STUDIES ON AN ELECTRON-BEAM MASK-DEFECT INSPECTION SYSTEM

Present optical defect inspection systems cannot detect submicron defects in photomasks used for VLSI chip fabrication because of their poor resolution. The higher resolution and the fast accurate positioning abilities of an electron beam permit submicron defect inspection. A description is presented of an experimental electron beam mask defect inspection system. A new blanking beam dc restoring method was developed to remove detected signal drift. Registration errors between measured pattern data and designed data are eliminated by a pseudo-defect removal algorithm newly introduced here. The signal-to-noise ratio must be larger than 10 to obtain practical reliability on inspection results. The system operates at a scanning speed of 1 mu s/step and detects 0. 5 mu m defects using a 0. 2 mu m square picture element.