Patterning challenges in the sub-10 nm era

Historically, progress in lithography has been driven by steady advances in exposure tool and optical technology; shorter wavelength, higher numerical aperture (NA) and resolution enhancement techniques to drive the k 1 factor as close as possible to the physical limit. Over the past decade, however, the pace of progress has been gated more by patterning – what we do after the resist image is printed – than by higher resolution imaging. The emphasis on patterning rather than just printing has created new pressures in many parts of the overall process, beginning with the design itself. The breakdown of lithographic error budgets into CD and OL tolerances has given way to total edge placement error (EPE) budgets where CD, OL and edge roughness, as well as film and etch variations, must all be controlled to meet the required tolerances. Contact hole and cut mask placement have likewise been tightened to single digit EPE budgets. Collaborative research between technology specialists in multiple areas, such as metrology, etch, process control and simulation, will all be required to deliver these patterning solutions for some years to come. This paper will describe some of these challenges in more detail, and suggest directions for future research to keep optical lithography relevant even below the 10 nm node.