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Proceedings Paper

EUV mask characterization with actinic scatterometry
Author(s): Stuart Sherwin; Andrew Neureuther; Patrick Naulleau
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Paper Abstract

With EUV Lithography rapidly approaching maturity, accurate metrology to thoroughly characterize EUV photomasks is needed. We present an actinic EUV reflection-based scatterometry technique to measure key parameters of EUV photomasks to characterize both the multilayer mirror substrate as well as periodic absorber targets fabricated on the multilayer. We show these measurements can be used both in determining the physical dimensions on the mask, and also in directly quantifying optical effects, which can provide invaluable feedback in the mask optimization and manufacturing processes. In this paper, we present four different methods of data analysis for EUV mask scatterometry: two for characterizing the multilayer mirror based on measurements of the reflected light intensity from a flat open area of the mask, and two more for characterizing absorber gratings fabricated on the multilayer substrate based on measurements of the diffraction efficiencies. Key findings include that a simple neural net architecture containing a single fullyconnected hidden layer that can characterize the multilayer’s angularly-varying complex reflection coefficient to 7 × 10-4 accuracy, and that dictionary-based scatterometry with 7 wavelengths from 13.2 − 13.8nm can measure the absorber thickness of a grating to 0.4nm even in the presence of random and systematic errors. With the presented methods and findings, we hope to demonstrate that actinic EUV scatterometry has the capabilities to accurately characterize EUV masks in terms of both multilayer and absorber.

Paper Details

Date Published: 3 October 2018
PDF: 14 pages
Proc. SPIE 10809, International Conference on Extreme Ultraviolet Lithography 2018, 108090T (3 October 2018); doi: 10.1117/12.2501970
Show Author Affiliations
Stuart Sherwin, Univ. of California, Berkeley (United States)
Andrew Neureuther, Univ. of California, Berkeley (United States)
Patrick Naulleau, Lawrence Berkeley National Lab. (United States)

Published in SPIE Proceedings Vol. 10809:
International Conference on Extreme Ultraviolet Lithography 2018
Kurt G. Ronse; Eric Hendrickx; Patrick P. Naulleau; Paolo A. Gargini; Toshiro Itani, Editor(s)

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