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Measuring small thickness changes of a thin film by white-light spectral interferometry

A white-light spectral interferometric technique is used for measuring small thickness changes of a SiO2 thin film grown by thermal oxidation on a Si substrate. The technique is based on recording of the spectral interferograms in a Michelson interferometer with one of its mirrors replaced by a thin-film structure. From the spectral interferograms, the nonlinear-like phase function related to the phase change on reflection from the thin-film structure is retrieved. The phase function is fitted to the theoretical one to obtain the thin-film thickness precisely provided that the optical constants of the thin-film structure are known. This procedure is used for measuring small thickness changes of a SiO2 thin film attributed to different dopant concentrations of a Si substrate. The results of the technique are compared with those obtained by spectral reflectometry and very good agreement is confirmed.