Reflection of polarized light
Ellipsometry is a spectral reflection experiment using polarized light in which the change of polarization is measured. The separate consideration of parallel and perpendicular components provides amplitude- and phase information (Ψ und Δ). Based on a parameterized model, simulated ellipsometric data are best fitted on experimental data using optical constants either experimentally determined or from a data basis. As a result of the fit procedure, optical (refractive index n and extinction coefficient k) or dielectric (real ε1 and imaginary part ε2) constants either for the substrate or one unknown layer can be determined as a function of wavelength.
Drude ellipsometer (large picture)
In addition, layer thickness as spectrally independent quantity can be calculated. Without any modeling, ellipsometric raw data and describe layer thickness and electronic structure, i.e. microstructure, stoichiometry and density, of a given layer substrate system in terms of a fingerprint. This is of great importance for identification-, homogeneity- and stability-testing.