Rod contg. fine silicon crystals - made by chemical vapour deposition and then zone melted to mfr. monocrystalline silicon rod

摘要

Fine silicon crystals are deposited onto a heated substrate. The Si is obtd. from a reaction gas mixt. contg. a halosilane and H2 and flowing through a reactor contg. the substrate. The process commences with a high molar ratio (MR) in the reaction gas, a high gas flow, and an optimum deposition temp. (DT). During the process the MR, gas flow and DT are lowered or raised according to a prescribed program. The process pref. starts using MR of SiHCl3/H2 = 0.5 and optimum DT 1100 degrees C. Gas flow is pref. 3000-15,000 l/h. After 10 minutes deposition, the MR is pref. reduced to 0.2 and, when half the desired Si rod dia. has been reached, the DT s reduced by max. 200 degrees C for one hour, and the gas flow reduced to 1/4 with MR increased to 0.5. The step involving a temp. decrease of max. 200 degrees C and redn. in gas flow may be repeated for max. three times. With conventional prodn. of polycrystalline rods, coarse crystals can occur which cause dislocations during subsequent zone melting of the rods to produce monocrystalline rods, e.g. for semiconductor mfr. This problem is avoided.