STUDY OF GROWTH-KINETICS IN SILICON GAS-SOURCE MOLECULAR-BEAM EPITAXY WITH DISILANE USING RHEED INTENSITY OSCILLATIONS

We have studied reflection high energy electron diffraction (RHEED) intensity oscillations during silicon deposition from disilane on Si(100) in a gas source molecular beam epitaxy (GSMBE) system. The intensity oscillations were used to determine the growth rate over a wide range of substrate temperatures, disilane mass flows, azimuths and angles of incidence. It was found that the oscillation frequency does not depend on azimuth (with the exception of the [110] azimuths) or angle of incidence of the electron beam. Oscillations were observed for substrate temperatures ranging from 400-degrees-C to 650-degrees-C. There is no lower temperature limit for the occurrence of oscillations. However, below 400-degrees-C the frequency becomes so low that experiments are impractical. Above about 600-degrees-C, the growth rate is no longer limited by the desorption of surface hydrogen; other reaction steps such as adsorption and dissociation of disilane become rate limiting. Remarkably, even at lower temperatures the growth rate never saturates owing to the complete termination of all surface bonds by hydrogen but keeps increasing slightly with increasing flux. Comparison with RHEED oscillations observed in silicon solid source MBE indicates that the surface adsorbates in GSMBE are much less mobile, probably because of their different nature. Differences and similarities between the deposition processes of the two techniques are discussed.