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Proceedings Paper

The effect of line roughness on the diffraction intensities in angular resolved scatterometry
Author(s): Akiko Kato; Frank Scholze
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Paper Abstract

Scatterometry is a common technique for the characterization of nano-structured surfaces. It is an indirect measuring method, where a chosen set of parameters describing the scattering object is fitted numerically to the data obtained from a scattering experiment. In order to detect several diffraction orders with an angular resolved measurement, it is necessary to choose the wavelength of the light to be of the same order or smaller than the size of the scattering structure. At PTB, detailed scatterometric investigations of an EUV photomask with periodic absorber line gratings on an EUV multilayer mirror have been performed using EUV and DUV radiation. Multiple propagating diffraction orders could be observed and it was possible to derive information about the line profile by means of rigorous numerical modeling. A comparison with microscopic measurements yields consistent results regarding the line width. The sidewall angle of the line profile, however, as determined in the scatterometry measurements performed in the EUV spectral range as well as in the DUV, was distinctly lower than the angle provided by atomic force microscopy. Analyzing different sources of uncertainty, it could be shown that structure disturbances such as line edge or line width roughness cause significant impact on the angular distribution of the diffraction intensity. This effect can be formulated analytically. On the one hand, this can be used to investigate the consequences of roughness for the structure reconstruction algorithm. For instance, a considerable variation of the reconstructed sidewall angle can be observed as a function of roughness. On the other hand, it is possible to determine a roughness parameter through an appropriate evaluation of the scatterometry experimental data. In this paper we will sum up the sources of uncertainty involved in scatterometry and focus on the line roughness and on how it affects the profile reconstruction.

Paper Details

Date Published: 23 May 2011
PDF: 8 pages
Proc. SPIE 8083, Modeling Aspects in Optical Metrology III, 80830K (23 May 2011); doi: 10.1117/12.889410
Show Author Affiliations
Akiko Kato, Physikalisch-Technische Bundesanstalt (Germany)
Frank Scholze, Physikalisch-Technische Bundesanstalt (Germany)

Published in SPIE Proceedings Vol. 8083:
Modeling Aspects in Optical Metrology III
Bernd Bodermann, Editor(s)

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