Using full wafer defect maps as process signatures to monitor and control yield

Experience with full-wafer data maps at many fabs has shown that defects on patterned wafers tend to cluster and be distributed in nonrandom patterns. The full-wafer defect map becomes a process signature which can be used to quickly determine if changes have occurred in the process. The authors show how the process signature map has been used in actual case studies to quickly identify process problems, often before an operator or engineer reviews any actual defects on the wafer. Fast optical processing, optical pattern filtering and holography, as used in the Insystems 8600 and the more advanced 8800, achieve sensitivity to submicron (and larger) defects across the full wafer. This allows for faster defect analysis and response time