Competitive reactions of carbon deposition and oxidation on the surface of Mo/Si multilayer mirrors by EUV irradiation

Three experiments were carried out to investigate carbon deposition and its mitigation on the surface of Mo/Si multilayer mirrors by EUV irradiation with the introduction of water vapor. In the first experiment of carbon deposition by EUV irradiation in the presence of n-decane gas as a hydrocarbon source, the reflectivity dropping rate of the multilayer mirror increases with increasing the n-decane pressure. In the second experiment of removing once-deposited carbon film by introducing water vapor, the carbon film was partly removed by EUV irradiation in the presence of water vapor. In the third experiment of carbon deposition mitigation by EUV irradiation in the coexistence of n-decane and water vapor, it was observed that carbon film deposition was mitigated by controlling the water vapor pressure. However, the mitigation effect on carbon deposition was not uniform for the EUV intensity, and a large non-linear dependency on the irradiation flux was observed.