Thickness Measurement for Thin Films and Coatings Using Millimeter Waves

Abstract

An accurate technique for measuring the thickness of dielectric thin films and coatings is presented in this paper. Millimeter-wave sensors operated at 80 GHz are placed near the sample surface. A better than \(1^{\circ}/\mu\) m sensitivity of the phase of the received signal with respect to sample thickness can be achieved. A theoretical model consisting of a vertical electric dipole over a two-layer structure is used to generate calibration information and to guide the optimization of sensor placement. To facilitate the theoretical study, we devise an efficient and reliable numerical algorithm for evaluating Sommerfeld integrals. This algorithm surpasses the performance of conventional numerical methods and renders fast convergence even in the worst-case scenario, when the transmitter and the receiver have the same elevation and the materials are lossless.