Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Patent
1998-01-08
1999-06-29
Garrett, Felisa
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
117 44, C30B 1520
Patent
active
059163640
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to methods and apparatus for pulling a single crystal and, more particularly, to methods and apparatus for pulling a single crystal wherein a single crystal of silicon or the like is pulled by a pulling method such as the Czochralski method (hereinafter, referred to as the CZ method).
BACKGROUND ART
At present, as the majority of silicon single crystal ingots used for manufacturing a substrate for forming a circuit component of a LSI (large scale integrated circuit) and the like, silicon single crystals pulled by the CZ method have been used. FIG. 8 is a diagrammatic sectional view of a conventional apparatus for pulling a single crystal used for the CZ method, and in the figure, reference numeral 61 represents a crucible.
The crucible 61 comprises a bottomed cylindrical quartz crucible 61a and a bottomed cylindrical graphite crucible 61b fitted on the outer side of the quartz crucible 61a and supporting the quartz crucible 61a. The crucible 61 is supported with a support shaft 68 which rotates in the direction shown by the arrow in the figure at a prescribed speed. A cylindrical heater 62 of a resistance heating type and a cylindrical heat insulating mould 67 are concentrically arranged around the crucible 61. The crucible 61 is charged with a melt 63 of a material for forming a crystal which is melted by the heater 62. On the central axis of the crucible 61, a pulling axis 64 made of a pulling rod or wire is suspended, and at the lower end portion thereof, a seed crystal 65 is held by a holder 64a. Each part mentioned above is arranged at a fixed place in a water cooled type chamber 69 wherein pressure and temperature can be controlled.
A method for pulling a single crystal 66 using the above-mentioned apparatus for pulling a single crystal is described below by reference to FIGS. 8 and 9. FIGS. 9(a)-(d) are partial magnified front views diagrammatically showing the seed crystal and the vicinity thereof in part of the steps in pulling a single crystal.
Although it is not shown in FIG. 9, the material for forming a crystal is melted by the heater 62. The pressure in the chamber 69 is reduced and is maintained for a period of time so as to sufficiently release gas contained in the melt 63. Then, an inert gas is induced into the chamber 69 from the upper part thereof so as to make an inert gas atmosphere under reduced pressure within the chamber 69.
While the pulling axis 64 is rotated on the same axis in the reverse direction of the support shaft 68 at a prescribed speed, the seed crystal 65 held by the holder 64a is caused to descend. The front portion 65a thereof is brought into contact with the surface of the melt 63 so as to make the seed crystal 65 partially melt into the melt 63 (hereinafter, referred to as the seeding step) (FIG. 9(a)).
In making a crystal grow at the front of the seed crystal 65, the pulling axis 64 is pulled at a higher speed than the below-described pulling speed in forming a main body 66c. The crystal is narrowed down to have a prescribed diameter, leading to the formation of a neck 66a (hereinafter, referred to as the necking step) (FIG. 9(b)).
By slowing down the pulling speed of the pulling axis 64 (hereinafter, simply referred to as the pulling speed), the neck 66a is made to grow to have a prescribed diameter, leading to the formation of a shoulder 66b (hereinafter, referred to as the shoulder formation step) (FIG. 9(c)).
By pulling the pulling axis 64 at a fixed rate, the main body 66c having a uniform diameter and a prescribed length is formed (hereinafter, referred to as the main body formation step) (FIG. 9(d)).
Although it is not shown in FIG. 9, in order to prevent induction of high density dislocation to the single crystal 66 by a steep temperature gradient, the diameter thereof is gradually decreased and the temperature of the whole single crystal 66 is gradually lowered, leading to the formation of an end-cone and a tail end. Then, the single crystal 66 is separated from the melt 63. Cooling the single crystal 66 is
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patent: 5292487 (1994-03-01), Tatsumi et al.
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Garrett Felisa
Sumitomo Sitix Corporation
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