Protection from Surface Oxidation of Ru Capping Layers for EUVL Projection Optics Mirrors by Introducing Hydrocarbon Gas

We investigated the protection of a Ru-capped Mo/Si multilayer from surface oxidation under exposure to EUV radiation in the presence of water vapor and isopropyl alcohol (IPA). Degradation of the reflectance of the Ru-capped Mo/Si multilayer by EUV irradiation was controlled by introducing IPA gas. We also investigated the reduction effect of the oxide layer in a multilayer mirror by introducing ethanol and exposed EUV. The Ru-capped multilayer sample was exposed to EUV radiation in the presence of only water vapor to oxidize its surface. The reflectance decreased by about 1.5%. Then the sample was exposed to EUV radiation in the presence of only ethanol vapor. The reflectivity of the sample was recovered to +0.5%, and the atomic concentration of oxygen in the irradiated area was decreased by EUV irradiation in the presence of ethanol.