Heat resistance of EUV multilayer mirrors for long-time applications

The effect of elevated temperature on the structural Stability of Mo/Si Mo2 C/Si and Mo/Mo2C/Si/Mo2C (d(Mo2C) = 0.6 nm) multilayers was investigated. T he multilayers deposited by dc magnetron sputtering are annealed at tempera tures ranging from 200 to 700 degreesC. The multilayer mirrors were designe d for normal incidence reflectivity at about 13 mn wavelength. We achieved maximal normal incidence reflectivities of 68.4% at 12.8 nm wavelength for Mo/Si and 66.8% at 12.8 nm for Mo2C/Si. While the reflectivity of Mo/Si mul tilayers decreased considerably after annealing above 300 degreesC the Mo2C /Si multilayers; showed a superior thermal stability up to 500 degreesC. (C ) 2001 Elsevier Science BY All rights reserved.