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Roughness characterization of large EUV mirror optics by laser light scattering

: Trost, M.; Schröder, S.; Feigl, T.; Duparre, A.; Tünnermann, A.


Duparre, A. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optical Fabrication, Testing, and Metrology IV : SPIE Optical System Design 2011, 5.-8.9.2011, Marseille, France
Bellingham, WA: SPIE, 2011 (Proceedings of SPIE 8169)
ISBN: 978-0-8194-8795-7
Paper 81690P
Conference "Optical Fabrication, Testing, and Metrology" <4, 2011, Marseille>
Fraunhofer IOF ()
roughness; light scattering; extreme ultraviolet; power spectral density

Optical components for extreme ultraviolet (EUV) lithography at a wavelength of 13.5 nm face tremendous requirements on the surface finish, because large amounts of the EUV light are lost as a result of roughness-induced scattering. In this paper we present a novel approach for the roughness characterization of large EUV mirror optics based on light scattering measurements at a wavelength of 442 nm. The high sensitivity to roughness and the robustness of this method are exemplified for a 660 mm diameter collector mirror substrate. Area covering images of the high-spatial frequency roughness are retrieved which enable a detailed prediction of the EUV reflectance prior to coating. The results are compared to EUV reflectance measurements after coating.