Enhanced Design Flow and Optimizations for Multiproject Wafers

The aggressive scaling of very large-scale integration feature size and the pervasive use of advanced reticle enhancement technologies lead to dramatic increases in mask costs, pushing prototype and low-volume production designs to the limit of economic feasibility. Multiproject wafers (MPWs), or “shuttle” runs, provide an attractive solution for such designs by providing a mechanism to share the cost of mask tooling among up to tens of designs. However, MPW reticle floorplanning and wafer dicing introduce complexities that are not encountered in typical single-project wafers. Recent works on wafer dicing adopt one or more of the following assumptions to reduce problem complexity: 1) equal production volume requirement for all designs; 2) same dicing plan used for all wafers or for all rows/columns of reticle images on a wafer; 3) unrealistic wafer models such as a rectangular array of projections; and 4) fixed wafer shot-map. Although using one or more of the aforementioned assumptions makes the problem solvable, the performance of the solutions is degraded. In this paper, a comprehensive MPW flow aimed at minimizing the number of wafers needed to fulfill given die production volumes is proposed. The proposed flow includes two main steps: 1) multiproject reticle floorplanning and 2) wafer shot-map and dicing plan definition. For each of these steps, improved algorithms are proposed as follows. The proposed reticle floorplanner uses a hierarchical quadrisection combined with simulated annealing to generate “diceable” floorplans, observing given maximum reticle sizes. The proposed dicing planner allows multiple side-to-side dicing plans for different wafers and different reticle projection rows/columns within a wafer and further improves the dicing yield by partitioning each wafer into a small number of parts before individual die extraction. A wafer shot-map definition heuristic is also proposed in order to fully utilize round wafer real estate by extracting the maximum number of functional dies from both fully and partially printed reticle images. Experiments on industry test cases show that the proposed methods outperform significantly not only previous methods in the literature but also reticle floorplans manually designed by experienced engineers.