Laser-induced fluorescence detection and kinetics of SiH2 radicals in Ar/H2/SiH4 RF discharges

Abstract

Laser-induced fluorescence spectroscopy is used to measure spatially- and time-resolved SiH2 radical densities in pure SiH4, H2/SiH4 and Ar/SiH4 radio-frequency glow discharges used for amorphous silicon thin film deposition. Absolute density calibration is obtained by a Rayleigh scattering experiment in pure nitrogen. Typical SiH2 densities on the plasma axis are 1-10 × 1016 m-3. Measurements of the SiH2 decay in the afterglow of argon/silane discharges are used to determine for the first time the SiH2 loss probability on a-Si:H surfaces and to confirm the reaction rate coefficient of SiH2 with SiH4. We find = 0.6±0.15 and kr = (2.3±0.5) × 10-17 m3 s-1 molecule-1 at T = 500 K and p = 9 Pa. The measured SiH2 densities are compared to those calculated by a previously published two-dimensional plasma simulation code.