Patent ID: 7505116
Filing Date: 2009-03-17
Classification: G03F

Abstract:
1. In a lithographic projection apparatus including an illuminator configured to provide a beam of radiation, a support configured to support a patterning device, the patterning device configured to pattern the beam according to a desired pattern, a substrate table configured to hold a substrate, and a projection system configured to project the patterned beam onto a target portion of the substrate, a reflector alignment system comprising: reflectors which form part of the projection system; and first and second folding mirrors configured to direct an alignment beam of radiation through the projection system to and from a first reference mark provided in a fixed position on a patterning device side of the projection system and to and from a second reference mark provided in a fixed position on a substrate side of the projection system, wherein the first folding mirror is an angled end of a first transparent rod, wherein the first reference mark comprises a first grating at an end of the first transparent rod opposite the angled end, and wherein the reflector alignment system is configured to measure apparent relative positions of the first reference mark and the second reference mark.