Taming the final frontier of optical lithography: design for sub-resolution patterning

The 20nm node, with a targeted wiring pitch of 64nm, is the first technology node to dip below the fundamental k1=0.25 resolution limit of high-NA 193nm immersion lithography. Double-patterning has been applied in previous technology nodes to address specific image quality issues such as line-end shortening or poor process window on contacts and vias, but never before has double-patterning been used to form images below the frequency-doubled resolution-limit of optical lithography. This paper describes the design-technology co-optimization efforts exercised by the alliance program for Bulk CMOS technology development at IBM in pursuit of cost-effective double-patterning for the 20nm technology node. The two primary double-patterning contenders, pitch-splitting and sidewall-image-transfer, are reviewed and their unique layout decomposition requirements are contrasted. Double-patterning design enablement solutions and their particular applicability to each step in the design flow are described. The paper closes with a review of the costeffectiveness of current double-patterning solutions, highlighting the important role of design-technology cooptimization in ensuring continued cost-effective semiconductor scaling.