Fast and efficient phase conflict detection and correction in standard-cell layouts

Alternating-aperture phase shift masking (AAPSM), a form of strong resolution enhancement technology (RET) is used to image critical features on the polysilicon layer at smaller technology nodes. This technology imposes additional constraints on the layouts beyond traditional design rules. Of particular note is the requirement that all critical features be flanked by opposite-phase shifters, while the shifters obey minimum width and spacing requirements. A layout is called phase-assignable if it satisfies this requirement. Phase conflicts between shifters have to be removed to enable the use of AAPSM for layouts that air not phase-assignable. Previous work has sought to detect a suitable set of phase conflicts to be removed, as well as correct them as well as correct them. This paper has two key contributions: (1) a new computationally efficient approach to detect a minimal set of phase conflicts, which when corrected produces a phase-assignable layout; (2) a novel layout modification scheme for correcting these phase conflicts in standard-cell blocks. Unlike previous formulations of this problem, the proposed solution for the conflict detection problem does not frame it as a graph bipartization problem. Instead, a simpler and more computationally efficient reduction is proposed. This simplification greatly improves the runtime, while maintaining the same improvements ill the quality of results. An average runtime speedup of 5.9× is achieved using the new flow. A new layout modification scheme for correcting phase conflicts in large standard-cell blocks is also proposed. The proposed layout modification scheme can handle all phase conflicts in large standard-cell blocks with small increases in area. Our experiments show that the percentage area increase for making typical standard-cell blocks phase-assignable ranges from 3.4-9.1%.