Optical characterization of SiO2thin films using universal dispersion model over wide spectral range

Abstract

Vacuum evaporated SiO2 thin films are very important in a design and manufacturing of optical devices produced in optics industry. In this contribution a reliable and precise optical characterization of such SiO2 thin films is performed using the combined method of spectrophotometry at normal incidence and variable-angle spectroscopic ellipsometry applied over spectral range from far IR to extreme UV (0.01-45 eV). This method uses the Universal Dispersion Model based on parametrization of the joint density of states and structural model comprising film defects such as nanometric boundary roughness, inhomogeneity and area non-uniformity. The optical characterization over the wide spectral range provides not only the spectral dependencies of the optical constants of the films within the wide range but, more significantly, it enables their correct and precise determination within the spectral range of interest, i.e. the range of their transparency. Furthermore, measurements in the ranges of film absorption, i. e. phonon excitations in IR and electron excitations in UV, reveal information about the material structure. The results of the optical characterization of the SiO2 thin films prepared on silicon single crystal substrates under various technological conditions are presented in detail for two selected samples. Beside film thicknesses and values of dispersion parameters and spectral dependencies of the optical constants of the SiO2 films, the characterization also enables quantification of film defects and their parameters are presented as well. The results concerning the optical constants of SiO2 films are compared with silica optical constants determined in our earlier studies.