Patent ID: 7230220

Claim:
A method of determining at least one optical property of a projection exposure system, the projection exposure system comprising a beam delivery system for supplying an exposure optical beam for illuminating a patterning structure and comprising a projection optical system for imaging the patterning structure onto a photosensitive substrate, wherein the beam delivery system comprises a light source generating light of a first wavelength and of at least a second wavelength different from the first wavelength, wherein a first ratio is defined as an intensity of light of the second wavelength in the exposure optical beam to an intensity of light of the first wavelength in the exposure optical beam, wherein the method comprises: supplying at least one measuring optical beam to the projection optical system, the at least one measuring optical beam comprising light of the first wavelength and at least the second wavelength and having wavefronts; detecting wavefronts of the at least one measuring optical beam having traversed the projection optical system and determining an optical property in dependence of the detected wavefronts; and wherein the detecting and determining includes correcting for contributions of the light of the second wavelength.