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

Abstract

This reflective mask blank comprises a substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorption film that absorbs EUV light, in the stated order. The reflective mask blank has an intermediate film configured from a compound that contains tantalum (Ta) and oxygen (O) between the protective film and the absorption film. The thickness of the intermediate film is 0.1-3.4 nm.

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 includes soft X-rays and vacuum ultraviolet light, and specifically refers to light with a wavelength of approximately 0.2 nm to 100 nm. At present, EUV light with a wavelength of approximately 13.5 nm is mainly being considered.

[0003] In EUVL, a reflective mask is used. The 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 transferring after reducing the size.

[0004] The absorbing film described in Patent Document 1 is a laminated film including an upper layer and a lower layer. The lower layer of the absorbing film contains tantalum (Ta) and oxygen (O). The oxygen (O) content in the lower layer of the absorbing film is 50 atomic % or more. The film thickness of the lower layer of the absorbing film is 4 nm to 40 nm.

[0005] Japanese Patent No. 7155316

[0006] The crystallinity of the protective film may be inherited by the absorbing film. When the absorbing film crystallizes and the crystals become coarse, the surface roughness of the absorbing film increases, and the detection rate of false defects in defect inspection increases. Here, false defects are irregularities that do not affect transfer in EUVL and are erroneously determined to be defects when inspected by a defect inspection device. When a large number of false defects are detected, defects that affect transfer in EUVL are buried among the numerous false defects, making them difficult to detect. Furthermore, when the absorbing film crystallizes, the line edge roughness of the opening pattern of the absorbing film increases.

[0007] Therefore, it is conceivable to provide an intermediate film between the protective film and the absorbing film to suppress crystallization of the absorbing film. However, if the intermediate film is too thick, the absorption of EUV light by the intermediate film becomes too great, and the decrease in reflectance of EUV light at the opening of the absorbing film becomes too great.

[0008] An embodiment of the present disclosure provides a technique for suppressing crystallization of an absorbing film and a decrease in reflectance of EUV light caused by the crystallinity of a protective film.

[0009] 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. The reflective mask blank also includes an intermediate film between the protective film and the absorbing film, the intermediate film being composed of a compound containing tantalum (Ta) and oxygen (O). The thickness of the intermediate film is 0.1 nm to 3.4 nm.

[0010] According to an embodiment of the present disclosure, it is possible to suppress crystallization of the absorbing film caused by the crystallinity of the protective film and a decrease in the reflectance of EUV light.

[0011] 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 flowchart showing an example of processing in S105. FIG. 4 is a cross-sectional view showing a reflective mask according to an embodiment. FIG. 5 is a flowchart showing a method for manufacturing a reflective mask according to an embodiment. FIG. 6(A) is a cross-sectional view showing an example of S201, FIG. 6(B) is a cross-sectional view showing an example of S202, and FIG. 6(C) is a cross-sectional view showing an example of S203. FIG. 7 is a cross-sectional view showing an example of EUV light reflected by the reflective mask of FIG. 4. FIG. 8 is a diagram showing X-ray diffraction patterns according to Examples 3, 7, and 8.

[0012] 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.

[0013] 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 7, 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.

[0014] 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 intermediate film 19, an absorbing film 13, and a hard mask film 14, in this order. The multilayer reflective film 11, the protective film 12, the intermediate film 19, the absorbing film 13, and the hard mask film 14 are formed on the 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 intermediate film 19 is provided between the protective film 12 and the absorbing film 13, and prevents the crystallinity of the protective film 12 from being inherited by the absorbing film 13. The intermediate film 19 suppresses crystallization of the absorbing film 13 compared to when the intermediate film 19 is not present. 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. That is, the absorbing film 13 may be a phase shift film. The hard mask film 14 protects a part of the absorbing film 13 from the first etching gas during processing of the absorbing film 13.

[0015] 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, intermediate film 19, 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.

[0016] 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 (see Fig. 4) 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.

[0017] Although not shown, the reflective mask blank 1 may have a buffer film between the intermediate film 19 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 and the intermediate film 19, the buffer film will ultimately have the same opening pattern as the opening pattern 13op of the absorbing film 13.

[0018] 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 S107 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 intermediate film 19 is formed on the protective film 12. In step S106, an absorbing film 13 is formed on the intermediate film 19. In step S107, a hard mask film 14 is formed on the absorbing film 13.

[0019] The order of steps S101 to S107 is not limited to the order shown in Fig. 2. For example, the order of step S102 and steps S103 to S107 may be reversed. Furthermore, the method for manufacturing the reflective mask blank 1 does not have to include all of steps S101 to S107. The method for manufacturing the reflective mask blank 1 may further include a step of forming a functional film not shown in Fig. 2.

[0020] Next, an example of the process in step S105 will be described with reference to FIG. 3 . In step S105, as described above, an intermediate film 19 is formed on the protective film 12. The intermediate film 19, which will be described in detail later, is composed of a compound containing tantalum (Ta) and oxygen (O). Hereinafter, this compound may be referred to as a TaO compound. The TaO compound may contain at least one of boron (B) and nitrogen (N). The intermediate film 19 is, for example, a TaO film, a TaOB film, a TaON film, or a TaOBN film. Step S105 preferably includes steps S105a to S105b as shown in FIG. 3 to prevent the protective film 12 from being exposed to oxygen and thereby prevent deterioration of the protective film 12 due to oxygen.

[0021] In step S105a, a non-oxide film containing tantalum (Ta) but not oxygen (O) is formed. Here, not containing oxygen (O) means that the O content is 0.1 at% or less. The non-oxide film need only contain no oxygen, and may contain at least one of boron (B) and nitrogen (N). The non-oxide film is, for example, a Ta film, a TaB film, a TaN film, or a TaBN film. The non-oxide film is formed by, for example, sputtering. By forming the non-oxide film on the protective film 12, it is possible to prevent the protective film 12 from being exposed to oxygen, and thus to prevent deterioration of the protective film 12.

[0022] Deterioration of the protective film 12 includes, for example, sublimation of the protective film 12. Sublimation of the protective film 12 can occur, for example, when the protective film 12 contains ruthenium (Ru) as a main component. Ru sublimes due to oxidation. Note that 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.

[0023] Deterioration of the protective film 12 includes non-uniformity in the composition of the protective film 12. Non-uniformity in the composition of the protective film 12 can occur, for example, when the protective film 12 is made of a Ru alloy. The Ru alloy contains Ru as well as another metal element (for example, niobium (Nb)). Nb bonds more easily with O than Ru. Therefore, when an oxide film is formed on the protective film 12, non-uniformity in the composition of the protective film 12 occurs.

[0024] In step S105b, the non-oxide film formed in step S105a is oxidized. The intermediate film 19 is obtained by oxidizing the non-oxide film. Oxidizing the non-oxide film includes, for example, exposing the non-oxide film to the atmosphere. Oxidizing the non-oxide film may further include cleaning the non-oxide film with a cleaning solution (e.g., pure water, SPM, SC-1, or gas-dissolved water). SPM includes, for example, 75% by volume of concentrated sulfuric acid and 25% by volume of hydrogen peroxide. SC-1 includes ammonia water, hydrogen peroxide, and pure water. The volume ratio of ammonia water, hydrogen peroxide, and pure water (ammonia water:hydrogen peroxide:pure water) is, for example, 1:1 to 2:5 to 7. The gas-dissolved water includes pure water and a gas dissolved in the pure water. The gas dissolved in the pure water includes, for example, at least one of oxygen, nitrogen, carbon dioxide, hydrogen, and ozone. Oxidation of the non-oxide film may involve exposure to oxygen gas plasma in a vacuum, or irradiating the surface of the non-oxide film with ultraviolet light in the presence of ozone.

[0025] Next, a reflective mask 2 according to one embodiment will be described with reference to Fig. 4. 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.

[0026] Next, a method for manufacturing a reflective mask 2 according to one embodiment will be described with reference to Figures 5 and 6. The method for manufacturing a reflective mask 2 includes steps S201 to S204 shown in Figure 5. In step S201, a reflective mask blank 1 is prepared, as shown in Figure 6(A). The reflective mask blank 1 includes a resist film 16, as shown in Figure 6(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.

[0027] 6B, 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.

[0028] 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 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 second 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 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.

[0029] In step S203, as shown in FIG. 6C , 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.

[0030] 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. The chlorine-based gas may be, for example, Cl ２ Gas, SiCl ４Gas, CHCl ３ Gas, CCl ４ Gas and BCl ３ The first etching gas may contain at least one selected from the group consisting of a chlorine-based gas, an inert gas, and a chlorine-based gas. 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.

[0031] 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 chlorine-based gas and an oxygen-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.

[0032] Next, referring back to FIG. 1, the substrate 10, the multilayer reflective film 11, the protective film 12, the intermediate film 19, the absorbing film 13, the hard mask film 14, and the conductive film 15 will be described in this order.

[0033] 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.

[0034] 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 is an area that coincides with the exposure area in plan view. The exposure area is an 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. 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. Furthermore, the quality assurance area preferably does not have defects that cause phase defects.

[0035] 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.

[0036] 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. 7 ) 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.

[0037] 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).

[0038] The protective film 12 is formed between the multilayer reflective film 11 and the absorbing film 13 and protects 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. In this embodiment, the intermediate film 19 protects the protective film 12 so that it is not exposed to the first etching gas. Therefore, thickness reduction of the protective film 12 can be suppressed. Furthermore, as will be described in detail later, the intermediate film 19 has superior resistance to a mixed gas of a chlorine-based gas and an oxygen-based gas, as well as superior resistance to UV ozone gas, compared to the protective film 12. Therefore, thickness reduction of the protective film 12 due to the third etching gas can be suppressed, and thickness reduction of the protective film 12 during cleaning with UV ozone gas can also be suppressed.

[0039] 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. 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.

[0040] 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.

[0041] 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 on the other hand, the protective film 12 has good resistance to the first etching gas. According to this embodiment, as will be described in detail later, the intermediate film 19 prevents the crystallinity of the protective film 12 from being inherited by the absorption film 13. Therefore, the protective film 12 may be crystallized.

[0042] 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 intermediate film 19. 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.

[0043] 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.

[0044] 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.

[0045] 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).

[0046] 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.

[0047] The intermediate film 19 is formed between the protective film 12 and the absorbing film 13 and prevents the crystallinity of the protective film 12 from being inherited by the absorbing film 13. The intermediate film 19 suppresses crystallization of the absorbing film 13 compared to when the intermediate film 19 is not present. Therefore, an increase in line edge roughness of the opening pattern 13op of the absorbing film 13 due to crystallization of the absorbing film 13 can be suppressed. Furthermore, surface roughness of the absorbing film 13 due to crystallization of the absorbing film 13 can be suppressed, thereby suppressing an increase in the detection rate of false defects. The arithmetic mean roughness Ra of the surface of the absorbing film 13 is preferably less than 0.4 nm. The arithmetic mean roughness Ra is measured in accordance with JIS B0601:2013. If the arithmetic mean roughness Ra of the surface of the absorbing film 13 is less than 0.4 nm, the detection rate of false defects is low. The arithmetic mean roughness Ra of the surface of the absorbing film 13 is more preferably 0.3 nm or less. The arithmetic mean roughness Ra of the surface of the absorbing film 13 is not particularly limited, but may be 0.1 nm or more.

[0048] Furthermore, the intermediate film 19 protects the protective film 12 from a mixed gas of a chlorine-based gas and an oxygen-based gas (e.g., a third etching gas). This makes it possible to suppress the thickness loss of the protective film 12 caused by the third etching gas. Compared to the protective film 12, the intermediate film 19 is more resistant to the mixed gas of a chlorine-based gas and an oxygen-based gas, and also has better resistance to UV ozone gas. This makes it possible to suppress the thickness loss of the protective film 12 during cleaning with UV ozone gas.

[0049] As described above, the intermediate film 19 prevents the crystallinity of the protective film 12 from being inherited by the absorbing film 13. Therefore, when the protective film 12 is crystalline, it is preferable to form the intermediate film 19 between the protective film 12 and the absorbing film 13. When the protective film 12 contains ruthenium (Ru) as a main component, the protective film 12 is likely to crystallize. The protective film 12 may contain only Ru, or may contain a Ru compound. The Ru compound may be a Ru alloy.

[0050] The intermediate film 19 is composed of a TaO compound containing tantalum (Ta) and oxygen (O). The TaO compound has a non-crystalline (amorphous) structure or a microcrystalline structure. Therefore, the intermediate film 19 is an amorphous film or a microcrystalline film. Therefore, the intermediate film 19 can prevent the crystallinity of the protective film 12 from being inherited by the absorbing film 13. When the TaO compound has an amorphous structure or a microcrystalline structure, the X-ray diffraction pattern of the TaO compound does not have a clear peak.

[0051] The TaO compound constituting the intermediate film 19 preferably contains tantalum (Ta) and oxygen (O) as main components. That is, the TaO compound constituting the intermediate film 19 preferably contains 25 at% to 50 at% tantalum (Ta) and 30 at% to 75 at% oxygen (O). The TaO compound constituting the intermediate film 19 may also contain 0 at% to 10 at% nitrogen (N). Furthermore, the TaO compound constituting the intermediate film 19 may also contain 0 at% to 10 at% boron (B).

[0052] If the Ta content in the TaO compound is 25 at% or more, the intermediate film 19 has good resistance to the internal atmosphere of the exposure apparatus. The internal atmosphere of the exposure apparatus is a reducing atmosphere containing hydrogen gas. The Ta content in the TaO compound is preferably 25 at% or more, more preferably 28 at% or more, even more preferably 30 at% or more, and particularly preferably 33 at% or more. On the other hand, if the Ta content in the TaO compound is 50 at% or less, crystallization of the intermediate film 19 and absorption of EUV light by the intermediate film 19 (and thus a decrease in the reflectivity of EUV light) can be suppressed. The Ta content in the TaO compound is preferably 50 at% or less, more preferably 47 at% or less, even more preferably 45 at% or less, and particularly preferably 40 at% or less.

[0053] If the O content in the TaO compound is 30 at% or more, crystallization of the intermediate film 19 and absorption of EUV light by the intermediate film 19 (and thus a decrease in the reflectivity of EUV light) can be suppressed. The O content in the TaO compound is preferably 30 at% or more, more preferably 40 at% or more, even more preferably 45 at% or more, still more preferably 50 at% or more, particularly preferably 55 at% or more, and most preferably 60 at% or more. On the other hand, if the O content in the TaO compound is 75 at% or less, the intermediate film 19 has good resistance to the internal atmosphere of the exposure apparatus. The O content in the TaO compound is preferably 75 at% or less, more preferably 70 at% or less, even more preferably 65 at% or less, and particularly preferably 63 at% or less.

[0054] If the N content in the TaO compound is 10 at% or less, the N content in the non-oxide film formed in step S105a shown in Figure 3 is sufficiently low, and oxidation of the non-oxide film in step S105b is likely to proceed. The N content in the TaO compound is preferably 10 at% or less, more preferably 7 at% or less, and even more preferably 5 at% or less. The N content in the TaO compound is preferably 1 at% or more. Note that if the TaO compound contains N, crystallization of the intermediate film 19 and absorption of EUV light by the intermediate film 19 (and thus a decrease in the reflectance of EUV light) can be suppressed.

[0055] If the B content in the TaO compound is 10 at% or less, the B content of the non-oxide film formed in step S105a shown in Figure 3 is sufficiently low, and oxidation of the non-oxide film in step S105b is likely to proceed. The B content in the TaO compound is preferably 10 at% or less, more preferably 7 at% or less, and even more preferably 5 at% or less. The B content in the TaO compound may be 0 at% or more, but is preferably 1 at% or more. Note that if the TaO compound contains B, crystallization of the intermediate film 19 and absorption of EUV light by the intermediate film 19 (and thus a decrease in the reflectance of EUV light) can be suppressed.

[0056] The thickness of the intermediate film 19 is 0.1 nm or more, preferably 0.2 nm or more, more preferably 0.3 nm or more, and even more preferably 0.5 nm or more, from the viewpoint of suppressing crystallization of the absorber film 13. The thickness of the intermediate film 19 is 3.4 nm or less, preferably 3.2 nm or less, and more preferably 3.0 nm or less, from the viewpoint of suppressing absorption of EUV light by the intermediate film 19 (and thus a decrease in the reflectance of EUV light).

[0057] Although the method for forming the intermediate film 19 is not particularly limited, as described above, it is preferable to form a non-oxide film containing tantalum (Ta) but not oxygen (O), and then oxidize the non-oxide film (see FIG. 3). Since the protective film 12 is not exposed to oxygen, deterioration of the protective film 12 due to oxygen can be suppressed.

[0058] The non-oxide film may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering. When a Ta film is formed by DC sputtering, an example of the film formation conditions is as follows: <Ta film formation conditions> Target: Ta target, Sputtering gas: Ar gas, Gas pressure: 1.0×10 －２ Pa ~ 1.0 x 10 ０ Pa, target power density: 1.0 W / cm ２ ~8.5 W / cm ２ , Film formation rate: 0.020 nm / sec to 1.000 nm / sec, Film thickness: 0.2 nm to 5 nm.

[0059] A method for oxidizing a non-oxide film is, for example, a plasma oxidation method. When oxidizing using the plasma oxidation method, an example of the film formation conditions is as follows: <Oxidation Conditions> Sputtering gas: Ar gas, O ２ Gas, Gas pressure: 1.0 x 10 －２ Pa~1.0×100Pa, O ２ Gas flow rate: 200 sccm to 3000 sccm, Ar gas flow rate: 100 sccm to 6000 sccm, O ２ O in the mixed gas of Ar gas ２Gas ratio: 0% to 90% by volume, Power supply frequency for plasma generation: 10 MHz to 60 MHz, Power for plasma generation: 50 W to 600 W, Processing time: 2 sec to 120 sec, Processing temperature: 80°C to 350°C, Processing pressure: 50 Pa to 1200 Pa.

[0060] 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. 7 .

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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 N２ 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] The hard mask film 14 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] The conductive film 15 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0081] [Examples] Experimental data will be described below. In Examples 1 to 9, reflective mask blanks 1 having the same configuration were produced except for the film formation conditions shown in Table 1, and the characteristics of the reflective mask blanks 1 were evaluated. Examples 1 to 6 are Examples, and Examples 7 to 9 are Comparative Examples.

[0082] 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 ２ The quality assurance area of ​​the first main surface 10a of the substrate 10 was polished to a root-mean-square roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less. A 100 nm-thick Cr film was formed on the second main surface 10b of the substrate 10 using magnetron sputtering. The sheet resistance of the Cr film was 100 Ω / □.

[0083] 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).

[0084] The protective film 12 was a Ru film formed by ion beam sputtering. The thickness of the Ru film was measured by X-ray reflectivity. The Ru film consisted of only Ru.

[0085] In Examples 1 to 6 and 9, a TaON film was formed as the intermediate film 19 by the method shown in FIG. 3 . Specifically, a TaN film was formed by DC sputtering, and then the TaN film was exposed to the air at room temperature to form a TaON film. The thickness of the TaON film was measured using a transmission electron microscope (HD-2700) manufactured by Hitachi High-Technologies Corporation. The chemical composition of the TaON film was measured using the transmission electron microscope (HD-2700) manufactured by Hitachi High-Technologies Corporation and an energy dispersive X-ray analyzer (AZtec Energy TEM Advanced Ultim Max TLE) manufactured by Oxford Instruments.

[0086] A TaN film (68 nm thick) was formed by reactive sputtering as the absorber film 13. The chemical composition of the TaN film was measured using a Hitachi High-Technologies transmission electron microscope (HD-2700) and an Oxford Instruments energy dispersive X-ray analyzer (AZtec Energy TEM Advanced Ultim Max TLE), and was found to have a Ta content of 85 at % and a N content of 15 at %.

[0087] The film formation conditions and evaluation results for Examples 1 to 9 are shown in Table 1.

[0088]

[0089] The surface roughness (specifically, the arithmetic mean roughness Ra) of the absorbing film 13 shown in Table 1 was measured in a square area with a side length of 2 μm using a Jupiter XR manufactured by Oxford University.

[0090] The presence or absence of crystallization of the absorbing film 13 shown in Table 1 was investigated by obtaining an X-ray diffraction pattern using a SmartLab manufactured by Rigaku Corporation and checking for the presence or absence of a peak due to the TaN film. As representative examples, the X-ray diffraction patterns of Examples 3, 7, and 8 are shown in FIG. 8. In FIG. 8, the X-ray diffraction patterns were obtained by performing a 2θ / ω scan using CuKα radiation. The peak at 2θ around 41° is due to the Mo layer that constitutes the multilayer reflective film 11. The peak at 2θ around 38° is due to the crystallization of the absorbing film 13. Note that the peak due to the crystallization of the absorbing film 13 is usually observed in the 2θ range of 34° to 39°.

[0091] The reflectance for EUV light shown in Table 1 is that immediately before the formation of the absorbing film 13, and was calculated using the optical simulation described in "Experimental Approach to EUV Imaging Enhancement by Mask Absorber Height Optimization (2013)" (authors: N. Davydova, R. Kruif, H. Rolff, B. Connolly, E. Setten, A. Lammers, D. Oorschot, N. Fukugami, Y. Kodera). The relative values ​​of the reflectance shown in Table 1 are relative values ​​when the reflectance of Example 7 is set to 1.00.

[0092] The presence or absence of detection of the pseudo defects shown in Table 1 was checked using a defect inspection device M9650 (wavelength of inspection light: 213 nm) manufactured by Lasertec Corporation.

[0093] As shown in Table 1, in Examples 1 to 6, unlike Examples 7 and 8, an intermediate film 19 was formed between the protective film 12 and the absorbing film 13. As a result, in Examples 1 to 6, unlike Examples 7 and 8, no peaks due to crystallization of the absorbing film 13 were observed in the X-ray diffraction patterns (see FIG. 8). Therefore, it was found that by forming the intermediate film 19 between the protective film 12 and the absorbing film 13, crystallization of the absorbing film 13 can be suppressed.

[0094] Unlike Examples 7 and 8, in Examples 1 to 6, as described above, the crystallization of the absorbing film 13 could be suppressed, and therefore the number of pseudo defects was zero. On the other hand, in Examples 7 and 8, the absorbing film 13 crystallized, and several thousand or more pseudo defects were detected.

[0095] Furthermore, as shown in Table 1, in Examples 1 to 6, the thickness of the intermediate film 19 was 3.40 nm or less, unlike Example 9. Therefore, in Examples 1 to 6, the absorption of EUV light by the intermediate film 19 could be suppressed more effectively than in Example 9, and a decrease in the reflectance of EUV light could be suppressed. In Examples 1 to 6, the reflectance of EUV light could be maintained at 50% or more.

[0096] 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.

[0097] This application claims priority based on Japanese Patent Application No. 2023-205056 filed with the Japan Patent Office on December 5, 2023, the entire contents of which are incorporated herein by reference.

[0098] REFERENCE SIGNS LIST 1 reflective mask blank 2 reflective mask 10 substrate 11 multilayer reflective film 12 protective film 13 absorbing film 19 intermediate film

Claims

1. 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, wherein an intermediate film is disposed between the protective film and the absorbing film and is composed of a compound containing tantalum (Ta) and oxygen (O), and the thickness of the intermediate film is 0.1 nm to 3.4 nm.

2. The reflective mask blank according to claim 1, wherein the compound constituting the intermediate film contains 25 at % to 50 at % tantalum (Ta) and 30 at % to 75 at % oxygen (O).

3. A reflective mask blank according to claim 1 or 2, wherein the compound constituting the intermediate film contains at least one of boron (B) and nitrogen (N).

4. The reflective mask blank according to claim 1 or 2, wherein the intermediate film is an amorphous film or a microcrystalline film.

5. A reflective mask blank according to claim 1 or 2, wherein the arithmetic mean roughness Ra of the surface of the absorbing film is less than 0.4 nm.

6. The reflective mask blank according to claim 1 or 2, wherein the protective film contains ruthenium (Ru) as a main component.

7. The reflective mask blank according to claim 1 or 2, wherein the absorbing film contains tantalum (Ta) as a main component.

8. A reflective mask comprising the reflective mask blank according to claim 1 or 2, and comprising an aperture pattern in the absorbing film.

9. A method for manufacturing 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, comprising forming an intermediate film composed of a compound containing tantalum (Ta) and oxygen (O) between the protective film and the absorbing film, wherein the thickness of the intermediate film is 0.1 nm to 3.4 nm.

10. A method for producing a reflective mask blank as described in claim 9, wherein forming the intermediate film comprises, in this order, forming a non-oxide film containing tantalum (Ta) and no oxygen (O), and oxidizing the non-oxide film.

11. The method for producing a reflective mask blank according to claim 10, wherein the protective film contains ruthenium (Ru) as a main component.

12. A method for manufacturing a reflective mask, comprising the steps of: preparing a reflective mask blank according to claim 1 or 2; and forming an opening pattern in the absorbing film, in this order.