Development of EUV light source by CO₂ laser-produced Xe 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 and a Xe cryogenic 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 about 0.1 % per 2π 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.