Eagle-picher Industries, Inc.

Thomas M Potts

Joe M Walker

Tetraethoxysilane is purified by passing impure material through a gas chromatographic separating column at a temperature below the boiling point of the pure tetraethoxysilane. Separation of pure material from impurities occurs on the column, and the pure material is thereafter cooled and collected in a receiver. The purified tetraethoxysilane has 99.999999% purity based on metals content.

Purified tetraethoxysilane and method of purifying

Thermally decomposable Group IIIa compounds are purified by conveying the relatively impure material through a prescrubber module, then heating the scrubbed Group IIIa compound and conveying same through a preconditioned gas chromatographic column packed with a porous polymeric material. After isolation, the purified material is cooled, demisted amd collected. Thermally decomposable Group Va compounds are purified by conveying the heated relatively impure material through a preconditioned gas chromatographic column packed with a porous polymeric material. After isolation, the purified material is cooled and collected. Epitaxial semiconductor films of purified thermally decomposable Group IIIa and Group Va compounds with added dopant are prepared by diluting the film components with inert carrier gas to predetermined concentration levels, thoroughly mixing the components, then depositing a crystal layer prepared from the mixed components onto a substrate by thermally decomposing the mixed components in a reactor.

Method of purifying and depositing group IIIa and group Va compounds to

Elemental silicon is produced by a process and apparatus wherein relatively impure silane (SiH.sub.4) is purified in the gaseous state, while mixed with an inert carrier gas, to a content of electronically active impurities which is no higher than that of 'electronic grade' silicon. The silane so purified is then thermally decomposed to form elemental silicon of electronic grade purity, without need for further purification of the elemental silicon itself. The silane purification is carried out by injecting the impure silane gas as a series of timed, spaced pulses into a carrier gas stream which transports the silane pulses to a gas chromatographic column, through which the pulses flow in sequence. The column has a porous polymer or a molecular sieve packing which is specially preconditioned to achieve high resolution separation of the components of the feed. The components of each pulse are differentially retarded by this packing so that they move through the column at different rates, as a result of which they exit at different but precisely spaced time intervals in relation to pulse input time. The emergence from the column of the silane 'peak' or portion of the respective pulse is detected individually or is timed from the pulse input. When detected or timed, the eluent silane peak and admixed carrier gas are valved to a receiver separately from the other components, which exit before and after that peak. The silane gas fraction of the peak is then thermally decomposed, to form elemental silicon which is of electronic purity, or it may be collected and pressurized before thermal decomposition. The admixed carrier gas is not decomposed, remains a gas, and thereby is separated from the silicon. Depending on the extent to which the gas purification is carried, the product silicon may have a measured resistivity of about 1500 ohms cm or better, and can be used in fabrication of solar cells or semiconductor device without further purification.

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Joplin, MO, United States of America

Thomas M Potts