High-repetition-rate (6 kHz) and long-pulse-duration (50 ns) ArF excimer laser for sub-65 nm lithography

Development of high-repetition-rate ArF excimer lasers is vital requirement for achieving high throughput and high energy-dose stability in a scanner system. ArF excimer laser, with increasing light pulse duration, can reduce the peak power without the energy-dose change. Then, the spectral bandwidth Δλ_FWHM becomes narrower by increasing the number of light round trips in a cavity, and optical damage is reduced from high-peak power. Laser operation exceeding 4 kHz is needed for next-generation technologies that can enable high numerical aperture and development of high-throughput scanners. In the present work, we examined the possibilities of achieving a repetition rate to 6 kHz from 4 kHz in the ArF laser the authors developed, taking the following innovations. The spatial width of discharge region was reduced by about 30%. The uniform gas flow condition between the electrodes was obtained by improving gas flow guides. As a result, we have obtained an average power of 42 W, a standard deviation for pulse-to-pulse energy of 3.5%, and an integral-square pulse width T_is of 44 ns at 6 kHz for Δλ_FWHM≪0.40 pm. Finally, it was concluded that developing a 6 kHz ArF excimer laser for the next-generation sub-65 nm lithography is feasible.