Compact source and beam delivery system for EUV radiation

摘要

We report on design, testing and first applications of an integrated EUV source and beam delivery system, composed of a miniaturized laser-produced plasma source with high pulse energy (～3.5 mJ @ 13.5 nm) and a modified EUV Schwarzschild objective with a numerical aperture of 0.44 and a demagnification of 10x. The objective consists of two spherical ULE substrates coated with Mo/Si multilayers (reflectivity ～ 65% @ 13.5 nm). After adaptation to the table-top EUV source, a focus with a diameter < 30 μm at energy densities of up to 100 mJ/cm~2 in a single pulse could be produced by demagnified imaging of the laser plasma. For reduction of aberrations the optical system was fine-adjusted with the help of a Hartmann-Shack wavefront sensor in the visible spectral range. The EUV imaging properties were determined and compared to ray-tracing calculations. 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, or photo-ablation studies in polymers, in particular PMMA.