Characterization of a multilayer highly reflecting mirror by spectroscopicphase-modulated ellipsometry

The characterization of optical multilayer coatings has been a challenging task for thin-film scientists and engineers because of the various complex, interdependent layer parameters that exist in the system. Spectroscopic ph ase-modulated ellipsometry has some advantages in the postanalysis of the l ayer parameters of such multilayer coatings because it suitably models the layer structure with respect to the ellipsometric measurements. An algorith m to characterize multilayer optical coatings with large numbers of layers has been described by spectroscopic ellipsometry by use of a discrete spect ral zone fitting approach. A 23-layer multilayer highly reflecting mirror h as been characterized by this technique in the wavelength range 280-1000 nm . The ellipsometric spectra (Psi and Delta versus wavelength) have been fit ted separately in three wavelength regimes. Fitting the ellipsometric spect ra in the wavelength regime of 700-1000 nm permitted the sample structure t o be determined. The data were then fitted in the wavelength range 280-340 nm, i.e., near the fundamental absorption edge of TiO2, to yield the disper sion relation for the optical constants of TiO2. Finally, the data were fit ted in the wavelength range 340-700 nm, and the true dispersion of the refr active index of TiO2, along with the best-fitting sample structure, was obt ained. (C) 2001 Optical Society of America.