Measurement and analysis of radio frequency glow discharge electrical impedance and network power loss

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Abstract
Impedance measurement of rf glow discharges is a convenient diagnostic tool that can be used to estimate specific discharge properties based on a simple electrical analog model. Accurate measurements require minimization and characterization of stray impedance. In this study, the stray impedance is minimized by using a triaxial power feedthrough and electrode shield configuration. The remaining stray impedance is characterized using a two-port circuit model to represent the impedance between the voltage and current probes and the electrode. The two-port parameters are determined by unterminating [R. F. Bauer and P. Penfield, Jr., IEEE Transactions on Microwave Theory and Techniques MTT-22, 282 (1974)] the network, which involves measuring the impedance of the reactor system with three or more known impedances inserted between the electrodes. Based on voltage and current measurement, the discharge impedance can then be determined during discharge operation. Impedance measurements and property estimations are made for Ar, CF4, and SF6 discharges. The actual power dissipated in the discharge is found to be as low as 10% of the power into the matching network for some Ar and CF4 discharges.

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