An analysis of substrate heating during a-Si: H Deposition using concentric cylindrical DC glow discharge

The surface temperatures of a cylindrical cathode substrate, an outer anode, and an inner heater were measured by thermocouples during amorphous silicon depositions using a DC glow discharge. These temperatures were found to increase due to the plasma input power. A phenomenological thermal analysis of the substrate was carried out to determine the relationship of the conversion ratio of the plasma input power to heat.dissipation on the substrate. To elucidate the heating mechanisms of the substrate, the energy distributions of both ionic and high-energy neutal molecular species in the cathode sheath were calculated using the Boltzmann equation. Collisions between the ions and the neutral molecules are assumed to be either elastic or to involve charge-transfer. The pressure used in depositing the films, 1 Torr, is high enough to ensure that the flux density of the high-energy neutral molecules reaching the substrate greatly exceeds that of the ions. If the high-energy neutral molecules are assumed to be unchanged after collision with other neutral molecules having low thermal energy, the high-energy neutrals carry sufficient thermal energy to increase the substrate temperature. It was concluded that 60 to 70% of the plasma input power dissipates on the cathode substrate.