Akifumi Tada

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.

Ultranarrow-bandwidth 4-kHz ArF excimer laser for 193-nm lithography

We have developed a 4-kHz ArF excimer laser with ultra-narrow bandwidth, which is applicable to high-NA scanners for sub-0.13-micrometers microlithography. In this paper, we describe a 4-kHz ArF excimer laser for mass production: the model G40A, which has an output power of 20 W and energy dose stability of less than +/- 0.3% (20-ms window) at 4 kHz. This dose stability is comparable to the performance of an existing 2-kHz ArF excimer laser, the model G20A. The new laser also has the following specifications: a long pulse duration of over 40 ns, spectral bandwidth of less than 0.35 pm (FWHM), and spectral purity of less than 1.0 pm (95%). These characteristics are better than those of the G20A. A lifetime test of over 7 billion pulses has been conducted at 4-kHz operation. The new laser has maintained an energy dose stability of less than +/- 0.3% (20-ms windows) and demonstrated performance suitable for mass production even after over 7 billion pulses.

Monochromatic Projection Optical System for ArF Excimer Laser Lithography

We have developed an ArF excimer laser exposure system that combines a monochromatic quartz projection lens system and a spectrally-narrowed ArF excimer laser. The bandwidth of the laser was narrowed to 0.7 pm by using three prisms and an etalon. We delineated 0.2 µm lines-and-spaces using a chemically amplified resist and 0.16 µm lines-and-spaces using a top surface imaging resist.

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.

Long pulse duration of F2 laser for 157-nm lithography

An ultra narrow line width of the F2 laser, narrower than 0.2pm, is required for a CaF2 only refractive optics exposure system. Also, a low peak laser power is needed for the extension of the optics lifetime. These ultra narrow line width and low peak power are achievable by long pulse duration. We, Association of Super-Advanced Electronics Technologies (ASET), are developing an ultra line narrowed F2 laser below 0.2pm, with 5mJ high output energy, by adopting a 2-stage F2 laser system, which consists of an oscillator and an amplifier. The oscillator for this 2-stage system is required to have an ultra narrow line width of below 0.2pm. We have developed F2 laser with very long laser pulse duration of over 65ns (Tis: the integral squire pulse width), in a free running operation. And, by installing a line-narrowing module (LNM) in this F2 laser, an ultra narrow line width of below 0.2 pm (FWHM, deconvolved) has been realized. This F2 laser was successfully used for the oscillator of 2-stage system.

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.

ArF excimer laser lithography using monochromatic projection lens coupled with narrowed-bandwidth laser

We have developed an ArF excimer laser exposure system that combines a monochromatic quartz projection lens system and a spectrally-narrowed ArF excimer laser. The bandwidth of the laser was narrowed to 0.7 pm by using three prisms and an etalon. We fabricated 0.12 micrometers lines-and-spaces using an alternating phase shifting mask and a top surface imaging resist.

A new gas purifier for ArF excimer lasers

We have developed a new gas purifier for ArF excimer lasers that can remove all the impurities from degraded ArF excimer laser gas. We found that cooled activated charcoal at temperatures below −50 °C effectively removes CF4, which is the preponderant impurity generated in ArF excimer laser gas mixtures. We also demonstrated that the new gas purifier can regenerate the ArF excimer laser gas up to its initial purity level after about 1×109 shots of operation.

1 kHz high repetition rate, compact ArF excimer laser and its applications

A 1 kHz operation for an ArF excimer laser has been achieved with a compact laser system. The average output power and the electrical efficiency are 13 W and 0.83%, respectively. The clearing ratio is measured to be 3.2. A spectrally narrowed ArF excimer laser for lithography experiments has also been developed on the basis of the design for the compact ArF excimer laser. A spectral bandwidth of 0.7 pm and a pulse energy of 5 mJ/pulse is obtained.