Emission characteristics of EUV light source by CO2 laser-produced Xe and Sn plasma

We propose CO2 laser-produced plasma as the extreme ultraviolet (EUV) light source for future optical lithography. The laser beam from a transversely-excited atmospheric (TEA) CO2 laser (4 J, 50 ns FWHM) was focused on a Xe gas target, a Xe cryogenic target and a nano-structured tin-based target to generate EUV radiation around 13.5 nm. The EUV pulse of about 100 ns in FWHM was measured 50 ns after the CO2 laser irradiation. The EUV spectra were measured by an X-ray CCD camera with a transmission grating spectrograph (TGS). A characteristic EUV spectrum was observed from CO2 laser produced Xe plasma. The EUV energy was measured by a Flying Circus II detecting system and an output energy of 3 mJ/pulse and a conversion efficiency of 0.2% per 2pi sr at 13.5 nm (2% B.W.) were obtained with Xe targets. These values are comparable to those of YAG laser-produced Xe plasma, indicating the potential scalability of the EUV light source using a CO2 laser produced plasma.