Estimating thickness based on number of peaks between two peaks in scanning white light interferometry

A method of measuring a thickness or a surface profile of a thin film layer formed on a base layer through white light scanning interferometry, the method comprising:

• generating a plurality of simulated interferograms corresponding to a plurality of sample thin film layers, wherein the plurality of sample thin film layers each have a different thickness;
• acquiring a real interferogram by illuminating the thin film layer with white light and measuring light intensity along an optical-axis direction, wherein the optical-axis direction is perpendicular to the base layer;
• determining a plurality of estimated thicknesses that the thin film layer may have by selecting two or more peaks from the real interferogram, wherein the plurality of estimated thicknesses are determined based on the number of peaks between the two or more selected peaks;
• selecting from the plurality of simulated interferograms only those simulated interferograms having thicknesses that correspond to the plurality of estimated thicknesses from the real interferogram;
• and
• comparing the selected simulated interferograms with the real interferogram to determine which selected simulated interferogram substantially matches the real interferogram, wherein the thickness of the thin film layer is the thickness of the selected simulated interferogram that substantially matches the real interferogram.