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8 April 2011 Damage testing of EUV optics using focused radiation from a table-top LPP source
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As a consequence of the steadily increasing EUV powers and radiation doses, damage and degradation testing of EUV optical elements has become an important issue. In this contribution we report on first damage tests on optics and detectors for the wavelength of 13.5nm using a high fluence micro-focus from a laboratory-scale EUV source. The setup consists of a laser-generated plasma from a pulsed gaseous Xenon jet or a solid Au target, respectively. In order to obtain a small focal spot resulting in a high EUV fluence, a modified Schwarzschild objective consisting of two spherical mirrors with Mo/Si multilayer coatings is adapted to the source, simultaneously blocking unwanted out-of-band radiation. By demagnified (10x) imaging of the Au plasma an EUV spot of 5 μm diameter with a maximum energy density of ~1.3 J/cm2 is generated at a wavelength of 13.5 nm and a pulse width of 8.8 ns. We demonstrate the potential of this integrated source and optics system for damage testing on EUV optical elements and sensoric devices. As an example, single pulse ("1-on-1") and multiple pulse ("S-on-1") damage thresholds were determined for Mo/Si multilayer mirrors, using both on-line optical microscopy, interferometry and atomic force microscopy for damage detection. The data are compared with in-situ measurements of the reflectivity change at 13.5nm. Moreover, thin metal coatings (Gold) used as grazing incidence mirrors were irradiated. Threshold energy densities for damage and film removal were determined, showing a linear dependence on the film thickness. Furthermore, EUV-to-VIS quantum convertors (Ce:YAG crystals, phosphor coatings) employed for beam characterization were investigated in terms of linearity, saturation behavior and conversion efficiency.
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K. Mann, F. Barkusky, A. Bayer, and S. Döring "Damage testing of EUV optics using focused radiation from a table-top LPP source", Proc. SPIE 7969, Extreme Ultraviolet (EUV) Lithography II, 796926 (8 April 2011);

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