Patent ID: 9678440
Date: 2017-06-13
CPC Classifications: G03F

Claim:
1. An apparatus, comprising: an illumination system configured to produce illumination radiation incident on an object bearing a pattern; a projection objective configured to project an image of the pattern onto a radiation-sensitive substrate; a scanning system configured to, during a scanning operation, move the object relative to an effective object field of the projection objective in a first direction and to simultaneously move the radiation-sensitive substrate relative to the effective image field of the projection objective in a second direction; and a control system configured to vary a field curvature of the projection objective and vary a distortion of the projection objective, wherein: the projection objective comprises a plurality of optical elements each coupled to one or more corresponding manipulators, the plurality of optical elements comprising at least one concave mirror and at least one transparent optical element; the at least one concave mirror comprises a reflective surface having a radius of curvature arranged in the projection beam path, the one or more manipulators coupled to the mirror being configured to adjust the radius of curvature from a first value to a second value thereby varying the field curvature of the projection objective at the effective image field; and the control system being configured to manipulate at least one of the plurality of optical elements during the scanning operation.