Post Pattern Inspection Strategy

Rapid yield ramp up in wafer processing fabs has become the most important task for process and yield engineers. In-line process monitoring using inspection tools are the traditional approaches to monitor excursion within the process line. Minor gains in yield ca increase revenue per wafer significantly, hence defect detection and defect feedback into process line is becoming the corner stone of fab yield success. Number of mask levels are becoming important to process fabs. Monitoring these mask levels so as to detect defects and feed information to the process line has become crucial to process yield. In order for this to happen a good understanding of the defects caused at the mask levels is important. An attempt will be made to discus the various types of defects present in the photomask levels and their relationships to their in-line detection. The discussion deals with scum defects, isolated bridging defects, pattern aspect ratio, and isolated and dense region patterning issues.