Wafer printability simulation of EUV mask defects using mask SEM and AFM

Abstract

The impact of mask defects on wafers has been successfully simulated by KLA's mask SEM-to-Aerial (S2A) image simulator. The high prediction accuracy, high throughput and low cost have been proven by mask shop production users [2][3]. S2A generates the reference mask SEM images by rendering the post-OPC design to match with measured mask SEM images containing defects. From the two mask SEM images, defect-free reference absorber contour and defective absorber contour are extracted, and the two contours are used for wafer-level aerial image simulation through EUV scanner conditions. Pass/Fail of %CDE, EPE, etc. are reported by automatically generating measurement cutlines.S2A can be used for wafer prediction for pre/post-repair full height absorber defects using top-down mask SEM images, but it cannot be used for EUV multi-layer buried defects or for partial height residues remaining after repair. KLA and SK hynix have been investigating a solution for this use case using AFM images, which can measure the height error from the buried defect or partial height residue in post-repair mask.