We report on a soft x-ray microscope using a gas-discharge plasma with pseudo spark-like electrode geometry as a light source. The source produces a radiant intensity of 4 x 10(13) photons/(sr pulse) for the 2.88 nm emission line of helium-like nitrogen. At a demonstrated 1 kHz repetition rate a brilliance of 4.3 x 10(9) photons/(microm2 sr s) is obtained for the 2.88 nm line. Ray-tracing simulations show that, employing an adequate grazing incidence collector, a photon flux of 1 x 10(7) photons/(microm2 s) can be achieved with the current source. The applicability of the presented pinch plasma concept to soft x-ray microscopy is demonstrated in a proof-of-principle experiment.
The mechanism of the soft x-ray generation in a pulsed high current discharge is investigated by means of time and space resolved characterization of the extreme ultraviolet emitting regions and discussion of the related electrical circuit parameters. The plasma is ignited in a pseudosparklike electrode geometry. In a discharge of 15 J, stored electrical energy characteristic emission of different gases (oxygen, argon, and nitrogen) is excited in the spectral range from 2 to 5 nm. Special interest is devoted to the 2.88 nm line emission of heliumlike nitrogen ions within the spectral range of the water window to be used for x-ray microscopy. For the nitrogen discharge, an admixture of xenon leads to axial shorter plasma emission as well as to a smaller diameter below 300 μm of the short wavelength emission. Investigation of the xenon related emission in the range of 10–16 nm indicates that radiative cooling is a possible reason for the observed decrease in the radius. Time and spatial resolved images show that the x-ray emission exhibits an axial dynamic in addition to the usual compression occurring in pinch plasmas.
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This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California.
The Semiconductor High-Numerical-aperture (NA) Actinic Reticle Review Project (SHARP) is an extreme ultraviolet (EUV)-wavelength, synchrotron-based microscope dedicated to advanced EUV photomask research. The instrument is designed to emulate current and future generations of EUV lithography (EUVL). The performance of the SHARP microscope has been well characterized for its low-NA lenses, emulating imaging in 0.25 and 0.33 NA lithography scanners. Evaluating the resolution of its higher-NA lenses, intended to emulate future generations of EUV lithography, requires a photomask with features down to 22-nm half pitch. The authors fabricated a sample with features down to 20-nm half pitch, exposing a wafer with a standard multilayer coating in the Berkeley microfield exposure tool, and used it to demonstrate real-space imaging down to 22-nm half pitch on the SHARP microscope. The demonstrated performance of SHARP's high-NA zoneplates, together with the extended capabilities of the tool, provide a platform that is available today, suited for research targeted at upcoming generations of EUVL many years into the future.
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