Plasma asymmetry and electron and ion energy distribution function in capacitive discharges excited by tailored waveforms

Abstract

Using a particle-in-cell simulation technique, we investigate the plasma and ionization asymmetry, higher harmonics generation, and electron and ion energy distribution function (IEDF) in capacitive discharges excited by tailored waveforms. At a base frequency of 13.56 MHz, three different waveforms, namely sinusoidal, sawtooth, and square, are applied for a constant current density amplitude of 50 A m−2 and gas pressure of 5 mTorr. 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 the 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 and high-frequency modulations up to 100 MHz on the instantaneous sheath position. The electron energy distribution function depicts three electron temperature and highly elevated tail-end electrons for the square waveform in comparison to the sinusoidal and sawtooth waveform. The IEDF is bimodal at both the powered and grounded electrodes with a large asymmetry and narrow-type distribution in the case of the sawtooth-like waveform. These results suggest that the choice of waveform is highly critical for achieving maximum asymmetry and plasma density simultaneously in capacitive discharges.