Nuisance Event Reduction Using Sensitivity Control Layers (SCL) for Advanced Photomask Inspection

Abstract:
Conventional photomask inspection techniques utilize global sensitivity for all inspected area in the die; SRAF and OPC features become the sensitivity-limiters for advanced photomasks which can result in reduced sensitivity to defects of interest (DOI). We describe the implementation of Sensitivity Control Layer (SCL), a novel database inspection methodology for the KLA-Tencor TerascanHR platform to improve sensitivity and reduce nuisance detections. This methodology enables inspection at maximum sensitivity in critical die-areas via “layer definition” and reducing sensitivity to sub-resolution features during inspection which can dramatically improve false-rate. DRAM and FLASH inspection performance was improved through the use of up to 6-control layers to increase sensitivity in the active area while reducing false detections by as much as 100X. Post-inspection defect analysis, and improved disposition accuracy of the SCL-enabled inspections will also benefit cycle time and higher throughput. In all test cases, sensitivity parameters were increased in the regions of interest over baseline inspections run with typical, production-type inspection methodologies. SCL inspection-sensitivity management, and layer partitioning of OPC structures, SRAF’s, and other sub-resolution features is discussed in detail.