Development of EUV phase shift mask metrology

Elba Gomar-Nadal; Malahat Tavassoli; Kowtilya Bijjula; Stuart Sherwin; Matt Hettermann; Christian Wilson; Feng Dong; Dave Houser; Alexander Khodarev; Chami Perera; Patrick Naulleau

doi:10.1117/12.2688453

21 November 2023 Development of EUV phase shift mask metrology

Elba Gomar-Nadal, Malahat Tavassoli, Kowtilya Bijjula, Stuart Sherwin, Matt Hettermann, Christian Wilson, Feng Dong, Dave Houser, Alexander Khodarev, Chami Perera, Patrick Naulleau

Author Affiliations +

Proceedings Volume 12751, Photomask Technology 2023; 127510O (2023) https://doi.org/10.1117/12.2688453
Event: SPIE Photomask Technology + EUV Lithography, 2023, Monterey, California, United States

Abstract

With EUV Attenuated Phase Shift Masks (aPSMs) rapidly approaching maturity, actinic metrology soon will be required to ensure phase accuracy, uniformity, and stability. The target phase shift is carefully designed to an optimized value, which is not 𝜋, but typically around 1.2𝜋 for optimal printing at critical feature sizes. The additional 0.2𝜋 phase shift is necessary due to mask 3D effects (M3D), which increasingly distort the nearfield scattering and phase as the feature size is reduced. Therefore, EUV attenuated phase shift masks require metrology, not only for the relative Fresnel phase shift between large-area multilayer and absorber regions, but also for the feature-dependent pattern phase shift in the near-field scattering. We demonstrate a metrology solution for measuring the in-pattern phase shift using spectroscopic variable angle scatterometry. The measurements are performed using the commercially available EUV Tech ENK (EUV n/k tool), based on a compact continuously tunable laser-produced plasma light source. In this presentation we describe experiments validating the accuracy and precision of actinic scatterometry-based pattern phase measurements conducted on the ENK platform on seven samples of EUV attenuated phase shift absorbers of varying thickness. We demonstrate good agreement with simulation on measurements of phase vs absorber thickness and phase vs grating pitch, validating the suitability of this measurement for measuring the actinic phase shift of an EUV mask.

Conference Presentation

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Elba Gomar-Nadal, Malahat Tavassoli, Kowtilya Bijjula, Stuart Sherwin, Matt Hettermann, Christian Wilson, Feng Dong, Dave Houser, Alexander Khodarev, Chami Perera, and Patrick Naulleau "Development of EUV phase shift mask metrology", Proc. SPIE 12751, Photomask Technology 2023, 127510O (21 November 2023); https://doi.org/10.1117/12.2688453

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