METHOD AND DEVICE FOR POLISHING SUBSTRATE, AND METHOD AND DEVICE FOR MEASURNG FILM THICKNESS

PROBLEM TO BE SOLVED: To maintain accuracy in film thickness measurement even in the continuous state of polishing. SOLUTION: A film thickness measuring means 8 is provided for measuring the film thickness of a substrate S while continuing or interrupting polishing, and a control means 11 is provided for controlling polishing conditions on the basis of a film thickness value measured by the film thickness measuring means 8. The film thickness measuring means 8 has a light source for irradiating a film layer with luminous flux; a plurality of light receiving elements for receiving reflected light or transmitted light generated in the film layer, by wavelength; and a host computer 10 for computing a plurality of solutions of film thickness values from signals detected by the light receiving elements. The host computer 10 selects a combination of the solutions with the mutually closest values out of a plurality of solutions of the film thickness values, obtains the average value, corrects the signal according to the dispersion degree of the combination of the solutions with the mutually closest values, obtains again the dispersion degree of the combination of the solutions with the mutually closest values, and sets a value when the dispersion degree becomes a specified value, as a film thickness value.