Patent ID: 7274434

Claim:
A lithographic apparatus, comprising: a support configured to support a patterning device, the patterning device configured to impart a pattern to a beam of radiation; a substrate table configured to hold a substrate; a projection system configured to project the patterned beam onto a target portion of the substrate; and a stop changer configured to exchangeably place a selected one of a plurality of separable stop discs in the projection system and adjacent to a focusing element of the lithographic apparatus, the selected stop disc selected from a group of two or more of the following: a first disc having a circular aperture of a first size, a second disc having a circular aperture of a second size greater than the first size, a disc having an aperture with a central obscuration, a disc having a square aperture, a disc having a hexagonal aperture, and a disc to correct pupil apodization, a size of an aperture of the selected stop disc determining a numerical aperture of the projection system.