Novel Impedance-Matching Method for Plasma Processing at Very High Frequency Band

Abstract

The paper concerns a method of impedance matching between an rf generator and a plasma for material processing at the VHF band. Unlike the conventional methods for the case of low frequency, e.g., 13.56 MHz, in this method, a transmission line and two variable capacitors are adopted and the use of inductors is avoided. The ranges of line length and capacitances are shown graphically and formulated for easy calculation using an electronic calculator. The efficiency of the matcher is derived, including the losses of the network elements. Experiments in an ECR plasma demonstrate that the theoretical derivations are valid within experimental error, that the method is effective up to 190 MHz with the rf-bias voltage independent of network parameters and a factor of 3 greater compared with direct connection, and that VHF-biasing increases ion energy without significant broadening of the ion energy distribution.