Radiation source and method for lithography

A radiation source configured to generate radiation from a plasma generated from a fuel within an enclosure comprising a gas, and the generated plasma resulting in emission of primary debris, the radiation source comprising:

• a component having an optically-active surface;
• and
• a debris-receiving surface positioned and/or oriented such that, in use, the emission of primary debris causes contamination of the debris-receiving surface with a fuel layer,
• wherein the debris-receiving surface is configured to be maintained at a temperature to maintain the fuel layer as a liquid and which is at least 100° C. in excess of a melting point of the fuel so as to reduce a formation of bubbles of the gas within liquid fuel and to reduce an emission of secondary debris by spitting.

A radiation source configured to receive an excitation beam such that, in use, the excitation beam is incident on a fuel at a plasma formation location resulting in emission of primary debris, the radiation source comprising:

• a shroud configured to shield the fuel from the primary debris while the fuel travels to the plasma formation location;
• a debris receiving surface comprising at least a part of a surface of the shroud and positioned and/or oriented such that, in use, the emission of primary debris causes contamination of the debris receiving surface;
• and
• a component having an optically active surface,
• wherein the debris receiving surface and the component are positioned and/or oriented such that substantially all lines normal to the debris receiving surface do not intersect the optically active surface of the component,
• wherein a surface of the shroud is maintained at a temperature above a melting point of the fuel.

A method of generating radiation comprising:

• providing an excitation beam to a plasma formation location within a radiation source comprising an enclosure comprising a gas;
• providing a fuel at the plasma formation location, wherein the excitation beam excites the fuel such that the fuel forms a radiation emitting plasma, the formation of the radiation emitting plasma causes emission of primary debris, and the emission of primary debris causes contamination of a debris-receiving surface of the radiation source with a fuel layer;
• and
• maintaining the debris-receiving surface at a temperature sufficiently high to maintain the fuel layer as a liquid and to provide a rate of formation of bubbles of gas within the liquid fuel layer that is substantially lower than a rate of formation of bubbles of the gas within the liquid fuel layer at a temperature 20° C. in excess of a melting point of the fuel, so as to reduce an emission of secondary debris by spitting.

A lithographic apparatus configured to project a conditioned radiation beam onto a substrate, the apparatus comprising:

• a radiation source configured to generate radiation from a plasma generated from a fuel within an enclosure comprising a gas, and the generated plasma resulting in emission of primary debris, the radiation source comprising:
• a component having an optically-active surface;
• and
• a debris-receiving surface positioned and/or oriented such that the emission of primary debris causes contamination of the debris-receiving surface with a fuel layer,
• wherein the debris-receiving surface is configured to be maintained at a temperature sufficiently high to maintain the fuel layer as a liquid and to provide a rate of formation of bubbles of the gas within the liquid fuel layer that is substantially lower than a rate of formation of bubbles of the gas within the liquid fuel layer at a temperature 20° C. in excess of a melting point of the fuel, so as to reduce an emission of secondary debris by spitting.