Thermal Conduction Properties of Mo/Si Multilayers for Extreme Ultraviolet Optics

Bozorg-Grayeli, E., Li, Z., Asheghi, M., Delgado, G., Pokrovsky, A., Panzer, M., Wack, D., and Goodson, K.E., 2012, "Thermal Conduction Properties of Mo/Si Multilayers for Extreme Ultraviolet Optics," Journal of Applied Physics, Vol. 112, pp 083504-1 - 083504-7.

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Extreme ultraviolet (EUV) lithography requires nanostructured optical components, whose reliability can be influenced by radiation absorption and thermal conduction. Thermal conduction analysis is complicated by sub-continuum electron and phonon transport and the lack of thermal property data. This paper measures and interprets thermal property data, and their evolution due to heating exposure, for Mo/Si EUV mirrors with 6.9 nm period and Mo/Si thickness ratios of 0.4/0.6 and 0.6/0.4. We use time-domain thermoreflectance and the 3w method to estimate the thermal resistance between the Ru capping layer and the Mo/Si multilayers (RRu-Mo/Si = 1.5 m2 K GW-1), as well as the out-of-plane thermal conductivity (kMo/Si 1.1 W m-1 K-1) and thermal anisotropy (η = 13). This work also reports the impact of annealing on thermal conduction in a co-deposited MoSi2 layer, increasing the thermal conductivity from 1.7 W m-1 K-1 in the amorphous phase to 2.8 W m-1 K-1 in the crystalline phase.

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