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A reflective mask blank has a substrate (11) on which a reflective layer (12) for reflecting exposure light in a short-wavelength region including an extreme ultraviolet region and an absorber layer (16) for absorbing the exposure light are successively formed. The absorber layer (16) has an at leas

A reflective mask blank has a substrate (11) on which a reflective layer (12) for reflecting exposure light in a short-wavelength region including an extreme ultraviolet region and an absorber layer (16) for absorbing the exposure light are successively formed. The absorber layer (16) has an at least two-layer structure including as a lower layer an exposure light absorbing layer (14) formed by an absorber for the exposure light in the short-wavelength region including the extreme ultraviolet region and as an upper layer a low-reflectivity layer (15) formed by an absorber for inspection light used in inspection of a mask pattern. The upper layer is made of a material containing tantalum (Ta), boron (B), and nitrogen (N). The content of B is 5 at % to 30 at %. The ratio of Ta and N (Ta:N) falls within a range of 8:1 to 2:7. Alternatively, the reflective mask blank has a substrate on which a multilayer reflective film and an absorber layer are successively formed. In this case, the absorber layer is made of a material containing tantalum (Ta), boron (B), and nitrogen (N). The content of B is 5 at % to 25 at %. The ratio of Ta and N (Ta:N) falls within a range of 8:1 to 2:7.

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The invention claimed is: 1. A reflective mask blank comprising a substrate on which a reflective layer for reflecting exposure light in a short-wavelength region including an extreme ultraviolet region and an absorber layer for absorbing the exposure light are successively formed, the absorber lay

The invention claimed is: 1. A reflective mask blank comprising a substrate on which a reflective layer for reflecting exposure light in a short-wavelength region including an extreme ultraviolet region and an absorber layer for absorbing the exposure light are successively formed, the absorber layer having an at least two-layer structure including as a lower layer an exposure light absorbing layer comprising an absorber for the exposure light and as an upper layer a low-reflectivity layer comprising an absorber for inspection light used in inspection of a mask pattern, the upper layer being farther from the substrate than the lower layer, wherein: the upper layer is made of a material containing tantalum (Ta), boron (B), and nitrogen (N), the content of B being 5 at % to 30 at %, the ratio of Ta and N (Ta:N) falling within a range of 8:1 to 2:7. 2. A reflective mask blank comprising a substrate on which a reflective layer for reflecting exposure light in a short-wavelength region including an extreme ultraviolet region and an absorber layer for absorbing the exposure light are successively formed, the absorber layer having an at least two-layer structure including as a lower layer an exposure light absorbing layer comprising an absorber for the exposure light and as an upper layer a low-reflectivity layer comprising an absorber for inspection light used in inspection of a mask pattern, the upper layer being farther from the substrate than the lower layer, wherein: the upper layer is made of a material containing tantalum (Ta), boron (B), and nitrogen (N) and having an amorphous state. 3. A reflective mask blank comprising a substrate on which a reflective layer for reflecting exposure light in a short-wavelength region including an extreme ultraviolet region and an absorber layer for absorbing the exposure light are successively formed, the absorber layer having an at least two-layer structure including as a lower layer an exposure light absorbing layer comprising an absorber for the exposure light and as an upper layer a low-reflectivity layer comprising an absorber for inspection light used in inspection of a mask pattern, the upper layer being farther from the substrate than the lower layer, wherein: the upper layer is made of a material containing tantalum (Ta), boron (B), and oxygen (O). 4. The reflective mask blank as claimed in claim 3, wherein the upper layer further contains nitrogen (N). 5. The reflective mask blank as claimed in claim 2 or 3, wherein the upper layer contains 5-25 at % boron (B). 6. A reflective mask blank comprising a substrate on which a reflective layer for reflecting exposure light in a short-wavelength region including an extreme ultraviolet region and an absorber layer for absorbing the exposure light are successively formed, the absorber layer having an at least two-layer structure including as a lower layer an exposure light absorbing layer comprising an absorber for the exposure light and as an upper layer a low-reflectivity layer comprising an absorber for inspection light used in inspection of a mask pattern, the upper layer being farther from the substrate than the lower layer, wherein: the upper layer is made of a material containing Ta, at least one of Si and Ge, and at least one of nitrogen and oxygen. 7. A reflective mask blank comprising a substrate on which a reflective layer for reflecting exposure light in a short-wavelength region including an extreme ultraviolet region and an absorber layer for absorbing the exposure light are successively formed, the absorber layer having an at least two-layer structure including as a lower layer an exposure light absorbing layer comprising an absorber for the exposure light and as an upper layer a low-reflectivity layer comprising an absorber for inspection light used in inspection of a mask pattern, the upper layer being farther from the substrate than the lower layer, wherein: the upper layer is formed by a substance containing Ta, nitrogen, and oxygen. 8. The reflective mask blank as claimed in any one of claims 2 3, 6 and 7 wherein the material of the upper layer has an amorphous state. 9. A reflective mask blank comprising a substrate on which a reflective layer for reflecting exposure light in a short-wavelength region including an extreme ultraviolet region and an absorber layer for absorbing the exposure light are successively formed, the absorber layer having an at least two-layer structure including as a lower layer an exposure light absorbing layer comprising an absorber for the exposure light and as an upper layer a low-reflectivity layer comprising an absorber for inspection light used in inspection of a mask pattern, the upper layer being farther from the substrate than the lower layer, wherein: the low-reflectivity layer as the upper layer comprises: at least one selected from a second group including: one of nitride, oxide, and oxynitride of one element selected from a first group including chromium, manganese, cobalt, copper, zinc, gallium, germanium, molybdenum, palladium, silver, cadmium, tin, antimony, tellurium, iodine, hafnium, tantalum, tungsten, titanium, and gold; one of the nitride, the oxide, and the oxynitride with silicon added thereto; one of nitride, oxide, and oxynitride of an alloy containing one element selected from the first group; one of the nitride, the oxide, and the oxynitride of the alloy with silicon added thereto; and silicon oxynitride. 10. The reflective mask blank as claimed in claim 9, wherein: the exposure light absorbing layer as the lower layer comprises: at least one selected from a third group including: one element selected from the first group; a substance containing at least one of nitrogen and oxygen and the selected one element; an alloy containing one element selected from the first group; and a substance containing at least one of nitrogen and oxygen and the alloy. 11. The reflective mask blank as claimed in anyone of claims 1 through 3, 6, 7 and 9, wherein the exposure light absorbing layer as the lower layer is made of a material containing Ta. 12. The mask blank as claimed in claim 11, wherein the material of the exposure light absorbing layer as the lower layer further contains B. 13. The reflective mask blank as claimed in any one of claims 1, 2, 3, 6, 7 and 9, wherein an intermediate region where a composition is continuously varied from a composition of the lower layer to a composition of the upper layer is interposed between the lower layer and the upper layer. 14. The reflective mask blank as claimed in any one of claims 1, 2, 3, 6, 7 and 9, comprising a buffer layer interposed between the reflective layer and the absorber layer to protect the reflective layer during pattern formation on the absorber layer. 15. The reflective mask blank as claimed in claim 14, wherein the lower layer of the absorber layer is formed by a substance containing Ta, the buffer layer being formed by Cr or a substance containing Cr as a main component. 16. The reflective mask blank as claimed in any one of claims 1, 2, 3, 6, 7 and 9, wherein a contrast between reflected light reflected on a surface of the reflective layer and reflected light reflected on a surface of the absorber layer is 40% or more at the wavelength of light used in inspection of a pattern formed on the absorber layer. 17. The reflective mask blank as claimed in any one of claims 1, 2, 3, 6, 7 and 9, further comprising a buffer layer formed between the reflective layer and the absorber layer to protect the reflective layer during pattern formation on the absorber layer; a contrast between reflected light reflected on a surface of the buffer layer and reflected light reflected on a surface of the absorber layer being 40% or more at the wavelength of light used in inspection of a pattern formed on the absorber layer. 18. The reflective mask blank as claimed in any one of claims 1, 2, 3, 6, 7 and 9, wherein the reflectivity on the surface of the absorber layer is 20% or less at the wavelength of light used in inspection of a pattern formed on the absorber layer. 19. The reflective mask blank as claimed in any one of claims 1, 2, 3, 6, 7 and 9, wherein the surface of the absorber layer has a surface roughness of 0.5 nmRms or less. 20. The reflective mask blank as claimed in any one of claims 1, 2, 3, 6, 7 and 9, wherein a substance forming the upper layer of the absorber layer has a refractive index n and an extinction coefficient k at the wavelength of inspection light, where n is 1.5 to 3.5 and k is 0.7 or less. 21. The reflective mask blank as claimed in any one of claims 1, 2, 3, 6, 7 and 9, wherein the thickness of the low-reflectivity layer as the upper layer is selected, with reference to the relationship between the reflectivity of the surface of the absorber layer for inspection light and the thickness of the low-reflectivity layer, so as to minimize the reflectivity of the surface of the absorber layer at the wavelength of the inspection light. 22. The reflective mask blank as claimed in any one of claims 1, 2, 3, 6, 7 and 9, wherein the thickness of the low-reflectivity layer is 5 to 30 nm. 23. A reflective mask obtained by patterning the absorber layer of the reflective mask blank claimed in any one of claims 1, 2, 3, 6, 7 and 9. 24. A reflective mask blank comprising a substrate on which a multilayer reflective film for reflecting exposure light and an absorber layer for absorbing the exposure light are successively formed, the absorber layer being made of a material containing tantalum (Ta), boron (B), and nitrogen (N), the content of B being 5 at % to 25 at %, the ratio of Ta and N (Ta:N) falling within a range of 8:1 to 2:7. 25. A reflective mask blank comprising a substrate on which a multilayer reflective film for reflecting exposure light and an absorber layer for absorbing the exposure light are successively formed, the absorber layer containing tantalum (Ta), boron (B), and nitrogen (N), the absorber layer having an amorphous state. 26. A reflective mask blank comprising a substrate on which a multilayer reflective film for reflecting exposure light and an absorber layer for absorbing the exposure light are successively formed, the absorber layer being made of a material containing tantalum (Ta), boron (B), and oxygen (O). 27. The reflective mask blank as claimed in claim 26, wherein the material of the absorber layer further contains nitrogen (N). 28. The reflective mask blank as claimed in claim 25 or 26, wherein the material of the absorber layer contains 5-25 at % boron (B). 29. The reflective mask blank as claimed in claim 25 or 26, wherein the material of the absorber layer has an amorphous state. 30. The reflective mask blank as claimed in any one of claims 24 through 26, wherein the absorber layer has a distribution of composition in which the content of oxygen or nitrogen is gradually increased in the thickness direction towards the surface of the absorber layer. 31. The reflective mask blank as claimed in any one of claims 24 through 26, further comprising a buffer layer formed between the multilayer reflective film and the absorber layer to protect the multilayer reflective film during pattern formation onto the absorber layer. 32. The reflective mask blank as claimed in claim 31, wherein the buffer layer is made of a material containing chromium (Cr). 33. The reflective mask blank as claimed in any one of claims 24 through 26, wherein a contrast between reflected light reflected on a surface of the multilayer reflective film and reflected light reflected on a surface of the absorber layer is 40% or more at the wavelength of light used in inspection of a pattern formed on the absorber layer. 34. The reflective mask blank as claimed in any one of claims 24 through 26, further comprising a buffer layer formed between the multilayer reflective film and the absorber layer to protect the multilayer reflective film during pattern formation on the absorber layer; a contrast between reflected light reflected on a surface of the buffer layer and reflected light reflected on a surface of the absorber layer being 40% or more at the wavelength of light used in inspection of a pattern formed on the absorber layer. 35. The reflective mask blank as claimed in any one of claims 24 through 26, wherein the reflectivity on the surface of the absorber layer is 20% or less at the wavelength of light used in inspection of a pattern formed on the absorber layer. 36. The reflective mask blank as claimed in any one of claims 24 through 26, wherein the surface of the absorber layer has a surface roughness of 0.5 nmRms or less. 37. A reflective mask obtained by patterning the absorber layer of the reflective mask blank claimed in any one of claims 24 through 26. 38. A method of producing a semiconductor, wherein a pattern is transferred onto a semiconductor substrate by the use of the reflective mask claimed in claim 37.