Electron power absorption in low pressure capacitively coupled electronegative oxygen radio frequency plasmas

TL;DR

This study investigates electron power absorption in low pressure electronegative oxygen CCPs, revealing dominance of Ohmic heating over stochastic mechanisms and the influence of electronegativity on energy transfer.

Contribution

It provides a detailed spatio-temporal analysis using Particle-In-Cell simulations, challenging conventional models by highlighting Ohmic absorption's prominence.

Findings

Ohmic power absorption dominates at low pressures.

Electronegativity attenuates ambipolar power absorption.

Electron temperature shows high temporal symmetry within RF cycles.

Abstract

A thorough understanding of the energy transfer mechanism from the electric field to electrons is of utmost importance for optimization and control of different plasma sources and processes. This mechanism, called electron power absorption, involves complex electron dynamics in electronegative capacitively coupled plasmas (CCPs) at low pressures, that are still not fully understood. Therefore, we present a spatio-temporally resolved analysis of electron power absorption in low pressure oxygen CCPs based on the momentum balance equation derived from the Boltzmann equation. Data are obtained from 1d3v Particle-In-Cell / Monte Carlo Collision simulations. In contrast to conventional theoretical models, which predict 'stochastic/collisionless heating' to be important at low pressure, we observe the dominance of Ohmic power absorption. In addition, there is an attenuation of ambipolar power absorption at low pressures due to the strong electronegativity, and the presence of electropositive edge regions in the discharge, which cause a high degree of temporal symmetry of the electron temperature within the RF period.