Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
2000-02-15
2002-10-01
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
C117S028000, C117S218000
Reexamination Certificate
active
06458201
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an improvement of apparatus for producing single crystals, which apparatus is for producing various crystal materials of semiconductors, dielectric material, magnetic material and the like by the Czochralski method.
BACKGROUND ART
For the production of single crystal materials such as semiconductor silicon single crystals, methods for obtaining them as rod-shaped single crystals by the Czochralski method (referred to as “CZ method” hereinafter) have been widely used so far.
Apparatuses for producing single crystals used for this CZ method usually comprise a crucible for accommodating a raw material melt disposed in a chamber, a support shaft for supporting the crucible, a pulling mechanism for pulling a crystal from the melt, a rotation mechanism for rotating the crucible, and a transfer mechanism for vertically moving the crucible, as well as members in a furnace such as heaters and heat insulating materials disposed in the chamber, so that a single crystal can be produced.
It has been widely known that, when crystal growth is attained by this CZ method, ingredients of the crucible such as quartz crucible for accommodating the raw material for the crystal growth, for example, oxygen, are immixed into the resulting crystals, in addition to those ingredients originally contained in the raw material.
The amount of the impurities to be immixed in the crystal may vary depending on the rotation number of the pulled crystal, the rotation number of the crucible, temperature distribution of the raw material melt and the like. That is, the crystal rotation number affects the convection in the melt, the crucible rotation number affects the oxygen concentration itself in the melt, and the temperature distribution in the raw material melt affects the convection in the melt.
Moreover, since depth of the melt in the crucible gradually decreases as the crystal grows, it must be devised that the melt surface should be controlled to position at a fixed position in order to control the diameter of the growing crystal, and it is necessary to move the crucible upward to secure constant relative locational relationship between the melt and the heaters as the crystal grows. Therefore, many of conventional apparatuses for producing crystals based on the CZ method have been provided with functions for rotating a crucible-supporting shaft as well as vertically moving the crucible. In particular, a rotation-driving unit for the crucible-supporting shaft must also be vertically moved with the crucible-supporting shaft. As shown in
FIG. 4
, in a conventional apparatus for producing single crystals, for example, the crucible rotation driving unit
26
has been provided on a slider
31
of the mechanism
30
for vertically moving the crucible, which vertically moves with the crucible-supporting shaft
4
.
In such a conventional apparatus as mentioned above, the melt surface may be vibrated. Such vibration of the melt surface may leads to disadvantages, that is, the growing single crystal may become a polycrystal, or even it becomes impossible to continue the crystal growth when the situation gets worse. Therefore, the cause for the vibration was investigated, and it has been revealed that vibration of the crucible-supporting shaft constitutes its major cause. That is, vibration is generated by rotation of an electric motor, which is the driving power source for the crucible rotation, this vibration in turn vibrates the mechanism for vertical movement, and this vibration is transmitted to the melt via the crucible-supporting shaft and the crucible.
The present invention has been accomplished in view of such problems, and its object is to provide means for absorbing and eliminating the vibration generated by the crucible rotation driving unit, or preventing transmission of the vibration to the melt, or attenuating the vibration.
DISCLOSURE OF INVENTION
In order to achieve the aforementioned object, the 1st embodiment of the invention relates to an apparatus for producing single crystals by the Czochralski method, the apparatus comprising at least a support shaft for supporting a crucible for accommodating a raw material melt, a pulling mechanism for pulling a crystal from the melt, a rotation mechanism for rotating the crucible, and a transfer mechanism for vertically moving the crucible, wherein a crucible rotation driving unit constituting the rotation mechanism for the crucible is fixedly installed on a substructure of the apparatus for producing single crystals.
When the crucible rotation driving unit consisting of an electric motor and means for speed change and reduction is fixedly installed on the substructure of the apparatus for producing single crystals as defined above, vibration generated by the electric motor constituting the crucible rotation driving unit is absorbed by a fixed end, i.e., the rigid substructure, and attenuated. Thus, the vibration is not substantially transmitted to the melt surface via the crucible-supporting shaft and the crucible. Therefore, the vibration of the melt surface, which may be a cause for generating dislocations in growing single crystal ingots, can be substantially eliminated.
In this case, the term “substructure” of the apparatus for producing single crystals means frames, concrete substructures, substructures of working houses and the like for supporting the apparatus for producing single crystals. It may be any means that can fix the crucible rotation driving unit without being vibrated by the unit, and it is not limited by a literal meaning of the word.
The 2nd embodiment of the invention relates to an apparatus for producing single crystals by the Czochralski method, the apparatus comprising at least a support shaft for supporting a crucible for accommodating a raw material melt, a pulling mechanism for pulling a crystal from the melt, a rotation mechanism for rotating the crucible, and a transfer mechanism for vertically moving the crucible, wherein, in the rotation mechanism for the crucible, a ball spline is used for power transmission between a crucible-supporting shaft and a crucible rotation driving unit, and the crucible rotation driving unit is fixedly installed on a substructure of the apparatus for producing single crystals.
When the crucible rotation driving unit consisting of an electric motor and means for speed change and reduction is fixedly installed on the substructure of the apparatus for producing single crystals, and a ball spline is used for power transmission between the crucible-supporting shaft and the crucible rotation driving unit in the rotation mechanism for the crucible as defined above, only vibration attenuated by being absorbed into the substructure is transmitted to the ball spline, and therefore the vibration of the melt surface is substantially eliminated without affecting at all the function of the ball spline for transmitting rotation simultaneously with the vertical movement. Thus, single crystals can be produced safely and efficiently.
In the 3rd embodiment of the invention, a rubber-like elastic belt and a pulley, or a rubber-like elastic timing belt and a timing pulley are used as means for transmitting rotation between the crucible-supporting shaft and a ball spline shaft, and between a ball spline sleeve and an output shaft of the crucible rotation driving unit.
By using a rubber-like elastomer as a material for transmitting rotation between the shafts as defined above, the vibration generated by the crucible rotation driving unit is attenuated and absorbed by rubber-like elastic deformation, and vibration transmitted to the melt surface is substantially eliminated. Therefore, the cause etc. for generating dislocations in growing crystals is eliminated, and crystals can be produced safely and efficiently.
The 4th embodiment of the invention relates to an apparatus for producing single crystals by the Czochralski method, the apparatus comprising at least a crucible-supporting shaft for supporting a crucible for accommodating a raw material melt, a rotation mechanism
Kitagawa Kouji
Mizuishi Kouji
Kunemund Robert
Shin-Etsu Handotai & Co., Ltd.
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