Removal of EUV exposed hydrocarbon from Ru capping layer of EUV mask using the mixture of alkaline solutions and organic solvents

Abstract

Under extreme ultraviolet (EUV) exposure, the surfaces of EUV mask and optics are exposed to hydrocarbon contaminant, which reduces the imaging performance and lifetime of EUV mask. Thus, an efficient method is required to remove hydrocarbon contaminant from the mask surface. In this work, a mixture of alkaline chemicals and organic solvents has been proposed for the removal of EUV exposed hydrocarbon contaminant from Ru (Ruthenium) capping layer of EUV mask. A hydrocarbon film with similar properties to EUV hydrocarbon contaminant was prepared by PECVD (plasma enhanced chemical vapor deposition). The hydrocarbon removal efficiency was evaluated by using four kinds of quaternary ammonium hydroxides as alkaline chemicals, and DMSO (dimethyl sulfoxide) and THF (tetrahydrofuran) as polar aprotic organic solvents. Among the alkaline chemicals, tetrabutyl ammonium hydroxide, together with an organic solvent, produced effective removal of hydrocarbon from Ru. Removal of hydrocarbon film using a higher polar organic DMSO solvent required a higher concentration and longer time than THF. The combination of megasonic power and cleaning chemistry enhanced the hydrocarbon removal efficiency significantly.