Investigation of Gd and Tb plasmas for beyond extreme ultraviolet lithography based on multilayer mirror performance

摘要

Recent work on multilayer mirror development for beyond extreme ultraviolet lithography indicates that their optimum reflectivity occurs at either 6.63 nm or 6.66 nm which may be too short a wavelength for Gd-based plasma sources. Calculations performed for Tb~(12+) to Tb~(28+) ions show that if the mirror reflectivity is fixed at one of these values, Tb may be a better source, though Gd is capable of providing greater intensity if the full reflection curve of the mirrors is exploited. Theoretical simulation shows that the Tb emission peaks close to 6.51 nm at an optimum electron temperature close to 120eV.