Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
2000-04-27
2002-10-01
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
C117S020000, C117S217000, C117S218000, C117S900000
Reexamination Certificate
active
06458203
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a System and method for manufacturing a single-crystal ingot by means of the Czochralski technique (herein after referred to simply as the “CZ technique”) and more particularly, to a system and method suitable for manufacturing a perfect-crystal silicon wafer of good quality.
2. Related Art
Crystal defects which arise in a CZ single-crystal silicon ingot during the course of growth of the ingot according to the CZ technique adversely affect the reliability of a gate oxide film of an MOS device or the leakage characteristic of a p-n junction. For these reasons, the crystal defects must be minimized. It has already been pointed out that appropriate control of a ratio V/G of a pull rate V of a single-crystal ingot which is being pulled in a furnace (hereinafter simply called a “single-crystal pulled ingot”) to the temperature gradient G of the single-crystal pulled ingot is effective for controlling generation of crystal defects (see, for example, Japanese Patent Laid-Open No. 337490/1996).
The inventors who contrived the invention described in publication No. 337490/1996 produced a perfect crystal by appropriate control of the ratio V/G from 1300° C. to the melting point of silicon [see the 54
th
Technical Meeting of the Japan Society of Applied Physics (held for four days from Sep. 27 to 30, 1993)]. However, as described in the collection of proceedings of the 54
th
Technical Meeting of the Japan Society of Applied Physics (Proceeding No. 1, p. 303, 29a-HA-7) and Japanese Patent Laid-Open No. 330316/1996, the applicant of the present patent application has reported that a silicon of a perfect crystal is produced under more appropriate conditions by adequate control of the ratio V/G from 1350° C. to the melting point of silicon.
In order to produce a perfect crystal through growth of a CZ single-crystal ingot, the pull rate V and the temperature gradient G must be controlled to a high degree of accuracy.
Even if the growth rate V is controlled constantly, the temperature gradient G changes incessantly during the course of growth of a crystal, and the value of the ratio V/G also changes so as to follow the change in the temperature gradient G. Eventually, a complete crystal region cannot be formed at good yield in the direction of crystal growth.
To overcome this problem, according to the related art (Japanese Patent Laid-Open No. 268794/1996), an internal temperature distribution of the single-crystal ingot is determined through calculation of temperature distribution of the entire furnace by use of heat transfer calculation. The heat radiated from a melt is shielded and/or reflected on the basis of the thus-calculated temperature distribution of the furnace, to thereby control the internal temperature distribution of a single-crystal ingot. Through such a control, the growth rate V is controlled such that the value of the ratio V/G (mm
2
/° C.×min.) approaches a target value, and the temperature gradient G is also controlled by means of shielding and/or reflecting the heat radiated from the melt.
According to the related art, the shielding of the heat radiated from the melt is controlled by changing the position of a heat-shielding member which is a standard component of a recent system for manufacturing a CZ single-crystal ingot. The recent system has a mechanism for vertically moving a radiation shield (i.e., a heat-shielding member) in order to control the degree to which the heat radiated from a melt to a single-crystal ingot is shielded. According to the background art, a radiation reflection member of high reflectivity is placed at a position above a melt, and the amount of heat radiated is controlled by means of controlling the angle of the radiation reflection member.
Further, according to the related art, a G-calculator is used for determining the temperature gradient G at temperatures ranging up to 1300° C. with respect to a crystal longitudinal axis. Various data sets, such as data pertaining to the position and angle of the radiation shield, are input to the G-calculator, thus calculating the temperature gradient G. On the basis of the temperature gradient G determined by the G-calculator and the growth rate V of a single-crystal, a V/G controller calculates the ratio V/G and controls the growth rate V such that the calculation result matches a predetermined V/G value, thereby regulating the position and angle of the radiation shield. Finally, the V/G ratio is controlled during the entire process.
However, in a case where the ratio V/G is controlled by changing the position and angle of the heat-shielding member, as in the case of the related art (i.e., Japanese Patent Laid-Open No. 268794/1996), additional members or mechanisms for actuating the heat-shielding member are required, thus introducing the disadvantages of an increase in the number of components and complicated control. More Specifically, under the method described in Japanese Patent Laid-Open No. 268794/1996, the heat radiated from a melt is shielded or reflected through use of various control devices such as those mentioned previously, thereby controlling a temperature gradient in the vicinity of the interface between solid and melt. An additional mechanism for controlling the position of the heat-shielding member and the angle of a reflecting member is required, thus greatly complicating the control of the ratio V/G.
Further, according to the related art, the temperature gradient G used for calculating the ratio V/G is computed basically through inference by use of simulation of a temperature. Therefore, the ratio V/G is not controlled so as to completely reflect the internal state of the furnace. Even if the growth rate V is constant, there may arise a case where the temperature gradient G is not actually controlled. In such a case, a perfect crystal cannot be produced with good yield in the direction of crystal growth.
The present invention has been conceived against the foregoing backdrop, and is aimed at providing a system and method of producing a perfect crystal with good reproducibility through growth of a single-crystal ingot. Further, the present invention provides a mechanism or method for use with a system of manufacturing a single-crystal ingot by means of the CZ technique, the mechanism or method being able to control a V/G ratio without involvement of a change in the position of a heat-shielding member.
SUMMARY OF THE INVENTION
To solve the drawbacks of the background art, there are provided a system and method of manufacturing a single-crystal ingot by means of the CZ technique according to the present invention, wherein a heat-shielding member is in principle placed in a fixed position, and the requirements for pulling a single-crystal ingot are controlled by means of measuring the distance between the bottom of the heat-shielding member and the level of molten raw material and feeding back the thus-measured distance.
In a system for manufacturing a single-crystal ingot by means of the CZ technique (hereinafter referred to simply as a “system”), a crucible for storing silicon melt is moved upward so as to compensate for a drop in the level of the molten raw material stemming from a reduction in the level of molten raw material caused by pulling of a single-crystal ingot. The distance between the bottom of the heat-shielding member and the level of the molten raw material remains essentially constant. However, there is a case where a minute change arises in the distance, for reasons of a discrepancy between the rate at which the crucible is moved vertically and reduction in the level of the molten raw material, improper control of vertical movement of the crucible, deformation of the heat-shielding member caused by the internal heat of the furnace, or a change in the state of the level of the molten raw material, such as ripples. The inventors have found that even a change in the distance between the bottom of the heat-shielding member and the level of the molten raw material is on
Hanamoto Tadayuki
Kotooka Toshirou
Morimoto Shigeo
Moriya Masato
Hiteshew Felisa
Welsh & Katz Ltd.
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