THE DESIGN OF ELECTRODE FOR IMPROVING THE PLAMSA UNIFORMITY IN LARGE AREA CAPACITIVE DISCHARGE AT VERY HIGH FREQUENCY

Abstract

Capacitively coupled plasma reactors have been widely used for thin film process in the fabrication of silicon-based IC chips and flat display panel as well as photovoltaic solar cells. Capacitive discharges driven with the radio frequency higher than the usual 13.56MHz have attracted much attention in plasma etching and deposition processes, due to higher etch/deposition rates from high plasma density. However, there are problems in utilizing the relatively smaller wavelength frequency than the diameter of a chamber. The standing surface wave effect is strongly related to high frequencies in large chambers where the reactor size is larger than about a tenth of the wavelength in vacuum. In large-area high-frequency capacitive discharge, the plasma non-uniformity caused by standing surface wave effects can be improved by modify the electrode shape. In this work, for the reduction of standing surface wave effect, we propose the two concentric circular shaped top electrodes. The improvement of standing surface wave effect was investigated using FDTD electromagnetic field simulator. The simulated results are in good agreement with recent experiments. In an industrial process chamber, electromagnetic effects (e.g. standing surface wave and surface wave skin effects as well as the electrostatic edge effect) and the electrostatic effect were exist simultaneously. However, this study was only focused on suppressing the electromagnetic effect such as standing-wave effects. Because, the driving frequency and chamber size are increased, the main cause of uniformity issue could not be resolved by balancing the electrostatic effect (the skin effect, maximal near the radial reactor edge) and electromagnetic effect (the standing-wave effect, maximal at the reactor center). The proposed electrode shape consisting of multiple concentric circular shaped elements can improve the plasma uniformity. We expect the same effect in rectangular shape chamber for display panel and photovoltaic solar cell manufacturing system.