Heating of a dual frequency capacitively coupled plasma via the plasma series resonance

Abstract

The behavior of dual frequency capacitively coupled plasma discharges (2f-CCP) is experimentally studied by Langmuir probe and rf current measurements and is compared with simulations from the literature. The driving frequency ratio, system pressure, high frequency (HF) power and low frequency (LF) power are varied in the experiments. An increase in LF power causes a moderate increase in electron density but a significant decrease in electron temperature. An increase in HF power causes a strong increase in electron density and populates the high energy part of the electron energy distribution function. These dependences can be explained on the basis of a global model. It is shown that the ratios of HF/LF power and driving frequency are the most important parameters. At integer frequency ratios a significant increase in electron density was found, which is explained by the indirect heating at the plasma series resonance. Several design guidelines are derived which address industrial applications and process stability.