US Patent 11552612 Impedance adjustment device and impedance adjustment method

A high frequency power supply alternately outputs a first AC voltage and a second AC voltage to a plasma generator. The amplitudes of the first AC voltage and the second AC voltage are different from each other. An impedance adjustment device is disposed in midway of the transmission line of the first AC voltage and the second AC voltage. When the AC voltage output from the high frequency power supply is switched to a first AC voltage, a microcomputer changes the capacitance of a variable capacitor circuit to a first target value. When the AC voltage output from the high frequency power supply is switched to a second AC voltage, the microcomputer changes the capacitance of the variable capacitor circuit to a second target value.