Study of rotational temperature and loss mechanisms of fluorocarbon radicals in an inductively coupled plasma reactor

For the first time, the time-resolved rotational temperature of CF ₂ was explored. The time-resolved rotational temperature of CF ₂ was extracted from time evolution of CF₂ absorbances, which were measured by wavelength modulated infrared diode laser absorption spectroscopy in an inductively coupled plasma reactor. Under the experimental conditions, the rotational temperature reaches the steady state value of 401 ± 38K with the first order decay time constant of 3.3 milliseconds upon plasma ignition. In the afterglow, the rotational temperature decays to 297 ± 18K with the first order decay time constant ranging from 7–14 milliseconds. The chamber wall temperature is the significant factor for the rotational temperature. At higher pressures, the rotational temperature decreases with increasing pressure. It decreases as the percentage of Ar in the feed gas increases. The non-uniformity in the rotational temperatures was found to be the possible reason for the initial increase in the absorbance of CF ₂ in the afterglow.; By applying the time-resolved rotational temperatures, the time evolution of [CF₂] was calculated. [CF₂] follows the first order decay in the rf-on periods and electron impact processes are the main loss process. In the afterglow, [CF₂] decays according to a combination of a 2nd order loss and a 1st order loss. The rate coefficient of the 2nd order loss reaction 2CF ₂ → C₂F ₄ at 298K is determined. The sticking coefficient of CF₂ in the afterglow is smaller than that in steady state plasmas.; [CF] follows the first order decay in the afterglow. The initial decay rates were investigated with the addition of H₂ and O₂. The recombination reaction between CF and F was found to be the gas phase loss process for CF radicals.; Actinometric optical emission spectroscopy was used for determining time-resolved behaviors of F atoms and H atoms. First order decays were found for both atoms in the rf-on periods and in the afterglow and the decay time constant was in the range of a few milliseconds.