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

Peter Lehmann; Jan Niehues; Weichang Xie; Jörg Riebeling

doi:10.1117/12.922358

4 May 2012 Measurement of rectangular edge and grating structures using extended low-coherence interferometry

Peter Lehmann, Jan Niehues, Weichang Xie, Jörg Riebeling

Proceedings Volume 8430, Optical Micro- and Nanometrology IV; 84300U (2012) https://doi.org/10.1117/12.922358
Event: SPIE Photonics Europe, 2012, Brussels, Belgium

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.

Citation Download Citation

Peter Lehmann, Jan Niehues, Weichang Xie, and Jörg Riebeling "Measurement of rectangular edge and grating structures using extended low-coherence interferometry", Proc. SPIE 8430, Optical Micro- and Nanometrology IV, 84300U (4 May 2012); https://doi.org/10.1117/12.922358

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