Requirements of the inspection for double patterning technology reticles

As the design rule shrinks continuously, a reticle inspection is getting harsh and harsh and is now one of the most critical issues in the mask fabrication process. The reticle inspection process burdens the entire mask process with the inspectability and detectability problems. Not only aggressive assist features but also small and dense main features themselves may cause many false detection alarms or nuisance defects, which makes the inspection TAT (Turn-around Time) longer. Moreover, small and dense patterns inspections always come with the defect detectability issues. Detectability of a defect in small and dense patterns is usually inferior to the printability of it because of the high MEEF (Mask Error Enhancement Factor) resulted by those small and dense patterns. Double Patterning Technology (DPT)[1] can relief the pattern pitch effectively, therefore, DPT reticle pattern can have a larger pitch than normal Single Patterning Technology (SPT) reticle. We investigate the effect of this pitch relaxation of DPT reticle on the inspection process. In this paper, we compare and analyze the difference of pattern inspectability and defect detectability between DPT reticles and SPT reticles when they have same size of patterns on them. In addition to these results, we also investigate the printability of defects in comparison with the detectability and derive the requirement of the inspection for 4x nodes DPT reticles from the results.