Patent ID: 8747608

Claim:
A plasma processing apparatus for etching a film on a surface of a sample in a vacuum chamber by using plasma generated in the vacuum chamber, comprising: a detector which detects interference light from the surface of the sample in the vacuum chamber, and a decision unit which (a) decides a thickness of the film using interference light data obtained from an output of the detector at a plurality of points of time with a predetermined time interval during the etching of the film, which (b) compares interference light data obtained by time differentiating the output from the detector at a given time within the plurality of points of time with a plurality of data patterns corresponding to two or more thicknesses of the film, and which (c) decides that a thickness of the film reaches a thickness corresponding to the data pattern having a minimum difference from the interference light data, the plurality of data patterns corresponding to the interference light data of multiple wavelengths obtained, before the etching of the film, by differentiating the output from the detector in processing of another sample, wherein when a difference between an output value of the detector indicative of the interference light of one wavelength at the given time point and at a previous point of time just before the given time point within the plurality of points of time is larger than a predetermined value, the interference light data from the output value of the detector at the given time point is corrected by being multiplied by a coefficient indicative of a ratio of an output value of a first detector at the given time point with respect to an output value of the first detector at the previous point of time so as to eliminate the difference between the output value of the detector at the given time point and the previous time point.