Patent ID: 7816658

Claim:
An extreme ultra-violet lithographic apparatus for imaging a pattern onto a substrate, said apparatus comprising: a radiation system constructed and arranged to provide a beam of an extreme ultra-violet radiation; an absorber arranged in the beam and constructed and arranged to absorb at least a portion of the extreme ultra-violet radiation in the beam of the extreme ultra-violet radiation, said absorber comprising a structure defining an internal volume configured to accommodate a flow of an absorbing gas, the flow being directed in a transverse direction with respect to the beam, said structure having an extreme ultra-violet radiation-transmissive beam entry area and an extreme ultra-violet radiation-transmissive beam exit area; and a gas inlet actuator array configured to inject said gas into the internal volume of the absorber and a gas outlet actuator array arranged to evacuate the gas from the internal volume of the absorber, wherein said absorber further comprises a first pump unit and a second pump unit, the gas inlet actuator array and the gas outlet actuator array being located between said first pump unit and said second pump unit along the beam path, said first pump unit and said second pump unit being arranged to substantially prevent the absorbing gas from escaping into an atmosphere of the lithographic apparatus by providing, in use, a vacuum seal for the internal volume of the absorber.