Method and apparatus for performing film thickness measurements using white light scanning interferometry

An apparatus for measuring a thickness of a transparent film with a specific frequency range by using broad band interferometry within the frequency range, the apparatus comprising:

• an interferometer that performs broad band interferometry within the frequency range and generates a correlogram;
• and
• a computer that
• performs a Fourier transformation to the correlogram to obtain a Fourier phase function;
• removes a linear component of the Fourier phase function to obtain a non-linear component of the Fourier phase function;
• applies a second integral transformation to the non-linear component to obtain an integral amplitude function of the non-linear component;
• identifies a peak location of the integral amplitude function;
• and
• determines 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.

A non-transitory computer readable media tangibly storing a program that causes a computer to:

• perform a Fourier transformation to a correlogram to obtain a Fourier phase function;
• remove a linear component of the Fourier phase function to obtain a non-linear component of the Fourier phase function;
• applies an integral transformation to the non-linear component to obtain an integral amplitude function of the non-linear component;
• identifies a peak location of the integral amplitude function of the integral amplitude diagram;
• and
• determine a thickness of a 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.