The optimization of in-line scanner defect sizing using a circuit's layout and critical area

Wafers containing a large number a defects on any layer should be discarded in order to avoid the cost associated with processing wafers that are unlikely to yield. Normally decisions about scrapping wafers are based on defect counts. However, including the size of defects can improve the accuracy of such dispositions. If the size of defects is taken into account, critical area provides an estimate of the kill ratio associated with defects of a given size, where the critical area of a layer of a circuit is computed from a circuit's layout. In this paper, the accuracy of the sizing of defects by in-line scanners is analyzed. Then, the impact of defect sizing inaccuracy on estimates of layer yield is discussed, and a methodology to find the defect radii contributing most significantly to inaccuracy in layer yield estimates is presented.