A method of measuring film thicknesses

Claim 2

The method of claim 1, wherein said step (c) comprises the steps of: (c-1) finding the total number of peaks and valleys in said interference waveform; (c-2) judging whether the total number is less than 2 or not; and (C-3) if the total number is not less than 2, determining a wavelength which is related to a peak or a valley which is located on the shorter wavelength side in said interference waveform as said first wavelength and determining a wavelength which is related to a peak or a valley which is located on the longer wavelength side in said interference waveform as said second wavelength thereby to determine said possible film thickness ranges of said transparent films based on said first and second wavelengths; or (c-4) if the total number is less than 2, calculating an approximate total number of peaks and valleys which could be found within said observation wavelength range as the total number based on wavelengths which are located at the shortest and longest wavelength sides and said optical constants regarding said transparent films determining the wavelength which is located at the shortest wavelength side of said observation wavelength range as said first wavelength while determining the wavelength which is located at the longest wavelength side of said observation wavelength range as said second wavelength, and thereafter determining said possible film thickness ranges of said transparent films based on said approximate total number of peaks and valleys and said first and second wavelengths.

Claim 3

The method of Claim 2, wherein said step (c-3) comprises a step of calculating a sum of optical thicknesses of said transparent films based on said first and second wavelengths and the total number of peaks and valleys found at said step (c-1) and thereafter determining a certain range around said sum as a first condition for a film thickness combination, wherein said step (c-4) includes a step of determining a certain range around said approximate total number of peaks and valleys as a second condition for a film thickness combination, and wherein said step (d) includes a step of judging whether said tentatively determined film thicknesses satisfy said first and second conditions for a film thickness combination prior to calculation of a deviation between theoretical spectral reflectance and measured spectral reflectance with respect to said tentatively determined film thicknesses, and thereafter calculating a deviation only when said first and second conditions for a film thickness combination are satisfied.

Claim 4

The method of claim 3, wherein prior to said step (d), said film thickness pitch is set for each one of said transparent films at a value which is smaller than a film thickness change which causes the total number of peaks and valleys appearing in said interference waveform to change by 1 with a change in said tentatively determined film thicknesses, and wherein said film thickness combination which is found at said step (d) is optimized by nonlinear optimization in finding thicknesses of said one or more transparent films.