Registration Metrology on Double Patterning Reticles

Double patterning is considered as an upcoming class of technologies for the 32nm node photolithography processes and beyond. Several different double patterning technologies have been published within the last years. The ability to use coarse patterns to define finer patterns offers an opportunity to achieve resolution below 30 nm by using optical DUV immersion lithography. The specifications for overlay registration on a pair of photomasks are expected to be much tighter than for standard photomasks. Especially the registration of related patterns, distributed on two separate photomasks, gives a new challenge to the metrology tools. Accordingly, we will present a new approach for overlay registration by the KLATencor LMS IPRO4 system. Similar to the standard overlay evaluation, the new algorithms allow pairing up related sites on both photomasks for registration. Even though the sites are not located on the same coordinates, the KLATencor LMS IPRO4 system is able to pair up each site on the second photomask to a dedicated site on the reference photomask. Thus the algorithm creates a set of common sites for the overlay registration. Results of this versatile method will be presented, showing the feasibility to several applications.