Development of a Transmission Line Model for the Thickness Prediction of Thin Films via the Infrared Interference Method

An efficient transmission line model in the micrometric order is presented in this paper, to determine the thickness of thin dielectric films deposited on highly-doped substrates. In particular, the estimation of the thickness is based on multiple reflections of an incident infrared electromagnetic wave generating interference on the sensor. To this objective, the periodicity of the local maxima and minima, including the phase shift and wavelength dependence of the reflection at the layer-substrate interface, leads in the extraction of the required thickness. Moreover, a theoretical transmission line circuit is designed, in order to model the multiple interferences scenario, and an iterative method is developed to converge towards the correct coating thickness. The featured theoretical transmission line model is validated, via a direct comparison with Certified Reference Materials, to indicate its overall accuracy and reliability level. Finally, the proposed method is utilized to calculate the thickness of coated metallic samples