18 March 2016 Improved Ru/Si multilayer reflective coatings for advanced extreme-ultraviolet lithography photomasks
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Extreme ultraviolet (EUV) lithography with reflective photomasks continues to be a potential patterning technology for high volume manufacturing at the 7 nm technology node and beyond. EUV photomasks with alternative materials to the commonly used Mo/Si multilayer (ML) reflector and patterned Ta-based absorber (both of which are known to require shadow effect corrections and lead to large through-focus pattern placement errors) are being actively explored. Because the reflective bandwidth of a Ru/Si ML is significantly wider than the reflective bandwidth of a Mo/Si ML and the effective reflectance plane in Ru/Si is closer to the ML surface, Ru/Si ML coatings may be viable alternatives to the Mo/Si ML coatings that are commercially available today because they will lead to smaller mask 3D effects. In this paper, increases in the peak reflectivity and the reflective bandwidth of Ru/Si ML reflectors by using B4C interlayers to improve the Ru-Si interfaces are discussed. The conclusions of this paper are supported with the results of both experimental measurements and rigorous simulations.
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Obert Wood, Keith Wong, Valentin Parks, Patrick Kearney, Julia Meyer-Ilse, Vu Luong, Vicky Philipsen, Mohammad Faheem, Yifan Liang, Ajay Kumar, Esther Chen, Corbin Bennett, Bianzhu Fu, Michael Gribelyuk, Wayne Zhao, Pawitter Mangat, Paul Van der Heide, "Improved Ru/Si multilayer reflective coatings for advanced extreme-ultraviolet lithography photomasks", Proc. SPIE 9776, Extreme Ultraviolet (EUV) Lithography VII, 977619 (18 March 2016); doi: 10.1117/12.2219215; https://doi.org/10.1117/12.2219215

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