Tailoring the support constraint of phase retrieval algorithms improves lensless EUV nanostructures metrology

Paolo Ansuinelli; Iacopo Mochi

doi:10.1117/12.3034696

12 November 2024 Tailoring the support constraint of phase retrieval algorithms improves lensless EUV nanostructures metrology

Paolo Ansuinelli, Iacopo Mochi

Author Affiliations +

Proceedings Volume 13215, International Conference on Extreme Ultraviolet Lithography 2024; 1321516 (2024) https://doi.org/10.1117/12.3034696
Event: SPIE Photomask Technology + EUV Lithography, 2024, Monterey, California, United States

Conference Poster

Abstract

Phase retrieval from diffraction data is an inverse problem which is in principle ill-posed and is made tractable by appropriately introducing constraints in the problem formulation. Particularly, phase retrieval is often formulated as an optimization problem which attempts to find a solution that simultaneously fulfills two sets of constraints. For example, the support constraint can be exploited in real space, by enforcing knowledge about the object boundaries. Similarly, the diffracted intensity measured in the far–field offers a constraint that is exploited upon propagation of the optical field from the near to the far zone. In the context of Extreme Ultraviolet (EUV) mask/wafer metrology, the fabricated nanostructures are often periodic and known a–priori by their nominal design. These structures are realized on top of a substrate whose optical properties are usually known, to some degree, in advance. We consider the case of an EUV photomask with a patterned field of periodic absorber nanostructures on top of a multilayer and present simulation results that illustrate that by developing inversion schemes that account for both the periodicity of the target and the expected multilayer reflectivity value, the phase of the reflected wave can be better determined, thereby enabling imaging where the traditional inversion algorithms (e.g. ER, HIO, Ptychography) struggle.

(2024) Published by SPIE. Downloading of the abstract is permitted for personal use only.

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Paolo Ansuinelli and Iacopo Mochi "Tailoring the support constraint of phase retrieval algorithms improves lensless EUV nanostructures metrology", Proc. SPIE 13215, International Conference on Extreme Ultraviolet Lithography 2024, 1321516 (12 November 2024); https://doi.org/10.1117/12.3034696

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