White-light spectral interferometric technique used to measure thickness of thin films

摘要

We present a white-light spectral interferometric technique for measuring the thickness of a thin film on a substrate. First, the channeled spectrum is expressed analytically for a setup of a slightly dispersive Michelson interferometer with a cube beam splitter of given effective thickness and a fiber-optic spectrometer of a Gaussian response function when one of the interferometer mirrors is replaced by the thin film on the substrate. Then we model the wavelength dependences of the reflectance, the visibility of the spectral interference fringes, the phase change on reflection and the so-called nonlinear phase function, respectively, for a SiO_2 thin film on a silicon wafer. In the modeling, the optical constants are known and multiple reflection within the thin-film structure is taken into account. Second, we perform interferometric experiments with a SiO thin film on aluminium and the SiO_2 thin film on the silicon wafer. Channeled spectra are recorded for determining the thin-film thickness, provided that the optical constants of the thin-film structure are known. We confirm very good agreement between theoretical and experimental channeled spectra and determine precisely the thicknesses for two cases including the SiO thin film on the aluminium and the SiO_2 thin film on the silicon wafer.