US Patent 7534552 Lithographic apparatus and device manufacturing method

In known lithographic apparatus the projection beam is symmetrical, while the process window can be asymmetrical. The invention addresses this problem by providing a lithographic apparatus comprising an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, wherein there is further provided a system for providing an asymmetric projection beam bandwidth distribution.