Patent ID: 6898306

Claim:
A method of measuring machine alignment offset of an optical machine having an alignment system, the machine used to form overlayed images of first and second patterns formed on a first or first and second reticles onto a substrate at respective first and second levels, the method comprising the steps of: a) creating one or more virtual zero-offset alignment patterns and one or more virtual zero-offset metrology patterns; b) imaging with the optical machine, using first and second exposures, first and second metrology patterns on the substrate at the first and second levels, respectively, in an overlayed manner, by aligning the second exposure to the first exposure using the zero-offset alignment patterns, said first and second metrology patterns based on the virtual zero-offset metrology patterns of said step a); c) obtaining an image of the overlayed first and second metrology patterns formed on the substrate using the alignment system of the optical machine; and d) comparing the virtual zero-offset metrology pattern to corresponding portions of the image obtained in said step c) to deduce an offset from an ideal alignment of the first and second metrology patterns.