Phase-shift effect in capacitively coupled plasmas with two radio frequency or very high frequency sources

Abstract

A two-dimensional fluid model was built to study the argon discharge in a capacitively coupled plasma reactor and the full set of Maxwell equations is included in the model to understand the electromagnetic effect in the capacitive discharge. Two electrical sources are applied to the top and bottom electrodes in our simulations and the phase-shift effect is focused on. We distinguish the difference of the phase-shift effect on the plasma uniformity in the traditional radio frequency discharge and in the very high frequency discharge where the standing wave effect dominates. It is found that in the discharges with frequency 13.56 MHz, the control of phase difference can less the influence of the electrostatic edge effect, and it gets the best radial uniformity of plasma density at the phase difference π. But in the very high frequency discharges, the standing wave effect plays an important role. The standing wave effect can be counteracted at the phase difference 0, and be enhanced at the phase difference π. The standing wave effect and the edge effect are balanced at some phase-shift value between 0 and π, which is determined by discharge parameters.