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Triggered by the roadmap of the semiconductor industry, tremendous progress has been achieved in the development of Extreme Ultraviolet (EUV) sources and high-quality EUV optical coatings in recent years, opening up also new fields of applications apart from microlithography, such as metrology, high-resolution microscopy, or surface analysis. In all these research areas the quality and imaging properties of the employed optics play a crucial role. In this contribution we present a comparison of different optical setups capable of guiding and imaging EUV radiation, which were tested in combination with a miniaturized laser-produced plasma source with high pulse energy (~ 3.5 mJ @ 13.5 nm) and a plasma size of about 300 μm.
First, a modified EUV Schwarzschild objective with a numerical aperture of 0.44 and a demagnification factor of 10 was developed within the research project "KOMPASS". After adaptation to the table-top EUV source, a focus with a diameter < 30 μm at energy densities of several mJ/cm2 could be produced. The setup is currently being used for comparative investigations of the interaction of EUV radiation with different materials, as e.g. the color center formation in LiF crystals. An attempt to use the Schwarzschild objective in reverse geometry as a EUV microscope will be part of future work.
Second, a Kirkpatrick-Baez arrangement was realized, using the reflections from two curved silicon wafers under grazing incidence (about 5°). The cylindrical curvature is obtained by bending the thin substrates, allowing for a continuous tuning to the desired radii. Due to an Au coating a high reflectivity (theoretically ~ 80 % per reflection) over a broad EUV spectral range can be achieved.
For reduction of aberrations the optical systems were fine-adjusted with the help of a Hartmann-Shack wavefront sensor both in the visible and in the EUV spectral range. The imaging properties in the EUV range were determined and compared to ray tracing calculations performed with ZEMAX.
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