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Roughness characterization of EUV multilayer coatings and ultra-smooth surfaces by light scattering

: Trost, Marcus; Schröder, Sven; Lin, C.C.; Duparré, Angela; Tünnermann, Andreas


Assoufid, Lahsen (Ed.) ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Advances in Metrology for X-Ray and EUV Optics IV : SPIE Optics + Photonics, 12.-16.8.2012, San Diego, CA, USA
Bellingham, WA: SPIE, 2012 (Proceedings of SPIE 8501)
ISBN: 978-0-8194-9218-0
Paper 85010F
Conference "Advances in Metrology for X-Ray and EUV Optics" <4, 2012, San Diego/Calif.>
Fraunhofer IOF ()
EUV optic; roughness; power spectral density; HSFR; multilayer coating; light scattering

Optical components for the extreme ultraviolet (EUV) face stringent requirements for surface finish, because even small amounts of surface and interface roughness can cause significant scattering losses and impair image quality. In this paper, we investigate the roughness evolution of Mo/Si multilayers by analyzing the scattering behavior at a wavelength of 13.5 nm as well as taking atomic force microscopy (AFM) measurements before and after coating. Furthermore, a new approach to measure substrate roughness is presented, which is based on light scattering measurements at 405 nm. The high robustness and sensitivity to roughness of this method are illustrated using an EUV mask blank with a highspatial frequency roughness of as low as 0.04 nm.