EVALUATION OF OPTICAL-PROPERTIES OF DECORATIVE COATINGS BY SPECTROSCOPIC ELLIPSOMETRY

Some of the hard coatings (e.g. TiN, TiC, TiCN, TiAlCN) occur in different colours. Using goniospectroscopy in the visible wavelength range colours are deduced by measuring the spectral reflectance factor R(lambda). This factor depends on both the samples and the white reference as well as on the geometry of illumination and measurement. It is very difficult or even impossible to distinguish colours according to their origin and to relate them to bulk material composition, thin film coatings and interference layers by means of goniospectroscopy as unpolarized light is used. By using polarized light in spectroscopic ellipsometry these difficulties could be overcome as there is no reference to white and the geometric influences of illumination and measurement are negligible, but on the contrary the visual impression is not correctly described. From the measurement of the relative amplitude ratio tan psi and the relative phase shift cos DELTA it is possible to calculate either the parallel and normal components R(p) and R(s) of the reflectivity R or the complex refractive index N = n + ik as well as the dielectric function epsilon = epsilon1 + iepsilon2 which are strongly related to the electronic structure of the material used. It is shown that in this way it is possible to describe optical properties more physically, to separate interference effects and to detect changes in stoichiometry.