Patent ID: 8467033

Claim:
A method, comprising: a) determining a set of illumination parameters that describe properties of a light bundle configured to converge at a point on a mask to be illuminated by an illumination system of a microlithographic projection exposure apparatus, the properties of the light bundle comprising an intensity distribution of the light bundle at an exit pupil associated with the point on the mask; b) describing the intensity distribution of the light bundle at the exit pupil as a perturbation of an ideal intensity distribution; c) describing the perturbation as a combination of an intensity modulation and a distortion, wherein the intensity modulation is described as a superposition of basis functions of a first complete function system, and the distortion is described as a superposition of basis functions of a second complete function system; d) determining optical elements of the illumination system whose optical effect on the illumination parameters can be modified based on control commands; e) for each optical element and for at least some functions of the first complete function system and for at least some functions of the second complete function system, determining sensitivities with which the illumination parameters react to an adjustment induced by the control commands; f) determining the control commands, while taking into account the sensitivities determined in e), such that deviations of the illumination parameters from a target set of illumination parameters satisfy a predetermined minimisation criterion; g) applying the control commands determined in f) to the optical elements; and h) illuminating the mask.