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Preparation and characterization of multilayers for EUV applications

: Foltyn, T.; Braun, S.; Friedrich, W.; Leson, A.; Menzel, M.


Amra,C.; Kaiser, N.; Macleod, H.A. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Advances in Optical Thin Films II : SPIE Conference on Optical Systems Design, 12-16 September 2005, Jena, Germany
Bellingham/Wash.: SPIE, 2005 (SPIE Proceedings Series 5963)
ISBN: 0-8194-5981-X
Paper 59632C, 10 S.
Conference on Optical Systems Design <2005, Jena, Germany>
Fraunhofer IWS ()
annealing; carbon; compressive strength; molybdenum; optical multilayer; silicon; sputter deposition

The dependency of EUV reflectance and of the stress present in Mo/Si/C multilayers on the constituent individual layers has been investigated. The heat treatment of highly EUV reflective Mo/Si/C multilayers has been examined in terms of annealing time and temperature. Irreversible stress change was found at annealing temperatures above 130 °C, where the change of period thickness and the change of stress increase more rapidly. It was found, that there is a saturation of stress change depending on the annealing time. Annealing at 100 °C reveals a saturation of stress change after 10 h, whereas annealing at 150 °C still shows stress reduction after 50 h. A second annealing of two samples shows a reversible stress-temperature behavior of the multilayers. Stress compensation layers for the coating of stress-mitigated Mo/Si/C multilayers were developed. The best results of composition for reflective multilayers and stress-compensation multilayers were joint together in order to fabricate stress-mitigated Mo/Si/C multilayers. Taking the condition of achieving an overall stress below ±100-150 MPa into account, two types of stress-mitigated multilayers were coated. The first type includes a buffer layer in order to compensate the compressive stress of the reflective multilayers without annealing. The stress was reduced to -76 MPa by keeping a high EUV near-normal incidence reflectance of ~70.0 %. The second type contains a thinner buffer layer and the stress reduction of the complete multilayer system was assisted by a post-annealing at 100 °C for 10 h. The stress was measured to be -108 MPa and an EUV reflectance of 69.5 % was obtained.