Thickness measurement of nontransparent free films by double-side white-light interferometry : Calibration and experiments

International audienceA double-side optical profilometer based on white-light interferometry was developed for thickness measurement of nontransparent films. The profile of the sample is measured simultaneously on both sides of the film. The resulting data allow the computation of the roughness, the flatness and the parallelism of the sides of the film, and the average thickness of the film. The key point is the apparatus calibration, i.e., the accurate determination of the distance between the reference mirrors of the complementary interferometers. Specific samples were processed for that calibration. The system is adaptable to various thickness scales as long as calibration can be made accurately. A thickness accuracy better than 30 nm for films thinner than 200 m is reported with the experimental material used. In this article, we present the principle of the method as well as the calibration methodology. Limitation and accuracy of the method are discussed. Experimental results are presented