Line width insensitive wafer target detection

Abstract From the Canadian patent

An alignment system for use in semiconductor manufacturing that matches pairs of like edges of alignment marks. Grating type alignment marks are illuminated by a predetermined illumination pattern with the reflected and/or scattered electromagnetic radiation collected by a detector. Like edges are selected from the collected electromagnetic radiation and matched. A signal analyzer analyses the matched like edges and obtains alignment information. The matching of like edges results in relatively process insensitive detection of wafer a alignment marks. The distance between like edges is substantially less effected by wafer processing. Wafer alignment marks can thereby be more accurately …