A solid-state 193 nm laser with high spatial coherence for sub-40 nm interferometric immersion lithography

We have developed a solid-state 193-nm laser source operating at 5-kHz that generates a near-diffraction-limited TEM 00 beam with 35 mW average power. The frequency spectrum is Gaussian, with a linewidth ∼7-pm (FWHM), corresponding to a coherence length of ∼2-mm. The output beam also has a very high degree of spatial coherence. This source was used in an interferometric liquid-immersion lithography test stand to produce 40- and 35-nm half-pitch grating structures over a ∼0.6-mm field of view with a commercially available chemically-amplified photoresist.