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

Abstract

To provide a reflective mask blank for EUVL, a reflective mask for EUVL, and a method of manufacturing the reflective mask for EUVL, which can suppress variations in the reflectance and the phase shift amount caused by variations in the thickness of an entire absorber film.SOLUTION: A reflective mask blank for EUVL, includes, on a substrate, a multilayer reflective film reflecting EUV light, an absorber film absorbing EUV light, and an antireflective film, in this order. The multilayer reflective film includes an aluminum alloy containing aluminum (Al), and at least one metallic element selected from the group consisting of tantalum (Ta), chromium (Cr), titanium (Ti), niobium (Nb), molybdenum (Mo), tungsten (W), and ruthenium (Ru), where the aluminum alloy may further contain at least one element (X) selected from the group consisting of oxygen (O), nitrogen (N), and boron (B). The aluminum (Al) content in the components of the aluminum alloy excluding the element (X) is 3-95 at%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a reflective mask for EUVL (Etreme Ultra Violet Lithography) used in the semiconductor manufacturing process, an original plate for the reflective mask, an EUVL reflective mask blank, and a method for manufacturing an EUVL reflective mask. [Background technology]

[0002] Conventionally, ultraviolet light with a wavelength of 365 to 193 nm has been used as the light source for exposure equipment used in semiconductor manufacturing. The shorter the wavelength, the higher the resolution of the exposure equipment. Therefore, in recent years, exposure equipment using EUV light with a central wavelength of around 13.5 nm as the light source has been put into practical use.

[0003] EUV light is easily absorbed by many materials, so refractive optics cannot be used in exposure tools. For this reason, reflective optics and reflective masks are used for EUV exposure.

[0004] In a reflective mask, a multilayer reflective film that reflects EUV light is formed on a substrate, and an absorber film that absorbs EUV light is formed in a pattern on the multilayer reflective film.

[0005] The substrate is often made of low-thermal expansion glass, which is synthetic quartz with a small amount of titanium added, in order to suppress pattern distortion caused by thermal expansion during exposure. The multilayer reflective film is usually made of about 40 alternating layers of molybdenum and silicon.

[0006] Tantalum-based materials have traditionally been used for absorber films. Because tantalum-based materials have a relatively large absorption coefficient, they function as binary masks with high light-blocking properties. In recent years, ruthenium-based materials, which have a relatively small absorption coefficient, have also been considered for use as absorber films, in order to improve resolution through the phase shift effect.

[0007] The absorber film is formed in a pattern on the multilayer reflective film, so that EUV light incident on the reflective mask from the reflective optical system of the exposure tool is reflected in areas where there is no absorber film (openings) and absorbed in areas where there is an absorber film (non-openings). As a result, the openings in the absorber film are transferred as a mask pattern onto the surface of the exposure material (a wafer coated with resist).

[0008] In EUV lithography, EUV light typically enters a reflective mask from a direction tilted at about 6° and is reflected in a direction tilted at about 6°.

[0009] The absorber film is formed by sputtering. It is usually deposited to a thickness of about 50 to 70 nm. At this time, the thickness of the absorber film may deviate slightly from the target thickness or may vary within the mask surface. Deviations in the absorber film thickness result in deviations in the reflectance and phase shift amount of the absorber film, which in turn leads to variations in the resist line width after wafer exposure.

[0010] Patent Document 1 claims that fluctuations in the reflectance of an absorber film (absorber film) can be suppressed by using a two-layer or more absorber film with the top layer being Si or a material containing 90 at% or more Si. Figure 4 of Patent Document 1 shows that even if the thickness of the top layer changes, the OD value of the entire absorber film only fluctuates. The OD value represents the effective reflectance of the absorber film (absorber film) when the reflectance of the multilayer film is set to 100%. Since the reflectance of an actual multilayer film is approximately 65% and does not fluctuate significantly, the OD value can be said to be an index representing the reflectance of the absorber film (absorber film). In other words, Patent Document 1 shows that even if the thickness of the top layer changes, the reflectance of the entire absorber film (absorber film) only fluctuates. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-268255 Summary of the Invention [Problem to be solved by the invention]

[0012] The refractive index n of Si for EUV light with a wavelength of 13.5 nm is 0.999, and the absorption coefficient k is 0.002, which are almost equal to the values in a vacuum. Similarly, if the material contains 90 at% or more Si, the refractive index is close to 1 and the absorption coefficient is almost 0. Therefore, Patent Document 1 merely shows that when the film thickness of the top layer changes, the change in reflectance of the top layer is small, and it is unclear whether the change in reflectance of the absorber film due to a change in the film thickness of the entire absorber film can be suppressed.

[0013] The present invention has been made in consideration of the above problems, and aims to provide an EUVL reflective mask blank, an EUVL reflective mask, and a method for manufacturing an EUVL reflective mask, which are capable of suppressing fluctuations in reflectivity and phase shift amount due to changes in the film thickness of the entire absorber film. [Means for solving the problem]

[0014] As a result of extensive research to achieve the above object, the inventors have found that variations in reflectance and phase shift amount due to variations in the film thickness of the absorber film can be suppressed by providing a predetermined anti-reflection film on the absorber film.

[0015] The reason why the reflectance and the phase shift amount vary due to the variation in the film thickness of the absorber film will be explained using Fig. 2. The reflective mask blank 100 for EUVL shown in Fig. 2 has a multilayer reflective film 120 that reflects EUV light and an absorber film 140 that absorbs EUV light formed in this order on a substrate 110. In Figure 2, incident light incident on the EUVL reflective mask blank 100 from a direction tilted by approximately 6° generates reflected light A and reflected light B. Reflected light A represents light that passes through the absorber film 140 and is reflected by the multilayer reflective film 120. If the film thickness of the absorber film 140 fluctuates, the optical path length changes, and therefore the phase of reflected light A fluctuates. Reflected light B represents light reflected on the surface of the absorber film 140. The phase of reflected light B does not change even if the thickness of the absorber film 140 changes. Therefore, when the film thickness of the absorber film 140 fluctuates, the phase difference between reflected light A and reflected light B also fluctuates. Because the amplitude of the reflected light from the absorber film 140 is the sum of the amplitudes of reflected light A and reflected light B, interference occurs, and the reflectance and the amount of phase shift also fluctuate due to the phase difference between reflected light A and reflected light B.

[0016] The above is explained using a formula. The amplitude of reflected light A is r A , the amplitude of reflected light B is r B Then, the amplitude r of the reflected light from the absorber film 140 can be written as follows:

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[0017] The EUVL reflective mask blank 200 shown in FIG. 3 has a multilayer reflective film 220 that reflects EUV light, an absorber film 240 that absorbs EUV light, and an anti-reflection film 250 formed in this order on a substrate 210. In Figure 3, light incident on the EUVL reflective mask blank 200 from a direction tilted by approximately 6° generates reflected light A, reflected light B, and reflected light C. Reflected light A represents light that passes through the antireflection film 250 and absorber film 240 and is reflected by the multilayer reflective film 220. Reflected light B represents light that passes through the antireflection film 250 and is reflected by the surface of the absorber film 240. Reflected light C represents light that is reflected by the surface of the antireflection film 250. In order to obtain an antireflection effect, it is necessary to make reflected light B from the surface of the absorber film 240 and reflected light C from the surface of the antireflection film 250 cancel each other out.

[0018] When the refractive index of the absorber film 240 at the wavelength of EUV light is n, the absorption coefficient is k, and the refractive index of the anti-reflection film 250 is n' and the absorption coefficient is k', the amplitude r of the reflected light B is calculated from Fresnel's law of reflection as follows: B is expressed as follows (2).

[0019]

number

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[0020] There is an optical path difference between reflected light B and reflected light C. If the film thickness of anti-reflection film 250 is d, then the optical path difference is 2n'd. In order for reflected light B and reflected light C to completely cancel each other out, the following equations (4) and (5) must be satisfied.

number

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[0021] Equation (4) is important from the viewpoint of the material of the antireflection coating 250. To obtain an antireflection effect, it is necessary to select an antireflection coating 250 with a refractive index n' and absorption coefficient k' that satisfies or approximately satisfies Equation (4) for an absorber film with a refractive index n and absorption coefficient k. To obtain a sufficient antireflection effect, it is preferable to satisfy Equation (6).

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[0022] Equation (4) is important from the viewpoint of the material of the antireflection coating 250. To obtain an antireflection effect, it is necessary to select an antireflection coating 250 with a refractive index n' and absorption coefficient k' that satisfies or approximately satisfies Equation (4) for an absorber film with a refractive index n and absorption coefficient k. To obtain a sufficient antireflection effect, it is more preferable to satisfy Equation (7).

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[0023] Based on the above findings, the present inventors have found that the above problems can be solved by the following configuration. [1] A reflective mask blank for EUVL having, on a substrate, a multilayer reflective film that reflects EUV light, an absorber film that absorbs EUV light, and an anti-reflection film in this order, The anti-reflective film is made of an aluminum alloy containing aluminum (Al) and at least one metal element selected from the group consisting of tantalum (Ta), chromium (Cr), titanium (Ti), niobium (Nb), molybdenum (Mo), tungsten (W) and ruthenium (Ru), and may further contain at least one element (X) selected from the group consisting of oxygen (O), nitrogen (N) and boron (B), and the Al content in the components of the aluminum alloy excluding the element (X) is 3 to 95 at%. [2] A reflective mask blank for EUVL having, on a substrate, a multilayer reflective film that reflects EUV light, an absorber film that absorbs EUV light, and an anti-reflection film in this order, The refractive index of the absorber film at a wavelength of 13.5 nm is n and the absorption coefficient is k. When the refractive index of the anti-reflection coating at a wavelength of 13.5 nm is n' and the absorption coefficient is k', A reflective mask blank for EUVL that satisfies formula 6 described below. [3] The reflective mask blank for EUVL according to [2], wherein the antireflective film contains at least one metal element selected from the group consisting of aluminum (Al), tantalum (Ta), chromium (Cr), titanium (Ti), niobium (Nb), molybdenum (Mo), tungsten (W) and ruthenium (Ru), and may further contain at least one element (Y) selected from the group consisting of oxygen (O), nitrogen (N), boron (B), hafnium (Hf), and hydrogen (H). [4] The reflective mask blank for EUVL according to [3], wherein the antireflection film is made of an aluminum alloy containing Al and at least one metal element selected from the group consisting of Ta, Cr, Ti, Nb, Mo, W and Ru, and may further contain an element (Y), and the Al content in the components excluding the element (Y) of the aluminum alloy is 3 to 95 at %. [5] The reflective mask blank for EUVL according to any one of [1] to [4], wherein the thickness of the anti-reflection film is 2 to 5 nm or 8 to 12 nm. [6] The reflective mask blank for EUVL according to any one of [1] to [5], wherein the absorber film contains one or more metals selected from the group consisting of Ru, Cr, tin (Sn), gold (Au), platinum (Pt), rhenium (Re), Hf, Ta, and Ti, and may further contain at least one element (Y) selected from the group consisting of O, N, B, Hf, and H. [7] The reflective mask blank for EUVL according to any one of [1] to [6], wherein the absorber film contains one or more metals selected from the group consisting of Ta, Ti, Sn, and Cr, and may further contain at least one element (Y) selected from the group consisting of O, N, B, Hf, and H. [8] The reflective mask blank for EUVL according to any one of [1] to [7], wherein the absorber film is made of an alloy of Ta and Nb, or a compound obtained by adding at least one element (Y) selected from the group consisting of O, N, B, Hf, and H to the alloy. [9] The reflective mask blank according to any one of [1] to [8], which has a protective film for the multilayer reflective film between the multilayer reflective film and the absorber film.

[10] A hard mask film is provided on the anti-reflective film. The reflective mask blank for EUVL according to any one of [1] to [9], wherein the hard mask film is made of one element selected from the group consisting of Si and Cr, or a compound in which at least one element selected from the group consisting of O, N, C, and hydrogen (H) is added to Si or Cr.

[11] A reflective mask for EUVL, in which a pattern is formed in the absorber film and the anti-reflection film of the reflective mask blank for EUVL according to any one of [1] to

[10] .

[12] A method for producing a reflective mask for EUVL, comprising the step of patterning an absorber film and an anti-reflection film of a reflective mask blank for EUVL according to any one of [1] to

[11] . [Effects of the Invention]

[0024] According to the present invention, it is possible to provide a reflective mask blank for EUVL and a reflective mask for EUVL in which the reflectance and the amount of phase shift change little in response to a change in the thickness of the absorber film. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic cross-sectional view of one example of the configuration of a reflective mask blank for EUVL according to the present invention. [Figure 2] FIG. 2 is a diagram illustrating reflected light from an absorber film of a reflective mask blank for EUVL. [Figure 3] FIG. 3 is a diagram illustrating reflected light from an absorber film of a reflective mask blank for EUVL provided with an anti-reflection film. [Figure 4] Figure 4 shows the complex refractive indices of Ta, Cr, Ti, Nb, Mo, W, Ru, Si and Al. [Figure 5] FIG. 5 shows the optimum region of the complex refractive index of the antireflection film 15 when the absorber film 14 is a RuO2 film. [Figure 6] FIG. 6 shows the optimum region of the complex refractive index of the antireflection film 15 when the absorber film 14 is a TaNb film. [Figure 7]FIG. 7 shows the optimum region of the complex refractive index of the antireflection film 15 when the absorber film 14 is made of TaN. [Figure 8] FIG. 8 is a schematic cross-sectional view of another example of the configuration of the reflective mask blank for EUVL of the present invention. [Figure 9] 9(a) to 9(d) are diagrams showing the manufacturing procedure of a reflective mask for EUVL. [Figure 10] Figure 10 shows the simulation results for cases where a RuO2 film is used as the absorber film and a 2-nm-thick TaAl film is provided as an anti-reflection film on top of it, and cases where no TaAl film is provided. Figure 10(a) shows the relationship between the thickness of the absorber film and the reflectance. Figure 10(b) shows the relationship between the thickness of the absorber film and the amount of phase shift. [Figure 11] Figure 11 shows the simulation results for cases where a TaNb film is used as the absorber film and a 2-nm-thick TaAl film is provided as an anti-reflection film on top of it, and cases where it is not provided. Figure 11(a) shows the relationship between the thickness of the absorber film and the reflectance. Figure 11(b) shows the relationship between the thickness of the absorber film and the amount of phase shift. [Figure 12] Figure 12 shows the simulation results for a TaN absorber film with a 2-nm-thick TaAl film on top as an anti-reflection film, and a 4-nm-thick TaON film used as an anti-reflection film for the inspection light. Figure 12(a) shows the relationship between the absorber film thickness and reflectance. Figure 12(b) shows the relationship between the absorber film thickness and the amount of phase shift. [Figure 13] Figure 13 shows the simulation results for cases where a RuO2 film is used as the absorber film and a 9-nm-thick TaAl film is provided as an anti-reflection film on top of it, and cases where it is not provided. Figure 13(a) shows the relationship between the thickness of the absorber film and the reflectance. Figure 13(b) shows the relationship between the thickness of the absorber film and the amount of phase shift. [Figure 14]FIG. 14 is a diagram showing simulation results when a TaNb film is used as an absorber film and a TaAl film with a film thickness of 9 nm is provided thereon as an antireflection film and when it is not provided. FIG. 14(a) shows the relationship between the film thickness of the absorber film and the reflectance. FIG. 14(b) shows the relationship between the film thickness of the absorber film and the phase shift amount. [Figure 15] FIG. 15 is a diagram showing simulation results when a TaN film is used as an absorber film and a TaAl film with a film thickness of 2 nm is provided thereon as an antireflection film and when a TaON film with a film thickness of 4 nm used as an antireflection film for inspection light is provided. FIG. 15(a) shows the relationship between the film thickness of the absorber film and the reflectance. FIG. 15(b) shows the relationship between the film thickness of the absorber film and the phase shift amount. [Figure 16] FIG. 16 shows the optimal region and the quasi-optimal region of the complex refractive index of the antireflection film 15 when the absorber film 14 is RuN. [Figure 17] FIG. 17 is a diagram showing simulation results when a RuN film is used as an absorber film and a Cr2O3 film with a film thickness of 2 nm is provided thereon as an antireflection film and when it is not provided. FIG. 17(a) shows the relationship between the film thickness of the absorber film and the reflectance. FIG. 17(b) shows the relationship between the film thickness of the absorber film and the phase shift amount.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] Hereinafter, the reflective mask blank of the present invention and the reflective mask of the present invention will be described with reference to the drawings. <Reflective mask blank for EUVL> FIG. 1 is a schematic cross-sectional view showing a configuration example of a reflective mask blank for EUVL of the present invention. The reflective mask blank 10 for EUVL shown in FIG. 1 includes a multilayer reflective film 12 that reflects EUV light, a protective film 13 of the multilayer reflective film 12, an absorber film 14 that absorbs EUV light, and an antireflection film 15, which are formed in this order on a substrate 11. However, in the reflective mask blank for EUVL of the present invention, in the configuration shown in FIG. 1, only the substrate 11, the multilayer reflective film 12, the absorber film 14, and the antireflection film 15 are essential, and the protective film 13 is an optional component. The protective film 13 of the multilayer reflective film 12 is provided for the purpose of protecting the multilayer reflective film 12 from etching when a mask pattern is formed on the absorber film 14 .

[0027] Hereinafter, the individual components of the EUVL reflective mask blank 10 will be described.

[0028] (substrate) The substrate 11 preferably has a small thermal expansion coefficient. A substrate with a small thermal expansion coefficient can suppress distortion of the pattern formed in the absorber film due to heat during exposure to EUV light. Specifically, the thermal expansion coefficient of the substrate is 0±0.05×10 at 20°C. -7 / ℃ is preferred, 0±0.03×10 -7 / °C is more preferred.

[0029] An example of a material with a low thermal expansion coefficient is SiO2-TiO2-based glass. SiO2-TiO2-based glass is preferably quartz glass containing 90-95% by mass of SiO2 and 5-10% by mass of TiO2. When the TiO2 content is 5-10% by mass, the linear expansion coefficient is approximately zero near room temperature, and there is almost no dimensional change near room temperature. SiO2-TiO2-based glass may contain trace components other than SiO2 and TiO2.

[0030] The first main surface of the substrate 11, on which the multilayer reflective film 12 is to be laminated, preferably has high surface smoothness. The surface smoothness of the first main surface can be evaluated by surface roughness. The surface roughness of the first main surface is preferably 0.15 nm or less in terms of root-mean-square roughness Rq. The surface smoothness can be measured using an atomic force microscope. The first main surface is preferably surface-processed to a predetermined flatness. This is to ensure that the reflective mask achieves high pattern transfer accuracy and positional accuracy. In a predetermined area of the first main surface (e.g., a 132 mm × 132 mm area), the substrate preferably has a flatness of 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less.

[0031] Furthermore, the substrate 11 preferably has resistance to cleaning solutions used for cleaning EUVL reflective mask blanks and EUVL reflective masks after pattern formation. Furthermore, the substrate 11 preferably has high rigidity to prevent deformation due to film stress of films formed on the substrate (such as the multilayer reflective film 12 and the absorber film 14). For example, the substrate 11 preferably has a high Young's modulus of 65 GPa or more.

[0032] (Multilayer reflective film) The multilayer reflective film 12 has high reflectivity for EUV light. Specifically, when EUV light is incident on the surface of the multilayer reflective film at an incident angle of 6°, the maximum reflectivity for EUV light is preferably 60% or more, more preferably 65% or more. Similarly, even when a protective film 13 is laminated on the multilayer reflective film 12, the maximum reflectivity for EUV light is preferably 60% or more, more preferably 65% or more.

[0033] The multilayer reflective film 12 is a multilayer film in which multiple layers each composed mainly of elements with different refractive indices are periodically stacked. Generally, the multilayer reflective film is formed by alternately stacking multiple high-refractive-index films that exhibit a high refractive index to EUV light and multiple low-refractive-index films that exhibit a low refractive index to EUV light from the substrate side. The multilayer reflective film 12 may be formed by laminating multiple periods, each period consisting of a high-refractive index film and a low-refractive index film stacked in this order from the substrate side, or may be formed by laminating multiple periods consisting of a low-refractive index film and a high-refractive index film stacked in this order. In this case, it is preferable that the outermost layer (top layer) of the multilayer reflective film be a high-refractive index film. Because low-refractive index films are easily oxidized, if a low-refractive index film is the top layer of the multilayer reflective film, the reflectance of the multilayer reflective film may decrease.

[0034] The high-refractive index film can be a film containing silicon (Si). Examples of materials containing Si include elemental Si and Si compounds containing one or more elements selected from the group consisting of boron (B), carbon (C), nitrogen (N), and oxygen (O). The use of a high-refractive index film containing Si enables the production of a reflective mask with excellent reflectivity for EUV light. The low-refractive index film can be a metal selected from the group consisting of molybdenum (Mo), ruthenium (Ru), rhodium (Rh), and platinum (Pt), or an alloy thereof. In the reflective mask blank of the present invention, it is preferable that the low-refractive index film is a Mo film and the high-refractive index film is a Si film. In this case, by using a high-refractive index film (Si film) as the top layer of the multilayer reflective film, a silicon oxide film containing Si and O is formed between the top layer (Si film) and the protective film 13, thereby improving the cleaning resistance of the reflective mask blank.

[0035] The thickness and period of each layer constituting the multilayer reflective film 12 can be appropriately selected depending on the film material used, the EUV light reflectivity required for the multilayer reflective film 12, the wavelength of the EUV light (exposure wavelength), etc. For example, if the multilayer reflective film 12 has a maximum EUV light reflectivity of 60% or more, a Mo / Si multilayer reflective film in which low refractive index films (Mo films) and high refractive index films (Si films) are alternately stacked in 30 to 60 periods is preferably used.

[0036] Each layer constituting the multilayer reflective film 12 can be deposited to a desired thickness using a known deposition method such as magnetron sputtering or ion beam sputtering. For example, when fabricating a multilayer reflective film using ion beam sputtering, ion particles are supplied from an ion source to a target of a high refractive index material and a target of a low refractive index material. When the multilayer reflective film 12 is a Mo / Si multilayer reflective film, for example, a Si film with a predetermined thickness is first deposited on a substrate using ion beam sputtering, for example, using a Si target. Then, a Mo film with a predetermined thickness is deposited using a Mo target. This Si film and Mo film constitute one cycle, and 30 to 60 cycles are stacked to form a Mo / Si multilayer reflective film.

[0037] (protective film) The protective film 13 protects the multilayer reflective film by suppressing damage to the surface of the multilayer reflective film 12 caused by etching (usually dry etching) when the absorber film 14 is etched to form a pattern during the manufacture of a reflective mask, which will be described later. Furthermore, when the resist film remaining on the reflective mask after etching is removed with a cleaning solution to clean the reflective mask, the protective film 13 protects the multilayer reflective film from the cleaning solution. Therefore, the resulting reflective mask has good reflectivity for EUV light. Although FIG. 1 shows a case where the protective film 13 is a single layer, the protective film may be a multi-layer film.

[0038] The material for the protective film 13 is selected from those that are resistant to etching damage during etching of the absorber film 14. Examples of materials that satisfy this condition include Ru metal alone, Ru alloys containing Ru and one or more metals selected from the group consisting of Si, titanium (Ti), niobium (Nb), Rh, tantalum (Ta), and zirconium (Zr), and Ru-based materials such as nitrides of Ru alloys containing nitrogen; Cr, aluminum (Al), and Ta metal alone, as well as nitrides of these metals containing nitrogen; SiO2, Si3N4, Al2O3, and mixtures thereof. Among these, Ru metal alone, Ru alloys, CrN, and SiO2 are preferred. Ru metal alone and Ru alloys are particularly preferred because they are resistant to etching by oxygen-free gases and function as an etching stopper during etching of the absorber film 14.

[0039] When the protective film 13 is made of a Ru alloy, the Ru content in the Ru alloy is preferably 30 at % or more and less than 100 at %. If the Ru content is within the above range, when the multilayer reflective film 12 is a Mo / Si multilayer reflective film, it is possible to suppress diffusion of Si from the Si film of the multilayer reflective film 12 into the protective film 13. Furthermore, the protective film 13 functions as an etching stopper when etching the absorber film 14 while ensuring sufficient reflectivity for EUV light. Furthermore, it is possible to improve the cleaning resistance of the reflective mask and prevent deterioration of the multilayer reflective film 12 over time.

[0040] The thickness of the protective film 13 is not particularly limited as long as it can function as the protective film 13. In order to maintain the reflectance of EUV light reflected by the multilayer reflective film 12, the thickness of the protective film 13 is preferably 1 to 8 nm, more preferably 1.5 to 6 nm, and even more preferably 2 to 5 nm.

[0041] (Absorber film) When using an EUVL reflective mask as a binary mask, the absorber film 14 must absorb EUV light and have low reflectance. Specifically, when EUV light is irradiated onto the surface of the absorber film 14, the maximum reflectance of EUV light at a wavelength of approximately 13.5 nm is preferably 2% or less. The absorber film 14 for a binary mask that satisfies the above requirements preferably contains one or more metals selected from the group consisting of Ta, Ti, tin (Sn), and Cr. Among these metals, Ta is more preferred. The absorber film 14 for a binary mask may contain, in addition to the above metals, one or more components selected from the group consisting of O, N, B, hafnium (Hf), and hydrogen (H). Among these, O, N, or B is preferred, and N or B is more preferred. The inclusion of N or B can make the crystalline state of the absorber film 14 amorphous or microcrystalline. This improves the surface smoothness and flatness of the absorber film 14. By improving the surface smoothness and flatness of the absorber film 14, the edge roughness of the absorber film pattern of the EUVL reflective mask is reduced, and the dimensional accuracy is improved.

[0042] Furthermore, when a reflective mask for EUVL is used as a phase shift mask, the absorber film 14 needs to have a reflectance of 2% or more for EUV light. To obtain a sufficient phase shift effect, a reflectance of 9 to 15% is preferable. Using a phase shift mask improves the contrast of the optical image on the wafer and increases the exposure margin.

[0043] Examples of materials for forming the absorber film 14 for a phase shift mask that satisfy the above requirements include Ru, Ru alloys containing Ru and one or more metals selected from the group consisting of Cr, gold (Au), Pt, rhenium (Re), Hf, Ta, and Ti, and Ta and Nb alloys. The Ru, Ru alloys, or Ta and Nb alloys may be oxides containing oxygen, nitrides containing nitrogen, oxynitrides containing oxygen and nitrogen, or borides containing boron. Among these, Ru, TaNb alloys, or oxides, nitrides, oxynitrides, and borides thereof are preferred, and RuO2 and TaNb alloys are more preferred.

[0044] The absorber film 14 may contain, for example, one or more metals selected from the group consisting of Ru, Cr, gold (Au), tin (Sn), Pt, rhenium (Re), Hf, Ta, and Ti, and preferably contains one or more metals selected from the group consisting of Ta, Ti, Sn, and Cr. The absorber film 14 may also contain one or more components selected from the group consisting of O, N, B, hafnium (Hf), and hydrogen (H).

[0045] The absorber film 14 is patterned by dry etching using a Cl-based gas containing Cl or an F-based gas containing F, regardless of whether the EUVL reflective mask is a binary mask or a phase shift mask. Therefore, the absorber film needs to be easily etched by these dry etching methods. Both the absorber film for the binary mask and the absorber film for the phase shift mask described above can be easily etched by these dry etching methods.

[0046] Furthermore, during the manufacture of a reflective mask for EUVL (described later), the absorber film 14 is exposed to a cleaning solution when the resist pattern remaining on the reflective mask blank after etching is removed with the cleaning solution. Examples of cleaning solutions used in this process include sulfuric acid hydrogen peroxide (SPM), sulfuric acid, ammonia, ammonia hydrogen peroxide (APM), OH radical cleaning water, and ozone water. In EUVL, SPM is generally used as a resist cleaning solution. SPM is a solution made by mixing sulfuric acid and hydrogen peroxide, e.g., a solution made by mixing sulfuric acid and hydrogen peroxide in a volume ratio of 3:1. In this case, the temperature of the SPM is preferably controlled to 100°C or higher to improve the etching rate. Therefore, the absorber film 14 needs to have high cleaning resistance to the cleaning solution. Both the absorber film for the binary mask and the absorber film for the phase shift mask described above have high cleaning resistance to the cleaning solution.

[0047] The absorber film 14 may be a single-layer film or a multilayer film made up of multiple films. When the absorber film 14 is a single-layer film, the number of steps in manufacturing the mask blank can be reduced, improving production efficiency. When the absorber film 14 is a multilayer film, by appropriately setting the optical constants and film thicknesses of the upper layers of the absorber film, it can be used as an anti-reflection film for the inspection light when inspecting the absorber pattern using inspection light (wavelength 248 to 193 nm). This improves the inspection sensitivity when inspecting the absorber pattern.

[0048] The absorber film 14 can be formed using a known film formation method such as magnetron sputtering or ion beam sputtering. For example, when a Ru oxide film (RuO2 film) is formed as the absorber film 14 using magnetron sputtering, the absorber film 14 can be formed by sputtering using a Ru target and Ar gas and oxygen gas. When a TaNb film is formed as the absorber film 14 using magnetron sputtering, the absorber film 14 can be formed by sputtering using a Ta target and an Nb target, or a target containing Ta and Nb, and Ar gas. When a TaN film is formed as the absorber film 14 using magnetron sputtering, the absorber film 14 can be formed by sputtering using a Ta target and Ar gas and nitrogen gas.

[0049] In both the case of an absorber film for a binary mask and an absorber film for a phase shift mask, the thickness of the absorber film 14 is preferably 20 to 80 nm, more preferably 30 to 70 nm, and further preferably 40 to 60 nm.

[0050] (Anti-reflective film) The anti-reflection film 15 is provided to prevent reflection of EUV light on the surface of the absorber film 14. The optimum film thickness d is determined by equation (5).

number

[0051] It is preferable that the material of the anti-reflection film 15 satisfies formula (6).

number

[0052] It is more preferable that the material of the anti-reflection film 15 satisfies formula (7).

number

[0053] The antireflection film 15 is also required to have the same cleaning resistance as the absorber film 14. Metals with good cleaning resistance include Ta, Cr, Ti, Nb, Mo, W, and Ru. Figure 4 shows the complex refractive indexes of Ta, Cr, Ti, Nb, Mo, W, and Ru. As shown in Figure 4, these metals alone do not fall within the optimum range of complex refractive index for the antireflection film 15.

[0054] As shown in Figure 4, the complex refractive index of Al is (n, k) = (1.00, 0.030). Furthermore, Al has good cleaning resistance. Therefore, it can be used as an anti-reflection coating by alloying it with at least one metal element selected from the group consisting of Ta, Cr, Ti, Nb, Mo, W, and Ru.

[0055] 5 shows the optimum region of the complex refractive index of the antireflection coating 15 when the absorber film 14 is a RuO2 film. When an aluminum alloy containing Ta and Al is selected as the antireflection coating 15, the complex refractive index falls within the optimum region if the Al content is 3 to 52 at%. Also, when an aluminum alloy containing Cr and Al is selected as the antireflection coating, the complex refractive index falls within the optimum region if the Al content is 32 to 70 at%.

[0056] 6 shows the optimum region of the complex refractive index of the antireflection coating 15 when the absorber film 14 is a TaNb film. When an aluminum alloy containing Ta and Al is selected as the antireflection coating 15, the complex refractive index falls within the optimum region if the Al content is 36 to 92 at%. When an aluminum alloy containing Cr and Al is selected as the antireflection coating 15, the complex refractive index falls within the optimum region if the Al content is 56 to 95 at%.

[0057] 7 shows the optimum region of the complex refractive index of the antireflection coating 15 when the absorber film 14 is TaN. When an aluminum alloy containing Ta and Al is selected as the antireflection coating 15, the complex refractive index falls within the optimum region if the Al content is 36 to 91 at%. When an aluminum alloy containing Cr and Al is selected as the antireflection coating 15, the complex refractive index falls within the optimum region if the Al content is 56 to 93 at%.

[0058] For these reasons, an aluminum alloy containing Al and at least one metal element selected from the group consisting of Ta, Cr, Ti, Nb, Mo, W, and Ru can be used as one embodiment of the antireflection film 15. The Al content in the aluminum alloy is preferably 3 to 95 at%, more preferably 20 to 80 at%, and even more preferably 30 to 60 at%.

[0059] The aluminum alloy used for the antireflection coating 15 may further contain at least one element (X) selected from the group consisting of O, N, and B. By containing the element (X), the crystalline state of the antireflection coating 15 can be made amorphous. This can also improve the cleaning stability of the antireflection coating 15. The complex refractive index of an aluminum alloy containing the element (X) is slightly different from that of an aluminum alloy that does not contain the element (X), but the difference is not large, so if an aluminum alloy with a similar composition ratio excluding the element (X) is used, the complex refractive index will fall within the optimum range for the antireflection coating 15. When an aluminum alloy containing the element (X) is used, the Al content in the components of the aluminum alloy excluding the element (X) is preferably 3 to 95 at%, more preferably 20 to 80 at%, and even more preferably 30 to 60 at%. When an aluminum alloy containing the element (X) is used, the total content of the element (X) is preferably 97 at % or less, more preferably 90 at % or less, and even more preferably 80 at % or less. The lower limit of the total content of the element (X) is not particularly limited, but is preferably 5 at % or more.

[0060] JP 2011-35104 A describes an example in which a low-reflection layer for mask pattern inspection light (wavelength 190 nm to 260 nm) is formed on an absorber layer, and the low-reflection layer contains at least one of Al and Zr, and at least one of O and N. This low-reflection layer is a low-reflection layer for mask pattern inspection light (wavelength 190 nm to 260 nm), and does not function as an anti-reflection film for EUV light.

[0061] As another embodiment of the antireflective film 15, the EUVL reflective mask blank may be made of a material that satisfies the above-mentioned formula (6). For example, the antireflective film 15 may contain at least one metal element selected from the group consisting of Al, Ta, Cr, Ti, Nb, Mo, W, and Ru, and may further contain at least one element (Y) selected from the group consisting of O, N, B, Hf, and H. In another embodiment of the antireflection film 15, the antireflection film may be made of an aluminum alloy containing Al and at least one metal element selected from the group consisting of Ta, Cr, Ti, Nb, Mo, W, and Ru, and may further contain the element (Y). The Al content in the components of the aluminum alloy excluding the element (Y) is preferably 3 to 95 at %, more preferably 20 to 80 at %, and even more preferably 30 to 60 at %. When an aluminum alloy containing the element (Y) is used, the total content of the element (Y) is preferably 97 at % or less, more preferably 90 at % or less, and even more preferably 80 at % or less. The lower limit of the total content of the element (Y) is not particularly limited, but is preferably 5 at % or more.

[0062] The antireflective coating 15 can be formed by a known film formation method such as magnetron sputtering, ion beam sputtering, etc. For example, when an aluminum alloy film containing Ta and Al is formed as the antireflective coating 15 by magnetron sputtering, the antireflective coating 15 can be formed by sputtering using a Ta target and an Al target, or a target containing Ta and Al, and Ar gas.

[0063] 16 shows the optimum and suboptimum regions of the complex refractive index of the antireflection coating 15 when the absorber film 14 is a RuN film. When Cr2O3 is selected as the antireflection coating 15, the complex refractive index of the antireflection coating does not fall within the optimum region (the region that satisfies formula (7)), but falls within the suboptimum region (the region that satisfies formula (6)).

[0064] For the reason explained above using formula (5), the thickness of the antireflection film 15 is preferably 2 to 5 nm or 8 to 12 nm.

[0065] (hard mask) Fig. 8 is a schematic cross-sectional view of another example of the configuration of the EUVL reflective mask blank of the present invention. The EUVL reflective mask blank 20 shown in Fig. 8 has a multilayer reflective film 22, a protective film 23, an absorber film 24, an anti-reflection film 25, and a hard mask film 26 formed in this order on a substrate 21. Of the components of the EUVL reflective mask blank 20, the substrate 21, multilayer reflective film 22, protective film 23, absorber film 24, and anti-reflection film 25 are the same as those of the EUVL reflective mask blank 10 described above, and therefore will not be described here.

[0066] The hard mask film 26 is made of a material highly resistant to the etching process of the absorber film 24 and the anti-reflection film 25, such as a Cr-based film containing Cr or a Si-based film containing Si. Examples of Cr-based films include Cr and materials containing Cr with added O or N. Specific examples include CrO and CrN. Examples of Si-based films include Si and materials containing Si with added one or more elements selected from the group consisting of O, N, C, and H. Specific examples include SiO2, SiON, SiN, SiO, Si, SiC, SiCO, SiCN, and SiCON. Forming the hard mask film 26 on the anti-reflection film 25 allows dry etching to be performed even if the minimum line widths of the absorber film pattern and the anti-reflection film pattern are small. This is therefore effective for miniaturizing the absorber film pattern.

[0067] The thickness of the hard mask film 26 is preferably 3 to 20 nm, more preferably 4 to 15 nm, and even more preferably 5 to 10 nm.

[0068] The hard mask film 26 can be formed by a known film forming method, for example, a sputtering method such as a magnetron sputtering method or an ion beam sputtering method.

[0069] The EUVL reflective mask blank 10 of the present invention may have a functional film known in the field of EUVL mask blanks, in addition to the multilayer reflective film 12, the protective film 13, the absorber film 14, and the anti-reflective film 15. The EUVL reflective mask blank 20 of the present invention may have a functional film known in the field of EUVL mask blanks, in addition to the multilayer reflective film 22, the protective film 23, the absorber film 24, the anti-reflective film 25, and the hard mask film 26.

[0070] (Backside conductive film) The EUVL reflective mask blank 10 of the present invention may be provided with a back surface conductive film for electrostatic chuck on the second main surface of the substrate 11, opposite to the side on which the multilayer reflective film 12 is laminated. The back surface conductive film is required to have a low sheet resistance as a characteristic. The sheet resistance of the back surface conductive film is preferably, for example, 200 Ω / □ or less.

[0071] The material containing the backside conductive film can be, for example, a metal such as Cr or Ta, or an alloy thereof. The Cr-containing alloy can be a Cr-based material containing Cr and one or more elements selected from the group consisting of B, N, O, and C. Examples of the Cr-based material include CrN, CrON, CrCN, CrCON, CrBN, CrBON, CrBCN, and CrBOCN. The Ta-containing alloy can be a Ta-based material containing Ta and one or more elements selected from the group consisting of B, N, O, and C. Examples of the Ta-based material include TaB, TaN, TaO, TaON, TaCON, TaBN, TaBO, TaBON, TaBCON, TaHf, TaHfO, TaHfN, TaHfON, TaHfCON, TaSi, TaSiO, TaSiN, TaSiON, and TaSiCON.

[0072] The thickness of the back surface conductive film is not particularly limited as long as it satisfies the function of the electrostatic chuck, but is, for example, 10 to 400 nm. This back surface conductive film can also adjust the stress on the second main surface side of the reflective mask blank. That is, the back surface conductive film can be adjusted to balance the stress from various layers formed on the first main surface side and flatten the reflective mask blank.

[0073] <Reflective mask and manufacturing method of reflective mask> An example of an EUVL reflective mask and a method for manufacturing an EUVL reflective mask will be described with reference to Fig. 9. Fig. 9(a) to Fig. 9(d) are diagrams showing the procedure for manufacturing an EUVL reflective mask. First, as shown in FIG. 9(a), a resist film is applied to an EUVL reflective mask blank 10, exposed to light, and developed to form a resist pattern 60 corresponding to the fine pattern within the chip. Then, as shown in FIG. 9(b), the antireflection film 15 and the absorber film 14 are dry-etched using the resist pattern as a mask to form an antireflection film 15 pattern and an absorber film 14 pattern. Note that the resist pattern has been removed in FIG. 9(b). Next, as shown in FIG. 9(c), a resist film is again applied to the EUVL reflective mask blank 10, exposed to light, and developed to form a resist pattern 60 corresponding to the exposure frame. Then, as shown in FIG. 9(d), the exposure frame V is dug down by dry etching using the resist pattern as a mask until it reaches the substrate. In this manner, the EUVL reflective mask 40 shown in FIG. 9(d) can be manufactured. In the EUVL reflective mask 40 shown in FIG. 9(d), patterns are formed in the absorber film 14 and the antireflection film 15 of the EUVL reflective mask blank 10. Therefore, the EUVL reflective mask can be manufactured at the stage of Fig. 9(b). However, to prevent light leakage from adjacent shots, it is preferable to have an EUVL reflective mask 40 and an exposure frame V, as shown in Fig. 9(d). [Example]

[0074] The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

[0075] <Example 1> Figure 10 shows the simulation results for a RuO2 absorber film with and without a 2-nm-thick TaAl anti-reflection film. The complex refractive index (n', k') of the TaAl film is (0.967, 0.033), with an Al content of 28 at%. The simulation used a Mo / Si multilayer reflective film as the multilayer reflective film and a Ru film as the protective film, as described in "Experimental approach to EUV imaging enhancement by mask absorber height optimization" Proc. SPIE 8886 (2013) 8860A. The complex refractive index of the TaAl film satisfies equation (5). As can be seen from Figure 10, the anti-reflection film reduces the dependence of the reflectivity and phase shift on the absorber film thickness.

[0076] <Example 2> Figure 11 shows the simulation results for a TaNb absorber film with and without a 2-nm-thick TaAl anti-reflection film on top. The complex refractive index of the TaAl film is (n', k') = (0.984, 0.031), and the Al content is 61 at%. The complex refractive index of the TaAl film satisfies equation (5). As can be seen from Figure 11, the presence of an anti-reflection film can reduce the dependency of the reflectivity and phase shift on the absorber film thickness.

[0077] <Example 3> Figure 12 shows the simulation results for a TaN absorber with a 2-nm-thick TaAl film on top as an anti-reflection coating, and a 4-nm-thick TaON film on top as an anti-reflection coating for the inspection light. The complex refractive index of the TaN film is (n, k) = (0.948, 0.033), and the complex refractive index of the TaON film is (n', k') = (0.955, 0.025). The complex refractive index of the TaON film does not satisfy equation (5) and therefore does not function as an anti-reflection coating for EUV light. The complex refractive index of the TaAl film is (n, k) = (0.984, 0.031), and the Al content in this case is 61 at%. As can be seen from Figure 12, the addition of an anti-reflection coating can suppress the dependence of the reflectivity and phase shift on the absorber thickness.

[0078] <Example 4> Figure 13 shows the simulation results for cases where a RuO2 film is used as the absorber film and a 9-nm-thick TaAl film is provided as an anti-reflection film on top of it, and where no TaAl film is provided. The complex refractive index of the TaAl film (n', k') is (0.967, 0.033), and the Al content in this case is 28 at%. As can be seen from Figure 13, the provision of an anti-reflection film can reduce the dependency of the reflectivity and phase shift on the absorber film thickness.

[0079] <Example 5> Figure 14 shows the simulation results for a TaNb absorber film with and without a 9-nm-thick TaAl anti-reflection film on top. The complex refractive index of the TaAl film is (n', k') = (0.984, 0.031), and the Al content is 61 at%. The complex refractive index of the TaAl film satisfies equation (5). As can be seen from Figure 14, the presence of an anti-reflection film can reduce the dependency of the reflectivity and phase shift on the absorber film thickness.

[0080] <Example 6> Figure 15 shows the simulation results for a TaN film used as the absorber film, with a 9-nm-thick TaAl film on top as an anti-reflection film, and for a 4-nm-thick TaON film used as an anti-reflection film against the inspection light. The complex refractive index of the TaAl film (n', k') = (0.984, 0.031), and the Al content in this case is 61 at%. As can be seen from Figure 15, the addition of an anti-reflection film can reduce the dependency of the reflectivity and phase shift amount on the absorber film thickness.

[0081] Figure 17 shows the simulation results for a RuN film used as the absorber film, with a 2-nm-thick Cr2O3 film on top as an anti-reflection film. The complex refractive index of the Cr2O3 film is (n', k') = (0.936, 0.033). As can be seen from Figure 17, the addition of an anti-reflection film can reduce the dependency of the reflectivity and phase shift on the absorber film thickness. [Explanation of symbols]

[0082] 10: Reflective mask blank for EUVL 11: Circuit board 12: Multilayer reflective film 13:Protective film 14: absorber membrane 15: Anti-reflection film 20: Reflective mask blank for EUVL 21: Circuit board 22: Multilayer reflective film 23:Protective film 24: Absorber membrane 25: Anti-reflection film 26: Hard mask film 40: EUV mask 60: Resist V: Exposure frame

Claims

1. A reflective mask blank for EUVL having, on a substrate, a multilayer reflective film that reflects EUV light, an absorber film that absorbs EUV light, and an anti-reflection film in this order, The refractive index of the absorber film at a wavelength of 13.5 nm is n and the absorption coefficient is k, When the refractive index of the antireflection film at a wavelength of 13.5 nm is n' and the absorption coefficient is k', A reflective mask blank for EUVL that satisfies formula 6. [Equation 1]

2. 2. The reflective mask blank for EUVL according to claim 1, wherein the antireflective film contains at least one metal element selected from the group consisting of aluminum (Al), tantalum (Ta), chromium (Cr), titanium (Ti), niobium (Nb), molybdenum (Mo), tungsten (W), and ruthenium (Ru), and may further contain at least one element (Y) selected from the group consisting of oxygen (O), nitrogen (N), boron (B), hafnium (Hf), and hydrogen (H).

3. 3. The reflective mask blank for EUVL according to claim 2, wherein the antireflective film is made of an aluminum alloy containing Al and at least one metal element selected from the group consisting of Ta, Cr, Ti, Nb, Mo, W, and Ru, and optionally further containing the element (Y), and the Al content in components excluding the element (Y) from the aluminum alloy is 3 to 95 at %.

4. 4. The reflective mask blank for EUVL according to claim 1, wherein the anti-reflection film has a thickness of 2 to 5 nm or 8 to 12 nm.

5. 5. The reflective mask blank for EUVL according to claim 1, wherein the absorber film contains one or more metals selected from the group consisting of Ru, Cr, tin (Sn), gold (Au), platinum (Pt), rhenium (Re), Hf, Ta, and Ti, and may further contain at least one element (Y) selected from the group consisting of O, N, B, Hf, and H.

6. The reflective mask blank for EUVL according to any one of claims 1 to 5, wherein the absorber film contains one or more metals selected from the group consisting of Ta, Ti, Sn, and Cr, and may further contain at least one element (Y) selected from the group consisting of O, N, B, Hf, and H.

7. 7. The reflective mask blank for EUVL according to claim 1, wherein the absorber film is made of an alloy of Ta and Nb, or a compound obtained by adding at least one element (Y) selected from the group consisting of O, N, B, Hf, and H to the alloy.

8. 8. The reflective mask blank according to claim 1, further comprising a protective film for the multilayer reflective film between the multilayer reflective film and the absorber film.

9. a hard mask film on the anti-reflective film; 9. The reflective mask blank for EUVL according to claim 1, wherein the hard mask film comprises one element selected from the group consisting of Si and Cr, or a compound in which at least one element selected from the group consisting of O, N, C, and hydrogen (H) is added to Si or Cr.

10. A reflective mask for EUVL, comprising the reflective mask blank for EUVL according to any one of claims 1 to 9, wherein a pattern is formed in the absorber film and the antireflection film.

11. A method for producing a reflective mask for EUVL, comprising the step of patterning the absorber film and the antireflection film of the reflective mask blank for EUVL according to any one of claims 1 to 10.

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