Control of plasma uniformity with dual phase Very High Frequency Capacitively Coupled Plsamas

Very High Frequency Capacitively Coupled Plasmas (VHF CCP) reactors which operate at 50-200 MHz are widely used in material and electronics industry [1]. It has many advantages for material processing. For example, high electron density, low electric potential, controllable dissociation and so on are available. However, standing wave effect takes place in a large scale CCP reactor, because of short wavelength of VHF source. So it is hard to maintain plasma uniformity [2-3]. There are many methods to relieve this non-uniformity. For example, lens-shaped electrode and segmented electrodes were suggested. However, they need a change of electrode structure which increases manufacturing cost. In contrast, dual phase method does not require any modification of the electrode, and it is more economical than the former suggested methods. In this study, we utilize a two-dimensional particle-in-cell (PIC) simulation which is parallelized using graphic processing units (GPUs) [4] for the investigation of phase shift effect on CCP discharge. We applied VHF power sources (50 MHz) to the upper and the lower electrodes of CCP with a phase difference from 90° to 180° between two sources, and observed the variation of plasma properties depending on the phase difference in electrostatic condition. From this simulation, the change of plasma uniformity and ion energy distribution function onto the wafer has been observed with the phase variation. The fundamental physics for the phenomena is to be explained.