US 4,070,444 A · Low cost, high volume silicon purification process

Abstract

Truly amorphous silicon having a low level of undesired impurities, and therefore suitable for semiconductor applications, may be prepared by the present process. Impure silicon, for example, metallurgical grade silicon, is prepared at an elevated temperature, e.g., above 1400.degree. C. The impure silicon and at least one binary silicon fluoride compound, e.g., silicon tetrafluoride, are chemically combined at the elevated temperature to form silicon difluoride gas. The silicon difluoride gas is polymerized. The silicon difluoride polymer is then thermally decomposed to produce the purified, amorphous silicon and binary silicon fluoride by-products. The binary silicon fluorides are recycled in the process to be chemically combined with the impure silicon. That step and the succeeding steps serve to reduce the level of unwanted impurities in the silicon produced by at least several orders of magnitude.

Claims12

Dependent claims

A process of producing pure semiconductor grade silicon which comprises:

chemically combining metallurgical grade silicon and at least one binary silicon fluoride compound to form silicon difluoride gas,
forming a polymer of said silicon difluoride at a partial pressure of said silicon difluoride gas greater than about 150 microns Hg and at a first temperature of from about -45.degree. C to about +200.degree. C which will allow formation of said polymer in a continuous form on a substrate having a different coefficient of thermal expansion than that of said polymer,
cooling said polymer and said substrate to a second lower temperature which will allow said polymer to be separated easily from said substrate,
thermally decomposing the silicon difluoride polymer to produce silicon and a binary silicon fluoride compound, and
introducing said binary silicon fluoride compound from said thermal decomposition to said step of combining with silicon, these process steps serving to remove unwanted impurities from said metallurgical grade silicon.

2 more elements

Dependencies are inferred from the claim text.

Low cost, high volume silicon purification process

Life of this patent

Low cost, high volume silicon purification process

Life of this patent

Abstract

Claims12