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Mathematische Modellierung und Datenanalyse

Fachbereich 8.4

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Artikel

Titel: A maximum likelihood approach to the inverse problem of scatterometry
Autor(en): M.-A. Henn, H. Gross, F. Scholze, M. Wurm, C. Elster and M. Bär
Journal: Optics Express
Jahr: 2012
Band: 20
Ausgabe: 12
Seite(n): 12771-86
Optical Society of America
DOI: 10.1364/OE.20.012771
ISSN: 1094-4087
Web URL: http://www.osapublishing.org/viewmedia.cfm?uri=oe-20-12-12771&seq=0&html=true
Marker: 8.41,Diffraction gratings,Metrology,Scatter-Inv,Scatterometrie,8.42
Zusammenfassung: Scatterometry is frequently used as a non-imaging indirect optical method to reconstruct the critical dimensions (CD) of periodic nanostructures. A particular promising direction is EUV scatterometry with wavelengths in the range of 13 - 14 nm. The conventional approach to determine CDs is the minimization of a least squares function (LSQ). In this paper, we introduce an alternative method based on the maximum likelihood estimation (MLE) that determines the statistical error model parameters directly from measurement data. By using simulation data, we show that the MLE method is able to correct the systematic errors present in LSQ results and improves the accuracy of scatterometry. In a second step, the MLE approach is applied to measurement data from both extreme ultraviolet (EUV) and deep ultraviolet (DUV) scatterometry. Using MLE removes the systematic disagreement of EUV with other methods such as scanning electron microscopy and gives consistent results for DUV.

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