Optical characterization of diamond-like carbon thin films non-uniform in thickness using spectroscopic reflectometry

Two formulae expressing the reflectance of non-uniform thin films are presented. The first of them corresponds to the arbitrary shapes of this non-uniformity and illuminated light spot under the assumption that this non-uniformity is sufficiently slight. The second formula corresponds to the wedge-shaped non-uniformity of arbitrary magnitude within the circular light spot. It is shown that both the formulae are suitable for the successful optical characterization of non-uniform diamond-like carbon (DLC) thin films in contrast to the usually used reflectance formula for the uniform thin films. Within the optical characterization the values of the standard deviation of non-uniformity is determined together with the correct values of the mean thickness and material parameters corresponding to the dispersion model based on the parametrization of the density of electronic states. On the basis of the material parameters determined the correct spectral dependences of the optical constants of the DLC films studied are calculated.