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Systematic approach on illustrating the challenges represented by optical bidirectional measurements using rigorous simulations
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Paper Abstract

Optical microscopy is widely used for the characterization of micro- and nanostructures in the field of unidirectional and bidirectional dimensional metrology. Despite the general high recognition in the metrological community, the inherent difficulties which are bound to optical bidirectional measurements using commercial vision-based metrology tools are not sufficiently investigated, yet, and require additional insight, which we intend to provide here. We demonstrate the need for sophisticated analysis methods to find a threshold value which locates the correct physical edge position within the microscopical image. The common assumption for the threshold to be at 50% of the intensity level of the edge signal is in essentially any imaging configuration wrong and leads to large systematic measurements errors. For example, the correct threshold values for transmission light microscopy using high NA objectives on chrome on quartz photomasks, are within 15% and 35% of the intensity level in the simulated images. For other measurement configurations the threshold variation can be even much larger. Since the correct threshold values depend on the illumination and imaging parameters of the imaging system as well as on the geometrical and optical parameters of the measurement object, we showcase a selection of them and their respective influence on the determination of the threshold values. Rigorous simulations are the key feature for this analysis since they require all the relevant parameters to be included in the simulation of a microscopical image which enables the correct threshold determination and to extract the correct bidirectional quantities out of the optical images.

Paper Details

Date Published: 21 June 2019
PDF: 9 pages
Proc. SPIE 11057, Modeling Aspects in Optical Metrology VII, 110570D (21 June 2019); doi: 10.1117/12.2527973
Show Author Affiliations
Jan Krüger, Physikalisch-Technische Bundesanstalt (Germany)
Rainer Köning, Physikalisch-Technische Bundesanstalt (Germany)
Bernd Bodermann, Physikalisch-Technische Bundesanstalt (Germany)


Published in SPIE Proceedings Vol. 11057:
Modeling Aspects in Optical Metrology VII
Bernd Bodermann; Karsten Frenner; Richard M. Silver, Editor(s)

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