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Proceedings Paper

Model based laser focus scanning: the path towards improved lateral accuracy
Author(s): Jörg Bischoff; Rostyslaw Mastylo; Gerard Granet; Eberhard Manske
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Paper Abstract

In principal, optical measurement methods suffer from physical limits related to finite wavelengths and diffraction. In laser focus scanning, vertical resolutions below 1 nm can be achieved while the lateral accuracy is more or less restricted by the diameter of the focused laser beam, i.e. values of half the wavelength can be reached in the best case. We present a model based approach having the potential to show a way out of this limitation. It is based on the rigorous modeling of the complete measurement device including sophisticated ray tracing in combination with Maxwell based modeling of the sample diffraction and scattering providing a simulated signal for an assumed sample profile. Furthermore, the sample profile is parametrized on the basis of a priori information. The simulated signal is then iteratively compared with the measured signal while updating the floating parameters of the model in order to improve the match between the two signals. Eventually, the improved sample profile obtained in this way is considered to represent the real sample profile as soon as a certain goodness of fit is achieved. On the other hand, the profile model has to be changed in case there is no satisfying fit. In this way, the lateral accuracy can be increased considerably. Edge detection errors below a few tens nanometer or even below 10 nm become possible while measuring with visible light. This is demonstrated by first comparisons of modeled and measured signals and validation by alternative metrology techniques.

Paper Details

Date Published: 21 June 2019
PDF: 12 pages
Proc. SPIE 11057, Modeling Aspects in Optical Metrology VII, 110570F (21 June 2019); doi: 10.1117/12.2525319
Show Author Affiliations
Jörg Bischoff, Technische Univ. Ilmenau (Germany)
Rostyslaw Mastylo, Technische Univ. Ilmenau (Germany)
Gerard Granet, Univ. Clermont Auvergne, CNRS, SIGMA (France)
Eberhard Manske, Technische Univ. Ilmenau (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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