Motohiro Arai

High-Energy Subnanosecond Compact Laser System with Diode-Pumped, Q-Switched Nd:YVO4 Laser

For a high-precision laser photomask repairing system, we have developed a high-energy, subnanosecond compact laser, consisting of a diode-pumped Q-switched Nd:YVO4 laser with 700 ps, TEM00, 0.76 mJ/pulse (1.1 MW) at 1064 nm. Using a MOPA system by a Xe-flashlamp-pumped Nd:YAG amplifier, we have obtained an output laser pulse of 700 ps, 12 mJ/pulse.

High-repetition-rate ArF excimer laser for 193-nm lithography

A line-narrowed excimer laser has been developed for use as a light source for DUV microlithography using a refractive lens system. We report on a newly developed 3000 Hz ArF excimer laser with a long duration pulse. The laser has the following specifications: 15W average power, 0.45 pm FWHM bandwidth, 1.5 pm spectral bandwidth at 95 percent integrated energy, and 7 percent energy stability of 3 sigma at 3000 Hz. The integral-square pulse width is longer than 45 ns during a single gas fill more than 50 million pulses. We also report on a 4000 Hz excimer laser, under development.

Long gas-lifetime operation of an ArF excimer laser

An experimental investigation to improve the lifetime of a discharge-excited ArF-excimer laser is presented. The three dominant factors restricting its lifetime are CF4 generation in the laser gas, color-center formation in the optics and input power density reduction due to electrode ablation. Copper electrodes were superior to nickel electrodes in regard to electrode ablation. A gas lifetime of more than 109 shots (about one month at 400 Hz) is shown for an ArF-excimer laser with a liquid-nitrogen trap and high-temperature zirconium alloy trap.

Ultrahigh-repetition-rate ArF excimer laser with long pulse duration for 193-nm lithography

High-repetition-rate ArF excimer lasers are needed to enable high throughput and energy-dose stability in 193-nm scanner systems. Last year we described a 4-kHz ArF excimer laser with long pulse duration, which can narrow the spectral bandwidth by increasing the number of round trips and reduce optical damage from low-peak power. The design of the 4-kHz ArF excimer laser has been improved for mass production. Operating rates exceeding 4 kHz are needed to optimize lasers for next-generation technologies that can enable high NA and the development of high-throughput scanners. We have analyzed the possibilities of achieving repetition rates higher than 4 kHz. The discharge width was reduced by about 25 % with a variation of the electric field at the discharge section, and the gas flow and gas-mixture conditions were improved. As a result, we obtained the following performance characteristics: 42-W average power, 3.5 % pulse-to-pulse energy stability of sigma, and a 44-ns integral-square pulse width at 6 kHz with a bandwidth of below 0.45 pm in FWHM. We concluded that developing 6-kHz ArF excimer lasers for next-generation 193-nm lithography is feasible.

Line-narrowed ArF excimer laser for 193 nm lithography

Recently, considerable progress has been made in the development of ArF excimer lasers for 193 nm lithography. A line-narrowed ArF excimer laser with a bandwidth of < 0.7 pm can be used with a refractive lens system. In this paper, we present a line-narrowed ArF excimer laser which we have developed for 193 nm lithography. This laser produces an output power of over 5 W with a 0.6 pm FWHM bandwidth at 1 kHz operation.