Effect of resonance in external radio-frequency circuit on very high frequency plasma discharge

Abstract

A fully electromagnetic plasma model for an asymmetric capacitively coupled plasma discharge is used to understand the interaction between the external radio-frequency (rf) distributed circuit and the plasma. The plasma is excited using a 150 MHz rf source connected to the top electrode, the bottom electrode is connected to a shorted transmission line, and the electrodes are separated from the chamber walls through dielectric rings. Under typical conditions, the electron density peaks in the center of the plasma chamber due to the standing electromagnetic wave and the rf current from the top electrode primarily returns through the bottom electrode. When the electrical length of the bottom transmission line is adjusted such that it presents a large (open-circuit) impedance at the plasma chamber interface, the rf return current shifts from the bottom electrode to the chamber wall. As a consequence, the peak in electron density also moves from the center of the chamber toward its outer periphery.