A system and method for processing substrates having an improved matching system. A matching controller (1) is utilized to control multiple matching networks (MNA, MNB, MNC), thus providing improved, more rapid and stable matching. The matching controller (1) can also automatically set up initial matching conditions required during and immediately after plasma initiation, to thereby provide faster and more reliable initial matching, and reduced operator involvement. The system also provides improved instrumentation, for more accurate phase and amplitude detection, and an improved arrangement of power detectors (6A, 6B, 6C). The matching network (MNA, MNB, MNC) also incorporates a circuit for reliable control of tunable elements in a matching network, and a device for protecting tunable elements against damage are also provided.