Low temperature selective growth of epitaxial Si and Si 1−xGe x layers from SiH 4 and GeH 4 in an ultrahigh vacuum, very low pressure chemical vapour deposition reactor: kinetics and possibilities

Abstract

The kinetics of the growth of epitaxial and polycrystalline undoped and heavily p-type-doped Si and Si 1− x Ge x layers have been studied over the pressure range from 4×10 −4 to 1.5 Torr at 625°C in an ultrahigh vacuum chemical vapour deposition reactor by growing layers for various times and measuring the resulting thicknesses. The pressure influence on the epitaxial as well as on the polycrystalline Si growth rate is discussed. We observed that nucleation of Si on Si as well as on SiO 2 is retarded. A model is proposed which explains this incubation time for the nucleation of Si on Si and the influence of the pressure on it. The addition of GeH 4 to the SiH 4 growth environment is found to retard the nucleation on SiO 2 even longer. On the other hand, a pressure increase and the addition of B 2H 6 accelerate nucleation. Epitaxial layers can be grown selectively on Si by limiting the growth period to below the incubation time of polycrystalline material. Maximum selective thicknesses for various types and combinations of layers have been determined.