Forbidden pitches for 130-nm lithography and below

Experiments and simulations were done to determine which pitches are forbidden for 130nm and 110nm features. Off axis illumination, annular and Quasar, and different reticle types, binary mask (BIM), 6 percent attenuating phase shift mask (PSM), 18 percent attenuating PSM, and alternating PSM were simulated and were exposed on an ASML PAS5500/700. Except for the 1:1 line to space ratio, Quasar for the BIM and the attenuated PSM had the largest process window without forbidden pitches. By increasing the transmission the exposure latitude increases. Increasing transmission, however, does not improve the depth of focus (DOF). Annular illumination was ineffective in increasing the DOF beyond 0.5micrometers for both the 130nm and 110nm features. The alternating PSM with low sigma had no forbidden pitches and had the largest DOF. Alternating PSM with high sigma however, was unable to resolve the dense pitches with sufficient process window.