Learning from native defects on EUV mask blanks

Abstract

Defects in the EUV mask blank are one of the largest hurdles to achieving manufacturing readiness of EUV masks. For defect-free masks, the obvious approach is to order blanks that do not have defects or to shift the pattern so that remaining defects do not create a printed defect on wafer. The approach during development should be different. At this learning phase, it is wise to study the defects as they occur naturally on the EUV mask blank. This paper outlines a comprehensive approach to building a mask specifically to showcase the native defects so that they can be studied and repairs can be attempted. The method applied to mask build, defect inspection and characterization will be reviewed in detail. Printability of the mask defects of interest are characterized using both wafer printing and EUV microscope data. Repairs are attempted and characterized. In the end, the impact of native defects is discussed along with the viability of various repair methods.