Development of kHz F/sub 2/ laser for 157 nm lithography

We have been developing a high repetition rate discharge-pumped molecular fluorine laser for 157 nm microlithography. We have developed a high repetition rate solid state pulsed power module (SSPPM) up to 800 Hz. This laser adopts a stable resonator composed of a MgF/sub 2/ high reflection plane mirror and a MgF/sub 2/ output coupler, which show high transmittance and durability for VUV light. To avoid attenuation of the 157 nm radiation due to the absorption of O/sub 2/, all the optical path including optics and detectors are continually flushed by pure nitrogen at least below 100 ppm O/sub 2/ concentration.