Patent ID: 9588445
Date: 2017-03-07
CPC Classifications: G02B,G03F

Claim:
1. A process for producing a projection objective for microlithography, comprising: assembling a plurality of optical elements to form the projection objective in an initial arrangement for directing light from a first field plane to a second field plane to form an image at the second field plane of an object at the first field plane, there being at least one intermediate image at a corresponding field plane and at least two pupil planes in a path of the light between the first field plane and the second field plane, the plurality of optical elements comprising a first lens and a second lens; removing the first lens from the assembled projection objective and forming a first corrective structure on a curved surface of the first lens; removing the second lens from the assembled projection objective and forming a second corrective structure on a curved surface of the second lens; and arranging the first and second lenses in the projection objective after forming the corrective structures, wherein: the first lens is positioned in the projection objective in the path downstream from an adjacent one of the field planes and upstream from an adjacent one of the pupil planes and the second lens is positioned in the path upstream from an adjacent one of the field planes and downstream from an adjacent one of the pupil planes, and arranging the first and second lenses in the projection objective comprises positioning the first and second corrective structures relative to each other so that their combined effect is to reduce an imaging error of the projection objective at the second field plane relative to the initial arrangement of the projection objective.