Substrate equipped with multilayer reflective film, method for manufacturing substrate equipped with multilayer reflective film, reflective mask blank, reflective mask, and method for manufacturing reflective mask

Abstract

Provided is a substrate equipped with a multilayer reflective film, in which the thickness of a diffusion layer in the multilayer reflective film does not readily change when the multilayer reflective film is heated.　This substrate equipped with a multilayer reflective film for a reflective mask blank has a substrate and a multilayer reflective film for reflecting EUV light, wherein: the multilayer reflective film has a structure in which low-refractive-index layers and high-refractive-index layers are alternately arranged; and in a diffraction chart obtained by performing X-ray diffraction measurement, the crystallite size calculated from the diffraction peak of the maximum intensity derived from the low-refractive-index layers is greater than 3.1 nm.

Description

Substrate with multilayer reflective film, method for manufacturing substrate with multilayer reflective film, reflective mask blank, reflective mask, and method for manufacturing reflective mask

[0001] The present invention relates to a multilayer reflective film-coated substrate used in the manufacture of a reflective mask blank, which is an original plate for a reflective mask used in EUV (Extreme Ultra Violet) exposure in an exposure process for semiconductor manufacturing. The present invention also relates to a reflective mask blank, a reflective mask, and a method for manufacturing a reflective mask.

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

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

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

[0005] In a substrate with a multilayer reflective film or a reflective mask blank, the above-mentioned multilayer reflective film is a multilayer reflective film having a structure in which low refractive index layers (e.g., molybdenum layers) and high refractive index layers (e.g., silicon layers) are alternately arranged. As a method for forming such a multilayer reflective film, for example, Patent Document 1 discloses a method in which the pressure during the formation of each layer is adjusted when low refractive index layers and high refractive index layers are alternately formed by a sputtering method.

[0006] JP 2021-139970 A

[0007] A multilayer reflective film-coated substrate (reflective mask blank) may be heated during the formation of other layers, during the mask formation process, etc. When a multilayer reflective film-coated substrate (reflective mask blank) is heated, elements of the materials constituting each layer may diffuse between the low refractive index layer and the high refractive index layer that are in contact with each other in the multilayer reflective film, resulting in a change in the thickness of the diffusion layer. Since a change in the thickness of the diffusion layer may change the reflective properties of the multilayer reflective film, it has been desired to suppress the change in the thickness of the diffusion layer due to heating. The present inventors have studied the technology described in Patent Document 1 and found that the thickness of the diffusion layer may change when a multilayer reflective film-coated substrate is heated, indicating that there is room for improvement.

[0008] The present invention has been made in view of the above-mentioned problems, and has an object of providing a multilayer reflective film-coated substrate in which the thickness of the diffusion layer in the multilayer reflective film is unlikely to change when heated. Another object of the present invention is to provide a reflective mask blank, a reflective mask blank, and a method for manufacturing a reflective mask.

[0009] As a result of intensive research into the above-mentioned problems, the inventors discovered that adjusting the crystallite size of the low refractive index layer in the multilayer reflective film is important, and arrived at the present invention. That is, the inventors discovered that the above-mentioned problems can be solved by the following configuration. [1] A multilayer reflective film-coated substrate for a reflective mask blank, comprising a substrate and a multilayer reflective film that reflects EUV light, wherein the multilayer reflective film has a structure in which low refractive index layers and high refractive index layers are alternately arranged, and the multilayer reflective film-coated substrate has a crystallite size of more than 3.1 nm calculated from the diffraction peak of maximum intensity derived from the low refractive index layer in a diffraction chart obtained by X-ray diffraction measurement. [2] The multilayer reflective film-coated substrate according to [1], wherein the low refractive index layer contains molybdenum, and the high refractive index layer contains silicon. [3] The multilayer reflective film-coated substrate according to [2], wherein, when analyzed by X-ray fluorescence analysis, the ratio of the detected intensity of ArKα radiation to the detected intensity of MoLα radiation is 0.0010 or less. [4] The multilayer reflective film-coated substrate according to [2] or [3], wherein, when analyzed by fluorescent X-ray analysis, the ratio of the detected intensity of AlKα radiation to the detected intensity of MoLα radiation is 0.0030 or less. [5] The multilayer reflective film-coated substrate according to any one of [2] to [4], wherein, when a rocking curve measurement is performed on a peak derived from the 110 reflection of molybdenum in the low refractive index layer, the half-width is 11.8° or more. [6] The multilayer reflective film-coated substrate according to any one of [1] to [5], wherein the ratio of the thickness of the low refractive index layer to the total thickness of the pair of the low refractive index layer and the high refractive index layer is 0.40 or more. [7] A method for producing a multilayer reflective film-coated substrate according to any one of [1] to [6], wherein the low refractive index layer and the high refractive index layer are formed by magnetron sputtering. [8] A reflective mask blank having, in this order, a substrate, a multilayer reflective film that reflects EUV light, and an absorber film, wherein the multilayer reflective film has a structure in which low refractive index layers and high refractive index layers are alternately arranged, and wherein the crystallite size calculated from the diffraction peak of maximum intensity derived from the low refractive index layer in X-ray diffraction measurement is greater than 3.1 nm.[9] The reflective mask blank according to [8], wherein the low refractive index layer contains molybdenum, and the high refractive index layer contains silicon.

[10] The reflective mask blank according to [9], wherein, when analyzed by fluorescent X-ray analysis, the ratio of the detected intensity of ArKα radiation to the detected intensity of MoLα radiation is 0.0010 or less.

[11] The reflective mask blank according to [9] or

[10] , wherein, when analyzed by fluorescent X-ray analysis, the ratio of the detected intensity of AlKα radiation to the detected intensity of MoLα radiation is 0.0030 or less.

[12] The reflective mask blank according to any one of [9] to

[11] , wherein, when rocking curve measurement is performed on the peak derived from the 110 reflection of molybdenum in the low refractive index layer, the half width is 11.8° or more.

[13] The reflective mask blank according to any one of [8] to

[12] , wherein a ratio of the thickness of the low refractive index layer to the total thickness of the pair of the low refractive index layer and the high refractive index layer is 0.40 or more.

[14] A reflective mask having a phase shift film pattern formed by patterning the absorber film of the reflective mask blank according to any one of [8] to

[13] .

[15] A method for manufacturing a reflective mask, comprising the step of patterning the absorber film of the reflective mask blank according to any one of [8] to

[13] .

[0010] According to the present invention, it is possible to provide a multilayer reflective film-coated substrate in which the thickness of the diffusion layer in the multilayer reflective film is unlikely to change when heated. Furthermore, according to the present invention, it is also possible to provide a reflective mask blank, a reflective mask blank, and a method for manufacturing a reflective mask.

[0011] 1 is a schematic diagram showing an example of an embodiment of a multilayer reflective film-coated substrate of the present invention; 2 is a schematic diagram showing an example of an embodiment of a reflective mask blank of the present invention; 3 is a schematic diagram showing an example of a manufacturing process of a reflective mask using a reflective mask blank;

[0012] The present invention will be described in detail below. The following description of the components may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0013] The meaning of each description in this specification is shown below. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In this specification, elements such as boron, carbon, nitrogen, oxygen, silicon, titanium, chromium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tantalum, rhenium, iridium, and platinum may be represented by their corresponding element symbols (B, C, N, O, Si, Ti, Cr, Zr, Nb, Mo, Ru, Rh, Pd, Ta, Re, Ir, and Pt, etc.).

[0014] <Substrate with multilayer reflective film> The substrate with multilayer reflective film of the present invention is a substrate with multilayer reflective film for a reflective mask blank, comprising a substrate and a multilayer reflective film that reflects EUV light. In the substrate with multilayer reflective film of the present invention, the multilayer reflective film has a structure in which low refractive index layers and high refractive index layers are alternately arranged, and in a diffraction chart obtained by X-ray diffraction measurement, the crystallite size calculated from the diffraction peak of maximum intensity derived from the low refractive index layer is greater than 3.1 nm. The substrate with multilayer reflective film may have a back surface conductive film described in the section on reflective mask blanks. The substrate with multilayer reflective film of the present invention will be described with reference to the drawings.

[0015] Fig. 1 is a cross-sectional view showing one example of an embodiment of a multilayer reflective film-coated substrate of the present invention. The multilayer reflective film-coated substrate 10 shown in Fig. 1 has a substrate 12 and a multilayer reflective film 14. The multilayer reflective film 14 has a structure in which low refractive index layers and high refractive index layers are alternately arranged, and in a diffraction chart obtained by X-ray diffraction measurement, the crystallite size calculated from the diffraction peak of maximum intensity derived from the low refractive index layer is greater than 3.1 nm.

[0016] Although the mechanism by which the thickness of the diffusion layer of the multilayer reflective film coated substrate of the present invention is less likely to change when heated is not entirely clear, the inventors speculate as follows: In the multilayer reflective film coated substrate of the present invention, the crystallite size calculated from the maximum intensity diffraction peak derived from the low refractive index layer is greater than 3.1 nm, so the crystal grain size is large, the interfacial energy is small, and the low refractive index layer is thermally stable. As a result, it is thought that when the multilayer reflective film coated substrate is heated, the elements of the material constituting the low refractive index layer are less likely to diffuse, and as a result, the thickness of the diffusion layer is less likely to change.

[0017] The configuration of the multilayer reflective film coated substrate of the present invention will be described below.

[0018] [Substrate] The substrate of the multilayer reflective film coated substrate of the present invention preferably has a small thermal expansion coefficient. A substrate with a small thermal expansion coefficient can suppress distortion of the absorber film pattern due to heat during exposure to EUV light. The thermal expansion coefficient of the substrate is 0±1.0×10 at 20° C. －７ / °C, and 0±0.3×10 －７ / °C is more preferable. Examples of materials with a small thermal expansion coefficient include SiO ２ -TiO ２ However, the present invention is not limited to this, and substrates made of crystallized glass in which β-quartz solid solution is precipitated, quartz glass, metallic silicon, metal, and the like can also be used. ２ -TiO ２ The SiO-based glass ２ 90 to 95 mass% of TiO ２ It is preferable to use quartz glass containing 5 to 10 mass % of TiO ２ When the content of SiO is 5 to 10 mass %, the linear expansion coefficient is approximately zero at around room temperature, and there is almost no change in dimension at around room temperature. ２ -TiO ２ The SiO-based glass ２ and TiO ２ It may contain other minor components.

[0019] The surface of the substrate on which the multilayer reflective film is disposed (hereinafter also referred to as the "first principal surface") preferably has high surface smoothness. The surface smoothness of the first principal surface can be evaluated by surface roughness. The surface roughness of the first principal surface is preferably 0.15 nm or less in terms of root-mean-square roughness Rq. Note that the surface roughness can be measured using an atomic force microscope, and the surface roughness is described as the root-mean-square roughness Rq based on JIS-B0601. The first principal surface is preferably surface-processed to achieve a predetermined flatness, in order to improve the pattern transfer accuracy and positional accuracy of a reflective mask obtained by further processing a reflective mask blank obtained using a multilayer reflective film-coated substrate. The flatness of the substrate in a predetermined region of the first principal surface (e.g., a 132 mm × 132 mm region) is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less. The flatness can be measured using a flatness measuring instrument manufactured by Fujinon Corporation. The size and thickness of the substrate are determined as appropriate based on the design values ​​of the mask, etc. For example, the outer dimensions may be 6 inches (152 mm) square and the thickness may be 0.25 inches (6.3 mm). Furthermore, the substrate preferably has high rigidity to prevent deformation due to film stress of a film (such as a multilayer reflective film) formed on the substrate. For example, the Young's modulus of the substrate is preferably 65 GPa or more.

[0020] [Multilayer reflective film] The multilayer reflective film of the multilayer reflective film-coated substrate of the present invention has a structure in which low refractive index layers and high refractive index layers are alternately arranged. The multilayer reflective film is not particularly limited as long as it reflects EUV light and has the desired properties as a reflective film for an EUV mask blank. The multilayer reflective film preferably has a high reflectivity for EUV light. Specifically, when EUV light is incident on the surface of the multilayer reflective film at an incident angle of 6°, the maximum reflectivity for EUV light at a wavelength of around 13.5 nm is preferably 60% or more, more preferably 65% ​​or more.

[0021] Since the multilayer reflective film can achieve a high reflectivity for EUV light, it has a structure in which high-refractive-index layers that exhibit a high refractive index to EUV light and low-refractive-index layers that exhibit a low refractive index to EUV light are alternately arranged, as described above. The multilayer reflective film may be formed by laminating multiple periods, each period being a stack structure in which a high-refractive-index layer and a low-refractive-index layer are arranged in this order from the substrate side, or by laminating multiple periods, each period being a stack structure in which a low-refractive-index layer and a high-refractive-index layer are arranged in this order.

[0022] The high refractive index layer may be a layer containing Si. Examples of the Si-containing material include simple Si and Si compounds containing Si and one or more elements selected from the group consisting of B, C, N, and O. By using a high refractive index layer containing Si, a reflective mask blank and a reflective mask with excellent EUV light reflectance can be obtained. The high refractive index layer may consist of a single layer or multiple layers. The thickness of the high refractive index layer is preferably 2.0 to 6.0 nm, more preferably 3.0 to 5.0 nm. The thickness of the high refractive index layer is determined by X-ray reflectivity (XRR). Detailed measurement conditions follow the method described in the Examples section below.

[0023] The low-refractive index layer may be a layer containing a metal selected from the group consisting of Mo, Ru, Rh, and Pt, or an alloy thereof. The low-refractive index layer is preferably a layer containing Mo. The low-refractive index layer may consist of a single layer or multiple layers. Si is commonly used for the high-refractive index layer, and Mo is commonly used for the low-refractive index layer. That is, a Mo / Si multilayer reflective film is the most common. However, the multilayer reflective film is not limited to this, and Ru / Si multilayer reflective film, Mo / Be multilayer reflective film, Mo compound / Si compound multilayer reflective film, Si / Mo / Ru multilayer reflective film, Si / Mo / Ru / Mo multilayer reflective film, Si / Ru / Mo multilayer reflective film, and Si / Ru / Mo / Ru multilayer reflective film may also be used. The thickness of the low-refractive index layer is preferably 3.2 nm or more. The upper limit of the thickness of the low-refractive index layer is, for example, 5.0 nm. The thickness of the low-refractive index layer is determined by XRR.

[0024] Here, in the multilayer reflective film-coated substrate of the present invention, the crystallite size calculated from the diffraction peak of maximum intensity derived from the low refractive index layer in a diffraction chart obtained by X-ray diffraction measurement is greater than 3.1 nm. The crystallite size is preferably 3.2 nm or more in order to make the thickness of the diffusion layer less susceptible to change when heated. There is no particular upper limit to the crystallite size, but in order to reduce the surface roughness of the multilayer reflective film-coated substrate, it is preferably 6.0 nm or less, and more preferably 5.0 nm or less. In this specification, X-ray diffraction (XRD) measurement is performed by the out-of-plane method. That is, the incident direction of X-rays and the arrangement direction of the X-ray detector are changed within a plane perpendicular to the surface of the multilayer reflective film of the multilayer reflective film-coated substrate. The out-of-plane method is a method in which, when the incident direction of X-rays is θ° with respect to the surface of the multilayer reflective film, scanning is performed while maintaining the arrangement direction of the X-ray detector at an angle of 2θ° with respect to the incident direction of the X-rays, and is also called θ-2θ scanning. Detailed conditions for the XRD measurement follow the methods in the examples shown later.

[0025] The crystallite size is calculated from the diffraction chart obtained by XRD measurement using the diffraction peak of maximum intensity derived from the low refractive index layer.In this specification, the crystallite size is calculated by Scherrer's equation, and the full half width of the diffraction peak is used for calculation, and the Scherrer constant K is 0.89.For example, when the low refractive index layer contains Mo, the diffraction peak of maximum intensity derived from the low refractive index layer is often a diffraction peak (appearing at 2θ: 39 to 42 °) derived from the 110 reflection of Mo.

[0026] Furthermore, when the low refractive index layer contains Mo, it is also preferable that the half-width of the rocking curve measurement of the peak resulting from the Mo 110 reflection is 11.8° or more. The rocking curve measurement is performed by changing only the orientation angle of the multilayer reflective film-coated substrate while maintaining the angles of the X-ray incidence direction and the X-ray detector orientation so as to obtain the peak top value of the peak resulting from the Mo 110 reflection. In this case, the orientation angle of the multilayer reflective film-coated substrate is changed around the same axis as the rotation axis of the X-ray incidence direction and the X-ray detector orientation. The half-width of the rocking curve may be calculated using a two-dimensional detector from a profile of the change in diffraction intensity in a direction corresponding to the tilt direction of the Debye ring (the circumferential direction of the Debye ring). The half-width is the total half-width of the curve obtained by the measurement. The half-width is more preferably 12.0° or more, and even more preferably 12.4° or more, since this makes it less likely that the thickness of the diffusion layer will change when heated. Although the upper limit of the half-width is not particularly limited, it is preferably 24° or less, more preferably 20° or less, and even more preferably 18° or less, in order to prevent the roughness of the interface from increasing. Note that the roughness of the interface is thought to be caused by the crystal planes becoming more easily exposed at the interface due to a decrease in orientation.

[0027] Furthermore, when the low refractive index layer contains Mo, it is also preferable that when the multilayer reflective film-coated substrate is analyzed by X-ray fluorescence analysis (XRF), the ratio of the detected intensity of ArKα radiation to the detected intensity of MoLα radiation is 0.0010 or less. When the low refractive index layer contains Mo, it is also preferable that when the multilayer reflective film-coated substrate is analyzed by XRF, the ratio of the detected intensity of AlKα radiation to the detected intensity of MoLα radiation is 0.0030 or less. When the multilayer reflective film-coated substrate is analyzed by XRF, the lower limit of the ratio of the detected intensity of ArKα radiation to the detected intensity of MoLα radiation is not particularly limited, and may be 0. Furthermore, the lower limit of the ratio of the detected intensity of AlKα radiation to the detected intensity of MoLα radiation is not particularly limited, and may be 0. Analysis by XRF can be performed by irradiating X-rays from the multilayer reflective film side of the multilayer reflective film-coated substrate. Details of the measurement method follow the method described in the examples below.

[0028] A diffusion layer may be disposed between the high refractive index layer and the low refractive index layer. The diffusion layer refers to a region containing elements contained in the material constituting the high refractive index layer and elements of the material constituting the low refractive index layer. The ratio of the thickness of the diffusion layer to the thickness of the low refractive index layer is preferably 1.0 or less, more preferably 0.9 or less, and more preferably 0.8 or less. The lower limit of the ratio of the thickness of the diffusion layer to the thickness of the low refractive index layer is not particularly limited, but may be 0. The thickness of the diffusion layer is determined by XRR.

[0029] In the multilayer reflective film of the multilayer reflective film-coated substrate of the present invention, the ratio of the thickness of the low refractive index layer to the total thickness of the pair of low refractive index layer and high refractive index layer is preferably 0.40 or more. This thickness ratio is more preferably 0.42 or more, and even more preferably 0.45 or more, in order to prevent the thickness of the diffusion layer from changing when heated. The upper limit of the ratio of the thickness of the low refractive index layer to the total thickness of the low refractive index layer and high refractive index layer is not particularly limited, but from the viewpoint of increasing reflectivity, it is preferably 0.60 or less, and more preferably 0.55 or less. The pair of low refractive index layer and high refractive index layer refers to a pair of adjacent low refractive index layer and high refractive index layer among the alternatingly arranged low refractive index layer and high refractive index layer. The thickness ratio can be calculated from the thickness of the low refractive index layer and the thickness of the high refractive index layer obtained by the above-mentioned method. When the multilayer reflective film includes a diffusion layer, the thickness ratio can be calculated using the following formula (I): In formula (I), R represents the thickness ratio, and d Ｌ is the thickness of the low refractive index layer, and d Ｈ is the thickness of the high refractive index layer, and d Ｄ is the thickness of the diffusion layer. R = (d Ｌ +d Ｄ / 2) / (d Ｌ +d Ｈ +d Ｄ ) Formula (I)

[0030] In the multilayer reflective film, the number of units each including one low refractive index layer and one high refractive index layer (a pair of low refractive index layer and high refractive index layer) can be appropriately selected depending on the required reflectivity for EUV light, and is preferably 20 to 60.

[0031] The low refractive index layer and the high refractive index layer constituting the multilayer reflective film can be formed by known methods, such as magnetron sputtering and ion beam sputtering. Among these, the low refractive index layer and the high refractive index layer are preferably formed by magnetron sputtering. When forming the low refractive index layer by magnetron sputtering, sputtering is performed by supplying a sputtering gas (e.g., a rare gas such as Ne gas, Ar gas, or Kr gas) using the material constituting the low refractive index layer as a target. During sputtering, the sputtering gas is converted into plasma by applying a magnetic field and voltage, and the plasma is caused to collide with the target, causing the material constituting the target to adhere to the substrate or the already formed high refractive index layer. The pressure inside the apparatus when forming the low refractive index layer by magnetron sputtering is 1.0×10 －３ ~1.0 x 10 －１ The input power when forming the low refractive index layer by magnetron sputtering is preferably 100 to 800 W, more preferably 100 to 600 W, and even more preferably 100 to 500 W.

[0032] The multilayer reflective film-coated substrate of the present invention may further have a protective film, which will be described in the section on the reflective mask blank, on the side of the multilayer reflective film opposite the substrate side. The multilayer reflective film-coated substrate of the present invention may also have an oxide film disposed between the multilayer reflective film and the protective film. The oxide film may be a film in which the surface layer on the side of the multilayer reflective film farthest from the substrate side is oxidized.

[0033] <Reflective Mask Blank> The multilayer reflective film-coated substrate of the present invention is for use in a reflective mask blank, and by further comprising an absorber film described below, it functions as a reflective mask blank (the reflective mask blank of the present invention). That is, the reflective mask blank of the present invention is a reflective mask blank having a substrate, a multilayer reflective film that reflects EUV light, and an absorber film, in this order. Here, the multilayer reflective film has a structure in which low refractive index layers and high refractive index layers are alternately arranged, and the crystallite size calculated from the diffraction peak of maximum intensity derived from the low refractive index layer in X-ray diffraction measurement is greater than 3.1 nm. The reflective mask blank of the present invention will be described with reference to the drawings.

[0034] Figure 2 is a cross-sectional view showing one example of an embodiment of the reflective mask blank of the present invention. The reflective mask blank 20 shown in Figure 2 has a back surface conductive film 22, a substrate 12, a multilayer reflective film 14, a protective film 16, and an absorber film 18, in this order. The reflective mask blank 20 shown in Figure 2 has the back surface conductive film 22 and the protective film 16, but the protective film 16 and the back surface conductive film 22 may be omitted. The multilayer reflective film 14 satisfies the above requirements. For the reasons described above, it is thought that the reflective mask blank of the present invention is less likely to have a change in thickness of the diffusion layer of the multilayer reflective film when heated.

[0035] Hereinafter, the configuration of the reflective mask blank of the present invention and the configuration that the reflective mask blank of the present invention may have will be described. Note that the multilayer reflective film and the substrate of the reflective mask blank of the present invention are similar to the multilayer reflective film and the substrate of the multilayer reflective film-coated substrate of the present invention described above, respectively, and therefore description thereof will be omitted.

[0036] [Protective Film] The reflective mask blank of the present invention may have a protective film between the multilayer reflective film and the absorber film. The protective film is provided to protect the multilayer reflective film from damage during etching (usually a dry etching process) when a pattern is formed on the absorber film. Examples of materials that can achieve this objective include materials containing at least one element selected from the group consisting of Ru and Rh. That is, the protective film preferably contains at least one element selected from the group consisting of Ru and Rh. More specifically, examples of such materials include Rh-based materials such as Ru metal alone, Ru alloys containing Ru and one or more metals selected from the group consisting of Si, Ti, Nb, Rh, and Zr, Rh alloys containing Rh and one or more metals selected from the group consisting of Si, Ti, Nb, Ru, Ta, and Zr, Rh-containing nitrides containing the Rh alloys and nitrogen, and Rh-containing oxynitrides containing the Rh alloys, nitrogen, and oxygen. Furthermore, as materials that can achieve the above object, Al and nitrides containing these metals and nitrogen, and Al ２ O ３ Among these, materials that can achieve the above object are preferably Ru metal alone, Ru alloys, Rh metal alone, or Rh alloys. As the Ru alloy, a Ru—Si alloy is preferred, and as the Rh alloy, a Rh—Si alloy is preferred.

[0037] The thickness of the protective film is not particularly limited as long as it can function as a protective film. In order to maintain the reflectivity of EUV light reflected by the multilayer reflective film, the thickness of the protective film is preferably 1 to 10 nm, more preferably 1.5 to 6 nm, and even more preferably 2 to 5 nm. It is also preferable that the material of the protective film is Ru metal alone, a Ru alloy, Rh metal alone, or a Rh alloy, and that the thickness of the protective film is within the above-mentioned preferred thickness range.

[0038] The protective film may be a film consisting of a single layer, or a multilayer film consisting of multiple layers. When the protective film is a multilayer film, each layer constituting the multilayer film is preferably made of the above-mentioned preferred material. Furthermore, when the protective film is a multilayer film, it is also preferable that the total thickness of the multilayer film is within the above-mentioned preferred range.

[0039] The protective film can be formed by a known film formation method such as magnetron sputtering, ion beam sputtering, etc. When forming a Ru film by magnetron sputtering, it is preferable to use a Ru target as the target and Ar gas as the sputtering gas.

[0040] [Absorber Film] The absorber film of the reflective mask blank of the present invention is required to have a high contrast between the EUV light reflected by the multilayer reflective film and the EUV light at the absorber film when the absorber film is patterned. The patterned absorber film (absorber film pattern) may function as a binary mask by absorbing EUV light, or may function as a phase shift mask that reflects EUV light and interferes with the EUV light from the multilayer reflective film to generate contrast.

[0041] When the absorber film pattern is used as a binary mask, the absorber film must absorb EUV light and have low reflectance for EUV light. Specifically, when EUV light is irradiated onto the surface of the absorber film, the maximum reflectance of EUV light at a wavelength of approximately 13.5 nm is preferably 2% or less. The absorber film may contain one or more metals selected from the group consisting of Ta, Ti, Sn, and Cr, as well as one or more components selected from the group consisting of O, N, B, Hf, and H. Among these, N or B is preferred. By including N or B, the crystalline state of the absorber film can be made amorphous or microcrystalline. The crystalline state of the absorber film is preferably amorphous. This improves the smoothness and flatness of the absorber film. Furthermore, improved smoothness and flatness of the absorber film reduces the edge roughness of the absorber film pattern, thereby improving the dimensional accuracy of the absorber film pattern. When the absorber film pattern is used as a binary mask, the film thickness of the absorber film is preferably 40 to 70 nm, more preferably 50 to 65 nm.

[0042] When the absorber film pattern is used as a phase shift mask, the reflectance of the absorber film to EUV light is preferably 2% or more. To obtain a sufficient phase shift effect, the reflectance of the absorber film is preferably 9 to 15%. Using the absorber film as a phase shift mask improves the contrast of the optical image on the wafer and increases the exposure margin. Examples of materials for forming the phase shift mask include simple Ru metal, Ru alloys containing Ru and one or more metals selected from the group consisting of Cr, Au, Pt, Re, Hf, Ta, Ti, and Si, Ta and Nb alloys, oxides containing Ru alloys or TaNb alloys and oxygen, nitrides containing Ru alloys or TaNb alloys and nitrogen, oxynitrides containing Ru alloys or TaNb alloys and oxygen and nitrogen, and compounds containing one or more noble metal elements selected from the group consisting of Ir, Pt, Pd, Ag, or Au. When the absorber film pattern is used as a phase shift mask, the thickness of the absorber film is preferably 30 to 60 nm, more preferably 35 to 55 nm.

[0043] The absorber film may be a single-layer film or a multilayer film made up of multiple films. When the absorber film is a single-layer film, the number of steps in manufacturing the mask blank can be reduced, thereby improving production efficiency. When the absorber film is a multilayer film, the layer disposed on the side of the absorber film opposite to the multilayer reflective protective film side may be an anti-reflection film used when inspecting the absorber film pattern using inspection light (for example, wavelength 193 to 248 nm).

[0044] The absorber film can be formed by a known film formation method such as magnetron sputtering, ion beam sputtering, etc. For example, when a Ru oxide film is formed as the absorber film by magnetron sputtering, the absorber film can be formed by sputtering using a Ru target and supplying a gas containing Ar gas and oxygen gas.

[0045] [Back Surface Conductive Film] The reflective mask blank of the present invention may have a back surface conductive film on the surface (second main surface) opposite to the first main surface of the substrate. Providing a back surface conductive film enables the reflective mask blank to be handled using an electrostatic chuck. The back surface conductive film preferably has a low sheet resistance. The sheet resistance of the back surface conductive film is preferably, for example, 200 Ω / sq. or less, more preferably 100 Ω / sq. or less. The constituent material of the back surface conductive film can be selected from a wide range of materials described in known literature. For example, a high-dielectric-constant coating described in JP-A-2003-501823, specifically a coating made of Si, Mo, Cr, CrON, or TaSi, can be applied. Furthermore, the constituent material of the back surface conductive film may be a Cr compound containing Cr and one or more elements selected from the group consisting of B, N, O, and C, or a Ta compound containing Ta and one or more elements selected from the group consisting of B, N, O, and C.

[0046] The thickness of the back surface conductive film is preferably 10 to 1,000 nm, more preferably 10 to 400 nm. The back surface conductive film may also have a function of adjusting stress on the second main surface side of the reflective mask blank. That is, the back surface conductive film can be adjusted to balance the stress from various films formed on the first main surface side and flatten the reflective mask blank. The back surface conductive film can be formed using a known film formation method, for example, a sputtering method such as magnetron sputtering or ion beam sputtering, a CVD method, a vacuum deposition method, or an electrolytic plating method.

[0047] [Other Films] The reflective mask blank of the present invention may have other films. Examples of such films include a hard mask film. The hard mask film is preferably disposed on the side opposite to the substrate side of the absorber film. As the hard mask film, it is preferable to use a material that is highly resistant to dry etching, such as a Cr-based film or a Si-based film. Examples of Cr-based films include Cr, and materials containing Cr and one or more elements selected from the group consisting of O, N, C, and H. Specific examples include CrO and CrN. Examples of Si-based films include Si, and materials containing Si and one or more elements selected from the group consisting of O, N, C, and H. Specific examples include SiO ２ , SiON, SiN, SiO, Si, SiC, SiCO, SiCN, and SiCON. When a hard mask film is formed on the absorber film, dry etching can be performed even if the minimum line width of the absorber film pattern is small. Therefore, it is effective for miniaturizing the absorber film pattern.

[0048] <Method for Manufacturing a Reflective Mask and a Reflective Mask> A reflective mask is obtained by patterning the absorber film of a reflective mask blank. An example of a method for manufacturing a reflective mask will be described with reference to FIG. 3. FIG. 3(a) shows a state in which a resist pattern 40 is formed on a reflective mask blank having, in this order, a backside conductive film 22, a substrate 12, a multilayer reflective film 14, a protective film 16, and an absorber film 18. The resist pattern 40 can be formed using a known method, for example, by applying a resist to the absorber film 18 of the reflective mask blank, exposing and developing the resist to form the resist pattern 40. The resist pattern 40 corresponds to a pattern formed on a wafer using a reflective mask. Then, using the resist pattern 40 in FIG. 3(a) as a mask, the absorber film 18 is etched and patterned, and the resist pattern 40 is removed to obtain a laminate having an absorber film pattern 18pt shown in FIG. 3(b). Next, as shown in Fig. 3(c), a resist pattern 42 corresponding to the frame of the exposure region is formed on the laminate of Fig. 3(b), and dry etching is performed using the resist pattern 42 of Fig. 3(c) as a mask. Dry etching is performed until it reaches the substrate 12. After dry etching, the resist pattern 42 is removed, and the reflective mask shown in Fig. 3(d) is obtained.

[0049] Dry etching for forming the absorber film pattern 18pt may be, for example, dry etching using a Cl-based gas or dry etching using an F-based gas. The resist pattern 40 or 42 may be removed by a known method, such as removal with a cleaning solution. Examples of cleaning solutions include sulfuric acid-hydrogen peroxide solution (SPM), sulfuric acid, ammonia water, ammonia-hydrogen peroxide solution (APM), OH radical cleaning water, and ozone water.

[0050] The reflective mask obtained by patterning the absorber film of the reflective mask blank of the present invention can be suitably used as a reflective mask used for exposure to EUV light. Although reflective masks may be heated during EUV exposure, the reflective mask of the present invention is less likely to change in thickness of the diffusion layer of the multilayer reflective film when heated.

[0051] The present invention will be described in more detail below based on examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the examples shown below. Note that Example 1 described below is an example, and Examples 2 to 4 are comparative examples.

[0052] Example 1 First, the procedure for obtaining a representative multilayer reflective film coated substrate of Example 1 will be described.

[0053] [Substrate] First, as a substrate, SiO ２ -TiO ２ A glass substrate (6-inch (152 mm) square outer diameter, 6.3 mm thick) of this type was prepared. This glass substrate had a thermal expansion coefficient of 0.02×10 at 20° C. －７ / °C, Young's modulus is 67 GPa, Poisson's ratio is 0.17, and specific rigidity is 3.07 × 10 ７ m ２ / s ２ The quality assurance area of ​​the first main surface of the substrate was polished to have a root mean square roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less.

[0054] [Multilayer Reflective Film] Next, a Mo / Si multilayer reflective film was formed on the first principal surface of the substrate as a multilayer reflective film. The Mo / Si multilayer reflective film was obtained by repeating the process of forming a Si layer (3.8 nm thick) and a Mo layer (3.2 nm thick) by magnetron sputtering 40 times, and then forming a Si layer (4.0 nm thick) after the 40th Mo layer. The thickness of each layer was calculated from the film formation rate and film formation time. The film formation rate was measured using a film thickness monitor installed in the magnetron sputtering device. Note that, in the magnetron sputtering, Ar gas was supplied to adjust the gas pressure during film formation to 0.05 Pa. The Ar gas supply rate was 25 sccm. Note that "sccm" is a unit representing the gas flow rate (mL / min) under standard conditions. In Example 1, the film formation conditions for each film were as follows. (Si layer) Input power: 1000W (Mo layer) Input power: 500W

[0055] [Protective Film] After forming the multilayer reflective film by the above procedure, a Ru layer (protective film) was formed on the side of the multilayer reflective film opposite the substrate side. The Ru layer was formed by magnetron sputtering, with an input power of 500 W and a film thickness of 2.5 nm. The gas pressure was the same as when forming the multilayer reflective film. The multilayer reflective film-coated substrate of Example 1 was obtained by the above procedure. In Examples 2 to 4, only the differences from the procedure for obtaining the multilayer reflective film-coated substrate of Example 1 are described.

[0056] Example 2 A multilayer reflective film coated substrate of Example 2 was obtained in the same manner as in Example 1, except that the input power during deposition of the Mo layer was changed to 600 W.

[0057] Example 3 A multilayer reflective film coated substrate of Example 3 was obtained in the same manner as in Example 1, except that the input power during deposition of the Mo layer was changed to 800 W.

[0058] Example 4 A multilayer reflective film coated substrate of Example 4 was obtained in the same manner as in Example 1, except that the input power during deposition of the Mo layer was changed to 900 W.

[0059] <Measurement Method> [Crystallite Size] The crystallite size of the low refractive index layer (Mo layer) of the multilayer reflective film coated substrate of each example was calculated from the diffraction chart obtained by XRD measurement using the diffraction peak of maximum intensity derived from the low refractive index layer. The calculation method is as described above. When XRD measurement was performed on the multilayer reflective film coated substrate of each example, a peak derived from the 110 reflection of Mo was observed. Note that the XRD measurement was performed using a "D8 DISCOVER Plus" manufactured by Bruker. The X-ray source was CuKα radiation (CuKα １ and CuKα ２ The X-ray source was equipped with a 2θ detector (including X-rays), a tube voltage of 45 kV, and a tube current of 120 mA. A two-dimensional detector was used for the measurements. A 1.0 mmφ microslit and a 1.0 mmφ collimator were used on the X-ray source side. The step width was 0.02°, the step time was 0.2 s / step, and the measurements were performed in the 2θ range of 20 to 80°.

[0060] [Rocking Curve] Using the above-mentioned device, rocking curves were measured for the diffraction peak of the Mo 110 reflection.

[0061] [Film Thickness] The thicknesses of the low refractive index layer and the high refractive index layer were determined by XRR. The XRR measurement device was the same as the device used for the XRD measurement described above. However, the measurement conditions were partially changed as follows. The X-ray source was CuKα radiation (CuKα １ and CuKα ２ The X-ray tube was set at 45 kV (including the X-ray line), with a tube voltage of 45 kV and a tube current of 120 mA. A two-dimensional detector was used for the measurements. A 0.05 mm slit and a 4.1° Soller slit were used on the X-ray source side, and a 4° Soller slit and a dual crystal analyzer were used on the detector side. The step width was 0.005°, and measurements were made over a range of 0 to 9°. The XRR fitting was performed assuming a layer structure from the substrate side of (Si layer / diffusion layer / Mo layer / diffusion layer) x 40 / Si layer / RuSi diffusion layer / Ru layer. The value of R obtained from the above formula (I) was calculated from the film thicknesses of the low-refractive-index layer and high-refractive-index layer and the film thickness of the diffusion layer obtained by the above procedure. In the tables below, this value is referred to as the "γ ratio."

[0062] [XRF Intensity Ratio] XRF measurement was performed on the obtained multilayer reflective film coated substrate of each example, and the ratio of the detected intensity of ArKα radiation to the detected intensity of MoLα radiation ("Ar / Mo" in the table) and the ratio of the detected intensity of AlKα radiation to the detected intensity of MoLα radiation ("Al / Mo" in the table) were calculated. The XRF measurement was performed using Rigaku's "ZSX Primus II".

[0063] <Evaluation Method> The heat resistance (change in thickness of the diffusion layer upon heating) of the multilayer reflective film-coated substrate of each example was evaluated by the following procedure. First, the obtained multilayer reflective film-coated substrate of each example was placed in a vacuum furnace and heated at 180°C for 30 minutes. After heating, XRR measurement was performed in the same manner as above to calculate the thickness of the diffusion layer after heating and to calculate the extent to which the thickness of the diffusion layer had increased from before heating. The results are shown in the table below.

[0064] <Results> The measurement results and evaluation results of the multilayer reflective film coated substrate of each example are shown in the table.

[0065]

[0066] From the results shown in the table, it was confirmed that when the crystallite size calculated from the diffraction peak of maximum intensity derived from the low refractive index layer exceeds 3.1 nm, the thickness of the diffusion layer is less likely to change when heated.

[0067] A reflective mask blank can be obtained by forming an absorber film on the side of the protective film opposite to the multilayer reflective film side of the multilayer reflective film coated substrate obtained by the above procedure.

[0068] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-132506, filed on August 16, 2023, are incorporated herein by reference as part of the disclosure of the present invention.

[0069] REFERENCE SIGNS LIST 10 Substrate with multilayer reflective film 12 Substrate 14 Multilayer reflective film 16 Protective film 18 Absorber film 18pt Absorber film pattern 20 Reflective mask blank 22 Back surface conductive film 40, 42 Resist pattern

Claims

1. A multilayer reflective film-coated substrate for a reflective mask blank, comprising: a substrate; and a multilayer reflective film that reflects EUV light, wherein the multilayer reflective film has a structure in which low refractive index layers and high refractive index layers are alternately arranged, and in a diffraction chart obtained by performing X-ray diffraction measurement, the crystallite size calculated from the diffraction peak of maximum intensity originating from the low refractive index layer is greater than 3.1 nm.

2. The multilayer reflective film coated substrate according to claim 1, wherein the low refractive index layer contains molybdenum, and the high refractive index layer contains silicon.

3. The multilayer reflective film coated substrate according to claim 2, wherein when analyzed by fluorescent X-ray analysis, the ratio of the detected intensity of ArKα radiation to the detected intensity of MoLα radiation is 0.0010 or less.

4. The multilayer reflective film coated substrate according to claim 2, wherein when analyzed by fluorescent X-ray analysis, the ratio of the detection intensity of AlKα radiation to the detection intensity of MoLα radiation is 0.0030 or less.

5. The multilayer reflective film coated substrate according to claim 2, wherein the half width of a peak resulting from the 110 reflection of molybdenum in the low refractive index layer when subjected to rocking curve measurement is 11.8° or more.

6. The multilayer reflective film coated substrate according to claim 1 or 2, wherein the ratio of the thickness of said low refractive index layer to the total thickness of the pair of said low refractive index layer and said high refractive index layer is 0.40 or more.

7. A method for producing a multilayer reflective film coated substrate according to claim 1 or 2, wherein the low refractive index layer and the high refractive index layer are formed by magnetron sputtering.

8. A reflective mask blank having, in this order, a substrate, a multilayer reflective film that reflects EUV light, and an absorber film, wherein the multilayer reflective film has a structure in which low refractive index layers and high refractive index layers are alternately arranged, and the crystallite size calculated from the diffraction peak of maximum intensity originating from the low refractive index layer when X-ray diffraction measurement is performed is greater than 3.1 nm.

9. The reflective mask blank according to claim 8, wherein the low refractive index layer contains molybdenum, and the high refractive index layer contains silicon.

10. The reflective mask blank according to claim 9, wherein when analyzed by fluorescent X-ray analysis, the ratio of the detected intensity of ArKα radiation to the detected intensity of MoLα radiation is 0.0010 or less.

11. The reflective mask blank according to claim 9, wherein when analyzed by fluorescent X-ray analysis, the ratio of the detection intensity of AlKα radiation to the detection intensity of MoLα radiation is 0.0030 or less.

12. The reflective mask blank according to claim 9, wherein the half-width of the peak resulting from the 110 reflection of molybdenum in the low refractive index layer when subjected to rocking curve measurement is 11.8° or more.

13. A reflective mask blank according to claim 8 or 9, wherein the ratio of the thickness of the low refractive index layer to the total thickness of the pair of the low refractive index layer and the high refractive index layer is 0.40 or more.

14. A reflective mask having a phase shift film pattern formed by patterning the absorber film of the reflective mask blank according to claim 8 or 9.

15. A method for manufacturing a reflective mask, comprising the step of patterning the absorber film of the reflective mask blank according to claim 8 or 9.

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