Patent ID: 7145640

Claim:
A lithographic apparatus comprising: an illumination system configured to provide a projection beam of radiation; a support structure configured to support patterning structure, said patterning structure constructed and arranged to impart a pattern to the projection beam; 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 variable attenuator forming a part of the illumination system and comprising: two substantially parallel reflective surfaces positioned such that an input beam of radiation is incident on a first of the reflective surfaces by which it is reflected towards a second of the reflective surfaces by which the radiation is reflected to produce an output beam of radiation of required intensity, wherein the reflective surfaces are positioned such that substantially all of the radiation from the input beam that is included in the output beam is reflected only a single time by each of the reflective surfaces, and an actuator to tilt the reflective surfaces such that the reflective surfaces remain substantially parallel to one another and an angle of incidence of the input beam on the first reflective surface and an angle of incidence of the reflected beam on the second reflective surface are changed so as to vary the intensity of the output beam while substantially maintaining a position of the output beam.