Point defect yield model for wafer scale integration

Yield projections are a primary consideration in wafer scale integration. The author develops a point defect yield model for a two-way redundancy scheme appropriate for random logic. The model assumes that the fault-causing defects are randomly distributed locally but that the defect density can vary across a wafer as well as from one wafer to another. Examples are given to illustrate the strong dependence of the results on clustering of defects and on the redundancy partitioning. The importance of the distinction between on-wafer and wafer-to-wafer variations in defect density is demonstrated. Complications associated with the occurrence of small numbers of highly correlated defects are discussed.