Non-traditional inspection strategy for inline monitoring in excursion scenarios: Defect inspection

Different tool platforms are used in conjunction for patterned wafer inspection like 9xxx & 29xx provided by KLA Tencor. Depending on the sensitivity & throughput requirements, a chip fabrication plant mixes and matches the inline inspection strategies to ensure early detection of defects on the chip, which could cause yield loss or reliability problems. This paper discusses the use of a novel concept of high sensitivity & high throughput inspection strategy using the 29xx tool. This is achieved by using a unique combination of Broad-Band light with Dark Field Apertures. This application can be used to monitor and screen a large number of wafers affected by out of control situations. A use-case is also discussed where optically strong defect locations uniquely seen on 29xx tool were found to be invisible after SEM review. After analyzing defects using see-through imaging on Scanning Electron Microscope (SEM), along with Transmission Electron Microscope (TEM) of the defect locations, those defects were confirmed to be buried defects inside the current layer. Due to low sampling on inspection tools, it was difficult to determine the quantity of wafers affected by the issue. By using high throughput (TPT) 29xx features, a methodology to screen out a high volume of wafers at high throughput was implemented & used to monitor the variability in the process and identify wafers at risk. This methodology enabled inspection of ~15 wafers per hour. The same methodology was subsequently successfully implemented to verify/monitor multiple excursion scenarios at different process steps.