Experimental and design information for calculating impedance matching networks for use in rf sputtering and plasma chemistry

Abstract

To calculate impedance matching networks for capacitively coupled rf excited plasmas (as used for sputtering and some type of chemical reactors) it is necessary to know the values of the plasma parameters, i.e. the capacitance and the conductance of the discharge and the variation of these with the operating conditions of the system, i.e. the pressure, the frequency and the input power. The paper presented here gives information on the foregoing and shows how the results can be used to design suitable matching networks. To provide basic information on the glow discharge conditions experiments have been carried out using an rf power supply with one side of the matching network connected via a blocking capacitor to an electrode and the remaining side grounded. This system has been operated under various conditions, i.e. the frequency has been varied between 2 and 14 MHz, the air pressure from 1 × 10 −1 down to 5 × 10 −3 torr and the input power density from 0.5 to 2 W cm −2. The results obtained for 14 MHz are in close agreement with those reported for 13.56 MHz by Logan et al 1. From the values obtained for the plasma parameters different types of matching network (L, π, T> and tuned transformer) have been calculated. The design equations for these networks are presented with calculated and tested examples to demonstrate their application. The procedure used, although common electrical engineering practice, should with the measured data be of value to those undertaking rf system design without experience of matching conditions.