Patent ID: 8184264

Claim:
A method for calibrating a photolithography system, the method comprising: simultaneously illuminating first and second grating patterns of a single reticle with an asymmetric monopole illumination source perpendicular to the first and second gratings, wherein the first grating pattern has a first pitch, and wherein the second grating pattern has a second pitch different from the first pitch; producing first and second refraction patterns on the photoresist layer corresponding to first and second grating patterns, respectively, wherein the first refraction pattern has refraction angles of at least two different refraction orders that are at least substantially equal to each other, and wherein the second refraction pattern has refraction angles of at least two different refraction orders that are different from each other; measuring an image shift between the first and second refraction patterns on the photoresist layer; and determining a defocus shift of the illumination source based on the image shift.