Plasma processing method and plasma processing apparatus

A plasma processing method of generating plasma by an electric discharge of a processing gas between a first electrode and a second electrode which are provided to face each other within an evacuable processing vessel that accommodates therein a substrate to be processed, which is loaded into or unloaded from the processing vessel, and of performing a plasma process on the substrate held on the first electrode under the plasma, the plasma processing method comprising:

• performing a power modulation on a first power having a frequency suitable for plasma generation in a pulse shape such that a first period during which the first power is turned on or set to be a first level and a second period during which the first power is turned off or set to be a second level lower than the first level are alternately repeated at a regular pulse frequency in the plasma process;
• and
• setting a duty ratio in the power modulation of the first power to be an initial value for plasma ignition, and then, reducing the duty ratio from the initial value to a set value for the plasma process gradually or in a step shape during a preset transition time,
• wherein the reducing of the duty ratio in the power modulation of the first power is started at the same time of starting application of the first power to either one of the first electrode and the second electrode, and
• wherein the first power has a frequency of about 13.56 MHz or higher.