Uniformity control in multi-electrode capacitive RF plasmas*

Multi-electrode capacitive RF plasmas are studied using 2D electrostatic Particle-In-Cell/Monte Carlo collision simulations to enhance their performance in industrial applications, especially to improve the plasma uniformity in e.g. etching processes. In contrast to typical CCP systems, where two parallel electrodes are used with one being powered and the other one being grounded, an additional individually driven ring electrode is introduced at different locations within the reactor, which induces drastic changes of the plasma generation and distribution. Such multi-electrode CCPs are studied starting with an analytical model to understand the fundamental mechanisms of DC self-bias generation at the two powered electrodes, and progressing to kinetic simulations to capture the spatio-temporal characteristics of electron power absorption. The area of the newly introduced powered electrode as well as the amplitude and phase of the voltage applied to it are varied systematically to improve plasma characteristics in applications. Significant improvement of the plasma density and uniformity is achieved. Such multi-electrode CCPs can be easily extended by further increasing the number of powered electrodes and are expected to provide improved flexibility in the control of plasma properties in industrial applications.