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Design and fabrication of broadband EUV multilayer mirrors

: Kuhlmann, T.; Yulin, S.A.; Feigl, T.; Kaiser, N.; Bernitzki, H.; Lauth, H.


Engelstad, R.L. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Emerging Lithographic Technologies VI. Vol.2 : 5 - 7 March 2002, Santa Clara, USA
Bellingham/Wash.: SPIE, 2002 (SPIE Proceedings Series 4688)
ISBN: 0-8194-4434-0
Emerging Lithographic Technologies Conference <6, 2002, Santa Clara/Calif.>
Conference Paper
Fraunhofer IOF ()
broadband EUV multilayer mirror fabrication; broadband EUV multilayer mirror design; magnetron sputtering system; nonperiodic multilayer; stochastic method; broadband plasma source; lithography

Multilayer mirrors with a significantly increased bandwidth in spectral and angular reflectance have been designed and deposited with a commercial magnetron sputtering system. A non-periodic multilayer design based on the thickness optimization of each layer by a stochastic method is compared to a design which consists of 3 different stacks. The EUV reflection of the samples was investigated with synchrotron radiation at the reflectometer of the PTB (Physikalisch-Technische Bundesanstalt) at BESSY II in Berlin. A reflectivity of more than 15 percent was reached in the whole wavelength range from 13 nm to 15 nm and a reflectivity of more than 30 percent was obtained for incidence angles from 0 degrees to 20 degrees with both designs. The increase in bandwidth is unavoidably connected with a decrease of peak reflectivity. Therefore, the application of such mirrors involves areas where a maximum peak reflectivity is not required, e.g. in EUV spectroscopy and for the metrology for EUV sources. Furthermore, the use of such mirrors in combination with a broadband plasma source will result in a higher integral reflectivity.