SURFACE PRODUCTIONS OF CF AND CF2 RADICALS IN HIGH-DENSITY FLUOROCARBON PLASMAS

Spatial distributions of CF and CF2 radical densities in high-density fluorocarbon plasmas were measured by laser-induced fluorescence spect roscopy. In both pulsed and continuous-wave (cw) C4F8 discharges, the radical densities were lower in the center of the discharge and higher near the walls. Namely, hollow-shape profiles of the radical densitie s were maintained in the C4F8 discharges. This indicates the presence of surface productions of the radicals on the chamber wall. The rf pow er dependences of the radical fluxes from the wall, which were estimat ed from the density gradients, showed similar trends to the gas-phase radical densities. This result revealed that the surface productions p redominantly determine the gas-phase CF and CF2 radical densities in h igh-density C4F8 plasmas. In contrast to C4F8, almost uniform profiles of the radical densities were always observed in cw CF4 discharges, w hile hollow profiles were observed in pulsed CF4 discharges. The CF2 f lux from the wall in the pulsed CF4 discharge was one or two orders sm aller than that in the C4F8 discharge, and the rf power dependence of the CF2 flux showed a dissimilar trend to the gas phase CF2 density. T he large difference in the radical flux from the wall observed in the C4F8 and CF4 discharges suggests that heavy neutral species (CxFy, x g reater than or equal to 2) in the C4F8 plasma make great contributions to the him deposition on the wall where the deposited films enhance t he surface productions of CF and CF2 radicals. (C) 1998 American Vacuu m Society. [S0734-21(98)11304-0].