Comprehensive EUV optical constants dataset published

Result of an international collaboration led by PTB and involving eight partner institutions

Illustrative image: EUV reflectometry measurements to determine the optical constants of transition metals © PTB

Optical constants, as fundamental material parameters, form an important basis for the development and optimisation of optical components, including applications in semiconductor lithography, at synchrotron and free-electron laser facilities, as well as in imaging techniques and future EUV technologies. A comprehensive study has now been published in the journal Optics Express (Optica), in which high-precision optical constants were determined for 16 transition metals – Sc, V, Cr, Co, Ni, Nb, Mo, Rh, Pd, Hf, W, Re, Os, Ir, Pt and Au – as well as for ZrO₂ in the extreme ultraviolet (EUV) spectral range.

The study combines measurements on specially fabricated thin-film samples with Bayesian analysis methods to determine the optical constants of coating materials relevant to technology. For several of the materials investigated, previously unresolved fine structures and significant deviations from established reference databases were identified. The results thus provide an improved data basis for the modelling and design of EUV optics.

The work represents an international collaboration led by PTB and involving eight partner institutions: Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Helmholtz-Zentrum Hereon, the University of Twente (MESA+ Institute for Nanotechnology), Lawrence Berkeley National Laboratory (Center for X-Ray Optics), ASML Research, imec, Laboratoire Charles Fabry (CNRS, Institut d'Optique Graduate School, Université Paris-Saclay), optiX fab GmbH.

Publication:

Optical constants of Sc, V, Cr, Co, Ni, Nb, Mo, Rh, Pd, Hf, W, Re, Os, Ir, Pt, Au, and ZrO₂ in the extreme ultraviolet range
Qais Saadeh, Andrey Sokolov, Michael Störmer, Gnanavel Vaidhyanathan Krishnamurthy, Robbert Van De Kruijs, Eric Gullikson, Richard Quintanilha, Vicky Philipsen, Evgueni Meltchakov, Franck Delmotte, Oliver Kieler, Mark Bieler, Frank Siewert, Ivo Rudolph, Karl Opsomer, Meiyi Wu, Zanyar Salami, Christian Laubis, Ayhan Babalik, Danilo Ocaña García, Philipp Naujok, Christian Buchholz, Victor Soltwisch, and Frank Scholze
Opt. Express 34, 28239-28292 (2026). https://doi.org/10.1364/OE.595748

Contact:

Qais Saadeh
PTB – National Metrology Institute of Germany
Working Group 7.14: EUV-Nanometrology
Qais.Saadeh(at)ptb.de

PTB press release, 13 August 2026