Radiation transport and scaling of optical depth in Nd:YAG laser-produced microdroplet-tin plasma

R. Schupp, F. Torretti, R. A. Meijer, M. Bayraktar, J. Sheil, J. Scheers, D. Kurilovich, A. Bayerle, A. A. Schafgans, M. Purvis, K. S.E. Eikema, S. Witte, W. Ubachs, R. Hoekstra, O. O. Versolato

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Experimental scaling relations of the optical depth are presented for the emission spectra of a tin-droplet-based, 1-μm-laser-produced plasma source of extreme-ultraviolet (EUV) light. The observed changes in the complex spectral emission of the plasma over a wide range of droplet diameters (16-65 μm) and laser pulse durations (5-25 ns) are accurately captured in a scaling relation featuring the optical depth of the plasma as a single, pertinent parameter. The scans were performed at a constant laser intensity of 1.4 × 1011 W/cm2, which maximizes the emission in a 2% bandwidth around 13.5 nm relative to the total spectral energy, the bandwidth relevant for industrial EUV lithography. Using a one-dimensional radiation transport model, the relative optical depth of the plasma is found to linearly increase with the droplet size with a slope that increases with the laser pulse duration. For small droplets and short laser pulses, the fraction of light emitted in the 2% bandwidth around 13.5 nm relative to the total spectral energy is shown to reach high values of more than 14%, which may enable conversion efficiencies of Nd:YAG laser light into - industrially - useful EUV radiation rivaling those of current state-of-the-art CO2-laser-driven sources.

Original languageEnglish
Article number124101
Pages (from-to)1-5
Number of pages5
JournalApplied Physics Letters
Volume115
Issue number12
DOIs
Publication statusPublished - 19 Sept 2019

Funding

This work was carried out at the Advanced Research Center for Nanolithography (ARCNL), a public-private partnership of the University of Amsterdam (UvA), the Vrije Universiteit Amsterdam (VU), the Netherlands Organisation for Scientific Research (NWO), and the semiconductor equipment manufacturer ASML. The part of this work concerning the CO2-laser-produced plasma was carried out at the ASML San Diego part of ASML U.S. LP. The used transmission grating spectrometer has been developed in the Industrial Focus Group XUV Optics at the University of Twente and supported by the FOM Valorisation Prize 2011 awarded to F. Bijkerk and NanoNextNL Valorization Grant awarded to M. Bayraktar in 2015. This project received funding from the European Research Council (ERC) Starting Grant No. 802648 and is part of the VIDI research programme with Project No. 15697, which is financed by NWO.

FundersFunder number
Horizon 2020 Framework Programme802648
European Research Council15697
University of Twente
Nederlandse Organisatie voor Wetenschappelijk Onderzoek
Foundation for Fundamental Research on Matter

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