Silicon prodn. by decomposition or redn. of silicon cpd. in plasma - produced in carrier gas stream gives pure silicon at very low cost

摘要

In Si prodn., a plasma (3) is produced in a gas stream (1) and a Si cpd. (2) is introduced. This is then decomposed or reduced to Si, which is transported away from the plasma by the gas stream. The plasma is pref. produced with a d.c. or a.c. current or by absorption of intensive electromagnetic or ionising radiation in the gas stream. The Si can be deposited on a substrate, pref. of monocrystalline Si, a metal, an insulator, an inert liq. e.g. liq. MgC12 or Pb at 750 deg.C, or a heated substrate (e.g. graphite or ceramic at 1000 deg. C) covered with a thin film of inert liq. e.g. NaF or Sn. Deposition is carried out in an 02-free atmos. opt. in vacuo. The plasma spraying equipment may have a gas- or water-stabilised plasma. The gas stream consists of H2, noble gas, N2, hydrocarbon, C0and/or steam, whilst the Si cpd. can be an O-free cpd., e.g. SiH4, SiCl4, SiHCl3, SiH2Cl2 etc. or a cpd. contg. 0, e.g. SiO2, a silicate or an organo-Si cpd. Gp. III or gp. V dopants can be added to the gas stream. Specified combinations of gas and Si cpd. are H2 and Si chloride; noble gas or H2 and silane; H2 and SiO2; or a mixt. of noble gas or H2 and a hydrocarbon cpd. and SiO2. The process is specified for the prodn. of mono- or polycrystalline Si, pref. wafers, Si solar cells, Si transistors with p- and n-zones and pn-junctiions, Si power and silicides by further reaction of the Si formed in the plasma. Pure Si is produced at very low cost.