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

TL;DR

This study uses particle-in-cell simulations to analyze how different tailored waveforms affect plasma asymmetry, electron and ion energy distributions, and plasma density in capacitive discharges, revealing waveform-dependent control over plasma characteristics.

Contribution

It provides a comparative analysis of sinusoidal, sawtooth, and square waveforms, highlighting their distinct effects on plasma density, asymmetry, and energy distributions in capacitive discharges.

Findings

Square waveform yields highest plasma density.

Sawtooth waveform causes maximum plasma asymmetry.

High-energy electron beams are generated by square and sawtooth waveforms.

Abstract

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.