The Electrical Asymmetry Effect in multi-frequency capacitively coupled radio frequency discharges

In capacitively coupled radio frequency discharges the Electrical Asymmetry Effect (EAE) provides the opportunity to generate a DC self bias $\eta $ electrically. In dual-frequency (df) discharges operated at two consecutive harmonics with adjustable phase shift $\theta $ between the driving voltages $\eta $ is generated as a function of $\theta $. The ion energy can be controlled separately from the ion flux at the electrodes by tuning $\theta $ in df discharges. Here, the EAE in geom. symmetric argon discharges driven at multiple consecutive harmonics is investigated by a PIC simulation: Compared to df discharges a significantly stronger self bias can be generated electrically. The mean ion energy at the electrodes can be controlled separately from the ion flux over a broader range. An analytical model demonstrates that df discharges represent only one particular - with respect to ion energy control less effective - scenario in the frame of a more abstract understanding of the EAE. A recipe how to customize the applied voltage waveform to generate the strongest possible DC self bias and to obtain maximum control of the ion energy will be presented.