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Damage resistant and low stress EUV multilayer mirrors

: Feigl, T.; Yulin, S.; Kuhlmann, T.; Kaiser, N.


Japanese Journal of Applied Physics. Part 1, Regular papers, short notes and review papers 41 (2002), No.6B
ISSN: 0021-4922
Journal Article
Fraunhofer IOF ()
damage resistance; thermal stability; DC magnetron sputtering; residual stress

This paper investigates the thermal stability as well as the residual stresses of Mo/Si and Mo/sub 2/C/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 degrees C to 500 degrees C, we found that the reflectivity of Mo/Si mirrors is markedly decreased after annealing above 300 degrees C, whereas the Mo/sub 2/C/Si multilayers show a superior thermal stability up to 400 degrees C. Additionally, the reduction of residual stress of Mo/Si and Mo/sub 2/C/Si multilayers with annealing has been investigated. Using slow thermal annealing (1 degrees C/min), it is possible to reduce the stress from -520 MPa to zero by heating the Mo/Si samples up to 310 degrees C. However, this results in a reflectivity drop of about 3-4%. On the other hand, one can reduce the stress of a Mo/sub 2/C/Si multilayer from -490 MPa to zero by annealing without a considerable reflectivity drop