Method and apparatus for measuring the thickness of a transparent layer on nanometer scale

A method for wet-chemical transparent layer thinning in a manufacturing process, including:

• using a spectrometer system and/or an imaging system to obtain a spectral reflectance measurement for the transparent layer;
• determining, by an electronic device, an approximate thickness dFFT of the transparent layer based on a precisely known dispersion n(λ) of a material of the transparent layer by performing Fast Fourier Transformation, FFT, analysis on Fabry-Pérot oscillation, FPO, in the spectral reflectance measurement;
• performing, by the electronic device, a FPO full-spectral fitting procedure with the approximated thickness dFFT as starting value doo to determine an initial local best fitting thickness dFPO,0, wherein the FPO full-spectral fitting procedure includes determining the thickness difference Δdfit between the initial local best fitting thickness dFPO,0 and the approximate thickness dFFT, or between neighboring local best FPO fitting results;
• repetitively performing the FPO full-spectral fitting procedure with the approximate thickness dFFT shifted by a limited set of integer multiples of the thickness difference Δdfit as alternative starting values d0,i to determine a global best fitting thickness dFPO, or
• repetitively performing the FPO full-spectral fitting procedure with the initial local best fitting thickness dFPO,0 shifted by a limited set of integer multiples of the thickness difference Δdfit as alternative starting values d0,i to determine a global best fitting thickness dFPO;
• and
• using the global best fitting thickness dFPO to stop the wet-chemical transparent layer thinning at a predetermined thickness corresponding to the global best fitting thickness dFPO.