Grounded radio-frequency electrodes in contact with high density plasmas

Abstract

An analytical model is developed of an asymmetric electrode system immersed in a plasma, consisting of two dc-grounded electrodes, where the smaller one is biased at 13.56MHz. The model is compared with a set of experiments performed in a high density low pressure plasma source (an electron cyclotron resonance source) where a second electrode is immersed into the plasma and powered by radio frequency. Excellent agreement is obtained between the analytical model and the experimental results. It is found that the time average plasma potential and the direct current (dc) flowing in the system during steady state are strongly dependent on both the rf voltage (or power) and the area ratio between the larger and smaller electrodes. For area ratios larger than 80, the dc current is large and the plasma potential is constant with respect to the applied rf voltage. For area ratios smaller than 80 but larger than unity, the plasma potential increases linearly with the applied rf voltage, and the dc current is reduced compared to the large area ratio case.