Kinetics of the Reactions Involving CF[sub 2] and CF in a Pure Tetrafluoromethane Plasma: I. Production of CF[sub 2] and CF via Electron-Impact Dissociation

The kinetics of the production and loss of CF[sub 2] and CF radicals in a glow discharge in pure CF[sub 4] is investigated by the laser-induced fluorescence method. The effective rate constants for electron-impact dissociation of CF[sub 4] molecules along the pathways toward CF[sub 2] and CF radicals are determined within a wide range of the reduced electric field (80–250 Td). It is shown that, along with the direct electron-impact dissociation of CF[sub 4], the radicals are also produced via the dissociation of the C[sub x]F[sub y] polymer fluorocarbon particles that form in the plasma. A detailed analysis of the kinetics of the radical production and loss in a modulated discharge made it possible to evaluate the contribution of the electron-impact dissociation of CF[sub 4] to the production of radicals and, consequently, to determine the dissociation rate constants k[sub CF[sub 2]] and k[sub CF] . A comparison of the obtained k[sub CF[sub 2]] and k[sub CF] values with the results of calculations by the Monte Carlo method and the literature data on the cross sections for electron-impact dissociation of CF[sub 4] molecules enabled the normalization of these cross sections in the threshold region and the construction of the model cross sections for the electron-impact dissociation of CF[sub 4] into neutral products. The calculated cross sections allow a satisfactory description of the experimental results throughout the entire range of E/N under study. A significant scatter (up to 100%) in the experimental data on k[sub CF[sub 2]] and k[sub CF] at low values of E/N is related to the considerable contribution of the C[sub x]F[sub y] polymer molecules (and, probably, C[sub x]F[sub y][sup +] ions and fluorocarbon grains) to the production of CF[sub 2] and CF radicals both in the plasma volume and on the surface of a fluorocarbon film covering the discharge tube wall.