Applications of compact laser-driven EUV/XUV plasma sources

In recent years, technological developments in the area of extreme ultraviolet lithography (EUVL) have experienced great improvements. So far, intense light sources based on discharge or laser plasmas, beam steering and imaging optics as well as sensitive detectors are available. Currently, applications of EUV radiation apart from microlithography, such as metrology, high-resolution microscopy, or surface analysis come more and more into focus. In this contribution we present an overview on the EUV/XUV activities of the Laser-Laboratorium Göttingen based on table-top laser-produced plasma (LPP) sources. As target materials gaseous or liquid jets of noble gases or solid Gold are employed. Depending on the applications, the very clean but low intense gaseous targets are mainly used for metrology, whereas the targets for high brilliances (liquid, solid) are used for microscopy and direct structuring. For the determination of interaction mechanisms between EUV radiation and matter, currently the solid Gold target is used. In order to obtain a small focal spot resulting in high EUV fluence, a modified Schwarzschild objective consisting of two spherical mirrors with Mo/Si multilayer coatings is adapted to this source. By demagnified (10x) imaging of the Au plasma an EUV spot of 3 μm diameter with a maximum energy density of ~1.3 J/cm2 is generated (pulse duration 8.8 ns). First applications of this integrated source and optics system reveal its potential for high-resolution modification and direct structuring of solid surfaces. For chemical analysis of various samples a NEXAFS setup was developed. It consists of a LPP, using gaseous Krypton as a broadband emitter in the water-window range, as well as a flat field spectrograph. The laboratory system is set to the XUV spectral range around the carbon K-edge (4.4 nm). The table-top setup allows measurements with spectral accuracy comparable to synchrotron experiments. NEXAFS-experiments in transmission and reflection are demonstrated. Beside chemical investigations, also microscopy applications are performed within the XUV spectral range. For this reason a water-window microscope was developed, based on a liquid argon LPP target. The XUV radiation is focused by a Cr/Sc multilayer mirror, leading to spectral narrow band radiation on the sample. For magnifying the sample, a Fresnel zone plate will be used with an outer zone width of 50 nm. Additionally to these applications, an EUV/XUV setup for structural analysis was developed. Using a spectral broad band emitting Xenon gaseous target combined with a grazing incidence optics (Kirkpatrick-Baez arrangement), it offers the possibility to perform angular resolved reflectivity-, diffraction- and scattering experiments as well as NEXAFS analysis in one setup. In completion to these experiments with LPP sources, an EUV/XUV Hartmann-type wavefront sensor has been developed in collaboration with DESY HASYLAB. It consists of a pinhole array, positioned in front of a XUV sensitive CCD camera with quantum converter. With custom-developed software the incident wavefront can be determined. This sensor is currently used at the free electron laser FLASH in Hamburg for beam characterization.