Redundant-wires-aware ECO timing and mask cost optimization

Spare cells are often used in engineering change order (ECO) timing optimization. By applying spare-cell rewiring techniques, timing-violated paths in a design can be fixed. In addition, mask re-spin cost economization has become a critical challenge for modern IC design, and it can be achieved by reducing the number of layers used to rewire spare cells. This paper presents the first work for the problem of ECO timing optimization considering redundant wires (unused wires or dummy metals) to minimize the number of rewiring layers. We first propose a multi-commodity flow model for the spare-cell selection problem and apply integer linear programming (ILP) to simultaneously optimize all timing-violated paths. The ILP formulation minimizes the number of used spare cells and considers the routability of the selected spare cells. Then, we develop a tile-based ECO router which minimizes the number of rewiring layers by reusing redundant wires. Experimental results based on five industry benchmarks show that our algorithm not only effectively resolves timing violations but also reduces the number of rewiring layers under reasonable runtime.