Modelling of the power dissipation and rovibrational heating and cooling in SiH₄-H₂RF glow discharges

The electrical power dissipation and the vibrational (v) and rotational-translational (RT) heating and cooling mechanisms in SiH 4 -H 2 radio-frequency (RF) glow discharges are analysed. Detailed balance of the various contributions leads to determination of the steady state v and RT temperatures T V and T R depending on the discharge geometry, total and partial pressures, wall temperature and power density. In low-power SiH 4 -dominated discharges (0.1-0.2 Torr range), v excitation is mostly due to low-energy electron-SiH 4 collisions, but in high-power discharges, dominated by H 2 (0.1-1 Torr), v excitation proceeds via collisional relaxation of hot H atoms and exothermic chemical reactions. v cooling is mostly controlled by v-RT transfer and thermal diffusion to the walls and by electron impact dissociation of v excited molecules. In any case the contribution of spontaneous decomposition highly v excited SiH 4 molecules (pyrolysis) remains negligible. The model is tested on various experimental situations and the computed values of T V and T R are in fair agreement with available measurements by IR emission spectroscopy and CARS. It is also shown that the spatial temperature profiles may induce thermophoresis on particulates generated within the discharge.