Marathon testing of optical materials for 193-nm lithographic applications

We have undertaken a systematic evaluation of both bulk materials and optical coatings designed for 193-nm lithographic applications. These studies are performed at realistic fluences (<1 to several mJ/cm(2)/pulse) and pulse counts in excess of 10(9). Measurements of absorption in fused silica show a large variation in performance for different samples in both initial and laser-induced absorption. Calcium fluoride samples show less variation in laser-induced absorption and appear to be more stable under irradiation of 0.2-1 billion pulses. Laser-induced densification of fused silica appears to follow an empirical power law; however, an order of magnitude spread in densification is observed among grades. For optical antireflectance coatings, we have characterized the initial "laser-cleaning" phenomenon for various coatings. We have observed that laser-cleaned coatings deposited on CaF2 substrates exhibit higher initial optical losses at 193 ma than their counterparts on SiO2 substrates. However, the losses for coatings on CaF2 substrates are reduced over irradiation times of 0.2-1 billion pulses to final values comparable to their SiO2 counterparts. Finally, we have characterized various catastrophic failures of coating material, such as induced losses, adhesion failure and laser-induced thinning.