Long-run-time performance characteristics of a line-selected 2-kHz F2 laser for optical microlithography

Driving optical lithography below the 100nm node is very demanding for optical materials due to the deep ultra-violet radiation to be used. Light sources enabling detailed material studies in the wavelength range of interest are therefore indispensable. For this purpose Gigaphoton Inc. developed a line-selected F 2 laser operating at 2kHz which is based on the well proven technology of its KrF and ArF lasers. The F 2 laser uses a line-selecting module in order to oscillate at the stronger (157.63nm) of the two F2 transition lines emitted under free running conditions (157.52nm and 157.63nm). The laser transition is not line-narrowed resulting in a deconvoluted bandwidth of 0.92pm (FWHM) with a 95% integrated energy width of 2.95pm. The F 2 laser delivers 7.5mJ pulses at 2000Hz with a fluctuation sigma of 3% (50 pulse window). Laser characteristics important for industrial applications and results of durability tests (> 2.5Bpls) will be presented. Discussed laser performance data include laser beam characteristics, especially beam profile and divergence, wavelength and pulse energy stability during gas lifetime cycles as well as the overall laser performance and reliability during a laser-chamber lifetime cycle.