Kinetics of fluorine atoms in high-density carbon-tetrafluoride plasmas

Reaction processes of fluorine (F) atoms in high-density carbon-tetrafluoride (CF4) plasmas were investigated using vacuum ultraviolet absorption spectroscopy. A scaling law n(F)(proportional to)(n(e)n(CF4))(0.5-0.7) was found experimentally, where n(F) is the F atom density and n(e) and n(CF4) stand for the electron and parent gas (CF4) densities, respectively. The lifetime measurement in the afterglow showed that the decay curve of the F atom density was composed of two components: a rapid decay in the initial afterglow and an exponential decrease in the late afterglow. The decay time constant in the initial afterglow tau(1) satisfied the scaling law tau(1) proportional to(n(e)n(CF4))(-(0.3-0.4)) which is a consistent relationship with the scaling law for the F atom density. The two scaling laws and the lifetimes of CFx radicals suggest that the major loss process of F atoms in the initial afterglow is the reaction with CFx radicals (probably, x = 3) on the wall surface. The loss process in the late afterglow was simple diffusion to the wall surface. The surface loss probability of F atoms on the chamber wall was evaluated from the decay time constant in the late afterglow, and was on the order of 10(-3). (C) 1997 American Institute of Physics.