White-light spectral interferometry and reflectometry to measure thickness of thin films

摘要

A white-light spectral interferometric technique is used for measuring the thickness of a SiO_2 thin film grown by thermal oxidation on a Si substrate. The technique is based on recording of the spectral interferograms at the output of 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 function is fitted to the theoretical one to obtain the thin-film thickness provided that the optical constants of the thin-film structure are known. This procedure is used for measuring four different thicknesses of the SiO_2 thin film on the Si substrate. The results of the technique are compared with those obtained in the same setup by spectral reflectometry and good agreement is confirmed. To minimize the errors introduced by optical elements of the interferometer, the measurements are performed with the reference sample of the known phase change on reflection and reflectance.