Dynamic actinometric optical emission spectroscopy for the elucidation of plasma processes in the production of fluorinated amorphous hydrogenated carbon films from glow discharges

A dynamic form of actinometric optical emission spectroscopy in which the flow of one of the feed gases to a glow discharge deposition system is cut and the relative concentrations of species of interest in the plasma monitored as a function of time is described. The method is applied to film-depositing discharges fed with the mixtures of C6H6-SF6 and C2H2-SF6, the actinometers Ar and He also being present in small proportions. Monitoring of the temporal trends in the relative concentrations of the species CF2, F, H and CH revealed the importance of gas-phase and plasma-polymer surface processes in the production of these species. For plasmas containing SF6, the species CF2 was found to be produced mainly by the action of the discharge on material previously deposited on the inner walls of the chamber. An SF6 plasma produced gas-phase CF2 species, possibly by the release of this species from the polymer surface by plasma electrons or by the impact of F atoms on surface CHF2 groups, liberating both CF2 and HF. The species F, CH and H were also found to be produced, at least in part, by plasma-polymer surface interactions. Separate experiments revealed that the species CF2, F, H and CH can be produced even by the action of Ar or He discharges on previously deposited a-C:H,F films. Thus both gas-phase and plasma-polymer surface reactions play important roles in the plasma-enhanced chemical vapor deposition of these films. The dynamic actinometric method is both simple to implement and widely applicable to the elucidation of the deposition and ablation processes occurring in glow discharges.