The role of the singlet metastables in capacitively coupled oxygen discharges

Abstract

We use the one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 to study the evolution of the charged particle density profiles, electron heating mechanism, effective electron temperature, and the electron energy probability function (EEPF) in a capacitively coupled oxygen discharge with pressure in the pressure range of 10–500 mTorr. We find that at higher pressure (50–500 mTorr) the electron heating occurs mainly in the sheath region, and detachment by the metastable singlet molecule O2(a1Δg) has a significant influence on the electron heating process and the EEPF [1,2]. At a low pressure (10 mTorr), Ohmic heating in the bulk plasma (the electronegative core) dominates, and detachment by O2(a1Δg) has only a small influence on the heating process. Thus at low pressure, the EEPF is convex and as the pressure is increased the number of low energy electrons increases and the number of higher energy electrons (>10 eV) decreases, and the EEPF develops a concave shape or becomes bi-Maxwellian [2]. Furthermore, we explore the effects of including the singlet metastable molecule O2(b1∑g) and energy-dependent secondary electron emission yields at the electrodes in a capacitively coupled single frequency rf driven oxygen discharge. We find that including the metastable O2(b1∑g) further decreases the Ohmic heating in the bulk region at higher pressures. Moreover, we find that including an energy-dependent secondary electron emission yield for O2+-ions has a significant influence on the discharge properties while the energy dependent secondary electron emission coefficient due to O+-ions and the neutrals has only marginal influence on the discharge properties.