Depolarization effects in ellipsometric measurements of thick layers

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Abstract
Ellipsometry is a powerful technique for the determination of complex refractive indices ^n equals n plus ik of thin absorbing films deposited on a substrate. If the films are deposited onto an opaque substrate, the calculation methods are well-known. However, sometimes it is advantageous for some other reason to deposit the films onto a transparent substrate. In this case the light reflected from the back surface of the substrate must also be taken into account. If the thickness of the substrate is much larger than the coherence length of the light, there is no correlation between the phases of the light beams reflected from the boundaries of the thin film and the beam reflected from the back surface of the substrate. Therefore, it is not possible to calculate the absolute phase of the total reflectance of the system, i.e. the film plus substrate. However, for the determination of the ellipsometric coefficients the relative phase must be known. In this publication a method of calculating the ellipsometric coefficients of such a system is presented. Instead of calculating the absolute phase, this method is based on the calculation of reflected intensities for arbitrary angles of polarization taking into account the relative phase shift at each boundary. Comparisons between measurements of ellipsometric coefficients of well-known materials and the calculations based on this method show excellent agreement.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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