Patent ID: 7508487

Claim:
A lithographic projection apparatus for imaging a pattern onto a substrate that is at least partially covered by a layer of radiation-sensitive material, the apparatus comprising: a radiation system configured to provide a beam of radiation; a support configured to support a patterning structure, the patterning structure configured to produce a desired pattern in the beam of radiation; a substrate table configured to hold a substrate; a projection system configured to project the patterned beam of radiation onto a target portion of the substrate; and a radiation absorber comprising a gas supply configured to supply an absorbent gas at a controlled concentration to at least one enclosure traversed by the beam of radiation, the absorbent gas serving to absorb radiation energy delivered by the beam of radiation to the substrate during exposure of the radiation-sensitive material to the patterned beam of radiation, wherein the radiation absorber is configured to have a gas concentration in a path of the beam of radiation that is controllably non-uniform in an unobstructed plane perpendicular to an optical axis of the radiation system, or the projection system, or both the radiation system and the projection system, and wherein the beam of radiation traverses through a top surface and a bottom surface of the at least one enclosure, the top and bottom surfaces substantially parallel to each other, while avoiding interaction with an optical element between the top and bottom surfaces of the at least one enclosure.