Double patterning for 32nm and below: an update

Double patterning lithography - either with two litho and etch steps or through the use of a sacrificial spacer layer, have equal complexity and particularly tight requirements on CDU and Overlay. Both techniques pose difficult challenges to process control, metrology and integration, but seem feasible for the 32nm node. In this paper, we report results in exploring CDU and overlay performance at 32nm 1/2 pitch resolution of two double patterning technology options, Dual Photo Etch, LELE and sidewall spacer with sacrificial layer. We discuss specific aspects of CD control present in any double patterning lithography, the existence of multiple populations of lines and spaces, with overlay becoming part of CDU budget. The existence of multiple and generally uncorrelated CD populations, demands utilization of full field and full wafer corrections to bring together the CDU of these multiple populations in order to meet comparable 10% CDU as in single exposure. We present experimental results of interfield and intrafield CD and overlay statistical and spatial distributions confirming capability to improve these distributions to meet dimensional and overlay control levels required by 32nm node. After compensation, we achieved a CDU control for each population, of 2nm or better and 3nm overlay on multiple wafers and multiple state of art, hyper NA immersion scanners. Results confirmed our assumptions for existence of multiple CDU populations entangled overlay into CDU.