Lithographic apparatus and device manufacturing method

A lithographic apparatus arranged to project a beam from a radiation source onto a substrate, the apparatus comprising:

• an optical element in a path of the beam;
• a first gas supply for supplying a first gas;
• a second gas supply for supplying a second gas that is lighter that the first gas;
• a first gas inlet coupled to the first gas supply and arranged to introduce the first gas from the first gas supply into the path of the beam;
• and
• a second gas inlet coupled to the second gas supply and arranged to introduce the second gas into a part of the path of the beam between the optical element and a location where the first gas is introduced into the path of the beam.

A lithographic apparatus arranged to project a pattern from a patterning device onto a substrate, the apparatus comprising:

• a radiation source comprising a cathode and anode, a hole being provided in the anode for passing radiation from a region between the anode and the cathode;
• a collector lens arranged to receive the radiation from said hole;
• and
• a foil trap located in a radiation path from the anode to the collector lens, the foil trap comprising electrically conductive strips that are electrically isolated from the anode so that an electric potential of the strips is free to float relative to a potential of the anode.

A device manufacturing method comprising:

• patterning a beam of radiation with a patterning device;
• projecting the patterned beam of radiation onto a substrate;
• using an optical element in a path of the beam;
• and
• introducing gas into the path of the beam so that the gas will be ionized by the beam to create electric fields with field lines toward the optical element,
• wherein the gas has a threshold of kinetic energy for sputtering the optical element that is greater than the kinetic energy developed by ions of the gas in the electric fields.

A device manufacturing method comprising:

• projecting a pattern from a patterning device onto a substrate with a beam of radiation;
• exciting radiation for use in the beam with a cathode-anode assembly;
• providing a foil trap interposed between the cathode-anode assembly and an initial collector lens in the beam path;
• and
• allowing an electrical potential of the foil trap to float relative to a potential of the anode.