Plasma processing apparatus and power supply control method

A plasma processing method comprising:

• providing a plasma processing apparatus comprising:
• a placement table provided in a processing container and serving as a lower electrode and including an electrostatic chuck, the placement table being configured to place a workpiece to be subjected to a plasma processing on the electrostatic chuck;
• a DC power supply connected to the placement table and configured to generate a positive DC voltage and a negative DC voltage to be alternately applied to the placement table;
• and
• a controller configured to control an overall operation of the plasma processing apparatus,
• alternately applying the positive DC voltage and the negative DC voltage to the placement table by the DC power supply in a pulse form;
• acquiring, with the controller, a set voltage value which is a sum of absolute values of the positive DC voltage and the negative DC voltage to be applied to be applied to the placement table;
• determining, by the controller, a voltage of the workpiece placed on the electrostatic chuck of the placement table corresponding to a period during which the negative DC voltage is applied to the placement table;
• calculating, by the controller and based on the determined voltage, a potential difference between the placement table and the workpiece corresponding to the period during which a negative DC voltage is applied to the placement table, the period being a portion of a period during which the positive DC voltage and the negative DC voltage are alternately applied to the placement table;
• determining, by the controller, whether the potential difference between the placement table and the workpiece corresponding to the period during which the negative DC voltage is applied is equal to or larger than a predetermined threshold value, and
• in response to a determination that the potential difference between the placement table and the workpiece is equal to or larger than the predetermined threshold value, controlling the power supply so that the potential difference between the placement table and the workpiece in the period during which the negative DC voltage is applied is reduced to below the threshold value, and wherein the controlling the power supply also includes at least one of:
• changing a duty ratio of the DC power supply applied to the placement table,
• changing a frequency of the DC power supply applied to the placement table, or
• changing a voltage value of the DC power supply applied to the placement table.