Improved oxidation resistance of Ru/Si capping layer for extreme ultraviolet lithography reflector

The authors report on the chemical durability and oxidation resistance of Ru/Si, Ru/B, Ru/C, and Ru capping layers on the extreme ultraviolet (EUV) reflector surface. Surface etching and changes in the oxidation state were probed with x-ray photoelectron spectroscopy. The changes in surface morphology and roughness are characterized using scanning electron microscopy and atomic force microscopy. Out of four different capping layers, Ru/Si layers exhibited the least surface oxidation after oxygen plasma and UV/ozone treatment, indicating a superior oxidation resistance. The authors found that the reflectivity of the Ru/Si capped reflector is similar to that of a bare Ru capped reflector. This study suggests that a Ru/Si layer can be an excellent capping layer for the EUV reflector.