New data-processing technique for measurement of metallic foil thickness with differential white-light interferometry

The thickness of metallic foil was measured by differential white-light interferometry (DWLI). Two tandem Michelson interferometers (MI), in which the reflective surfaces measured are the surfaces of the metallic foil, were used as a basic interferometry system to obtain interference fringes on a spectrometer. Therefore, the interference fringes depend only on the path differences caused by the thickness of the metallic foil. The interference fringes were analyzed using a modified extremum method based on the least root-mean-square (RMS) deviation. Experimental results for thickness measurements are presented. Measurement time is only 100 ms or less for a thickness of 1-80 μm.