Optimizing CD-SEM metrology for anamorphic high-NA EUV photomasks

Deepan Kishore Kumar; Varun Mohan; Hatsey W. Frezghi; Adam A. Seeger; Malahat Tavassoli; Masayuki Kuribara; Kiyoshi Oura; Wataru Ito; Soichi Shida; Tatsuro Okawa; Mark A. Sheppard; Toshimichi Iwai

doi:10.1117/12.2687660

21 November 2023 Optimizing CD-SEM metrology for anamorphic high-NA EUV photomasks

Deepan Kishore Kumar, Varun Mohan, Hatsey W. Frezghi, Adam A. Seeger, Malahat Tavassoli, Masayuki Kuribara, Kiyoshi Oura, Wataru Ito, Soichi Shida, Tatsuro Okawa, Mark A. Sheppard, Toshimichi Iwai

Author Affiliations +

Proceedings Volume 12751, Photomask Technology 2023; 127510R (2023) https://doi.org/10.1117/12.2687660
Event: SPIE Photomask Technology + EUV Lithography, 2023, Monterey, California, United States

Abstract

Anamorphic High-Numerical Aperture (NA) EUV photomask manufacturing presents some unique challenges and opportunities in Critical dimension (CD) Scanning electron microscope (SEM) metrology. Novel methods of beam scanning condition are needed to improve image resolution and reduce image blurring to enable reliable metrology for the curvilinear mask era. Additionally, electron optics stigmation monitoring plays a major role in ensuring the horizontal to vertical (X-Y) CD Average to target (ATT) tool matching is not drifting due to aberrations, which are key for anamorphic EUV mask metrology. In this paper, we show the correlation between offsets in Condenser lens, Aperture balance, and electron beam Stigmation offset and its impact on horizontal and vertical feature CD ATT and CD uniformity measurements. Using Advantest E36xx Scanning electron microscopes we also present preliminary results, from improving measurement repeatability (ATT and CDU) on different mask substrates by incorporating Shadow reduction scanning (SRS), enhanced charge suppression using Charge neutralization technology and modulating dose of the beam (which is a function of scan condition and beam condition) In conclusion, we summarize the key metrology advances needed for next generation CD-SEM tools for High NA EUV photomask metrology, such as automated column optics monitoring, shadow reduction scan, design-based site focusing, high degree of measurement precision better than 0.5 nm, charge mitigation capabilities, high Throughput (TPT), enhanced stage performance accuracy, among others.

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(2023) Published by SPIE. Downloading of the abstract is permitted for personal use only.

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Deepan Kishore Kumar, Varun Mohan, Hatsey W. Frezghi, Adam A. Seeger, Malahat Tavassoli, Masayuki Kuribara, Kiyoshi Oura, Wataru Ito, Soichi Shida, Tatsuro Okawa, Mark A. Sheppard, and Toshimichi Iwai "Optimizing CD-SEM metrology for anamorphic high-NA EUV photomasks", Proc. SPIE 12751, Photomask Technology 2023, 127510R (21 November 2023); https://doi.org/10.1117/12.2687660

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