Abstract: The invention relates to a lithographic apparatus that includes a system configured to condition a radiation beam or project a patterned radiation beam onto a target portion of a substrate. The system includes an optically active device configured to direct the radiation beam or the patterned radiation beam, respectively, and a support structure configured to support the optically active device. The apparatus further includes a gas supply for providing a background gas into the system. The radiation beam or patterned radiation beam react with the background gas to form a plasma that includes a plurality of ions. The support structure includes an element that includes a material that has a low sputtering yield, a high sputter threshold energy, or a high ion implantation yield, to reduce sputtering and the creation of sputtering products.

Abstract: A lithographic projection apparatus includes an alignment sensor having an electron beam source constructed and arranged to provide an electron beam for impinging on an alignment marker on a substrate, and a back-scattered electron detector constructed and arranged to detect electrons back-scattered from the alignment marker. The alignment sensor is independent of the projection system and projection radiation, and is an off-axis alignment sensor.