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Abstract: The determination of the thickness of thin transparent films with reflectometry is a well‐established cost‐effective robust method that can be used even in inline measurements. The method is based on measurements of the reflectance of the film and a numerical evaluation of the reflectance either by fast Fourier transform or nonlinear regression. In both cases the significance of the result depends upon several parameters in the used algorithms. We demonstrate how reliable the obtained thickness values are. [ABSTRACT FROM AUTHOR]

For determination of film thickness with a reflectometer, the incident light is usually perpendicular to the film. Often, however, measuring heads are used that keep the aperture of the optical fiber constant or even microscopes are used to increase the lateral resolution in film thickness determination. Analogous to a fixed angle of incidence α the thickness determination is influenced in both cases. In contrast to a fixed angle now all angles between 0° and the aperture angle αapt are present for a measuring head or a microscope objective. We demonstrate here, how the aperture of the measuring head affects the thickness determination and give a quantitative estimation of the influence by assigning an effective angle of incidence αeff to a measuring head with aperture angle αapt. [ABSTRACT FROM AUTHOR]