Modelling of the power dissipation and rovibrational heating and cooling in SiH₄-H₂ RF glow discharges

The electrical power dissipation and the vibrational (v) and rotational-translational (RT) heating and cooling mechanisms in SiH₄-H₂ 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 SiH₄-dominated discharges (0.1-0.2 Torr range), v excitation is mostly due to low-energy electron-SiH₄ collisions, but in high-power discharges, dominated by H₂ (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 SiH₄ 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.