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Proceedings Paper

Measurement of rectangular edge and grating structures using extended low-coherence interferometry
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Paper Abstract

Due to its outstanding depth resolution capabilities vertical scanning low-coherence or white-light interferometry is one of the most used optical techniques in the field of 3D micro-metrology. Unfortunately, step height structures often lead to disturbing effects known as batwings in SWLI measurement that overlay the real profile heights of a rectangular structure. As a consequence, the lateral resolution capabilities and the transfer characteristics of white-light interference microscopes are difficult to characterize. In general, the lateral resolution of such instruments is assumed to agree with the lateral resolution of a conventional light microscope for 2D imaging and the measurement process of an optical profiler is assumed to be linear similar to a microscopic imaging process. Our results show that there are significant discrepancies between the instrument transfer function of a white-light interferometer and the optical transfer function of a conventional microscope. In this paper we analyze the transfer characteristics of current white-light interferometers based on theoretical considerations, simulation studies, and experimental investigations. It turns out that under certain conditions a correct measurement of a rectangular profile is possible even if only the first order diffraction component is captured by an objective lens with a given numerical aperture. In addition to the discussion of current instruments new approaches to overcome existing limits will be introduced: In order to reduce the batwing effect we combine a Mirau white-light interferometer with a confocal illumination system. Furthermore, it is shown that proper adaption of the evaluation wavelength of the low-coherent light can improve the measurement accuracy significantly if rectangular profiles are obtained from the phase information inherent in WLI signals.

Paper Details

Date Published: 4 May 2012
PDF: 11 pages
Proc. SPIE 8430, Optical Micro- and Nanometrology IV, 84300U (4 May 2012); doi: 10.1117/12.922358
Show Author Affiliations
Peter Lehmann, Univ. Kassel (Germany)
Jan Niehues, Univ. Kassel (Germany)
Weichang Xie, Univ. Kassel (Germany)
Jörg Riebeling, Univ. Kassel (Germany)

Published in SPIE Proceedings Vol. 8430:
Optical Micro- and Nanometrology IV
Christophe Gorecki; Anand K. Asundi; Wolfgang Osten, Editor(s)

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