Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
1999-04-21
2001-04-17
Garrett, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
C117S015000, C117S217000, C117S218000, C117S911000
Reexamination Certificate
active
06217648
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a single crystal pulling apparatus and a single crystal pulling method for manufacturing a dislocation-free single crystal of Si (silicon) by pulling Czochralski (CZ) method.
BACKGROUND ART
In general, in a single crystal manufacturing apparatus based on the pulling CZ method, pressure in a highly pressure-proof airtight chamber is reduced to about 10 torr, and fresh argon (Ar) gas is sent into it. Polycrystals in a quartz crucible placed at the lower portion of the chamber are heated and molten, and seed crystal is immersed from above into the surface of the melt. Then, the seed crystal and the quartz crucible are rotated and moved up and down, and the seed crystal is pulled up. At the same time, a single crystal is grown, which comprises an upper cone portion in shape of a cone with its upper end protruding under the seed crystal and a lower cone portion in shape of a cone with a part of cylindrical body and the lower end protruded (the so-called ingot).
As the method to grow the crystal, Dash method is known. In this method, in order to eliminate dislocation (to turn to dislocation-free), which occurs on a seed crystal by thermal shock when the seed crystal is immersed into the surface of a melt, pulling rate is relatively quickened after immersing the seed crystal into the surface of the melt, and a portion with smaller diameter than the diameter of the seed crystal or a neck portion of 3-4 mm in diameter is formed, and then, the pulling operation of the upper cone portion is started.
Further, a single crystal with larger diameter and heavier weight (150-200 kg or more) cannot be pulled up via the neck portion with smaller diameter, and the following method has been proposed in the Japanese Patent Publication 5-65477, for example: After the neck portion with smaller diameter has been formed by Dash method, the pulling rate is relatively slowed down to form a portion with larger diameter. Then, the pulling rate is relatively quickened to form a portion with smaller diameter. Thus, “a spherical constricted portion” is formed, and by holding this constricted portion by a holder, a single crystal with larger diameter and heavier weight can be pulled up. As the conventional apparatus to hold the constricted portion, those disclosed in Japanese Patent Publications 7-103000 and 7-515 are known.
Also, a method to hold a part of the crystal body without forming the constricted portion as described above has been disclosed in Japanese Patent Publications Laid-Open 5-270974 and 7-172981. Further, Japanese Patent Publications Laid-Open 63-252991 and 5-270975 have proposed a method to form an “annular constricted portion” with diameter larger than that of the body portion between the upper cone portion and the body portion instead of the “spherical constricted portion” as described above and to hold this “annular constricted portion”.
However, the single crystal pulling process is a process, which is very sensitive to vibration from outside and the crystal can be easily turned to polycrystal. Therefore, the problem in the pulling operation of the single crystal lies in that the crystal itself must be smoothly and gently moved from the necking position toward holding position such as the constricted portion without giving disturbances from outside. The holders as used in the past are mostly of squeezing type to squeeze the portion with larger diameter or straight body of the single crystal using two or more component members. In adopting such a structure, the squeezing force may be lost during trouble such as power suspension, and the single crystal may be dropped down. Further, because of high temperature inside the pulling furnace, holding mechanism must have heat-resistant property. Also, dust and particles generated from mechanical friction parts such as driving units must be removed as far as possible because these may adversely affect the single crystal. None of the conventional methods can perfectly solve all of these problems.
DISCLOSURE OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a single crystal pulling apparatus with relatively simple arrangement and produced at low cost. By such an apparatus, it is possible to prevent the single crystal from being turned to polycrystal during pulling operation when the single crystal is held by the holder, to move the crystal itself smoothly and gently from the necking portion to a holding position such as a constricted portion during single crystal pulling operation, and to reliably hold the single crystal even in case of trouble such as power suspension.
To attain the above object, the apparatus according to the present invention uses a support base as a dish-like member to hold a portion with larger diameter by supporting and placing it from below, which is formed under the seed crystal, and the support base is rotated by pulley means, and the support base can be moved between a position not to support and a position to support the lower end of the constricted portion and/or the portion with larger diameter of the single crystal depending on rotation angle, and by lifting the pulley means while controlling the lifting rate, a single crystal is grown by moving up the support base.
Also, the apparatus may comprise both the means for rotating the pulley means and the means for lifting the pulley means as the winding mechanism. Or, only the latter means may be designed as a winding mechanism, and the former means may be designed as means for moving a part of wire in horizontal direction.
Specifically, the present invention provides a single crystal pulling apparatus, which comprises rotating means for rotating a seed crystal holder around pulling direction to support a seed crystal above a crucible capable to hold a molten crystal, seed crystal pulling means for pulling up the seed crystal by moving up the seed crystal holder while controlling pulling rate, a support base as a dish-like member to support a portion with larger diameter by supporting and placing the portion with larger diameter formed under the seed crystal, pulley means for rotating the support base and being movable between a position not to support and a position to support the lower end of a constricted portion and/or the portion with larger diameter of a single crystal depending on rotation angle, pulley rotating means for rotating the pulley means and for moving the support base between the two positions, pulley lifting means for moving up the support base by lifting up the pulley means while controlling the lifting rate, and means for rotating the pulley rotating means and the pulley lifting means around pulling direction of the seed crystal.
Also, the present invention provides a single crystal pulling apparatus, which comprises rotating means for rotating a seed crystal holder around pulling direction to support a seed crystal above a crucible capable to hold a molten crystal, seed crystal pulling means for pulling up the seed crystal by moving up the seed crystal holder while controlling the pulling rate, a support base having a through-hole to receive a constricted portion of a single crystal to support the lower end of the constricted portion and/or a portion with larger diameter below the portion with larger diameter formed under the seed crystal and provided with a slit for communicating the through-hole with outer peripheral portion in order to guide the constricted portion through the through-hole, pulley means being movable between a position not to support and a position to support the lower end of the constricted portion and/or the portion with larger diameter of the single crystal depending on rotation angle, pulley rotating means for rotating the pulley means and controlling rotating angular position, pulley lifting means being rotatable together with the seed crystal holder and for lifting up the pulley rotating means while controlling the lifting rate, and capable to grow the single crystal by moving up the support base, and means for rotating th
Garrett Felisa
McDermott & Will & Emery
Super Silicon Crystal Research Institute Corporation
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