Multiple-Layer Multiple-Patterning Aware Placement Refinement for Mixed-Cell-Height Designs

Conventional lithography techniques are unable to achieve the resolution required by advance technology nodes. Multiple patterning lithography (MPL) has been introduced as a viable solution. Besides, new standard cell structure with multiple middle-of-line (MOL) layers is adopted to improve intra-cell routability. A mixed-cell-height standard cell library, consisting of cells of single-row and multiple-row heights, is also used in designs for power, performance and area concerns. As a result, it becomes increasingly difficult to get a feasible placement for a mixed-cell-height design where multiple cell layers require MPL. In this paper, we present a methodology to refine a given mixed-cell-height standard cell placement for satisfying MPL requirements on multiple cell layers as much as possible, while minimizing the total cell displacement. We introduce the concept of uncolored cell group (UCG) to facilitate the effective removal of coloring conflicts. By eliminating UCGs without generating any new coloring conflict around them, the number of UCGs is effectively reduced in the local and global refinement stages of our methodology. We report promising experimental results to demonstrate the efficacy of our methodology.