Reflective mask blank, reflective mask, reflective mask blank manufacturing method, and reflective mask manufacturing method

Abstract

The purpose of the present invention is to provide a technology that solves the problem wherein it is difficult to correct the position of an opening pattern formed on an absorption film when defects that are present between a substrate and the absorption film are clustered together, and thus improves the likelihood of success of correcting the position of the opening pattern formed on the absorption film.　This reflective mask blank, in which a protection film and an absorption film are formed on a multilayered reflection film, has a quality assurance region that matches with a light exposure region in plan view, and the quality assurance region is configured such that after the formation of the protection film and before the formation of the absorption film, in an arbitrary inspection region that is a square shape with each side having a length of 20 mm, the number of first defects that are detectable by EUV light and have a sphere equivalent diameter of 14 nm or greater is less than or equal to 1.

Description

Reflective mask blank, reflective mask, method for manufacturing a reflective mask blank, and method for manufacturing a reflective mask

[0001] The present disclosure relates to a reflective mask blank, a reflective mask, a method for manufacturing a reflective mask blank, and a method for manufacturing a reflective mask.

[0002] In recent years, with the miniaturization of semiconductor devices, EUV lithography (EUVL), an exposure technology using extreme ultraviolet (EUV) light, has been developed. EUV light has a wavelength of approximately 13.5 nm. A reflective mask is used in EUVL. A reflective mask includes, in this order, a substrate such as a glass substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs EUV light. The absorbing film may not only absorb EUV light but also shift the phase of the EUV light. In other words, the absorbing film may be a phase shift film. An aperture pattern is formed in the absorbing film. In EUVL, the aperture pattern in the absorbing film is transferred to a target substrate such as a semiconductor substrate. Transferring includes reducing and transferring.

[0003] Patent Document 1 describes a method for inspecting substrates with a multilayer reflective film. This inspection method detects and stores the positions of defects. This makes it possible to correct the positions of the opening patterns formed in the absorbing film so that the defects are covered by the absorbing film. As a result, it is possible to prevent the defects from affecting the transfer accuracy of EUVL. This technique is called mitigation.

[0004] Japanese Patent Application Publication No. 2022-165217

[0005] Conventionally, defects existing between the substrate and the absorbing film are concentrated, making it difficult to correct the position of the opening pattern formed in the absorbing film.

[0006] An embodiment of the present disclosure provides a technique for improving the success rate of position correction of an opening pattern formed in an absorbing film.

[0007] A reflective mask blank according to an embodiment of the present disclosure includes, in this order, a substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs EUV light, wherein the absorbing film has an exposure area to which an exposure tool is to expose the substrate with EUV light. The protective film has a quality assurance area that coincides with the exposure area in a planar view. The quality assurance area has, after the formation of the protective film but before the formation of the absorbing film, one or less first defects that are detectable by EUV light and have a sphere-equivalent diameter of 14 nm or greater in an arbitrary inspection area having a square shape with sides of 20 mm.

[0008] According to an embodiment of the present disclosure, it is possible to improve the success rate of correcting the position of an opening pattern formed in an absorbing film.

[0009] FIG. 1 is a cross-sectional view showing a reflective mask blank according to an embodiment. FIG. 2 is a flowchart showing a method for manufacturing a reflective mask blank according to an embodiment. FIG. 3 is a cross-sectional view showing a reflective mask according to an embodiment. FIG. 4 is a flowchart showing a method for manufacturing a reflective mask according to an embodiment. FIG. 5A is a cross-sectional view showing an example of step S201, FIG. 5B is a cross-sectional view showing an example of step S202, and FIG. 5C is a cross-sectional view showing an example of step S203. FIG. 6 is a cross-sectional view showing an example of EUV light reflected by the reflective mask of FIG. 3. FIG. 7 is a cross-sectional view showing an example of the positional relationship between an opening pattern of an absorbing film and defects. FIG. 8 is a diagram showing an example of the relationship between a set of defects detectable with EUV light and a set of defects detectable with DUV light. FIG. 9 is a diagram showing an example of a spin cleaning apparatus. FIG. 10 is a plan view showing a first example of the positional relationship between a quality assurance area, an inspection area, first defects DA, and second defects DB. FIG. 11 is a plan view showing a second example of the positional relationship between a quality assurance area, an inspection area, first defects DA, and second defects DB. FIG. 12 is a plan view showing a third example of the positional relationship between the quality assurance area, the inspection area, the first defect DA, and the second defect DB.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and their description may be omitted. In the specification, the symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. The range of values ​​includes the range rounded up or down.

[0011] In each drawing, the X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to one another. The Z-axis direction is perpendicular to the first main surface 10a of the substrate 10. The X-axis direction is perpendicular to the plane of incidence of the EUV light (the plane including the incident light beam and the reflected light beam). As shown in Figure 6, the incident light beam is tilted more in the positive Y-axis direction as it moves in the negative Z-axis direction, and the reflected light beam is tilted more in the positive Y-axis direction as it moves in the positive Z-axis direction.

[0012] A reflective mask blank 1 according to one embodiment will be described with reference to FIG. 1 . The reflective mask blank 1 includes, for example, a substrate 10, a multilayer reflective film 11, a protective film 12, an absorbing film 13, and a hard mask film 14, in this order. The multilayer reflective film 11, the protective film 12, the absorbing film 13, and the hard mask film 14 are formed on a first main surface 10a of the substrate 10 in this order. The multilayer reflective film 11 reflects EUV light. The protective film 12 protects the multilayer reflective film 11 from a first etching gas during processing of the absorbing film 13. The absorbing film 13 absorbs EUV light. The absorbing film 13 may not only absorb EUV light but also shift the phase of the EUV light. In other words, the absorbing film 13 may be a phase shift film. The hard mask film 14 protects a portion of the absorbing film 13 from the first etching gas during processing of the absorbing film 13.

[0013] The reflective mask blank 1 has a conductive film 15 on the opposite side of the substrate 10 from the multilayer reflective film 11. That is, the reflective mask blank 1 may have the conductive film 15, substrate 10, multilayer reflective film 11, protective film 12, absorbing film 13, and hard mask film 14, in this order. The conductive film 15 is formed on the second main surface 10b of the substrate 10. The second main surface 10b is the surface facing opposite to the first main surface 10a. The conductive film 15 is used to attach the reflective mask 2 to an electrostatic chuck of an exposure tool.

[0014] The reflective mask blank 1 may further have a functional film not shown in Fig. 1. For example, the reflective mask blank 1 may have an anti-reflection film not shown between the absorbing film 13 and the hard mask film 14. The anti-reflection film improves the optical contrast during inspection of the opening pattern 13op of the absorbing film 13. The reflective mask blank 1 may also have a diffusion barrier film not shown between the multilayer reflective film 11 and the protective film 12. The diffusion barrier film suppresses diffusion of metal elements contained in the protective film 12 into the multilayer reflective film 11.

[0015] Although not shown, the reflective mask blank 1 may have a buffer film between the protective film 12 and the absorbing film 13. The buffer film protects the protective film 12 from the first etching gas that forms the opening pattern 13op in the absorbing film 13. The buffer film is etched more slowly than the absorbing film 13. Unlike the protective film 12, the buffer film will ultimately have the same opening pattern as the opening pattern 13op of the absorbing film 13.

[0016] Next, a method for manufacturing a reflective mask blank 1 according to one embodiment will be described with reference to Fig. 2. The method for manufacturing a reflective mask blank 1 includes, for example, steps S101 to S106 shown in Fig. 2. In step S101, a substrate 10 is prepared. In step S102, a conductive film 15 is formed on the second main surface 10b of the substrate 10. In step S103, a multilayer reflective film 11 is formed on the first main surface 10a of the substrate 10. In step S104, a protective film 12 is formed on the multilayer reflective film 11. In step S105, an absorbing film 13 is formed on the protective film 12. In step S106, a hard mask film 14 is formed on the absorbing film 13.

[0017] The order of steps S101 to S106 is not limited to the order shown in Fig. 2. For example, the order of step S102 and steps S103 to S106 may be reversed. Furthermore, the method for manufacturing the reflective mask blank 1 does not have to include all of steps S101 to S106. The method for manufacturing the reflective mask blank 1 may further include a step of forming a functional film not shown in Fig. 2.

[0018] Next, a reflective mask 2 according to one embodiment will be described with reference to Fig. 3. The reflective mask 2 includes, for example, the reflective mask blank 1 shown in Fig. 1 and includes an opening pattern 13op in an absorbing film 13. In EUVL, the opening pattern 13op in the absorbing film 13 is transferred to a target substrate such as a semiconductor substrate. Transferring includes reducing and transferring. Note that the hard mask film 14 shown in Fig. 1 is not included in the reflective mask 2.

[0019] Next, a method for manufacturing a reflective mask 2 according to one embodiment will be described with reference to Figures 4 and 5. The method for manufacturing a reflective mask 2 includes steps S201 to S204 shown in Figure 4. In step S201, a reflective mask blank 1 is prepared, as shown in Figure 5(A). The reflective mask blank 1 includes a resist film 16, as shown in Figure 5(A). The resist film 16 is formed on a hard mask film 14. An opening pattern to be transferred to the absorption film 13 is formed in the resist film 16.

[0020] 5B, the hard mask film 14 is processed using the resist film 16 having an opening pattern. In the openings in the resist film 16, the hard mask film 14 is exposed to a second etching gas, and the second etching gas etches the hard mask film 14. At the end of step S202, the resist film 16 remains. As a result, the opening pattern of the resist film 16 is transferred to the hard mask film 14.

[0021] The second etching gas is selected depending on the combination of the material of the resist film 16 and the material of the hard mask film 14, and is not particularly limited, but may include, for example, a fluorine-based gas. The fluorine-based gas may be, for example, CF ４ Gas, CHF ３ Gas, C ２ F ６ Gas, C ３ F ６ Gas, C ４ F ６ Gas, C ４ F ８ Gas, CH ２ F ２ Gas, CH ３ F gas, C ３ F ８Gas, F ２ Gas, SF ６ Gas and NF ３ The second etching gas may contain at least one selected from the group consisting of a fluorine-based gas, an active gas, and an inert gas. The active gas may be, for example, O ２ Gas and O ３ The inert gas includes at least one selected from the group consisting of N ２ The second etching gas preferably contains at least one selected from the group consisting of a nitrogen gas, a He gas, and an Ar gas. The second etching gas is preferably a plasma.

[0022] In step S203, as shown in FIG. 5C , the absorber film 13 is processed using the hard mask film 14 having an opening pattern. In the openings in the hard mask film 14, the absorber film 13 is exposed to a first etching gas, and the first etching gas etches the absorber film 13. The hard mask film 14 has higher resistance to the first etching gas than the absorber film 13. At the end of step S203, the hard mask film 14 remains. As a result, the opening pattern of the hard mask film 14 is transferred to the absorber film 13.

[0023] The first etching gas is selected depending on the combination of the material of the hard mask film 14 and the material of the absorption film 13, and is not particularly limited, but includes, for example, a chlorine-based gas and an oxygen-based gas. The chlorine-based gas is, for example, Cl ２ Gas, SiCl ４ Gas, CHCl ３ Gas, CCl ４ Gas and BCl ３ The oxygen-based gas includes at least one selected from the group consisting of O ２ Gas and O ３ The first etching gas may contain at least one selected from the group consisting of a chlorine-based gas, an oxygen-based gas, and an inert gas. The inert gas may be, for example, N ２ The first etching gas preferably contains at least one selected from the group consisting of a nitrogen gas, a He gas, and an Ar gas. The first etching gas is preferably a plasma.

[0024] In step S204, although not shown, the hard mask film 14 is removed. A third etching gas, for example, is used to remove the hard mask film 14. The third etching gas, like the second etching gas, contains, for example, a fluorine-based gas. The third etching gas is preferably a plasma gas. A chemical solution may be used to remove the hard mask film 14.

[0025] Next, referring back to FIG. 1, the substrate 10, the multilayer reflective film 11, the protective film 12, the absorbing film 13, the hard mask film 14, and the conductive film 15 will be described in this order.

[0026] The substrate 10 is, for example, a glass substrate. The material of the substrate 10 is TiO ２ The quartz glass has a smaller coefficient of linear expansion and a smaller change in dimension due to temperature changes than common soda lime glass. ２ 80% by mass to 95% by mass of TiO ２ It may contain 4% to 17% by mass of TiO ２ When the content is 4% by mass to 17% by mass, the linear expansion coefficient is approximately zero around room temperature, and there is almost no dimensional change around room temperature. ２ and TiO ２ The substrate 10 may contain a third component or impurities other than the above. The material of the substrate 10 may be crystallized glass in which a β-quartz solid solution is precipitated, silicon, a metal, or the like.

[0027] The substrate 10 has a first major surface 10a and a second major surface 10b facing opposite to the first major surface 10a. A multilayer reflective film 11 and the like are formed on the first major surface 10a, and a conductive film 15 is formed on the second major surface 10b. In plan view (Z-axis direction), the substrate 10 measures, for example, 152 mm in length and 152 mm in width. The length and width may be 152 mm or greater. The first major surface 10a has a rectangular quality assurance area. The quality assurance area coincides with the exposure area in plan view. The exposure area is the area where the exposure device is intended to irradiate the absorber film 13 with EUV light. The size of the quality assurance area is appropriately selected depending on the size of the substrate 10; for example, the long side length is 132 mm and the short side length is 104 mm. The quality assurance area preferably has a root-mean-square roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less. It is also preferable that the quality assurance area does not have any defects that cause phase defects.

[0028] The multilayer reflective film 11 reflects EUV light. The multilayer reflective film 11 is formed by alternately stacking, for example, high-refractive-index layers and low-refractive-index layers. The high-refractive-index layers are made of, for example, silicon (Si), and the low-refractive-index layers are made of, for example, molybdenum (Mo), so that a Mo / Si multilayer reflective film is used. Note that other films that can be used as the multilayer reflective film 11 include a Ru / Si multilayer reflective film, a Mo / Be multilayer reflective film, a Mo compound / Si compound multilayer reflective film, a Si / Mo / Ru multilayer reflective film, a Si / Mo / Ru / Mo multilayer reflective film, a Si / Ru / Mo / Ru multilayer reflective film, and a Si / Ru / Mo multilayer reflective film.

[0029] The thickness of each layer constituting the multilayer reflective film 11 and the number of repeating units of the layers can be appropriately selected depending on the material of each layer and the reflectivity for EUV light. When the multilayer reflective film 11 is a Mo / Si multilayer reflective film, in order to achieve a reflectivity of 60% or more for EUV light at an incident angle θ (see FIG. 6 ) of 6°, Mo layers with a thickness of 2.3±0.1 nm and Si layers with a thickness of 4.5±0.1 nm can be stacked so that the number of repeating units is 30 to 60. The multilayer reflective film 11 preferably has a reflectivity of 60% or more for EUV light at an incident angle θ of 6°. The reflectivity is more preferably 65% ​​or more.

[0030] The method for forming each layer constituting the multilayer reflective film 11 is, for example, DC sputtering, magnetron sputtering, or ion beam sputtering. When the Mo / Si multilayer reflective film is formed using ion beam sputtering, an example of the film formation conditions for the Mo layer and the Si layer is as follows: <Si layer formation conditions> Target: Si target, Sputtering gas: Ar gas, Gas pressure: 1.3×10 －２ Pa ~ 2.7 x 10 －２ Pa, Ion acceleration voltage: 300 V to 1500 V, Film formation rate: 0.030 nm / sec to 0.300 nm / sec, Thickness of Si layer: 4.5±0.1 nm, <Film formation conditions for Mo layer> Target: Mo target, Sputtering gas: Ar gas, Gas pressure: 1.3×10 －２ Pa ~ 2.7 x 10 －２ Pa, ion acceleration voltage: 300 V to 1500 V, film formation rate: 0.030 nm / sec to 0.300 nm / sec, film thickness of Mo layer: 2.3±0.1 nm, <Repeating units of Si layer and Mo layer> Number of repeating units: 30 to 60 (preferably 40 to 50).

[0031] The protective film 12 is formed between the multilayer reflective film 11 and the absorbing film 13 to protect the multilayer reflective film 11. The protective film 12 protects the multilayer reflective film 11 from the first etching gas when processing the absorbing film 13, i.e., in step S203. The protective film 12 is not removed even when exposed to the first etching gas, but remains on the multilayer reflective film 11.

[0032] The protective film 12 contains at least one element selected from, for example, Ru, Rh, and Si. The protective film 12 preferably contains ruthenium (Ru) as a main component. As described above, the protective film 12 containing Ru as a main component means that the Ru content in the protective film 12 is 40 at% or more. The Ru content in the protective film 12 is preferably 45 at% or more, and more preferably 50 at% or more. When the protective film 12 contains Ru, it may contain only Ru, or it may also contain a Ru compound. The Ru compound may be a Ru alloy. The Ru alloy contains, for example, Ru and at least one metal element selected from Rh, Nb, Mo, Ta, Ir, Pd, Zr, Y, and Ti.

[0033] The Ru compound may contain, in addition to Ru, at least one nonmetallic element selected from N, O, C, and B. These nonmetallic elements reduce the resistance of the protective film 12 to the first etching gas, but reduce the crystallinity of the protective film 12, thereby improving the smoothness of the protective film 12. When the Ru compound has a non-crystalline (amorphous) structure or a microcrystalline structure, the X-ray diffraction pattern of the Ru compound does not have a clear peak.

[0034] However, it is preferable that the protective film 12 does not contain at least one nonmetallic element selected from N, O, C, and B. In other words, it is preferable that the total content of N, O, C, and B is 0.1 at% or less. If the total content of N, O, C, and B is 0.1 at% or less, the protective film 12 is likely to crystallize, but the protective film 12 has good resistance to the first etching gas.

[0035] In this embodiment, the protective film 12 is a single-layer film made of a single layer, but it may also be a multi-layer film having a lower layer and an upper layer. The lower layer of the protective film 12 is a layer formed in contact with the uppermost surface of the multilayer reflective film 11. The upper layer of the protective film 12 is in contact with the lowermost surface of the absorbing film 13. By making the protective film 12 have such a multi-layer structure, materials with excellent predetermined functions can be used for each layer, thereby making the protective film 12 as a whole multifunctional.

[0036] The upper layer of the protective film 12 preferably contains at least one metal element selected from Ru and Rh, and more preferably contains Rh. The lower layer of the protective film 12 preferably contains at least one element selected from Ru, Rh, Nb, Mo, Zr, Y, and Si, and more preferably contains Ru. When the protective film 12 is a multi-layer film, the thickness of the protective film 12 below refers to the total film thickness of the multi-layer film. Note that a mixing layer formed by mixing components contained in the multi-layer reflective film 11 and components contained in the lower layer of the protective film 12 may be formed between the multi-layer reflective film 11 and the lower layer of the protective film 12.

[0037] The thickness of the protective film 12 is preferably 1.0 nm to 4.0 nm. If the thickness of the protective film 12 is 1.0 nm or more, the etching resistance is good. Furthermore, if the thickness of the protective film 12 is 4.0 nm or less, the reflectance to EUV light is good. The thickness of the protective film 12 is more preferably 2.0 nm to 3.5 nm, and even more preferably 2.5 nm to 3.0 nm.

[0038] The density of the protective film 12 is preferably 10.0 g / cm ３ ~14.0g / cm ３ The density of the protective film 12 is 10.0 g / cm ３ If the density of the protective film 12 is 14.0 g / cm or more, the etching resistance is good. ３ If the thickness is equal to or less than this, it is possible to suppress the absorption of EUV light by the protective film 12 (and thus the reduction in reflectance for EUV light).

[0039] The protective film 12 can be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering. When the Ru film is formed by ion beam sputtering, an example of the film formation conditions is as follows: <Ru film formation conditions> Target: Ru target, Sputtering gas: Ar gas, Gas pressure: 0.010 Pa to 0.020 Pa, Target power density: 1.0 W / cm ２ ~8.5 W / cm ２ , Film formation rate: 0.01 nm / sec to 0.10 nm / sec, Film thickness: 1 nm to 10 nm.

[0040] The absorbing film 13 absorbs EUV light. The absorbing film 13 is a film in which an opening pattern 13op is to be formed. The opening pattern 13op is not formed in the manufacturing process of the reflective mask blank 1, but is formed in the manufacturing process of the reflective mask 2. The absorbing film 13 may not only absorb EUV light, but also shift the phase of the EUV light. In other words, the absorbing film 13 may be a phase shift film. The phase shift film shifts the phase of the second EUV light L2 relative to the first EUV light L1 shown in FIG. 6 .

[0041] The first EUV light L1 is light that passes through the opening pattern 13op of the absorbing film 13 without being absorbed by the absorbing film 13, is reflected by the multilayer reflective film 11, and passes through the opening pattern 13op of the absorbing film 13 without being absorbed again by the absorbing film 13. The second EUV light L2 is light that passes through the absorbing film 13 while being absorbed by the absorbing film 13, is reflected by the multilayer reflective film 11, and passes through the absorbing film 13 while being absorbed again by the absorbing film 13.

[0042] The phase difference (≧0) between the first EUV light L1 and the second EUV light L2 is, for example, 170° to 250°. The phase of the first EUV light L1 may be ahead of or behind the phase of the second EUV light L2. The absorbing film 13 improves the contrast of the transferred image by utilizing interference between the first EUV light L1 and the second EUV light L2. The transferred image is an image obtained by transferring the opening pattern 13op of the absorbing film 13 onto the target substrate.

[0043] In EUVL, a so-called shadowing effect occurs. The shadowing effect refers to the occurrence of a region in the vicinity of the sidewall of the opening pattern 13op where the sidewall blocks the EUV light due to the incident angle θ of the EUV light being not 0° (for example, 6°), resulting in a positional or dimensional deviation of the transferred image. In order to reduce the shadowing effect, it is effective to reduce the height of the sidewall of the opening pattern 13op, and it is also effective to thin the absorbing film 13.

[0044] The thickness of the absorbing film 13 is, for example, 60 nm or less, and preferably 50 nm or less, in order to reduce the shadowing effect, and is preferably 20 nm or more, and more preferably 30 nm or more, in order to ensure a phase difference between the first EUV light L1 and the second EUV light L2.

[0045] In order to reduce the thickness of the absorbing film 13 so as to reduce the shadowing effect while ensuring the phase difference between the first EUV light L1 and the second EUV light L2, it is effective to reduce the refractive index n of the absorbing film 13. Furthermore, in order to reduce the reflectance for the second EUV light L2, it is effective to increase the extinction coefficient k of the absorbing film 13. Thus, the absorbing film 13 is required to have excellent optical properties.

[0046] The absorbing film 13 preferably contains at least one metal element selected from Cr, Ta, Nb, Ir, Pt, Pd, Os, Re, Au, and Ru. These metal elements have a relatively small refractive index, so the film thickness of the absorbing film 13 can be reduced while ensuring a phase difference. The absorbing film 13 preferably contains a compound of a metal element. The compound of a metal element preferably contains at least one non-metal element selected from O, B, C, and N. Adding at least one of these non-metal elements can suppress crystallization while suppressing deterioration of optical properties.

[0047] The absorber film 13 more preferably contains Ta as a main component. The absorber film 13 containing Ta as a main component means that the Ta content in the absorber film 13 is 50 at% or more. The absorber film 13 may contain only Ta, but more preferably contains a Ta compound. The Ta compound more preferably contains N in addition to Ta. The Ta compound containing N can suppress crystallization of the absorber film 13. Therefore, an increase in line edge roughness of the opening pattern 13op of the absorber film 13 due to crystallization of the absorber film 13 can be suppressed. Furthermore, surface roughness of the absorber film 13 due to crystallization of the absorber film 13 can be suppressed, and an increase in the detection rate of pseudo defects can be suppressed. The Ta compound may contain at least one metal element selected from Cr, Nb, Ir, Pt, Pd, Os, Re, Au, and Ru, in addition to Ta.

[0048] In this embodiment, the absorber film 13 is a single-layer film consisting of a single layer, but it may also be a multi-layer film having a lower layer and an upper layer. The lower layer and upper layer constituting the absorber film 13 are formed on the protective film 12 in this order. The uppermost layer of the absorber film 13 is the layer farthest from the protective film 12. The uppermost layer of the absorber film 13 preferably contains at least one metal element selected from Cr, Ta, Nb, Ir, Pt, Pd, Os, Re, Au, and Ru, and more preferably contains a compound of the metal element. The uppermost layer of the absorber film 13 more preferably contains Ta as a main component, and even more preferably contains a Ta compound. When the absorber film 13 is a multi-layer film, the thickness of the absorber film 13 means the total thickness of the multi-layer film.

[0049] When the Ta compound contains Ta and N, the content of N atoms in the Ta compound is preferably 10.0 at% to 35.0 at%, more preferably 10.0 at% to 25.0 at%, further preferably 10.5 at% to 18.0 at%, and particularly preferably 11.0 at% to 16.0 at%, in order to increase the etching selectivity.

[0050] When the Ta compound contains N, it may further contain at least one element selected from hafnium (Hf), silicon (Si), zirconium (Zr), titanium (Ti), germanium (Ge), boron (B), tin (Sn), nickel (Ni), cobalt (Co), and hydrogen (H). The total content of these elements is preferably 10 at% or less.

[0051] The method for forming the absorbing film 13 is, for example, a DC sputtering method, a magnetron sputtering method, an ion beam sputtering method, or the like. ２ The nitrogen content of the absorbing film 13 can be controlled by adjusting the gas content.

[0052] When a TaN film is formed by reactive sputtering, an example of the film formation conditions is as follows: <TaN film formation conditions> Target: Ta target, Output density of Ta target: 1.0 W / cm ２ ~8.5 W / cm ２ , Sputtering gas: Ar gas and N ２ Gas mixture, N in sputtering gas ２ Gas volume ratio (N ２ / (Ar+N ２ )): 0.01 to 0.25, Gas pressure: 1.0 x 10 －２ Pa ~ 1.0 x 10 ０ Pa, Ta target power density: 1.0 W / cm ２ ~8.5 W / cm ２ , Film formation rate: 0.020 nm / sec to 0.060 nm / sec, Film thickness: 20 nm to 60 nm.

[0053] The hard mask film 14 is formed on the opposite side of the protective film 12 with respect to the absorbing film 13, and is used to form an opening pattern 13op in the absorbing film 13. The hard mask film 14 enables the resist film 16 to be made thinner.

[0054] The hard mask film 14 preferably contains at least one metal element or semi-metal element selected from Al, Hf, Y, Cr, Nb, Ti, Mo, Ta, and Si. The hard mask film 14 preferably contains a compound of the above metal element or semi-metal element. The compound preferably contains at least one element selected from O, N, C, and B.

[0055] The thickness of the hard mask film 14 is preferably 2 nm or more and 30 nm or less, more preferably 2 nm or more and 25 nm or less, and further preferably 2 nm or more and 10 nm or less.

[0056] The hard mask film 14 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0057] The conductive film 15 is formed on the opposite side of the substrate 10 from the multilayer reflective film 11, and is used to attract the reflective mask 2 to an electrostatic chuck 21 of the exposure tool 20. In this embodiment, the conductive film 15 is a single-layer film made of a single layer, but it may also be a multi-layer film having a lower layer and an upper layer.

[0058] From the viewpoints of conductivity and stability, the conductive film 15 preferably contains at least one metal element selected from Cr and Ta. The conductive film 15 preferably contains a compound of the above metal element. The compound preferably contains at least one nonmetal element selected from N, O, C, B, and Si. The oxygen content of the compound is preferably 30 at % or less.

[0059] The thickness of the conductive film 15 is preferably 50 nm to 400 nm, and more preferably 70 nm to 350 nm. When the conductive film 15 is a multi-layer film, the thickness of the conductive film 15 is the total thickness of the multi-layer film.

[0060] The conductive film 15 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0061] Next, an example of the positional relationship between the opening pattern of the absorbing film and the defects will be described with reference to Figure 7. As shown in Figure 7, it is preferable to correct the position of the opening pattern 13op formed in the absorbing film 13 so that defects D1 and D2 present between the substrate 10 and the absorbing film 13 are covered by the absorbing film 13. This makes it possible to prevent the defects D1 and D2 from affecting the transfer accuracy of EUVL. This technique is called mitigation. Note that, as will be described in more detail later, it is not necessary for some of the defects D1 and D2 to be covered by the absorbing film 13.

[0062] Defect D1 is a phase defect. The phase defect changes the phase of the EUV light by disrupting the layer structure of the multilayer reflective coating 11. The phase defect is formed, for example, on the first main surface 10a of the substrate 10 or inside the multilayer reflective coating 11. On the other hand, defect D2 is an amplitude defect. The amplitude defect changes the amplitude of the EUV light by absorbing the EUV light. The amplitude defect is formed, for example, on the surface 11a of the multilayer reflective coating 11 or on the surface 12a or inside the protective coating 12.

[0063] Next, an example of the relationship between a set of defects detectable with EUV light and a set of defects detectable with DUV light will be described with reference to Fig. 8. In Fig. 8, set A is a set of defects detectable with EUV light (wavelength: 10 nm to 20 nm), and set B is a set of defects detectable with DUV light (wavelength: 200 nm to 360 nm). Sets A and B partially overlap. Whether or not duplicate defects are detected is determined based on whether or not the position coordinates of the defects are the same. If the position coordinates of the defects are the same, then the defects are detected as duplicate defects.

[0064] EUV light is suitable for detecting phase defects. On the other hand, DUV light is suitable for detecting amplitude defects. EUV light has a shorter wavelength than DUV light and can detect small defects. Therefore, the number of defects belonging to set A is generally greater than the number of defects belonging to set B. Note that defects detectable with EUV light may include not only phase defects but also amplitude defects. Also, defects detectable with DUV light may include not only amplitude defects but also phase defects.

[0065] Next, an example of a spin cleaning apparatus 100 will be described with reference to Fig. 9. The spin cleaning apparatus 100 spin-cleans the substrate 10 or various films (e.g., the protective film 12) formed on the substrate 10 with pure water L, for example, immediately before or after at least one of steps S102 to S106 shown in Fig. 2. The spin cleaning apparatus 100 may apply ultrasonic waves to the pure water L to improve cleaning efficiency.

[0066] The spin cleaning apparatus 100 includes a spin chuck 110 and a nozzle 120. The spin chuck 110 rotates the substrate 10 while holding the substrate 10 horizontally with the first main surface 10a of the substrate 10 facing upward. The nozzle 120 supplies pure water L to the substrate 10 from above. The pure water L spreads radially across the substrate 10 due to centrifugal force. In the process, the pure water L washes away foreign matter adhering to the substrate 10 or various films radially outward from the substrate 10. After the supply of the pure water L is stopped, spin drying is performed.

[0067] As will be explained in detail in the Examples section, the inventors of the present application focused on the number of particles (particles / mL) having a sphere-equivalent diameter of 20 nm or more per unit volume (1 mL) of pure water L immediately before the supply of pure water L was stopped. Experiments have shown that if this number is 0 particles / mL, the concentration of defects can be suppressed. It is believed that the concentration of defects can be suppressed by cleaning the surface with pure water L that does not contain particles at the end of spin cleaning. Note that when the supply of pure water L begins, particles are generated due to, for example, the operation of the on-off valve 131 (described later), so the number of particles does not have to be 0 particles / mL.

[0068] The spin cleaning apparatus 100 may include a supply line 130, a branch line 140, and a particle counter 150. The supply line 130 supplies pure water L to the nozzle 120. An open / close valve 131 is provided midway along the supply line 130. The branch line 140 branches off from the supply line 130 and sends the pure water L to the particle counter 150. The branch line 140 may branch off from the supply line 130 downstream of the open / close valve 131. The particle counter 150 detects the number of particles (particles / mL) having a spherical equivalent diameter of 20 nm or more per unit volume (1 mL) of pure water L. The spherical equivalent diameter of the particles to be detected is preferably 1000 nm or less.

[0069] While the spin cleaning apparatus 100 supplies the pure water L from the nozzle 120 to the substrate 10, the particle counter 150 detects the number of particles (particles / mL) contained in the pure water L. After the spin cleaning apparatus 100 confirms that the number of particles contained in the pure water L has reached 0 particles / mL, it stops the supply of the pure water L and performs spin drying. This allows the surface to be cleaned with particle-free pure water L at the end of the spin cleaning, thereby suppressing the accumulation of defects. The time from when the number of particles reaches 0 particles / mL until the supply of the pure water L is stopped is determined based on factors such as the time it takes for the particle-free pure water L to spread over the entire radial direction of the substrate 10.

[0070] In the method for manufacturing the reflective mask blank 1, it is preferable to perform the spin cleaning at the timing (1) below: (1) After step S101 (preparation of substrate) and before step S103 (formation of multilayer reflective film). By performing the spin cleaning at the timing (1) above, it is possible to suppress the concentration of phase defects.

[0071] In the manufacturing method of the reflective mask blank 1, it is preferable to perform the spin cleaning at the timing (2) below: (2) After step S104 (forming a protective film) and before step S105 (forming an absorbing film). By performing the spin cleaning at the timing (2) above, it is possible to suppress the concentration of amplitude defects.

[0072] The spin cleaning is not necessary after step S103 (forming the multilayer reflective film) and before step S104 (forming the protective film) when the multilayer reflective film 11 and the protective film 12 are formed consecutively using the same film forming apparatus. However, when the multilayer reflective film 11 and the protective film 12 are formed using different film forming apparatuses, the spin cleaning may be performed after step S103 (forming the multilayer reflective film) and before step S104 (forming the protective film).

[0073] Next, a first example of the positional relationship between the quality assurance area A1, the inspection area A2, the first defect DA, and the second defect DB will be described with reference to FIG. 10 . The protective film 12 has a quality assurance area A1 that coincides with the exposure area in a plan view (Z-axis direction view). In a plan view, the substrate 10 has a square shape with, for example, sides 152 mm long. In this case, the quality assurance area A1 has a rectangular shape with, for example, long sides 132 mm long and short sides 104 mm long. Each side of the quality assurance area A1 is perpendicular or parallel to each side of the substrate 10. The quality assurance area A1 is set in the center of the protective film 12.

[0074] In this example, the quality assurance area A1 is vertically long as indicated by the dashed-dotted line, but it may also be horizontally long as indicated by the dashed-two-dot line. The shape (i.e., vertically long or horizontally long) of the quality assurance area A1 can be selected so as to reduce the total number of first defects DA in the quality assurance area A1. The first defects DA are defects that can be detected with EUV light. In other words, the first defects DA are defects that belong to set A shown in FIG. 8. On the other hand, the second defects DB are defects that cannot be detected with EUV light but can be detected with DUV light. In other words, the second defects DB are defects that do not belong to set A but belong to set B shown in FIG. 8. The shape (i.e., vertically long or horizontally long) of the quality assurance area A1 can be selected so as to reduce the total number of first defects DA and second defects DB.

[0075] In the quality assurance area A1 of this example, after the formation of the protective film 12 and before the formation of the absorbing film 13, at least one of the following (A) to (D) is satisfied in any inspection area A2: (A) The number of first defects DA having a sphere-equivalent diameter of 14 nm or more is one or less; (B) The number of first defects DA having a sphere-equivalent diameter of 12 nm or more is one or less; (C) The total number of first defects DA having a sphere-equivalent diameter of 14 nm or more and the number of second defects DB having a sphere-equivalent diameter of 40 nm or more is one or less; (D) The total number of first defects DA having a sphere-equivalent diameter of 12 nm or more and the number of second defects DB having a sphere-equivalent diameter of 40 nm or more is one or less. Note that the sphere-equivalent diameter of the first defects DA is preferably 300 nm or less; and the sphere-equivalent diameter of the second defects DB is preferably 500 nm or less. In the quality assurance area A1, it is sufficient that at least the above condition (A) is satisfied in any inspection area A2 after the formation of the protective film 12 and before the formation of the absorbing film 13.

[0076] In this example, the inspection area A2 has a square shape with each side being 20 mm long. Each side of the inspection area A2 is perpendicular or parallel to each side of the quality assurance area A1. The inspection area A2 is continuously translated throughout the entire quality assurance area A1, and it is determined whether at least one of the above conditions (A) to (D) is met in any given inspection area A2. The locations and numbers of the first defects DA and second defects DB may be inspected after the formation of the protective film 12 and before the formation of the absorbing film. The first defects DA and second defects DB may be present on the first major surface 10a of the substrate 10, on the surface 11a or inside the multilayer reflective film 11, or on the surface 12a or inside the protective film 12. Inspecting the surface 12a of the protective film 12 allows detection of not only the surface 12a of the protective film 12, but also the first defects DA and second defects DB from the surface 12a of the protective film 12 to the first major surface 10a of the substrate 10.

[0077] In EUVL, the opening pattern 13op of the absorbing film 13 is transferred onto a semiconductor substrate or the like. The reduction ratio during transfer is generally 1 / 4. Therefore, the transferred image of the inspection area A2 has a square shape with each side measuring 5 mm (20 mm × 1 / 4), which is approximately the same size as the semiconductor chip. According to this example, in the production of the circuit pattern of one semiconductor chip, the number of defects to be concealed by the absorbing film 13 can be reduced to one or less. Therefore, the probability of successful position correction of the opening pattern 13op formed in the absorbing film 13 can be improved so that all of the target defects are covered by the absorbing film 13.

[0078] In (A) above, the target defect is a first defect DA having a spherical equivalent diameter of 14 nm or more. In (B) above, the target defect is a first defect DA having a spherical equivalent diameter of 12 nm or more. In (C) above, the target defect is both a first defect DA having a spherical equivalent diameter of 14 nm or more and a second defect DB having a spherical equivalent diameter of 40 nm or more. In (D) above, the target defect is both a first defect DA having a spherical equivalent diameter of 12 nm or more and a second defect DB having a spherical equivalent diameter of 40 nm or more.

[0079] The type of target defect to be set, i.e., which of the four conditions (A) to (D) above to adopt, may be determined, for example, according to the required accuracy of EUVL transfer, in other words, according to the circuit pattern of the semiconductor chip. A first defect DA having a sphere-equivalent diameter of less than 14 nm has almost no effect on the EUVL transfer accuracy. However, depending on the circuit pattern of the semiconductor chip, a first defect DA having a sphere-equivalent diameter of 12 nm or more but less than 14 nm may affect the EUVL transfer accuracy. Furthermore, depending on the circuit pattern of the semiconductor chip, a second defect DB having a sphere-equivalent diameter of 40 nm or more may affect the EUVL transfer accuracy.

[0080] It is more preferable that the quality assurance area A1 as a whole, after the formation of the protective film 12 and before the formation of the absorbing film 13, satisfy the following condition (E): (E) The total number of first defects DA having a sphere-equivalent diameter of 12 nm or more and the number of second defects DB having a sphere-equivalent diameter of 40 nm or more is 10 or less. If the above condition (E) is satisfied, the probability of successful position correction of the opening pattern 13op formed in the absorbing film 13 can be further improved.

[0081] Next, referring to FIG. 11 , a second example of the positional relationship between the quality assurance area A1, the inspection area A2, the first defect DA, and the second defect DB will be described. Differences from the first example shown in FIG. 10 will be mainly described below. The inspection area A2 in this example has a rectangular shape with long sides of 40 mm and short sides of 20 mm. The long sides of the inspection area A2 are parallel to the long sides of the quality assurance area A1. The short sides of the inspection area A2 are also parallel to the short sides of the quality assurance area A1. In this example, the reduction ratio during transfer in the long side direction is 1 / 8, and the reduction ratio during transfer in the short side direction is 1 / 4. Therefore, in this example, as in the first example, the transferred image in the inspection area A2 has a square shape with each side measuring 5 mm (20 mm × 1 / 4 or 40 mm × 1 / 8), which is approximately the same size as the semiconductor chip. Therefore, in this example, as in Example 1, it is sufficient that at least one of the above (A) to (D) is satisfied in any inspection area A2. Also, in this example, as in Example 1, it is more preferable that the above (E) is satisfied in the entire quality assurance area A1.

[0082] Next, with reference to FIG. 12 , a third example of the positional relationship between the quality assurance area A1, the inspection area A2, the first defect DA, and the second defect DB will be described. Below, differences from the first example shown in FIG. 10 will be mainly described. In a plan view, the substrate 10 has a rectangular shape with, for example, a long side length of 304 mm and a short side length of 152 mm. In this case, the quality assurance area A1 has a rectangular shape with, for example, a long side length of 264 mm and a short side length of 104 mm. The inspection area A2 in this example has a rectangular shape with a long side length of 40 mm and a short side length of 20 mm. The long side of the inspection area A2 is parallel to the long side of the quality assurance area A1. The short side of the inspection area A2 is also parallel to the short side of the quality assurance area A1. In this example, the reduction ratio during transfer in the long side direction is 1 / 8, and the reduction ratio during transfer in the short side direction is 1 / 4. Therefore, in this example, as in the first example, the transferred image in the inspection area A2 has a square shape with each side measuring 5 mm (20 mm x 1 / 4 or 40 mm x 1 / 8), which is approximately the same size as the semiconductor chip. Therefore, in this example, as in the first example, it is sufficient that at least one of the above (A) to (D) is satisfied in any inspection area A2. Furthermore, in this example, as in the first example, it is more preferable that the above (E) is satisfied throughout the entire quality assurance area A1.

[0083] [Examples] Experimental data will be described below. In Examples 1 to 5, multilayer reflective film coated substrates were produced under the same conditions except for the cleaning conditions (number of particles immediately before the supply of pure water was stopped) shown in Tables 1 and 2. The multilayer reflective film coated substrates had a substrate 10, a multilayer reflective film 11, and a protective film 12. Examples 1 and 2 are comparative examples, and Examples 3 to 5 are working examples.

[0084] The substrate 10 is made of SiO ２ -TiO ２ A glass substrate (6-inch (152 mm) square outer diameter, 6.3 mm thick) was prepared. This glass substrate had a thermal expansion coefficient of 0.02×10 at 20° C. －７ / °C, Young's modulus is 67 GPa, Poisson's ratio is 0.17, and specific rigidity is 3.07 × 10 ７ m ２ / s ２The quality assurance area of ​​the first main surface 10a of the substrate 10 was polished to have a root-mean-square roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less.

[0085] A Mo / Si multilayer reflective film was formed as the multilayer reflective film 11. The Mo / Si multilayer reflective film was formed by repeating the process of forming a Si layer (4.5 nm thick) and a Mo layer (2.3 nm thick) by ion beam sputtering 40 times, and then forming one Si layer (8.0 nm thick). The total thickness of the Mo / Si multilayer reflective film was 280 nm ((4.5 nm + 2.3 nm) × 40 + 8.0).

[0086] An Ru film (thickness: 2.5 nm) was formed by ion beam sputtering as the protective film 12. In Examples 1 to 5, the multilayer reflective film 11 and the protective film 12 were formed consecutively using the same film forming apparatus, and therefore spin cleaning was not performed after the formation of the multilayer reflective film 11 and before the formation of the protective film 12.

[0087] After forming the protective film 12, the number and positions of the first defects DA and second defects DB in the quality assurance area A1 were checked. The maximum number of defects in the inspection area A2, which had a square shape with each side measuring 20 mm, was calculated for each target defect (see Table 1). The maximum number of defects in the inspection area A2, which had a rectangular shape with a long side measuring 40 mm and a short side measuring 20 mm, was calculated for each target defect (see Table 2).

[0088] Furthermore, the success probability of correcting the position of the opening pattern 13op of the absorbing film 13 was calculated for each target defect by simulation. Specifically, 10 types of opening patterns 13op were prepared, and it was investigated whether the position of the opening pattern 13op could be corrected so that the target defect would not affect the EUVL transfer accuracy. A success probability of 100% means that, for all 10 types of opening patterns 13op, the position of the opening pattern 13op could be corrected so that all of the target defects were hidden by the absorbing film 13.

[0089]

[0090]

[0091] Comparing Example 1 and Example 2, it can be seen that the fewer the number of target defects in the entire quality assurance area A1, the higher the probability of successful position correction of the opening pattern 13op of the absorbing film 13. However, in Examples 1 and 2, since the maximum number of target defects in the inspection area A2 was 2 or more, the probability of successful position correction was 40% or less.

[0092] Comparing Example 1 with Example 3, or Example 2 with Example 4, it can be seen that even if the number of target defects in the entire quality assurance area A1 is approximately the same, if the maximum number of target defects in the inspection area A2 is small (i.e., 1 or less), the probability of successful position correction will be 70% or more.

[0093] Comparing Example 3 and Example 4, it can be seen that even if the maximum number of target defects in the inspection area A2 is the same (i.e., 1), the fewer the number of target defects in the entire quality assurance area A1, the higher the probability of successful position correction.

[0094] In Example 5, when the target defects were both the first defect DA and the second defect DB, the maximum value of the target defects in inspection area A2 exceeded 1, and the probability of successful position correction was low. The reason for the large number of second defect DBs in Example 5 is presumably because the number of particles exceeded 0 / mL immediately before the supply of pure water to surface 12a of protective film 12 was stopped.

[0095] The reflective mask blank, reflective mask, reflective mask blank manufacturing method, and reflective mask manufacturing method according to the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure.

[0096] This application claims priority based on Japanese Patent Application No. 2023-205053 filed with the Japan Patent Office on December 5, 2023, and Japanese Patent Application No. 2024-018396 filed with the Japan Patent Office on February 9, 2024. The entire contents of Japanese Patent Application Nos. 2023-205053 and 2024-018396 are incorporated by reference into this application.

[0097] REFERENCE SIGNS LIST 1 reflective mask blank 2 reflective mask 10 substrate 11 multilayer reflective film 12 protective film 13 absorbing film 13op aperture pattern

Claims

1. A reflective mask blank having, in that order, a substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs EUV light, the absorbing film having an exposure area to which an exposure apparatus is to expose EUV light, wherein the protective film has a quality assurance area that coincides with the exposure area in a planar view, and wherein, after formation of the protective film and before formation of the absorbing film, the quality assurance area has one or less first defects that are detectable by EUV light and have a sphere equivalent diameter of 14 nm or more in any inspection area having a square shape with each side length of 20 mm.

2. The reflective mask blank of claim 1, wherein the quality assurance area is such that, after formation of the protective film and before formation of the absorbing film, in any of the inspection areas, the total number of first defects detectable by EUV light and having a sphere-equivalent diameter of 14 nm or more and the number of second defects undetectable by EUV light but detectable by DUV light and having a sphere-equivalent diameter of 40 nm or more is 1 or less.

3. The reflective mask blank according to claim 1, wherein the quality assurance area is such that, after formation of the protective film and before formation of the absorbing film, in any of the inspection areas, the number of first defects detectable by EUV light and having a sphere equivalent diameter of 12 nm or more is one or less.

4. The reflective mask blank of claim 3, wherein the quality assurance area is such that, after formation of the protective film and before formation of the absorbing film, in any of the inspection areas, the total number of first defects detectable by EUV light and having a sphere-equivalent diameter of 12 nm or more and the number of second defects undetectable by EUV light but detectable by DUV light and having a sphere-equivalent diameter of 40 nm or more is 1 or less.

5. The reflective mask blank described in claim 4, wherein the quality assurance area, after formation of the protective film and before formation of the absorbing film, has a total of 10 or less first defects that are detectable by EUV light and have a sphere-equivalent diameter of 12 nm or more, and a total of 10 second defects that are not detectable by EUV light but are detectable by DUV light and have a sphere-equivalent diameter of 40 nm or more.

6. A reflective mask blank having, in that order, a substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs EUV light, the absorbing film having an exposure area to which an exposure apparatus is to expose EUV light, wherein the protective film has a quality assurance area that coincides with the exposure area in a planar view, and the quality assurance area has, after formation of the protective film and before formation of the absorbing film, one or less first defects detectable by EUV light and having a sphere equivalent diameter of 14 nm or more in any inspection area having a rectangular shape with a long side length of 40 mm and a short side length of 20 mm.

7. The reflective mask blank according to claim 6, wherein in any one of the quality assurance areas after formation of the protective film and before formation of the absorbing film, the total number of first defects detectable by EUV light and having a sphere-equivalent diameter of 14 nm or more and the number of second defects not detectable by EUV light but detectable by DUV light and having a sphere-equivalent diameter of 40 nm or more is 1 or less.

8. The reflective mask blank according to claim 6, wherein the quality assurance area is such that, after formation of the protective film and before formation of the absorbing film, in any of the inspection areas, the number of first defects detectable by EUV light and having a sphere equivalent diameter of 12 nm or more is one or less.

9. A reflective mask blank as described in claim 8, wherein the quality assurance area is such that, after formation of the protective film and before formation of the absorbing film, in any of the inspection areas, the total number of first defects detectable by EUV light and having a sphere equivalent diameter of 12 nm or more and the number of second defects not detectable by EUV light but detectable by DUV light and having a sphere equivalent diameter of 40 nm or more is 1 or less.

10. A reflective mask blank as described in claim 9, wherein the quality assurance area, after formation of the protective film and before formation of the absorbing film, has a total of 10 or less first defects that are detectable by EUV light and have a sphere-equivalent diameter of 12 nm or more, and a total of 10 or less second defects that are not detectable by EUV light but are detectable by DUV light and have a sphere-equivalent diameter of 40 nm or more.

11. A reflective mask comprising the reflective mask blank according to any one of claims 1 to 10, and including an opening pattern in the absorbing film.

12. A method for manufacturing a reflective mask blank comprising a substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs EUV light, in that order, the absorbing film having an exposure area to which an exposure apparatus is to expose EUV light, the method comprising forming the multilayer reflective film, the protective film, and the absorbing film in that order on a first main surface of the substrate, the protective film having a quality assurance area that coincides with the exposure area in a planar view, and the quality assurance area having, after formation of the protective film and before formation of the absorbing film, one or less first defects detectable by EUV light and having a sphere equivalent diameter of 14 nm or more in any inspection area having a square shape with each side length of 20 mm.

13. A method for manufacturing a reflective mask blank comprising a substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs EUV light, in that order, the absorbing film having an exposure area to which an exposure apparatus is to expose EUV light, the method comprising forming the multilayer reflective film, the protective film, and the absorbing film in that order on a first main surface of the substrate, the protective film having a quality assurance area that coincides with the exposure area in a planar view, and the quality assurance area having, after formation of the protective film and before formation of the absorbing film, one or less first defects detectable by EUV light and having a sphere equivalent diameter of 14 nm or more in any inspection area having a rectangular shape with a long side length of 40 mm and a short side length of 20 mm.

14. A method for producing a reflective mask blank as described in claim 12 or 13, comprising: spin-cleaning the first main surface of the substrate with pure water before forming the multilayer reflective film; and spin-cleaning a surface of the protective film with pure water after forming the protective film and before forming the absorbing film, wherein immediately before the supply of the pure water to the substrate or the protective film is stopped, the number of particles having a sphere equivalent diameter of 20 nm or more per unit volume (1 mL) of the pure water is 0 particles / mL.

15. A method for manufacturing a reflective mask, comprising the steps of: preparing a reflective mask blank according to any one of claims 1 to 10; and forming an aperture pattern in the absorbing film, in this order.

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