Surface morphology change of protective film on collector mirror related to implantation of Sn emitted from laser produced plasma in EUV light source

The change in surface morphology of an amorphous TiO2 protective film coated on a Mo/Si multilayer of an extreme ultraviolet (EUV) light collector mirror has been investigated. After long-time operation of an EUV light source, many pinholes of about 10 nm diameter were observed on the protective TiO2 film surface. Accelerated aging tests with thin film samples that simulated surface conditions on the collector mirror suggest that crystallization of the protective film induced by Sn implantation is the main cause of the formation of the observed pinholes.