Scanning spot metrology for testing of photolithographic masks

We investigated an optical method for characterizing submicrometer structures of photolithographic masks, enabling fast and non-destructive testing over large areas. The scanning spot metrology provides accurate information about edge locations of opaque structures on chrome masks. Algorithms for the extraction of edge locations from the detector signal are discussed and applied to the characterization of a modulated grating mask. Local fabrication errors of the order of 10 to 50 nm can be detected.