Comparison between optical proximity effect of positive and negative tone patterns in KrF lithography

In this study, the optical proximity effect (OPE) of positive and negative tone line patterns is compared under a variety of exposure conditions. 0.25 micrometers lines with various pitch sizes were printed by a KrF stepper, and the CD variation as a function of pitch was evaluated. We found that the OPE was suppressed significantly in negative patterns under various conditions. The effect of resolution enhancement techniques on the OPE is also investigated. We found that negative patterning with the combination of off- axis illumination and attenuated phase-shift masks not only improved DOF but also gave a small OPE.