Automatic Impedance Matching System for RF Sputtering

A previously described' “L” type matching network used for rf sputtering is shown here as part of Fig. 1. The purpose of the network is to transform the complex impedance of a sputtering system to a purely resistive value of 50 Ω. This makes possible the use of a transmission line with a characteristic impedance of 50 for the conveyance of rf power to the system. The rf power is conveniently monitored by a power meter in the transmission line. Since the power meter is capable of measuring both forward and reflected power, the voltage standing wave ratio (VSWR) on the transmission line can be computed. The VSWR will be unity when the matching network is adjusted so that the transmission line is terminated in its characteristic impedance. Practically, it is difficult to achieve a VSWR of unity (zero reflected power), so the network is adjusted to approach that optimum state as nearly as possible.