Correlation of inspection methods in characterizing nanomachined photomask repairs

Nanomachining has become a mainstream process for repairing photomasks. The advantages of nanomachining versus other repair techniques are improved edge placement, reliable depth control, and minimized substrate damage. This technique can be applied to any defect that requires a subtractive repair process. The process can be equally well applied to defects of any material including unknown materials. This paper evaluates the correlation of different inspection methods in characterizing nanomachined photomask repairs. The repairs were made using an nm650 mask repair tool manufactured by RAVE LLC. The repairs were inspected using a 248nm Aerial Image Measurement System (AIMS) and the Atomic Force Microscope (AFM) image produced by the nanomachining tool itself. These repairs were performed on 248nm MoSi photomasks. Results were compared to measurements by SEM and optical edge placement measurement techniques.