Optical exposure characterization and comparisons for discharge produced plasma Sn extreme ultraviolet system

Abstract

A critical issue for EUV lithography EUVL is the minimization of collector degradation from intense plasma erosion, debris deposition, and hydrocarbon/oxide contamination. Collector optics reflectivity and lifetime heavily depend on surface chemistry and interactions between fuels and various mirror materials, such as silicon, in addition to high- energy ion and neutral particle erosion effects. As a continuation of our prior investigations of discharge-produced plasma DPP and laser- produced plasma LPP Xe plasma interactions with collector optics sur- faces, the University of Illinois at Urbana-Champaign UIUC has ana- lyzed collector samples before and after exposure in a Sn-upgraded Xtreme Technologies EUV source. Sn DPP postexposure characteriza- tion includes multiple samples, Si/Mo multilayer film with normal inci- dence, 200-nm-thick Ru film with grazing incidence, as well as a Gibb- sian segregated GS Mo-Au alloy developed on silicon using a dc dual- magnetron cosputtering system at UIUC for enhanced surface roughness properties, erosion resistance, and self-healing characteris- tics to maintain reflectivity over a longer period of mirror lifetime. Surface analysis draws heavily on the expertise of the Center for Microanalysis of Materials at UIUC, and investigates mirror degradation mechanisms by measuring changes in surface roughness and film thickness as well as analysis of deposition of energetic Sn ions, Sn diffusion, and mixing of multilayer. Results from atomic force microscopy AFM and auger elec- tron spectroscopy AES measurements show exposure effects on sur- face roughness and contamination. The best estimates of thickness and the resultant erosion measurements are obtained from scanning electron microscopy SEM. Deposition, diffusion, and mixing effects are ana-