Abstract: A method includes: determining height Z1 of a focus by an optical microscope having autofocus function which uses irradiation light of wavelength ?0 to adjust the focus; determining a wavelength ?1 of irradiation light used for obtaining observation image of second thin film; obtaining observation image of second thin film by using irradiation light of the wavelength ?1, while altering heights of the focus with the Z1 as reference point; calculating standard deviation of reflected-light intensity distribution within the observation image, obtaining height Z2 of the focus corresponding to a peak position where standard deviation is greatest, and calculating a difference ?Z between Z1 and Z2; correcting the autofocus function with ?Z as a correction value; and using the corrected autofocus function to adjust the focus, obtaining the observation image of the second thin film, and calculating the film thickness distribution from the reflected-light intensity distribution within the observation image.

Abstract: A method includes: determining height Z1 of a focus by an optical microscope having autofocus function which uses irradiation light of wavelength ?0 to adjust the focus; determining a wavelength ?1 of irradiation light used for obtaining observation image of second thin film; obtaining observation image of second thin film by using irradiation light of the wavelength ?1, while altering heights of the focus with the Z1 as reference point; calculating standard deviation of reflected-light intensity distribution within the observation image, obtaining height Z2 of the focus corresponding to a peak position where standard deviation is greatest, and calculating a difference ?Z between Z1 and Z2; correcting the autofocus function with ?Z as a correction value; and using the corrected autofocus function to adjust the focus, obtaining the observation image of the second thin film, and calculating the film thickness distribution from the reflected-light intensity distribution within the observation image.