Comparison of single- and dual-exposure phase-shift mask approaches for polygate patterning

Single, multi-phase, and dual, 'hidden-shifter,' phase shift masks are compared via simulation and experiment in terms of line-end patterning fidelity and printability of phase defects. Four phase mask line-ends bend through focus while 'hidden-shifter' line-ends show acceptable performance. For a given phase difference, phase defects are found to be more severe than phase errors in terms of resist CD variations. Phase defect printability is highest at positive defocus. For a typical process window, 60 degree phase defects as small as 100 nm may cause unacceptable CD variations.