The role of the metastable O2(b1Σg+) and energy-dependent secondary electron emission yields in capacitively coupled oxygen discharges

The effects of including the singlet metastable molecule O-2(b(1)Sigma(+)(g)) in the discharge model of a capacitively coupled rf driven oxygen discharge are explored. We furthermore examine the addition of energy-dependent secondary electron emission yields from the electrodes to the discharge model. The one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 is used for this purpose, with the oxygen discharge model considering the species O-2(X-3 Sigma(-)(g)), O-2(a(1)Delta(g)), O-2(b(1)Sigma(+)(g)), O(P-3), O(D-1), O-2(+), O+, O-, and electrons. The effects on particle density profiles, the electron heating rate profile, the electron energy probability function and the sheath width are explored including and excluding the metastable oxygen molecules and secondary electron emission. Earlier we have demonstrated that adding the metastable O-2(a(1)Delta(g)) to the discharge model changes the electron heating from having contributions from both bulk and sheath heating to being dominated by sheath heating for pressures above 50 mTorr. We find that including the metastable O-2(b(1)Sigma(+)(g)) further decreases the ohmic heating and the effective electron temperature in the bulk region. The effective electron temperature in the electronegative core is found to be less than 1 eV in the pressure range 50-200 mTorr which agrees with recent experimental findings. Furthermore, we find that including an energy-dependent secondary electron emission yield for O-2(+)-ions has a significant influence on the discharge properties, including decreased sheath width.