Plasma treatment apparatus and film deposition method

A plasma processing apparatus for alternately performing a first plasma processing step using first and second processing gases and a second plasma processing step using third and fourth processing gases. The apparatus includes: a processing container that has a dielectric window in a ceiling and removably accommodates a workpiece; an exhaust unit that evacuates the processing container; a processing gas supply unit that supplies the first, second, third, and fourth processing gases into the processing container; a first gas introduction unit including a top plate gas injection port, a dielectric window gas flow path, and a first external gas flow path; a second gas introduction unit including a sidewall gas injection port, a sidewall gas flow path, and a second external gas flow path; an electromagnetic wave supply unit that supplies electromagnetic waves into the plasma generating space; a bypass exhaust path; and an opening/closing valve.