Cleaning of extreme ultraviolet lithography optics and masks using 13.5nm and 172nm radiation

Under extreme ultraviolet (EUV) exposure, the surfaces of the imaging optics and mask, which are coated with a Mo∕Si multilayer, become contaminated with organic compounds. Thus, an efficient method of removing carbon contamination from masks and the imaging optics is required. Then, we propose two methods as a removal method of contamination: one is in situ cleaning method without heating a sample by synchrotron radiation irradiation that is mainly targeted at the imaging optics, and another is cleaning method without heating a sample using by 172nm light irradiation that is targeted at an EUV lithography finished mask. For in situ cleaning so called online cleaning, the contamination removal rate is 0.24nm∕min in the condition of O2-rich-vacuum environment at a pressure of 5.0×10−2Pa and an electron beam current of 130mA of 1.0GeV electron storage ring. For offline cleaning using 172nm light, the contamination removal rate is 2nm∕min in the O2-rich-vacuum environment at the pressure of 2×10−3Pa. Both two methods restore the reflectivity of a Mo∕Si multilayer to its original level without causing any surface damage. The effectiveness of both in situ and offline contamination removal are confirmed.