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1 April 2011First steps towards traceability in scatterometry
Scatterometry is a common technique for the characterization of nano-structured surfaces. The goal is to establish
scatterometry as a traceable and absolute metrological method for dimensional measurements. Scatterometry is an
indirect measuring method. There are three aspects to be investigated for a proper estimation of the measurement
uncertainties. Firstly, the measured optical properties will have measurement uncertainties. The optimization theory
provides well-proven algorithms to propagate the uncertainties of the input parameters to the output, using covariance or
Monte Carlo methods. Secondly, it must be assured that the model represents the measurement object sufficiently well.
Due to the large number of parameters it takes to model a real object, it is not possible to simultaneously determine all of
them from the measured data. Therefore, a priori knowledge about reasonable values for certain model parameters and
their associated variances is needed. Their impact on the uncertainties of the reconstructed parameters describing the
nano-structured surface has to be considered too. Thirdly, there are assumptions in the model which are inherent
properties of the mathematical methods used. The assumption that the structures are periodic over a sufficiently large
area, i.e. the measurement field, is of the most importance. Line-edge or line-width roughness are obviously effects
disturbing the periodicity and the corresponding uncertainty contribution can be derived by an analytical approach to
estimate their influence on the diffracted intensities. In our example the latter contribution is the dominant one.
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Frank Scholze, Bernd Bodermann, Hermann Groß, Akiko Kato, Matthias Wurm, "First steps towards traceability in scatterometry," Proc. SPIE 7985, 27th European Mask and Lithography Conference, 79850G (1 April 2011);