Contamination Evaluation System for Extreme Ultraviolet Mirrors with the Use of Undulator Radiation

A high-intensity extreme ultraviolet (EUV) irradiation and reflectivity measurement system was developed in order to add a contamination inhibition mechanism to Mo/Si multilayer mirrors for EUV lithography. The system can irradiate EUV light at a high flux density of 500 mW/mm2, and it can measure the reflectivity change in situ. As a first experiment using this equipment, irradiation on a Si-capped multilayer was carried out. In this experiment, the water vapor pressure was changed, and changes in the reflectivity were examined. As a result, the decrease in reflectivity increased with an increase in the water vapor pressure. In the meantime, it was indicated that the decrease in reflectivity at an equal dose reversed when the irradiation intensity was lowered using a filter. As a result of surface analysis, the Si-capping layer was oxidized in the irradiation area, and there was deposition of C in the outer part of the irradiation area.