Automatic phase adjusting circuit for a plasma processing apparatus

A plasma processing apparatus wherein outputs of two high frequency power generators for processing of semiconductor wafers are respectively supplied to two plate electrodes in a plasma generation chamber thereby to generate plasma, outputs of said two high frequency power generators being shifted a predetermined value in phase by a phase adjustment circuit,

• said plasma processing apparatus comprises:
• a frequency setting circuit for outputting pulse signals every predetermined interval;
• a phase difference setting circuit;
• first and second processing voltage detection circuits for detecting respectively terminal voltages at the plate electrodes in said plasma generation chamber;
• a first waveform synthesizing circuit having an input from said frequency setting circuit thereby synthesizing/forming a high frequency signal of a predetermined waveform with a frequency f0 corresponding to the input;
• a second waveform synthesizing circuit having an input from said frequency setting circuit thereby synthesizing/forming a high frequency signal of the same waveform as that generated in said first waveform synthesizing circuit and a frequency different by .DELTA.f (.DELTA.f<<f0) from the frequency of said first waveform synthesizing circuit;
• a phase difference detection circuit having inputs of an output from said second waveform synthesizing circuit and detection signals of said first and second processing voltage detection circuits, said phase difference detection circuit outputting a voltage of the frequency .DELTA.f and corresponding to a phase difference of the detection signals of said processing voltage detection circuits;
• a third waveform synthesizing circuit for outputting a high frequency signal with a phase determined by a difference signal between a set value of said phase difference setting circuit and an output of said phase difference detection circuit and the same frequency and the same waveform as those of said first waveform synthesizing circuit, and
• a central processing unit (CPU) for supervising said frequency setting circuit, phase difference setting circuit, first and second processing voltage detection circuits, first through third waveform synthesizing circuits and phase difference detection circuit,
• whereby said phase adjustment circuit determines one output power of said two high frequency power generators in accordance with the output of said first waveform synthesizing circuit and the other output power in accordance with the output of said third waveform synthesizing circuit.