Ion damage analysis on EUV collector mirrors

Abstract

Collector mirror lifetime evaluation and damage prevention are important technical challenge for the EUV light source development. High-energy xenon ions emitted from laser-produced EUV plasmas are expected to considerably damage the collector mirror of the light source. Related to future collector mirror lifetime considerations, fast ions from the laserproduced plasma have been characterized by time-of -flight (TOF) measurements. Using a low repetition rate 8-ns, 100- mJ Nd:YAG laser, Xe⁺ to Xe⁶⁺ ions were observed with Xe²⁺ being the main charge state. In addition, the effects of fast ions on Mo/Si multilayer mirrors have been studied using a Xe ion gun. Ion sputtering of the multilayer structure is the main damage mechanism but layer boundary mixing and surface roughness increase are also observed. A magnetic confinement scheme is evaluated for ion mitigation.