Patent ID: 7930654

Claim:
A method of correcting scaling errors, the method comprising: providing a photomask having a layout pattern comprising test structures and a plurality of assist structures; forming a test pattern by projecting the layout pattern of the photomask onto a patterning layer; recording an image of the test pattern with a scanning electron microscope; extracting feature edges of the test pattern within the image; differentiating between patterning layer assist structures and patterning layer test structures during the extraction; calculating at least one scaling error of the image by comparing the extracted feature edges of the test pattern with the layout pattern; and modifying feature edges of the test structures within the layout pattern by correcting the at least one scaling error so as to at least partially compensate the scaling errors, wherein an electronic data representation is capable of providing at least two sub-representations, and storing the assist structures in a first of the at least two sub-representations and the test structures in a second of the at least two sub-representations.