Approach for Estimating Material Properties of Thin Film on Substrate by Inverse Analysis with Surface Wave Spectroscopy

The characterization of thin film on a substrate is very important for basic research and development of thin-film-coated materials. In this study, an inverse analysis with an ultrasonic spectroscopic technique is presented for quantitatively estimating elastic properties and density of the thin film on a substrate. The inverse problem is reduced to the optimum problem of minimizing the differences between dispersion curves obtained experimentally and numerically, where the dispersion curve is determined by analyzing the ultrasonic reflectivity measured or calculated from the elastic properties and density of the thin film. First, the stability and accuracy of the solution in the inverse problem are discussed. Secondly, numerical simulation using the optimization procedure with the complex method is carried out for a few sample problems, and the validity of the present procedure is examined. Furthermore, the experiment was demonstrated for TiN-coated tool steel.