Patent ID: 7915563
Filing Date: 2011-03-29
Classification: H05H

Abstract:
1. A plasma processing system comprising a high frequency power source, a plasma processing unit for processing a workpiece by plasma generation using high frequency power from the high frequency power source, a voltage/current signal detection circuit for detecting an AC voltage signal and an AC current signal applied to the plasma processing unit signal and an AC current signal, and an arc detector for detecting generation of an arc at the plasma processing unit, the plasma protecting system comprising: a phase difference calculation circuit that calculates a phase difference between the AC voltage signal and the AC current signal; a voltage effective value calculation circuit that calculates a voltage root-mean-square value of the AC voltage signal; a current effective value calculation circuit that calculates a current root-mean-square value of the AC current signal; a FFT processing unit that calculates a frequency spectrum of at least one of the AC voltage signal and the AC current signal; and an arc analysis unit connected to the phase difference calculation circuit, the voltage effective value calculation circuit, the current effective value calculation circuit, and the FFT processing unit for receiving the calculated phase difference, the calculated voltage root-mean-square value, the calculated current root-mean-square value and the calculated frequency spectrum, respectively; wherein the arc analysis unit determines generation of an arc in the plasma processing unit when at least one of the following conditions is met; (a) an output level of a predetermined frequency component contained in the frequency spectrum of the AC voltage signal calculated by the FET processing unit is not lower than a predetermined value, (b) an output level of a predetermined frequency component contained in the frequency spectrum of the AC current signal calculated by the FET processing unit is not lower than a predetermined value, (c) a fluctuation rate of the voltage root-mean-square value of the AC voltage signal calculated by the voltage effective value calculation circuit is not higher than a predetermined value, (d) a fluctuation rate of the current root-mean-square value of the AC current signal calculated by the current effective value calculation circuit is not lower than a predetermined value, and (e) a fluctuation rate of the phase difference calculated by the phase difference calculation circuit is outside of a predetermined range.