Plasma processing method and plasma processing apparatus

A plasma processing method for etching a wafer located in a processing chamber using a plasma generated therein, the plasma processing method comprising:

• a first step of irradiating light from a light source onto a surface of the wafer;
• a second step of receiving light reflected from the surface of the wafer at a plurality of predetermined times during the processing of the wafer;
• a third step of performing signal processing on data indicating amounts of the light with a plurality of wavelengths, the data indicating of the amount of the light including vibration components in amplitudes vibrating in a wavelength direction of the plurality of wavelengths corresponding to an increase or a decrease of wavelengths or wavenumbers with a plurality of maximum values or minimum values, and the signal processing including a step of removing the vibration components vibrating in the wavelength direction in a range of frequencies of vibration that are larger than a predetermined value, and the signal processing includes a step of detecting a lower envelope or an upper envelope of the vibration components in the data indicating the amount of the light;
• a fourth step of determining an amount of etching for at least one of the predetermined times during the processing of the wafer by using a result of the signal processing in the third step;
• and
• a fifth step of determining an end point of the processing of the wafer based on the result of the determining of the amount of etching in the forth step and stopping or changing a condition for the processing of the wafer.