<title>Magnetron sputtered EUV mirrors with high-thermal stability</title>

Abstract

Many applications of multilayers in the EUV spectral region require not only high normal incidence reflectivity but also high thermal stability. We instigated the thermal stability of Mo/Si multilayers in comparison with the new material combination Mo<SUB>2</SUB>C/Si in the temperature range from 200 degrees Celsius to 700 degrees Celsius. Additionally, we deposited and studied Mo/Si multilayers having Mo<SUB>2</SUB>C diffusion barriers with 0.6 nm single layer thickness. The multilayer mirrors were designed for normal incidence reflectivity at about 13 nm wavelength and were deposited by dc magnetron sputtering. X-ray scattering, transmission electron microscopy and atomic force microscopy were used for characterization of the multilayer structures. The results are correlated to the measured normal incidence reflectivity using synchrotron radiation. We achieved maximal normal incidence reflectivities of 61.8% 13.0 nm wavelength for Mo<SUB>2</SUB>C/Si and 59.9% 13.3 nm for Mo/Si multilayers having Mo<SUB>2</SUB>C diffusion barriers. While the reflectivity of Mo/Si multilayers decreased considerably after annealing above 300 degrees Celsius the Mo<SUB>2</SUB>C/Si multilayers showed a superior thermal stability up to 600 degrees Celsius.