Unveiling the role of dielectric trap states on capacitively coupled radio-frequency plasma discharge: dynamic charging behaviors

TL;DR

This paper investigates how dielectric trap states influence capacitively coupled RF plasma discharges, revealing their impact on sheath potential, plasma stability, and asymmetry through combined theoretical modeling and simulations.

Contribution

It introduces a comprehensive SEE model considering surface charging and trap states, advancing understanding of their role in plasma behavior and discharge asymmetry.

Findings

Trap states affect sheath potential and plasma density.

Increased charge trapping shifts ionization towards the sheath.

Trap states enable asymmetric discharges in symmetric setups.

Abstract

The influence of charge trap states in the dielectric boundary material on capacitively coupled radio frequency plasma discharge is investigated with theory and Particle in cell/Monte Carlo Collision simulation. It is found that the trap states of the wall material manipulated discharge properties mainly through the varying ion induced secondary electron emission (SEE) coefficient in response to dynamic surface charges accumulated within solid boundary. A comprehensive SEE model considering surface charging is established first, which incorporates the valence band electron distribution, electron trap density, and charge trapping through Auger neutralization and de-excitation. Theoretical analysis is carried out to reveal the effects of trap states on sheath solution, stability, plasma density and temperature, particle and power balance, etc. The theoretical work is supported by simulation results, showing the reduction of the mean radio frequency sheath potential as charging-dependent emission coefficient increases. As the gas pressure increases, a shift of the maximum ionization rate from the bulk plasma center to the plasma-sheath interface is observed, which is also influenced by the trap states of the electrode material where the shift happens at a lower pressure with traps considered. In addition, charge traps are proved helpful for creating asymmetric plasma discharges with geometrically symmetric structures, such effect is more pronounced in {\gamma} mode discharges.