Alt-PSM for 0.10-μm and 0.13-μm polypatterning

While the use of phase shift masks can improve CD control and allow the patterning of smaller poly gate features, it also introduces new error terms for overlay. Four error terms are discussed: increased sensitivity of image placement to coma-type aberrations, image placement shifts resulting form phase errors, image placement shifts resulting from intensity imbalance between zero and 180 degrees shifter regions, and phase shift mask to trim mask overlay issues. These overlay issues become increasingly important for lower k1 patterning. Likewise, phase defect printability is magnified for lower k1 patterning, increasing the requirements for phase shift mask inspection and repair.