Speaker
Description
X-Ray Reflectivity (XRR) is a well-established metrology method for multilayer characterization. With XRR, we determine the structural parameters describing the optical structure of a given sample (i.e., layer thickness, intermixing/roughness and optical density); we do so by solving the related inverse problem. To do so, one uses a model which calculates the reflectivity given a set of parameters. Depending on the chosen model, different features in the optical structure can be simulated and fitted. Normally, one would use a model-dependent approach, which assumes a pre-determined interface shape. In our work however, we use the Free-Form model [1]. This model gives us the ability to fit structures without a pre-assumed layer structure and interface shape; this is done by splicing up the multilayer structure into small lamellae of width d and individual refractive index. Solving this inverse problem is then done by fitting the correct refractive index for each considered lamella. We now aim at determining the estimated error in the fitted refractive indices. We use a Monte Carlo Markov Chain uncertainty quantification routine and investigate regularisation methods to repress multimodalities.
[1] S. N. Yakunin, I. A. Makhotkin, K. V. Nikolaev, R. W. E. van de Kruijs, M. A. Chuev, and F. Bijkerk. Combined EUV reflectance and X-ray reflectivity data analysis of periodic multilayer structures. Optics Express, 22(17):20076–20086, August 2014. ISSN 1094-4087. doi: 10.1364/OE.22.020076.
