New approach to determine best beam focus

As patterning technology advances beyond 45-nm half-pitch, the process window shrinks dramatically even with advanced resolution enhancement techniques. Beamfocus represents one of the process parameters that has a significant contribution to the overall critical feature dimension error budget. In building an optical model for proximity correction, the final model quality strongly depends on matching the focus used in the simulation to the experimental focus conditions. In this paper, we present a new method to determine the best beamfocus and verify its accuracy using actual test pattern measurements.