Method for determining an imaging quality of an optical system when illuminated by illumination light within a pupil to be measured

Abstract

To determine an imaging quality of an optical system when illuminated by illumination light within a pupil to be measured of the optical system and/or to qualify the phase effect of a test structure, a test structure that is periodic in at least one dimension is initially arranged in an object plane of the optical system. An initial illumination angle distribution for illuminating the test structure with an initial pupil region, whose area is less than 10% of a total pupil area, is specified and the test structure is illuminated thereby in different distance positions relative to the object plane. In this way, an initial measured aerial image of the test structure is determined. Specifying the illumination distribution, illuminating and determining the aerial image are then repeated for a further illumination angle distribution and an imaging contribution of the optical system is determined from a comparison of the measured aerial images, the imaging quality parameter to be determined and/or a complex-valued diffraction spectrum of the test structure being determined from said imaging contribution. A metrology system for carrying out the method comprises a holder for the test structure, an illumination optical unit, a specification device for specifying the illumination angle distributions, the optical system to be examined in respect of its imaging quality, and a spatially resolving detection device for determining aerial images. This yields an improved imaging quality determination method.