EUV mask

EUV mask blank defectivity is the dominant yield-limiting factor in EUV mask manufacturing, because a defect buried anywhere within the roughly 40-to-50-layer molybdenum-silicon reflective stack distorts the mirror surface above it and cannot be corrected after the multilayer is deposited. Standard optical inspection tools, which use visible or UV light, cannot reliably predict how such a defect behaves under actual 13.5nm EUV exposure, so blank qualification depends on actinic inspection — testing with EUV light itself — to see the defect the way the lithography scanner eventually will. This defectivity constraint, more than any other single factor, has made EUV mask blanks one of the costliest and most tightly supply-constrained components in the entire EUV lithography ecosystem.