pulling up silicon single crystal were respectively suppressed to be equal to or less than 0.5 mm and equal to or less than 40%. Accordingly, stability of pulling up performance was found to be greatly improved, which leads to completion of the present invention.
It is an object of the present invention to provide a quartz glass crucible for pulling up a silicon single crystal, with which not only can a defectless silicon single crystal be pulled up but a single crystallization ratio can greatly be improved, and a production method therefor.
DISCLOSURE OF INVENTION
In order to achieve the object, a first aspect of a quartz glass crucible for pulling up a silicon single crystal of the present invention resides in that the quarts glass crucible comprises a crucible base body constituted of a semi-transparent quartz glass layer and a transparent quartz glass layer formed on an wall inner surface of the crucible base body, and is characterized in that no expanded bubbles equal to or more than 0.5 mm in diameter are present in a layer 1 mm in depth from an inner surface of the quartz glass crucible after the silicon single crystal is pulled up using the quartz glass crucible. It is more preferred that no expanded bubbles equal to or more than 0.3 mm are present in the layer 1 mm in depth.
A total sectional area of bubbles is preferably equal to or less than 40% and more preferably equal to or less than 20% in the layer 1 mm in depth from the inner surface of the quartz glass crucible after the silicon single crystal is pulled up using the quartz glass crucible.
A second aspect of a quartz glass crucible for pulling up a silicon single crystal of the present invention resides in that the quartz glass crucible comprises a crucible base body constituted of a semi-transparent quartz glass layer and a transparent quartz glass layer formed on an inner wall surface of the crucible base body, and is characterized in that, in the transparent quartz glass layer, the maximum of diameters of bubbles is equal to or less than 0.2 mm, a total sectional area of bubbles is equal to or less than 20% and a gas content is equal to or less than 1 &mgr;l/g. It is more preferred that, in the transparent quartz glass layer, the maximum of diameters of bubbles is equal to or less than
Mizuno Shigeo
Ohama Yasuo
Sato Tatsuhiro
Arent & Fox PLLC
Kunemund Robert
Shin Etsu Quartz Products Co., Ltd.
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