Thermal conduction properties of Mo/Si multilayers for extreme ultraviolet optics

摘要

20%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 3ω method to estimate the thermal resistance between the Ru capping layer and the Mo/Si multilayers (R_(Ru-Mo/si)= 1.5 m ~2 K GW~(-1)), as well as the out-of-plane thermal conductivity (k_(Mo/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 MoSi_2 layer, increasing the thermal conductivity from 1.7 W m~(-1)K~(-1) in the amorphous phase to 2.8 W m~(-1) KT~(-1) in the crystalline phase.