Advanced process control based on lithographic defect inspection and reduction

Defect monitoring is increasingly required for advanced line maintenance. The resulting information from wafer inspection can be used in two ways, (1) excursion detection, which requires an appropriately measured response, and (2) pro-active process control. For the first, a critical decision is how to proceed with lot deposition if an excursion is detected. A methodology based on post-lithographic defect inspection and defective die count analysis was employed which provided effective process monitoring and yield maintenance. The methodology allows rapid decision-making with a minimum of information for post-litho lot disposition. For the second application of proactive control, the wafer inspection was utilized for dose forecasting with a feedforward mode used to appropriately modify the dose for optimization. Good line control and yield maintenance were observed as a result of the both the lot-disposition and dose forecasting. The purpose of the lot disposition is to separate significant excursions from temporary fluctuations in order to appropriately focus defect reduction resources. Wafers are systematically inspected post-litho with a patterned wafer inspection system, the WF736, and the number of die with killer defects is counted and then monitored with time. Every lot is inspected, full wafer inspection is performed, and all defect types are captured. By determining the killer defect progression after re-work, it is possible to establish lot disposition. If the count is still high, defect reduction analysis is then applied. Various defects were flagged and addressed, arising both from litho and from prior steps.