Optical characterization of thin films non-uniform in thickness by a multiple-wavelength reflectance method

An original method enabling us to characterize the non-uniformity of thin-film thickness is described. This method employs the interpretation of data obtained by multiple-wavelength reflectometry (MWR). Within this MWR method the values of the reflectance are measured for several wavelengths in many points lying along the area of the film. The spectral dependence of the refractive index of the material forming the film is determined using variable-angle spectroscopic ellipsometry (VASE). The MWR method is then used to evaluate the values of the thickness along the area of the non-uniform film under investigation. Within the experimental set-up employed for applying the MWR method, a multi-wavelength laser is used as a light source. A CCD camera equipped with a zoom objective is utilized as a detector. A suitable beamsplitter allows to measure the values of the relative reflectance of the film against a reference sample with known reflectance. By using the set-up employed it is possible to characterize the thin-film spreading over large areas of substrates. Copyright (C) 2002 John Wiley Sons, Ltd.