Proceedings Article | 18 May 2009
KEYWORDS: Extreme ultraviolet, Plasma, Solids, Gold, Mirrors, Wavefronts, Liquids, Laser applications, Reflectivity, Extreme ultraviolet lithography
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.
