Method of inspecting reflective mask blank, method of manufacturing reflective mask blank, and method of manufacturing reflective mask

Abstract

To provide a technique for accurately detecting the number and positions of defects.SOLUTION: In a method of inspecting a reflective mask blank, a reflective mask blank having a substrate, a multilayer reflection film reflecting EUV light, a protective film protecting the multilayer reflection film, and an absorption film absorbing EUV light in this order is inspected. The method of inspecting a reflective mask blank has the steps of: acquiring a brightness map of an image formed by imaging the substrate, the multilayer reflection film, the protective film or the absorption film; detecting the number and positions of defects by binarizing the brightness map; and setting a slice level for binarizing the brightness map in such a manner that the number of the defects to be detected becomes the maximum.SELECTED DRAWING: Figure 9

Description

[Technical Field]

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

[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 has a wavelength of approximately 13.5 nm. EUVL uses a reflective mask. A reflective mask has, 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 opening pattern is formed in the absorbing film. In EUVL, the opening pattern in the absorbing film is transferred to a target substrate such as a semiconductor substrate. Transferring includes reducing and transferring.

[0003] The surface defect inspection method described in Patent Document 1 acquires an image of a substrate, processes the image to obtain a binary image, and determines the presence or absence of defects based on the binary image. The binary image is created using a preset slice level. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-304703 Summary of the Invention [Problem to be solved by the invention]

[0005] In the past, multiple defects were often clustered together, making it difficult to accurately detect the number and locations of defects.

[0006] One embodiment of the present disclosure provides a technique for detecting the number and locations of defects with high accuracy. [Means for solving the problem]

[0007] A reflective mask blank inspection method according to an embodiment of the present disclosure inspects a reflective mask blank having, 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. The reflective mask blank inspection method includes acquiring an intensity map of an image obtained by capturing the substrate, the multilayer reflective film, and the protective film or the absorbing film, and detecting the number and positions of defects by binarizing the intensity map. The reflective mask blank inspection method also includes setting a slice level for binarizing the intensity map so as to maximize the number of defects detected. [Effects of the Invention]

[0008] According to an embodiment of the present disclosure, the number and positions of defects can be detected with high accuracy. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a reflective mask blank according to one embodiment. [Figure 2] FIG. 2 is a flowchart showing a method for manufacturing a reflective mask blank according to one embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing a reflective mask according to an embodiment. [Figure 4] FIG. 4 is a flowchart showing a method for manufacturing a reflective mask according to an embodiment. [Figure 5] FIG. 5(A) is a cross-sectional view showing an example of S201, FIG. 5(B) is a cross-sectional view showing an example of S202, and FIG. 5(C) is a cross-sectional view showing an example of S203. [Figure 6] FIG. 6 is a cross-sectional view showing an example of EUV light reflected by the reflective mask of FIG. [Figure 7] FIG. 7 is a cross-sectional view showing an example of the positional relationship between the opening pattern of the absorbing film and the defect. [Figure 8] FIG. 8 is a flowchart showing a reflective mask blank inspection method according to one embodiment. [Figure 9] FIG. 9 is a diagram showing an example of defect detection using a dark-field image in the secondary inspection. [Figure 10] FIG. 10 is a diagram showing an example of defect detection using a bright-field image in the secondary inspection. DETAILED DESCRIPTION OF THE INVENTION

[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 numerical range means that the numerical values ​​before and after it are included as the lower and upper limits. The numerical range 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 FIG. 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 in this order on a first main surface 10a of the substrate 10. 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 a first etching gas during processing of the absorbing film 13.

[0013] The reflective mask blank 1 has a conductive film 15 on the side opposite to the multilayer reflective film 11 with respect to the substrate 10. 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 a first etching gas that forms an 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] In step S202, as shown in FIG. 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 materials of the resist film 16 and the hard mask film 14, and is not particularly limited, and may include, for example, a fluorine-based gas. The fluorine-based gas may include, for example, at least one selected from CF4 gas, CHF3 gas, C2F6 gas, C3F6 gas, C4F6 gas, C4F8 gas, CH2F2 gas, CH3F gas, C3F8 gas, F2 gas, SF6 gas, and NF3 gas. The second etching gas may include, in addition to the fluorine-based gas, an active gas or an inert gas. The active gas may include, for example, at least one selected from O2 gas and O3 gas. The inert gas may include, for example, at least one selected from N2 gas, He gas, and Ar gas. The second etching gas is preferably a plasma-converted gas.

[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, and may include, for example, a chlorine-based gas and an oxygen-based gas. The chlorine-based gas may include, for example, at least one selected from Cl2 gas, SiCl4 gas, CHCl3 gas, CCl4 gas, and BCl3 gas. The oxygen-based gas may include, for example, at least one selected from O2 gas and O3 gas. The first etching gas may include an inert gas in addition to the chlorine-based gas and the oxygen-based gas. The inert gas may include, for example, at least one selected from N2 gas, He gas, and Ar gas. The first etching gas is preferably plasmatized.

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

[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 preferably quartz glass containing TiO2. Compared to common soda-lime glass, quartz glass has a smaller linear expansion coefficient and undergoes less dimensional change due to temperature changes. The quartz glass may contain 80% to 95% by mass of SiO2 and 4% to 17% by mass of TiO2. When the TiO2 content is 4% to 17% by mass, the linear expansion coefficient is approximately zero near room temperature, and there is almost no dimensional change near room temperature. The quartz glass may contain a third component or impurity other than SiO2 and TiO2. The material of the substrate 10 may also be crystallized glass in which a β-quartz solid solution is precipitated, silicon, 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, for example, formed by alternately laminating high refractive index layers and low refractive index layers. The material of the high refractive index layer is, for example, silicon (Si), and the material of the low refractive index layer is, for example, molybdenum (Mo), and a Mo / Si multilayer reflective film is used. In addition, 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, a Si / Ru / Mo multilayer reflective film, etc. can also be used as the multilayer reflective film 11.

[0029] The film thickness of each layer constituting the multilayer reflective film 11 and the number of repeating units of the layer can be appropriately selected according to the material of each layer and the reflectivity with respect to 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 with respect to EUV light with an incident angle θ (see FIG. 6) of 6°, a Mo layer with a film thickness of 2.3 ± 0.1 nm and a Si layer with a film thickness of 4.5 ± 0.1 nm may be laminated so that the number of repeating units is 30 or more and 60 or less. The multilayer reflective film 11 preferably has a reflectivity of 60% or more with respect to EUV light with an incident angle θ of 6°. More preferably, the reflectivity is 65% or more.

[0030] The film formation method of each layer constituting the multilayer reflective film 11 is, for example, a DC sputtering method, a magnetron sputtering method, an ion beam sputtering method, or the like. When forming a Mo / Si multilayer reflective film using the ion beam sputtering method, an example of the film formation conditions for each of the Mo layer and the Si layer is as follows. <Film formation conditions for Si layer> Target: Si target, Sputtering gas: Ar gas, Gas pressure: 1.3×10 , ,

[0030] , , , -2 , , , -2 , , ,

[0029] , , , , Pa~2.7×10 -2 Pa, Ion acceleration voltage: 300 V~1500 V, Film formation rate: 0.030 nm / sec~0.300 nm / sec, Film 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~2.7×10 -2 Pa, Ion acceleration voltage: 300V~1500V, Film formation rate: 0.030 nm / sec~0.300 nm / sec, Thickness of Mo layer: 2.3 ± 0.1 nm, <Repeating unit of Si layer and Mo layer> Number of repeating units: 30~60 (preferably 40~50).

[0031] The protective film 12 is formed between the multilayer reflective film 11 and the absorption film 13 and protects the multilayer reflective film 11. The protective film 12 protects the multilayer reflective film 11 from the first etching gas during the processing of the absorption film 13, that is, in step S203. The protective film 12 remains on the multilayer reflective film 11 without being removed even when exposed to the first etching gas.

[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 the main component. That the protective film 12 contains Ru as the main component means that the Ru content in the protective film 12 is 40 at% or more as described above. 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 have only Ru, or may have a Ru compound. The Ru compound may be a Ru alloy. The Ru alloy contains, for example, at least one metal element selected from Rh, Nb, Mo, Ta, Ir, Pd, Zr, Y, and Ti in addition to Ru.

[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 entire protective film 12 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 or Nb. When the protective film 12 is a multilayer film, the thickness of the protective film 12 below refers to the total film thickness of the multilayer film. Note that a mixing layer formed by mixing components contained in the multilayer reflective film 11 and components contained in the lower layer of the protective film 12 may be formed between the multilayer 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. Also, if the thickness of the protective film 12 is 4.0 nm or less, the reflectivity with respect 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 ~14.0 g / cm 3 . If the density of the protective film 12 is 10.0 g / cm 3 or more, the etching resistance is good. Also, if the density of the protective film 12 is 14.0 g / cm 3 or less, the absorption of EUV light by the protective film 12 (and thus the decrease in reflectivity with respect to EUV light) can be suppressed.

[0039] The method for forming the protective film 12 is, for example, a DC sputtering method, a magnetron sputtering method, an ion beam sputtering method, or the like. When forming a Ru film using the ion beam sputtering method, an example of the film formation conditions is as follows. <Film formation conditions of Ru film> Target: Ru target, Sputtering gas: Ar gas, Gas pressure: 0.010 Pa to 0.020 Pa, Output density of the target: 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 or behind the phase of the second EUV light L2. The absorbing film 13 improves the contrast of the transferred image by utilizing the 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 projection effect (shadowing effect) occurs. The shadowing effect refers to the occurrence of an area near 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. The thickness of the absorbing film 13 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 film thickness of the absorbing film 13 so as to reduce the shadowing effect while maintaining 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, W, Nb, Ir, Pt, Pd, Os, Re, Au, and Ru. These metal elements have a relatively small refractive index, so the thickness of the absorbing film 13 can be reduced while maintaining a sufficient 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 nonmetal element selected from O, B, C, and N. Adding at least one of these nonmetal elements can suppress crystallization while suppressing deterioration in optical properties, and can reduce the roughness of the sidewalls of the opening pattern 13op.

[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. When the Ta compound contains N, crystallization of the absorber film 13 can be suppressed. 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 false 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] The refractive index n of the absorbing film 13 is preferably 0.930 or less, more preferably 0.920 or less, even more preferably 0.910 or less, and particularly preferably 0.90 or less. The refractive index n is preferably 0.885 or more. In this specification, the refractive index is the refractive index for light with a wavelength of 13.5 nm.

[0049] The extinction coefficient k of the absorbing film 13 is preferably 0.015 or more, and more preferably 0.020 or more. The extinction coefficient k is preferably 0.065 or less. In this specification, the extinction coefficient is the extinction coefficient for light with a wavelength of 13.5 nm.

[0050] The absorbing film 13 preferably has an etching rate of 0 nm / min to 0.05 nm / min with sulfuric acid / hydrogen peroxide. If the etching rate of the absorbing film 13 with sulfuric acid / hydrogen peroxide is 0.05 nm / min or less, damage to the absorbing film 13 during cleaning can be suppressed.

[0051] In this embodiment, the absorption film 13 is a single-layer film composed 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 the upper layer constituting the absorption film 13 are formed on the protective film 12 in this order. The uppermost layer of the absorption film 13 is the layer farthest from the protective film 12. The uppermost layer of the absorption film 13 preferably contains at least one metal element selected from Cr, Ta, W, Nb, Ir, Pt, Pd, Os, Re, Au, and Ru, and more preferably contains a compound of the metal element. The uppermost layer of the absorption film 13 more preferably contains Ta as a main component, and even more preferably contains a Ta compound. When the absorption film 13 is a multi-layer film, the thickness of the absorption film 13 means the total film thickness of the multi-layer film.

[0052] 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% for increasing the etching selectivity ratio, more preferably 10.0 at% to 25.0 at%, even more preferably 10.5 at% to 18.0 at%, and particularly preferably 11.0 at% to 16.0 at%.

[0053] 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.

[0054] The film formation method of the absorption film 13 is, for example, a DC sputtering method, a magnetron sputtering method, an ion beam sputtering method, or the like. The nitrogen content of the absorption film 13 can be controlled by the content of N2 gas in the sputtering gas.

[0055] When forming a TaN film using a reactive sputtering method, an example of the film formation conditions is as follows. <Film formation conditions of TaN film> Target: Ta target, Output density of Ta target: 1.0 W / cm2 ~8.5W / cm 2 , Sputtering gas: A mixture of Ar gas and N2 gas. Volume ratio of N2 gas in sputtering gas (N2 / (Ar+N2)): 0.01 to 0.25, Gas pressure: 1.0 x 10 -2 Pa~1.0×10 0 Pa, Power density of Ta target: 1.0 W / cm 2 ~8.5W / cm 2 , Deposition rate: 0.020nm / sec~0.060nm / sec, Film thickness: 20nm~60nm.

[0056] The hard mask film 14 is formed on the opposite side of the absorbing film 13 from the protective film 12, 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.

[0057] 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.

[0058] 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.

[0059] The hard mask film 14 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0060] 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, but it may be a multi-layer film having a lower layer and an upper layer.

[0061] 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.

[0062] 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.

[0063] The conductive film 15 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0064] Next, an example of the positional relationship between the opening pattern of the absorbing film and the defect will be described with reference to Fig. 7. As shown in Fig. 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 in the substrate 10, multilayer reflective film 11, protective film 12, or absorbing film 13 are covered by the absorbing film 13. This prevents the defects D1 and D2 from affecting the transfer accuracy of EUVL. This technique is called mitigation.

[0065] Defect D1 is a phase defect. The phase defect changes the phase of EUV light by disturbing the layer structure of the multilayer reflective film 11. The phase defect is formed, for example, on the first main surface 10a of the substrate 10 or inside the multilayer reflective film 11. On the other hand, defect D2 is an amplitude defect. The amplitude defect changes the amplitude of EUV light by absorbing the EUV light. The amplitude defect is formed, for example, on the surface 11a of the multilayer reflective film 11, the surface 12a of the protective film 12, or inside them.

[0066] Referring to FIG. 8, a method for inspecting the reflective mask blank 1 according to an embodiment will be described. The following inspection is performed, for example, immediately after steps S101, S102, S103, S104, or S105 shown in FIG. 2. In the inspection, the number and position of defects D1 or D2 are detected. As shown in FIG. 8, the inspection includes, for example, a primary inspection (step S301) and a secondary inspection (step S302). The primary inspection detects the approximate number and position of defects D1 or D2. The secondary inspection reinspects the defects D1 or D2 detected in the primary inspection and detects the exact number and position of defects D1 or D2.

[0067] In the primary inspection, while moving the substrate 10 at the first moving speed V1, the inspection target (such as the substrate 10) is imaged, and the number and position of defects D1 or D2 are detected by image processing the captured image. Compared with the case where the substrate is moved at the second moving speed V2 (V2 < V1), which will be described later, or the inspection target is imaged while the movement is stopped, the entire inspection target can be imaged in a short time, and the inspection time can be shortened. The first moving speed V1 is, for example, 10 mm / sec to 1000 mm / sec, preferably 50 mm / sec to 200 mm / sec.

[0068] In the secondary inspection, the inspection target (such as the substrate 10) is imaged while the substrate 10 is moving at a second movement speed V2 or while it is stopped, and the image is processed to detect the defect D1 or D2. Because the approximate position of the defect D1 or D2 has already been detected in the primary inspection (step S301), the number of images taken while the substrate 10 is moving at a slow speed or while it is stopped can be reduced, thereby shortening the inspection time. Furthermore, because the inspection target is imaged while the substrate 10 is moving at a slow speed or while it is stopped, clear images can be obtained, and the exact number and position of the defect D1 or D2 can be detected. The second movement speed V2 is, for example, 0 mm / sec to 50 mm / sec, and preferably 0 mm / sec to 10 mm / sec.

[0069] The pixel resolution of the image acquired in the secondary inspection is smaller than the pixel resolution of the image acquired in the primary inspection. The smaller the pixel resolution, the better the detection accuracy of defects D1 or D2. Pixel resolution is the size of the field of view per pixel ((vertical field of view / number of vertical pixels) or (horizontal field of view / number of horizontal pixels)), and is the maximum value of (vertical field of view / number of vertical pixels) and (horizontal field of view / number of horizontal pixels). The pixel resolution in the primary inspection is, for example, 50 nm to 1000 nm, and preferably 50 nm to 400 nm. The pixel resolution in the secondary inspection is, for example, 5 nm to 100 nm, and preferably 5 nm to 20 nm.

[0070] In the primary inspection or secondary inspection, the wavelength of light used to capture an image is preferably 5 nm to 600 nm. The light used to capture an image is preferably EUV light (wavelength: 10 nm to 20 nm) or DUV light (wavelength: 200 nm to 360 nm). 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 smaller defects.

[0071] Commercially available inspection devices for inspecting phase defects include, but are not limited to, the ABICS E120 (wavelength 13.5 nm) manufactured by Lasertec Corp. Commercially available inspection devices for inspecting amplitude defects include, but are not limited to, the M8650 (wavelength 355 nm) manufactured by Lasertec Corp., the M1350 (wavelength 488 nm) manufactured by Lasertec Corp., or the M9650 (wavelength 213 nm) manufactured by Lasertec Corp.

[0072] The images acquired in the primary or secondary inspection may be either dark-field images or bright-field images. Dark-field images are created by irradiating the surface of the object to be inspected (such as the substrate 10) with light perpendicularly or obliquely, and receiving the light scattered by the surface of the object to be inspected with a light-receiving element. Bright-field images are created by irradiating the surface of the object to be inspected (such as the substrate 10) with light obliquely, and receiving the light specularly reflected by the surface of the object to be inspected with a light-receiving element. It is also possible to acquire both dark-field images and bright-field images with a single inspection device.

[0073] With reference to FIG. 9, an example of detecting defect D1 or D2 using a dark-field image in a secondary inspection will be described. Note that the detection of defect D1 or D2 shown in FIG. 9 can also be applied to a primary inspection. The secondary inspection includes the following steps (A1) to (A2): (A1) A luminance map of a dark-field image of the substrate 10, the multilayer reflective film 11, the protective film 12, or the absorbing film 13 is obtained. (A2) The luminance map is binarized to detect the number and positions of defects D1 or D2. In the dark-field image, defect D1 or D2 has a luminance equal to or higher than the slice level at which the luminance map is binarized. Note that in (A2), the luminance map may be multi-valued.

[0074] The secondary inspection further includes the following (A3): (A3) A slice level for binarizing the brightness map is set so as to maximize the number of defects D1 or D2 detected in (A2). (A3) includes, for example, counting the number of defects D1 or D2 each time the slice level is increased by 1 from the reference value. The reference value is, for example, the average value of brightness not derived from defects D1 or D2. The reference value is set using multiple brightness maps.

[0075] For example, in the embodiment shown in FIG. 9, by increasing the slice level by 3 to 10 from the reference value, the number of defects D1 or D2 to be detected is maximized (for example, 2). By maximizing the number of defects D1 or D2, it is possible to resolve multiple defects D1 or D2 that are closely spaced. Therefore, it is possible to detect the number and positions of defects D1 or D2 with high accuracy. Note that the maximum number of defects D1 or D2 is not limited to 2, and may be 3 or more.

[0076] The slice level is preferably set so that the brightness of the slice level is the lowest within the range in which the number of defects D1 or D2 is maximized. For example, in the embodiment shown in FIG. 9, it is preferable to increase the slice level by 3 from the reference value. The lower the brightness of the slice level, the larger the estimated size of the defects D1 or D2. Therefore, the position of the opening pattern 13op of the absorbing film 13 can be corrected so that the defects D1 or D2 are reliably covered by the absorbing film 13.

[0077] With reference to FIG. 10, an example of detecting defect D1 or D2 using a bright-field image in a secondary inspection will be described. Note that the detection of defect D1 or D2 shown in FIG. 10 can also be applied to a primary inspection. The secondary inspection includes the following steps (B1) to (B2). (B1) A brightness map of a bright-field image of the substrate 10, the multilayer reflective film 11, the protective film 12, or the absorbing film 13 is obtained. (B2) The brightness map is binarized to detect the number and positions of defects D1 or D2. In the bright-field image, defect D1 or D2 has a brightness equal to or lower than the slice level at which the brightness map is binarized. Note that in (B2), the brightness map may be multi-valued.

[0078] The secondary inspection further includes the following (B3): (B3) setting a slice level for binarizing the brightness map so as to maximize the number of defects D1 or D2 detected in (B2). (B3) includes, for example, counting the number of defects D1 or D2 each time the slice level is decreased by 1 from the reference value. The reference value is, for example, the average value of brightness not derived from defects D1 or D2. The reference value is set using multiple brightness maps.

[0079] For example, in the embodiment shown in FIG. 10, by lowering the slice level by 3 to 10 from the reference value, the number of defects D1 or D2 to be detected is maximized (for example, 2). By maximizing the number of defects D1 or D2, it is possible to resolve multiple defects D1 or D2 that are closely spaced. Therefore, it is possible to detect the number and positions of defects D1 or D2 with high accuracy. Note that the maximum number of defects D1 or D2 is not limited to 2, and may be 3 or more.

[0080] The slice level is preferably set so that the brightness of the slice level is maximized within the range in which the number of defects D1 or D2 is maximized. For example, in the embodiment shown in FIG. 10, the slice level is preferably reduced by 3 from the reference value. The higher the brightness of the slice level, the larger the estimated size of the defect D1 or D2. Therefore, the position of the opening pattern 13op of the absorber film 13 can be corrected so that the defect D1 or D2 is reliably covered by the absorber film 13.

[0081] The reflective mask blank inspection method, 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. [Explanation of symbols]

[0082] 1. Reflective mask blank 2 Reflective mask 10 Substrate 11 Multilayer reflective film 12 Protective film 13 Absorbent membrane

Claims

1. A method for inspecting a reflective mask blank, the method comprising the steps of: inspecting a reflective mask blank having, 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; acquiring a brightness map of an image of the substrate, the multilayer reflective film, the protective film, or the absorbing film; detecting the number and positions of defects by binarizing the brightness map; and A method for inspecting a reflective mask blank, comprising: setting a slice level for binarizing the brightness map so as to maximize the number of defects detected.

2. 2. The method for inspecting a reflective mask blank according to claim 1, wherein the image is a dark-field image, and the defect in the dark-field image has a brightness equal to or greater than the slice level.

3. 3. The reflective mask blank inspection method according to claim 2, wherein the slice level is set so that the brightness of the slice level is the lowest within a range in which the number of the defects to be detected is the greatest.

4. 2. The method for inspecting a reflective mask blank according to claim 1, wherein the image is a bright-field image, and the defect in the bright-field image has a brightness equal to or lower than the slice level.

5. 5. The reflective mask blank inspection method according to claim 4, wherein the slice level is set so that brightness at the slice level is maximized within a range in which the number of defects to be detected is maximized.

6. The reflective mask blank inspection method according to claim 1 , wherein the defect is a phase defect or an amplitude defect.

7. 2. The method for inspecting a reflective mask blank according to claim 1, wherein the wavelength of light used to capture the image is 5 nm to 600 nm.

8. A method for producing a reflective mask blank, the method comprising the steps of: producing a reflective mask blank having, 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, the method comprising the steps of: depositing the multilayer reflective film, the protective film, and the absorbing film in this order on the substrate; 8. The inspection method according to claim 1, further comprising: detecting the number and positions of defects in the substrate, the multilayer reflective film, the protective film, or the absorbing film; A method for producing a reflective mask blank, comprising:

9. Preparing a reflective mask blank manufactured by the reflective mask blank manufacturing method according to claim 8; forming an opening pattern in the absorbing film; A method for manufacturing a reflective mask, comprising the steps of:

Images