Plasma processing apparatus and plasma processing method

A plasma processing apparatus configured to process, using plasma generated in a processing chamber inside a vacuum container, a film layer to be processed on a wafer disposed in the processing chamber, the plasma processing apparatus comprising:

• a detector configured to detect, during processing of the wafer, an intensity of a first light of a plurality of wavelengths in a first wavelength range and an intensity of a second light of a plurality of wavelengths in a second wavelength range which includes at least one wavelength different from each of the plurality of wavelengths in the first wavelength range, the first light being obtained by receiving a light which is emitted into the processing chamber from a light source disposed outside the processing chamber and which is reflected by an upper surface of the wafer, and the second light being a light transmitted from the light source without passing through the processing chamber;
• and
• a determination unit configured to determine a remaining film thickness of the film layer by comparing the intensity of the first light in the first wavelength range, that is obtained during the processing and corrected by using a change rate of the intensity of the second light in the second wavelength range, with pattern data which is obtained in advance and indicates a correlation between an intensity of a light and a remaining film thickness of the film layer where a wavelength is used as a parameter.