An Improved Global Model for Electronegative Discharge and Ignition Conditions for Peripheral Plasma Connected to a Capacitive Discharge

An improved volume-averaged global model is developed for a cylindrical electronegative (EN) plasma that is applicable over a wide range of electron densities, electronegativities, and pressures. It is applied to steady and pulsed-power oxygen discharges. The model incorporates effective volume and surface loss factors for positive ions, negative ions, and electrons combining three EN discharge regimes: a two-region regime with a parabolic EN core surrounded by an electropositive edge, a one-region parabolic EN plasma, and a one-region flat-topped EN plasma, spanning the plasma parameters and gas pressures of interest for low pressure. Pressure-dependent effective volume and surface loss factors for the neutral species, and an updated set of reaction rate coefficients for oxygen based on the latest results were incorporated. The model solutions yield important processing quantities as the neutral/ion flux ratio ΓO/Γi, with the discharge aspect ratio, pulsed-power period, and duty ratio as parameters. For steady discharges, increasing 2R/L from 1 to 6 leads to a factor of 0.45 reduction in ΓO/Γi. For pulsed discharges with a fixed duty ratio, ΓO/Γi is found to have a minimum with respect to pulse period. A 25% duty ratio pulse reduces ΓO/Γi by a factor of 0.75 compared to the steady-state case.