Abstract

The ellipsometric function ρ of a film–substrate system is analyzed through successive transformations from the plane of the two independent variables angle of incidence and film thickness (ϕd plane) to the complex ρ plane. This analysis is achieved by introducing two intermediate planes: the unimodular plane (Zi plane) and the translated ellipsometric plane (ρ* plane). The analysis through the Zi plane leads to classification of the film–substrate systems into two classes: clockwise and counterclockwise. The class of the film–substrate system governs the inversion from the ρ* plane to the Zi-plane. It identifies the number of branch points of ρ*-1 from the ρ* plane to the Zi plane. The branch points of ρ*-1 and its preimage in the ϕd plane are identified and studied. The domain of the double-valued function ρ*-1 is divided into two or four subdomains according to the class of the film–substrate system. In each of these subdomains, the single-valued branch of ρ*-1 is fixed, and we introduce a closed-form solution for the determination of the film thickness of the system. Mathematically, ρ*-1 exists in any domain that does not include the branch points. Hence the exceptive points are divided into two types: removable and essential. The closed-form inversion is obtained for the removable exceptive points. The conformality of both ρ and ρ*, as well as their inverses, leads to identification of the two essential exceptive inversion points, which exist at ϕ=0° and 90°. Accordingly, the closed-form solution is available throughout the ρ plane except at the two points ±1 (corresponding to ϕ=0° and 90°). A study of the extrema of the magnitude and the phase of both ρ and ρ* provides full information on the number of zeros and essential singularities for each of the three categories of film–substrate systems: negative, zero, and positive. Numerical examples are given to illustrate the introduced closed forms. Also, the table of transformation of regions between the ϕd plane and the ρ plane induced by ρ and ρ-1 is given.

© 1999 Optical Society of America

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