Threshold ionization mass spectrometry in the presence of excited silane radicals

The presence of excited radicals in plasma-assisted chemical vapour deposition silane processes leads to overestimation of radical densities in threshold ionization mass spectrometry analysis. A method to discriminate the signal due to excited radicals is proposed and applied to estimate the relative density trends of the ground-state silane radicals (SiHx, x < 4) with hydrogen input flow rates (0-50 sccm) in an argon-silane-hydrogen plasma at total pressures of 0.01-0.04 mbar used for the deposition of nano-crystalline silicon (nc-Si) layers for photovoltaic applications. The SiHx/SiH4 density trends with hydrogen input show a turning point where SiH becomes dominant, in the process region where nc-Si layers were previously obtained.