Patent ID: 8804129

Claim:
A method for measuring a thickness of a transparent film within a specific light frequency range by using broad band interferometry within the frequency range, the method comprising: preparing a correlogram of the film by using an interferometer adapted for broad band interferometry within the frequency range; applying a Fourier transformation to the correlogram to obtain a Fourier phase function; removing a linear component of the Fourier phase function to obtain a non-linear component of the Fourier phase function; applying a second integral transformation to the non-linear component to obtain an integral amplitude function of the non-linear component; identifying a peak location of the integral amplitude function; and determining the thickness of the film as a double value of an abscissa at the peak location considering a refractive index of the film which is dependent on wavelength, wherein after the thickness of the film is determined, the thickness of the film is tested to determine whether the determined thickness is less than a threshold; and when the determined thickness is less than the threshold, the non-linear component of the Fourier phase function is compared with a mathematical model of the non-linear component of the Fourier phase function as a function of the film thickness only, and the film thickness is determined to be the thickness for which the mathematical model of the non-linear component of the Fourier phase function is closest to the obtained non-linear component of the Fourier phase function.