A liquid-xenon-jet laser-plasma source for extreme-ultraviolet ͑EUV͒ and soft-x-ray generation has been characterized. Being a source candidate for EUV lithography ͑EUVL͒, we especially focus on parameters important for the integration of the source in EUVL systems. The deep-ultraviolet ͑DUV͒ out-of-band radiation ͑ϭ120-400 nm͒ was quantified, to within a factor of two, using a flying-circus tool together with a transmission-grating spectrograph resulting in a total DUV conversion efficiency ͑CE͒ of ϳ0.33%/2sr. The size and the shape of the xenon plasma was investigated using an in-band-only EUV microscope, based on a spherical Mo/Si multilayer mirror and a charge-coupled device detector. Scalability of the source size from 20-270 m full width at half maximum was shown. The maximum repetition-rate sustainable by the liquid-xenon-jet target was simulated by a double-pulse experiment indicating feasibility of Ͼ17 kHz operation. The xenon-ion energy distribution from the plasma was determined in a time-of-flight experiment with a Faraday-cup detector showing the presence of multi-kilo-electron-volt ions. Sputtering of silicon witness plates exposed to the plasma was observed, while a xenon background of Ͼ1 mbar was shown to eliminate the sputtering. It is concluded that the source has potential to meet the requirements of future EUVL systems.
The liquid-xenon-jet laser-plasma source is one of the extreme-ultraviolet (EUV) source technologies under development for EUV lithography. This paper presents some recent improvements of the technology, including the ability to operate a stable plasma at a distance of 50 mm from the nozzle, the first positive mirror-lifetime results, and improved laser-to-EUV conversion efficiency of 0.75 %/(2%BW 2πsr) at λ=13.45 nm.
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