Polarization resolved measurements with the new EUV Ellipsometer of PTB

After having developed metrology with synchrotron radiation at the storage rings BESSY I and BESSY II for more than 25 years, particularly also for the characterization of EUV optical components and detectors, PTB extended its capabilities for EUV metrology with respect to polarization resolved measurements, particularly in the spectral region around 13.5 nm. With the development of larger numerical aperture optics for EUV and advanced illumination concepts for lithographic imaging, the polarization performance of the optical elements and EUV photomasks with respect to high-NA EUV imaging becomes ever more important. At PTB, we use monochromatized bending magnet radiation for the characterization of the optical elements because of the superior temporal stability and rapid tuneability of the wavelength. Thus the polarization of the radiation is almost linear, depending on the vertical beamline acceptance angle, and cannot be manipulated. Therefore, we decided to equip the soft X-ray beamline which delivers particularly well collimated and highly linearly polarized radiation with a sample manipulator which allows freely setting the orientation of the plane of deflection. Thus we are able to characterize samples in any orientation with respect to the linear polarized direction. We additionally can add a linear polarization analyzer working with a rotatable Brewster reflector to analyze the state of polarization of the reflected beam. We present first results on the polarization properties of EUV multilayer mirrors close to the Brewster angle where polarization selectivity up to s10(4) is predicted from model calculations. We also present polarization resolved measurements of the EUV diffraction of absorber line patterns at EUV photomasks.