Surface Kinetics of CFx Radicals and Fluorine Atoms in the Afterglow of High-Density C4F8 Plasmas

Temporal variations of absolute densities of CF, CF2 and atomic fluorine (F) were measured in the afterglow of high-density C4F8 plasmas generated by helicon-wave discharges. Laser-induced fluorescence (LIF) spectroscopy was adopted for CF and CF2 radicals, while vacuum ultraviolet (VUV) absorption spectroscopy was employed for the F atom. CF and F densities gradually decreased for 20–80 ms after the extinction of the rf power, while CF2 density steadily increased during the same period. This slow increase in CF2 density can be explained by surface kinetics of the radicals. In the afterglow of discharges with a high degree of dissociation, the increase in CF2 density is approximately equal to CF density at the beginning of the afterglow. The mechanism for the surface production of CF2 in the afterglow is discussed based on the close relationships between the temporal variations of CF and CF2 densities.