Plasma processing method and plasma processing apparatus

A plasma processing method performed using a plasma processing apparatus, wherein the plasma processing apparatus includes:

• a chamber including a side wall having an inner wall surface;
• a substrate support including a lower electrode provided in the chamber;
• an upper electrode provided above the substrate support;
• a radio frequency power source for generating plasma in the chamber;
• and
• a direct-current power source device electrically connected to the upper electrode, the direct-current power source device being configured to periodically generate a pulsed negative direct-current voltage,
• the plasma processing method comprising:
• generating plasma from a film formation gas in the chamber by supplying radio frequency power from the radio frequency power source;
• and
• forming a protective film on the inner wall surface by depositing a chemical species from the plasma on the inner wall surface,
• wherein the pulsed negative direct-current voltage is periodically applied from the direct-current power source device to the upper electrode in said forming a protective film.