Enhancement of Surface Productions of CFx Radicals by the Addition of H 2 into CF 4 Plasmas

Abstract

Spatially resolved CF and CF2 radical densities were measured in low-pressure, high-density CF4 plasmas with the addition of H2 by laser-induced fluorescence spectroscopy. Hollow radial distributions (the densities in the outside region were higher than those in the plasma column) were observed for the radical densities. Diffusion fluxes of the radicals from the outside region to the plasma column were evaluated from the slope of the hollow density distributions. Linear correlations were found between the inward diffusion fluxes and the gas-phase radical densities, suggesting that the gas-phase CF and CF2 radical densities were determined not by the electron-impact dissociation of CF4 in the plasma column but by the production of radicals in the outside region. The source of the radicals in the outside region is the surface of the chamber wall covered with fluorocarbon film.