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P: Fachverband Plasmaphysik

P 6: Low Temperature Plasmas I

P 6.3: Vortrag

Dienstag, 9. März 2010, 14:55–15:10, B 305

The Electrical Asymmetry Effect in geometrically asymmetric capacitively coupled radio frequency discharges — •Edmund Schüngel, Julian Schulze, and Uwe Czarnetzki — Institute for Plasma and Atomic Physics, Ruhr-University Bochum

If the voltage waveform applied to a capacitively coupled radio frequency discharge contains a fundamental frequency and its second harmonic (13.56MHz + 27.12MHz), the discharge symmetry can be adjusted by the phase angle between these two frequencies. Recent results have shown that this Electrical Asymmetry Effect (EAE) provides the opportunity to control the ion energy and the ion flux on a surface separately in a geometrically symmetric discharge. In this work, the EAE is investigated experimentally in a geometrically asymmetric discharge, i.e. the bottom powered electrode surface area is smaller than the grounded (top electrode and side walls) surface area. The geometrical asymmetry is varied by changing the electrode gap in a GEC reference cell. The voltage drops across the sheaths can be manipulated via the EAE. In particular, high voltage drops across the sheath adjacent to grounded surfaces are generated for the first time in such strongly geometrically asymmetric discharges. Consequently, ions hit the grounded chamber walls at high energies. This might allow a more effective wall cleaning by highly energetic ion bombardment also in geometrically asymmetric discharges instead of chemical methods. Measurements in an argon discharge at low pressures are performed, and the opportunities and limitations of the EAE in a geometrically asymmetric discharge are discussed.