We have developed the reflectometer to evaluate EUV mirrors and masks at BL-10 beamline of NewSUBARU synchrotron light facility. This reflectometer usually measures s-polarized reflectance. Reflectance of an EUV mirror is strongly depends on polarization state of incident light, if angle of incidence to the sample is not normal. The center radiation from a bending source of a synchrotron source is almost horizontally polarized. However, there was several percent of vertical polarized component at the center radiation on NewSUBARU. For accurate reflectometry, a horizontal-polarization control unit (PCU) has been developed to remove the unnecessary vertically-polarized EUV component. This unit consisted of two reflection polarizer mirrors coated with aperiodic Mo/Si broadband multilayer, which multilayer was coated in our laboratory. Using this unit, degree of horizontal polarization was improved to be 1.00. In addition, vertical-PCU has been developed for p-polarized reflectance measurement. There is vertical polarized light component on off-axis radiation from the bending source. This vertical-PCU also generated the fully-verticalpolarized light. As the results, the reflectometer measures accurate s- and p-polarized reflectance without setup change of the sample stage and the detector stage.
Tetsuo Harada and Takeo Watanabe, "Reflectance measurement of EUV mirrors with s- and p-polarized light using polarization control units," Proc. SPIE 10809, International Conference on Extreme Ultraviolet Lithography 2018, 108091T (Presented at SPIE Photomask Technology + Extreme Ultraviolet Lithography: September 18, 2018; Published: 3 October 2018); https://doi.org/10.1117/12.2502009.
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