Plasma processor and processing method

Plasma processor including: reaction chamber having a base for placing a wafer; a source radio-frequency power supply outputting high frequency radio-frequency power into the reaction chamber to ignite and maintain plasma; a first bias radio-frequency power supply and a second bias radio-frequency power supply, the first bias radio-frequency power supply outputting a first radio-frequency signal with first frequency, the second bias radio-frequency power supply outputting a second radio-frequency signal with second frequency higher than the first frequency, the first radio-frequency signal and the second radio-frequency signal being superimposed to form a periodical first compound signal that is applied to the base; and a controller configured for tuning at least one of amplitude, frequency, average voltage or phase of the first radio-frequency signal and of the second radio-frequency signal, such that the first compound signal experiences three consecutive stages in each cycle: falling stage, flat stage, and rising stage.