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Proceedings Paper

Quantitative phase retrieval for EUV photomasks
Author(s): Stuart Sherwin; Isvar Cordova; Ryan Miyakawa; Laura Waller; Andrew Neureuther; Patrick Naulleau
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Paper Abstract

We present a comparison of experimental techniques for measuring the as-built phase shift of EUV photomasks to meet the unique requirements for EUV lithography at the resolution limit. Attenuated phase-shift masks provide superior image quality for certain applications such as low-k1 contact and pillar arrays, offering increased throughput and reduced stochastic printing failures. But whereas the traditional phase-shift is π, rigorous electromagnetic simulations suggest the optimal phase-shift for an EUV photomask must be adjusted to account for Mask 3D effects, which are themselves difficult to measure. In this work, we explore at-wavelength metrology including reflectometry, scatterometry, and phase imaging for measuring multilayer and absorber reflectance, as well as complex scattering amplitudes for a grating with pitch p = 420nm and duty-cycle D = 0.33. Using rigorous electromagnetic simulations, we find that relying only on reflectometery and the Fresnel thin-mask model predicts the complex scattering amplitudes with 22% accuracy due to 3D effects, whereas a combination of scatterometry and through-focus imaging can achieve a promising 0.6% accuracy, and a combination of scatterometry and Zernike Phase-Contrast imaging can achieve a superior 0.1% accuracy. Experimental results based on imaging and scatterometry clearly display 3D effects that differ substantially from idealized rigorous simulations, suggesting the difficulty of accurately predicting 3D effects and hence the need to accurately measure them.

Paper Details

Date Published: 23 March 2020
PDF: 10 pages
Proc. SPIE 11323, Extreme Ultraviolet (EUV) Lithography XI, 1132315 (23 March 2020); doi: 10.1117/12.2552967
Show Author Affiliations
Stuart Sherwin, Univ. of California, Berkeley (United States)
Isvar Cordova, Lawrence Berkeley National Lab. (United States)
Ryan Miyakawa, Lawrence Berkeley National Lab. (United States)
Laura Waller, 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. 11323:
Extreme Ultraviolet (EUV) Lithography XI
Nelson M. Felix; Anna Lio, Editor(s)

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