The effects of surface processes on the plasma parameters in low-pressure multi-frequency capacitive discharges*

Based on Particle-in-cell/Monte Carlo collisions (PIC/MCC) simulations, a systematic investigation of the effects of surface processes on the plasma parameters and control of particle flux-energy distributions at the electrodes is performed in geometrically symmetric capacitively coupled Ar discharges driven by tailored voltage waveforms. The simulations are based on a discharge model in which realistic approaches are implemented for the description of the secondary electron (SE) emission induced by electrons and heavy-particles at the electrodes, as well as for the sputtering of the electrodes by heavy-particles. The driving voltage waveform is composed of multiple consecutive harmonics of the fundamental frequency and is tailored by adjusting the identical phases of the even harmonics. The variation of the energy of heavy-particles at the electrodes by adjusting the phase angle of the driving harmonics affects the surface processes involving these particles, which in turn influences the plasma parameters and the quality of the control of ion properties at the electrodes. For all conditions investigated, electron induced SEs (δ-electrons) induce strong ionization in the α-mode and dominate the ionization dynamics at high voltage amplitudes.