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1. A plasma processing apparatus comprising:
a vacuum evacuable processing chamber; a processing gas supply unit for supplying a processing gas into the processing chamber; a first radio frequency power supply unit for supplying a first radio frequency power to a first electrode or to an antenna provided inside or near the processing chamber to generate a plasma by exciting the processing gas in the processing chamber; and a control unit configured to control the first radio frequency power supply unit such that an amplitude of the first radio frequency power is modulated at a predetermined interval and a frequency of the first radio frequency power is modulated in substantially synchronously with the amplitude modulation of the first radio frequency power, wherein the control unit is configured to divide one cycle into a first, a second, a third and a fourth state, and control the amplitude of the first radio frequency power to maintain a first amplitude set value in the first state, change from the first amplitude set value to a second amplitude set value higher than the first amplitude set value in the second state, maintain the second amplitude set value in the third state, and change from the second amplitude set value to the first amplitude set value in the fourth state, wherein the control unit is configured to control the frequency of the first radio frequency power to maintain a first frequency set value in the first state, change from the first frequency set value to a second frequency set value lower than the first frequency set value in the second state, maintain the second frequency set value in the third state, and change from the second frequency set value to the first frequency set value in the fourth state, wherein the first radio frequency power supply unit includes: a first radio frequency power supply for generating the first radio frequency power; and a matching unit having a matching circuit equipped with variable reactance elements electrically connected between an output terminal of the first radio frequency power supply and the first electrode; a sensor equipped with the matching circuit, for measuring a load impedance; and a controller for varying the variable reactance elements so as to match the load impedance to a reference impedance in response to an output signal from the sensor, wherein the control unit is configured to control the matching unit to perform impedance matching in either the first state or the third state, wherein the control unit is configured to feedback the output signal from the sensor to the controller only for a predetermined period set during the first state or the third state, wherein the first radio frequency power supply unit further includes a reflection wave measuring unit for measuring a power of a reflection wave transmitted on a transmission line from the first electrode to the first radio frequency power supply, wherein the control unit is configured to correct the first amplitude set value based on the reflection wave power measured by the reflection wave measuring unit during the first state to determine a corrected first amplitude set value so that the corrected first amplitude set value is used for the first state of a subsequent cycle, and wherein the control unit is configured to correct the second amplitude set value based on the reflection wave power measured by the reflection wave measuring unit during the third state to determine a corrected second amplitude set value so the corrected second amplitude set value is used for the third state of a subsequent cycle.
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