Behavior of Ru surfaces after ozonated water treatment

In order for the development of cleaning technology of extreme ultra violet lithography photomask, the behavior of Ru surfaces after treatment with ozonated deionized water (DIO3) solution was studied using Ru and ruthenium oxide particles and 2 nm-thick Ru capping layers. No significant changes in crystalline structures or chemical states of the Ru surfaces, nor any similarities with the structures or states of ruthenium oxide, were observed after DIO3 treatment. Oxidation of ruthenium to form RuO2 or RuO3 was not observed. Adsorption of H2O molecules on the Ru layer increased the surface roughness, but the desorption of H2O molecules recovered it. Local chemisorption of H2O molecules on the Ru surface may be the reason why rougher Ru surfaces were observed after DIO3 cleaning.