Study of defect printability analysis on alternating phase shifting masks for 193 mm lithography

For alternating aperture phase shift masks (AAPSM), phase-defect detection and disposition is more difficult for 193 nm (ArF) lithography than for 248 nm (KrF) lithography, as pattern geometry is tighter and quartz etching is shallower. For ArF lithography, we designed and fabricated a new test mask to confirm detectability and printability of phase defects, extending our previous work for KrF lithography. This test mask has precise defect sizes and phase-error angles of 25, 50, and 75 degrees. Detectability was demonstrated on KLA-Tencor's SLF27 and investigated by acquiring defect images on SLF27 and LaserTec's MD3000 inspection systems. Printability was compared between actual wafer prints, and simulations from Carl Zeiss' Aerial Image Measurement System (AIMS(TM)). Wafer prints were also simulated using Numerical Technologies' software-based Virtual Stepper((R)) System, which takes inspection images as input and models the optical aspects of lithography. Virtual Stepper critical-dimension measurements show good general agreement with those from AIMS images and wafer-print SEM images. Compared to AIMS, which is a hardware-based simulator that uses the actual mask as input, the software-based Virtual Stepper System is easier to adapt to different processes and to integrate into the production flow.