LOW-TEMPERATURE SELECTIVE GROWTH OF EPITAXIAL SI AND SI1-XGEX LAYERS FROM SIH4 AND GEH4 IN AN ULTRAHIGH-VACUUM, VERY-LOW PRESSURE CHEMICAL-VAPOR-DEPOSITION REACTOR - KINETICS AND POSSIBILITIES

The kinetics of the growth of epitaxial and polycrystalline undoped an d heavily p-type-doped Si and Si1-xGex layers have been studied over t he pressure range from 4 x 10(-4) to 1.5 Torr at 625-degrees-C in an u ltrahigh vacuum chemical vapour deposition reactor by growing layers f or various times and measuring the resulting thicknesses. The pressure influence on the epitaxial as well as on the polycrystalline Si growt h rate is discussed. We observed that nucleation of Si on Si as well a s on SiO2 is retarded. A model is proposed which explains this incubat ion time for the nucleation of Si on Si and the influence of the press ure on it. The addition of GeH4 to the SiH4 growth environment is foun d to retard the nucleation on SiO2 even longer. On the other hand, a p ressure increase and the addition of B2H6 accelerate nucleation. Epita xial layers can be grown selectively on Si by limiting the growth peri od to below the incubation time of polycrystalline material. Maximum s elective thicknesses for various types and combinations of layers have been determined.