# US 9,753,372 B2 · Radiation source for an EUV optical lithographic apparatus, and lithographic apparatus comprising such a radiation source > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,753,372 B2 - Document ID: US9753372B2 - Status: Granted - Kind: B2 - Application number: 14/899,196 - Filed: 2014-06-05 - Published: 2016-05-26 - Granted: 2017-09-05 - Earliest claimed: 2013-06-28 - Assignees: ASML Netherlands B.V. - Applicants: ASML Netherlands B.V. - Inventors: Johannes Christiaan Leonardus Franken - Web page: https://patentgrep.com/patent/US9753372B2 ## CPC - G03F 7/70033: {by plasma extreme ultraviolet [EUV] sources} - G03F 7/70916: {Pollution mitigation, i.e. mitigating effect of contamination or debris, e.g. foil traps} - H05G 2/0094: {Reduction, prevention or protection from contamination; Cleaning} - G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G) - H05G: X-RAY TECHNIQUE (investigating or analysing materials by the use of X-rays G01N23/00; apparatus for X-ray photography G03B42/02; X-ray tubes H01J35/00; TV systems having X-ray input H04N5/321) ## Abstract A radiation source generates extreme ultraviolet radiation. The radiation source comprises a plasma formation site located at a position in which a fuel will be contacted by a beam of radiation to form a plasma. A receiving structure is provided to trap debris particles on its surface that are generated with the formation of the plasma. The receiving structure has a rod-shaped heater element for heating the receiving surface, the device preventing large droplets of fuel from forming on the receiving surface. Instead, the trapped fuel is melted off the receiving surface. ## Claims ### Claim 1 A radiation source apparatus configured to generate a beam of radiation by excitation of a fuel into a plasma, said apparatus comprising: a plasma formation site located at a position in which a fuel will be contacted by a laser beam of radiation to form a plasma; a receiving structure having a receiving surface for capturing fuel debris that is generated with the formation of the plasma; and a heating arrangement for heating one or more receiving surfaces of said receiving structure to a temperature sufficient to liquefy said fuel debris such that it can be made to flow along the surface to another part of the apparatus, said arrangement comprising a heater element for heating of said receiving surface, wherein a portion of the heater element has an adjustable length for providing heating control of the heater element. ### Claim 2 (depends on 1) The apparatus according to claim 1, wherein the portion of the heater element has a spring like shape. ### Claim 3 (depends on 1) The apparatus as claimed in claim 1, wherein said receiving structure comprises a plurality of local structural elements and each local structural element is provided with the at least one opening constructed to allow inserting of the heater element. ### Claim 4 (depends on 3) The apparatus as claimed in claim 3, wherein said at least some of said local structural elements comprise elongated vanes running substantially parallel to one another and at angles oblique to a direction of said radiation beam. ### Claim 5 (depends on 1) The apparatus as claimed in claim 1, wherein said receiving structure comprises a substantially cylindrical or frusto-conical structure surrounding a path of said radiation beam, and lined with a plurality of local structural elements, each element being provided with one or more heater elements for heating the vane. ### Claim 6 (depends on 5) The apparatus according to claim 5, wherein an outer periphery of the local structural elements are made of, or coated with, a material having properties which repel the fuel. ### Claim 7 (depends on 6) The apparatus according to claim 6, wherein the receiving structure is coupled to a wall of the radiation source apparatus, the receiving surface of the receiving structure being configured to reduce an amount of debris particles that scatter or splash from the wall of the source onto a collector of the source. ### Claim 8 (depends on 7) The apparatus according to claim 7, wherein the receiving structure is provided outside an outer boundary of an EUV radiation cone formed by the collector. ### Claim 9 (depends on 1) The apparatus according to claim 1, wherein the heater element is a heater rod comprising: a sheath of material surrounding a carrying core, and an electrical wire coiled around and coupled to the sheath of material. ### Claim 10 (depends on 9) The apparatus according to claim 9, wherein the electrical wire is a resistive wire coiled around the sheath of material at a pitch that ensures an effective wire length for a temperature level sufficient to liquefy said fuel debris such that it can be made to flow along the surface to another part of the apparatus. ### Claim 11 (depends on 10) The apparatus according to claim 10, wherein the sheath of material is provided with a groove following said pitch, wherein the resistive wire is coupled to the groove. ### Claim 12 (depends on 10) The apparatus according to claim 10, wherein one or more cuts are provided in the sheath of material in between the corresponding location of the coiled resistive wire. ### Claim 13 (depends on 12) The apparatus according to claim 12, wherein the cut is provided along the full length of the sheath of material to provide an adjustable sheath length along the axial direction of the heater element. ### Claim 14 (depends on 10) The apparatus according to claim 10, wherein the pitch is modulated along the length of the heater element such as to compensate local temperature variations of the receiving surface. ### Claim 15 (depends on 1) The apparatus according to claim 1, wherein said heating arrangement is configured to heat said surface to a temperature in the range 250° C. to 500° C., for example a temperature above 280° C. and below 350° C. ### Claim 16 (depends on 1) The apparatus as claimed in claim 1, wherein the fuel is excited by laser radiation to generate said beam of EUV radiation. ### Claim 17 A lithographic apparatus, comprising: a radiation source apparatus configured to generate a beam of radiation by excitation of a fuel into a plasma, said apparatus comprising: a plasma formation site located at a position in which a fuel will be contacted by a laser beam of radiation to form a plasma, a receiving structure having a receiving surface for capturing fuel debris that is generated with the formation of the plasma, and a heating arrangement for heating one or more receiving surfaces of said receiving structure to a temperature sufficient to liquefy said fuel debris such that it can be made to flow along the surface to another part of the apparatus, said arrangement comprising a heater element for heating of said receiving surface, wherein a portion of the heater element has an adjustable length for providing heating control of the heater element; and wherein the lithographic apparatus is configured to generate a beam of EUV radiation, and EUV optical systems configured to receive said beam and to use it to transfer a pattern from a patterning device to a substrate. ### Claim 18 An optical apparatus, comprising: a radiation source apparatus configured to generate a beam of radiation by excitation of a fuel into a plasma, said apparatus comprising: a plasma formation site located at a position in which a fuel will be contacted by a laser beam of radiation to form a plasma, a receiving structure having a receiving surface for capturing fuel debris that is generated with the formation of the plasma, and a heating arrangement for heating one or more receiving surfaces of said receiving structure to a temperature sufficient to liquefy said fuel debris such that it can be made to flow along the surface to another part of the apparatus, said arrangement comprising a heater element for heating of said receiving surface, wherein a portion of the heater element has an adjustable length for providing heating control of the heater element; and wherein the optical apparatus is configured to generate a beam of EUV radiation, and EUV optical systems configured to receive and condition the beam and to deliver the beam to a target location. ### Claim 19 A method of generating extreme ultraviolet radiation, the method comprising: contacting a fuel with a beam of radiation, thereby forming a plasma at a plasma formation site; configuring a receiving structure having a receiving surface to trap debris particles that are generated with the formation of the plasma; and heating the receiving surface with a heating element inserted in an opening of the receiving structure. ### Claim 20 (depends on 19) The method according to claim 19, further comprising heating the receiving surface to a temperature sufficient to melt debris that is trapped by the receiving surface.