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Proceedings Paper

Measuring the Phase of EUV Photomasks
Author(s): Stuart Sherwin; Isvar Cordova; Laura Waller; Andrew Neureuther; Patrick Naulleau
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Paper Abstract

We demonstrate complementary reflectometry and scatterometry methods to measure the phase and amplitude of a patterned EUV photomask at its operating wavelength (13.5nm) and angle range (2 − 10°). We carried out experimental measurements at ALS Reflectometry and Scattering Beamline 6.3.2 on an EUV photomask with a 40-bilayer MoSi multilayer mirror and 60nm TaN absorber. We took three types of measurements: reflectometry for blank multilayer, reflectometry for blank absorber-coated multilayer, and scatterometry for line- space gratings. We used the reflectometry data to fit the Fresnel reflectance amplitude by adjusting the thickness, atomic density, and interface roughness of multilayer and absorber layers. We then fit the scatterometry data using a thin-mask approximation. The advantage of reflectometry is the higher level of model fidelity (2 − 4% vs 6% − 15% error), whereas the advantage of scatterometry is its direct sensitivity to relative phase through spatial interference. Despite differences between the two approaches, both gave similar phase values, mutually-consistent to within π/51 RMS. We observe the phase to vary from 0.78μ at 2° to 0.88μ at 10°, suggesting that engineering phase effects to improve image contrast will need to consider phase values across a range of illumination angles rather than simply the chief ray.

Paper Details

Date Published: 11 November 2019
PDF: 11 pages
Proc. SPIE 11147, International Conference on Extreme Ultraviolet Lithography 2019, 111471F (11 November 2019); doi: 10.1117/12.2538107
Show Author Affiliations
Stuart Sherwin, Univ. of California, Berkeley (United States)
Isvar Cordova, The Ctr. for X-Ray Optics, Lawrence Berkeley National Lab. (United States)
Laura Waller, Univ. of California, Berkeley (United States)
Andrew Neureuther, Univ. of California, Berkeley (United States)
Patrick Naulleau, The Ctr. for X-Ray Optics, Lawrence Berkeley National Lab. (United States)


Published in SPIE Proceedings Vol. 11147:
International Conference on Extreme Ultraviolet Lithography 2019
Toshiro Itani; Paolo A. Gargini; Patrick P. Naulleau; Kurt G. Ronse, Editor(s)

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