Inspecting method and apparatus for a photomask pattern

Abstract

A method and the apparatus for inspecting the unit pattern arrangements on a photomask to determine relative shear between the unit patterns where each unit pattern has the same shape and size and is printed repeatedly at equal intervals on the photomask. Shear-detecting-patterns are provided on each unit pattern. Adjacent shear-detecting-patterns on adjacent unit patterns are designated as combined patterns. The combined patterns arranged in the same directions make a group. To detect an irregular shear, a standard pattern is designated from the combined patterns in a group and comparison is made between each combined pattern in the group and the standard pattern. An optical image of each combined pattern in a group is and converted into electric signals. The electrical signals for the standard pattern and for the other combined patters are stored a memory. The two sets of signals are read out and compared to provide a shear difference between the patterns. The difference is determined by counting the number of occupied or unoccupied memory locations in both the standard and the other images. The difference in count produces the shear difference. The shear difference is compared with a or tolerance level and it is determined whether the combined pattern arrangement in the group is correct based on the comparison.By repeating the comparison in other groups, it can be determined whether the unit pattern arrangement is correct.