Patent Number: 
Section: claims

1. A spectral purity filter configured to transmit extreme ultraviolet (EUV) radiation and to deflect non-EUV secondary electromagnetic radiation, the spectral purity filter comprising a body of material having a transmissivity for EUV radiation in the range of 5-20 nm of at least 20% and a layer of material having reflection to the non-EUV secondary electromagnetic radiation of at least 50%, said layer being located on a radiation incident side of the body. 2. The spectral purity filter according to claim 1, further comprising a layer of high emissivity material at a radiation exit surface of the body. 3. The spectral purity filter according to claim 2, wherein the emissivity of the material is greater than 0.3. 4. The spectral purity filter according to claim 2, wherein the layer of high emissivity material is located on a radiation incident side of the said layer of material. 5. The spectral purity filter according to claim 1, wherein the layer of material having reflection to the non-EUV secondary electromagnetic radiation is selected from the group: molybdenum, ruthenium, gold, copper and carbon. 6. The spectral purity filter according to claim 1, wherein the layer of material has at least 10% absorption for electromagnetic radiation having a wavelength in a sub-micrometer range. 7. A spectral purity filter configured to transmit at least 20% of extreme ultraviolet (EUV) radiation in the range of 5-20 nm and to deflect at least 50% of non-EUV secondary electromagnetic radiation, the spectral purity filter comprising a body of material and a layer of high emissivity material having emissivity of at least 0.3, said layer of high emissivity material being arranged on a radiation exit surface of the body. 8. The spectral purity filter according to claim 7, wherein the layer of high emissivity material is located on a radiation incident side of the body. 9. The spectral purity filter according to claim 7, wherein the body comprises a multilayer structure of material transmissive of EUV radiation and material suppressive of non-EUV secondary electromagnetic radiation. 10. The spectral purity filter according to claim 7, wherein a material of the body is selected from the group: rubidium (Rb), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), carbon (C), ruthenium (Ru), and silicon (Si). 11. A source module constructed to generate extreme ultraviolet (EUV) radiation and to output the EUV radiation and non-EUV secondary electromagnetic radiation, the source module comprising a spectral purity filter configured to transmit extreme ultraviolet (EUV) radiation and to deflect non-EUV secondary electromagnetic radiation, the spectral purity filter comprising a body of material having a transmissivity for EUV radiation in the range of 5-20 nm of at least 20% and a layer of material having reflection to the non-EUV secondary electromagnetic radiation of at least 50%, said layer being located on a radiation incident side of the body. 12. A lithographic apparatus arranged to project a pattern from a patterning device onto a substrate, the lithographic apparatus comprising a spectral purity filter configured to transmit extreme ultraviolet (EUV) radiation and to deflect non-EUV secondary electromagnetic radiation, the spectral purity filter comprising a body of material having a transmissivity for EUV radiation in the range of 5-20 nm of at least 20% and a layer of material having reflection to the non-EUV secondary electromagnetic radiation of at least 50%, said layer being located on a radiation incident side of the body. 13. A device manufacturing method comprising:generating radiation comprising extreme ultraviolet (EUV) radiation and non-EUV secondary electromagnetic radiation using a radiation source;filtering the radiation to transmit EUV radiation and deflect non-EUV secondary electromagnetic radiation using a spectral purity filter comprising a body of material having at least 50% transmissivity to EUV radiation in the range of 5-20 nm and a layer of material having at least 50% reflection of non-EUV secondary electromagnetic radiation located on a radiation incident side of the body; andprojecting a patterned beam of the transmitted EUV radiation onto a substrate. 14. A device manufacturing method comprising:generating radiation comprising extreme ultraviolet (EUV) radiation and non-EUV secondary electromagnetic radiation using a radiation source;filtering the radiation to transmit EUV radiation and deflect non-EUV secondary electromagnetic radiation using a spectral purity filter comprising a body of material having at least 20% transmissivity to EUV radiation in the range of 5-20 nm and a layer material having emissivity of at least 0.3 at a radiation exit surface of the body; andprojecting a patterned beam of the transmitted EUV radiation onto a substrate. 15. The spectral purity filter according to claim 6, wherein the layer of material has at least 50% absorption for electromagnetic radiation having a wavelength in a sub-micrometer range. 16. The spectral purity filter according to claim 1, wherein the body of material is constructed to absorb at least 90% of the non-EUV secondary electromagnetic radiation that enters the body. 17. The spectral purity filter according to claim 1, wherein the body of material comprises layers of Zr and Si. 18. The spectral purity filter according to claim 17, wherein the body of material comprises a layer structure of Zr/ZrSi2/Si/ZrSi2/Zr. 19. The spectral purity filter according to claim 18, wherein a thickness of each layer of the layer structure is in the range of 0.2 nm- 10 nm.