Patent ID: 8587767

Claim:
An illumination optics configured to guide an illumination light bundle from a radiation source to an object field, the object field having an aspect ratio of a longer field dimension to a shorter field dimension, the aspect ratio being greater than 1, the illumination optics comprising: a field facet mirror comprising a plurality of field facets configured to set illumination conditions in the object field; and a following optics downstream of the field facet mirror, the following optics being configured to transmit the illumination light into the object field; wherein: the following optics comprises a pupil facet mirror comprising a plurality of pupil facets; the plurality of pupil facets including a first pupil facet and a second pupil facet which is point symmetric to the first pupil facet relative to a center of a pupil defined by the pupil facet mirror; each field facet has a corresponding pupil facet so that a portion of the illumination light bundle impinging upon a given field facet is guided to the object field via its corresponding pupil facet; the field facet mirror comprises a plurality of basic illumination field facets configured to provide a basic illumination of the object field via corresponding basic illumination pupil facets; the field facet mirror comprises a plurality of correction illumination field facets configured to allow illumination of the object field to be corrected via corresponding correction illumination pupil facets; for a first group of the correction illumination field facets, each correction illumination field facet has a longer field facet dimension and a shorter field facet dimension; for the first group of the correction illumination field facets, each correction illumination field facet has a reflectivity for the illumination light which follows a reflectivity pattern along the longer field facet dimension that deviates from a constant reflectivity; the first group of correction illumination field facets comprises first and second correction illumination field facets having the same reflectivity pattern; the first correction illumination field facet is assigned to the first pupil facet; the second correction illumination field facet is assigned to the second pupil facet; and the illumination optics are configured to be used in EUV microlithography.