Slope and amplitude asymmetry effects on low frequency capacitively coupled carbon tetrafluoride plasmas

Bruneau, B. and Korolov, Ihor and Lafleur, T. and Gans, T. and O’Connell, D. and Greb, A. and Derzsi, Aranka and Donkó, Zoltán and Brandt, S. and Schüngel, Edmund and Schulze, Julian and Johnson, E. and Booth, J-P. (2016) Slope and amplitude asymmetry effects on low frequency capacitively coupled carbon tetrafluoride plasmas. Journal of Applied Physics, 119. p. 163301. ISSN 0021-8979 (print), 1089-7550 (online)

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Abstract

We report investigations of capacitively coupled carbon tetrafluoride (CF4) plasmas excited with tailored voltage waveforms containing up to five harmonics of a base frequency of 5.5 MHz. The impact of both the slope asymmetry, and the amplitude asymmetry, of these waveforms on the discharge is examined by combining experiments with particle-in-cell simulations. For all conditions studied herein, the discharge is shown to operate in the drift-ambipolar mode, where a comparatively large electric field in the plasma bulk (outside the sheaths) is the main mechanism for electron power absorption leading to ionization. We show that both types of waveform asym- metries strongly influence the ion energy at the electrodes, with the particularity of having the high- est ion flux on the electrode where the lowest ion energy is observed. Even at the comparatively high pressure (600 mTorr) and low fundamental frequency of 5.5 MHz used here, tailoring the volt- age waveforms is shown to efficiently create an asymmetry of both the ion energy and the ion flux in geometrically symmetric reactors.

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