The density of atomic oxygen in pulsed microwave excited oxygen plasmas has been measured by means of time-resolved two-photon laser-induced fluorescence. The plasma source is a slot antenna type that is operated at 2.45 GHz. Calibration of the measurements has been performed by the use of a two-photon transition of xenon in order to obtain absolute densities of atomic oxygen in the downstream zone. Besides the influence of pulse frequency on the time-averaged density, we also studied pulsed plasmas at higher pressures, which show a significant delay between the onset of microwave power and the rise of the atomic oxygen density. By changing pulse frequency, an optimum frequency is obtained which leads to a gain in the measured time-averaged atomic oxygen density as compared to cw plasmas. This effect is compared to the properties of deposited films generated in a pulsed oxygen/hexamethyldisiloxane process plasma. The results are discussed in the framework of a volume-averaged model for oxygen plasmas, which takes into account molecular and atomic oxygen, metastable oxygen, and positive and negative oxygen ions.
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Georg et al. (2002) studied this question.
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