Reflective photomask substrate, reflective photomask, and manufacturing method thereof

Abstract

This invention relates to a reflective photomask substrate, which is a binary reflective photomask substrate comprising a substrate, a multilayer reflective film for reflecting EUV light, and a patterned film in sequence. The patterned film has a stacked structure of layers with different refractive indices totaling L layers, and satisfies the following formula (1) (where L, P, i, and d are defined in the specification).

Description

Technical Field

[0001] This invention relates to a reflective photomask substrate and a reflective photomask and a method for manufacturing the same, particularly to a substrate for an EUV (Etreme Ultra Violet) exposure photomask used in the exposure process of semiconductor manufacturing, namely an EUV lithography reflective photomask substrate, and a reflective photomask formed by forming a photomask pattern on a patterned film in the EUV lithography reflective photomask substrate, and a method for manufacturing the same. Prior Technology

[0002] Previously, the light source for exposure equipment used in semiconductor manufacturing used ultraviolet light with wavelengths of 193-365 nm. The shorter the wavelength, the higher the resolution of the exposure equipment. Therefore, as a new generation of exposure equipment, it is hoped that EUV light with a center wavelength of 13.5 nm can be used as the light source.

[0003] Because EUV light is easily absorbed by most substances, it cannot be exposed using refractive optical systems. Therefore, reflective photomasks are used for EUV light.

[0004] This type of reflective photomask involves forming a multilayer reflective film that reflects EUV light on a substrate, and then patterning an absorber film that absorbs EUV light on the multilayer reflective film. Between the multilayer reflective film and the absorber film, a protective film (sometimes called a "capping layer") is typically formed to protect the multilayer reflective film from etching during the formation of the photomask pattern. Furthermore, to facilitate the inspection of pattern defects after photomask processing, a low-reflection layer is sometimes formed on the absorber film.

[0005] As the substrate, a low-thermal-expansion glass with a small amount of titanium added to synthetic quartz can be used to suppress pattern deformation caused by thermal expansion during exposure. As the multilayer reflective film, a film formed by alternating layers of molybdenum (Mo) and silicon films for approximately 40 cycles can be used. The protective film can be a ruthenium-based material with a thickness of 1–5 nm. Ruthenium (Ru)-based materials are very difficult to etch relative to oxygen-free gases, thus functioning as an etching stop layer during photomask processing. The absorber film can be a tantalum-based material.

[0006] EUV light incident on a reflective photomask from the illumination optics of the exposure apparatus is reflected at openings where there is no absorber film and absorbed at non-openings where there is an absorber film. The photomask pattern is transferred onto the wafer via the reduction projection optics of the exposure apparatus. EUV light is incident on the reflective photomask from a direction typically tilted at 6 degrees. If the absorber film is thick, a portion becomes the shadow of the absorber film, making it impossible to faithfully transfer the photomask pattern onto the wafer. Since this problem becomes more pronounced as the linewidth of the photomask pattern decreases, it is necessary to make the absorber film thinner.

[0007] Furthermore, in the case of a binary photomask, in order to perform high-precision pattern transfer during EUV exposure, the reflectivity of the non-aperture area must be suppressed to below 2%. In Patent Document 1, by forming a surface reflection enhancement film optically designed to meet specified conditions on an absorber film, the amplitude of EUV light reflected from the surface of the patterned film, which is locally etched during photomask processing, is increased. By utilizing the interference effect with EUV light reflected by the multilayer reflective film, the absorber film thickness can be reduced, and the reflectivity of non-opening areas is suppressed to below 2%. Furthermore, the patterned film is composed of an absorber film and a surface reflection enhancement film. Furthermore, Patent Document 2 discloses a reflective photomask substrate comprising a laminated film formed by alternately stacking low-refractive-index and high-refractive-index material films for multiple cycles, which serves as an absorber film. Previous technical documents Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2018-180544 Patent Document 2: Japanese Patent Application Publication No. 2015-8283 Summary of the Invention

[0009] [The problem the invention aims to solve]

[0010] However, generally speaking, because the absolute value of the refractive index difference Δn between adjacent layers in the laminated structure of the patterned film in a reflective photomask substrate is relatively small, the amplitude of EUV light reflected from the interface of the laminated structure of the patterned film is particularly small compared to the amplitude of light reflected from the multilayer reflective film. Therefore, there is a limit to the thinner patterned film that can achieve a further reduction in EUV light reflectivity by simply using EUV light reflected from the interface of the laminated structure of the patterned film to counteract the interference effect of light reflected from the multilayer reflective film. Furthermore, in Patent Document 2, there is a problem that damage occurs to the sidewalls of the laminated film when etching or cleaning the laminated film, which serves as the absorber film, for photomask processing.

[0011] The purpose of this invention is to provide a reflective photomask substrate that can reduce the thickness of a patterned film and significantly reduce the reflectivity of the patterned film, as well as a reflective photomask and a method thereof for manufacturing the same. More specifically, this invention provides a reflective photomask substrate capable of achieving a reflectivity of less than 1% with a patterned film thickness of less than 45 nm, as well as a reflective photomask and a method thereof for manufacturing the same. [Technical means to solve the problem]

[0012] In order to solve the above problems, the inventors conducted intensive research and found that, in a reflective photomask substrate having a substrate, a multilayer reflective film that reflects EUV light, and a patterned film having a total of L layers with different refractive indices, the above problems can be solved by making the patterned film satisfy the following formula (1), thereby completing the present invention.

[0013] [Number 1] …Formula (1)

[0014] That is, the present invention is as follows. [1] A reflective photomask substrate, which is a binary reflective photomask substrate comprising a substrate, a multilayer reflective film for reflecting EUV light, and a patterned film in sequence, wherein the patterned film has a stacked structure of layers with different refractive indices in total L layers (where L is a natural number of 2 or more), and when the absorption coefficient of the i-th layer in the patterned film from the side opposite to the substrate is set as ki, the film thickness of the i-th layer in the patterned film from the side opposite to the substrate is set as di (nm), the total film thickness of the patterned film is set as d, the exposure wavelength is set as λ (nm), and Pi is set as 1-exp(-2π / λ*d ik i), the following equation (1) is satisfied.

[0015] [Number 2] …Formula (1)

[0016] [2] As described in [1] above, when the reflection amplitude of the i-th layer in the patterned film from the side opposite to the substrate is set as ri, the following formula (2) is satisfied.

[0017] [Number 3] …Formula (2)

[0018] [3] As described in [1] above, the refractive index n1 of the outermost layer of the first layer of the patterned film from the side opposite to the substrate is 0.950 or less. [4] As described in [1] above, the reflective photomask substrate, wherein at least one of the differences in absorption coefficients k between two adjacent layers in the patterned film, |Δk|, is 0.0200 or more. [5] As described in [1] above, the refractive index of the i-th layer in the patterned film from the side opposite to the substrate is set as ni, and the film thickness d1 of the outermost layer of the first layer in the patterned film from the side opposite to the substrate satisfies the following formula (3). |(λ / 4n 1+λ / 2n 1*x)-d 1|<2.50···Formula (3) In equation (3), x is an integer greater than or equal to 0. [6] The reflective photomask substrate described in [1] above, wherein the reflectivity of the patterned film is less than 1.3%. [7] As described in [1] above, the reflective photomask substrate has a reflectivity of less than 1%. [8] As described in [1] above, the reflective photomask substrate, wherein the total thickness d of the patterned film is less than 45 nm. [9] As described in [1] above, a reflective photomask substrate is provided between the multilayer reflective film and the patterned film.

[10] A reflective photomask having a pattern obtained by patterning the patterned film in the reflective photomask substrate as described in any one of [1] to [9] above.

[11] A method for manufacturing a reflective photomask, wherein the patterned film in the reflective photomask substrate described in any one of [1] to [9] above is patterned. [Effects of the Invention]

[0019] According to the present invention, a reflective photomask substrate that can reduce the thickness of the patterned film and significantly reduce the reflectivity of the patterned film, as well as a reflective photomask and a method thereof, can be provided. The reflective photomask substrate of this invention has a simple film structure, making photomask processing easy. Simple Explanation of the Diagram

[0020] Figure 1 is a schematic cross-sectional view showing one embodiment of the reflective photomask substrate of the present invention. Figure 2 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 1, which has a two-layer structure of a TaN film (substrate side: film thickness d2: 37.0 nm) and a Ru film (opposite side to the substrate: film thickness d1: 3.3 nm). Figure 3 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 2, which has a two-layer structure of a TaN film (substrate side: film thickness d2: 44.0 nm) and a Ru film (opposite side to the substrate: film thickness d1: 3.8 nm). Figure 4 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 3, which has a three-layer structure consisting of a TaN film (substrate side: film thickness d3: 32.6 nm), a SiN film (film thickness d2: 2.6 nm), and a TaN film (opposite to the substrate side: film thickness d1: 4.5 nm). Figure 5 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 4, which has a two-layer structure of a TaN film (substrate side: film thickness d2: 28.4 nm) and a Pt film (opposite side to the substrate: film thickness d1: 12.1 nm). Figure 6 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 5, which has a two-layer structure of a TaN film (substrate side: film thickness d2: 27.3 nm) and a Pt film (opposite to the substrate side: film thickness d1: 13.4 nm). Figure 7 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 6, which has a two-layer structure of a TaN film (substrate side: film thickness d2: 28.2 nm) and a Pt film (opposite side to the substrate: film thickness d1: 12.4 nm). Figure 8 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 7, which has a two-layer structure of a Cr film (substrate side: film thickness d2: 38.0 nm) and a Ru film (opposite side to the substrate: film thickness d1: 2.8 nm). Figure 9 is a graph showing the relationship between exposure wavelength λ and reflectivity R for Example 8, a reflective photomask substrate with a three-layer structure consisting of a Cr film (substrate side: film thickness d3: 33.1 nm), a Si film (film thickness d2: 3.1 nm), and a Cr film (opposite side to the substrate: film thickness d1: 3.9 nm). Figure 10 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 9, which has a two-layer structure of a SnO2 film (substrate side: film thickness d2: 24.1 nm) and a Ru film (opposite side to the substrate: film thickness d1: 2.2 nm). Implementation

[0021] The definitions and meanings of the terms used in this specification are as follows. In this specification, the preferred options can be used arbitrarily, and the combination of the preferred options is even better. Furthermore, in this specification, the phrase "XX~YY" refers to "XX or above, YY or below". Furthermore, in the specification of this case, "exp(t)" refers to "et". Furthermore, in this specification, the lower and upper limits of the preferred numerical ranges (e.g., the range of content, etc.) can be combined independently. For example, the lower limit (10) and the upper limit (60) can be combined from the description of "preferably 10 to 90, more preferably 30 to 60" to set "10 to 60". Also, the upper or lower limit of the numerical range described in this specification can be replaced with the values ​​shown in the embodiments.

[0022] [Reflective photomask substrate] The reflective photomask substrate of this embodiment sequentially comprises a substrate, a multilayer reflective film for reflecting EUV light, and a patterned film, and may further comprise other layers such as a protective film as needed. The patterned film is a layer that is locally etched during photomask processing and includes an absorber film. In addition to the absorber film, the patterned film may also include a buffer layer, a low-reflection layer, etc. The reflective photomask substrate of this embodiment is a binary type that reflects EUV light through a multilayer reflective film in the opening where there is no absorber film, and reduces the reflection of EUV light by patterning a film in the non-opening part where there is an absorber film.

[0023] Figure 1 is a schematic cross-sectional view showing one embodiment of the reflective photomask substrate of the present invention. The reflective photomask substrate 10 shown in Figure 1 has multiple layers of reflective film 12, protective film 13, and absorber film 14 serving as pattern film 15 sequentially formed on substrate 11.

[0024] <Substrate> The substrate 11 meets the characteristics of a substrate used as an EUV photomask substrate. Therefore, the substrate 11 has a low coefficient of thermal expansion (specifically, the coefficient of thermal expansion at 20°C is preferably 0±0.05×10⁻⁷ / °C, more preferably 0±0.03×10⁻⁷ / °C), and excellent smoothness, flatness, and resistance to cleaning solutions used in cleaning photomask substrates or photomasks after patterning. Specifically, a glass with a low coefficient of thermal expansion, such as SiO₂-TiO₂ based glass, is used as the substrate 11, but it is not limited to this; crystallized glass with precipitated β-quartz solid solution, quartz glass, silicon, or metal substrates may also be used.

[0025] If the substrate 11 has a smooth surface with a surface roughness (rms) of less than 0.15 nm and a flatness of less than 100 nm, then the photomask after the pattern is formed will have high reflectivity and transfer accuracy, which is better.

[0026] The size or thickness of the substrate 11 is appropriately determined by the design values ​​of the photomask. Preferably, there are no defects on the surface of the substrate 11 on the side where the multilayer reflective film 12 is formed. However, even if defects exist, they are acceptable as long as they do not cause phase defects due to concave defects and / or convex defects. Specifically, it is preferable that the depth of the concave defects and the height of the convex defects are 2 nm or less, and the half-width at half-maximum (WHM) of these concave and convex defects is 60 nm or less. The WHM of a concave defect refers to the width at a position where the depth of the concave defect is half its depth. The WHM of a convex defect refers to the width at a position where the height of the convex defect is half its height.

[0027] Multilayer reflective film The multilayer reflective film 12 achieves high EUV light reflectivity by repeatedly depositing alternating layers of high and low refractive index layers. In the multilayer reflective film 12, Mo is widely used for the high refractive index layer, and Si is widely used for the low refractive index layer. That is, the Mo / Si multilayer reflective film is the most common.

[0028] The multilayer reflective film 12 is not particularly limited as long as it possesses the desired characteristics of a reflective layer serving as a reflective photomask substrate. Here, a particularly required characteristic of the multilayer reflective film 12 is high EUV light reflectivity. Specifically, when EUV light in its wavelength range is incident on the surface of the multilayer reflective film 12 at an angle of 6 degrees, the peak reflectivity of the EUV wavelength range (i.e., the maximum reflectivity of light near a wavelength of 13.5 nm, hereinafter referred to as "EUV light peak reflectivity") is preferably 60% or more, more preferably 65% ​​or more. Furthermore, when a protective film 13 is provided on the multilayer reflective film 12, the EUV light peak reflectivity is also preferably 60% or more, more preferably 65% ​​or more.

[0029] The thickness of each layer constituting the multilayer reflective film 12 and the number of repeating units of the layers can be appropriately selected according to the film material used and the required EUV light reflectivity of the reflective layer. Taking a Mo / Si multilayer reflective film as an example, in order to form a multilayer reflective film 12 with a maximum EUV light reflectivity of 60% or more, for example, the multilayer reflective film can simply be formed by stacking a Mo layer with a thickness of 2.3 nm ± 0.1 nm and a Si layer with a thickness of 4.5 nm ± 0.1 nm in a repeating unit ratio of 30 to 60. The thickness of the multilayer reflective film 12 can be measured, for example, by means of a transmission electron microscope (TEM) through a cross-section cut along the thickness direction (Z direction) of the reflective photomask substrate.

[0030] To prevent oxidation of the surface of the multilayer reflective film 12, it is preferable that the uppermost layer of the multilayer reflective film 12 is made of a material that is not easily oxidized. This layer of material, which is not easily oxidized, functions as a capping layer of the multilayer reflective film 12. A specific example of this type of material that is not easily oxidized and functions as a capping layer is a Si layer. When the multilayer reflective film 12 is a Mo / Si multilayer reflective film, by making the uppermost layer a Si layer, it functions as a capping layer. In this case, the thickness of the capping layer is preferably 11 ± 2 nm. The thickness of the capping layer can be measured, for example, by using a transmission electron microscope (TEM) to measure a cross-section cut along the thickness direction (Z direction) of the reflective photomask substrate.

[0031] <Protective film> The protective film 13 is an arbitrary layer disposed to protect the multilayer reflective film 12 from damage during the etching process, typically a dry etching process, when a pattern is formed on the absorber film 14. Therefore, the material of the protective film 13 is chosen to be less susceptible to the effects of the etching process on the absorber film 14, i.e., the etching rate is slower than that of the absorber film 14, and it is less prone to damage caused by the etching process. To satisfy the above characteristics, it is preferable that the protective film 13 contains at least one of Rh and Ru (such as a Ru alloy, Rh alloy, etc.).

[0032] More specifically, examples of the aforementioned materials include elemental Ru, Ru alloys comprising Ru and one or more metals selected from the group consisting of Si, Ti, Nb, Mo, Rh, and Zr, elemental Rh, Rh alloys comprising Rh and one or more metals selected from the group consisting of Si, Ti, Nb, Mo, Ru, Ta, and Zr, Rh-containing nitrides comprising the aforementioned Rh alloys and N, and Rh-containing nitrides comprising the aforementioned Rh alloys, N, and O, etc. Furthermore, examples of materials that can achieve the above objectives include nitrides containing Al and such metals and N, and Al₂O₃. Among these, the preferred materials for achieving the above objectives are elemental Ru, Ru alloys, elemental Rh, or Rh alloys. As Ru alloys, Ru-Si alloys and Ru-Rh alloys are preferred; as Rh alloys, Rh-Si alloys and Rh-Ru alloys are preferred.

[0033] The thickness of the protective film 13 is preferably 1~10 nm, and more preferably 1~5 nm. The thickness of the protective film 13 can be measured, for example, by means of a transmission electron microscope (TEM) on a cross section cut along the thickness direction (Z direction) of the reflective photomask substrate.

[0034] The protective film may be a single-layer film or a multilayer film comprising multiple layers. When the protective film is a multilayer film, each layer constituting the multilayer film preferably includes the aforementioned preferred materials. Furthermore, when the protective film is a multilayer film, the total thickness of the multilayer film is preferably within the aforementioned preferred range of protective film thickness.

[0035] The protective film can be formed using known film formation methods such as magnetron sputtering and ion beam sputtering. When forming a Ru film by magnetron sputtering, it is preferable to use a Ru target as the target and Ar gas as the sputtering gas.

[0036] <Absorbent membrane> The binary absorber film 14 is particularly required to have an extremely low reflectivity for EUV light. Specifically, when light in the wavelength range of EUV light is irradiated onto the surface of the absorber film 14, the peak reflectivity of the EUV light is preferably 1.3% or less, more preferably 1% or less, further preferably 0.98% or less, particularly preferably 0.50% or less, and most preferably 0.30% or less. Furthermore, the reflectance of the absorber membrane 14 can be measured, for example, by an EUV reflectometer. To achieve the aforementioned characteristics, the absorber membrane 14 is made of a material with a high absorption coefficient for EUV light. Preferably, the material with a high absorption coefficient for EUV light is a material primarily composed of tantalum (Ta). In this specification, when referring to a material primarily composed of tantalum (Ta), it means that the material contains 20 at% or more of Ta.

[0037] The material used for the absorber membrane 14, which is mainly composed of Ta, preferably contains, in addition to Ta, at least one of the following components: hafnium (Hf), Si, zirconium (Zr), germanium (Ge), boron (B), palladium (Pd), tin (Sn), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), silver (Ag), cadmium (Cd), indium (In), antimony (Sb), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), bismuth (Bi), carbon (C), titanium (Ti), zirconium (Zr), Mo, Ru, rhodium (Rh), palladium (Pd), calcium (Ca), magnesium (Mg), Al, nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), arsenic (As), selenium (Se), tellurium (Te), hydrogen (H), and nitrogen (N). Specific examples of materials containing elements other than Ta include TaN, TaNH, TaHf, TaHfN, TaBSi, TaBSiN, TaB, TaBN, TaSi, TaSiN, TaGe, TaGeN, TaZr, TaZrN, TaPd, TaSn, TaPdN, TaSn, TaCr, TaMn, TaFe, TaCo, TaAg, TaCd, TaIn, TaSb, and TaW.

[0038] The thickness of the absorber membrane 14 is preferably 20~90 nm. Furthermore, the thickness of the absorber film 14 can be measured, for example, by means of a transmission electron microscope (TEM) through a cross-section cut along the thickness direction (Z direction) of the reflective photomask substrate.

[0039] Patterned film The patterned film system containing the above-mentioned absorber film has a laminated structure with layers of different refractive indices, totaling L layers (where L is a natural number greater than 2). L is not particularly restricted as long as it is a natural number greater than or equal to 2, but it is preferably less than or equal to 8, more preferably less than or equal to 6, and even more preferably less than or equal to 5. That is, L can be, for example, between 2 and 8. As patterned films, examples that are preferable include "a two-layer structure of TaN film (substrate side) and Pt film (opposite side of substrate)," "a two-layer structure of Cr film (substrate side) and Ru film (opposite side of substrate)," "a three-layer structure of Cr film (substrate side), Si film and Cr film (opposite side of substrate)," and "a two-layer structure of SnO2 film (substrate side) and Ru film (opposite side of substrate)," etc.

[0040] In this embodiment, the reflective photomask substrate satisfies the following equation (1) when the refractive index of the i-th layer (i is a natural number) in the patterned film from the side opposite to the substrate is set as ni, the absorption coefficient of the i-th layer in the patterned film from the side opposite to the substrate is set as ki, the film thickness of the i-th layer in the patterned film from the side opposite to the substrate is set as di (nm), the total film thickness of the patterned film is set as d, the exposure wavelength is set as λ (nm), and Pi is set as 1-exp(-2π / λ*d ik i). It is more preferably satisfied by the following equation (1-1), and even more preferably satisfied by the following equation (1-2). By satisfying equation (1), a reflective photomask substrate is obtained that allows for thinning of the patterned film and sufficiently reduces the reflectivity of the patterned film. Furthermore, the refractive index ni and absorption coefficient ki are, for example, values ​​for a wavelength of 13.5 nm.

[0041] [Number 4] …Formula (1)

[0042] [Number 5] …Equation (1-1)

[0043] [Number 6] …Equation (1-2)

[0044] When the reflection amplitude of the i-th layer in the patterned film from the side opposite to the substrate is set as ri, from the viewpoint of utilizing the mutual cancellation of reflected waves, it is preferable to satisfy the following equation (2), more preferably to satisfy the following equation (2-1), and especially preferably to satisfy the following equation (2-2). Furthermore, the reflection amplitude rL of the Lth layer in the patterned film, starting from the side opposite to the substrate, is calculated using |(nL-1-nL)| / (nL-1+nL).

[0045] [Number 7] …Formula (2)

[0046] [Number 8] …Equation (2-1)

[0047] [Number 9] …Equation (2-2)

[0048] The refractive index n1 of the outermost layer of the patterned film, starting from the side opposite to the substrate, is not particularly limited. However, from the viewpoint of generating reflection amplitude at the interface with vacuum, it is preferably 0.950 or less, more preferably 0.945 or less, and especially preferably 0.940 or less. From the viewpoint of utilizing the mutual cancellation of reflected waves caused by the reflection amplitudes of the outermost and second layers of material, it is preferably 0.830 or more, more preferably 0.860 or more, and especially preferably 0.870 or more.

[0049] The refractive index n1 and film thickness d1 of the outermost layer of the first layer from the opposite side of the substrate in the patterned film preferably satisfy the following formula (3), more preferably satisfy the following formula (3-1), and especially preferably satisfy the following formula (3-2). |(λ / 4n 1+λ / 2n 1*x)-d 1|<2.50···Formula (3) 0.10<|(λ / 4n 1+λ / 2n 1*x)-d 1|<2.30···Formula (3-1) 0.20<|(λ / 4n 1+λ / 2n 1*x)-d 1|<2.10···Formula (3-2) In equations (3), (3-1), and (3-2), x is set to an integer greater than or equal to 0.

[0050] The difference |Δk| between the absorption coefficients k of two adjacent layers in a patterned film is not particularly limited, but from the viewpoint of utilizing the mutual cancellation of reflected waves, at least one of the differences |Δk| is preferably 0.0200 or more, more preferably 0.0210 or more, and particularly preferably 0.0220 or more. On the other hand, the upper limit of the difference |Δk| is not particularly limited, but it is preferably 0.0700 or less, more preferably 0.0600 or less, and particularly preferably 0.0550 or less.

[0051] The reflectivity of the patterned film is not particularly limited as long as it is sufficiently reduced, but it is preferably 1.3% or less, more preferably 1% or less, even more preferably 0.98% or less, particularly preferably 0.50% or less, and most preferably 0.30% or less. Furthermore, the reflectivity of the patterned film can be measured using an EUV reflectometer, and optical multilayer film simulation can be implemented.

[0052] The total film thickness d of the patterned film is not particularly limited as long as it is sufficiently reduced, but it is preferably 45 nm or less, more preferably 43 nm or less, further preferably 42 nm or less, and especially preferably 41 nm or less. The total thickness of the patterned film can be measured, for example, by using a transmission electron microscope (TEM) to measure a cross-section cut along the thickness direction (Z direction) of the reflective photomask substrate.

[0053] <Buffer Layer> Furthermore, in the reflective photomask substrate of the present invention, a buffer layer may also be formed between the protective film 13 and the absorber film 14. The so-called buffer layer refers to the layer that protects the multilayer reflective film during dry etching and defect correction. The material used as a buffer layer is not particularly limited; for example, SiO2 and CrN can be cited.

[0054] <Low-reflective layer> Furthermore, a low-reflection layer can also be formed on the absorber film 14 in the reflective photomask substrate of this embodiment. The low-reflectance layer is composed of a film that exhibits low reflectance under inspection light used for inspecting photomask patterns. During the fabrication of a reflective photomask, after a pattern is formed on the absorber film, the pattern is inspected to ensure it conforms to the design. In inspecting this photomask pattern, an inspection machine typically uses light around 193 nm and 257 nm as the inspection light. Specifically, the inspection is conducted by the difference in reflectance between this light (around 193 nm and 257 nm), specifically by the difference in reflectance between the surface exposed after the absorber film has been removed by pattern formation and the surface of the absorber film remaining after pattern formation. Here, the former refers to the surface of the protective film. Therefore, if the difference in reflectance between the protective film surface and the absorber film surface relative to the wavelength of the inspection light is small, the contrast during inspection becomes poor, making accurate inspection impossible. When the difference in reflectance between the protective film surface and the absorber film surface relative to the wavelength of the inspection light is small, the formation of a low-reflectance layer improves the contrast during inspection. The material used for the low-reflection layer is not particularly limited; for example, tantalum oxynitride can be used. Since the low-reflection layer is equivalent to the outermost layer of the first layer in the patterned film from the side opposite to the substrate, it is preferable to satisfy equation (3).

[0055] [Reflective photomask] The reflective photomask of this embodiment has a pattern obtained by patterning a patterned film in the reflective photomask substrate of the present invention. That is, the reflective photomask of this embodiment sequentially includes a substrate, a multilayer reflective film for reflecting EUV light, and a pattern obtained by patterning the patterned film, and may further include other layers such as a protective film as needed. Regarding layers other than the pattern (substrate, multilayer reflective film, protective film, etc.), as explained in the section on reflective photomask substrate. The pattern will be explained in the section on "Manufacturing Method of Reflective Photomask" below.

[0056] [Manufacturing Method of Reflective Photomasks] In the manufacturing method of the reflective photomask of this embodiment, the patterned film in the reflective photomask substrate of this embodiment is patterned. That is, the reflective photomask of this embodiment is manufactured using the reflective photomask substrate of this embodiment described above. For manufacturing a reflective photomask for EUV lithography, a photolithography method capable of high-precision patterning is preferred.

[0057] In this embodiment, the method for manufacturing a reflective photomask using photolithography will be described using the reflective photomask substrate 10 shown in FIG1 as an example.

[0058] First, a resist film (not shown) is formed on the outermost surface of the reflective photomask substrate 10 shown in Figure 1 (the absorber film 14, which serves as the uppermost layer of the patterned film 15). The thickness of the resist film can be set to, for example, 100 nm. Next, the desired pattern is drawn (exposed) on the resist film, and then developed and washed to form the specified resist pattern (not shown).

[0059] Next, for the patterned film 15 (absorber film 14), the resist pattern (not shown) is used as a mask, and dry etching is performed using an etching gas containing fluorine-based gases such as SF6 to form the pattern (not shown). After the pattern is formed, the resist pattern (not shown) is removed.

[0060] Here, the etching rate of the patterned film 15 (absorber film 14) depends on the material forming the patterned film 15 (absorber film 14) and the etching gas conditions. Since the patterned film 15 (absorber film 14) includes multiple layers of different materials, the etching rate or etching gas conditions for each layer of different materials may vary.

[0061] The pattern is formed in the manner described above. When the patterned film 15 (absorber film 14), which includes multiple layers, is continuously etched by dry etching using an etching gas, the process is simplified. Next, wet cleaning is performed using an acidic or alkaline aqueous solution to obtain a reflective photomask for EUV lithography that achieves a high reflectivity.

[0062] Furthermore, as etching gases, in addition to SF6, fluorine-based gases such as CHF3, CF4, C2F6, C3F6, C4F6, C4F8, CH2F2, CH3F, C3F8, and F, as well as mixed gases containing these fluorine gases and O2 in a specified ratio, can also be used. During the etching of the patterned film 15 (absorber film 14), which includes a multilayer film, other gases can also be used as long as they are useful for the process. Examples of other gases include, for example, chlorine-based gases such as Cl2, SiCl4, CHCl3, CCl4, and BCl3, and mixed gases thereof; mixed gases containing chlorine-based gases and He in a specified ratio; mixed gases containing chlorine-based gases and Ar in a specified ratio; halogen gases containing at least one selected from fluorine, chlorine, bromine, and iodine gases; and at least one or more selected from the group consisting of hydrogen halide gases. Furthermore, examples include mixtures of such gases and oxygen.

[0063] As explained above, the following structure is disclosed in this specification. <1> A reflective photomask substrate comprises a substrate, a multilayer reflective film for reflecting EUV light, and a patterned film in sequence, forming a binary reflective photomask substrate. The patterned film has a stacked structure with a total of L layers of different refractive indices (where L is a natural number greater than 2). When the absorption coefficient of the i-th layer in the patterned film from the side opposite to the substrate is set as ki, the film thickness of the i-th layer in the patterned film from the side opposite to the substrate is set as di (nm), the total film thickness of the patterned film is set as d, the exposure wavelength is set as λ (nm), and Pi is set as 1-exp(-2π / λ*d ik i), the following equation (1) is satisfied.

[0064] [Number 10] …Formula (1)

[0065] <2> As described in [1] above, when the reflection amplitude of the i-th layer in the patterned film from the side opposite to the substrate is set as ri, the following formula (2) is satisfied.

[0066] [Number 11] …Formula (2)

[0067] <3> As mentioned above <1> or <2> The described reflective photomask substrate has a refractive index n1 of 0.950 or less for the outermost layer of the first layer from the side opposite to the substrate in the patterned film. <4> As mentioned above <1> to <3> The reflective photomask substrate described in any one of the above-mentioned methods, wherein at least one of the differences in absorption coefficients k between two adjacent layers of the patterned film, |Δk|, is 0.0200 or more. <5> As mentioned above <1> to <4> The reflective photomask substrate described in any one of the above, wherein the refractive index of the i-th layer of the patterned film from the side opposite to the substrate is set as ni, and the film thickness d1 of the outermost layer of the first layer of the patterned film from the side opposite to the substrate satisfies the following formula (3). |(λ / 4n 1+λ / 2n 1*x)-d 1|<2.50···Formula (3) In equation (3), x is an integer greater than or equal to 0. <6> As mentioned above <1> to <5> The reflective photomask substrate described in any one of the above-mentioned methods, wherein the reflectivity of the patterned film is 1.3% or less. <7> As mentioned above <1> to <6> The reflective photomask substrate described in any one of the above-mentioned methods, wherein the reflectivity of the patterned film is less than 1%. <8> As mentioned above <1> to <7> The reflective photomask substrate described in any one of the above descriptions, wherein the total thickness d of the patterned films is 45 nm or less. <9> As mentioned above <1> to <8> The reflective photomask substrate described in any one of the above-mentioned methods, wherein a protective film is further provided between the multilayer reflective film and the patterned film. <10> A reflective photomask, which has the following characteristics as described above <1> to <9> The pattern obtained by patterning the aforementioned patterned film in the reflective photomask substrate described in any one of the above. <11> A method for manufacturing a reflective photomask, which will be as described above. <1> to <9> The patterned film in the reflective photomask substrate described in any one of the above is patterned. [Example]

[0068] The invention will now be described in detail by way of examples. However, the invention is not limited to the examples described below. Examples 1-3 are comparative examples, and Examples 4-9 are exemplary examples.

[0069] (Example 1) Example 1's reflective photomask substrate includes a substrate, a multilayer reflective film formed on the substrate, a protective film formed on the multilayer reflective film, and an absorber film as a pattern film formed on the protective film. A SiO₂-TiO₂ glass substrate (film thickness: 6.3 mm) was selected as the substrate. A multilayer reflective film (film thickness: 272 nm) consisting of alternating layers of silicon (film thickness: 4.5 nm) and molybdenum (film thickness: 2.3 nm) at a repeating unit number of 40 was selected. A ruthenium (Ru) film (film thickness: 2.5 nm) was selected as the protective film. A multilayer patterned film (absorber film) (pattern film thickness d: 40.3 nm) consisting of tantalum nitride (TaN) film (film thickness d₂: 37.0 nm) and ruthenium (Ru) film (film thickness d₁: 3.3 nm) was selected (L=2). Furthermore, the substrate side of the absorber film is a tantalum nitride (TaN) film, and the opposite side of the absorber film is a ruthenium (Ru) film. Furthermore, the values ​​of refractive index n1 and absorption coefficient k1 for ruthenium film using a wavelength of 13.5 nm are (n1, k1) = (0.886, 0.017), and the values ​​of refractive index n2 and absorption coefficient k2 for tantalum nitride (TaN) film using a wavelength of 13.5 nm are (n2, k2) = (0.947, 0.031). As a result, the left side of equation (1) = 0.0109, the left side of equation (2) = 0.094, and the left side of equation (3) = 0.52 (where x = 0) (Table 1). Figure 2 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 1, which has a two-layer structure consisting of a TaN film (substrate side: film thickness d2: 37.0 nm) and a Ru film (opposite to the substrate side: film thickness d1: 3.3 nm). The reflectivity of the patterned film at a wavelength of 13.5 nm is 2.62% (Table 1). Figure 2 was obtained by performing an optical multilayer film simulation.

[0070] (Example 2) In Example 1, instead of selecting a stacked structure (L=2) of tantalum nitride (TaN) film (film thickness d 2: 37.0 nm) and ruthenium (Ru) film (film thickness d 1: 3.3 nm) as the patterned film (absorber film) (patterned film thickness d: 40.3 nm), a stacked structure (L=2) of tantalum nitride (TaN) film (film thickness d 2: 44.0 nm) and ruthenium (Ru) film (film thickness d 1: 3.8 nm) as the patterned film (absorber film) (patterned film thickness d: 47.8 nm) is selected, otherwise the same as in Example 1. As a result, the left side of equation (1) = 0.0104, the left side of equation (2) = 0.094, and the left side of equation (3) = 0.02 (where x = 0) (Table 1). Figure 3 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 2, which has a two-layer structure consisting of a TaN film (substrate side: film thickness d2: 44.0 nm) and a Ru film (opposite to the substrate side: film thickness d1: 3.8 nm). The reflectivity of the patterned film at a wavelength of 13.5 nm is 1.36% (Table 1). Figure 3 was obtained by performing an optical multilayer film simulation.

[0071] (Example 3) In Example 1, instead of selecting a stacked structure of tantalum nitride (TaN) film (thickness d2: 37.0 nm) and ruthenium (Ru) film (thickness d1: 3.3 nm) (L=2) as the patterned film (absorber film) (patterned film thickness d: 40.3 nm), a stacked structure of TaN film (substrate side: thickness d3: 32.6 nm), SiN film (thickness d2: 2.6 nm), and TaN film (opposite side to the substrate: thickness d1: 4.5 nm) (L=3) as the patterned film (absorber film) (patterned film thickness d: 39.7 nm) is selected, otherwise the same as in Example 1. Furthermore, the refractive index n2 and absorption coefficient k2 of the SiN film are used at a wavelength of 13.5 nm, (n2, k2) = (0.973, 0.009). As a result, the left side of equation (1) = 0.0113, the left side of equation (2) = 0.054, and the left side of equation (3) = 0.93 (where x = 0) (Table 1). Figure 4 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 3, which has a three-layer structure consisting of a TaN film (substrate side: thickness d3: 32.6 nm), a SiN film (thickness d2: 2.6 nm), and a TaN film (opposite to the substrate: thickness d1: 4.5 nm). The reflectivity of the patterned film at a wavelength of 13.5 nm is 4.01% (Table 1). Figure 4 was obtained by performing an optical multilayer film simulation.

[0072] (Example 4) In Example 1, instead of selecting a stacked structure (L=2) of tantalum nitride (TaN) film (film thickness d2: 37.0 nm) and ruthenium (Ru) film (film thickness d1: 3.3 nm) as the patterned film (absorber film) (patterned film thickness d: 40.3 nm), a stacked structure (L=2) of TaN film (substrate side: film thickness d2: 28.4 nm) and Pt film (opposite side to the substrate: film thickness d1: 12.1 nm) as the patterned film (absorber film) (patterned film thickness d: 40.5 nm) is selected, otherwise the same as in Example 1. Furthermore, the refractive index n1 and absorption coefficient k1 of the Pt film are used at a wavelength of 13.5 nm, (n1, k1) = (0.891, 0.060). As a result, the left side of equation (1) = 0.0153, the left side of equation (2) = 0.088, and the left side of equation (3) = 0.71 (where x = 1) (Table 1). Figure 5 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 4, which has a two-layer structure consisting of a TaN film (substrate side: film thickness d2: 28.4 nm) and a Pt film (opposite to the substrate side: film thickness d1: 12.1 nm). The reflectivity of the patterned film at a wavelength of 13.5 nm is 0.84% ​​(Table 1). Figure 5 was obtained by performing an optical multilayer film simulation.

[0073] (Example 5) In Example 1, instead of selecting a stacked structure (L=2) of tantalum nitride (TaN) film (film thickness d 2: 37.0 nm) and ruthenium (Ru) film (film thickness d 1: 3.3 nm) as the patterned film (absorber film) (patterned film thickness d: 40.3 nm), a stacked structure (L=2) of TaN film (substrate side: film thickness d 2: 27.3 nm) and Pt film (opposite side to the substrate: film thickness d 1: 13.4 nm) as the patterned film (absorber film) (patterned film thickness d: 40.7 nm) is selected, otherwise the same as in Example 1. As a result, the left side of equation (1) = 0.0156, the left side of equation (2) = 0.088, and the left side of equation (3) = 2.01 (where x = 1) (Table 1). Figure 6 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 5, which has a two-layer structure consisting of a TaN film (substrate side: film thickness d2: 27.3 nm) and a Pt film (opposite to the substrate side: film thickness d1: 13.4 nm). The reflectivity of the patterned film at a wavelength of 13.5 nm is 0.94% (Table 1). Figure 6 was obtained by performing an optical multilayer film simulation.

[0074] (Example 6) In Example 1, instead of selecting a stacked structure (L=2) of tantalum nitride (TaN) film (film thickness d 2: 37.0 nm) and ruthenium (Ru) film (film thickness d 1: 3.3 nm) as the patterned film (absorber film) (patterned film thickness d: 40.3 nm), a stacked structure (L=2) of TaN film (substrate side: film thickness d 2: 28.2 nm) and Pt film (opposite side to the substrate: film thickness d 1: 12.4 nm) as the patterned film (absorber film) (patterned film thickness d: 40.6 nm) is selected, otherwise the same as in Example 1. As a result, the left side of equation (1) = 0.0154, the left side of equation (2) = 0.088, and the left side of equation (3) = 1.01 (where x = 1) (Table 1). Figure 7 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 6, which has a two-layer structure consisting of a TaN film (substrate side: film thickness d2: 28.2 nm) and a Pt film (opposite to the substrate side: film thickness d1: 12.4 nm). The reflectivity of the patterned film at a wavelength of 13.5 nm is 0.85% (Table 1). Figure 7 was obtained through simulation of optical multilayer film implementation.

[0075] (Example 7) In Example 1, instead of selecting a stacked structure (L=2) of tantalum nitride (TaN) film (film thickness d2: 37.0 nm) and ruthenium (Ru) film (film thickness d1: 3.3 nm) as the patterned film (absorber film) (patterned film thickness d: 40.3 nm), a stacked structure (L=2) of Cr film (substrate side: film thickness d2: 38.0 nm) and Ru film (opposite side to the substrate: film thickness d1: 2.8 nm) as the patterned film (absorber film) (patterned film thickness d: 40.8 nm) is selected, otherwise the same as in Example 1. Furthermore, the refractive index n2 and absorption coefficient k2 of the Cr film are used at a wavelength of 13.5 nm, (n2, k2) = (0.932, 0.039). As a result, the left side of equation (1) = 0.0127, the left side of equation (2) = 0.086, and the left side of equation (3) = 1.02 (where x = 0) (Table 1). Figure 8 is a graph showing the relationship between exposure wavelength λ and reflectivity R for the reflective photomask substrate of Example 7, which has a two-layer structure consisting of a Cr film (substrate side: film thickness d2: 38 nm) and a Ru film (opposite to the substrate: film thickness d1: 2.8 nm). The reflectivity of the patterned film at a wavelength of 13.5 nm is 0.95% (Table 1). Figure 8 was obtained by performing an optical multilayer film simulation.

[0076] (Example 8) In Example 1, instead of selecting a stacked structure of tantalum nitride (TaN) film (thickness d2: 37.0 nm) and ruthenium (Ru) film (thickness d1: 3.3 nm) (L=2) as the patterned film (absorber film) (patterned film thickness d: 40.3 nm), a stacked structure of Cr film (substrate side: thickness d3: 33.1 nm), Si film (thickness d2: 3.1 nm), and Cr film (opposite side to the substrate: thickness d1: 3.9 nm) (L=3) as the patterned film (absorber film) (patterned film thickness d: 40.1 nm) is selected, otherwise the same as in Example 1. The refractive index n2 and absorption coefficient k2 of the Si film are used at a wavelength of 13.5 nm, (n2, k2) = (0.999, 0.002). As a result, the left side of equation (1) = 0.0130, the left side of equation (2) = 0.105, and the left side of equation (3) = 0.27 (where x = 0) (Table 1). Figure 9 is a graph showing the relationship between exposure wavelength λ and reflectivity R for the reflective photomask substrate of Example 8, which has a three-layer structure consisting of a Cr film (substrate side: thickness d3: 33.1 nm), a Si film (thickness d2: 3.1 nm), and a Cr film (opposite to the substrate side: thickness d1: 3.9 nm). The reflectivity of the patterned film at a wavelength of 13.5 nm is 0.82% (Table 1). Figure 9 was obtained by performing an optical multilayer film simulation.

[0077] (Example 9) In Example 1, instead of selecting a stacked structure (L=2) of tantalum nitride (TaN) film (film thickness d 2: 37 nm) and ruthenium (Ru) film (film thickness d 1: 3.3 nm) as the patterned film (absorber film) (patterned film thickness d: 40.3 nm), a stacked structure (L=2) of SnO 2 film (substrate side: film thickness d 2: 24.1 nm) and Ru film (film thickness d 1: 2.2 nm) as the patterned film (absorber film) (patterned film thickness d: 26.3 nm) is selected as the patterned film (absorber film), otherwise the same as in Example 1. As a result, the left side of equation (1) = 0.0213, the left side of equation (2) = 0.082, and the left side of equation (3) = 1.62 (where x = 0) (Table 1). Figure 10 is a graph showing the relationship between exposure wavelength λ and reflectivity R for a reflective photomask substrate of Example 9, which has a two-layer structure consisting of a SnO2 film (substrate side: film thickness d2: 24.1 nm) and a Ru film (opposite to the substrate: film thickness d1: 2.8 nm). The reflectivity of the patterned film at a wavelength of 13.5 nm is 0.29% (Table 1). Figure 10 was obtained through simulation of optical multilayer film.

[0078] [Table 1] Table 1 n k Film thickness(nm) Equation (1) Equation (2) Equation (3) Reflectance R (%) Example 1 Ru (opposite side of the substrate) 0.886 0.017 3.3 0.0109 0.094 0.52 2.62 TaN (substrate side) 0.947 0.031 37.0 total - - 40.3 Example 2 Ru (opposite side of the substrate) 0.886 0.017 3.8 0.0104 0.094 0.02 1.36 TaN (substrate side) 0.947 0.031 44.0 total - - 47.8 Example 3 TaN (opposite side of the substrate) 0.947 0.031 4.5 0.0113 0.054 0.93 4.01 SiN 0.973 0.009 2.6 TaN (substrate side) 0.947 0.031 32.6 total - - 39.7 Example 4 Pt (opposite side to the substrate) 0.891 0.060 12.1 0.0153 0.088 0.71 0.84 TaN (substrate side) 0.947 0.031 28.4 total - - 40.5 Example 5 Pt (opposite side to the substrate) 0.891 0.060 13.4 0.0156 0.088 2.01 0.94 TaN (substrate side) 0.947 0.031 27.3 total - - 40.7 Example 6 Pt (opposite side to the substrate) 0.891 0.060 12.4 0.0154 0.088 1.01 0.85 TaN (substrate side) 0.947 0.031 28.2 total - - 40.6 Example 7 Ru (opposite side of the substrate) 0.886 0.017 2.8 0.0127 0.086 1.02 0.95 Cr (substrate side) 0.932 0.039 38.0 total - - 40.8 Example 8 Cr (opposite side of the substrate) 0.932 0.039 3.9 0.0130 0.105 0.27 0.82 Si 0.999 0.002 3.1 Cr (substrate side) 0.932 0.039 33.1 total - - 40.1 Example 9 Ru (opposite side of the substrate) 0.886 0.017 2.2 0.0213 0.082 1.62 0.29 SnO2 (substrate side) 0.925 0.070 24.1 total - - 26.3

[0079] According to Table 1, the reflective photomask substrates that satisfy Equation (1) (Examples 4 to 9) can reduce the thickness of the patterned film and sufficiently reduce the reflectivity of the patterned film (reflectivity: 0.29 to 0.95%). On the other hand, the reflective photomask substrates that do not satisfy Equation (1) (Examples 1 to 3) cannot sufficiently reduce the reflectivity of the patterned film (reflectivity: 1.36 to 4.01%).

[0080] Furthermore, while the present invention has been described in detail with reference to specific embodiments, those skilled in the art will understand that various changes or modifications may be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2022-035462, filed on March 8, 2022, the contents of which are incorporated herein by reference.

[0081] 10: Reflective photomask substrate 11:Substrate 12: Multilayer reflective film 13: Protective film 14: Absorbent membrane 15: Patterned film

Claims

1. A reflective photomask substrate, comprising, sequentially, a substrate, a multilayer reflective film for reflecting EUV light, and a patterned film, wherein the patterned film has a laminated structure consisting of L layers with different refractive indices (wherein, L is a natural number greater than 2), and when the absorption coefficient of the i-th layer in the patterned film from the side opposite to the substrate is set as ki, the film thickness of the i-th layer in the patterned film from the side opposite to the substrate is set as di (nm), the total film thickness of the patterned film is set as d, the exposure wavelength is set as λ (nm), and Pi is set as 1-exp(-2π / λ*d ik i), the following equation (1) is satisfied, [number 1] … equation (1).

2. The reflective photomask substrate of claim 1, wherein when the reflection amplitude of the i-th layer in the patterned film from the side opposite to the substrate is set as ri, the following equation (2) is satisfied, [number 2] … equation (2).

3. The reflective photomask substrate of claim 1, wherein the refractive index n1 of the outermost layer of the first layer of the patterned film from the side opposite to the substrate is 0.950 or less.

4. The reflective photomask substrate of claim 1, wherein at least one of the differences in absorption coefficients k |Δk| between two adjacent layers in the patterned film is 0.0200 or more.

5. The reflective photomask substrate of claim 1, wherein the refractive index of the i-th layer in the patterned film from the side opposite to the substrate is set as ni, and the film thickness d1 of the outermost layer of the first layer in the patterned film from the side opposite to the substrate satisfies the following equation (3): |(λ / 4n1+λ / 2n1*x)-d1|<2.50・・・Equation (3) Wherein, In equation (3), x is an integer greater than or equal to 0.

6. The reflective photomask substrate of claim 1, wherein the reflectivity of the patterned film is 1.3% or less.

7. The reflective photomask substrate of claim 1, wherein the reflectivity of the patterned film is less than 1%.

8. The reflective photomask substrate of claim 1, wherein the total thickness d of the patterned films is 45 nm or less.

9. The reflective photomask substrate of claim 1, wherein a protective film is further provided between the multilayer reflective film and the patterned film.

10. A reflective photomask having a pattern obtained by patterning the aforementioned patterned film in a reflective photomask substrate as claimed in any one of claims 1 to 9.

11. A method for manufacturing a reflective photomask, wherein the patterned film in the reflective photomask substrate of any one of claims 1 to 9 is patterned.

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