Patent ID: 7026173

Claim:
A method for detecting an end point used in processing a to-be-processed layer using a mask layer formed on the to-be-processed layer, said method comprising the steps of: irradiating the mask layer and the to-be-processed layer with light to measure interference light formed of reflected lights from the mask layer and reflected lights from the to-be-processed layer; removing an interference component brought by the mask layer from the waveform of the measured interference light to calculate the waveform of the interference light brought by the to-be-produced layer; and determining the thickness of the remaining to-be-processed layer on the basis of the calculated waveform of the interference light and comparing the determined thickness of the remaining to-be-processed layer to a desired thickness thereof, thereby detecting the end point of processing on the to-be-processed layer, wherein the step of calculating the waveform of the interference light brought by the to-be-processed layer comprises the step of determining the ratio of the intensity of the measured interference light for at least one kind of specific wavelength to the sum of the intensities of the measured interference light for at least ten kinds of wavelengths within a predetermined wavelength range to remove the interference component brought by the mask layer from the measured interference light.