Damage Resistant and Low Stress EUV Multilayer Mirrors

概要

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This paper investigates the thermal stability as well as the residual stresses of Mo/Si and Mo_2/Si multilayer mirrors. The mirrors were designed for normal incidence reflectivity at about 13 nm wavelength and were deposited by dc magnetron sputtering. Investigating the thermal stability of the multilayers in the temperature range from 300°C to 500°C, we found that the reflectivity of Mo/Si minors is markedly decreased after annealing above 300°C, whereas the Mo_2C/Si multilayers show a superior thermal stability up to 400°C. Additionally, the reduction of residual stress of Mo/Si and Mo2C/Si multilayers with annealing has been investigated. Using slow thermal annealing (1°C/min), it is possible to reduce the stress from -520 MPa to zero by heating the Mo/Si samples up to 310°C. However, this results in a reflectivity drop of about 3-4%. On the other hand, one can reduce the stress of a Mo2C/Si multilayer from -490 MPa to zero by annealing without a considerable reflectivity drop.
社団法人応用物理学会の論文
2002-06-30