Ion chemistry in silane dc discharges

The ion production and reactions in dc silane discharges are calculated. It is noted that almost all ion production and reaction occur in the cathode sheath region for typical low-pressure silicon-deposition discharges, so that the calculation considers ion production, drift, and reactions in the sheath region. Sheath models, for inert gas discharges, that utilize local and nonlocal electron energy distributions are compared, and one is adapted to silane conditions. The distribution of ion species (SilH+m) arriving at the cathode is calculated for a range of discharge pressures and currents, for comparison to mass spectrometer measurements. However, we do not make quantitative comparisons to reported observations due to sampling-bias issues that have not been taken into account.