Analysis of the DC self-bias voltage in geometrically asymmetric capacitive discharges using global model simulations

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Abstract The DC self-bias voltage in geometrically asymmetric capacitive discharges is investigated as a function of RF power and argon gas pressure using experiments and a modified global-model analysis for a fixed reactor geometry. In the model, the grounded sidewall is treated separately from the grounded electrode, and the appropriate sheath description is selected by comparing the ion mean free path with the sheath width under each discharge condition. The analysis is constrained by measured voltage waveforms, absorbed power, harmonic content, and axial plasma-density profiles. The measured normalized DC self-bias voltage increases with RF power and exhibits a transition in pressure dependence over the investigated pressure range. The model-based analysis indicates that this transition can be interpreted in terms of changes in current partitioning between the powered electrode and grounded surfaces. Differences between the measured DC self-bias voltage and the simulated sheath-voltage ratio are attributed to harmonic distortion in the driving voltage waveform. These results provide an experimentally constrained framework for interpreting pressure-dependent DC self-bias behavior in asymmetric capacitive discharges.

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