20 August 2001 Damage-resistant and low stress EUV multilayer mirrors
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Proceedings Volume 4343, Emerging Lithographic Technologies V; (2001); doi: 10.1117/12.436715
Event: 26th Annual International Symposium on Microlithography, 2001, Santa Clara, CA, United States
Applications of multilayer mirrors for extreme ultraviolet lithography (EUVL) require not only a high normal incidence reflectivity but also a long lifetime and a minimum residual stress. We focused our interests on a comparative study of two perspective Si-based multilayer systems: Mo/Si and Mo2C/Si. The mirrors were designed for normal incidence reflection at about 13 nm wavelength. The multilayer mirrors were deposited by dc magnetron sputtering. X-ray scattering, transmission electron microscopy, atomic force microscopy and mechanical stress measurements were used for the characterization of the multilayer structures. Maximum normal incidence reflectivities of 67.5% 13 nm for Mo/Si multilayer mirrors and 66.3% 12.8 nm for Mo2C/Si have been achieved. Investigating the thermal stability of the multilayers in the temperature range from 200 degree(s)C to 600 degree(s)C it was shown that the reflectivity of Mo/Si mirrors is drastically decreasing after annealing above 300 degree(s)C, whereas the Mo2C/Si multilayers show a superior thermal stability up to 600 degree(s)C. It was found that as-deposited Mo/Si and Mo2/C/Si multilayer mirrors have a similar level of compressive stress of -520+/- 20 MPa. The reduction of residual stress in Mo/Si and Mo(subscript 2C/Si multilayer systems with post-deposition thermal treatment has been investigated. Using a slow thermal annealing (2 degree(s)C/min), it is possible to reduce the stress form -520 MPa to nearly zero by heating the Mo/Si specimen up to ~310 degree(s)C. However, it results in a reflectivity drop of ~3% (absolute) at the wavelength of 13 nm. For the Mo2C/Si system, a stress reduction from -520 MPa to nearly zero is possible by a post annealing at ~290 degree(s)C without a considerable drop in the reflective properties.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Sergey A. Yulin, Thomas Kuhlmann, Torsten Feigl, Norbert Kaiser, "Damage-resistant and low stress EUV multilayer mirrors", Proc. SPIE 4343, Emerging Lithographic Technologies V, (20 August 2001); doi: 10.1117/12.436715; https://doi.org/10.1117/12.436715





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