Purification of chlorosilanes
AssigneeDow Corning Corporation
InventorRichard S. Doornbos
Life of this patent
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Abstract
Chlorosilanes contaminated with boron-containing impurities can be purified by passing the chlorosilane vapor through a silica fixed bed. Normally the boron level in trichlorosilane is reduced by about 90-99+% by the use of this process. The capacities of the silica columns for the purification of trichlorosilane generally are in the range of 1500-2000 pounds trichlorosilane per pound of silica. The purified chlorosilane is particularly well suited for the production of polycrystalline silicon. Polycrystalline silicon containing 0.03 ppba (parts per billion atomic) has been prepared from trichlorosilane purified with this process.
Claims20
A process for purification of a chlorosilane selected from the group consisting of monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane where said chlorosilane is contaminated with boron-containing impurities, said process comprising the steps of
- (A) passing the chlorosilane, in the vapor phase, through a bed of silica, said bed of silica consisting of silica containing about 0 to 10% by weight free water and more than about about 0.25% by weight total hydroxyl, said bed of silica being at a temperature greater than 3.degree. C. above the boiling point of the chlorosilane at the operating pressure of step (A) and a temperature of less than or equal to about 99.degree. C., and
- (B) collecting the purified chlorosilane having a significantly reduced amount of the boron-containing impurities.
A process for the purification of trichlorosilane where said trichlorosilane is contaminated with boron-containing impurities, said process comprising the steps of
- (A) passing the trichlorosilane, in the vapor phase, through as bed of silica, said bed of silica consisting of silica containing about 0 to 10% by weight free water and more than about 0.25% by weight total hydroxyl, said bed of silica being at a temperature greater than 3.degree. C. above the boiling point of trichlorosilane at the operating pressure of step (A) and at a temperature of less than 85.degree. C., said silica has a surface area greater than about 500 m.sup.2 /g, and said silica has a particle size distribution such that about 35-65% of the particles are retained on a 65 mesh screen, and
- (B) collecting the purified chlorosilane.
Dependencies are inferred from the claim text.