Simulation of capacitively coupled Ar/O₂ discharges based on global/equivalent circuit model and an extended reaction set

Radio frequency capacitively coupled plasmas (RF CCPs) operated in Ar/O₂ gas mixtures which are widely adopted in microelectronics, display, and photovoltaic industry, are investigated based on an equivalent circuit model coupled with a global model. This study focuses on the effects of singlet metastable molecule ${\mathrm{O}}_2({\mathrm{b}}^1{\Sigma }_{\mathrm{g}}^{+})$, highly excited Herzberg states ${\mathrm{O}}_2({\mathrm{A}}^3{\Sigma }_{\mathrm{u}}^{+},{\mathrm{A}}^3{\Delta }_{\mathrm{u}},{\mathrm{c}}^1{\Sigma }_{\mathrm{u}}^{-})$, and the negative ion ${\mathrm{O}}_2^{-}$, which are usually neglected in simulation studies. Specifically, their impact on particle densities, electronegativity, electron temperature, voltage drop across the sheath, and absorbed power in the discharge is analyzed. The results indicate that ${\mathrm{O}}_2\left({\mathrm{b}}^1{\Sigma }_{\mathrm{g}}^{+}\right)$ and ${\mathrm{O}}_2^{-}$ exhibit relatively high densities in argon–oxygen discharges. While ${\mathrm{O}}_2({\mathrm{A}}^3{\Sigma }_{\mathrm{u}}^{+},{\mathrm{A}}^3{\Delta }_{\mathrm{u}},{\mathrm{c}}^1{\Sigma }_{\mathrm{u}}^{-})$ play a critical role in ${\mathrm{O}}_2\left({\mathrm{b}}^1{\Sigma }_{\mathrm{g}}^{+}\right)$ production, especially at higher pressure. The inclusion of these particles reduces the electronegativity, electron temperature, and key species densities, especially the O⁻ and O* densities. Moreover, the sheath voltage drop, as well as the inductance and resistance of the plasma bulk are enhanced, while the sheath dissipation power and total absorbed power decrease slightly. With the increasing pressure, the influence of these particles on the discharge properties becomes more significant. The study also explores the generation and loss of main neutral species and charged particles within the pressure range of 20 mTorr–100 mTorr (1 Torr = 1.33322×10² Pa), offering insights into essential and non-essential reactions for future low-pressure O₂ and Ar/O₂ CCP discharge modeling.