Polycrystal silicon rod and production process therefor

Details Polycrystal silicon rod and production process therefor Polycrystal silicon rod and production process therefor

1998-01-20

1999-11-02

Nguyen, Ngoc-Yen

Chemistry of inorganic compounds

Silicon or compound thereof

Elemental silicon

423349, 423350, C01B 3302, C30B 2906

Patent

active

059764813

DESCRIPTION:

BRIEF SUMMARY
FIELD OF TECHNOLOGY

This invention relates to a polycrystal silicon rod having small internal strain and uniform high-crystallinity, and a production process therefor. More specifically, it relates to a high-purity polycrystal silicon rod whose residual strain is reduced to such an extent that trouble caused by cracking can be prevented even when it is fed directly into a melting furnace in the production of silicon single crystals to be used for the production of devices and the like by recharging and yet which has stable melt properties; and a process for the production thereof.


BACKGROUND OF TECHNOLOGY

A polycrystal silicon rod is generally produced by a chemical vapor deposition (to be abbreviated as CVD hereinafter). That is, the CVD is generally carried out by bringing hydrogen and one member of silane gases such as monosilane, dichlorosilane, trichlorosilane and the like or a mixture of two or more of these gases into contact with a core material kept at a high temperature, in a gaseous atmosphere diluted with an inert gas as required, to deposit silicon on the surface of the core material. Out of methods for depositing polycrystal silicon by the CVD method, there is a method for producing a polycrystal silicon rod by using silicon as a core material and thickening the rod, in particular. This method is also called a Siemens method, and is generally and widely employed.
Meanwhile, an attempt is made to melt a polycrystal silicon rod produced by the above Siemens method, as it is, and convert it into single crystals by recharging. Japanese Laid-Open Patent Publication 7-277874 teaches a technology for producing single crystal silicon by supplying the silicon rod directly as a rod for recharging.
This Laid-open Publication discloses the necessity for reducing the residual stress of a polycrystal silicon rod to prevent a fall caused by the cracking of the polycrystal silicon rod as a raw material during the preparation of single crystals. As specific means of reducing the residual stress, there is disclosed a method of producing a polycrystal silicon rod from monosilane as a raw material. This publication teaches also that since a polycrystal silicon rod obtained from raw materials other than monosilane has large residual stress, a heat treatment such as annealing is carried out before melting of the rod to remove the residual stress.
However, a polycrystal silicon rod produced from monosilane as a raw material on an industrial scale generally has low crystallinity. In other words, the polycrystal silicon rod produced from monosilane has a half value width of a peak (may be also referred to as "peak (111)" hereinafter) in the vicinity of 2.theta.=28.5.degree. of an X-ray diffraction pattern obtained using copper as a target of around 0.4.degree. to 0.50.degree..
Therefore, the polycrystal silicon rod produced from such monosilane as a raw material has a low crystallinity and in consequence, such trouble is invited that an amorphous portion remains as a hole and an etching solution remains therein when a treatment for obtaining high-purity single crystal silicon, particularly a treatment for etching the surface thereof with a view to prevent inclusion of heavy metals, is carried out.
This can be presumed from Japanese Laid-Open Patent Publication 8-169797 which teaches that fine powders formed through a homogenous reaction are contained in a polycrystal silicon rod produced by the deposition of monosilane.
Japanese Laid-Open Patent Publication 8-67510 discloses that the surface area of the above polycrystal polysilicon having a low crystallinity is increased when it is etched.
In contrast to this, a polycrystal silicon rod produced using trichlorosilane as a raw material has a high crystallinity and does not contain fine powders because it is free from a homogenous reaction.
Therefore, when trichlorosilane is used as a raw material for the production of a polycrystal silicon rod, the resulting polycrystal silicon rod does not deteriorate in quality by etching because it has a smooth surface even aft

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Translation of JP 08-067,510, Mar. 1996.
Translation of JP 7-277,874, Oct. 1995.

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