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Mo/Si multilayers with enhanced TiO2- and RuO2-capping layers

: Yulin, S.; Benoit, N.; Feigl, T.; Kaiser, N.; Fang, M.; Chandhok, M.


Schellenberg, F.M. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Emerging lithographic technologies XII : 26 - 28 February 2008, San Jose, California, USA
Bellingham, WA: SPIE, 2008 (SPIE Proceedings 6921)
ISBN: 978-0-8194-7106-2
ISBN: 0-8194-7106-2
Paper 692118
Conference "Emerging Lithographic Technologies" <12, 2008, San Jose/Calif.>
Fraunhofer IOF ()
Beschichtung=Überzug; Rutheniumverbindung; Titanverbindung; Ultraviolettlithographie; Titandioxid; EUVL; Mo/Si multilayer; capping layer; TiO2; RuO2; surface oxidation; carbon growth; optics lifetime

The lifetime of Mo/Si multilayer-coated projection optics is one of the outstanding issues on the road of commercialization of extreme-ultraviolet lithography (EUVL). The application of Mo/Si multilayer optics in EUVL requires both sufficient radiation stability and also the highest possible normal-incidence reflectivity. A serious problem of conventional high-reflective Mo/Si multilayers capped by silicon is the considerable degradation of reflective properties due to carbonization and oxidation of the silicon surface layer under exposure by EUV radiation. In this study, we focus on titanium dioxide (TiO2) and ruthenium dioxide (RuO2) as promising capping layer materials for EUVL multilayer coatings. The multilayer designs as well as the deposition parameters of the Mo/Si systems with different capping layers were optimized in terms of maximum peak reflectivity at the wavelength of 13.5 nm and longterm stability under high-intensive irradiation. Optimized TiO2-capped Mo/Si multilayer mirrors with an initial reflectivity of 67.0% presented a reflectivity drop of 0.6% after an irradiation dose of 760 J/mm2. The reflectivity drop was explained by the partial oxidation of the silicon sub-layer. No reflectivity loss after similar irradiation dose was found for RuO2-capped Mo/Si multilayer mirrors having initial peak reflectivity of 66%. In this paper we present data on improved reflectivity of interface-engineered TiO2- and RuO2-capped Mo/Si multilayer mirrors due to the minimization of both interdiffusion processes inside the multilayer stack and absorption loss in the oxide layer. Reflectivities of 68.5% at the wavelength of 13.4 nm were achieved for both TiO2- and RuO2-capped Mo/Si multilayer mirrors.
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