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

Abstract

Provided is a reflective mask blank having excellent flatness and having a conductive film that has a narrow distribution of transmittance of 632 nm and 1064 nm light.　This reflective mask blank includes a substrate, a conductive film disposed on one surface side of the substrate, a multilayer reflective film that is disposed on the other surface side of the substrate and that reflects EUV light, and an absorber film disposed on the side of the multilayer reflective film that is opposite to the substrate side. The conductive film contains one or more elements selected from the group consisting of tantalum and chromium, the total content of nitrogen and boron contained in the conductive film is more than 33 at.% in relation to the total atoms of the conductive film, the film thickness of the conductive film is 20–150 nm, the film thickness of the conductive film at the center of the substrate is greater than the film thickness of the conductive film at the end of the substrate, and the maximum film thickness difference of the conductive film in an in-plane direction is 0.30–1.00 nm.

Description

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

[0001] The present invention relates to a reflective mask used for EUV (Extreme Ultra Violet) exposure (i.e., for EUV lithography) used in the exposure process of semiconductor manufacturing, a method for manufacturing the same, and a reflective mask blank that is an original plate for the reflective mask, and a method for manufacturing the same. Note that in this specification, a reflective mask blank for EUV lithography is also simply referred to as a "reflective mask blank." A reflective mask for EUV lithography is also simply referred to as a "reflective mask."

[0002] In recent years, in order to further miniaturize semiconductor devices, EUV lithography using EUV light with a central wavelength of around 13.5 nm as a light source has been considered.

[0003] Due to the characteristics of EUV light, EUV exposure uses a reflective optical system and a reflective mask. A reflective mask has a multilayer reflective film that reflects EUV light formed on a substrate, and an absorber film that absorbs EUV light is patterned on the multilayer reflective film.

[0004] The EUV light incident on the reflective mask from the illumination optical system of the exposure tool is reflected by the areas without an absorber film (openings) and absorbed by the areas with an absorber film (non-openings). As a result, the mask pattern is transferred as a resist pattern onto the wafer through the reduced projection optical system of the exposure tool, and subsequent processing is carried out.

[0005] On the other hand, in the reflective mask blank before patterning the reflective mask and the absorber film, a conductive film for electrostatic chucking is often provided on the surface of the substrate opposite to the absorber film side. For example, Patent Document 1 discloses a reflective mask blank in which the conductive film contains at least one element selected from the group consisting of tantalum and chromium, and nitrogen.

[0006] Japanese Patent Application Laid-Open No. 2021-015295

[0007] In a reflective mask, a desired pattern is formed during the transfer of a mask pattern, so the reflective mask blank is required to have high flatness. Here, a reflective mask blank having high flatness means that the reflective mask blank itself is flat and free from warping. Furthermore, in order to improve substrate deformation due to internal stress in the multilayer reflective film or absorption layer, laser light having a wavelength of 632 nm and laser light having a wavelength of 1064 nm are also irradiated from the conductive film side of the reflective mask blank and the reflective mask. When improving substrate deformation by irradiating the laser light as described above, it is very complicated to adjust the irradiation amount of the laser light in the in-plane direction, so the transmittance of the laser light of the above wavelengths is required to be uniform in the in-plane direction of the conductive film.

[0008] The present inventors have studied the reflective mask blank described in Patent Document 1 and have found that it is sometimes impossible to simultaneously achieve the above-mentioned flatness and uniformity of laser light transmittance at the levels currently required, and therefore improvement in this regard has been desired.

[0009] The present invention has been made in view of the above-mentioned problems, and has an object of providing a reflective mask blank having a conductive film with a narrow distribution of transmittance for light of 632 nm and 1064 nm and excellent flatness. Another object of the present invention is to provide a method for manufacturing the reflective mask blank, as well as a reflective mask and a reflective mask manufacturing method.

[0010] As a result of intensive research into the above-mentioned problems, the inventors have found that it is important to adjust the content of elements contained in the conductive film and the film thickness of the conductive film in the in-plane direction, and have arrived at the present invention. That is, the inventors have found that the above-mentioned problems can be solved by the following configuration. [1] A reflective mask blank for EUV lithography having a substrate, a conductive film disposed on one surface of the substrate, a multilayer reflective film that reflects EUV light and is disposed on the other surface of the substrate, and an absorber film disposed on the side of the multilayer reflective film opposite to the substrate, wherein the conductive film contains one or more elements selected from the group consisting of tantalum and chromium, the total content of nitrogen and boron contained in the conductive film is more than 33 atomic % with respect to all atoms in the conductive film, the thickness of the conductive film is 20 to 150 nm, the thickness of the conductive film at the center of the substrate is greater than the thickness of the conductive film at an edge of the substrate, and the maximum thickness difference of the conductive film in an in-plane direction is 0.30 to 1.00 nm. [2] The reflective mask blank for EUV lithography according to [1], wherein the nitrogen content of the conductive film is 35 to 65 atomic % with respect to all atoms in the conductive film. [3] The reflective mask blank for EUV lithography according to [1] or [2], wherein the conductive film has a boron content of more than 0 atomic % and not more than 35 atomic % relative to all atoms in the conductive film. [4] The reflective mask blank for EUV lithography according to any one of [1] to [3], wherein the conductive film has an electrical resistivity of 0.05 to 0.35 mΩ cm. [5] The reflective mask blank for EUV lithography according to any one of [1] to [4], wherein the conductive film has a surface roughness of 0.60 nm or less on the surface opposite to the substrate side. [6] The reflective mask blank for EUV lithography according to any one of [1] to [5], wherein the conductive film has a multilayer structure consisting of two or more layers, and the outermost layer of the layers located farthest from the substrate contains tantalum and one or more elements selected from the group consisting of nitrogen and oxygen. [7] The reflective mask blank for EUV lithography according to [6], wherein the oxygen content of the outermost layer is 20 to 60 atomic % based on all atoms in the outermost layer.[8] The reflective mask blank for EUV lithography according to [6] or [7], wherein the oxygen content of the outermost layer is 40 to 50 atomic % based on all atoms in the outermost layer. [9] The reflective mask blank for EUV lithography according to any one of [1] to [8], wherein, when the transmittance of the conductive film for light at 632 nm is measured at three different points, the arithmetic mean value of the transmittances at the three points is defined as the average transmittance for light at 632 nm, and the difference between the maximum transmittance and the minimum transmittance among the transmittances at the three points is defined as the maximum transmittance difference for light at 632 nm, the ratio of the maximum transmittance difference for light at 632 nm of the conductive film to the average transmittance for light at 632 nm of the conductive film is less than 2.0%.

[10] The reflective mask blank for EUV lithography according to any one of [1] to [9], wherein, when the transmittance of the conductive film for light at 1064 nm is measured at three different points, the arithmetic mean value of the transmittances at the three points is defined as the average transmittance for light at 1064 nm, and the difference between the maximum transmittance and the minimum transmittance among the transmittances at the three points is defined as the maximum transmittance difference for light at 1064 nm, a ratio of the maximum transmittance difference for light at 1064 nm for the conductive film to the average transmittance for light at 1064 nm for the conductive film is less than 2.0%.

[11] A reflective mask for EUV lithography, having an absorber film pattern formed by patterning the absorber film of the reflective mask blank for EUV lithography according to any one of [1] to

[10] .

[12] A method for manufacturing a reflective mask for EUV lithography, comprising a step of patterning the absorber film of the reflective mask blank for EUV lithography according to any one of [1] to

[10] .

[13] A method for manufacturing a reflective mask blank for EUV lithography, comprising forming a conductive film on one surface of a substrate, forming a multilayer reflective film that reflects EUV light on the other surface of the substrate, and forming an absorber film on the side of the multilayer reflective film opposite to the substrate side, wherein the conductive film is formed in the presence of nitrogen gas, and the pressure during the formation of the conductive film is 0.1 to 0.4 Pa.

[14] A substrate with a conductive film, comprising: a substrate; and a conductive film disposed on one surface of the substrate, wherein the conductive film contains one or more elements selected from the group consisting of tantalum and chromium, the combined content of nitrogen and boron contained in the conductive film is greater than 33 atomic % relative to all atoms in the conductive film, the conductive film has a thickness of 20 to 150 nm, the thickness of the conductive film at the center of the substrate is greater than the thickness of the conductive film at the edge of the substrate, and the maximum difference in thickness of the conductive film in an in-plane direction is 0.30 to 1.00 nm.

[15] The substrate with a conductive film according to

[14] , wherein the nitrogen content of the conductive film is 35 to 65 atomic % relative to all atoms in the conductive film.

[16] The substrate with a conductive film according to

[14] or

[15] , wherein the boron content of the conductive film is greater than 0 atomic % and not more than 35 atomic % relative to all atoms in the conductive film.

[17] The substrate with a conductive film according to any one of

[14] to

[16] , wherein the conductive film has an electrical resistivity of 0.05 to 0.35 mΩ cm.

[18] The substrate with a conductive film according to any one of

[14] to

[17] , wherein the conductive film has a multilayer structure consisting of two or more layers, and among the layers, the outermost layer located farthest from the substrate contains tantalum and one or more elements selected from the group consisting of nitrogen and oxygen.

[19] The substrate with a conductive film according to

[18] , wherein the oxygen content of the outermost layer is 20 to 60 atomic % based on all atoms in the outermost layer.

[20] The substrate with a conductive film according to

[18] , wherein the oxygen content of the outermost layer is 40 to 50 atomic % based on all atoms in the outermost layer.

[21] The substrate with a conductive film according to any one of

[14] to

[20] , wherein when the transmittance of the conductive film at 632 nm light is measured at three different points, the arithmetic mean value of the transmittances at the three points is defined as the average transmittance of 632 nm light, and the difference between the maximum transmittance and the minimum transmittance among the transmittances at the three points is defined as the maximum transmittance difference of 632 nm light, the ratio of the maximum transmittance difference of the conductive film at 632 nm light to the average transmittance of the conductive film at 632 nm light is less than 2.0%.

[22] The substrate with a conductive film according to any one of

[14] to

[21] , wherein when the transmittance of the conductive film at 1064 nm light is measured at three different points, the arithmetic mean value of the transmittances at the three points is defined as the average transmittance of 1064 nm light, and the difference between the maximum transmittance and the minimum transmittance among the transmittances at the three points is defined as the maximum transmittance difference of 1064 nm light, the ratio of the maximum transmittance difference of the conductive film at 1064 nm light to the average transmittance of the conductive film at 1064 nm light is less than 2.0%.

[0011] According to the present invention, it is possible to provide a reflective mask blank having a conductive film with a narrow distribution of transmittance for light of 632 nm and 1064 nm and excellent flatness. Furthermore, according to the present invention, it is possible to provide a method for manufacturing a reflective mask blank, a reflective mask, and a method for manufacturing a reflective mask.

[0012] 1 is a schematic diagram showing an example of an embodiment of a reflective mask blank of the present invention. FIG. 2 is a plan view of the reflective mask blank of the present invention shown in FIG. 1 as seen from the conductive film side. FIG. 3 is a schematic diagram showing an example of a manufacturing process of a reflective mask using the reflective mask blank of the present invention.

[0013] The present invention will be described in detail below. The following description of the components may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0014] The meaning of each description in this specification is shown below. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In this specification, elements such as boron, carbon, nitrogen, oxygen, silicon, titanium, chromium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tantalum, rhenium, iridium, and platinum may be represented by their corresponding element symbols (B, C, N, O, Si, Ti, Cr, Zr, Nb, Mo, Ru, Rh, Pd, Ta, Re, Ir, and Pt, etc.).

[0015] <Reflective Mask Blank> The reflective mask blank of the present invention comprises a substrate, a conductive film disposed on one side of the substrate, a multilayer reflective film that reflects EUV light disposed on the other side of the substrate, and an absorber film disposed on the side of the multilayer reflective film opposite the substrate. In the reflective mask blank of the present invention, the conductive film contains one or more elements selected from the group consisting of tantalum and chromium, and the total content of nitrogen (N) and boron (B) contained in the conductive film is more than 33 atomic % based on the total atoms in the conductive film. Furthermore, in the reflective mask blank of the present invention, the conductive film has a thickness of 20 to 150 nm, the thickness of the conductive film at the center of the substrate is greater than the thickness of the conductive film at the edge of the substrate, and the maximum thickness difference of the conductive film in the in-plane direction is 0.30 to 0.80 nm. The reflective mask blank of the present invention will be described with reference to the drawings.

[0016] FIG. 1 is a cross-sectional view showing one example of an embodiment of the reflective mask blank of the present invention. The reflective mask blank 10 shown in FIG. 1 has a conductive film 22, a substrate 12, a multilayer reflective film 14, a protective film 16, and an absorber film 18, in this order. The conductive film 22 contains the predetermined elements described above, and the contents thereof also satisfy the conditions described above. Furthermore, the conductive film 22 has a film thickness that satisfies the conditions described above. Note that the protective film 16 shown in FIG. 1 may be omitted. Furthermore, the reflective mask blank 10 may have a hard mask film, described below, on the side of the absorber film 18 opposite the substrate 12 side.

[0017] Although the mechanism by which the reflective mask blank of the present invention has a conductive film with a narrow distribution of transmittances for 632 nm and 1064 nm light and excellent flatness is not entirely clear, the present inventors speculate as follows. The conductive film of the reflective mask blank of the present invention has a total content of N and B of more than 33 atomic % relative to all atoms in the conductive film and a predetermined film thickness, and therefore can transmit light of 632 nm and 1064 nm. Here, the present inventors have discovered that when the film thickness of the conductive film at the center of the substrate is greater than the film thickness of the conductive film at the edge of the substrate, and the maximum film thickness difference is within the above range, the distribution of the transmittances of the conductive film for 632 nm and 1064 nm light is narrowed. Furthermore, when the total content of N and B exceeds 33 atomic % relative to all atoms in the conductive film, it is believed that the stress generated by the conductive film is likely to be large. This makes it easier to balance the stress generated by the multilayer reflective film and the absorber film disposed on the other side of the substrate, and thus a reflective mask blank with excellent flatness can be obtained.

[0018] The structure of the reflective mask blank of the present invention will be described below.

[0019] [Substrate] The substrate of the reflective mask blank of the present invention preferably has a small thermal expansion coefficient. A substrate with a small thermal expansion coefficient can suppress distortion of the absorber film pattern due to heat during exposure to EUV light. The thermal expansion coefficient of the substrate is 0±1.0×10 at 20° C. －７ / °C, and 0±0.3×10 －７ / °C is more preferable. Examples of materials with a small thermal expansion coefficient include SiO ２ -TiO ２ However, the present invention is not limited to this, and substrates made of crystallized glass in which β-quartz solid solution is precipitated, quartz glass, metallic silicon, metal, and the like can also be used. ２ -TiO ２ The SiO-based glass ２ 90 to 95 mass% of TiO ２ It is preferable to use quartz glass containing 5 to 10 mass % of TiO ２When the content of SiO is 5 to 10 mass %, the linear expansion coefficient is approximately zero at around room temperature, and there is almost no change in dimension at around room temperature. ２ -TiO ２ The SiO-based glass ２ and TiO ２ It may contain other minor components.

[0020] The surface of the substrate on which the multilayer reflective film is laminated (hereinafter also referred to as the "first principal surface") preferably has high surface smoothness. The surface smoothness of the first principal surface can be evaluated by surface roughness. The surface roughness of the first principal surface is preferably 0.15 nm or less in terms of root-mean-square roughness Rq. Note that the surface roughness can be measured using an atomic force microscope, and the surface roughness is described as the root-mean-square roughness Rq based on JIS-B0601. The first principal surface is preferably surface-processed to achieve a predetermined flatness, in order to improve the pattern transfer accuracy and positional accuracy of a reflective mask obtained using the reflective mask blank. In a predetermined region of the first principal surface (e.g., a 132 mm × 132 mm region), the flatness of the substrate is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less. The flatness can be measured using a flatness measuring instrument manufactured by Fujinon Corporation. The size and thickness of the substrate are determined appropriately based on the design values ​​of the mask, etc. For example, the outer shape may be 6 inches (152 mm) square and the thickness may be 0.25 inches (6.3 mm). The substrate is often rectangular (oblong) or square. Furthermore, it is preferable that the substrate has high rigidity in order to prevent deformation due to film stress of films (multilayer reflective films, absorber films, etc.) formed on the substrate. For example, it is preferable that the Young's modulus of the substrate is 65 GPa or more.

[0021] [Multilayer reflective film] The multilayer reflective film of the reflective mask blank of the present invention is not particularly limited as long as it has the desired properties as a reflective film for an EUV mask blank. The multilayer reflective film preferably has a high reflectivity for EUV light. Specifically, when EUV light is incident on the surface of the multilayer reflective film at an incident angle of 6°, the maximum reflectivity for EUV light with a wavelength of around 13.5 nm is preferably 60% or more, more preferably 65% ​​or more. Similarly, even when a protective film is laminated on the multilayer reflective film, the maximum reflectivity for EUV light with a wavelength of around 13.5 nm is preferably 60% or more, more preferably 65% ​​or more.

[0022] Since multilayer reflective films can achieve high reflectivity for EUV light, they are typically formed by alternately stacking multiple high-refractive index layers, which exhibit a high refractive index for EUV light, and multiple low-refractive index layers, which exhibit a low refractive index for EUV light. The multilayer reflective film may be formed by stacking multiple cycles of a stack structure in which high-refractive index layers and low-refractive index layers are stacked in this order from the substrate side, or multiple cycles of a stack structure in which low-refractive index layers and high-refractive index layers are stacked in this order. The high-refractive index layer may be a layer containing Si. Examples of materials containing Si include elemental Si and Si compounds containing one or more elements selected from the group consisting of B, C, N, and O. The use of a high-refractive index layer containing Si results in a reflective mask with excellent reflectivity for EUV light. The low-refractive index layer may be a layer containing a metal selected from the group consisting of Mo, Ru, Rh, and Pt, or an alloy thereof. Si is commonly used for the high-refractive index layer, and Mo is commonly used for the low-refractive index layer. That is, Mo / Si multilayer reflective films are most common, but the multilayer reflective films are not limited to this, and Ru / Si multilayer reflective films, Mo / Be multilayer reflective films, Mo compound / Si compound multilayer reflective films, Si / Mo / Ru multilayer reflective films, Si / Mo / Ru / Mo multilayer reflective films, Si / Ru / Mo multilayer reflective films, and Si / Ru / Mo / Ru multilayer reflective films can also be used.

[0023] The thickness of each layer constituting the multilayer reflective film and the number of repeating units of the layer can be appropriately selected depending on the film material used and the reflectivity of the reflective layer required for EUV light. Taking a Mo / Si multilayer reflective film as an example, to obtain a multilayer reflective film with a maximum reflectivity of 60% or more for EUV light, it is sufficient to laminate a Mo film with a thickness of 2.3±0.1 nm and a Si film with a thickness of 4.5±0.1 nm so that the number of repeating units is 30 to 60.

[0024] Each layer constituting the multilayer reflective film can be formed to a desired thickness using a known film formation method, such as magnetron sputtering or ion beam sputtering. For example, when forming a multilayer reflective film using ion beam sputtering, ion particles are supplied from an ion source to a target of a high refractive index material and a target of a low refractive index material. When the multilayer reflective film is a Mo / Si multilayer reflective film, for example, a Si layer having a predetermined thickness is first formed on a substrate using an ion beam sputtering method, followed by a Mo layer having a predetermined thickness using an Mo target. This Si layer and Mo layer constitute one cycle, and 30 to 60 cycles are stacked to form the Mo / Si multilayer reflective film.

[0025] [Protective Film] The reflective mask blank of the present invention may have a protective film between the multilayer reflective film and the absorber film. The protective film is provided for the purpose of protecting the multilayer reflective film from damage during etching (usually a dry etching process) when a pattern is formed on the absorber film by the etching process. Examples of materials that can achieve the above purpose include materials containing at least one element selected from the group consisting of Ru and Rh. That is, it is preferable that the protective film contains at least one element selected from the group consisting of Ru and Rh. More specifically, the above-mentioned materials include Ru metal alone, Ru alloys containing Ru and one or more metals selected from the group consisting of Si, Ti, Nb, Rh, and Zr, Rh metal alone, Rh alloys containing Rh and one or more metals selected from the group consisting of Si, Ti, Nb, Ru, Ta, and Zr, Rh-containing nitrides containing the above-mentioned Rh alloys and nitrogen, and Rh-containing oxynitrides containing the above-mentioned Rh alloys, nitrogen, and oxygen. Also, materials that can achieve the above-mentioned object include Al and nitrides containing these metals and nitrogen, and Al. ２ O ３ Among these, materials that can achieve the above object are preferably Ru metal alone, Ru alloys, Rh metal alone, or Rh alloys. As the Ru alloy, a Ru—Si alloy is preferred, and as the Rh alloy, a Rh—Si alloy is preferred.

[0026] The thickness of the protective film is not particularly limited as long as it can function as a protective film. In order to maintain the reflectivity of EUV light reflected by the multilayer reflective film, the thickness of the protective film is preferably 1 to 10 nm, more preferably 1.5 to 6 nm, and even more preferably 2 to 5 nm. It is also preferable that the material of the protective film is Ru metal alone, a Ru alloy, Rh metal alone, or a Rh alloy, and that the thickness of the protective film is within the above-mentioned preferred thickness range.

[0027] The protective film may be a film consisting of a single layer, or may be a multilayer film consisting of multiple layers. When the protective film is a multilayer film, each layer constituting the multilayer film is preferably made of the above-mentioned preferred material. Furthermore, when the protective film is a multilayer film, it is also preferable that the total thickness of the multilayer film is within the above-mentioned preferred range. When the protective film is a multilayer film, it is preferable that the layer of the multilayer film arranged closest to the absorber film contains Rh. Furthermore, when the layer of the multilayer film arranged closest to the absorber film contains Rh, it is preferable that at least one of the other layers contains Ru.

[0028] The protective film can be formed by a known film formation method such as DC sputtering, magnetron sputtering, or 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. When forming a Rh film by magnetron sputtering, it is preferable to use a Rh target as the target and Ar gas as the sputtering gas.

[0029] [Absorber Film] The absorber film of the reflective mask blank of the present invention is required to have a high contrast between the EUV light reflected by the multilayer reflective film and the EUV light at the absorber film when the absorber film is patterned. The patterned absorber film (absorber film pattern) may function as a binary mask by absorbing EUV light, or may function as a phase shift mask that reflects EUV light and interferes with the EUV light from the multilayer reflective film to generate contrast.

[0030] When the absorber film pattern is used as a binary mask, the absorber film must absorb EUV light and have low reflectance for EUV light. Specifically, when EUV light is irradiated onto the surface of the absorber film, the maximum reflectance of EUV light at a wavelength of approximately 13.5 nm is preferably 2% or less. The absorber film may contain one or more metals selected from the group consisting of Ta, Ti, Sn, and Cr, as well as one or more components selected from the group consisting of O, N, B, Hf, and H. Among these, the absorber film preferably contains Ta and N or B. By containing N or B, the crystalline state of the absorber film can be made amorphous or microcrystalline. The crystalline state of the absorber film is preferably amorphous. This improves the smoothness and flatness of the absorber film. Furthermore, improving the smoothness and flatness of the absorber film reduces the edge roughness of the absorber film pattern, thereby improving the dimensional accuracy of the absorber film pattern. When the absorber film pattern is used as a binary mask, the film thickness of the absorber film is preferably 40 to 70 nm, more preferably 50 to 65 nm.

[0031] When the absorber film pattern is used as a phase shift mask, the reflectance of the absorber film to EUV light is preferably 2% or more. To obtain a sufficient phase shift effect, the reflectance of the absorber film is preferably 9 to 15%. Using the absorber film as a phase shift mask improves the contrast of the optical image on the wafer and increases the exposure margin. Examples of materials for forming the phase shift mask include simple Ru metal, Ru alloys containing Ru and one or more metals selected from the group consisting of Cr, Au, Pt, Re, Hf, Ta, W, Ti, and Si, Ta and Nb alloys, oxides containing Ru alloys or TaNb alloys and oxygen, nitrides containing Ru alloys or TaNb alloys and nitrogen, oxynitrides containing Ru alloys or TaNb alloys, oxygen, and nitrogen, and compounds containing at least one metal element selected from the group consisting of Pd, Ir, Pt, Ag, Ni, and Co. When the absorber film pattern is used as a phase shift mask, the thickness of the absorber film is preferably 30 to 60 nm, more preferably 35 to 55 nm.

[0032] The absorber film may be a single layer film or a multilayer film made up of multiple films. When the absorber film is a single layer film, the number of steps in manufacturing the mask blank can be reduced, thereby improving production efficiency. When the absorber film is a multilayer film, the layer disposed on the side opposite to the protective film side of the absorber film may be an anti-reflection film used when inspecting the absorber film pattern using inspection light (e.g., wavelength 193 to 248 nm). Examples of materials that form the anti-reflection film include materials containing Ta and O.

[0033] The absorber film can be formed by a known film formation method such as magnetron sputtering, ion beam sputtering, etc. For example, when a Ta nitride film is formed as the absorber film by magnetron sputtering, the absorber film can be formed by sputtering using a Ta target and supplying a gas containing Ar gas and nitrogen gas.

[0034] [Conductive film] The reflective mask blank of the present invention has a conductive film on the surface (second main surface) opposite to the first main surface of the substrate. By providing the conductive film, the reflective mask blank can be handled using an electrostatic chuck. The conductive film of the reflective mask blank of the present invention will be described in detail below.

[0035] The conductive film of the reflective mask blank of the present invention contains one or more elements selected from the group consisting of Ta and Cr. The conductive film preferably contains Ta in order to obtain better flatness of the reflective mask blank.

[0036] The total content of N and B contained in the conductive film is greater than 33 atomic % relative to all atoms in the conductive film. When the conductive film contains N and B, the N content is preferably 35 to 65 atomic %, more preferably 40 to 55 atomic %, relative to all atoms in the conductive film. When the conductive film contains N and B, the B content is preferably greater than 0 atomic % and not greater than 45 atomic %, more preferably 10 to 40 atomic %, relative to all atoms in the conductive film. The B content may also be greater than 0 atomic % and not greater than 35 atomic %, relative to all atoms in the conductive film. The content of each element in the conductive film is determined by analysis using X-ray photoelectron spectroscopy (XPS). Detailed content analysis methods follow the methods described in the Examples section below. Furthermore, when the conductive film has a multilayer structure, the analysis is performed while etching the surface of the conductive film from the side opposite the substrate side, for example, by using ion sputtering with argon or the like, and the content of each element in each layer of the conductive film is analyzed.

[0037] When the conductive film contains N but not B, the N content is preferably 35 to 65 atomic %, more preferably 40 to 60 atomic %, and even more preferably 45 to 55 atomic %, based on the total atoms in the conductive film.

[0038] When the conductive film does not contain N but contains B, the content of B is preferably more than 33 atomic % and not more than 45 atomic %, more preferably 35 to 40 atomic %, based on all atoms in the conductive film. The content of B may also be not more than 35 atomic % based on all atoms in the conductive film.

[0039] The conductive film may contain elements other than Cr, Ta, N, and B. Examples of elements that the conductive film may contain include C, O, fluorine (F), hydrogen (H), silicon (Si), and Ar.

[0040] Specific materials constituting the conductive film include, for example, CrN, CrON, CrB, CrBN, CrCN, TaN, TaON, TaB, TaBN, TaCN, and CrTaN, with CrN, TaN, or TaBN being preferred. Note that notations such as "CrON" refer to materials containing Cr, O, and N, and the content ratios of these elements are not limited as long as the above requirements are met.

[0041] The conductive film may have a single layer structure or a multilayer structure. When the conductive film has a multilayer structure, the number of layers constituting the conductive film is not particularly limited, but is preferably four layers or less, more preferably three layers or less, and even more preferably two layers. When the conductive film has a multilayer structure, any of the layers constituting the conductive film contains one or more elements selected from the group consisting of Ta and Cr. It is more preferable that all of the layers constituting the conductive film contain one or more elements selected from the group consisting of Ta and Cr. When the conductive film has a multilayer structure, the conductive film as a whole satisfies the above-mentioned requirements for the N and B contents.

[0042] When the conductive film has a multilayer structure and contains N but not B, the N content is preferably 35 to 55 atomic %, more preferably 40 to 50 atomic %, based on the total atoms in the conductive film.

[0043] Here, when the layer furthest from the substrate among the layers constituting the conductive film is defined as the outermost layer, the outermost layer preferably contains Ta. Furthermore, it is also preferable that the outermost layer is a layer containing Ta and one or more elements selected from the group consisting of N and O. When the outermost layer is a layer containing Ta and one or more elements selected from the group consisting of N and O, the O content is preferably 20 to 60 atomic %, more preferably 30 to 50 atomic %, and particularly preferably 40 to 50 atomic %, based on all atoms in the outermost layer. The outermost layer does not have to contain N.

[0044] The conductive film has a thickness of 20 to 150 nm. When the conductive film has a multilayer structure, the total thickness of the layers constituting the conductive film is 20 to 150 nm. The conductive film preferably has a thickness of 25 to 120 nm, more preferably 30 to 100 nm, in terms of achieving better flatness. The conductive film thickness is determined by X-ray reflectivity (XRR). A method for calculating the conductive film thickness will be described later.

[0045] When the conductive film has a multilayer structure, the ratio of the thickness of the layer containing one or more elements selected from the group consisting of Ta and Cr and having a total content of N and B of more than 33 atomic % to the total thickness of the conductive film is preferably 0.50 or more, more preferably 0.70 or more, and even more preferably 0.80 or more. The upper limit of this ratio is less than 1.00 and is often 0.95 or less.

[0046] In the reflective mask blank of the present invention, the film thickness of the conductive film at the center of the substrate (hereinafter also simply referred to as the "center") is greater than the film thickness of the conductive film at the edge of the substrate (hereinafter also simply referred to as the "edge"). For example, when the substrate is rectangular or square, the center of the substrate refers to the intersection of two diagonals. In this specification, the edge of the substrate is defined as follows. When the substrate is rectangular or square, first, in the in-plane direction of the substrate, the center of the substrate is set as the origin, and an X axis parallel to one side of the substrate and a Y axis perpendicular to the X axis are defined. Next, the distance from the origin to the intersection of the X axis and one side of the substrate is defined as Lx, and the distance from the origin to the intersection of the Y axis and one side of the substrate is defined as Ly. Here, the edge of the substrate refers to a point that is (0.868Lx, 0.868Ly) in a coordinate system described by the X axis and Y axis when the center of the substrate is set as the origin. The film thickness at the edge may be any film thickness at any position within a circular region with a radius of 0.5 mm centered on the edge. The film thickness at the center of the substrate may be any film thickness at any position within a circular region with a radius of 0.5 mm centered on the center of the substrate. For example, if the substrate is a square with sides of 152 mm, the center of the substrate is defined as the intersection of the diagonals, and an X-axis parallel to one side and a Y-axis perpendicular to the X-axis are defined. The edge of the substrate is a point 66 mm away from the origin in the X-axis direction and 66 mm away from the Y-axis direction.

[0047] That is, "the thickness of the conductive film at the center is greater than the thickness of the conductive film at the edge of the substrate" means that the thickness of the conductive film at the center is greater than the thickness of the conductive film at the edge (the point at the coordinates). A Smart Lab HTP from Rigaku Corporation was used to measure the thickness of the conductive film at the center and the edge by XRR. CuKα rays were used as the X-ray source, with a tube voltage of 40 kV and a tube current of 30 mA. The accompanying software (GlobalFit) was used for analysis. Furthermore, in the XRR measurement, X-rays were irradiated onto the conductive film so that the center of the X-ray beam coincided with the center or the edge of the substrate.

[0048] The above describes the center and edges of a rectangular or square substrate, but when the substrate is circular, the center of the substrate is the center of the circle, and the edges of the substrate are points that are 0.868 times the radius of the substrate from the center of the substrate in the in-plane direction of the substrate.

[0049] The thickness of the conductive film is determined by the following method. First, the center and the edge are determined by the method described above. Here, the distance between the center and the edge on a line (a diagonal of the substrate) passing through the center and the edge is defined as Ld. A point is determined on the diagonal toward the edge where the distance from the center is 33Ld / 66. The thickness of the conductive film is measured at three points, including the above point, the center, and the edge, using the method described above, and the arithmetic mean value is defined as the thickness of the conductive film. The thicknesses at the three points may be measured at any position within a circular region with a radius of 0.5 mm centered on each of the three points. For example, if the substrate is a square with sides of 152 mm, the center of the substrate is defined as the intersection of the diagonals, and an X axis parallel to one side and a Y axis perpendicular to the X axis are defined. XRR measurements are performed at points (0,0), (33,33), and (66,66), and the arithmetic mean value is defined as the thickness of the conductive film. The units of the values ​​in the above coordinates are mm. When the substrate is a square with sides of 152 mm, the above three points are arranged as shown in Figure 2. Figure 2 is a plan view of the reflective mask blank 10 shown in Figure 1 as seen from the conductive film 22 side, and points A to C correspond to points (0,0) (center), (33,33), and (66,66) (edge), respectively.

[0050] In the reflective mask blank of the present invention, the maximum film thickness difference in the in-plane direction of the conductive film is 0.30 to 0.80 nm. In this specification, the maximum film thickness difference refers to the value obtained by subtracting the minimum film thickness from the maximum film thickness of the conductive film at each point measured when determining the film thickness of the conductive film described above. The maximum film thickness difference is preferably 0.40 to 0.65 nm, more preferably 0.50 to 0.60 nm, since this tends to narrow the distribution of the transmittance of 632 nm light. Similarly, the maximum film thickness difference determined from (0,0), (-33,33), and (-66,66) is preferably 0.30 to 0.80 nm, more preferably within the preferred range described above. Similarly, the maximum film thickness difference determined from (0,0), (-33,-33), and (-66,-66) is preferably 0.30 to 0.80 nm, more preferably within the preferred range described above. Furthermore, in the same manner as above, the maximum film thickness difference calculated from (0,0), (33,-33) and (66,-66) is preferably 0.30 to 0.80 nm, and more preferably within the above-mentioned preferred range.

[0051] The electrical resistivity of the conductive film is preferably 0.35 mΩ cm or less in order to obtain a sufficient holding force when electrostatic chucking. The lower limit of the electrical resistivity is often 0.05 mΩ cm or more. The electrical resistivity of the conductive film is measured by the method shown in the examples below.

[0052] The surface roughness of the conductive film on the surface opposite the substrate side is preferably 0.60 nm or less, more preferably 0.50 nm or less. The surface roughness is often 0.01 nm or more. The surface roughness of the conductive film on the surface opposite the substrate side is the root-mean-square roughness (Rq), and can be measured in the same manner as the surface roughness of the substrate. Details of the method for measuring the surface roughness follow the method described in the Examples below.

[0053] The transmittance of a conductive film at 632 nm preferably satisfies the following relationship: First, the transmittance of 632 nm light is measured at the three points, and the average transmittance of 632 nm light, which is the arithmetic mean of the transmittances at the three points, and the maximum transmittance difference of 632 nm light, which is the maximum transmittance minus the minimum transmittance, are calculated. Here, the ratio of the maximum transmittance difference of 632 nm light to the average transmittance of 632 nm light is preferably less than 2.0%, more preferably less than 1.5%, and even more preferably less than 1.2%. The transmittance of a conductive film at 632 nm is measured using the following method: First, a substrate with a conductive film formed on the substrate is prepared. If a multilayer reflective film, an absorber film, or the like is formed on the substrate, these are removed. Next, at the three points, light is incident from the side where the conductive film is formed, in the direction normal to the surface of the conductive film, and the transmittance at 632 nm is calculated using a spectrophotometer. The spectrophotometer used is a "V-780" manufactured by JASCO Corporation, and the wavelength range is 175 to 2000 nm.

[0054] Furthermore, it is preferable that the transmittance of the conductive film at 1064 nm light satisfy the following relationship: First, the transmittance of 1064 nm light is measured at the above three points, and the average transmittance of 1064 nm light, which is the arithmetic mean of the transmittances at the three points, and the maximum transmittance difference of 1064 nm light, which is the value obtained by subtracting the minimum transmittance from the maximum transmittance, are determined. Here, the ratio of the maximum transmittance difference of 1064 nm light to the average transmittance of 1064 nm light is preferably less than 2.0%, more preferably less than 1.5%, and even more preferably less than 1.2%. The transmittance of the conductive film at 1064 nm light can be measured in the same manner as in the measurement of the transmittance of 632 nm light described above.

[0055] The conductive film may be formed by any known film-forming method without any particular limitation, provided that it satisfies the above-mentioned requirements. For example, the conductive film may be formed by a sputtering method such as magnetron sputtering or ion beam sputtering, a CVD method, or a vacuum deposition method. The method for manufacturing a reflective mask blank, which will be described later, is preferably applicable.

[0056] [Other Films] The reflective mask blank of the present invention may have other films. Examples of such films include a hard mask film. The hard mask film is preferably disposed on the side opposite to the substrate side of the absorber film. As the hard mask film, it is preferable to use a material that is highly resistant to dry etching, such as a Cr-based film or a Si-based film. Examples of Cr-based films include Cr, and materials containing Cr and one or more elements selected from the group consisting of O, N, C, and H. Specific examples include CrO and CrN. Examples of Si-based films include Si, and materials containing Si and one or more elements selected from the group consisting of O, N, C, and H. Specific examples include SiO ２ , SiON, SiN, SiO, Si, SiC, SiCO, SiCN, and SiCON. When a hard mask film is formed on the absorber film, dry etching can be performed even if the minimum line width of the absorber film pattern is small. Therefore, it is effective for miniaturizing the absorber film pattern.

[0057] <Method for manufacturing a reflective mask blank> One embodiment of the method for manufacturing a reflective mask blank of the present invention includes a method for manufacturing a reflective mask blank, which comprises forming a conductive film on one surface of a substrate, forming a multilayer reflective film that reflects EUV light on the other surface of the substrate, and forming an absorber film on the side of the multilayer reflective film opposite to the substrate side. Here, the conductive film is formed in the presence of one or more gases selected from the group consisting of nitrogen gas and oxygen gas, and the pressure during the formation of the conductive film is 0.1 to 0.4 Pa. Note that "forming a conductive film in the presence of nitrogen gas" means that nitrogen gas (N ２ Note that forming a conductive film in the presence of oxygen gas means that oxygen gas (O ２ The phrase "forming a conductive film in the presence of nitrogen gas and oxygen gas" refers to the inclusion of nitrogen gas (N ２ gas) and oxygen gas (O ２Furthermore, the phrase "the pressure during the formation of the conductive film is within the above pressure range" means that the pressure in the space (e.g., chamber) where the conductive film is formed is within the above pressure range.

[0058] The conductive film is preferably formed by a sputtering method, and more preferably by a magnetron sputtering method. The conductive film is formed by controlling the pressure in the space where the conductive film is formed to 0.1 to 0.4 Pa. When the conductive film is formed by a sputtering method (preferably a magnetron sputtering method), the pressure in the chamber where the sputtering is performed is controlled within the above range to form the conductive film. The pressure is controlled, for example, by evacuating the chamber with a vacuum pump connected to the chamber while supplying gas from a gas supply means connected to the chamber while controlling the flow rate. In this case, a vacuum gauge may be placed in the chamber, and the gas flow rate may be adjusted while monitoring the pressure in the chamber with the vacuum gauge. In the above method, the gas supplied is preferably a mixed gas containing a rare gas and one or more gases selected from the group consisting of nitrogen gas and oxygen gas. Examples of rare gases include Ne gas, Ar gas, Kr gas, and Xe gas, with Ar gas being preferred. The content of nitrogen gas in the mixed gas is preferably 5 to 50% by volume, more preferably 10 to 30% by volume, based on the total volume of the mixed gas.

[0059] When the conductive film is formed by sputtering (preferably magnetron sputtering), the film formation rate is preferably 0.5 to 20 nm / min, more preferably 1 to 20 nm / min, further preferably 2 to 10 nm / min, and particularly preferably 2 to 4.7 nm / min. When the conductive film is formed by magnetron sputtering, the input power is preferably 500 to 1500 W, more preferably 700 to 1200 W.

[0060] When the conductive film had a multi-layer structure consisting of two or more layers, the first layer on the substrate side was formed, and then the second and subsequent layers were formed under the same film-forming conditions as the first layer.

[0061] The method for forming the multilayer reflective film and the absorber film is as described above, and known methods can be applied.

[0062] <Method for manufacturing a reflective mask and a reflective mask> The reflective mask of the present invention is obtained by patterning the absorber film of the reflective mask blank of the present invention. One example of the method for manufacturing a reflective mask will be described with reference to FIG.

[0063] FIG. 3A shows a state in which a resist pattern 40 is formed on a reflective mask blank having, in this order, a conductive film 22, a substrate 12, a multilayer reflective film 14, a protective film 16, an absorber film 18, and a hard mask film 20. The resist pattern 40 can be formed using a known method, for example, by applying a resist to the hard mask film 20 of the reflective mask blank, exposing it to light, and developing it to form the resist pattern 40. The resist pattern 40 corresponds to a pattern formed on a wafer using a reflective mask. Then, using the resist pattern 40 in FIG. 3A as a mask, the absorber film 18 is etched and patterned, and the resist pattern 40 is removed to obtain a laminate having the absorber film pattern 18pt shown in FIG. 3B. Next, as shown in FIG. 3C, a resist pattern 42 corresponding to the frame of the exposed region is formed on the laminate in FIG. 3B, and dry etching is performed using the resist pattern 42 in FIG. 3C as a mask. Dry etching is performed until the substrate 12 is reached. After the dry etching, the resist pattern 42 is removed to obtain the reflective mask shown in FIG.

[0064] A reflective mask obtained by patterning the absorber film of the reflective mask blank of the present invention can be suitably used as a reflective mask for exposure to EUV light.

[0065] The present invention will be described in more detail below based on examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the examples shown below. Note that Examples 1, 2, and 5 described below are examples, and Examples 3, 4, 6, and 7 are comparative examples.

[0066] Example 1 First, the procedure for obtaining the substrate with a conductive film of Example 1 will be described as a representative example.

[0067] [Substrate] First, as a substrate, SiO ２ -TiO ２ A glass substrate (6-inch (152 mm) square outer diameter, 6.3 mm thick) of this type was prepared. This glass substrate had a thermal expansion coefficient of 0.02×10 at 20° C. －７ / °C, Young's modulus is 67 GPa, Poisson's ratio is 0.17, and specific rigidity is 3.07 × 10 ７ m ２ / s ２ The quality assurance area of ​​the first main surface of the substrate was polished to have a root mean square roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less.

[0068] [Conductive Film] A TaN film (conductive film) was formed on one surface of the substrate by magnetron sputtering. The TaN film formation conditions were as follows: Target: Ta metal target Sputtering gas: Ar gas and N ２ Mixture of Ar gas with N gas (Ar gas: 81% by volume, N ２ Gas: 19% by volume Film formation pressure: 0.23 Pa Input power: 1000 W Film formation rate: 4.62 nm / min

[0069] By the above procedure, a substrate with a conductive film was obtained in Example 1. The obtained substrate with a conductive film was measured in the following manner.

[0070] [Measurement] (Conductive film composition) The composition of the formed conductive film was analyzed by XPS. For XPS, a "PHI 5000 VersaProbe" manufactured by ULVAC-PHI, Inc. was used. The compositions determined by analysis are shown in the table below. Note that elements other than those shown in the table below were the elements used in the target.

[0071] (Film Thickness) The film thickness of the conductive film was measured by the method described above. That is, XRR measurements were performed at each of the points (0,0), (33,33), and (66,66) around the intersection of the diagonal lines of the substrate, and the film thickness (arithmetic mean value) of the conductive film, the film thickness of the conductive film at the center of the substrate, the film thickness of the conductive film at the edge of the substrate, and the maximum film thickness difference in the in-plane direction of the conductive film were calculated.

[0072] Examples 2 to 7 Substrates with conductive films were obtained in the same manner as in Example 1, except that the film formation conditions were changed as shown in the table below. The measurement results are shown in the table below. In Examples 2 and 5, conductive film 1 was formed first, and then conductive film 2 was formed. The composition of conductive film 1 was measured after conductive film 2 was removed by argon ion sputtering from the region where XPS measurement was to be performed.

[0073] <Evaluation Methods and Criteria> The obtained substrates with conductive film were evaluated for the distribution of the transmittance of 632 nm light of the conductive film, flatness, electrical resistivity of the conductive film, and surface roughness. The evaluation methods and evaluation criteria are shown below.

[0074] [Transmittance Distribution] The transmittance distribution at 632 nm and the transmittance distribution at 1064 nm were measured using the method described above. That is, for the three points where the film thickness was measured, the transmittance at each wavelength was measured using a spectrophotometer (U-4100, manufactured by Hitachi High-Technologies Corporation), and the average transmittance at each wavelength and the maximum transmittance difference, which is the value obtained by subtracting the minimum transmittance from the maximum transmittance, were determined. From the ratio of the maximum transmittance difference to the determined average transmittance, the transmittance distribution at each wavelength was evaluated according to the following criteria. The results are shown in the table below. A: The ratio of the maximum transmittance difference to the average transmittance at 632 nm is less than 2.0%, and the ratio of the maximum transmittance difference to the average transmittance at 1064 nm is less than 2.0%. B: The requirement A above is not met.

[0075] [Flatness] The flatness of the conductive film-coated substrate was evaluated using the following procedure. The flatness of the conductive film-coated substrate was measured using a flatness measuring instrument manufactured by Fujinon Corporation. The flatness was evaluated based on the obtained flatness value according to the following criteria. The results are shown in the table below. A: Flatness of 0.4 μm or more B: Flatness of less than 0.4 μm Note that a flatness of a conductive film-coated substrate of A according to the above criteria corresponds to warping of the conductive film-coated substrate. If the conductive film-coated substrate is warped, when films such as a multilayer reflective film and an absorber film are formed on the side opposite the conductive film side of the substrate, the warping of the conductive film-coated substrate balances the stresses generated by the formation of these films, resulting in an increased flatness of the resulting reflective mask blank.

[0076] [Electrical Resistivity] The electrical resistivity of the conductive film on the substrate with the conductive film was evaluated by the following procedure. The thickness of the conductive film obtained by the above procedure was used to calculate the electrical resistivity. The results are shown in the table below. Evaluation equipment: Nitto Seiko Analytech Co., Ltd. Loresta GX Number of measurement points: 3 Measurement range: 149 mm x 149 mm

[0077] [Surface Roughness] The surface roughness (root mean square roughness Rq) of the surface of the conductive film opposite the substrate side was measured. The surface roughness was calculated by analyzing the results of measurements using an atomic force microscope manufactured by SII Corporation. The measurement range was 2 μm × 2 μm. The results are shown in the table below.

[0078] <Results> The configuration of each conductive film-coated substrate, the measurement results, and the evaluation results are shown in Table 1. In the table, in the column "Center film thickness > Edge film thickness," if the thickness of the conductive film at the center is thicker than the thickness of the conductive film at the edge, it is recorded as "A," and if not, it is recorded as "B."

[0079]

[0080] As shown in Table 1, it was confirmed that when the predetermined conditions for the conductive film described above are satisfied, the transmittance distribution of the conductive film becomes small. Furthermore, when the predetermined conditions for the conductive film described above are satisfied, the flatness of the substrate with the conductive film decreases, resulting in a high flatness of the resulting reflective mask blank. On the other hand, the results of Example 3 confirmed that the transmittance distribution of the conductive film does not become small when the film thickness of the conductive film at the center of the substrate is not greater than the film thickness of the conductive film at the edge of the substrate. The results of Example 4 confirmed that when the total content of nitrogen and boron contained in the conductive film is 33% or less relative to the total atoms of the conductive film, the flatness of the substrate with the conductive film increases, resulting in a high flatness of the resulting reflective mask blank.

[0081] Furthermore, by forming a multilayer reflective film and an absorber film by the above-mentioned method on the side opposite to the conductive film side of the conductive film-coated substrate obtained by the above procedure, a reflective mask blank of the present invention can be obtained.

[0082] The entire contents of the specifications, claims, drawings and abstracts of Japanese Patent Application No. 2023-169979 filed on September 29, 2023 and Japanese Patent Application No. 2024-009653 filed on January 25, 2024 are hereby incorporated by reference as the disclosure of the present invention.

[0083] REFERENCE SIGNS LIST 10 reflective mask blank 12 substrate 14 multilayer reflective film 16 protective film 18 absorber film 18pt absorber film pattern 22 conductive film 40, 42 resist pattern

Claims

1. A reflective mask blank for EUV lithography having: a substrate; a conductive film disposed on one surface of the substrate; a multilayer reflective film that reflects EUV light and is disposed on the other surface of the substrate; and an absorber film disposed on the side of the multilayer reflective film opposite to the substrate, wherein the conductive film contains one or more elements selected from the group consisting of tantalum and chromium, the total content of nitrogen and boron contained in the conductive film is more than 33 atomic % with respect to all atoms in the conductive film, the conductive film has a thickness of 20 to 150 nm, the thickness of the conductive film at the center of the substrate is greater than the thickness of the conductive film at an end of the substrate, and the maximum thickness difference of the conductive film in an in-plane direction is 0.30 to 1.00 nm.

2. A reflective mask blank for EUV lithography according to claim 1, wherein the nitrogen content of said conductive film is 35 to 65 atomic % based on the total atoms in said conductive film.

3. A reflective mask blank for EUV lithography according to claim 1 or 2, wherein the conductive film has a boron content of more than 0 atomic % and not more than 35 atomic % relative to all atoms in the conductive film.

4. A reflective mask blank for EUV lithography according to claim 1 or 2, wherein the electrical resistivity of the conductive film is 0.05 to 0.35 mΩ·cm.

5. A reflective mask blank for EUV lithography according to claim 1 or 2, wherein the surface roughness of the surface of said conductive film opposite to said substrate side is 0.60 nm or less.

6. A reflective mask blank for EUV lithography according to claim 1 or 2, wherein the conductive film has a multilayer structure consisting of two or more layers, and among the layers, the outermost layer located farthest from the substrate is a layer containing tantalum and one or more elements selected from the group consisting of nitrogen and oxygen.

7. A reflective mask blank for EUV lithography according to claim 6, wherein the oxygen content in the outermost layer is 20 to 60 atomic % based on all atoms in the outermost layer.

8. A reflective mask blank for EUV lithography according to claim 6, wherein the oxygen content in the outermost layer is 40 to 50 atomic % based on all atoms in the outermost layer.

9. A reflective mask blank for EUV lithography according to claim 1 or 2, wherein when the transmittance of the conductive film for 632 nm light is measured at three different points, an arithmetic mean value of the transmittances at the three points is defined as an average transmittance for 632 nm light, and a difference between the maximum transmittance and the minimum transmittance among the transmittances at the three points is defined as a maximum transmittance difference for 632 nm light, a ratio of the maximum transmittance difference for 632 nm light of the conductive film to the average transmittance for 632 nm light of the conductive film is less than 2.0%.

10. A reflective mask blank for EUV lithography according to claim 1 or 2, wherein when the transmittance of the conductive film for 1064 nm light is measured at three different points, the arithmetic mean value of the transmittances at the three points is defined as the average transmittance of 1064 nm light, and the difference between the maximum transmittance and the minimum transmittance among the transmittances at the three points is defined as the maximum transmittance difference for 1064 nm light, the ratio of the maximum transmittance difference for 1064 nm light of the conductive film to the average transmittance of 1064 nm light of the conductive film is less than 2.0%.

11. A reflective mask for EUV lithography, comprising an absorber film pattern formed by patterning the absorber film of the reflective mask blank for EUV lithography according to claim 1 or 2.

12. A method for producing a reflective mask for EUV lithography, comprising the step of patterning the absorber film of the reflective mask blank for EUV lithography according to claim 1 or 2.

13. A method for manufacturing a reflective mask blank for EUV lithography, comprising forming a conductive film on one surface of a substrate, forming a multilayer reflective film that reflects EUV light on the other surface of the substrate, and forming an absorber film on the side of the multilayer reflective film opposite to the substrate, wherein the conductive film is formed in the presence of nitrogen gas, and the pressure during the formation of the conductive film is 0.1 to 0.4 Pa.

14. A substrate with a conductive film, comprising: a substrate; and a conductive film disposed on one surface side of the substrate, wherein the conductive film contains one or more elements selected from the group consisting of tantalum and chromium, the total content of nitrogen and boron contained in the conductive film is more than 33 atomic % with respect to all atoms in the conductive film, the conductive film has a thickness of 20 to 150 nm, the thickness of the conductive film at the center of the substrate is greater than the thickness of the conductive film at an end portion of the substrate, and the maximum thickness difference of the conductive film in an in-plane direction is 0.30 to 1.00 nm.

15. The substrate with a conductive film according to claim 14, wherein the nitrogen content of said conductive film is 35 to 65 atomic % based on the total atoms in said conductive film.

16. The substrate with a conductive film according to claim 14 or 15, wherein the content of boron in the conductive film is more than 0 atomic % and 35 atomic % or less with respect to all atoms in the conductive film.

17. The substrate with a conductive film according to claim 14 or 15, wherein the electrical resistivity of the conductive film is 0.05 to 0.35 mΩ·cm.

18. The substrate with a conductive film according to claim 14 or 15, wherein the conductive film has a multilayer structure consisting of two or more layers, and among the layers, the outermost layer located furthest from the substrate is a layer containing tantalum and one or more elements selected from the group consisting of nitrogen and oxygen.

19. The substrate with a conductive film according to claim 18, wherein the oxygen content in the outermost layer is 20 to 60 atomic % based on all atoms in the outermost layer.

20. The substrate with a conductive film according to claim 18, wherein the oxygen content in the outermost layer is 40 to 50 atomic % based on all atoms in the outermost layer.

21. The substrate with a conductive film according to claim 14 or 15, wherein when the transmittance of the conductive film for light at 632 nm is measured at three different points, the arithmetic mean value of the transmittances at the three points is defined as the average transmittance of light at 632 nm, and the difference between the maximum transmittance and the minimum transmittance among the transmittances at the three points is defined as the maximum transmittance difference for light at 632 nm, the ratio of the maximum transmittance difference for light at 632 nm of the conductive film to the average transmittance for light at 632 nm of the conductive film is less than 2.0%.

22. The substrate with a conductive film according to claim 14 or 15, wherein when the transmittance of the conductive film for light at 1064 nm is measured at three different points, the arithmetic mean value of the transmittances at the three points is defined as the average transmittance of light at 1064 nm, and the difference between the maximum transmittance and the minimum transmittance among the transmittances at the three points is defined as the maximum transmittance difference for light at 1064 nm, the ratio of the maximum transmittance difference for light at 1064 nm of the conductive film to the average transmittance for light at 1064 nm of the conductive film is less than 2.0%.

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