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

Abstract

To provide a reflective mask blank and a reflective mask that allow the reflection factor of a pattern film to be sufficiently reduced while reducing the thickness of the pattern film, and a method for manufacturing the same.SOLUTION: A binary reflective mask blank comprises a substrate, a multi-layer reflection film that reflects EUV light, and a pattern film in this order. The pattern film has a laminated structure with a total of L layers with different refractive indices from each other, and satisfies Formula (1) below (where ki represents the absorption coefficient of an i-th layer from an opposite side of the substrate in the pattern film, di (nm) represents the film thickness of the i-th layer from the opposite side of the substrate in the pattern film, d represents the total film thickness of the pattern film, λ (nm) represents the exposure wavelength, and Pi is 1-exp(-2π / λ*diki).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a reflective mask blank, a reflective mask, and a manufacturing method thereof, and in particular to a reflective mask blank for EUV lithography, which is a master plate for manufacturing an EUV (Etreme Ultra Violet) exposure mask used in the exposure process of semiconductor manufacturing, and a reflective mask obtained by forming a mask pattern on a pattern film in the reflective mask blank for EUV lithography, and a manufacturing method thereof. [Background technology]

[0002] Conventionally, the light source of exposure equipment used in semiconductor manufacturing is ultraviolet light with a wavelength of 193 to 365 nm. The shorter the wavelength, the higher the resolution of the exposure equipment. Therefore, EUV light with a central wavelength of 13.5 nm is seen as promising as the light source for next-generation exposure equipment.

[0003] EUV light is easily absorbed by many materials, so refractive optical exposure tools cannot be used, and therefore reflective masks are used for EUV light.

[0004] In such 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 patterned on the multilayer reflective film. A protective film (sometimes called a "cap layer") is usually formed between the multilayer reflective film and the absorber film to protect the multilayer reflective film from etching when forming the mask pattern. Furthermore, a low-reflective layer may be formed on the absorber film to facilitate pattern defect inspection after mask processing.

[0005] The substrate may be 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 may be made of a film in which molybdenum (Mo) films and silicon films are alternately stacked for about 40 periods. The protective film may be made of a ruthenium-based material with a thickness of 1 to 5 nm. Ruthenium (Ru)-based materials are very difficult to etch with gases that do not contain oxygen, and function as an etching stopper during mask processing. The absorber film may be made of a tantalum-based material.

[0006] EUV light incident on a reflective mask from the illumination optical system of the exposure tool is reflected by the openings where there is no absorber film and absorbed by the non-openings where the absorber film is present, and the mask pattern is transferred onto the wafer through the reduced projection optical system of the exposure tool. EUV light is usually incident on a reflective mask from a direction tilted by 6 degrees. If the absorber film is too thick, areas will be shaded by the absorber film, making it impossible to faithfully transfer the mask pattern onto the wafer. This problem becomes more pronounced as the line width of the mask pattern becomes smaller, so there is a demand for thinner absorber films.

[0007] In addition, in the case of a binary mask, in order to perform high-precision pattern transfer in EUV exposure, the reflectance of the non-aperture area needs to be suppressed to 2% or less. In Patent Document 1, by forming an enhanced surface reflection film, which is optically designed to satisfy certain conditions, on an absorber film, the amplitude of EUV light reflected on the surface of a pattern film that is partially etched during mask processing is increased, and by utilizing the interference effect with the EUV light reflected on the multilayer reflection film, it is possible to suppress the reflectance of non-opening portions to 2% or less while making the thickness of the absorber film thinner. Note that the pattern film is composed of an absorber film and an enhanced surface reflection film. Furthermore, Patent Document 2 discloses a reflective mask blank that includes, as an absorber film, a laminated film in which low refractive index material films and high refractive index material films are alternately laminated in multiple periods. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2018-180544 [Patent Document 2] Japanese Patent Publication No. 2015-8283 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in general, the absolute value of the refractive index difference Δn between adjacent layers in the laminated structure of the pattern film in a reflective mask blank is small, so the amplitude (amplitude) of the EUV light reflected at the interface of the laminated structure of the pattern film is much smaller than the amplitude (intensity) of the reflected light from the multilayer reflective film. Therefore, there is a limit to realizing a thin pattern film with a reduced reflectance of EUV light only by utilizing the interference effect of canceling out the reflected light from the multilayer reflective film using the EUV light reflected at the interface of the laminated structure of the pattern film. Furthermore, in Patent Document 2, when the laminated film, which is an absorber film, is etched or cleaned for mask processing, there is a problem that damage occurs to the sidewall of the laminated film.

[0010] An object of the present invention is to provide a reflective mask blank, a reflective mask, and a method for manufacturing the same, which can sufficiently reduce the reflectance of a pattern film while thinning the film thickness of the pattern film. More specifically, an object of the present invention is to provide a reflective mask blank, a reflective mask, and a method for manufacturing the same, which can realize a reflectance of 1% or less with a pattern film having a film thickness of 45 nm or less. [Means for solving the problem]

[0011] The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that in a reflective mask blank comprising, in this order, a substrate, a multilayer reflective film that reflects EUV light, and a pattern film that has a laminated structure having a total of L layers each having a different refractive index, the pattern film satisfies the following formula (1), thereby solving the above-mentioned problems and completing the present invention.

[0012]

number

[0013] That is, the present invention is as follows. [1] A binary-type reflective mask blank comprising, in this order, a substrate, a multilayer reflective film that reflects EUV light, and a pattern film, the pattern film having a laminated structure having a total of L layers each having a different refractive index (where L is a natural number of 2 or more), and an absorption coefficient of the i-th layer in the pattern film from the side opposite to the substrate is k i The thickness of the i-th layer from the opposite side of the substrate in the pattern film is d i (nm), the total thickness of the pattern film is d, the exposure wavelength is λ (nm), and P i 1-exp(-2π / λ*d i k i ) a reflective mask blank which satisfies the following formula (1):

[0014]

number

[0015] [2] The reflection amplitude of the i-th layer in the pattern film from the opposite side of the substrate is r i The reflective mask blank according to the above [1], which satisfies the following formula (2):

[0016]

number

[0017] [3] The reflective mask blank according to [1] above, wherein the refractive index n1 of the outermost layer of the first layer in the pattern film from the side opposite to the substrate is 0.950 or less. [4] The reflective mask blank according to the above [1], wherein at least one of the differences |Δk| in absorption coefficient k between two adjacent layers in the pattern film is 0.0200 or more. [5] The refractive index of the i-th layer in the pattern film from the side opposite to the substrate is n i and a film thickness d1 of an outermost layer of the pattern film that is a first layer from the side opposite to the substrate satisfies the following formula (3): |(λ / 4n1+λ / 2n1*x)-d1|<2.50...Equation (3) In the formula (3), x is an integer of 0 or more. [6] The reflective mask blank according to the above [1], wherein the reflectance of the pattern film is 1.3% or less. [7] The reflective mask blank according to [1] above, wherein the reflectance of the pattern film is 1% or less. [8] The reflective mask blank according to [1] above, wherein the pattern film has a total thickness d of 45 nm or less. [9] The reflective mask blank according to [1] above, further comprising a protective film between the multilayer reflective film and the pattern film.

[10] A reflective mask having a pattern formed by patterning the pattern film in the reflective mask blank according to any one of [1] to [9] above.

[11] A method for producing a reflective mask, comprising patterning the pattern film in the reflective mask blank according to any one of the above [1] to [9]. Effect of the Invention

[0018] According to the present invention, it is possible to provide a reflective mask blank and a reflective mask capable of sufficiently reducing the reflectance of a pattern film while reducing the film thickness of the pattern film, and a method for manufacturing the same. Since the reflective mask blank of the present invention has a simple film structure, mask processing is also easy. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic cross-sectional view showing one embodiment of a reflective mask blank of the present invention. [Diagram 2]FIG. 2 is a graph showing the relationship between the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 1, in which the pattern film 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). [Diagram 3] FIG. 3 is a graph showing the relationship between the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 2, in which the pattern film 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] FIG. 4 is a graph showing the relationship between the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 3, in which the pattern film has a three-layer structure of a TaN film (substrate side: thickness d3: 32.6 nm), a SiN film (thickness d2: 2.6 nm), and a TaN film (opposite side to the substrate: thickness d1: 4.5 nm). [Diagram 5] FIG. 5 is a graph showing the relationship between the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 4, in which the pattern film 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] FIG. 6 is a graph showing the relationship between the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 5, in which the pattern film has a two-layer structure of a TaN film (substrate side: film thickness d2: 27.3 nm) and a Pt film (opposite side to the substrate: film thickness d1: 13.4 nm). [Figure 7] FIG. 7 is a graph showing the relationship between the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 6, in which the pattern film 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] FIG. 8 is a graph showing the relationship between the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 7, in which the pattern film 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]FIG. 9 is a graph showing the relationship between the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 8, in which the pattern film has a three-layer structure 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 (side opposite to the substrate: film thickness d1: 3.9 nm). [Figure 10] FIG. 10 is a graph showing the relationship between the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 9, in which the pattern film 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). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In this specification, the definitions and meanings of terms are as follows. In this specification, any of the items that are considered to be preferred may be adopted arbitrarily, and it can be said that a combination of preferred items is more preferable. In addition, in this specification, the expression "XX to YY" means "at least XX and at most YY." In addition, in this specification, "exp(t)" means "e t " means " Furthermore, in this specification, the lower limit and upper limit described in stages for the preferred numerical ranges (e.g., ranges of content, etc.) can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60." In addition, in the numerical ranges described in this specification, the upper limit or lower limit of the numerical range may be replaced with a value shown in the examples.

[0021] [Reflective mask blank] The reflective mask blank of this embodiment comprises, in this order, a substrate, a multilayer reflective film that reflects EUV light, and a pattern film, and may further comprise other layers such as a protective film, as necessary. The pattern film is a layer that is partially etched during mask processing, and includes an absorber film. The pattern film may include a buffer layer, a low-reflection layer, and the like in addition to the absorber film. The reflective mask blank of this embodiment is a binary type in which EUV light is reflected by a multilayer reflective film in openings where no absorber film is present, and a pattern film reduces reflection of EUV light in non-openings where an absorber film is present.

[0022] Fig. 1 is a schematic cross-sectional view showing one example of an embodiment of a reflective mask blank of the present invention. The reflective mask blank 10 shown in Fig. 1 has a multilayer reflective film 12, a protective film 13, and an absorber film 14 as a pattern film 15 formed in this order on a substrate 11.

[0023] <Substrate> The substrate 11 satisfies the characteristics required for an EUV mask blank substrate. To this end, the substrate 11 has a low thermal expansion coefficient (specifically, a thermal expansion coefficient at 20° C. of preferably 0±0.05×10 -7 / ℃, more preferably 0±0.03×10 -7 / °C), and has excellent smoothness, flatness, and resistance to cleaning solutions used for cleaning mask blanks or photomasks after pattern formation. Specifically, glass having a low thermal expansion coefficient, such as SiO2-TiO2 glass, is used as the substrate 11, but is not limited thereto, and substrates such as crystallized glass in which a β-quartz solid solution is precipitated, quartz glass, silicon, and metal can also be used.

[0024] It is preferable that the substrate 11 has a smooth surface with a surface roughness (rms) of 0.15 nm or less and a flatness of 100 nm or less, because this allows high reflectance and transfer accuracy to be obtained in the photomask after pattern formation.

[0025] The size, thickness, etc. of the substrate 11 are appropriately determined based on the design values ​​of the mask, etc. It is preferable that there are no defects on the surface of the substrate 11 on which the multilayer reflective film 12 is formed. However, even if defects are present, it is acceptable as long as no phase defects are caused by concave defects and / or convex defects. Specifically, it is preferable that the depth of the concave defect and the height of the convex defect are 2 nm or less, and the half-width of these concave defects and convex defects are 60 nm or less. The half-width of a concave defect refers to the width at a position half the depth of the concave defect. The half-width of a convex defect refers to the width at a position half the height of the convex defect.

[0026] <Multilayer reflective film> The multilayer reflective film 12 reflects EUV light by alternately stacking high refractive index layers and low refractive index layers multiple times, thereby achieving high EUV light reflectance. In the multilayer reflective film 12, Mo is widely used for the high refractive index layers, and Si is widely used for the low refractive index layers. That is, Mo / Si multilayer reflective films are the most common.

[0027] The multilayer reflective film 12 is not particularly limited as long as it has the desired characteristics as a reflective layer of a reflective mask blank. Here, a characteristic that is particularly required for the multilayer reflective film 12 is a high EUV light reflectance. Specifically, when a light beam in the wavelength region of EUV light is irradiated onto the surface of the multilayer reflective film 12 at an incident angle of 6 degrees, the peak reflectance of light in the EUV wavelength region (i.e., the maximum value of the light reflectance at a wavelength of about 13.5 nm. Hereinafter, in this specification, this will be referred to as the "peak reflectance of EUV light") is preferably 60% or more, more preferably 65% ​​or more. Even in a state where a protective film 13 is provided on the multilayer reflective film 12, the peak reflectance of EUV light is preferably 60% or more, more preferably 65% ​​or more.

[0028] The thickness of each layer constituting the multilayer reflective film 12 and the number of repeat units of the layers can be appropriately selected depending on the film material used and the EUV light reflectance required for the reflective layer. Taking a Mo / Si multilayer reflective film as an example, to obtain a multilayer reflective film 12 with a maximum EUV light reflectance of 60% or more, for example, the multilayer reflective film may be formed by laminating Mo layers with a thickness of 2.3 nm±0.1 nm and Si layers with a thickness of 4.5 nm±0.1 nm so that the number of repeat units is 30 to 60. The film thickness of the multilayer reflective film 12 can be measured, for example, by a transmission electron microscope (TEM) on a cross section cut along the thickness direction (Z direction) of the reflective mask blank.

[0029] In order to prevent oxidation of the surface of the multilayer reflective film 12, it is preferable that the top layer of the multilayer reflective film 12 is a layer of a material that is not easily oxidized. The layer of the material that is not easily oxidized functions as a capping layer for the multilayer reflective film 12. A specific example of a layer of a material that is not easily oxidized that functions as a capping layer is a Si layer. When the multilayer reflective film 12 is a Mo / Si multilayer reflective film, the top layer is a Si layer, so that the top layer functions as a capping layer. In this case, the thickness of the capping layer is preferably 11±2 nm. The film thickness of the cap layer can be measured, for example, by a transmission electron microscope (TEM) on a cross section cut along the thickness direction (Z direction) of the reflective mask blank.

[0030] <Protective film> The protective film 13 is an optional layer provided for the purpose of protecting the multilayer reflective film 12 from damage during the etching process, usually a dry etching process, in which a pattern is formed on the absorber film 14. Therefore, a material that is not easily affected by the etching process of the absorber film 14, that is, a material that has an etching rate slower than that of the absorber film 14 and is not easily damaged by this etching process, is selected as the material for the protective film 13. To satisfy the above characteristics, it is preferable that the protective film 13 contains at least one of Rh and Ru (a Ru alloy, a Rh alloy, etc.).

[0031] More specifically, examples of the above-mentioned materials include Rh-based materials such as simple Ru metal, Ru alloys containing Ru and one or more metals selected from the group consisting of Si, Ti, Nb, Mo, Rh, and Zr, simple Rh metal, Rh alloys containing Rh and one or more metals selected from the group consisting of Si, Ti, Nb, Mo, Ru, Ta, and Zr, Rh-containing nitrides containing the above-mentioned Rh alloys and N, and Rh-containing oxynitrides containing the above-mentioned Rh alloys, N, and O. Further, examples of materials that can achieve the above object include Al and nitrides containing these metals and N, and Al2O3. Among them, materials capable of achieving the above object are preferably Ru metal alone, Ru alloys, Rh metal alone, or Rh alloys. As Ru alloys, Ru-Si alloys and Ru-Rh alloys are preferred, and as Rh alloys, Rh-Si alloys and Rh-Ru alloys are preferred.

[0032] The thickness of the protective film 13 is preferably from 1 to 10 nm, and more preferably from 1 to 5 nm. The film thickness of the protective film 13 can be measured, for example, by a transmission electron microscope (TEM) on a cross section cut along the thickness direction (Z direction) of the reflective mask blank.

[0033] The protective film may be a film consisting of a single layer, or may be a multi-layer film consisting of multiple layers. When the protective film is a multi-layer film, each layer constituting the multi-layer film is preferably made of the above-mentioned preferred material. In addition, when the protective film is a multi-layer film, it is also preferable that the total thickness of the multi-layer film is within the above-mentioned preferred range.

[0034] The protective film can be formed by a known film formation method such as magnetron sputtering, ion beam sputtering, etc. When forming a Ru film by magnetron sputtering, it is preferable to form the film using a Ru target as the target and Ar gas as the sputtering gas.

[0035] <Absorber membrane> A particularly required characteristic of the binary type absorber film 14 is an extremely low EUV light reflectance. Specifically, when the surface of the absorber film 14 is irradiated with light in the wavelength region of EUV light, the peak reflectance of EUV light 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. The reflectance of the absorber film 14 can be measured by, for example, an EUV reflectometer. In order to achieve the above characteristics, the absorber film 14 is made of a material with a high absorption coefficient for EUV light. As a material with a high absorption coefficient for EUV light, a material containing tantalum (Ta) as a main component is preferable. In this specification, a material containing tantalum (Ta) as a main component means a material containing 20 at % or more of Ta.

[0036] The material containing Ta as a main component for use in the absorber film 14 may further include 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), and tantalum (Tb). It is preferable that the metal oxide contains at least one component selected from the group consisting of 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 the above elements other than Ta include, for example, 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, TaW, etc.

[0037] The thickness of the absorber film 14 is preferably 20 to 90 nm. The film thickness of the absorber film 14 can be measured, for example, by a transmission electron microscope (TEM) on a cross section cut along the thickness direction (Z direction) of the reflective mask blank.

[0038] <Patterned film> The pattern film including the absorber film described above has a laminated structure having a total of L layers (where L is a natural number of 2 or more) each having a different refractive index. L is not particularly limited as long as it is a natural number of 2 or more, but is preferably 8 or less, more preferably 6 or less, and even more preferably 5 or less. Suitable examples of the pattern film include a two-layer structure of a TaN film (substrate side) and a Pt film (opposite side from the substrate); a two-layer structure of a Cr film (substrate side) and a Ru film (opposite side from the substrate); a three-layer structure of a Cr film (substrate side), a Si film and a Cr film (opposite side from the substrate); and a two-layer structure of a SnO2 film (substrate side) and a Ru film (opposite side from the substrate).

[0039] In the reflective mask blank of the present embodiment, the refractive index of the i-th layer (i is a natural number) from the side opposite to the substrate in the pattern film is n i The absorption coefficient of the i-th layer from the opposite side of the substrate in the pattern film is k i The thickness of the i-th layer from the opposite side of the substrate in the pattern film is d i (nm), the total thickness of the pattern film is d, the exposure wavelength is λ (nm), and P i 1-exp(-2π / λ*d i k i ), the following formula (1) is satisfied, preferably the following formula (1-1) is satisfied, and more preferably the following formula (1-2) is satisfied. By satisfying formula (1), a reflective mask blank can be obtained that can reduce the thickness of the pattern film while sufficiently reducing the reflectance of the pattern film. i and the absorption coefficient k i is the value at a wavelength of 13.5 nm, for example.

[0040]

number

[0041]

number

[0042]

number

[0043] The reflection amplitude of the i-th layer from the opposite side of the substrate in the patterned film is r i In this case, from the viewpoint of utilizing the cancellation of reflected waves, it is preferable to satisfy the following formula (2), it is more preferable to satisfy the following formula (2-1), and it is particularly preferable to satisfy the following formula (2-2). The reflection amplitude r of the Lth layer from the opposite side of the substrate in the pattern film is L is |(n L-1 -n L )| / (n L-1 +n L ) is calculated as follows:

[0044]

number

[0045]

number

[0046]

number

[0047] The refractive index n1 of the outermost layer, which is the first layer from the side opposite the substrate in the pattern film, is not particularly limited, but from the viewpoint of generating a reflection amplitude at the interface with a vacuum, it is preferably 0.950 or less, more preferably 0.945 or less, and particularly preferably 0.940 or less, and from the viewpoint of utilizing the cancellation of reflected waves due to the reflection amplitude between the outermost layer and the material of the second layer, it is preferably 0.830 or more, more preferably 0.860 or more, and particularly preferably 0.870 or more.

[0048] The refractive index n1 and thickness d1 of the outermost layer of the first layer from the side opposite the substrate in the patterned film preferably satisfy the following formula (3), more preferably the following formula (3-1), and particularly preferably the following formula (3-2). |(λ / 4n1+λ / 2n1*x)-d1|<2.50...Equation (3) 0.10<|(λ / 4n1+λ / 2n1*x)-d1|<2.30...Equation (3-1) 0.20<|(λ / 4n1+λ / 2n1*x)-d1|<2.10...Equation (3-2) However, in the formulas (3), (3-1) and (3-2), x is an integer of 0 or more.

[0049] The difference |Δk| in the absorption coefficient k between two adjacent layers in the pattern film is not particularly limited, but from the viewpoint of utilizing the 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, there is no particular limit on the upper limit of the difference |Δk|, but it is preferably 0.0700 or less, more preferably 0.0600 or less, and particularly preferably 0.0550 or less.

[0050] The reflectance of the pattern film is not particularly limited as long as it is sufficiently reduced, but 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. The reflectance of the patterned film can be measured by an EUV reflectometer, and an optical multilayer film simulation can be performed.

[0051] The total film thickness d of the pattern film is not particularly limited as long as it is sufficiently reduced, but is preferably 45 nm or less, more preferably 43 nm or less, even more preferably 42 nm or less, and particularly preferably 41 nm or less. The total film thickness of the pattern film can be measured, for example, by a transmission electron microscope (TEM) on a cross section cut along the thickness direction (Z direction) of the reflective mask blank.

[0052] <Buffer layer> In addition, in the reflective mask blank of the present invention, a buffer layer may be formed between the protective film 13 and the absorber film 14 . The buffer layer is a layer that protects the multilayer reflective film when dry etching and defect repair are performed. The material for the buffer layer is not particularly limited, and examples thereof include SiO2 and CrN.

[0053] <Low reflective layer> Furthermore, in the reflective mask blank of this embodiment, a low reflective layer may be formed on the absorber film 14. The low-reflection layer is composed of a film that has low reflection in the inspection light used to inspect the mask pattern. When manufacturing a reflective mask, after forming a pattern on the absorber film, it is inspected whether the pattern is formed as designed. In the inspection of this mask pattern, an inspection machine that uses light of about 193 nm or 257 nm as the inspection light is usually used. That is, the inspection is performed based on the difference in reflectance of the light of about 193 nm or 257 nm, specifically, the difference in reflectance between the surface where the absorber film is removed and exposed by pattern formation and the absorber film surface that is not removed by pattern formation and remains. Here, the former is the protective film surface. Therefore, if the difference in reflectance between the protective film surface and the absorber film surface for the wavelength of the inspection light is small, the contrast during inspection will be poor, and accurate inspection will not be possible. If the difference in reflectance between the protective film surface and the absorber film surface for the wavelength of the inspection light is small, the formation of the low-reflection layer will improve the contrast during inspection. The material of the low reflective layer is not particularly limited, and examples thereof include tantalum oxynitride, etc. Since the low reflective layer corresponds to the first outermost layer from the side opposite to the substrate in the pattern film, it is preferable that the formula (3) is satisfied.

[0054] [Reflective mask] The reflective mask of this embodiment has a pattern formed by patterning the pattern film in the reflective mask blank of the present invention. That is, the reflective mask of this embodiment includes, in this order, a substrate, a multilayer reflective film that reflects EUV light, and a pattern formed by patterning the pattern film, and further includes other layers such as a protective film as necessary. The layers other than the pattern (other layers such as the substrate, multilayer reflective film, and protective film) are as explained for the reflective mask blank. The pattern will be explained in the "Method of Manufacturing a Reflective Mask" below.

[0055] [Reflection mask manufacturing method] In the manufacturing method of the reflective mask of this embodiment, the pattern film in the reflective mask blank of this embodiment is patterned. That is, the reflective mask of this embodiment can be manufactured by using the above-mentioned reflective mask blank of this embodiment. For manufacturing the reflective mask for EUV lithography, a photolithography method capable of high-definition patterning is most suitable.

[0056] In this embodiment, a method for manufacturing a reflective mask using photolithography will be described by taking as an example a case in which a reflective mask blank 10 shown in FIG. 1 is used.

[0057] First, a resist film (not shown) is formed on the outermost surface (the absorber film 14 which is the uppermost layer of the pattern film 15) of the reflective mask blank 10 shown in Fig. 1. The thickness of the resist film may be, for example, 100 nm. Next, a desired pattern is drawn (exposed) on this resist film, and the resist film is further developed and rinsed to form a predetermined resist pattern (not shown).

[0058] Next, the pattern film 15 (absorber film 14) is dry-etched with an etching gas containing a fluorine-based gas such as SF6 using a resist pattern (not shown) as a mask to form a pattern (not shown). After the pattern is formed, the resist pattern (not shown) is removed.

[0059] Here, the etching rate of the pattern film 15 (absorber film 14) depends on the material forming the pattern film 15 (absorber film 14) and conditions such as etching gas, etc. Since the pattern film 15 (absorber film 14) is made of a multilayer film of different materials, the etching rate and conditions such as etching gas may change for each layer of different materials.

[0060] In this way, a pattern is formed. If the pattern film 15 (absorber film 14) made of a multilayer film can be continuously etched by dry etching using one type of etching gas, the effect of simplifying the process can be obtained. Next, wet cleaning is performed using an acidic or alkaline aqueous solution, and a reflective mask for EUV lithography that achieves high reflectance is obtained.

[0061] In addition, as the etching gas, in addition to SF6, fluorine-based gases such as CHF3, CF4, C2F6, C3F6, C4F6, C4F8, CH2F2, CH3F, C3F8, and F, and mixed gases containing these fluorine gases and O2 at a predetermined ratio can be used. When etching the pattern film 15 (absorber film 14) made of a multilayer film, other gases may be used as long as they are useful for processing. Examples of other gases include chlorine-based gases such as Cl2, SiCl4, CHCl3, CCl4, and BCl3, and mixed gases thereof, mixed gases containing chlorine-based gases and He at a predetermined ratio, mixed gases containing chlorine-based gases and Ar at a predetermined ratio, halogen gases containing at least one selected from fluorine gas, chlorine gas, bromine gas, and iodine gas, and at least one or more selected from the group consisting of hydrogen halide gas. Furthermore, mixed gases containing these gases and oxygen gas, etc. can be used.

[0062] As described above, the present specification discloses the following configurations. <1> A binary-type reflective mask blank including a substrate, a multilayer reflective film that reflects EUV light, and a pattern film in this order, the pattern film having a laminated structure including a total of L layers each having a different refractive index (where L is a natural number of 2 or more), and an absorption coefficient of the i-th layer in the pattern film from the side opposite to the substrate being k i The thickness of the i-th layer in the pattern film from the side opposite to the substrate is d i (nm), the total thickness of the pattern film is d, the exposure wavelength is λ (nm), and P i 1-exp(-2π / λ*d i k i ) a reflective mask blank which satisfies the following formula (1):

[0063]

number

[0064] <2> The reflection amplitude of the i-th layer from the opposite side of the substrate in the pattern film is defined as r i The reflective mask blank according to the above [1], which satisfies the following formula (2):

[0065]

number

[0066] <3> the refractive index n1 of the outermost layer of the first layer from the side opposite to the substrate in the pattern film is 0.950 or less; <1> or <2> The reflective mask blank according to claim 1. <4> At least one of the differences |Δk| in absorption coefficient k between two adjacent layers in the pattern film is 0.0200 or more; <1> ~ <3> 13. The reflective mask blank according to claim 12, <5> The refractive index of the i-th layer in the pattern film from the opposite side to the substrate is n i and a film thickness d1 of the outermost layer of the pattern film from the side opposite to the substrate satisfies the following formula (3): <1> ~ <4> 13. The reflective mask blank according to claim 12, |(λ / 4n1+λ / 2n1*x)-d1|<2.50...Equation (3) In the formula (3), x is an integer of 0 or more. <6> The reflectance of the pattern film is 1.3% or less. <1> ~ <5> 13. The reflective mask blank according to claim 12, <7> The reflectance of the pattern film is 1% or less. <1> ~ <6> 13. The reflective mask blank according to claim 12, <8> The total thickness d of the pattern film is 45 nm or less. <1> ~ <7> 13. The reflective mask blank according to claim 12, <9> The method further comprises providing a protective film between the multilayer reflective film and the pattern film. <1> ~ <8> 13. The reflective mask blank according to claim 12, <10> the above <1> ~ <9> 13. A reflective mask having a pattern formed by patterning the pattern film in the reflective mask blank according to any one of claims 1 to 12. <11> the above <1> ~ <9> 13. A method for producing a reflective mask, comprising patterning the pattern film in the reflective mask blank according to any one of claims 1 to 12. EXAMPLES

[0067] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples. Examples 1 to 3 are comparative examples, and Examples 4 to 9 are working examples.

[0068] (Example 1) The reflective mask blank of Example 1 comprises 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-based glass substrate (thickness: 6.3 mm) was selected as the substrate, a laminated structure (thickness: 272 nm) in which a silicon film (thickness: 4.5 nm) and a molybdenum film (thickness: 2.3 nm) were alternately stacked so that the number of units was 40 was selected as the multilayer reflective film, a ruthenium (Ru) film (thickness: 2.5 nm) was selected as the protective film, and a laminated structure (L=2) of a tantalum nitride (TaN) film (thickness d2: 37.0 nm) and a ruthenium (Ru) film (thickness d1: 3.3 nm) was selected as the pattern film (absorber film) (thickness d of the pattern film: 40.3 nm). Note that the substrate side of the absorber film is a tantalum nitride (TaN) film, and the opposite side of the absorber film to the substrate is a ruthenium (Ru) film. The refractive index n1 and absorption coefficient k1 of the ruthenium film were set to values ​​at a wavelength of 13.5 nm, (n1, k1) = (0.886, 0.017), and the refractive index n2 and absorption coefficient k2 of the tantalum nitride (TaN) film were set to values ​​at a wavelength of 13.5 nm, (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 the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 1, in which the pattern film has a two-layer structure of a TaN film (substrate side: thickness d2: 37.0 nm) and a Ru film (opposite side to the substrate: thickness d1: 3.3 nm). The reflectance of the pattern film at a wavelength of 13.5 nm was 2.62% (Table 1). Figure 2 was obtained by performing an optical multilayer film simulation.

[0069] (Example 2) In Example 1, instead of selecting a layered structure (L=2) of a tantalum nitride (TaN) film (film thickness d2: 37.0 nm) and a ruthenium (Ru) film (film thickness d1: 3.3 nm) as the pattern film (absorber film) (film thickness d: 40.3 nm), a layered structure (L=2) of a tantalum nitride (TaN) film (film thickness d2: 44.0 nm) and a ruthenium (Ru) film (film thickness d1: 3.8 nm) was selected as the pattern film (absorber film) (film thickness d: 47.8 nm). 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 the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 2, in which the pattern film 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). The reflectance of the pattern film at a wavelength of 13.5 nm was 1.36% (Table 1). Figure 3 was obtained by performing an optical multilayer film simulation.

[0070] (Example 3) In Example 1, instead of selecting a laminated structure (L=2) of a tantalum nitride (TaN) film (film thickness d2: 37.0 nm) and a ruthenium (Ru) film (film thickness d1: 3.3 nm) as a pattern film (absorber film) (film thickness d: 40.3 nm), a laminated structure (L=3) 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 side to the substrate: film thickness d1: 4.5 nm) was selected as a pattern film (absorber film) (film thickness d: 39.7 nm), except that it was the same as Example 1. Note that the refractive index n2 and absorption coefficient k2 of the SiN film were used as values ​​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 the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 3, which has a three-layer structure of a pattern film 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 side to the substrate: thickness d1: 4.5 nm). The reflectance of the pattern film at a wavelength of 13.5 nm was 4.01% (Table 1). Figure 4 was obtained by performing an optical multilayer film simulation.

[0071] (Example 4) In Example 1, instead of selecting a laminated structure (L=2) of a tantalum nitride (TaN) film (film thickness d2: 37.0 nm) and a ruthenium (Ru) film (film thickness d1: 3.3 nm) as the pattern film (absorber film) (film thickness d: 40.3 nm), a laminated structure (L=2) 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) was selected as the pattern film (absorber film) (film thickness d: 40.5 nm), except that it was the same as Example 1. Note that the refractive index n1 and absorption coefficient k1 of the Pt film were used as values ​​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 the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 4, in which the pattern film has a two-layer structure of a TaN film (substrate side: thickness d2: 28.4 nm) and a Pt film (opposite side to the substrate: thickness d1: 12.1 nm). The reflectance of the pattern film at a wavelength of 13.5 nm was 0.84% ​​(Table 1). Figure 5 was obtained by performing an optical multilayer film simulation.

[0072] (Example 5) In Example 1, instead of selecting a layered structure (L=2) of a tantalum nitride (TaN) film (film thickness d2: 37.0 nm) and a ruthenium (Ru) film (film thickness d1: 3.3 nm) as the pattern film (absorber film) (film thickness d: 40.3 nm), a layered structure (L=2) of a TaN film (substrate side: film thickness d2: 27.3 nm) and a Pt film (opposite side to the substrate: film thickness d1: 13.4 nm) was selected as the pattern film (absorber film) (film thickness d: 40.7 nm). 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 the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 5, in which the pattern film has a two-layer structure of a TaN film (substrate side: thickness d2: 27.3 nm) and a Pt film (opposite side to the substrate: thickness d1: 13.4 nm). The reflectance of the pattern film at a wavelength of 13.5 nm was 0.94% (Table 1). Figure 6 was obtained by performing an optical multilayer film simulation.

[0073] (Example 6) In Example 1, instead of selecting a layered structure (L=2) of a tantalum nitride (TaN) film (film thickness d2: 37.0 nm) and a ruthenium (Ru) film (film thickness d1: 3.3 nm) as the pattern film (absorber film) (film thickness d: 40.3 nm), a layered structure (L=2) 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) was selected as the pattern film (absorber film) (film thickness d: 40.6 nm). 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 the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 6, in which the pattern film 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). The reflectance of the pattern film at a wavelength of 13.5 nm was 0.85% (Table 1). Figure 7 was obtained by performing an optical multilayer film simulation.

[0074] (Example 7) In Example 1, instead of selecting a laminated structure (L=2) of a tantalum nitride (TaN) film (film thickness d2: 37.0 nm) and a ruthenium (Ru) film (film thickness d1: 3.3 nm) as the pattern film (absorber film) (film thickness d: 40.3 nm), a laminated structure (L=2) 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) was selected as the pattern film (absorber film) (film thickness d: 40.8 nm), except that it was the same as Example 1. Note that the refractive index n2 and absorption coefficient k2 of the Cr film were used as values ​​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 the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 7, in which the pattern film has a two-layer structure of a Cr film (substrate side: film thickness d2: 38 nm) and a Ru film (opposite side to the substrate: film thickness d1: 2.8 nm). The reflectance of the pattern film at a wavelength of 13.5 nm was 0.95% (Table 1). Figure 8 was obtained by performing an optical multilayer film simulation.

[0075] (Example 8) In Example 1, instead of selecting a laminated structure (L=2) of a tantalum nitride (TaN) film (film thickness d2: 37.0 nm) and a ruthenium (Ru) film (film thickness d1: 3.3 nm) as the pattern film (absorber film) (film thickness d: 40.3 nm), a laminated structure (L=3) 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) was selected as the pattern film (absorber film) (film thickness d: 40.1 nm), except that it was the same as Example 1. The refractive index n2 and absorption coefficient k2 of the Si film were used as values ​​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 the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 8, which has a three-layer structure of a pattern film 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 side to the substrate: thickness d1: 3.9 nm). The reflectance of the pattern film at a wavelength of 13.5 nm was 0.82% (Table 1). Figure 9 was obtained by performing an optical multilayer film simulation.

[0076] (Example 9) In Example 1, instead of selecting a layered structure (L=2) of a tantalum nitride (TaN) film (film thickness d2: 37 nm) and a ruthenium (Ru) film (film thickness d1: 3.3 nm) as the pattern film (absorber film) (film thickness d: 40.3 nm), a layered structure (L=2) of a SnO2 film (substrate side: film thickness d2: 24.1 nm) and a Ru film (film thickness d1: 2.2 nm) was selected as the pattern film (absorber film) (film thickness d: 26.3 nm). 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 the exposure wavelength λ and the reflectance R for the reflective mask blank of Example 9, in which the pattern film has a two-layer structure of an SnO2 film (substrate side: thickness d2: 24.1 nm) and a Ru film (opposite side to the substrate: thickness d1: 2.8 nm). The reflectance of the pattern film at a wavelength of 13.5 nm was 0.29% (Table 1). Figure 10 was obtained by performing an optical multilayer film simulation.

[0077] [Table 1]

[0078] From Table 1, it can be seen that the reflective mask blanks (Examples 4 to 9) satisfying formula (1) can sufficiently reduce the reflectance of the pattern film (reflectance: 0.29 to 0.95%) while thinning the film thickness of the pattern film, whereas the reflective mask blanks (Examples 1 to 3) not satisfying formula (1) cannot sufficiently reduce the reflectance of the pattern film (reflectance: 1.36 to 4.01%).

[0079] Although the present invention has been described in detail and with reference to specific embodiments, it is apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2022-035462) filed on March 8, 2022, the contents of which are incorporated herein by reference. [Explanation of symbols]

[0080] 10 Reflective mask blanks 11 Substrate 12 Multilayer reflective film 13 Protective film 14 Absorber membrane 15 Patterned membrane

Claims

1. A reflective mask blank comprising, in this order, a substrate, a multilayer reflective film that reflects EUV light, and a pattern film, the pattern film contains at least one component of ruthenium (Ru) and platinum (Pt); The pattern film has a laminated structure having a total of L layers each having a different refractive index (where L is a natural number of 2 or more), The absorption coefficient of the i-th layer from the opposite side of the substrate in the pattern film is k ｉ The film thickness of the ith layer from the opposite side of the substrate in the pattern film is d ｉ (nm), the total film thickness of the pattern film is d, the exposure wavelength is λ (nm), and P ｉ 1-exp(-2π / λ*d ｉ k ｉ ) a reflective mask blank that satisfies the following formula (1): [Equation 1]

2. The reflective mask blank according to claim 1 , wherein the following formula (2) is satisfied, where r i is the reflection amplitude of the ith layer in the pattern film from the opposite side to the substrate: [Equation 2]

3. The refractive index n of the outermost layer of the pattern film from the opposite side to the substrate １ The reflective mask blank according to claim 1 , wherein the reflective mask blank has a reflective index of 0.950 or less.

4. 2. The reflective mask blank according to claim 1, wherein at least one difference |Δk| in absorption coefficient k between two adjacent layers in the pattern film is 0.0200 or more.

5. the refractive index of the i-th layer in the pattern film from the side opposite to the substrate is defined as n i , The film thickness d of the outermost layer of the pattern film from the opposite side to the substrate １ The reflective mask blank according to claim 1 , wherein the following formula (3) is satisfied: |(λ / 4n １ + λ / 2n １ *x) - d １ |< 2.50... Equation (3) In the formula (3), x is an integer of 0 or more.

6. 2. The reflective mask blank according to claim 1, wherein the reflectance of the pattern film is 1.3% or less.

7. 2. The reflective mask blank according to claim 1, wherein the reflectance of the pattern film is 1% or less.

8. 2. The reflective mask blank according to claim 1, wherein the total thickness d of the pattern film is 45 nm or less.

9. The reflective mask blank according to claim 1 , further comprising a protective film between the multilayer reflective film and the pattern film.

10. A reflective mask blank as described in claim 1, wherein the reflective mask blank is a binary type.

11. A reflective mask, wherein the pattern film in the reflective mask blank according to any one of claims 1 to 10 has a patterned pattern.

12. A method for manufacturing a reflective mask, comprising patterning the pattern film in the reflective mask blank according to any one of claims 1 to 10.

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