Combined method of multi-pixel and multi-sample imaging spectroscopic reflectometry for the optical characterization of non-uniform thin films with transition layers

Abstract Three samples of non-uniform polymer-like thin films are characterized using imaging spectroscopic reflectometry, which measures maps of spectral dependencies of reflectance of sample surface. It was necessary to consider transition layers between these films and silicon substrates. The goal of the optical characterization was to determine the maps of local thicknesses, optical constants of the non-absorbing films, and the parameters (thickness and the optical constants) of the transition layers. Because the transition layers have complicated spectral dependencies of the optical constants, it was difficult to correctly determine all parameters. Three methods of data processing were introduced to deal with this problem. In the first approach, the data for each sample were processed separately. The second approach considered the data for all three samples together and assumed that the parameters of the transition layers are the same for all samples. The third approach is a slight extension of the second one, which also assumes the same optical constants of the non-uniform films on all three samples. The processing of the data utilizes the least-squares method, with parameters divided into three groups: those sought within each pixel, those that are the same for all pixels of the given sample (multi-pixel method), and those that are the same for all pixels and all samples (multi-sample method). While the first method considering the samples independently, failed to give reasonable results for the parameters of the transition layer, the other two methods utilizing the multi-sample approach, were successful.