  SiC epitaxial films grown in an inverted chimney CVD reactor are analyzed and
compared for growth rates, doping concentration and surface morphology using
silane-propane-hydrogen and dichlorosilane (DCS)-propane-hydrogen chemistry
systems. A general 1-D analytical model is presented to estimate the
diffusivity of precursor gases, boundary layer thickness and growth rates for
both gas systems. Decomposition of precursor gases into Si growth species is
investigated by a commercial simulation tool, Virtual Reactor (VR). DCS
suppresses the formation of elemental Si at lower pressures, reduces precursor
losses, and leads to increased growth rate. However, at higher pressures, even
DCS decomposes into elemental Si, which contributes to high Si depletion,
limiting the maximum achievable growth rate. Reduction of Si loss using DCS is
verified by mass measurements of parasitic depositions in the injector tube.
The doping concentration of the epitaxial film is governed by the effective
C/Si ratio at the growth surface rather than the inlet C/Si ratio, which is
examined at various growth pressures. In addition to the widely known
Si-depletion, C-depletion is also shown to exist and it plays a critical role
in determining the doping concentration at various growth conditions. Increased
roughness for the DCS growth at higher pressures is addressed and attributed to
excessive HCl etching at higher pressures.
