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Spectroscopic ellipsometry is a powerful method with high surface sensitivitythat can be used to monitor the growth of even sub-monolayer film. However, theanalysis of ultrathin films is complicated by the correlation of the dielectricconstant and the thickness. This problem is usually resolved by fixing one orthe other value, limiting the information that can be extracted. Here, wepropose a method to determine unambiguously the refractive index, extinctioncoefficient and thickness of a film when a transparent range is available inthe energy range investigated. We decompose the analysis in three steps. First,the thickness of the film is determined from the transparent range of the film.Then, knowing the thickness of the layer, an initial estimation of therefractive index and extinction coefficient is made based on a first-orderTaylor expansion of the ellipsometric ratio. Finally, using this estimation, anumerical regression is done to ensure the convergence of the fit towards thesolution. A theoretical example of the method is given for two differentthicknesses of TiO2 films. Finally, the method is applied to the experimentaldata measured during the atomic layer deposition of a thin film of Hf0.5Zr0.5O2grown on Si. The thickness, refractive index and extinction coefficient areretrieved with a high precision in the energy range of 3.5 - 6.5 eV. A detailedanalysis is presented on the accuracy of the retrieved values and theirdependency on random and systematic errors for different energy ranges.

journal of applied physics

A fully automatized method for the unambiguous wavelength-by-wavelength  determination of the thickness and optical property of a very thin film with  a transparent range