Wafer level defect density distribution using checkerboard test structures

Defect density distributions play an important role in process control and yield prediction. To improve the accuracy in modeling of defect density distributions, we present a wafer level methodology to analyze defect data measured anywhere on a wafer. The inspected area may thus be limited to test structures that just cover a fraction of each wafer. For that, imaginary wafer maps are generated for a variety of different chip areas to calculate a yield-to-area dependency. Based on these calculations, a micro density distribution (MDD) is determined for each wafer that reflects the degree of defect clustering. The single MDDs per wafer may be summarized to also provide a general defect density distribution per lot or any other sample size.