PARTICLE ACCUMULATION IN A FLOWING SILANE DISCHARGE

Particle trapping in different areas of a parallel-plate, radio freque ncy silane discharge, and its effect on plasma optical emission of SiH and H-alpha, has been studied under high gas-flow and low power-densi ty conditions, as used for ''device-quality'' hydrogenated amorphous s ilicon (a-Si:H) film deposition. The largest density of particles occu rs between the electrodes, near the downstream corners of the rectangu lar electrodes. Particles are trapped in these positions by sheath fie lds, until reaching sufficient size to escape with the flow. The regio n of strong particle trapping has an increased intensity of optical em ission, with H-alpha increased nearly fourfold. Slow oscillatory behav ior of particle scattering and discharge emission was observed for pre ssures near 30 Pa. Power deposited in the discharge has also been meas ured; for a constant rf voltage and gas-flow speed it changes weakly w ith pressure, with the maximum at similar to 40 Pa. Combined with film growth-rate measurements, this yields a discharge energy deposition o f similar to 17 eV per deposited Si atom. (C) 1997 American Institute of Physics.