Radiation-induced defect formation and reactivity of model TiO_2capping layers with MMA: a comparison with Ru

摘要

Our goal is to provide insights into surface processes that affect the reflectivity and lifetimes of TiO_2 and Ru-capped multilayer mirrors used in extreme ultraviolet (EUV) lithography. Several surface-sensitive ultrahigh-vacuumtechniques are used to characterize thermally-induced and electron-induced surface reactions of methyl methacrylate(MMA), a model for hydrocarbons found in EUV lithography vacuum chambers; low-energy electron beams are used tomimic excitations initiated by EUV radiation. Carbon film growth is measured on TiO_2 surfaces during electronbombardment (at 20 eV and 100 eV) in MMA vapor; C growth rates are compared on Ru surfaces. The initial rates onthe clean surfaces are very different: a C film grows more rapidly on TiO_2 than on Ru. However, the limiting growthrates are the same for C thicknesses greater than ~1 to 1.5 nm, when MMA interacts with a C film. Irradiation of the Cfilms in O_2gas, or in MMA + O_2, has a mitigating effect on TiO_2gas, or in MMA + O_2, has a mitigating effect on TiO_2surfaces.