On Electron Heating in Capacitively Coupled Oxygen Discharges

Abstract

We apply the one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 to explore the evolution of the charged particle density profiles, electron heating mechanism, the electron energy probability function (EEPF), and the ion energy distribution in a single frequency capacitively coupled oxygen discharge, with driving frequency in the range 12–100 MHz. Furthermore, we explore the influence of the quenching coefficient for the singlet metastable $\mathrm{O}_{2}(\mathrm{a}^{1}\Delta_{\mathrm{g}})$ on the electrode surface. At a low driving frequency and low pressure (5 and 10 mTorr), a combination of stochastic ( $\alpha$ -mode) and drift ambipolar (DA) heating in the bulk plasma (the electronegative core) is observed and the DA-mode dominates the time averaged electron heating [1]. As the driving frequency or pressure are increased, the heating mode transitions into a pure a-mode, where electron heating in the sheath region dominates. At low pressure (5 and 10 mTorr), this transition coincides with a sharp decrease in electronegativity [1]. At low pressure and low driving frequency, the EEPF is concave [2]. As the driving frequency is increased, the number of low energy electrons increases and the relative number of higher energy electrons (> 10 e V) increases. The surface quenching coefficient has a significant influence on the density of the singlet metastable $\mathrm{O}_{2}(\mathrm{a}^{1}\Delta_{\mathrm{g}})$ and thus the discharge electronegativity and electron heating mechanisms.