Metrology challenges for double exposure and double patterning

Double patterning has emerged as a likely lithography technology to bridge the gap between water-based ArF immersion lithography and EUV. Water immersion, single exposure lithography is limited to about 40nm half pitch with NA 1.35. Extension of immersion with high index fluids and glasses is theoretically possible, but faces severe challenges in technology, economics, and timing. In order to extend water immersion lithography further, much attention is given to reducing effective k(1) to less than 0.25 using double patterning. This paper explores the unique challenges IC metrology faces to enable double patterning, first in development, then in production.