Kinetics of the reactions involving CF2 and CF in a pure tetrafluoromethane plasma: II. Production and loss of CF2 and CF in the processes of fluorocarbon polymerization

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Mechanisms for the production and loss of CF2 and CF radicals in a glow discharge in pure CF4 are investigated by the time-resolved laser-induced fluorescence method. The fluorocarbon polymerization processes are shown to contribute significantly to the production of radicals both in the plasma volume and on the surface of the discharge tube. The effective frequencies of both the volume and surface processes of radical production and loss are determined. An analysis of these frequencies allowed us to study the polymerization mechanism in a CF4 plasma at a high relative concentration of F atoms and low ion energy. It is shown that, at elevated pressures, when the density of CxFy polymer particles in the plasma volume becomes comparable with the density of simple fluorocarbon radicals, the electron-impact dissociation of these particles is the main channel for the production of CF2 and CF radicals. Another source of CF2 and CF radicals is related to the reactions of CnF2m+1 unsaturated fluorocarbon particles both in the plasma volume and on the surface of a fluorocarbon film arising on the discharge tube wall. The CxFy fluorocarbon polymer particles form both in the discharge volume and on the fluorocarbon filmsurface also in the course of the film destruction. At lowered pressures, the main channel for the production of CF2 and CF is the direct electron-impact dissociation of CF4 molecules, whereas the loss of these radicals at the tube wall is the main loss channel. The probabilities of the heterogeneous losses of CF2 and CF radicals on the heavily fluorinated surface of the fluorocarbon film at low ion energies are determined. Under these conditions, the surface recombination of the Fch chemisorbed fluorine atoms and CF x ph physisorbed radicals with the production of an activated complex is shown to be the most probable mechanism for the heterogeneous losses of CF2 and CF. The approximate activation energies for the production of Fch · CF 2 ph and Fch · CFph surface complexes are found to be 750±70 K and 1030±100 K, respectively.