Analysis and Design of Tracking Control for the RF Matching Box of Plasma System

Based on a good RF power supply, the plasma density control is the most important work for getting a good product success rate. The RF power is transmitted from RF generator to the plasma chamber through a RF matching box. The matching box is used to match the impedance between the transmitter and receiver by tuning a series adjustable capacitor and a parallel one. Unfortunately, only an unsatisfied result is given since the matching is not an easy work for the traditional matching box with an analog controller. In this paper, an auto-tracking and rapidly matching controller will be developed by analyzing the behaviors of reflectance while the capacitances of the matching components vary. Since the reflectance is a complex nonlinear function in terms of the matching capacitances. These is not a linear controller can be design to tune the matching capacitances. Some simulation examples are presented to analyze the variation of magnitude and phase of the reflectance while the matching capacitances are changing. A control strategy is proposed to tune two matching capacitances in the matching box while the impedance of plasma load is varying.