Coatings for next generation lithography

The latest generation of 193nm immersion lithography optics, with a numerical aperture (NA) of 1.35 and ultra pure water as immersion fluid serves the 45nm node on the ITRS roadmap. The potential solutions for the next step, the 32nm node, as presented in December 2007 by the ITRS are: 193nm double patterning / exposure, 193nm with 2^nd generation fluid and EUVL. The performance of such next generation lithography optics is increasingly driven by the coating performance. For 193nm the performance of the antireflection and high reflection coatings is driven by the increasing NA, which requires the control of polarisation effects and transmission uniformity over light incidence angles. For EUV only high reflection coatings are needed and the NA is comparatively small. But the performance is limited by higher absorption and lower refractive index contrasts of the applicable coating materials at 13.5nm with respect to 193nm. In this talk we discuss and compare the different requirements and challenges in coating material, design, process, lifetime and accuracy for next generation lithography optics.