Yield optimization of redundant multimegabit RAM´s using the center-satellite model

Redundant wafer scale memories are analyzed using the center satellite model to determine the optimal redundancy organization for yield enhancement. It is suggested that the degree of redundancy for a memory module be determined depending on its distance from the periphery, as defect density increases as one moves toward the periphery. New analytical expressions for the yield of memory modules with extra rows and/or extra columns, coding, and coding with extra rows are formulated. Results suggest that coding can be more effective than extra rows and columns for higher levels of defect densities. On the other hand, for lower levels of defect densities, having only extra rows and columns may be sufficient. Using the model it is shown that, by taking into account the precise distributions of clusters on the wafer, defects in a cluster, and the radial variation of these defects, an optimal account of redundancy can be found to achieve the highest possible yield