Patent ID: 7887978

Claim:
A method of detecting defects on a photolithography mask, the method comprising: performing a plurality of exposure processes with said photolithography mask on the basis of a first exposure parameter setting to generate a first plurality of images of said photolithography mask, wherein said first exposure parameter setting is selected to be outside a range of allowable parameter values for exposure parameters when using said photolithography mask during production, said first exposure parameter setting being above said range; performing a plurality of exposure processes with said photolithography mask on the basis of a second exposure parameter setting to generate a second plurality of images of said photolithography mask, wherein said second exposure parameter setting is selected to be outside said range, said second exposure parameter setting being below said range; and performing a defect inspection process on said first and second pluralities of images to determine the presence of a repeating defect in at least some of said first and second pluralities of images.