  Using particle-in-cell simulation technique, we investigate the plasma and
ionization asymmetry, electron and ion energy distribution function in
capacitive discharges excited by tailored waveforms. At a base frequency of
13.56 MHz, three different waveforms namely, sinusoidal, saw-tooth, and square
are applied for a constant current density of 50 A/m2 and 5 mTorr argon gas
pressure. The simulation results show that the square waveform produces the
highest plasma density in the discharge, whereas maximum asymmetry is observed
for plasma excited by sawtooth like waveform. Both square and sawtooth
waveforms generate multiple beams of high-energy electrons from near to the
expanding phase of the sheath edge followed by the high-frequency modulations
up to 100 MHz on the instantaneous sheath position. The electron energy
distribution function depicts 3 electron temperature and highly elevated
tail-end electrons for the square waveform in comparison to the sinusoidal and
sawtooth waveform. The ion energy distribution function is bimodal at both
powered and grounded electrodes with a large asymmetry and narrow type
distribution in the case of sawtooth like waveform. These results suggest that
the choice of the waveform is highly critical for achieving maximum asymmetry
and plasma density simultaneously in the discharge.
