TIME-RESOLVED OBSERVATION OF CVD-GROWTH OF SILICON ON SI(111) WITH STM

Scanning tunneling microscopy is used to study the epitaxial growth of silicon on Si(111)-(7 x 7) by Chemical Vapour Deposition (CVD) of disilane (Si2H6) at elevated substrate temperatures directly during the growth process. Different kinetic processes, as island nucleation, growth and coarsening and step flow have directly been imaged as a function of temperature and Si2H6 flow. On a substrate with a low defect concentration several growth modes depending on the flux and the total coverage are distinguished: the formation of multi-level islands as a transient mode leaving the substrate partially uncovered up to 20 bilayers, a transition to layer-by-layer growth when the multi-level islands initially formed coalesce and the formation of three-dimensional islands with tetrahedral shape at higher growth rates which are only metastable due to the presence of hydrogen at the surface. The equilibrium shape of two-dimensional islands is a hexagon whereas the kinetically influenced shape during growth is triangular.