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Defect monitoring and control in the semiconductor fab has been well documented over the years. The methodologies typically described in the literature involve controls through full-wafer defect counts, or defect densities, with attempts to correlate defects to electrical fail modes in order to predict the yield impact. These wafer-based methodologies are not adequate for determining the impact of defects on yield. Most notably, severe complications arise when applying wafer-based methods on wafers with mixed distributions (mix of random and clustered defects). This paper describes the proper statistical treatment of defect data to estimate yield impact for mixed-distribution wafer maps. This die-based, defect-limited yield (DLY) methodology properly addresses random and clustered defects, and applies a die-based multi-stage sampling method to select defects for review. The estimated yield impact of defects on the die can then be determined. Additionally, a die normalization technique is described that permits application of this die-based methodology on multiple products with different die sizes.
Date of Conference: 11-13 July 2010