Masahiko Kowaka

Stability of krypton fluoride laser in real stepper mode operation

The stable performance of the line-narrowed Krypton Fluoride Excimer Laser for production steppers, the KLES-G6, in real stepper mode operation is presented. Wavelength stability of < +/- 0.1 pm and pulse-to-pulse energy stability of < 2% ((sigma) ) were achieved in the real stepper mode operation. Further the durability test was made at 6 W(10 mJ, 600 Hz) in 1 sec. ON - 1 sec. OFF (50%) burst mode and in cw mode. The central wavelength stability < +/- 0.2 pm including the drift at the head of burst, spectral bandwidth < 1.5 pm, and pulse-to-pulse energy stability < 2.5% ((sigma) ) over 1.6 X 109 shots were achieved. The KLES-G6 will assist us to utilize the excimer stepper in real commercial production successfully.

Narrow band KrF excimer laser for mass production of ULSI ICs

A narrow band KrF excimer laser system for lithography has been developed. Its durability has been proved up to 2 billion shots that correspond to one year operation in mass production line. The system has kept the average power of 6W with the power stability within +- 3% and the spectral line-width 1.2 pm (FWHM) with the wavelength stability within +- 0.2 pm. The integration of the spectrum has indicated that 95% of the spectral energy lay inside 4.6 pm band during 2 billion shots

High-average-power narrow-band KrF excimer laser

The conventional line-narrowing methods employed by narrow-band KrF excimer lasers are (1) intracavity etalons and (2) a Littrow grating with beam expansion. They have the following problems in high average power operation: (a) short lifetime of the etalons and large wavelength drift and large line-width change (the etalons method), or (b) low output power and short lifetime of electrodes (the grating method). To solve there problems, a hybrid method consisting of two prism beam expanders, an etalon and a Littrow grating, it proposed. These prism beam expanders decrease the light intensity on the etalon, so that the lifetime of the etalon is increased drastically, the passive wavelength drift is minimized, and the wavelength is adjusted quickly. By employing this system, average power of more than 8 W, line-width of less than 2.5 pm(FWHM), and long-term wavelength stability of less than +-0.5 pm were achieved.

Recent advances of a KrF excimer laser on a plant's practical requirements

In this paper we describe the performance of the newest model of line-narrowed KrF excimer laser KLES-G6 (1995 model) developed in factory on the practical requirements. The KLES- G6 exhibits: (1) spectral bandwidth < 0.8 pm; (2) wavelength stability < +/- 0.1 pm; (3) pulse-to-pulse energy stability < 1.8% ((sigma) ); (4) output power equals 6 W at 600 Hz; (5) gas life > 100 million pulses or 7 days; (6) window cleaning or exchange > 1 billion pulses; (7) laser chamber exchange > 2 billion pulses; (8) mean time between failures > 1500 hours; (9) running cost per a billion pulses is about 29 thousand dollars. These advanced performances will save the running cost and guarantee the high uptime ratio needed to satisfy the plants practical requirements.