Characterization of Ru4-xTax (x = 1,2,3) alloy as material candidate for EUV low-n mask

Abstract

Ru 4-x Ta x (x = 1,2,3) alloys are studied as absorber candidates for EUV low-n mask. We report the morphology, surface roughness as well as the chemical composition of the as-deposited alloy films for better theoretical model building of the EUVL absorber stack. Their refractive indices are reconstructed by optimizing measured EUV reflectivity data for the purpose of enabling rigorous EUVL imaging calculations in the future work. The stabilities (both physical and chemical) of these absorber candidates are verified which contribute to a long lifetime of the mask in its working environment. This includes the resistance assessments of the thin films against high temperature up to 500 °C, different mask cleaning solutions and hydrogen environment which is present in EUV scanners. Etching of RuTa is explored using halogen-based reactive ion etch technique. A low etch rate is obtained with a moderate etch selectivity to Ru, which is the capping layer of multilayer mirror on a EUVL mask. • This work highlights the systematic characterization of Ru 4-x Ta x (x = 1,2,3) alloy as EUV mask absorber candidate. • The optical constants reconstructed from EUV reflectivity measurements allow realistic EUV imaging simulations. • The alloys are characterized based on film morphology, surface roughness, and composition. • The alloys show excellent resistance to mask cleaning, hydrogen plasma (scanner) and heating (mask processing and exposure). • RuTa RIE etching shows satisfactory etch selectivity against Ru (multilayer cap of EUV mask) required for mask patterning.