EUV lithography reflective photomask substrate and substrate with conductive film

Abstract

This invention relates to a reflective photomask substrate for EUV lithography, comprising: a substrate, a conductive film disposed on the back side of the substrate, a reflective layer disposed on the front side of the substrate, and an absorption layer disposed on the reflective layer, wherein the conductive film contains at least one of nitrogen (N) and boron (B), the total content of N and B contained in the conductive film is greater than 0 at% and less than 65 at%, and the refractive index, extinction coefficient, film thickness t, and resistivity of the conductive film at wavelengths of 1000–1100 nm, 600–700 nm, and 400–500 nm are within specific ranges.

Description

Technical Field

[0001] The present invention relates to a reflective mask substrate for EUV (Extreme Ultra Violet) lithography for semiconductor manufacturing and the like (hereinafter referred to as "EUV mask substrate" in this specification), and a substrate with a conductive film for manufacturing the EUV mask substrate. Prior Art

[0002] Previously in the semiconductor industry, as a transfer technology for fine patterns necessary for forming integrated circuits including fine patterns on an Si substrate or the like, the industry has been using optical lithography using visible light or ultraviolet light. However, as the miniaturization process of semiconductor devices has been accelerating, the previous optical lithography method has gradually approached its limit. For optical lithography, the resolution limit of a pattern is about 1 / 2 of the exposure wavelength. Even with the immersion method, the resolution limit is considered to be about 1 / 4 of the exposure wavelength. Even with the ArF laser (193 nm) immersion method, its resolution limit is predicted to be about 20 - 30 nm. Therefore, EUV lithography using an exposure technology with EUV light having a shorter wavelength than the ArF laser is expected to be an exposure technology for 20 - 30 nm and higher wavelengths. In this specification, EUV light refers to light with a wavelength in the soft X-ray region or the vacuum ultraviolet region. Specifically, it refers to light with a wavelength of about 10 - 20 nm, especially about 13.5 nm ± 0.3 nm.

[0003] EUV light is easily absorbed by all substances, and the refractive index of substances at this wavelength is close to 1. Therefore, a refractive optical system such as the previous optical lithography using visible light or ultraviolet light cannot be used. Therefore, a reflective optical system, that is, a reflective mask and a mirror, is used in EUV lithography.

[0004] On the other hand, in addition to the shortening of the wavelength of light, a resolution improvement technology using a phase shift mask has also been proposed. The phase shift mask makes the transmissive portions of the mask pattern be of a different substance or shape from the adjacent transmissive portions, so that the light passing through these transmissive portions has a phase difference of 180 degrees. Therefore, in the region between the two transmissive portions, the diffracted light passing through with a phase difference of 180 degrees cancels each other out, and the light intensity becomes extremely small, thereby improving the mask contrast. As a result, the depth of focus during transfer is expanded, and the transfer accuracy is improved. Furthermore, in principle, the optimal phase difference is 180 degrees, but as long as it is substantially about 175 - 185 degrees, the resolution improvement effect can be sufficiently obtained.

[0005] A photomask substrate is a laminate before patterning for manufacturing a photomask. In the case of an EUV photomask substrate, it has a structure in which a reflective layer that reflects EUV light and an absorption layer that absorbs EUV light are sequentially formed on a substrate such as made of glass.

[0006] As the reflective layer, a multilayer reflective film is usually used, which improves the light reflectance when EUV light is irradiated onto the layer surface by alternately laminating a low-refractive-index layer with a low refractive index with respect to EUV light and a high-refractive-index layer with a high refractive index with respect to EUV light. As the low-refractive-index layer of the multilayer reflective film, a molybdenum (Mo) layer is usually used, and as the high-refractive-index layer, a silicon (Si) layer is usually used.

[0007] As the absorption layer, a material having a high absorption coefficient for EUV light can be used. Specifically, for example, a material mainly composed of chromium (Cr) or tantalum (Ta) can be used.

[0008] The multilayer reflective film and the absorption layer are formed on the optical surface of the glass substrate by using an ion beam sputtering method or a magnetron sputtering method. When forming the multilayer reflective film and the absorption layer, the glass substrate is held by a support mechanism. As the support mechanism for the glass substrate, there are a mechanical chuck and an electrostatic chuck. Considering the problem of dust generation, it is preferably to use an electrostatic chuck. Also, during the photomask patterning process or during the operation of the photomask during exposure, an electrostatic chuck is also used as the support mechanism for the glass substrate.

[0009] The electrostatic chuck is a technology that has been used previously, and it is used as a support mechanism for a silicon (Si) wafer in the manufacturing process of semiconductor devices. Therefore, in the case of a substrate with a relatively low dielectric constant and conductivity such as a glass substrate, a high voltage must be applied to obtain the same level of clamping force as in the case of a Si wafer, so there is a risk of dielectric breakdown.

[0010] Therefore, in order to promote the electrostatic clamping of the substrate, a conductive film is formed on the side opposite to the multilayer reflective film隔着基板之与多层反射膜相反一侧 across the substrate.

[0011] Problems such as substrate deformation may occur in EUV photomasks and the EUV photomask substrates used due to the internal stress of the multilayer reflective film or the absorption layer as the reflective layer. Currently, a new technology is being introduced, that is, from the back side of the EUV photomask or the EUV photomask substrate, pulsed laser light is locally irradiated to locally heat the glass substrate, thereby improving the substrate deformation caused by the internal stress of the multilayer reflective film or the absorption layer.

[0012] In order to apply the above technology, Patent Document 1 provides an EUV mask substrate having a high light transmittance for light with a wavelength of 400 to 800 nm and having a conductive film formed on the back surface. Prior Art Documents Patent Documents

[0013] Patent Document 1: Japanese Patent Laid-Open No. 2015-15420 Summary of the Invention

[0014] [Problems to be Solved by the Invention] On the other hand, an Ar laser with a wavelength of 488 nm is used in the defect inspection after the formation of the conductive film. If the light transmittance of the conductive film in this wavelength region is high, the defect inspection cannot be carried out. Therefore, a low light transmittance of the conductive film in this wavelength region is required.

[0015] When an Ar laser with a wavelength of 488 nm is used in the defect inspection after the formation of the conductive film, the laser light is locally irradiated to improve the substrate deformation caused by the internal stress of the multilayer reflective film or the absorption layer. For this purpose, a Nd:YAG laser with a wavelength of 1064 nm or a He:Ne laser with a wavelength of 632 nm can be used. When these lasers are used, a high light transmittance of the conductive film in these wavelength regions is required.

[0016] Furthermore, after forming a pattern on the absorption layer, the EUV mask substrate is applied to an exposure apparatus. At this time, the EUV mask substrate having a conductive film sometimes has insufficient fixing force when fixed to the exposure apparatus. In order to prevent such insufficient fixing force, it is effective to reduce the resistivity of the conductive film.

[0017] In order to solve the problems of the above prior art, an object of the present invention is to provide an EUV mask substrate and a substrate with a conductive film for manufacturing the EUV mask substrate, wherein when incident from the conductive film side, the EUV mask substrate allows light in the wavelength range of 1000 to 1100 nm and light in the wavelength range of 600 to 700 nm to pass through sufficiently, suppresses the transmission of light in the wavelength range of 400 to 500 nm, and has excellent fixing force when fixed to an exposure apparatus. [Technical Means for Solving the Problems]

[0018] The inventors of the present invention have found that the above problems can be solved by the following configuration. (1) A reflective mask substrate for EUV lithography, comprising: a substrate, A conductive film disposed on the back side of the substrate, A reflective layer disposed on the front side of the substrate and reflecting EUV light, and An absorption layer disposed on the reflective layer and absorbing EUV light, and The above-mentioned conductive film contains at least one of nitrogen (N) and boron (B), The total content of N and B contained in the above-mentioned conductive film exceeds 0 at% and is 65 at% or less, The refractive index nλ1000 - 1100 nm of the conductive film at a wavelength of 1000 to 1100 nm is 5.300 or less, and the extinction coefficient kλ1000 - 1100 nm is 5.200 or less, The refractive index nλ600 - 700 nm of the conductive film at a wavelength of 600 to 700 nm is 4.300 or less, and the extinction coefficient kλ600 - 700 nm is 4.500 or less, The refractive index nλ400 - 500 nm of the conductive film at a wavelength of 400 to 500 nm is 2.500 or more, and the extinction coefficient kλ400 - 500 nm is 0.440 or more, The film thickness t of the conductive film is 20 to 350 nm, The resistivity of the conductive film is 3.5 mΩ·cm or less. (2) A reflective mask substrate for EUV lithography, comprising: A substrate, A conductive film disposed on the back side of the substrate, A reflective layer disposed on the front side of the substrate and reflecting EUV light, and An absorption layer disposed on the reflective layer and absorbing EUV light, and The conductive film contains at least one of nitrogen (N) and boron (B), The total content of N and B contained in the conductive film exceeds 0 at% and is 65 at% or less, The refractive index nλ1000 - 1100 nm of the conductive film at a wavelength of 1000 to 1100 nm is 5.300 or less, and the extinction coefficient kλ1000 - 1100 nm is 5.200 or less, The refractive index nλ600 - 700 nm of the conductive film at a wavelength of 600 to 700 nm is 4.300 or less, and the extinction coefficient kλ600 - 700 nm is 4.500 or less, The refractive index nλ480 - 500 nm of the conductive film at a wavelength of 480 to 500 nm is 2.500 or more, and the extinction coefficient kλ480 - 500 nm is 0.440 or more, The film thickness t of the conductive film is 20 to 350 nm, The resistivity of the conductive film is 3.5 mΩ·cm or less. (3) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the conductive film contains at least one of tantalum (Ta) and chromium (Cr). (4) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the conductive film contains Ta and N. (5) The reflective mask substrate for EUV lithography according to (4), wherein the conductive film contains more than 0 at% and 65 at% or less of N. (6) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the conductive film contains Ta and B. (7) The reflective mask substrate for EUV lithography according to (6), wherein the conductive film contains more than 0 at% and 35 at% or less of B. (8) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the resistivity of the conductive film is 0.050 mΩ·cm or more and 3.5 mΩ·cm or less. (9) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the conductive film contains Ta, and among the diffraction peaks originating from the conductive film observed by the out-of-plane XRD (X-ray diffraction) method, the full width at half maximum FWHM of the diffraction peak belonging to the bcc (110) plane of Ta is 1.5 to 4.0°. (10) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the light transmittance of the conductive film for light with a wavelength of 1000 to 1100 nm is 1.0% or more, the light transmittance for light with a wavelength of 600 to 700 nm is 1.0% or more, and the light transmittance for light with a wavelength of 400 to 500 nm is 1.0% or less. (11) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the sheet resistance value of the conductive film is 250 Ω / □ or less. (12) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the surface hardness of the conductive film is 10.0 GPa or more. (13) The reflective mask substrate for EUV lithography according to (1) or (2), wherein an upper layer is further provided on the conductive film, The upper layer contains chromium (Cr) and at least one element selected from the group consisting of nitrogen (N) and oxygen (O). (14) The reflective mask substrate for EUV lithography as described in (1) or (2), wherein the surface roughness (Rq) of the above conductive film is 0.600 nm or less. (15) A substrate with a conductive film, which has a conductive film on the substrate, and the above conductive film contains at least one of nitrogen (N) and boron (B), the total content of N and B contained in the above conductive film exceeds 0 at% and is 65 at% or less, the refractive index nλ1000 - 1100 nm of the above conductive film at a wavelength of 1000 - 1100 nm is 5.300 or less, and the extinction coefficient kλ1000 - 1100 nm is 5.200 or less, the refractive index nλ600 - 700 nm of the above conductive film at a wavelength of 600 - 700 nm is 4.300 or less, and the extinction coefficient kλ600 - 700 nm is 4.500 or less, the refractive index nλ400 - 500 nm of the above conductive film at a wavelength of 400 - 500 nm is 2.500 or more, and the extinction coefficient kλ400 - 500 nm is 0.440 or more, the film thickness t of the above conductive film is 20 - 350 nm, the resistivity of the conductive film is 3.5 mΩ·cm or less. (16) A substrate with a conductive film, which has a conductive film on the substrate, and the above conductive film contains at least one of nitrogen (N) and boron (B), the total content of N and B contained in the above conductive film exceeds 0 at% and is 65 at% or less, the refractive index nλ1000 - 1100 nm of the above conductive film at a wavelength of 1000 - 1100 nm is 5.300 or less, and the extinction coefficient kλ1000 - 1100 nm is 5.200 or less, the refractive index nλ600 - 700 nm of the above conductive film at a wavelength of 600 - 700 nm is 4.300 or less, and the extinction coefficient kλ600 - 700 nm is 4.500 or less, the refractive index nλ480 - 500 nm of the above conductive film at a wavelength of 480 - 500 nm is 2.500 or more, and the extinction coefficient kλ480 - 500 nm is 0.440 or more, the film thickness t of the above conductive film is 20 - 350 nm, the resistivity of the conductive film is 3.5 mΩ·cm or less. (17) The substrate with a conductive film as described in (15) or (16), wherein the conductive film contains at least one of tantalum (Ta) and chromium (Cr). (18) The substrate with a conductive film as described in (15) or (16), wherein the conductive film contains Ta and N. (19) The substrate with a conductive film as described in (18), wherein the conductive film contains N in an amount greater than 0 at% and not more than 65 at%. (20) The substrate with a conductive film as described in (15) or (16), wherein the conductive film contains Ta and B. (21) The substrate with a conductive film as described in (20), wherein the conductive film contains B in an amount greater than 0 at% and not more than 35 at%. (22) The substrate with a conductive film as described in (15) or (16), wherein the resistivity of the conductive film is 0.050 mΩ·cm or more and 3.5 mΩ·cm or less. (23) The substrate with a conductive film as described in (15) or (16), wherein the conductive film contains Ta, and in the diffraction peaks from the conductive film observed by out-of-plane XRD method, the full width at half maximum (FWHM) of the diffraction peak attributed to the bcc(110) plane of Ta is 1.5 to 4.0°. (24) The substrate with a conductive film as described in (15) or (16), wherein the light transmittance of the conductive film at a wavelength of 1000 to 1100 nm is 1.0% or more, the light transmittance at a wavelength of 600 to 700 nm is 1.0% or more, and the light transmittance at a wavelength of 400 to 500 nm is 1.0% or less. (25) The substrate with a conductive film as described in (15) or (16), wherein the sheet resistance of the conductive film is 250 Ω / □ or less. (26) The substrate with a conductive film as described in (15) or (16), wherein the surface hardness of the conductive film is 10.0 GPa or more. (27) The substrate with a conductive film as described in (15) or (16), wherein an upper layer is further provided on the conductive film, the upper layer contains chromium (Cr) and at least one element selected from the group consisting of nitrogen (N) and oxygen (O). (28) The substrate with a conductive film as described in (15) or (16), wherein the surface roughness (Rq) of the conductive film is 0.600 nm or less. [Advantages of the Invention]

[0019] Regarding the EUV mask substrate of the embodiment of the present invention (hereinafter also referred to as the EUV mask substrate of the present embodiment), when light is incident from the conductive film side, light in the wavelength range of 1000 to 1100 nm and light in the wavelength range of 600 to 700 nm are transmitted, and the transmission of light in the wavelength range of 400 to 500 nm is suppressed. Also, by making the resistivity of the conductive film sufficiently low, excellent fixing force can be obtained when fixed to the exposure apparatus. Brief Explanation of Drawings

[0020] FIG. 1 is a schematic cross-sectional view showing an embodiment of the EUV mask substrate of the present invention. Embodiment

[0021] The first aspect of the EUV mask substrate of the present embodiment is a reflective mask substrate for EUV lithography, characterized by having: a substrate, a conductive film disposed on the back side of the substrate, a reflective layer disposed on the front side of the substrate and reflecting EUV light, and an absorption layer disposed on the reflective layer and absorbing EUV light, and the conductive film contains at least one of nitrogen (N) and boron (B), the total content of N and B contained in the conductive film exceeds 0 at% and is 65 at% or less, the refractive index nλ1000 - 1100 nm of the conductive film at a wavelength of 1000 to 1100 nm is 5.300 or less, the extinction coefficient kλ1000 - 1100 nm is 5.200 or less, the refractive index nλ600 - 700 nm of the conductive film at a wavelength of 600 to 700 nm is 4.300 or less, the extinction coefficient kλ600 - 700 nm is 4.500 or less, the refractive index nλ400 - 500 nm of the conductive film at a wavelength of 400 to 500 nm is 2.500 or more, the extinction coefficient kλ400 - 500 nm is 0.440 or more, the film thickness t of the conductive film is 20 to 350 nm, and the resistivity of the conductive film is 3.5 mΩ·cm or less.

[0022] A second aspect of the EUV mask substrate according to an embodiment of the present invention is a reflective mask substrate for EUV lithography, characterized by having: a substrate, a conductive film disposed on the back side of the substrate, a reflective layer disposed on the front side of the substrate and reflecting EUV light, and an absorption layer disposed on the reflective layer and absorbing EUV light, and the conductive film contains at least one of nitrogen (N) and boron (B), the total content of N and B contained in the conductive film exceeds 0 at% and is 65 at% or less, the refractive index nλ1000 - 1100 nm of the conductive film at a wavelength of 1000 to 1100 nm is 5.300 or less, the extinction coefficient kλ1000 - 1100 nm is 5.200 or less, the refractive index nλ600 - 700 nm of the conductive film at a wavelength of 600 to 700 nm is 4.300 or less, the extinction coefficient kλ600 - 700 nm is 4.500 or less, the refractive index nλ480 - 500 nm of the conductive film at a wavelength of 480 to 500 nm is 2.500 or more, the extinction coefficient kλ480 - 500 nm is 0.440 or more, the film thickness t of the conductive film is 20 to 350 nm, and the resistivity of the conductive film is 3.5 mΩ·cm or less.

[0023] Hereinafter, the EUV mask substrate of the present embodiment will be described with reference to the drawings. Furthermore, unless otherwise specified, the description of the EUV mask substrate of the present embodiment below applies to both the first aspect and the second aspect of the EUV mask substrate of the present embodiment.

[0024] FIG. 1 is a schematic cross-sectional view showing an embodiment of the EUV mask substrate of the present invention. In the EUV mask substrate 10 shown in FIG. 1, a reflective layer 13 that reflects EUV light and an absorption layer 14 that absorbs EUV light are sequentially formed on one surface (in the figure, the upper surface of the substrate 11) of the substrate 11. A conductive film 12 is formed on the other surface (in the figure, the lower surface of the substrate 11) of the substrate 11. Hereinafter, in this specification, the surface of the substrate 11 on which the reflective layer 13 and the absorption layer 14 are disposed is defined as the front surface of the substrate 11, and the surface of the substrate 11 on which the conductive film 12 is disposed is defined as the back surface of the substrate 11.

[0025] Hereinafter, each component of the EUV mask substrate 10 of the present embodiment will be described.

[0026] The substrate 11 satisfies the characteristics of a substrate for an EUV photomask blank. Therefore, the substrate 11 has a low coefficient of thermal expansion, excellent smoothness, flatness, and resistance to cleaning liquids for photomask cleaning, etc. after forming the photomask blank or pattern. Here, regarding the above-mentioned low coefficient of thermal expansion, specifically, the coefficient of thermal expansion at 20 °C is preferably 0 ± 0.05 × 10-7 / °C, more preferably 0 ± 0.03 × 10-7 / °C. As the substrate 11, specifically, glass having a low coefficient of thermal expansion, such as SiO2-TiO2-based glass, etc. is used, but it is not limited thereto, and a crystallized glass in which β-quartz solid solution is precipitated, quartz glass, silicon, or a substrate such as metal, etc. may also be used.

[0027] When the substrate 11 has a smooth surface with a surface roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less, a high reflectivity and transfer accuracy can be obtained for the photomask after pattern formation, so it is preferable.

[0028] The size, thickness, etc. of the substrate 11 are appropriately determined according to the design values of the photomask, etc. In the examples shown below, SiO2-TiO2-based glass with an outer shape of 6 inches (152 mm) square and a thickness of 0.25 inches (6.3 mm) is used.

[0029] Preferably, there are no defects on the surface of the substrate 11. However, even if there are defects, as long as phase defects are not generated due to concave defects and / or convex defects. Specifically, it is preferable that the depth of the concave defects and the height of the convex defects are 2 nm or less, and the full width at half maximum of these concave defects and convex defects is 60 nm or less. The full width at half maximum of the concave defects refers to the width at the 1 / 2 depth position of the depth of the concave defects. The full width at half maximum of the convex defects refers to the width at the 1 / 2 height position of the height of the convex defects.

[0030] The refractive index nλ1000-1100 nm of the conductive film 12 at a wavelength of 1000 to 1100 nm is 5.300 or less, and the extinction coefficient kλ1000-1100 nm is 5.200 or less.

[0031] If the refractive index nλ1000-1100 nm and the extinction coefficient kλ1000-1100 nm are in the above ranges, the light transmittance of the conductive film 12 at a wavelength of 1000 to 1100 nm is high. Therefore, it is ideal when using a Nd:YAG laser with a wavelength of 1064 nm to improve substrate deformation.

[0032] The light transmittance of the conductive film 12 at a wavelength of 1000 to 1100 nm is preferably 1.0% or more, more preferably 2.0% or more, and still more preferably 2.5% or more. The upper limit of the light transmittance of the conductive film 12 at a wavelength of 1000 to 1100 nm is not particularly limited, and is, for example, 3.5% or less.

[0033] The refractive index nλ1000 - 1100 nm of the conductive film 12 is preferably 5.200 or less. The lower limit of the refractive index nλ1000 - 1100 nm of the conductive film 12 is not particularly limited, and is, for example, 4.000 or more.

[0034] The extinction coefficient kλ1000 - 1100 nm of the conductive film 12 is preferably 5.100 or less. The lower limit of the extinction coefficient kλ1000 - 1100 nm of the conductive film 12 is not particularly limited, and is, for example, 3.000 or more.

[0035] The refractive index nλ600 - 700 nm of the conductive film 12 at a wavelength of 600 to 700 nm is 4.300 or less, and the extinction coefficient kλ600 - 700 nm is 4.500 or less.

[0036] If the refractive index nλ600 - 700 nm and the extinction coefficient kλ600 - 700 nm are within the above ranges, the light transmittance of the conductive film 12 at a wavelength of 600 to 700 nm is high. Therefore, it is more ideal when using a He:Ne laser with a wavelength of 632 nm to improve the substrate deformation.

[0037] The light transmittance of the conductive film 12 at a wavelength of 600 to 700 nm is preferably 1.0% or more, more preferably 1.5% or more. The upper limit of the light transmittance of the conductive film 12 at a wavelength of 600 to 700 nm is not particularly limited, and is, for example, 2.5% or less.

[0038] The refractive index nλ600 - 700 nm of the conductive film 12 is preferably 4.200 or less. The lower limit of the refractive index nλ600 - 700 nm of the conductive film 12 is not particularly limited, and is, for example, 3.100 or more.

[0039] The extinction coefficient kλ600 - 700 nm of the conductive film 12 is preferably 4.400 or less. The upper limit of the extinction coefficient kλ600 - 700 nm of the conductive film 12 is not particularly limited, and is, for example, 2.500 or more.

[0040] In the first aspect of the EUV mask substrate of the present embodiment, the refractive index nλ400 - 500 nm of the conductive film 12 at a wavelength of 400 to 500 nm is 2.500 or more, and the extinction coefficient kλ400 - 500 nm is 0.440 or more. In the second aspect of the EUV mask substrate of the present embodiment, the refractive index nλ400 - 500 nm of the conductive film 12 at a wavelength of 400 to 500 nm is preferably 2.500 or more, and the extinction coefficient kλ400 - 500 nm is preferably 0.440 or more.

[0041] If the refractive index nλ400 - 500 nm and the extinction coefficient kλ400 - 500 nm are within the above ranges, the light transmittance of the conductive film 12 at a wavelength of 400 to 500 nm is low. Therefore, it is ideal to use an Ar laser with a wavelength of 488 nm in defect inspection.

[0042] The light transmittance of the conductive film 12 at a wavelength of 400 to 500 nm is preferably 1.0% or less, more preferably less than 1.0%. There is no particular limitation on the lower limit of the light transmittance of the conductive film 12 at a wavelength of 400 to 500 nm, for example, it is 0.7% or more.

[0043] The refractive index nλ400 - 500 nm of the conductive film 12 is preferably 2.600 or more, more preferably 2.650 or more, and still more preferably 2.700 or more. There is no particular limitation on the upper limit of the refractive index nλ400 - 500 nm of the conductive film 12, for example, it is 3.300 or less.

[0044] The extinction coefficient kλ400 - 500 nm of the conductive film 12 is preferably 0.500 or more, more preferably 1.000 or more, still more preferably 1.500 or more, and particularly preferably 1.800 or more. There is no particular limitation on the upper limit of the extinction coefficient kλ400 - 500 nm of the conductive film 12, for example, it is 4.300 or less.

[0045] In the first aspect of the EUV mask substrate of the present embodiment, the refractive index nλ480 - 500 nm of the conductive film 12 at a wavelength of 480 to 500 nm is preferably 2.500 or more, and the extinction coefficient kλ480 - 500 nm is preferably 0.440 or more. In the second aspect of the EUV photomask substrate of the present embodiment, the refractive index nλ480 - 500 nm of the conductive film 12 at a wavelength of 480 to 500 nm is 2.500 or more, and the extinction coefficient kλ480 - 500 nm is 0.440 or more.

[0046] The refractive index nλ480 - 500 nm of the conductive film 12 is preferably 2.600 or more, more preferably 2.700 or more, and still more preferably 2.800 or more. The upper limit of the refractive index nλ480 - 500 nm of the conductive film 12 is not particularly limited, for example, it is 3.300 or less.

[0047] The extinction coefficient kλ480 - 500 nm of the conductive film 12 is preferably 0.500 or more, more preferably 1.000 or more, still more preferably 1.500 or more, particularly preferably 2.000 or more, and most preferably 2.200 or more. The upper limit of the extinction coefficient kλ480 - 500 nm of the conductive film 12 is not particularly limited, for example, it is 4.300 or less.

[0048] The film thickness t of the conductive film 12 is 20 to 350 nm. By making the film thickness t 20 nm or more, the light transmittance at a wavelength of 400 to 500 nm can be sufficiently reduced. If the film thickness t exceeds 350 nm, then even if the refractive index nλ1000 - 1100 nm and the extinction coefficient kλ1000 - 1100 nm satisfy the above ranges, the light transmittance at a wavelength of 1000 to 1100 nm does not become sufficiently high. Also, even if the refractive index nλ600 - 700 nm and the extinction coefficient kλ600 - 700 nm satisfy the above ranges, the light transmittance at a wavelength of 600 to 700 nm does not become sufficiently high.

[0049] The film thickness t of the conductive film 12 is preferably 20 nm or more, more preferably 25 nm or more, and still more preferably 30 nm or more. The film thickness t of the conductive film 12 is preferably 300 nm or less, more preferably 200 nm or less, and still more preferably 100 nm or less.

[0050] The conductive film 12 in which the refractive index nλ1000 - 1100 nm, the refractive index nλ600 - 700 nm, and the refractive index nλ400 - 500 nm satisfy the above ranges, and the extinction coefficient kλ1000 - 1100 nm, the extinction coefficient kλ600 - 700 nm, and the extinction coefficient kλ400 - 500 nm satisfy the above ranges contains at least one of nitrogen (N) and boron (B). Further, the conductive film 12 having a refractive index nλ of 1000 - 1100 nm, a refractive index nλ of 600 - 700 nm, and a refractive index nλ of 480 - 500 nm satisfying the above ranges, and an extinction coefficient kλ of 1000 - 1100 nm, an extinction coefficient kλ of 600 - 700 nm, and an extinction coefficient kλ of 480 - 500 nm satisfying the above ranges contains at least one of nitrogen (N) and boron (B).

[0051] The conductive film 12 contains at least one of nitrogen (N) and boron (B). That is, the total content of N and B contained in the conductive film 12 exceeds 0 at%. Thereby, the conductive film 12 can be made amorphous. The total content of N and B is preferably 2 at% or more, more preferably 5 at% or more, and still more preferably 10 at% or more.

[0052] Further, from the viewpoint of the resistivity of the conductive film, the total content of N and B is 65 at% or less, preferably 60 at% or less, and more preferably 40 at% or less. That is, the total content of N and B exceeds 0 at% and is 65 at% or less.

[0053] Furthermore, from the same above viewpoints, when the conductive film 12 contains N, the content of N is preferably more than 0 at%, more preferably 2 at% or more, still more preferably 5 at% or more, and even more preferably 10 at% or more. Also, when the conductive film 12 contains N, the content of N is preferably 65 at% or less, more preferably 60 at% or less, and still more preferably 40 at% or less.

[0054] Further, from the same above viewpoints, when the conductive film 12 contains B, the content of B is preferably more than 0 at%, more preferably 5 at% or more, still more preferably 10 at% or more, and even more preferably 15 at% or more. Also, when the conductive film 12 contains B, the content of B is preferably 65 at% or less, more preferably 50 at% or less, still more preferably 40 at% or less, particularly preferably 35 at% or less, and most preferably 30 at% or less.

[0055] The conductive film 12 preferably further contains at least one of tantalum (Ta) and chromium (Cr). Specifically, examples include: a TaN film containing Ta and N, a TaB film containing Ta and B, a CrN film containing Cr and N, and a CrB film containing Cr and B. Among these, the TaN film is preferred because of its relatively high film hardness and large film stress.

[0056] When using a TaN film as the conductive film 12, if the content rate of N in the TaN film exceeds 0 at%, the hardness of the TaN film relative to the substrate 11 increases, which is preferable, more preferably 2 at% or more, further preferably 10 at% or more, and particularly preferably 15 at% or more. If the content rate of N in the TaN film is 65 at% or less, the surface smoothness of the TaN film increases and the sheet resistance value of the TaN film decreases, which is preferable, more preferably 60 at% or less, further preferably 55 at% or less.

[0057] When using a TaB film as the conductive film 12, if the content rate of B in the TaB film exceeds 0 at%, the film adhesion increases and the surface smoothness increases, which is preferable, more preferably 5 at% or more, further preferably 10 at% or more, particularly preferably 15 at% or more, and most preferably 20 at% or more. If the content rate of B in the TaB film is 35 at% or less, the hardness increases, which is preferable, more preferably 30 at% or less.

[0058] When using a CrN film as the conductive film 12, if the content rate of N in the CrN film exceeds 0 at%, the hardness of the CrN film relative to the substrate 11 increases, which is preferable, more preferably 1 at% or more, further preferably 2 at% or more. If the content rate of N in the CrN film is 65 at% or less, the surface smoothness of the CrN film increases and the sheet resistance value of the CrN film decreases, which is preferable, more preferably 50 at% or less, further preferably 30 at% or less, and particularly preferably 15 at% or less.

[0059] A laminated film of a TaN film and a CrN film can also be used as the conductive film 12. Since the laminated film having the above configuration contains a TaN film, the hardness of the film is high and the film stress is large.

[0060] When using the laminated film having the above configuration, it is preferable to use a laminated film in which a TaN film and a CrN film are laminated in order from the substrate 11 side. Furthermore, when using the laminated film having the above configuration, the total film thickness of the laminated film satisfies the film thickness of the above conductive film 12. Also, the content rate of N in the TaN film and the content rate of N in the CrN film respectively satisfy the above ranges.

[0061] Further, an upper layer may be further provided on the conductive film 12. The upper layer is preferably a film containing chromium (Cr) and at least one element selected from the group consisting of nitrogen (N) and oxygen (O). By further providing an upper layer on the conductive film 12, mechanical properties can be improved, and changes in optical properties due to the formation of a natural oxide film can be suppressed.

[0062] When using a CrO film as the upper layer of the conductive film 12, if the O content rate in the CrO film is 5 at% or more, the hardness of the CrO film is improved, so it is preferable, more preferably 8 at% or more, and still more preferably 10 at% or more. If the O content rate in the CrO film is 30 at% or less, the surface smoothness of the CrO film is improved, and the sheet resistance value of the CrO film is reduced, so it is preferable, more preferably 25 at% or less, and still more preferably 20 at% or less, particularly preferably 15 at% or less.

[0063] The film thickness t' of the upper layer of the conductive film 12 is preferably 5 nm or more, more preferably 10 nm or more, still more preferably 15 nm or more, and particularly preferably 20 nm or more. The film thickness t' of the upper layer of the conductive film 12 is preferably 100 nm or less, more preferably 70 nm or less, and still more preferably 50 nm or less.

[0064] When the conductive film 12 contains Ta, among the diffraction peaks from the conductive film 12 observed by the out-of-plane XRD method, the full width at half maximum FWHM of the diffraction peak attributed to the bcc(110) plane of Ta is preferably 1.5 to 4.0°. If the full width at half maximum FWHM is 1.5° or more, crystallization of the conductive film is suppressed, and the smoothness of the surface of the conductive film 12 is improved. The full width at half maximum FWHM is more preferably 2.0° or more, and still more preferably 3.0° or more.

[0065] On the other hand, if the full width at half maximum FWHM is 4.0° or less, the crystallinity of the conductive film does not become too low, so the hardness of the film does not decrease. Therefore, the film is not worn due to repeated use, and the overlay accuracy does not decrease.

[0066] The resistivity of the conductive film 12 is 3.5 mΩ·cm or less. Generally, the lower the resistivity of the conductive film 12 becomes, the higher the fixing force of the EUV mask to the exposure apparatus will be. In the present embodiment, the resistivity of the conductive film 12 is low enough, being 3.5 mΩ·cm or less. Therefore, when the EUV mask is fixed to the exposure apparatus, excellent fixing force can be obtained. The resistivity of the conductive film 12 is preferably 1.0 mΩ·cm or less, more preferably 0.320 mΩ·cm or less, still more preferably 0.300 mΩ·cm or less, and particularly preferably 0.250 mΩ·cm or less.

[0067] Also, the lower limit of the resistivity of the conductive film 12 is not particularly limited, and is preferably 0.050 mΩ·cm or more, more preferably 0.060 mΩ·cm or more, and still more preferably 0.065 mΩ·cm or more.

[0068] The resistivity of the conductive film 12 is measured using a resistivity meter, and the detailed measurement conditions are based on the measurement method of the following examples.

[0069] In order to make the resistivity of the conductive film 12 within the above range, methods such as adjusting the nitrogen or boron content contained in the conductive film can be cited. Furthermore, even when an upper layer is further provided on the conductive film 12, when the resistivity of the conductive film is low enough compared with the upper layer, the resistivity at the time of lamination can be directly regarded as the resistivity of the conductive film. As a combination of the conductive film and the upper layer in which the resistivity of the conductive film is low enough compared with the upper layer, for example, a combination of a TaN film as the conductive film and a CrO film as the upper layer can be cited.

[0070] If the sheet resistance value of the conductive film 12 is low, the clamping force of the electrostatic chuck is increased, which is preferable. The sheet resistance value of the conductive film 12 is preferably 250 Ω / □ or less, more preferably 200 Ω / □ or less, still more preferably 150 Ω / □ or less, still more preferably 100 Ω / □ or less, and particularly preferably 80 Ω / □ or less.

[0071] Also, the sheet resistance value of the conductive film 12 is preferably 0.1 Ω / □ or more, more preferably 0.5 Ω / □ or more, and still more preferably 1.0 Ω / □ or more.

[0072] If the surface roughness of the conductive film 12 is small, the adhesion to the electrostatic chuck is improved, which is preferable. In terms of Rq (root mean square height, JIS B0601:2013), the surface roughness of the conductive film 12 is preferably 0.600 nm or less, more preferably 0.400 nm or less, still more preferably 0.200 nm or less, particularly preferably 0.150 nm or less, and most preferably 0.100 nm or less. In terms of Rq, the surface roughness of the conductive film 12 is preferably 0.030 nm or more, more preferably 0.050 nm or more, and still more preferably 0.070 nm or more. Further, when the gas pressure of the gas used during film formation is 0.3 Pa or more, the surface roughness of the conductive film tends to increase.

[0073] If the surface hardness of the conductive film 12 is high, generation of particles due to friction with the electrostatic chuck is suppressed, which is preferable. The surface hardness of the conductive film 12 is preferably 10.0 GPa or more.

[0074] Also, the surface hardness of the conductive film 12 is preferably 16.0 GPa or less, more preferably 14.0 GPa or less, and still more preferably 12.0 GPa or less. Here, the method for measuring the surface hardness of the conductive film 12 is not particularly limited. Specifically, known methods such as a Vickers hardness test, a Rockwell hardness test, a Brinell hardness test, and a nanoindentation test can be used. Among these, the nanoindentation test is widely used for measuring the surface hardness of thin films.

[0075] Further, if a TaN film, a CrN film, or a laminated film of a CrN film and a TaN film is used as the conductive film 12, the surface hardness of the conductive film 12 is high and the surface hardness becomes 10.0 GPa or more.

[0076] In the EUV mask substrate 10 shown in FIG. 1, film stress is generated in the reflective layer 13 and the absorption layer 14 formed on the front side of the substrate 11. Film stress is also generated in the conductive film 12 formed on the back side of the substrate 11. In the EUV mask substrate, the stress generated on the front side of the substrate 11 and the stress generated on the back side of the substrate 11 cancel each other out, and as a result, deformation of the substrate due to applied stress is suppressed.

[0077] As an example of the EUV mask substrate, when suppressing substrate deformation in the EUV mask substrate having the following configuration, the flatness of the substrate with the conductive film 12 formed on the back side of the substrate 11 is preferably 500 nm or less, more preferably 400 nm or less, and still more preferably 300 nm or less.

[0078] (Structure) Substrate: SiO₂-TiO₂-based glass substrate (outer shape: 152 mm square, thickness: 6.3 mm) Reflection layer: Si / Mo multilayer reflection film (alternately laminated Si film (4.5 nm) and Mo film (2.3 nm) for 40 cycles (total film thickness: 272 nm)) Absorption layer: TaNH film (film thickness: 60 nm)

[0079] Furthermore, when using a TaN film, a TaB film, or a laminated film of a CrN film and a TaN film as the conductive film 12, the film stress of the conductive film 12 increases, and the flatness of the substrate with the conductive film becomes 500 nm or less.

[0080] When manufacturing an EUV mask from an EUV mask substrate, heat treatment is sometimes performed as a pretreatment. By this heat treatment, the film stress of the reflection layer 13 or the absorption layer 14 formed on the front side of the substrate 11 is reduced due to the relaxation of the film stress. Also, the film stress of the conductive film 12 formed on the back side of the substrate 11 is reduced due to the relaxation of the film stress. If the stress is reduced due to the relaxation of the film stress, it gradually becomes impossible to suppress the deformation of the substrate 11, and there is a risk of positional deviation of the pattern formed on the EUV mask manufactured using the EUV mask substrate.

[0081] The conductive film 12 preferably has less film stress relaxation caused by heat treatment. The difference in the flatness of the substrate with the conductive film measured before and after heat treatment can be used as an index of the film stress relaxation caused by heat treatment. When the substrate with the conductive film having the conductive film 12 formed on the back side of the substrate 11 is heat-treated at 136°C for 20 minutes, the heat relaxation rate of the flatness (warpage) of the substrate with the conductive film measured before and after heat treatment is preferably 15% or less, more preferably 12% or less, and still more preferably 10% or less. The lower limit of the heat relaxation rate of the flatness (warpage) is not particularly limited, and is, for example, 1.0% or more. Heat relaxation rate of flatness (%) = {(Flatness of the substrate with TaN conductive film before heat treatment - Flatness of the substrate with TaN conductive film after heat treatment) / Flatness of the substrate with TaN conductive film before heat treatment} × 100

[0082] Furthermore, the above flatness is measured using a flatness measuring machine manufactured by FUJINON Corporation.

[0083] The conductive film 12 can be formed by a known film formation method, such as a sputtering method such as a magnetron sputtering method or an ion beam sputtering method.

[0084] When forming a TaN film as the conductive film 12 by, for example, a sputtering method, the sputtering method can be carried out using a Ta target in an atmosphere containing an inert gas including at least one of helium (He), argon (Ar), neon (Ne), krypton (Kr), and xenon (Xe), and nitrogen gas (N₂). When using a magnetron sputtering method, specifically, it can be carried out under the following film formation conditions.

[0085] (Film formation conditions) Target: Ta target Sputtering gas: A mixed gas of Ar and N₂ (concentration of nitrogen gas (N₂): preferably 2 to 50 vol%, more preferably 2 to 40 vol%, still more preferably 2 to 30 vol%. Gas pressure: preferably 1×10⁻¹ Pa to 3×10⁻¹ Pa, more preferably 1×10⁻¹ Pa to 2×10⁻¹ Pa, still more preferably 1×10⁻¹ Pa to 1.5×10⁻¹ Pa) Input power: preferably 300 to 1500 W, more preferably 500 to 1000 W Film formation rate: preferably 0.010 to 0.200 nm / sec, more preferably 0.050 to 0.100 nm / sec

[0086] When forming a TaB film as the conductive film 12 by, for example, a sputtering method, the sputtering method can be carried out using a Ta target and a B target, or a TaB compound target in an atmosphere containing an inert gas including at least one of helium (He), argon (Ar), neon (Ne), krypton (Kr), and xenon (Xe). When using a magnetron sputtering method, specifically, it can be carried out under the following film formation conditions.

[0087] (Film formation conditions) Target: Ta target and B target, or TaB compound target Sputtering gas: Argon (Ar) (gas pressure: preferably 1.0×10⁻¹ Pa to 5.0×10⁻¹ Pa, more preferably 1.0×10⁻¹ Pa to 4.0×10⁻¹ Pa, still more preferably 1.0×10⁻¹ Pa to 3.0×10⁻¹ Pa) Input power: preferably 300 to 1500 W, more preferably 500 to 1000 W Film formation rate: preferably 0.010 to 0.200 nm / sec, more preferably 0.010 to 0.100 nm / sec

[0088] When forming a CrN film as the conductive film 12 by, for example, a sputtering method, the sputtering method can be carried out using a Cr target in an atmosphere containing an inert gas including at least one of helium (He), argon (Ar), neon (Ne), krypton (Kr), and xenon (Xe), and nitrogen gas (N₂). When using a magnetron sputtering method, specifically, it can be carried out under the following film formation conditions.

[0089] (Film formation conditions) Target: Cr target Sputtering gas: A mixed gas of Ar and N₂ (concentration of nitrogen gas (N₂): preferably 20 to 60 vol%, more preferably 30 to 60 vol%, still more preferably 40 to 60 vol%. Gas pressure: preferably 1×10⁻¹ Pa to 3×10⁻¹ Pa, more preferably 1×10⁻¹ Pa to 2×10⁻¹ Pa, still more preferably 1×10⁻¹ Pa to 1.5×10⁻¹ Pa.) Input power: preferably 300 to 2000 W, more preferably 500 to 2000 W Film formation rate: preferably 0.010 to 0.200 nm / sec, more preferably 0.050 to 0.200 nm / sec

[0090] When forming a CrO film as the upper layer on the conductive film 12 by, for example, a sputtering method, the sputtering method can be carried out using a Cr target in an atmosphere containing an inert gas including at least one of helium (He), argon (Ar), neon (Ne), krypton (Kr), and xenon (Xe), and oxygen gas (O₂). When using a magnetron sputtering method, specifically, it can be carried out under the following film formation conditions.

[0091] (Film formation conditions) Target: Cr target Sputtering gas: A mixed gas of Ar and O₂ (concentration of oxygen gas (O₂): preferably 10 to 40 vol%, more preferably 20 to 40 vol%, still more preferably 30 to 40 vol%. Gas pressure: preferably 1×10⁻¹ Pa to 2.0×10⁻¹ Pa, more preferably 1×10⁻¹ Pa to 1.8×10⁻¹ Pa, still more preferably 1×10⁻¹ Pa to 1.6×10⁻¹ Pa) Input power: preferably 300 to 1000 W, more preferably 500 to 1000 W Film formation rate: preferably 0.010 to 0.200 nm / sec, more preferably 0.050 to 0.200 nm / sec

[0092] The reflective layer 13 only needs to have the characteristics required for a reflective layer of an EUV mask substrate, and there are no particular limitations. Here, the particularly required characteristic of the reflective layer 13 is high EUV light reflectivity. Specifically, when light in the wavelength region of EUV light is incident on the surface of the reflective layer 13 at an incident angle of 6 degrees, the maximum value of the light reflectivity near a wavelength of 13.5 nm is preferably 60% or more, and more preferably 65% or more.

[0093] In order to achieve high EUV light reflectivity, the reflective layer 13 generally uses a multilayer reflective film formed by alternately laminating a high refractive index layer and a low refractive index layer a plurality of times. In the multilayer reflective film forming the reflective layer 13, Mo is widely used for the high refractive index layer, and Si is widely used for the low refractive index layer. That is, the most common is the Mo / Si multilayer reflective film. However, the multilayer reflective film is not limited to this, and a Ru / Si multilayer reflective film, a Mo / Be multilayer reflective film, a Mo compound / Si compound multilayer reflective film, a Si / Mo / Ru multilayer reflective film, a Si / Mo / Ru / Mo multilayer reflective film, or a Si / Ru / Mo / Ru multilayer reflective film may also be used.

[0094] The film thickness of each layer constituting the multilayer reflective film for forming the reflective layer 13 and the number of repeating units of the layer can be appropriately selected according to the film material used and the EUV light reflectivity required for the reflective layer. Taking the Mo / Si multilayer reflective film as an example, in order to fabricate the reflective layer 13 with a maximum EUV light reflectivity of 60% or more, the multilayer reflective film only needs to laminate a Mo layer with a film thickness of 2.3 ± 0.1 nm and a Si layer with a film thickness of 4.5 ± 0.1 nm in such a way that the number of repeating units is 30 to 60.

[0095] Furthermore, each layer constituting the multilayer reflective film for forming the reflective layer 13 may be formed to a required thickness by using a well-known film-forming method such as a magnetron sputtering method or an ion beam sputtering method. For example, in the case of forming a Si / Mo multilayer reflective film by using an ion beam sputtering method, it is preferable to use a Si target as the target, use argon (Ar) (atmospheric pressure 1.3×10 -2 to 2.7×10 -2 Pa) as the sputtering gas, and form a Si film to a thickness of 4.5 nm under the conditions of an ion acceleration voltage of 300 to 1500 V and a film-forming speed of 0.030 to 0.300 nm / sec. Then, use a Mo target as the target, use argon (Ar) (atmospheric pressure 1.3×10 -2 to 2.7×10 -2 Pa) as the sputtering gas, and form a Mo film to a thickness of 2.3 nm under the conditions of an ion acceleration voltage of 300 V to 1500 V and a film-forming speed of 0.030 to 0.300 nm / sec. This is set as one cycle, and the Si film and the Mo film are laminated 40 to 50 cycles, thereby forming a Si / Mo multilayer reflective film.

[0096] A particularly required characteristic of the absorption layer 14 is an extremely low EUV light reflectivity. Specifically, when light in the wavelength region of EUV light is irradiated onto the surface of the absorption layer 14, the maximum light reflectivity near a wavelength of 13.5 nm is 5% or less, more preferably 3% or less, and even more preferably 1% or less.

[0097] In order to achieve the above characteristics, the absorption layer 14 contains a material having a high absorption coefficient for EUV light. As a material having a high absorption coefficient for EUV light, it is preferable to use a material mainly composed of tantalum (Ta). In this specification, when referring to a material mainly composed of tantalum (Ta), it means a material containing 20 at% or more of Ta. The absorption layer 14 preferably contains 30 at% or more of Ta, more preferably contains 35 at% or more, even more preferably contains 40 at% or more, particularly preferably contains 45 at% or more, and most preferably contains 50 at% or more.

[0098] The material mainly composed of Ta used in the absorption layer 14 preferably contains at least one component among hafnium (Hf), silicon (Si), zirconium (Zr), germanium (Ge), boron (B), palladium (Pd), tin (Sn), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), silver (Ag), cadmium (Cd), indium (In), antimony (Sb), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), bismuth (Bi), carbon (C), titanium (Ti), zirconium (Zr), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), palladium (Pd), calcium (Ca), magnesium (Mg), aluminum (Al), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), arsenic (As), selenium (Se), tellurium (Te), hydrogen (H), and nitrogen (N) in addition to Ta.

[0099] As specific examples of the material containing the above elements other than Ta, 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. can be cited.

[0100] The absorption layer 14 having the above structure can be formed by a film-forming method such as a sputtering method such as a magnetron sputtering method or an ion beam sputtering method.

[0101] For example, when forming a TaNH film as the absorption layer 14 using the magnetron sputtering method, it is preferable to use a Ta target as the target and a mixed gas of Ar, N2, and H2 (hydrogen (H2) concentration: 1 to 30 vol%, nitrogen (N2) concentration: 5 to 75 vol%, argon concentration: 10 to 94 vol%, gas pressure: 0.5×10-1 to 1.0 Pa) as the sputtering gas, and form a film to a thickness of 20 to 90 nm under the conditions of an input power of 300 to 2000 W and a film-forming speed of 0.5 to 60 nm / min.

[0102] The EUV mask substrate 10 of the present embodiment may also have a structure other than the structure shown in FIG. 1, that is, the substrate 11, the conductive film 12, the reflective layer 13, and the absorption layer 14.

[0103] In the EUV mask substrate of the present embodiment, a protective layer may also be formed between the reflective layer 13 and the absorption layer 14. When forming a pattern on the absorption layer 14 using an etching process, usually a dry etching process, the purpose of setting the protective layer is to protect the reflective layer 13 from being damaged by the etching process. Therefore, as the material of the protective layer, a substance is selected that is not easily affected by the etching process of the absorption layer 14, that is, the etching rate is slower than that of the absorption layer 14, and it is not easily damaged by the etching process. To satisfy the above characteristics, the protective layer preferably contains a material containing ruthenium (Ru). Specific examples of the material containing Ru include Ru and Ru compounds (RuB, RuSi, RuNb, RuTi, RuY, RuZr, RuLa, etc.). As the material containing Ru, a material containing 40.0 at% or more of Ru in the material is preferred, more preferably containing 50.0 at% or more, and still more preferably containing 55.0 at% or more.

[0104] When forming the protective layer, its thickness is preferably 1 to 20 nm, more preferably 1 to 5 nm.

[0105] When forming the protective layer, a well-known film-forming method such as a magnetron sputtering method or an ion beam sputtering method is used for film formation. When forming a Ru film by the magnetron sputtering method, it is preferable to use a Ru target as the target, use argon (Ar) (gas pressure: 1.0×10 -2 to 10×10 -1 Pa) as the sputtering gas, and form a film with a thickness of 2 to 5 nm under the conditions of an input voltage of 30 to 1500 V and a film-forming speed of 0.020 to 1.000 nm / sec.

[0106] Furthermore, even when a protective layer is provided on the reflective layer 13, the maximum value of the light reflectance near a wavelength of 13.5 nm is preferably 60% or more, more preferably 63% or more, and still more preferably 65% or more.

[0107] Furthermore, in the EUV mask substrate of the present embodiment, a low-reflection layer under inspection light for inspecting the mask pattern may also be formed on the absorption layer 14.

[0108] The low-reflection layer includes a film that has low reflectance under inspection light for inspecting a mask pattern. When manufacturing an EUV mask, after forming a pattern on the absorption layer, it is checked whether the pattern is formed as designed. During the inspection process of the mask pattern, an inspection machine that usually uses light of around 257 nm as inspection light is adopted. That is, the inspection is carried out by the reflectance difference of the light of around 257 nm. Specifically, it is carried out by the reflectance difference between the surface exposed after removing the absorption layer by pattern formation and the surface of the absorption layer remaining without being removed by pattern formation.

[0109] Here, the former refers to the surface of the reflection layer or the protective layer, usually the surface of the protective layer. Therefore, if the reflectance difference between the surface of the reflection layer or the protective layer and the surface of the absorption layer is small relative to the wavelength of the inspection light, the contrast during inspection becomes poor and precise inspection cannot be carried out. In the case where the reflectance difference between the surface of the reflection layer or the protective layer and the surface of the absorption layer is small relative to the wavelength of the inspection light, by forming a low-reflection layer, the contrast during inspection becomes good. When forming a low-reflection layer on the absorption layer, when light in the wavelength region of the inspection light irradiates the surface of the low-reflection layer, the maximum light reflectance of the low-reflection layer at the inspection light wavelength is preferably 15% or less, more preferably 10% or less, and still more preferably 5% or less.

[0110] In order to achieve the above characteristics, the low-reflection layer preferably includes a material having a refractive index lower than that of the absorption layer at the wavelength of the inspection light.

[0111] As a low-reflection layer that satisfies this characteristic, there are the following: those containing at least one selected from the group consisting of tantalum (Ta), palladium (Pd), chromium (Cr), silicon (Si), and hafnium (Hf), and at least one selected from the group consisting of oxygen (O) and nitrogen (N). As a preferred example of such a low-reflection layer, TaPdO layer, TaPdON layer, TaON layer, CrO layer, CrON layer, SiON layer, SiN layer, HfO layer, HfON layer can be cited.

[0112] The total content rate of Ta, Pd, Cr, Si, and Hf in the low-reflection layer is preferably 10 to 55 at%, especially 10 to 50 at%, because the optical properties in the wavelength region of the pattern inspection light can be controlled.

[0113] Also, the total content of O and N in the low-reflection layer is preferably 45 to 90 at%, particularly 50 to 90 at%, because the optical properties in the wavelength region of the pattern inspection light can be controlled. Furthermore, the total content of Ta, Pd, Cr, Si, Hf, O, and N in the low-reflection layer is preferably 95 to 100 at%, more preferably 97 to 100 at%, and still more preferably 99 to 100 at%.

[0114] The low-reflection layer having the above-described configuration can be formed by a sputtering method using a target containing at least one of Ta, Pd, Cr, Si, and Hf. Here, as the target, two or more of the above-described metal targets and compound targets can be used.

[0115] Furthermore, the use of two or more metal targets is suitable for adjusting the constituent components of the low-reflection layer. Furthermore, in the case of using two or more metal targets, the constituent components of the absorption layer can be adjusted by adjusting the input power to the targets. On the other hand, in the case of using a compound target, it is preferable to pre-adjust the target composition so that the formed low-reflection layer becomes the desired composition.

[0116] The sputtering method using the above-described target, like the sputtering method for forming the absorption layer, can be carried out in an inert gas atmosphere.

[0117] However, when the low-reflection layer contains oxygen (O), the sputtering method is carried out in an inert gas atmosphere containing at least one of He, Ar, Ne, Kr, and Xe and O2. When the low-reflection layer contains N, the sputtering method is carried out in an inert gas atmosphere containing at least one of He, Ar, Ne, Kr, and Xe and N2. When the low-reflection layer contains O and N, the sputtering method is carried out in an inert gas atmosphere containing at least one of He, Ar, Ne, Kr, and Xe, O2, and N2.

[0118] The specific implementation conditions of the sputtering method also vary depending on the target used or the composition of the inert gas atmosphere in which the sputtering method is carried out, but in any case, the sputtering method can be carried out under the following conditions. Hereinafter, taking the case where the inert gas atmosphere is a mixed gas atmosphere of Ar and O2 as an example, the formation conditions of the low-reflection layer will be described.

[0119] (Formation Conditions of Low-Reflection Layer) Air pressure: 1.0×10 -1 to 50×10 -1 Pa, preferably 1.0×10 -1 to 40×10 -1 Pa, more preferably 1.0×10 -1 to 30×10 -1 Pa. Sputtering gas: A mixed gas of Ar and O 2 (oxygen concentration: 3 to 80 vol%, preferably 5 to 60 vol%, more preferably 10 to 40 vol%) Input power: 30 to 1000 W, preferably 50 to 750 W, more preferably 80 to 500 W Film formation rate: 0.01 to 60 nm / min, preferably 0.05 to 45 nm / min, more preferably 0.1 to 30 nm / min

[0120] Furthermore, when using an inert gas other than Ar or a plurality of inert gases, the total concentration of the inert gas is set to the same concentration range as the above-mentioned argon gas concentration. Also, when the inert gas atmosphere contains N 2, the N 2 concentration is set, and when the inert gas atmosphere contains N 2 and O 2, the total concentration is set to the same concentration range as the above-mentioned oxygen concentration.

[0121] Furthermore, in the EUV mask substrate of the present embodiment, it is preferable to form a low-reflection layer on the absorption layer because the wavelength of the inspection light of the pattern is different from the wavelength of the EUV light. Therefore, when using EUV light (around 13.5 nm) as the inspection light of the pattern, it is considered that there is no need to form a low-reflection layer on the absorption layer. As the pattern size continues to shrink, the wavelength of the inspection light tends to shift to the short-wavelength side, and it is also considered that it will shift to 193 nm and then to 13.5 nm in the future. When the wavelength of the inspection light is 13.5 nm, it is considered that there is no need to form a low-reflection layer on the absorption layer.

[0122] In the EUV mask substrate of the present embodiment, a hard mask layer described in Japanese Patent Application Laid-Open No. 2009-54899 or Japanese Patent Application Laid-Open No. 2009-21582, that is, a layer of a material resistant to the etching conditions of the absorption layer (the absorption layer and the low reflection layer when the low reflection layer is formed on the absorption layer), may also be formed on the absorption layer 14 (on the absorption layer when the low reflection layer is formed on the absorption layer). By forming such a hard mask layer, the etching selectivity between the absorption layer (the absorption layer and the low reflection layer when the low reflection layer is formed on the absorption layer) and the hard mask layer under the etching conditions of the absorption layer (the absorption layer and the low reflection layer when the low reflection layer is formed on the absorption layer) is improved. Specifically, the ratio of the etching rate of the absorption layer (the etching rate of the absorption layer and the low reflection layer when the low reflection layer is formed on the absorption layer) to the etching rate of the hard mask layer under the etching conditions of the absorption layer (the absorption layer and the low reflection layer when the low reflection layer is formed on the absorption layer) can be increased, enabling the resist film to be thinned.

[0123] Next, the substrate with a conductive film of the present embodiment will be described. The substrate with a conductive film of the present embodiment has a conductive film on the substrate. Here, the substrate and the conductive film are the same as those of the EUV mask substrate of the present embodiment. That is, the EUV mask substrate of the present embodiment is formed with a reflective layer and an absorption layer on the surface opposite to the surface of the substrate with a conductive film of the present embodiment where the above-mentioned conductive film is provided.

[0124] As described above, the following configurations are disclosed in this specification. (1) A reflective mask substrate for EUV lithography, comprising: a substrate, a conductive film disposed on the back side of the substrate, a reflective layer disposed on the front side of the substrate and reflecting EUV light, and an absorption layer disposed on the reflective layer and absorbing EUV light, and the above-mentioned conductive film contains at least one of nitrogen (N) and boron (B), the total content of N and B contained in the above-mentioned conductive film exceeds 0 at% and is 65 at% or less, the refractive index nλ1000 - 1100 nm of the conductive film at a wavelength of 1000 - 1100 nm is 5.300 or less, and the extinction coefficient kλ1000 - 1100 nm is 5.200 or less, the refractive index nλ600 - 700 nm of the conductive film at a wavelength of 600 - 700 nm is 4.300 or less, and the extinction coefficient kλ600 - 700 nm is 4.500 or less, The refractive index nλ400 - 500 nm of the conductive film at a wavelength of 400 to 500 nm is 2.500 or more, and the extinction coefficient kλ400 - 500 nm is 0.440 or more. The film thickness t of the conductive film is 20 to 350 nm. The resistivity of the conductive film is 3.5 mΩ·cm or less. (2) A reflective mask substrate for EUV lithography, comprising: A substrate, A conductive film disposed on the back side of the substrate, A reflective layer disposed on the front side of the substrate and reflecting EUV light, and An absorption layer disposed on the reflective layer and absorbing EUV light, and The conductive film contains at least one of nitrogen (N) and boron (B). The total content of N and B contained in the conductive film exceeds 0 at% and is 65 at% or less. The refractive index nλ1000 - 1100 nm of the conductive film at a wavelength of 1000 to 1100 nm is 5.300 or less, and the extinction coefficient kλ1000 - 1100 nm is 5.200 or less. The refractive index nλ600 - 700 nm of the conductive film at a wavelength of 600 to 700 nm is 4.300 or less, and the extinction coefficient kλ600 - 700 nm is 4.500 or less. The refractive index nλ480 - 500 nm of the conductive film at a wavelength of 480 to 500 nm is 2.500 or more, and the extinction coefficient kλ480 - 500 nm is 0.440 or more. The film thickness t of the conductive film is 20 to 350 nm. The resistivity of the conductive film is 3.5 mΩ·cm or less. (3) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the conductive film contains at least one of tantalum (Ta) and chromium (Cr). (4) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the conductive film contains Ta and N. (5) The reflective mask substrate for EUV lithography according to (4), wherein the conductive film contains N exceeding 0 at% and being 65 at% or less. (6) The reflective mask substrate for EUV lithography according to (1) or (2), wherein the conductive film contains Ta and B. (7) The reflective mask substrate for EUV lithography according to (6), wherein the conductive film contains B exceeding 0 at% and being 35 at% or less. (8) The reflective mask substrate for EUV lithography as described in (1) or (2), wherein the resistivity of the conductive film is 0.050 mΩ·cm or more and 3.5 mΩ·cm or less. (9) The reflective mask substrate for EUV lithography as described in (3) or (4), wherein the conductive film contains Ta, and in the diffraction peaks originating from the conductive film observed by out-of-plane XRD method, the full width at half maximum FWHM of the diffraction peak attributed to the bcc(110) plane of Ta is 1.5 to 4.0°. (10) The reflective mask substrate for EUV lithography as described in any one of (1) to (4), wherein the light transmittance of the conductive film at a wavelength of 1000 to 1100 nm is 1.0% or more, the light transmittance at a wavelength of 600 to 700 nm is 1.0% or more, and the light transmittance at a wavelength of 400 to 500 nm is 1.0% or less. (11) The reflective mask substrate for EUV lithography as described in any one of (1) to (4), wherein the sheet resistance value of the conductive film is 250 Ω / □ or less. (12) The reflective mask substrate for EUV lithography as described in any one of (1) to (4), wherein the surface hardness of the conductive film is 10.0 GPa or more. (13) The reflective mask substrate for EUV lithography as described in any one of (1) to (4), wherein an upper layer is further provided on the conductive film, The upper layer contains chromium (Cr) and at least one element selected from the group consisting of nitrogen (N) and oxygen (O). (14) The reflective mask substrate for EUV lithography as described in any one of (1) to (4), wherein the surface roughness (Rq) of the conductive film is 0.600 nm or less. (15) A substrate with a conductive film, which has a conductive film on the substrate, and The conductive film contains at least one of nitrogen (N) and boron (B), The total content of N and B contained in the conductive film exceeds 0 at% and is 65 at% or less, The refractive index nλ1000 - 1100 nm of the conductive film at a wavelength of 1000 to 1100 nm is 5.300 or less, and the extinction coefficient kλ1000 - 1100 nm is 5.200 or less, The refractive index nλ600 - 700 nm of the conductive film at a wavelength of 600 to 700 nm is 4.300 or less, and the extinction coefficient kλ600 - 700 nm is 4.500 or less, The refractive index nλ400 - 500 nm of the above conductive film is 2.500 or more at a wavelength of 400 to 500 nm, and the extinction coefficient kλ400 - 500 nm is 0.440 or more. The film thickness t of the above conductive film is 20 to 350 nm. The resistivity of the conductive film is 3.5 mΩ·cm or less. (16) A substrate with a conductive film, which has a conductive film on the substrate, and the above conductive film contains at least one of nitrogen (N) and boron (B). The total content of N and B contained in the above conductive film exceeds 0 at% and is 65 at% or less. The refractive index nλ1000 - 1100 nm of the above conductive film is 5.300 or less at a wavelength of 1000 to 1100 nm, and the extinction coefficient kλ1000 - 1100 nm is 5.200 or less. The refractive index nλ600 - 700 nm of the above conductive film is 4.300 or less at a wavelength of 600 to 700 nm, and the extinction coefficient kλ600 - 700 nm is 4.500 or less. The refractive index nλ480 - 500 nm of the above conductive film is 2.500 or more at a wavelength of 480 to 500 nm, and the extinction coefficient kλ480 - 500 nm is 0.440 or more. The film thickness t of the above conductive film is 20 to 350 nm. The resistivity of the conductive film is 3.5 mΩ·cm or less. (17) The substrate with a conductive film as described in (15) or (16), wherein the above conductive film contains at least one of tantalum (Ta) and chromium (Cr). (18) The substrate with a conductive film as described in (15) or (16), wherein the above conductive film contains Ta and N. (19) The substrate with a conductive film as described in (18), wherein the above conductive film contains N exceeding 0 at% and being 65 at% or less. (20) The substrate with a conductive film as described in (15) or (16), wherein the above conductive film contains Ta and B. (21) The substrate with a conductive film as described in (20), wherein the above conductive film contains B exceeding 0 at% and being 35 at% or less. (22) The substrate with a conductive film as described in (15) or (16), wherein the resistivity of the above conductive film is 0.050 mΩ·cm or more and 3.5 mΩ·cm or less. (23) The substrate with a conductive film as described in (17) or (18), wherein the conductive film contains Ta, and in the diffraction peaks originating from the conductive film observed by the out-of-plane XRD method, the full width at half maximum (FWHM) of the diffraction peak attributed to the bcc (110) plane of Ta is 1.5 to 4.0°. (24) The substrate with a conductive film as described in any one of (15) to (18), wherein the light transmittance of the conductive film for light with a wavelength of 1000 to 1100 nm is 1.0% or more, the light transmittance for light with a wavelength of 600 to 700 nm is 1.0% or more, and the light transmittance for light with a wavelength of 400 to 500 nm is 1.0% or less. (25) The substrate with a conductive film as described in any one of (15) to (18), wherein the sheet resistance of the conductive film is 250 Ω / square or less. (26) The substrate with a conductive film as described in any one of (15) to (18), wherein the surface hardness of the conductive film is 10.0 GPa or more. (27) The substrate with a conductive film as described in any one of (15) to (18), wherein an upper layer is further provided on the conductive film. The upper layer contains chromium (Cr) and at least one element selected from the group consisting of nitrogen (N) and oxygen (O). (28) The substrate with a conductive film as described in any one of (15) to (18), wherein the surface roughness (Rq) of the conductive film is 0.600 nm or less. Examples

[0125] Hereinafter, Examples 1 to 10 are used to explain the present invention in more detail, but the present invention is not limited to these examples. Furthermore, Examples 1 to 3, 5, and 10 are examples, and Examples 4, 6 to 9 are comparative examples.

[0126] <Example 1> In this example, a TaN film was formed as a conductive film on one surface of the substrate. As the film-forming substrate, a SiO 2-TiO 2-based glass substrate (outer shape: 6 inches (152 mm) square, thickness: 6.3 mm) was used. The thermal expansion coefficient of this glass substrate at 20°C is 0.02×10 -7 / °C, the Young's modulus is 67 GPa, the Poisson's ratio is 0.17, and the specific stiffness is 3.07×10 7m 2 / s 2. By polishing this glass substrate, a smooth surface with a surface roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less was formed.

[0127] On one surface side of a substrate, a TaN film is formed as a conductive film using a magnetron sputtering method. The film formation conditions of the TaN film are as described below. (Film formation conditions) Target: Ta target Sputtering gas: Mixed gas of Ar and N2 (Ar: 90 vol%, N2: 10 vol%, gas pressure: 0.12 Pa) Input power: 1000 W Film formation rate: 6 nm / min Film thickness: 56 nm

[0128] (Composition analysis of TaN film) Using a Rutherford Backscattering Spectrometry (RBS) and an X-ray photoelectron spectroscopy device, the composition of the TaN film is measured. The N content rate of the TaN film is 21.0 at%.

[0129] (Refractive index n and extinction coefficient k) For the formed TaN film, using a spectroscopic ellipsometer (manufacturer: manufactured by J.A. Woollam Co., Ltd., model: M2000-DI), the refractive index nλ1000 - 1100 nm and the extinction coefficient kλ1000 - 1100 nm at a wavelength of 1000 to 1100 nm are obtained. The light is incident from the surface side where the TaN film is formed, and the polarization state is measured at room temperature, and the analysis is carried out to calculate the refractive index nλ1000 - 1100 nm and the extinction coefficient kλ1000 - 1100 nm at a wavelength of 1000 to 1100 nm. Also, following the same procedure, the refractive index nλ600 - 700 nm and the extinction coefficient kλ600 - 700 nm at a wavelength of 600 to 700 nm, the refractive index nλ400 - 500 nm and the extinction coefficient kλ400 - 500 nm at a wavelength of 400 to 500 nm, and the refractive index nλ480 - 500 nm and the extinction coefficient kλ480 - 500 nm at a wavelength of 480 to 500 nm are calculated. The results are shown in Table 2.

[0130] (Light transmittance) For the substrate after TaN film formation, light is perpendicularly incident from the side of the surface where the TaN film is formed, and a spectrophotometer (manufacturer: Hitachi High-Technologies Corporation, model: U-4100) is used to measure the light transmittance in the wavelength range of 175 to 2000 nm, and the light transmittance at wavelengths of 1000 to 1100 nm, the light transmittance at wavelengths of 600 to 700 nm, and the light transmittance at wavelengths of 400 to 500 nm are obtained. The case where the light transmittance at wavelengths of 1000 to 1100 nm is 1.0% or more, the light transmittance at wavelengths of 600 to 700 nm is 1.0% or more, and the light transmittance at wavelengths of 400 to 500 nm is 1.0% or less is evaluated as 〇, and the case where any one of these is not satisfied is evaluated as ×. The results are shown in Table 1.

[0131] (XRD full width at half maximum FWHM) For the TaN film, out-of-plane XRD measurement is performed. In the range of diffraction angles of 30 to 40°, the full width at half maximum FWHM of the main peak of the diffraction peak attributed to the bcc(110) plane of Ta in the diffraction peaks from the TaN film is measured. The results are shown in Table 1.

[0132] (Surface hardness) The surface hardness of the TaN film is measured by a nanoindentation test. The case where the surface hardness is 10.0 GPa or more is evaluated as 〇, and the case where the surface hardness is less than 10.0 GPa is evaluated as ×. The results are shown in Table 1.

[0133] (Resistivity) The resistivity of the TaN film is calculated under the following conditions. The case where the resistivity is 3.5 mΩ·cm or less is evaluated as 〇, and the case where it exceeds 3.5 mΩ·cm is evaluated as ×. Furthermore, if the resistivity is sufficiently low, 3.5 mΩ·cm or less, it can be considered that sufficient fixing force can be obtained when fixing the EUV mask made of the EUV mask substrate to the exposure device. The resistivity is evaluated from the surface of the sample conductive film. · Evaluation device: Loresta-GX manufactured by Nitto Seiko ANALYTECH Co., Ltd. · Number of measurement points: 9 points · Measurement range: 149 mm × 149 mm

[0134] (Surface roughness) The surface roughness (root mean square surface roughness RQ) is measured within a range of 2 μm × 2 μm using an atomic force microscope (AFM) manufactured by SII Corporation.

[0135] (Thermal relaxation rate of flatness) Using a flatness measuring machine manufactured by FUJINON Corporation, measure the flatness of the substrate with a TaN film formed thereon after the TaN film is formed. Next, perform heat treatment on the substrate with the TaN film at 136 °C for 20 minutes, and then use a flatness measuring machine manufactured by FUJINON Corporation to measure the flatness of the substrate with the TaN film after the heat treatment. Next, calculate the thermal relaxation rate of flatness according to the following formula, and evaluate the case where the thermal relaxation rate of flatness is 15% or less as 〇, and the case where it exceeds 15% as ×. Thermal relaxation rate of flatness (%) = {(Flatness of the substrate with the TaN film before heat treatment - Flatness of the substrate with the TaN film after heat treatment) / Flatness of the substrate with the TaN film before heat treatment} × 100

[0136] <Example 2> In this example, on one side of the substrate, a laminated film of a TaN film and a CrN film is formed as a conductive film using a magnetron sputtering method. The film formation conditions of the TaN film and the CrN film are as described below. (TaN film) Target: Ta target Sputtering gas: Mixed gas of Ar and N2 (Ar: 60 vol%, N2: 40 vol%, gas pressure: 0.11 Pa) Input power: 1000 W Film formation rate: 3.9 nm / min Film thickness: 23 nm (CrN film) Target: Cr target Sputtering gas: Mixed gas of Ar and N2 (Ar: 53 vol%, N2: 47 vol%, gas pressure: 0.10 Pa) Input power: 1700 W Film formation rate: 11.4 nm / min Film thickness: 26 nm

[0137] (Composition analysis of TaN film and CrN film) Using RBS, measure the composition of the TaN film and the CrN film. The N content rate of the TaN film is 59.0 at%, and the N content rate of the CrN film is 4.2 at%.

[0138] (Refractive index n, extinction coefficient k) Following the same procedure as in Example 1, the refractive index n and extinction coefficient k of the laminated film were measured. The results are shown in Table 2. Furthermore, the refractive index n and extinction coefficient k described in Table 2 represent the values of the TaN film, and the refractive index n and extinction coefficient k of the CrN film are the same as those in Examples 3, 4, and 9.

[0139] (Light transmittance) Following the same procedure as in Example 1, the light transmittance of the laminated film was measured. The results are shown in Table 1. (XRD full width at half maximum FWHM) Using the out-of-plane XRD method, the TaN film was measured. In the range of diffraction angles from 30° to 40°, the full width at half maximum FWHM of the main peak of the diffraction peak attributed to the bcc(110) plane of Ta in the diffraction peak of the TaN film was measured. The results are shown in Table 1.

[0140] (Surface hardness) Following the same procedure as in Example 1, the surface hardness of the laminated film was measured. The results are shown in Table 1.

[0141] (Resistivity) Using the same measurement method as in the case of Example 1, the resistivity of the laminated film was measured. At this time, the resistivity of the TaN film and the CrN film was measured. The results are shown in Table 1.

[0142] (Surface roughness) Following the same procedure as in Example 1, the surface roughness of the laminated film was measured. The results are shown in Table 1.

[0143] (Thermal relaxation rate of flatness) Following the same procedure as in Example 1, the thermal relaxation rate of the flatness of the substrate with the laminated film was measured. The results are shown in Table 1.

[0144] <Example 3> In this example, on one surface of the substrate, a CrN film was formed as a conductive film using the magnetron sputtering method. The film formation conditions of the CrN film are as follows. (Film formation conditions) Target: Cr target Sputtering gas: Mixed gas of Ar and N2 (Ar: 53 vol%, N2: 47 vol%, gas pressure: 0.10 Pa) Input power: 1700 W Film formation rate: 11.4 nm / min Film thickness: 40 nm

[0145] (Composition analysis of CrN film) Using RBS, the composition of the CrN film was measured. The N content rate of the CrN film was 4.2 at%.

[0146] (Refractive index n, extinction coefficient k) Following the same procedure as in Example 1, the refractive index n and extinction coefficient k of the CrN film were measured. The results are shown in Table 2.

[0147] (Light transmittance) Following the same procedure as in Example 1, the light transmittance of the CrN film was measured. The results are shown in Table 1.

[0148] (Surface hardness) Following the same procedure as in Example 1, the surface hardness of the CrN film was measured. The results are shown in Table 1.

[0149] (Resistivity) Using the same measurement method as in Example 1, the resistivity of the CrN film was measured. The results are shown in Table 1.

[0150] (Thermal relaxation rate of flatness) Following the same procedure as in Example 1, the thermal relaxation rate of the flatness of the substrate with the CrN film was measured. The results are shown in Table 1.

[0151] <Example 4> In this example, the film thickness of the CrN film was set to 360 nm, and other than that, the same procedure as in Example 3 was carried out.

[0152] (Composition analysis of CrN film) Using RBS, the composition of the CrN film was measured. The N content rate of the CrN film was 4.2 at%.

[0153] (Refractive index n, extinction coefficient k) Following the same procedure as in Example 1, the refractive index n and extinction coefficient k of the CrN film were measured. The results are shown in Table 2.

[0154] (Light transmittance) Following the same procedure as in Example 1, the light transmittance of the CrN film was measured. The results are shown in Table 1.

[0155] (Surface hardness) The surface hardness of the CrN film was measured according to the same procedure as in Example 1. The results are shown in Table 1.

[0156] (Resistivity) The resistivity of the CrN film was measured using the same measurement method as in Example 1. The results are shown in Table 1.

[0157] (Thermal relaxation rate of flatness) The thermal relaxation rate of the flatness of the substrate with the CrN film was measured according to the same procedure as in Example 1. The results are shown in Table 1.

[0158] <Example 5> In this example, a TaB film was formed as a conductive film on one surface of the substrate using a magnetron sputtering method. The film formation conditions of the TaB film are as follows. (Film formation conditions) Target: TaB compound target Sputtering gas: Argon (gas pressure: 0.205 Pa) Input power: 1000 W Film formation rate: 1.67 nm / min Film thickness: 56 nm

[0159] (Composition analysis of TaB film) The composition of the TaB film was measured using RBS and X-ray photoelectron spectroscopy (XPS). The N content rate of the TaB film is 0.0 at%, and the content of B is 28.0 at%.

[0160] (Refractive index n, extinction coefficient k) The refractive index n and extinction coefficient k of the TaB film were measured according to the same procedure as in Example 1. The results are shown in Table 2.

[0161] (Light transmittance) The light transmittance of the multilayer film was measured according to the same procedure as in Example 1. The results are shown in Table 1.

[0162] (XRD full width at half maximum FWHM) Using the out-of-plane XRD method, the TaB film was measured. In the range of diffraction angles from 30° to 40°, the full width at half maximum (FWHM) of the main peak of the diffraction peak attributed to the bcc(110) plane of Ta in the diffraction peaks from the TaB film was measured. The results are shown in Table 1.

[0163] (Surface hardness) Following the same procedure as in Example 1, the surface hardness of the TaB film was measured. The results are shown in Table 1.

[0164] (Resistivity) Using the same measurement method as in Example 1, the resistivity of the TaB film was measured. The results are shown in Table 1.

[0165] (Surface roughness) Following the same procedure as in Example 1, the surface roughness of the TaB film was measured. The results are shown in Table 1.

[0166] (Thermal relaxation rate of flatness) Following the same procedure as in Example 1, the thermal relaxation rate of the flatness of the substrate with the TaB film was measured. The results are shown in Table 1.

[0167] <Example 6> In this example, on one side of the substrate, a TaON film was formed as a conductive film using the magnetron sputtering method. The film formation conditions of the TaON film are as follows. (Film formation conditions) Target: Ta target Sputtering gas: A mixed gas of N2 and O2 (N2: 88 vol%, O2: 12 vol%, gas pressure: 0.18 Pa) Input power: 1000 W Film formation rate: 0.9 nm / min Film thickness: 60 nm

[0168] (Composition analysis of TaON film) Using RBS, the composition of the TaON film was measured. The N content rate of the TaON film was 6.0 at%, and the content of O was 68.0 at%.

[0169] (Refractive index n, extinction coefficient k) Following the same procedure as in Example 1, the refractive index n and extinction coefficient k of the TaON film were measured. The results are shown in Table 2.

[0170] (Light transmittance) Following the same procedure as in Example 1, the light transmittance of the TaON film was measured. The results are shown in Table 1.

[0171] (Resistance value) Using the same measurement method as in Example 1, the resistivity of the TaON film was measured. The results are shown in Table 1.

[0172] <Example 7> In this example, a CrON film was formed as a conductive film on one surface of the substrate using a magnetron sputtering method. The film formation conditions of the CrON film are as follows. (Film formation conditions) Target: Cr target Sputtering gas: Mixed gas of Ar, N2 and O2 (Ar: 33 vol%, N2: 22 vol%, O2: 45 vol%, gas pressure: 0.09 Pa) Input power: 750 W Film formation rate: 1.86 nm / min Film thickness: 60 nm

[0173] (Refractive index n, extinction coefficient k) Following the same procedure as in Example 1, the refractive index n and extinction coefficient k of the CrON film were measured. The results are shown in Table 2.

[0174] (Light transmittance) Following the same procedure as in Example 1, the light transmittance of the CrON film was measured. The results are shown in Table 1.

[0175] <Example 8> In this example, the film thickness of the TaN film was set to 17 nm, and other than that, the same procedure as in Example 1 was carried out.

[0176] (Composition analysis of TaN film) Using RBS, the composition of the TaN film was measured. The N content rate of the TaN film was 21.0 at%.

[0177] (Refractive index n, extinction coefficient k) Following the same procedure as in Example 1, the refractive index n and extinction coefficient k of the TaN film were measured. The results are shown in Table 2.

[0178] (Light transmittance) In the same procedure as in Example 1, the light transmittance of the TaN film was measured. The results are shown in Table 1.

[0179] (Thermal relaxation rate of flatness) In the same procedure as in Example 1, the thermal relaxation rate of flatness of the substrate with the TaN film was measured. The results are shown in Table 1.

[0180] <Example 9> In this example, the film thickness of the CrN film was set to 12 nm, and except for this, the same procedure as in Example 3 was carried out.

[0181] (Composition analysis of CrN film) Using RBS, the composition of the CrN film was measured. The N content rate of the CrN film was 4.2 at%.

[0182] (Refractive index n, extinction coefficient k) In the same procedure as in Example 1, the refractive index n and extinction coefficient k of the CrN film were measured. The results are shown in Table 2.

[0183] (Light transmittance) In the same procedure as in Example 1, the light transmittance of the CrN film was measured. The results are shown in Table 1.

[0184] (Thermal relaxation rate of flatness) In the same procedure as in Example 1, the thermal relaxation rate of flatness of the substrate with the CrN film was measured. The results are shown in Table 1.

[0185] <Example 10> In this example, on one side of the substrate, a TaN film was formed as a conductive film using a magnetron sputtering method, and then a CrO film was formed as the upper layer. The film thickness of the TaN film was changed, and except for this, the film formation was carried out under the same film formation conditions as the TaN film in Example 2. The film formation conditions of the TaN film and the CrO film are as described below.

[0186] (TaN film) Target: Ta target Sputtering gas: Mixed gas of Ar and N2 (Ar: 60 vol%, N2: 40 vol%, gas pressure: 0.11 Pa) Input power: 1000 W Film formation rate: 3.9 nm / min Film thickness: 30 nm

[0187] (CrO film) Target: Cr target Sputtering gas: Mixed gas of Ar and O2 (Ar: 66 vol%, O2: 34 vol%, gas pressure: 0.16 Pa) Input power: 750 W Film formation rate: 9.0 nm / min Film thickness: 27 nm

[0188] (Composition analysis of TaN film and CrO film) Using RBS, the composition of TaN film and CrO film was measured. The N content rate of TaN film is 59.0 at%, and the O content rate of CrO film is 15.0 at%.

[0189] (Refractive index n, extinction coefficient k) According to the same procedure as in Example 1, the refractive index n and extinction coefficient k of the laminated film were measured. The results are shown in Table 2. Furthermore, the refractive index n and extinction coefficient k described in Table 2 represent the values of the CrO film, and the refractive index n and extinction coefficient k of the TaN film are the same as those of the TaN film in Example 2.

[0190] (Light transmittance) According to the same procedure as in Example 1, the light transmittance of the laminated film was measured. The results are shown in Table 1.

[0191] (Surface hardness) According to the same procedure as in Example 1, the surface hardness of the laminated film was measured. The results are shown in Table 1.

[0192] (Resistivity) Using the same measurement method as in Example 1, the resistivity of the TaN film was measured. The results are shown in Table 1.

[0193] (Surface roughness) According to the same procedure as in Example 1, the surface roughness of the laminate was measured. The results are shown in Table 1.

[0194] (Thermal relaxation rate of flatness) Following the same procedure as in Example 1, the thermal relaxation rate of the flatness of the substrate with the laminated film was measured. The results are shown in Table 1.

[0195] [Table 1] Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Film type TaN TaN / CrN CrN CrN TaB TaON CrON TaN CrN TaN / CrO TaN CrN TaN (Conductive film) CrO (Upper layer) Film formation conditions Film formation method Magnetron sputtering Gas type Ar+N 2 Ar+N 2 Ar+N 2 Ar+N 2 Ar+N 2 Noble gas Ar+O 2 Ar+N 2+O 2 Ar+N 2 Ar+N 2 Ar+N 2 Ar+O 2 N 2(vol%) 10 40 47 47 47 0 88 22 10 47 40 - O2 (vol%) - - - - - - 12 45 - - - 34 Film thickness (nm) 56 23 26 40 360 56 60 60 17 12 30 27 Evaluation N (at%_RBS) 21.0 59.0 4.2 4.2 4.2 0.0 6.0 - 21.0 4.2 59.0 - O (at%_RBS) - - - - - - 68.0 - - - - 15.0 B(at%_XPS) - - - - - 28.0 - - - - - - n, k Refer to Table 2 Light transmittance (%) 400 - 500 nm 0.8 0.8 0.5 0.0 0.9 72.0 40.0 13.0 12.0 0.8 600 - 700 nm 1.5 1.6 1.0 0.0 1.7 75.0 49.0 14.0 12.0 1.5 1000 - 1100 nm 2.8 3.2 2.3 0.0 3.0 84.0 64.0 16.0 15.0 3.4 determination 〇 〇 〇 × 〇 × × × × 〇 XRD FWHM, (Ta bcc110 surface) (°) 3.5 2.1 - - - 4.9 - - - - 2.1 - Surface hardness (Gpa) 10.2 14.9 16.3 17 8.8 - - - - 8.9 determination 〇 〇 〇 〇 × - - - - × Flatness (curvature) determination 〇 〇 × 〇 〇 - - - - ○ Resistivity of the conductive film (mΩ·cm) 0.230 0.157 0.108 0.094 0.228 >2.4×10 5 - - - 0.185 Judgment ○ ○ ○ ○ ○ × - - - ○ Surface roughness 0.083 0.132 - - 0.066 - - - - 0.35 Thermal relaxation rate of flatness (warpage) (%) 7 13 50 50 7 - - 7 50 2 Judgment ○ ○ × × ○ - - ○ × ○

[0196] [Table 2] Table 2 Wavelength Example 1, 8 TaN Example 2 TaN / CrN Example 3, 4, 9 CrN Example 5 TaB Example 6 TaON Example 7 CrON Example 10 TaN / CrO n k n k n k n k n k n k n k 1000 - 1100 nm min 4.419 3.709 4.321 3.049 5.007 4.966 4.238 3.749 2.052 0.000 2.243 0.121 4.877 3.416 max 4.593 3.836 4.501 3.104 5.214 5.164 4.410 3.900 2.056 0.000 2.429 0.142 5.004 3.478 600-700 nm min 3.490 3.148 3.266 2.629 3.894 4.407 3.379 3.106 2.080 0.000 2.425 0.232 3.937 3.358 max 3.769 3.304 3.590 2.797 4.288 4.485 3.630 3.275 2.098 0.000 2.420 0.270 4.292 3.371 400-500 nm min 2.775 2.764 2.698 1.989 2.517 3.849 2.737 2.758 2.132 0.000 2.428 0.319 2.748 3.106 max 3.167 2.971 2.931 2.358 3.278 4.264 3.092 2.931 2.203 0.000 2.460 0.430 3.425 3.333 480-500 nm min 3.095 2.933 2.871 2.289 3.130 4.208 3.028 2.896 2.132 0.000 2.428 0.319 3.301 3.308 max 3.167 2.971 2.931 2.358 3.278 4.264 3.092 2.931 2.141 0.000 2.433 0.334 3.425 3.333

[0197] Examples 1, 2, 3, 5, and 10 where the refractive index n at λ 1000 - 1100 nm is 5.300 or less, the extinction coefficient k at λ 1000 - 1100 nm is 5.200 or less, the refractive index n at λ 600 - 700 nm is 4.300 or less, the extinction coefficient k at λ 600 - 700 nm is 4.500 or less, the refractive index n at λ 400 - 500 nm is 2.600 or more, the extinction coefficient k at λ 400 - 500 nm is 0.440 or more, the refractive index n at λ 480 - 500 nm is 2.500 or more, the extinction coefficient k at λ 480 - 500 nm is 0.440 or more, and the film thickness t of the conductive film is 20 - 350 nm. The evaluation of the light transmittance is ○. Furthermore, the evaluation of the resistivity of the conductive film is ○.

[0198] Examples 1 where the conductive film 12 is a TaN film, Example 2 where the conductive film 12 is a laminated film of a CrN film and a TaN film, Example 5 where the conductive film 12 is a TaB film, and Example 10 where a CrO film is provided as the upper layer on the TaN film. The evaluation of the thermal relaxation rate of the flatness of the substrate with the conductive film is ○.

[0199] Examples 1 where the conductive film 12 is a TaN film, Example 2 where the conductive film 12 is a laminated film of a CrN film and a TaN film, and Example 3 where the conductive film 12 is a CrN film. The surface hardness of the conductive film 12 is 10.0 GPa or more, and the surface hardness is ○.

[0200] Examples 6 and 7 where the refractive index n at λ 400 - 500 nm is less than 2.500, the extinction coefficient k at λ 400 - 500 nm is less than 0.440, the refractive index n at λ 480 - 500 nm is less than 2.500, and the extinction coefficient k at λ 480 - 500 nm is less than 0.440. The light transmittance at a wavelength of 400 - 500 nm is relatively high, exceeding 1.0%, and the evaluation of the light transmittance is ×. Also, in Comparative Example 6, the evaluation of the resistivity of the conductive film is ×.

[0201] For Example 4 where the film thickness t of the conductive film exceeds 350 nm, the light transmittance at a wavelength of 1000 - 1100 nm and the light transmittance at a wavelength of 600 - 700 nm are both 0.0%, and the evaluation of the light transmittance is ×.

[0202] In Examples 8 and 9 where the film thickness t of the conductive film is less than 20 nm, the light transmittance of light with wavelengths of 400 to 500 nm is relatively high, exceeding 1.0%, and the evaluation of the light transmittance is ×.

[0203] As described above, various embodiments have been described with reference to the drawings. Of course, the present invention is not limited to this example. Those skilled in the art will understand that various variations or modifications can be conceived within the scope described in the claims, and these examples also naturally belong to the technical scope of the present invention. Also, within the scope of not departing from the gist of the invention, the constituent elements of the above-described embodiments can be arbitrarily combined.

[0204] Furthermore, this application is based on a Japanese patent application (Japanese Patent Application No. 2023-043149) filed on March 17, 2023, and its content is incorporated herein by reference.

[0205] 10: EUV mask substrate 11: Substrate 12: Conductive film 13: Reflective layer (multilayer reflective film) 14: Absorbing layer

Claims

1. A reflective photomask substrate for EUV lithography, comprising: a substrate, a conductive film disposed on the back side of the substrate, a reflective layer disposed on the front side of the substrate and reflecting EUV light, and an absorbent layer disposed on the reflective layer and absorbing EUV light, wherein the conductive film contains at least one of nitrogen (N) and boron (B), the total content of N and B contained in the conductive film is more than 0 at% and less than 65 at%, the transmittance of the conductive film for light with wavelengths of 1000 to 1100 nm is more than 1.0%, the transmittance of the conductive film for light with wavelengths of 600 to 700 nm is more than 1.0%, the transmittance of the conductive film for light with wavelengths of 400 to 500 nm is less than 1.0%, and the resistivity of the conductive film is less than 3.5 mΩ·cm.

2. A reflective photomask substrate for EUV lithography, comprising: a substrate, a conductive film disposed on the back side of the substrate, a reflective layer disposed on the front side of the substrate and reflecting EUV light, and an absorbent layer disposed on the reflective layer and absorbing EUV light, wherein the conductive film contains at least one of nitrogen (N) and boron (B), the total content of N and B contained in the conductive film is more than 0 at% and less than 65 at%, the transmittance of the conductive film at wavelengths of 1000 to 1100 nm is 1.0% or more, the transmittance of the conductive film at wavelengths of 600 to 700 nm is 1.0% or more, the refractive index nλ480-500 nm of the conductive film at wavelengths of 480 to 500 nm is 2.500 or more, the extinction coefficient kλ480-500 nm is 0.440 or more, and the resistivity of the conductive film is 3.5 mΩ·cm or less.

3. The EUV lithography reflective photomask substrate of claim 1 or 2, wherein the conductive film contains at least one of tantalum (Ta) and chromium (Cr).

4. The EUV lithography reflective photomask substrate as claimed in claim 1 or 2, wherein the conductive film contains Ta and N.

5. The EUV lithography reflective photomask substrate as claimed in claim 4, wherein the conductive film contains more than 0 at% and less than 65 at% N.

6. The EUV lithography reflective photomask substrate as claimed in claim 1 or 2, wherein the conductive film contains Ta and B.

7. The EUV lithography reflective photomask substrate of claim 6, wherein the conductive film contains more than 0 at% and less than 35 at% of B.

8. The EUV lithography reflective photomask substrate as claimed in claim 1 or 2, wherein the resistivity of the conductive film is 0.050 mΩ·cm or more and 3.5 mΩ·cm or less.

9. The EUV lithography reflective photomask substrate of claim 1 or 2, wherein the conductive film contains Ta, and the half-width (FWHM) of the diffraction peak attributable to the bcc(110) plane of Ta, as observed by out-of-plane XRD, is 1.5 to 4.0°.

10. The reflective photomask substrate for EUV lithography as claimed in claim 2, wherein the transmittance of the conductive film at a wavelength of 400 to 500 nm is less than 1.0%.

11. The EUV lithography reflective photomask substrate as claimed in claim 1 or 2, wherein the sheet resistance of the conductive film is 250 Ω / □ or less.

12. The EUV lithography reflective photomask substrate as claimed in claim 1 or 2, wherein the surface hardness of the conductive film is 10.0 GPa or higher.

13. The EUV lithography reflective photomask substrate of claim 1 or 2, wherein an upper layer is further disposed on the conductive film, the upper layer containing chromium (Cr) and at least one element selected from the group consisting of nitrogen (N) and oxygen (O).

14. The EUV lithography reflective photomask substrate of claim 1 or 2, wherein the surface roughness (Rq) of the conductive film is less than 0.600 nm.

15. The EUV lithography reflective photomask substrate as claimed in claim 1 or 2, wherein the thickness t of the conductive film is 20 to 350 nm.

16. A substrate with a conductive film, wherein the conductive film is present on the substrate, and the conductive film contains at least one of nitrogen (N) and boron (B), wherein the total content of N and B contained in the conductive film is more than 0 at% and less than 65 at%, the transmittance of the conductive film for light with a wavelength of 1000 to 1100 nm is more than 1.0%, the transmittance of the conductive film for light with a wavelength of 600 to 700 nm is more than 1.0%, the transmittance of the conductive film for light with a wavelength of 400 to 500 nm is less than 1.0%, and the resistivity of the conductive film is less than 3.5 mΩ·cm.

17. A substrate with a conductive film, wherein the conductive film is present on the substrate, and the conductive film contains at least one of nitrogen (N) and boron (B), wherein the total content of N and B contained in the conductive film is more than 0 at% and less than 65 at%, the transmittance of the conductive film at wavelengths of 1000 to 1100 nm is more than 1.0%, the transmittance of the conductive film at wavelengths of 600 to 700 nm is more than 1.0%, the refractive index nλ480-500 nm of the conductive film at wavelengths of 480 to 500 nm is more than 2.500, the extinction coefficient kλ480-500 nm is more than 0.440, and the resistivity of the conductive film is less than 3.5 mΩ·cm.

18. The substrate with a conductive film as claimed in claim 16 or 17, wherein the conductive film contains at least one of tantalum (Ta) and chromium (Cr).

19. The substrate with a conductive film as claimed in claim 16 or 17, wherein the conductive film contains Ta and N.

20. The substrate with a conductive film as claimed in claim 19, wherein the conductive film contains more than 0 at% and less than 65 at% N.

21. The substrate with a conductive film as claimed in claim 16 or 17, wherein the conductive film contains Ta and B.

22. The substrate with a conductive film as claimed in claim 21, wherein the conductive film contains more than 0 at% and less than 35 at% of B.

23. The substrate with a conductive film as claimed in claim 16 or 17, wherein the resistivity of the conductive film is 0.050 mΩ·cm or more and 3.5 mΩ·cm or less.

24. The substrate with a conductive film as claimed in claim 16 or 17, wherein the conductive film contains Ta, and the half-width (FWHM) of the diffraction peak attributable to the bcc(110) plane of Ta, as observed by out-of-plane XRD, is 1.5 to 4.0°.

25. The substrate with a conductive film as claimed in claim 17, wherein the transmittance of light with a wavelength of 400 to 500 nm of the conductive film is less than 1.0%.

26. The substrate with a conductive film as claimed in claim 16 or 17, wherein the sheet resistance of the conductive film is 250 Ω / □ or less.

27. The substrate with a conductive film as claimed in claim 16 or 17, wherein the surface hardness of the conductive film is 10.0 GPa or higher.

28. The substrate with a conductive film as claimed in claim 16 or 17, wherein an upper layer is further provided on the conductive film, the upper layer containing chromium (Cr) and at least one element selected from the group consisting of nitrogen (N) and oxygen (O).

29. The substrate with a conductive film as claimed in claim 16 or 17, wherein the surface roughness (Rq) of the conductive film is 0.600 nm or less.

30. The substrate with a conductive film as claimed in claim 16 or 17, wherein the thickness t of the conductive film is 20 to 350 nm.

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