$m$-Line method for reflectometry of ultrathin layers

A solution to the vector electrodynamic problem of describing the intensity distribution of a coherent light beam reflected from a plane-layered medium is obtained. The conditions for observing $m$-lines in the named distribution upon reflection of a Gaussian beam from an ultrathin (nanoscale) layer on the substrate are determined. It has been established that the contrast of $m$-lines is very sensitive to the thickness of such a layer. On this basis, a new method for controlling the thickness and refraction index of ultrathin layers has been proposed. Its features include local layer control, the absence of a reference signal and the absence of the need for mechanical rotation of the sample, contributing to the stability of measurements. An analysis of method errors was performed. Experiments on observing and processing $m$-lines when solving the inverse optical problem for oxide layers on a silicon surface are presented. The results are compared with multi-angle coherent ellipsometry data.