Particle accumulation in a flowing silane discharge

Abstract

Particle trapping in different areas of a parallel-plate, radio frequency silane discharge, and its effect on plasma optical emission of SiH and Hα, has been studied under high gas-flow and low power-density conditions, as used for “device-quality” hydrogenated amorphous silicon (a-Si:H) film deposition. The largest density of particles occurs between the electrodes, near the downstream corners of the rectangular electrodes. Particles are trapped in these positions by sheath fields, until reaching sufficient size to escape with the flow. The region of strong particle trapping has an increased intensity of optical emission, with Hα increased nearly fourfold. Slow oscillatory behavior of particle scattering and discharge emission was observed for pressures near 30 Pa. Power deposited in the discharge has also been measured; for a constant rf voltage and gas-flow speed it changes weakly with pressure, with the maximum at ∼40 Pa. Combined with film growth-rate measurements, this yields a discharge energy deposition of ∼17 eV per deposited Si atom.