BEX-a novel wafer yield distribution model and analysis

Baseline Excursion Analysis (BEX) provides a statistical method to analyze wafer yield distributions. A novel graphical visualization scheme has been developed that supports inspection, analysis, and comparison of yield distributions much more effectively than standard yield histograms. In a first step, wafer yield is transformed to defect density by an appropriate model such as Poisson or Stopper model. Total defect density is subsequently modeled as the sum of Baseline and Excursion defect density components. Parameters of both distributions are extracted from a curve fit to the data. Key figures such as Baseline limited yield and Excursion limited yield are estimated and allow to tailor, focus and control yield improvement activities.