The pressure dependence of the discharge properties in a capacitively coupled oxygen discharge

We use 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, 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. 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.