Patent ID: 6838684

Claim:
A lithographic projection apparatus, comprising: a radiation system configured to form a projection beam of radiation from radiation emitted by a radiation source; a support configured to hold a patterning device which is to be irradiated by the projection beam to pattern the projection beam; a substrate table configured to hold a substrate; a projection system configured to image an irradiated portion of the patterning device onto a target portion of the substrate; and a channel barrier near the source configured to prevent material emanating from the source from propagating along an optical axis, the channel barrier comprising a center and a number of elongated channel members each having a width direction transverse to the optical axis and a length direction extending generally in the direction of the optical axis, wherein the channel barrier is rotatable around the optical axis, the lithographic projection apparatus further comprising a drive connected to the channel barrier configured to rotate the channel barrier around the optical axis.