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

Abstract

To provide an absorption film which can be etched by a chlorine-based gas or a fluorine-based gas, is excellent in resistance to SPM, and has a low refractive index.SOLUTION: The reflective mask blank includes a substrate, a multilayer reflective film, a protective film, and an absorber film in this order. The multilayer reflective film reflects EUV light. The protective film protects the multilayer reflection film from a first etching gas during processing of the absorption film. The absorption film absorbs EUV light. The absorption film has a Ta compound containing Ta and W. In the Ta compound, a total ratio of Ta and W to all metal elements excluding non-metal elements is 50at% or more, and an atomic ratio (Ta: W) of Ta and W is 30:70 to 90:10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[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. [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. The reflective mask has a substrate, a multilayer reflective film, a protective film, and an absorbing film, in that order. The multilayer reflective film reflects EUV light. The protective film protects the multilayer reflective film from the first etching gas during processing of the absorbing film. The absorbing film 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 reflective mask blank described in Patent Document 1 comprises a substrate, a multilayer reflective film, and an absorbing film, in this order. The absorbing film in Patent Document 1 contains tantalum (Ta), boron (B), and nitrogen (N). The opening pattern of the absorbing film in Patent Document 1 is formed using an etching gas. The etching gas is a chlorine-based gas or a fluorine-based gas. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7002700 Summary of the Invention [Problem to be solved by the invention]

[0005] Ta compounds are being considered as materials for the absorbing film. Ta can be etched with chlorine-based gases or fluorine-based gases. Ta also has excellent resistance to sulfuric peroxide mixture (SPM). SPM is used for cleaning reflective masks, etc. However, Ta has a relatively large refractive index.

[0006] One embodiment of the present disclosure provides an absorbing film that can be etched with a chlorine-based gas or a fluorine-based gas, has excellent resistance to SPM, and has a low refractive index. [Means for solving the problem]

[0007] A reflective mask blank according to an embodiment of the present disclosure comprises a substrate, a multilayer reflective film, a protective film, and an absorbing film, in this order. The multilayer reflective film reflects EUV light. The protective film protects the multilayer reflective film from a first etching gas during processing of the absorbing film. The absorbing film absorbs EUV light. The absorbing film contains a Ta compound containing Ta and W. The Ta compound has a total ratio of Ta and W to all metal elements of 50 at% or more, and an atomic ratio of Ta to W (Ta:W) of 30:70 to 90:10. [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, by adding W to Ta and adjusting the compounding ratio of Ta and W to a desired range, it is possible to provide an absorbing film that can be etched with a chlorine-based gas or a fluorine-based gas, has excellent resistance to SPM, and has a low refractive index. [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 diagram showing the refractive index and extinction coefficient of the Ta compounds according to Examples 1 to 7. In FIG. 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 similar 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 (see FIG. 3) 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 mixed gas of 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, O2 gas. The second etching gas may further include, for example, at least one selected from N2 gas, He gas, and Ar gas. The second etching gas is preferably plasmatized.

[0022] An example of processing conditions for the hard mask film 14 is shown below. <Hard mask film processing conditions> Etching gas: plasma-enhanced mixed gas (e.g., a mixture of Cl2 gas and O2 gas), Source power: 150W~1000W, Bias: 50W~150W, Pressure: 0.2Pa~1.0Pa.

[0023] 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.

[0024] 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 may include, for example, a fluorine-based gas. The fluorine-based gas may include, for example, at least one selected from CF gas, CHF gas, C2F6 gas, C3F6 gas, C4F6 gas, C4F8 gas, CH2F2 gas, CH3F gas, C3F8 gas, F gas, SF gas, and NF3 gas.

[0025] The first etching gas may contain a chlorine-based gas instead of a fluorine-based gas. The chlorine-based gas may include at least one selected from Cl2 gas, SiCl4 gas, CHCl3 gas, CCl4 gas, and BCl3 gas. The first etching gas may contain both a fluorine-based gas and a chlorine-based gas.

[0026] The first etching gas may contain an inert gas in addition to at least one of a fluorine-based gas and a chlorine-based gas. The inert gas contains, for example, at least one selected from N2 gas, He gas, and Ar gas. The first etching gas preferably does not substantially contain an oxygen-based gas. By making the first etching gas substantially free of an oxygen-based gas, oxidation of the absorber film 13 can be suppressed. As a result, a decrease in the etching rate of the absorber film 13 can be suppressed. The content of the oxygen-based gas in the first etching gas is preferably 0.5% by volume or less. The first etching gas is preferably plasmatized.

[0027] An example of processing conditions for the absorbing film 13 is shown below. <Absorbent film processing conditions> Etching gas: plasma CF4 gas, Source power: 150W~2000W, Bias: 20W~150W, Pressure: 0.2Pa~1.0Pa.

[0028] 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 is the same gas as 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The multilayer reflective film 11 reflects EUV light. The multilayer reflective film 11 has, for example, high refractive index layers and low refractive index layers alternately. 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 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.

[0033] The thickness of each layer constituting the multilayer reflective film 11 and the number of repeating units of the layers can be appropriately selected depending on the material of each layer and the reflectivity for EUV light. When the multilayer reflective film 11 is a Mo / Si multilayer reflective film, in order to achieve a reflectivity of 60% or more for EUV light at an incident angle θ (see FIG. 6) of 6°, Mo layers with a thickness of 2.3±0.1 nm and Si layers with a thickness of 4.5±0.1 nm can be stacked so that the number of repeating units is 30 or more and 60 or less. 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.

[0034] The film formation method for 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 the Si layer> Target: Si target, Sputtering gas: Ar gas, Gas pressure: 1.3×10 -2 Pa to 2.7×10 -2 Pa, Ion acceleration voltage: 300V to 1500V, Film formation rate: 0.030 nm / sec to 0.300 nm / sec, Film thickness of the Si layer: 4.5 ± 0.1 nm. <Film formation conditions for the Mo layer> Target: Mo target, Sputtering gas: Ar gas, Gas pressure: 1.3×10 -2 Pa to 2.7×10 -2 Pa, Ion acceleration voltage: 300V to 1500V, Film formation rate: 0.030 nm / sec to 0.300 nm / sec, Film thickness of the Mo layer: 2.3 ± 0.1 nm. <Repeating unit of the Si layer and the Mo layer> Number of repeating units: 30 to 60 (preferably 40 to 50).

[0035] The protective film 12 is formed between the multilayer reflective film 11 and the absorption film 13 to protect 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.

[0036] The protective film 12 preferably contains 50 at % or more of Rh. The protective film 12 may contain only Rh, or may contain an Rh compound. The Rh compound may contain, in addition to Rh, at least one metal element selected from Ru, Nb, Mo, Ta, Ir, Pd, Zr, Y, and Ti. By adding Ru, Nb, Mo, Zr, Y, or Ti to Rh, it is possible to reduce the extinction coefficient while suppressing an increase in the refractive index, and it is possible to suppress absorption of EUV light by the protective film 12 (and thus a decrease in reflectance for EUV light). Furthermore, by adding Ru, Ta, Ir, Pd, or Y to Rh, it is possible to improve resistance to the first etching gas.

[0037] The Rh compound may contain, in addition to Rh, at least one nonmetallic element selected from N, O, C, and B. While these nonmetallic elements reduce the resistance of the protective film 12 to the first etching gas, they also reduce the crystallinity of the protective film 12, thereby improving the smoothness of the protective film 12. Rh compounds containing these nonmetallic elements have an amorphous structure or a microcrystalline structure. When the Rh compound has an amorphous structure or a microcrystalline structure, the X-ray diffraction profile of the Rh compound does not have a clear peak.

[0038] 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.

[0039] In this embodiment, the protective film 12 is a single-layer film made up 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 that make up the protective film 12 are formed in this order on the multilayer reflective film 11. The uppermost layer of the protective film 12 is the film that is farthest from the multilayer reflective film 11. By making the protective film 12 a multi-layer structure, materials with excellent predetermined functions can be used for each layer, making it possible to make the protective film 12 as a whole multifunctional.

[0040] The upper layer of the protective film 12 preferably contains Rh, and more preferably contains a Rh compound. The lower layer of the protective film 12 preferably contains at least one element selected from Ru, Nb, Mo, Zr, Y, C, and B, and more preferably contains Ru. When the protective film 12 is a multilayer film, the Rh content in the upper layer of the protective film 12 is preferably 50 at% or more, more preferably more than 50 at%, and further preferably 90 at% or more. When the protective film 12 is a multilayer film, the thickness of the following protective film 12 means the total film thickness of the multilayer film.

[0041] 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 absorption of EUV light by the protective film 12 (and thus the decrease in reflectivity to EUV light) can be suppressed. The thickness of the protective film 12 is more preferably 2.0 nm to 3.5 nm, and further preferably 2.5 nm to 3.0 nm.

[0042] 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 3 10.0 g / cm or more, the etching resistance is good. Also, if the density of the protective film 12 is 3 14.0 g / cm or less, the absorption of EUV light by the protective film 12 (and thus the decrease in reflectivity to EUV light) can be suppressed.

[0043] The film formation method of the protective film 12 is, for example, a DC sputtering method, a magnetron sputtering method, or an ion beam sputtering method. When forming a Rh film using the DC sputtering method, an example of the film formation conditions is as follows. <Film formation conditions of Rh film> Target: Rh target, Sputtering gas: Ar gas, [[ID=,28]]Gas pressure: 1.0×10 -2 Pa~1.0×10 0 Pa, Target power density: 1.0W / cm 2 ~8.5W / cm 2 , Film formation rate: 0.020nm / sec~1.000nm / sec, Film thickness: 1.0nm~4.0nm.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The refractive index n of the absorbing film 13 is preferably 0.954 or less, more preferably 0.950 or less, and even more preferably 0.945 or less. The smaller the refractive index n of the absorbing film 13, the thinner the absorbing film 13 can be. The refractive index n of the absorbing film 13 is preferably 0.930 or more, more preferably 0.935 or more, and even more preferably 0.940 or more. In this specification, the refractive index is the refractive index for EUV light (for example, light with a wavelength of 13.5 nm).

[0051] The extinction coefficient k of the absorbing film 13 is preferably 0.020 or more, more preferably 0.025 or more, and even more preferably 0.030 or more. The larger the extinction coefficient k of the absorbing film 13, the easier it is to obtain a desired reflectance with a thin film thickness. The extinction coefficient k of the absorbing film 13 is preferably 0.040 or less, and more preferably 0.035 or less. In this specification, the extinction coefficient refers to the extinction coefficient for EUV light (for example, light with a wavelength of 13.5 nm).

[0052] The optical properties (refractive index n and extinction coefficient k) of the absorbing film 13 are taken from the database of the Center for X-Ray Optics, Lawrence Berkeley National Laboratory, or values ​​calculated from the "incident angle dependence" of reflectance described below.

[0053] The incident angle θ of the EUV light, the reflectance R for the EUV light, the refractive index n of the absorbing film 13, and the extinction coefficient k of the absorbing film 13 satisfy the following formula (1). R=|(sinθ-((n+ik) 2 -cos 2 θ) 1 / 2 ) / (sinθ+((n+ik) 2 -cos 2 θ) 1 / 2 )|···(1) A plurality of combinations of the incident angle θ and the reflectance R are measured, and the refractive index n and the extinction coefficient k are calculated by the least squares method so that the error between the plurality of measurement data and Equation (1) is minimized.

[0054] The absorbing film 13 has a Ta compound containing Ta and W. Ta can be etched with a chlorine-based gas or a fluorine-based gas. Ta also has excellent resistance to sulfuric peroxide mixture (SPM). SPM is used for cleaning the reflective mask 2, etc. However, Ta has a relatively large refractive index. Therefore, the Ta compound contains W in addition to Ta to reduce the refractive index.

[0055] As shown in FIG. 7, the refractive index of a Ta compound can be reduced by including W. W not only reduces the refractive index, but also can be etched with a chlorine-based gas or a fluorine-based gas under the same conditions as before. However, adding excessive W reduces SPM resistance. Therefore, it is preferable that the Ta compound satisfy the following (A) and (B).

[0056] (A) In the Ta compound, the total ratio (TaW / M) of Ta and W to all metal elements excluding non-metal elements is 50 at% or more. (TaW / M) represents the total content of Ta and W when the total content of all metal elements excluding non-metal elements is 100 at%. If (TaW / M) is 50 at% or more, Ta and W dominate the properties of the absorbing film 13.

[0057] The larger (TaW / M) is, the better, preferably 70 at% or more, more preferably 90 at% or more, and even more preferably 98 at%. (TaW / M) is 100 at% or less. It is particularly preferable that the Ta compound contains substantially only Ta and W as metal elements. In other words, it is particularly preferable that (TaW / M) is 98 at% to 100 at%.

[0058] As described above, it is particularly preferable that the Ta compound contains substantially only Ta and W as metal elements. However, the Ta compound may contain metal elements other than Ta and W. For example, the Ta compound may contain at least one selected from Nb, Mo, and Re as the metal element other than Ta and W. Nb, Mo, and Re can set the refractive index and extinction coefficient of the reflective mask 2 within desired ranges while maintaining the SPM resistance and etching rate.

[0059] (B) The Ta compound has an atomic ratio of Ta to W (Ta:W) of 30:70 to 90:10. If the ratio value (Ta / W) is 30 / 70 or more, the SPM resistance is good. From the viewpoint of SPM resistance, the ratio value (Ta / W) is preferably 33 / 67 or more, more preferably 40 / 60 or more, and even more preferably 42 / 58 or more. On the other hand, if the ratio value (Ta / W) is 90 / 10 or less, the refractive index is small. From the viewpoint of refractive index, the ratio value (Ta / W) is preferably 80 / 20 or less, more preferably 70 / 30 or less, even more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0060] When the Ta compound satisfies the above (A) and (B), it is possible to obtain an absorbing film 13 that can be etched with a chlorine-based gas or a fluorine-based gas, has excellent resistance to SPM, and has a low refractive index.

[0061] The refractive index n of the Ta compound is preferably 0.954 or less, more preferably 0.950 or less, and even more preferably 0.945 or less. The smaller the refractive index n of the Ta compound, the thinner the absorbing film 13 can be. The refractive index n of the Ta compound is preferably 0.930 or more, more preferably 0.935 or more and less, and even more preferably 0.940 or more and less.

[0062] The extinction coefficient k of the Ta compound is preferably 0.020 or more, more preferably 0.025 or more, and even more preferably 0.030 or more. The larger the extinction coefficient k of the Ta compound, the easier it is to obtain a desired reflectance with a thin film thickness. The extinction coefficient k of the Ta compound is preferably 0.040 or less, and more preferably 0.035 or less.

[0063] The Ta compound preferably contains at least one non-metallic element selected from N, B, and C. These non-metallic elements can suppress crystallization while suppressing a decrease in optical properties, and can reduce the roughness of the side surface of the aperture pattern 13op. The Ta compound more preferably contains N as the non-metallic element. From the viewpoint of hydrogen resistance, the Ta compound preferably does not substantially contain O as the non-metallic element. The O content in the Ta compound is preferably 0.1 at% or less.

[0064] The Ta compound preferably contains 5 at% or more of N. If the N content in the Ta compound is 5 at% or more, crystallization can be suppressed while suppressing a decrease in optical properties, and the roughness of the side surface of the aperture pattern 13op can be reduced. The N content in the Ta compound is more preferably 7 at% or more, still more preferably 9 at% or more, and particularly preferably 11 at% or more. The N content in the Ta compound may be 20 at% or less, or may be 16 at% or less.

[0065] The method for forming 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.

[0066] When forming a TaWN film using a reactive sputtering method, an example of the film formation conditions is as follows. Note that it is also possible to use a TaW target instead of the Ta target and the W target. <Film Formation Conditions of TaWN Film> Targets: Ta target and W target, Output density of Ta target: 1.0 W / cm 2 ~8.5 W / cm 2 , Output density of W target: 1.0 W / cm 2 ~8.5 W / cm 2 , Sputtering gas: Mixed gas of Ar gas and N2 gas, Volume ratio of N2 gas in sputtering gas (N2 / (Ar+N2)): 0.01 to 0.30, Deposition rate: 0.020nm / sec~0.080nm / sec, Film thickness: 20nm~60nm.

[0067] The hard mask film 14 is formed on the opposite side of the protective film 12 with respect to the absorbing film 13. The hard mask film 14 protects a part of the absorbing film 13 from the second etching gas. An opening pattern 13op is formed in the remaining part of the absorbing film 13. The hard mask film 14 enables the resist film 16 to be made thinner.

[0068] The hard mask film 14 preferably contains at least one metal element or semi-metal element selected from Ru, Al, Cr, Si, Ta, Ti, Hf, and Y. From the viewpoints of ensuring etching selectivity and processability of the hard mask film 14, the hard mask film 14 more preferably contains Cr. 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.

[0069] 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.

[0070] The hard mask film 14 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0071] The conductive film 15 is formed on the opposite side of the substrate 10 from the multilayer reflective film 11, and is used to attach the reflective mask 2 to an electrostatic chuck of an exposure tool. In this embodiment, the conductive film 15 is a single-layer film, but it may also be a multi-layer film having a lower layer and an upper layer.

[0072] 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.

[0073] 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.

[0074] The conductive film 15 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0075] [Example] The experimental data will be explained below. In Examples 1 to 12, absorbing films having the compositions shown in Table 1 were formed on glass substrates, and the optical properties (refractive index n and extinction coefficient k), SPM resistance, and etching rate were measured. Examples 1 to 6 and 12 are working examples, and Examples 7 to 11 are comparative examples.

[0076] The SPM resistance of the absorber film was evaluated by immersing the film in sulfuric acid / hydrogen peroxide solution at 100°C for 20 minutes, measuring the change in film thickness using X-ray reflectometry (XRR), and measuring the etching rate of the absorber film in sulfuric acid / hydrogen peroxide solution. The sulfuric acid / hydrogen peroxide solution was obtained by mixing concentrated sulfuric acid and hydrogen peroxide solution at a ratio of 75% by volume:25% by volume (concentrated sulfuric acid:hydrogen peroxide solution). The concentrated sulfuric acid contained 96% by volume of sulfuric acid and 4% by volume of water. The hydrogen peroxide solution contained 30-35% by volume of hydrogen peroxide and 65-70% by volume of water.

[0077] The SPM resistance of the absorbing film was evaluated according to the following criteria. "A": Etching rate is 0.025 nm / min or less, "B": Etching rate is greater than 0.025 nm / min and less than 0.050 nm / min; "C": Etching rate greater than 0.050 nm / min. The smaller the etching rate, the better the SPM resistance.

[0078] The etching rate of the absorbing film was determined by performing plasma etching under the following conditions using an inductively coupled plasma (ICP) generator and measuring the film thickness before and after plasma etching using an X-ray reflectometry (XRR) method. Etching gas: CF4 gas, Antenna RF power output: 1200W, Bias RF power output: 50W, CF4 gas flow rate: 60sccm, CF4 gas pressure: 0.4 Pa.

[0079] The etching rate of the absorbing film was evaluated according to the following criteria. "A": Etching speed is 2.0 nm / min or more, "B": Etching rate less than 2.0 nm / min. If the etching rate is 2.0 nm / min or more, the etching rate with CF4 gas is fast and an opening pattern can be formed.

[0080] [Table 1]

[0081] As shown in Table 1, unlike Examples 7 to 11, Examples 1 to 6 and 12 had (TaW / M) of 50 at% or more and Ta to W atomic ratios (Ta:W) of 30:70 to 90:10, so the refractive index was 0.954 or less, the SPM resistance was "A" or "B", and the etching rate with CF4 gas was "A". Among Examples 1 to 6 and 12, Examples 1 to 2 and Examples 4 to 5 had ratio values ​​(Ta / W) of 40 / 60 or more, so the SPM resistance was "A". Furthermore, among Examples 1 to 6 and 12, Examples 2 to 3 and Examples 5 to 6 had ratio values ​​(Ta / W) of 50 / 50 or less, so the refractive index was 0.945 or less.

[0082] 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. [Explanation of symbols]

[0083] 1. Reflective mask blank 2 Reflective mask 10 Substrate 11 Multilayer reflective film 12 Protective film 13 Absorbent membrane

Claims

1. A reflective mask blank comprising a substrate, a multilayer reflective film, a protective film, and an absorbing film in this order, wherein the multilayer reflective film reflects EUV light, the protective film protects the multilayer reflective film from a first etching gas during processing of the absorbing film, and the absorbing film absorbs EUV light, the absorbing film comprises a Ta compound containing Ta and W; The Ta compound has a total ratio of Ta and W to all metal elements excluding non-metal elements of 50 at % or more, and an atomic ratio of Ta to W (Ta:W) of 30:70 to 90:

10.

2. 2. The reflective mask blank according to claim 1, wherein the Ta compound contains substantially only Ta and W as metal elements.

3. The reflective mask blank according to claim 1 , wherein the Ta compound contains at least one nonmetallic element selected from N, B, and C.

4. 4. The reflective mask blank according to claim 3, wherein the Ta compound contains N in an amount of 5 at % or more.

5. 2. The reflective mask blank according to claim 1, wherein the Ta compound has a refractive index of 0.954 or less for EUV light.

6. 2. The reflective mask blank according to claim 1, wherein the protective film contains 50 at % to 100 at % of Rh.

7. 2. The reflective mask blank according to claim 1, further comprising a hard mask film on the opposite side of said absorbing film to said protective film.

8. 8. The reflective mask blank according to claim 7, wherein the hard mask film contains at least one element selected from Ru, Al, Cr, Si, Ta, Ti, Hf, and Y.

9. A reflective mask blank according to any one of claims 1 to 6 is provided, A reflective mask including an aperture pattern in the absorbing film.

10. A method for manufacturing a reflective mask blank, comprising: a substrate; a multilayer reflective film; a protective film; and an absorbing film, in this order; the multilayer reflective film reflects EUV light; the protective film protects the multilayer reflective film from a first etching gas during processing of the absorbing film; and the absorbing film absorbs EUV light, forming the multilayer reflective film, the protective film, and the absorbing film in this order on the substrate; the absorbing film comprises a Ta compound containing Ta and W; the Ta compound has a total ratio of Ta and W to all metal elements excluding non-metal elements of 50 at % or more, and an atomic ratio of Ta to W (Ta:W) of 30:70 to 90:

10.

11. Preparing a reflective mask blank according to claim 7 or 8; and transferring an opening pattern of the hard mask film to the absorbing film using the first etching gas.

12. The method for manufacturing a reflective mask according to claim 11, wherein the first etching gas contains a fluorine-based gas.

13. The method for manufacturing a reflective mask according to claim 11, wherein the first etching gas contains a chlorine-based gas.

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