Modeling electronegative plasma discharges

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Abstract
A macroscopic analytic model for a three‐component electronegative plasma has been developed. Assuming the negative ions to be in Boltzmann equilibrium, a positive ion ambipolar diffusion equation is found. The electron density is nearly uniform, allowing a parabolic approximation to the plasma profile to be employed. The resulting equilibrium equations are solved analytically and matched to an electropositive edge plasma. The solutions are compared to a simulation of a parallel‐plane rf driven oxygen plasma for two cases: (1) p=50 mTorr, ne0=2.4×1015 m−3, and (2) 10 mTorr, ne0=1.0×1016 m−3. In the simulation, for the low power case (1), the ratio of negative ion to electron density was found to be α0≊8, while in the higher power case α0≊1.3. Using an electron energy distribution that approximates the simulation distribution by a two‐temperature Maxwellian, the analytic values of α0 are found to be close to, but somewhat larger than, the simulation values. The average electron temperature found self‐cosistently in the model is close to that in the simulation. The results indicate the need for determining a two‐temperature electron distribution self‐consistently within the model.

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