Electron heating and control of ion properties in capacitive discharges driven by customized voltage waveforms

We investigate the electron heating dynamics in capacitive radio frequency plasmas driven by customized voltage waveforms and study the effects of modifying this waveform on the DC self-bias, $\eta $, the ion flux, $\Gamma _{i}$, and the mean ion energy, E$_{i}$, at the electrodes by PIC simulations. The driving voltage waveform is customized by adding N consecutive harmonics (N $\le $ 4) of 13.56 MHz with specific harmonics' amplitudes and phases. In an argon plasma, we find $\eta $ to be generated via the Electrical Asymmetry Effect for N $\ge $ 2. $\eta $ can be controlled by adjusting the harmonics' phases and is enhanced by adding more consecutive harmonics. At 3 Pa, the discharge is operated in the $\alpha $-mode and E$_{i}$ can be controlled by adjusting the phases at constant $\Gamma_{i}$. The ion flux can be increased by adding more harmonics due to the enhanced electron sheath heating. However, we find E$_{i}$ not to remain constant as a function of N at both electrodes due to a change of $\eta $ as a function of N. At 100 Pa and using a high secondary electron emission coefficient of $\gamma =$ 0.4, the discharge is operated in the $\gamma $-mode. Due to this mode transition and the specific ionization dynamics in the $\gamma $-mode, $\Gamma_{i}$ is no longer constant as a function of the harmonics' phases and decreases with increasing N.