19 October 2012 Roughness characterization of EUV multilayer coatings and ultra-smooth surfaces by light scattering
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Abstract
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.
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M. Trost, S. Schröder, C. C. Lin, A. Duparré, A. Tünnermann, "Roughness characterization of EUV multilayer coatings and ultra-smooth surfaces by light scattering", Proc. SPIE 8501, Advances in Metrology for X-Ray and EUV Optics IV, 85010F (19 October 2012); doi: 10.1117/12.929887; https://doi.org/10.1117/12.929887
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