Reflection-type mask blank, reflection-type mask, and method for producing reflection-type mask

Abstract

Provided is a reflection-type mask blank that has excellent phase shift film workability and suppresses a reduction in the reflectance of the resulting reflection-type mask.　This reflection-type mask blank comprises, in order, a substrate, a multilayered reflection film for reflecting EUV light, a protective film, a buffer layer, and a phase shift film. The buffer layer contains ruthenium. The phase shift film contains at least one element selected from the group consisting of iridium and platinum.

Description

Reflective mask blank, reflective mask, and method for manufacturing a reflective mask

[0001] The present invention relates to a reflective mask used in EUV (Extreme Ultra Violet) exposure used in the exposure process of semiconductor manufacturing, a method for manufacturing the same, and a reflective mask blank that is an original plate for the reflective mask.

[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] EUV light incident on a reflective mask from the illumination optical system of an exposure tool is reflected by areas without an absorber film (openings) and absorbed by areas with an absorber film (non-openings). As a result, the mask pattern is transferred as a resist pattern onto a wafer through the reduction projection optical system of the exposure tool, and subsequent processing is performed. A phase shift film, which shifts the phase of EUV light to reduce the reflectance of EUV light, is also used as the absorber film. Phase shift films reduce the reflectance of EUV light by interfering with EUV light reflected from the surface of the absorber film opposite the multilayer reflective film side. Patent Document 1, for example, discloses a phase shift film containing platinum (Pt) as such a phase shift film in terms of optical properties. More specifically, an absorber film (phase shift film) made of Pt is disclosed.

[0005] International Publication No. 2022 / 065421

[0006] The above patent document also discloses an embodiment using a buffer layer containing chromium, oxygen, and nitrogen. The buffer layer is disposed between the phase shift film and the protective film. The phase shift film in the reflective mask blank is required to have excellent processability in order to obtain a desired pattern shape. Furthermore, in a reflective mask obtained by processing the reflective mask blank, it is required that a decrease in reflectance at the openings of the phase shift film be suppressed. The present inventors have studied the embodiment described in the above patent document and found that a decrease in reflectance was observed in the resulting reflective mask and that this improvement was necessary.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide a reflective mask blank that has excellent processability for a phase shift film and that suppresses a decrease in reflectance in the resulting reflective mask. Another aim of the present invention is to provide a reflective mask and a method for manufacturing a reflective mask.

[0008] As a result of extensive research into the above-mentioned problems, the inventors discovered that providing a buffer layer between a phase shift film and a protective film and the combination of the materials of the phase shift film and the buffer layer are 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 reflective mask blank having, in this order, a substrate, a multilayer reflective film that reflects EUV light, a protective film, a buffer layer, and a phase shift film, wherein the buffer layer contains ruthenium, and the phase shift film contains at least one element selected from the group consisting of iridium and platinum. [2] The reflective mask blank according to [1], wherein the iridium content in the phase shift film is 30 to 100 atomic % based on all atoms in the phase shift film. [3] The reflective mask blank according to [1], wherein the platinum content in the phase shift film is 30 to 100 atomic % based on all atoms in the phase shift film. [4] The reflective mask blank according to any one of [1] to [3], wherein the phase shift film further contains at least one element selected from the group consisting of boron, carbon, nitrogen, oxygen, and silicon. [5] The reflective mask blank according to any one of [1] to [4], wherein the phase shift film contains at least one element selected from the group consisting of silicon, chromium, niobium, molybdenum, tantalum, tungsten, and rhenium. [6] The reflective mask blank according to any one of [1] to [5], wherein the buffer layer has a ruthenium content of 5 to 100 atomic % based on all atoms in the buffer layer. [7] The reflective mask blank according to [6], wherein the buffer layer has a ruthenium content of 50 to 100 atomic % based on all atoms in the buffer layer. [8] The reflective mask blank according to any one of [1] to [7], wherein the buffer layer further contains at least one element selected from the group consisting of chromium, hafnium, tantalum, tungsten, rhenium, and osmium. [9] The reflective mask blank according to [8], wherein the buffer layer further contains at least one element selected from the group consisting of chromium and tantalum.

[10] The reflective mask blank according to [8] or [9], wherein, in the buffer layer, a ratio of a content of chromium relative to a content of ruthenium relative to a content of all atoms in the buffer layer is 0.10 to 9.00.

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

[10] , wherein, in the buffer layer, a ratio of a content of chromium relative to a content of ruthenium relative to a content of all atoms in the buffer layer is 0.50 to 4.00.

[12] The reflective mask blank according to any one of [1] to

[11] , wherein the buffer layer further contains at least one element X1 selected from the group consisting of boron, carbon, nitrogen, oxygen, and silicon.

[13] The reflective mask blank according to

[12] , wherein the content of the element X1 in the buffer layer is 1 to 20 atomic % relative to the total atoms in the buffer layer.

[14] The reflective mask blank according to any one of [1] to

[13] , wherein the protective film contains rhodium.

[15] A reflective mask having a phase shift film pattern formed by patterning the phase shift film of the reflective mask blank according to any one of [1] to

[14] .

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

[14] .

[0009] According to the present invention, a reflective mask blank that has excellent processability for forming a phase shift film and that suppresses a decrease in reflectance in the resulting reflective mask can be provided. Furthermore, according to the present invention, a reflective mask and a method for manufacturing a reflective mask can also be provided.

[0010] 1A and 1B are schematic diagrams showing an example of an embodiment of a reflective mask blank of the present invention, and FIG. 1C are schematic diagrams showing an example of a manufacturing process of a reflective mask using the reflective mask blank of the present invention.

[0011] 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.

[0012] 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, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, and platinum may be represented by their corresponding element symbols (B, C, N, O, Si, Ti, Cr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, and Pt, etc.).

[0013] <Reflective Mask Blank> The reflective mask blank of the present invention is a reflective mask blank having, in this order, a substrate, a multilayer reflective film that reflects EUV light, a protective film, a buffer layer, and a phase shift film. In the reflective mask blank of the present invention, the buffer layer contains Ru, and the phase shift film contains at least one element selected from the group consisting of Ir and Pt. The reflective mask blank of the present invention will be described with reference to the drawings.

[0014] FIG. 1 is a cross-sectional view showing one embodiment of a reflective mask blank of the present invention. The reflective mask blank 10 shown in FIG. 1 has a conductive film 22, a substrate 12, a multilayer reflective film 14, a protective film 16, a buffer layer 18, and a phase shift film 20, in this order. The buffer layer 18 contains Ru, and the phase shift film 20 contains at least one element selected from the group consisting of Ir and Pt. The conductive film 22 shown in FIG. 1 may be omitted. The reflective mask blank 10 may also have an etching mask film, described below, on the side of the phase shift film 20 opposite the substrate 12 side.

[0015] Although the mechanism by which the reflective mask blank of the present invention provides excellent processability of the phase shift film and suppresses a decrease in reflectance in the resulting reflective mask is not entirely clear, the present inventors speculate as follows. In the reflective mask blank of the present invention, the phase shift film contains at least one element selected from the group consisting of Ir and Pt, and the buffer layer contains Ru. Therefore, it is believed that the phase shift film and the buffer layer have different chemical properties (e.g., etchability). Typically, when a reflective mask blank is processed to obtain a reflective mask, dry etching is performed. Here, if an etching gas that easily etches the phase shift film is selected, the difference in chemical properties makes it easier to etch only the phase shift film while suppressing etching of the buffer layer. As a result, when etching the phase shift film, the buffer layer protects the protective film from etching, making it less likely for the thickness of the protective film to change, and reducing the impact on the multilayer reflective film. Therefore, it is believed that when a reflective mask is obtained, the multilayer reflective film present in the openings of the phase shift film is less affected by etching, and a decrease in the reflectance of the resulting reflective mask is suppressed. Furthermore, for the reasons mentioned above, even if the etching rate of the phase shift film is increased, only the phase shift film is likely to be removed, and the processing rate of the phase shift film can be increased, so it is considered that the reflective mask blank of the present invention has excellent processability for the phase shift film.

[0016] The structure of the reflective mask blank of the present invention will be described below.

[0017] [Substrate] The substrate of the reflective mask blank of the present invention preferably has a small thermal expansion coefficient. A substrate with a small thermal expansion coefficient can suppress distortion of the phase shift 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 ２However, 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.

[0018] The surface of the substrate on which the multilayer reflective film is laminated (hereinafter also referred to as the "first principal surface") preferably has high surface smoothness. The surface smoothness of the first principal surface can be evaluated by surface roughness. The surface roughness of the first principal surface is preferably 0.15 nm or less in terms of root-mean-square roughness Rq. Note that the surface roughness can be measured using an atomic force microscope, and the surface roughness is described as the root-mean-square roughness Rq based on JIS-B0601. The first principal surface is preferably surface-processed to achieve a predetermined flatness, in order to improve the pattern transfer accuracy and positional accuracy of a reflective mask obtained using the reflective mask blank. In a predetermined region of the first principal surface (e.g., a 132 mm × 132 mm region), the flatness of the substrate is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less. The flatness can be measured using a flatness measuring instrument manufactured by Fujinon Corporation. The size and thickness of the substrate are determined appropriately based on the design values ​​of the mask, etc. For example, the outer shape may be 6 inches (152 mm) square and the thickness may be 0.25 inches (6.3 mm). The substrate is often rectangular (oblong) or square. Furthermore, it is preferable that the substrate has high rigidity in order to prevent deformation due to film stress of films (multilayer reflective films, phase shift films, etc.) formed on the substrate. For example, it is preferable that the Young's modulus of the substrate is 65 GPa or more.

[0019] [Multilayer reflective film] The multilayer reflective film of the reflective mask blank of the present invention is not particularly limited as long as it has the desired properties as a reflective film for an EUV mask blank. The multilayer reflective film preferably has a high reflectivity for EUV light. Specifically, when EUV light is incident on the surface of the multilayer reflective film at an incident angle of 6°, the maximum reflectivity for EUV light with a wavelength of around 13.5 nm is preferably 60% or more, more preferably 65% ​​or more. Similarly, even when a protective film is laminated on the multilayer reflective film, the maximum reflectivity for EUV light with a wavelength of around 13.5 nm is preferably 60% or more, more preferably 65% ​​or more.

[0020] Since multilayer reflective films can achieve high reflectivity for EUV light, they are typically formed by alternately stacking multiple high-refractive index layers, which exhibit a high refractive index for EUV light, and multiple low-refractive index layers, which exhibit a low refractive index for EUV light. The multilayer reflective film may be formed by stacking multiple cycles of a stack structure in which high-refractive index layers and low-refractive index layers are stacked in this order from the substrate side, or multiple cycles of a stack structure in which low-refractive index layers and high-refractive index layers are stacked in this order. The high-refractive index layer may be a layer containing Si. Examples of materials containing Si include elemental Si and Si compounds containing one or more elements selected from the group consisting of B, C, N, and O. The use of a high-refractive index layer containing Si results in a reflective mask with excellent reflectivity for EUV light. The low-refractive index layer may be a layer containing a metal selected from the group consisting of Mo, Ru, Rh, and Pt, or an alloy thereof. Si is commonly used for the high-refractive index layer, and Mo is commonly used for the low-refractive index layer. That is, Mo / Si multilayer reflective films are most common, but the multilayer reflective films are not limited to this, and Ru / Si multilayer reflective films, Mo / Be multilayer reflective films, Mo compound / Si compound multilayer reflective films, Si / Mo / Ru multilayer reflective films, Si / Mo / Ru / Mo multilayer reflective films, Si / Ru / Mo multilayer reflective films, and Si / Ru / Mo / Ru multilayer reflective films can also be used.

[0021] The thickness of each layer constituting the multilayer reflective film and the number of layer repeat units can be appropriately selected depending on the film material used and the reflectivity of EUV light required for the reflective layer. Taking a Mo / Si multilayer reflective film as an example, to obtain a multilayer reflective film with a maximum reflectivity of 60% or more for EUV light, Mo films with a thickness of 2.3±0.1 nm and Si films with a thickness of 4.5±0.1 nm can be stacked so that the number of repeat units is 30 to 60. The multilayer reflective film preferably has a reflectivity of 60% or more for EUV light at an incident angle θ of 6°. More preferably, the reflectivity is 65% or more.

[0022] Each layer constituting the multilayer reflective film can be deposited to a desired thickness using known deposition methods such as DC sputtering, magnetron sputtering, and ion beam sputtering. For example, when fabricating a multilayer reflective film using ion beam sputtering, ion particles are supplied from an ion source to a target of a high refractive index material and a target of a low refractive index material. When the multilayer reflective film is a Mo / Si multilayer reflective film, for example, a Si layer of a predetermined thickness is first deposited on a substrate using an ion beam sputtering method. Then, a Mo layer of a predetermined thickness is deposited using an Mo target. This Si layer and Mo layer constitute one cycle, and for example, 30 to 60 cycles (preferably 40 to 50 cycles) are stacked to form a Mo / Si multilayer reflective film.

[0023] [Protective Film] The reflective mask blank of the present invention has a protective film between the multilayer reflective film and the phase shift 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 phase shift film. Examples of materials that can achieve this objective include materials containing at least one element selected from the group consisting of Si, Ru, and Rh. That is, the protective film preferably contains at least one element selected from the group consisting of Si, Ru, and Rh. Furthermore, the protective film preferably contains Rh. More specifically, examples of such materials include Ru metal alone, Ru alloys containing Ru and one or more metals selected from the group consisting of Si, Y, Ti, Zr, Nb, Mo, Rh, Pd, Ta, and Ir, and Rh metal alone, Rh alloys containing Rh and one or more metals selected from the group consisting of Si, Y, Ti, Zr, Nb, Mo, Ru, Pd, Ta, and Ir. Adding Ru, Nb, Mo, Zr, Y, or Ti to Rh can reduce the extinction coefficient while suppressing an increase in the refractive index, and can easily improve the reflectance to EUV light. Also, adding Ta, Ir, Pd, or Y to Rh can easily improve the resistance to the etching process. Furthermore, materials that can achieve the above object include Al and nitrides containing these metals and nitrogen, and Al ２ O ３ Among these, metal Ru alone, a Ru alloy, metal Rh alone, or a Rh alloy is preferred as a material that can achieve the above-mentioned object.

[0024] When the protective film contains Ru or Rh, the protective film may also contain at least one element selected from the group consisting of B, C, N, and O. Addition of these elements tends to reduce the crystallinity of the protective film and improve the surface smoothness of the buffer layer side of the protective film. A protective film with low crystallinity refers to a small crystallite diameter calculated using a diffraction chart obtained by X-ray diffraction (XRD). The Scherrer's equation is used to calculate the crystallite diameter. The full half-width of the diffraction peak with the highest intensity in the 2θ range of 30 to 55° is used to calculate the crystallite diameter using the Scherrer's equation. If no clear diffraction peak is observed in the diffraction chart, the protective film is considered to be amorphous. The crystallite diameter of the protective film is preferably 10 nm or less, more preferably 6.0 nm or less, and even more preferably 4.0 nm or less. The lower limit of the crystallite size is not particularly limited, but is often 0.1 nm or more. The protective film may be amorphous.

[0025] The thickness of the protective film is not particularly limited as long as it can function as a protective film. From the viewpoint of maintaining the reflectivity of EUV light reflected by the multilayer reflective film, the thickness of the protective film is preferably 10 nm or less, more preferably 6 nm or less, even more preferably 5 nm or less, and particularly preferably 3.5 nm or less. Furthermore, from the viewpoint of obtaining good etching resistance, the thickness of the protective film is preferably 1 nm or more, more preferably 1.5 nm or more, and even more preferably 2 nm or more. 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. The thickness of the protective film is determined by X-ray reflectivity.

[0026] The density of the protective film is preferably 10.0 to 14.0 g / cm ３ The density of the protective film is 10.0 g / cm ３ When the density of the protective film is 14.0 g / cm or more, good etching resistance is easily obtained. ３ If it is equal to or less than this, it is easy to suppress a decrease in reflectance for EUV light.

[0027] The upper surface of the protective film, i.e., the surface of the protective film on the phase shift film side, preferably has a root-mean-square roughness (Rq) of 0.300 nm or less, more preferably 0.150 nm or less. If the root-mean-square roughness (Rq) is 0.300 nm or less, it is easy to form a smooth buffer layer, phase shift film, etc. on the protective film. In addition, scattering of EUV light can be suppressed, and the reflectance for EUV light can be easily improved. The root-mean-square roughness (Rq) is preferably 0.050 nm or more.

[0028] The protective film may be a film consisting of a single layer, or may be a multilayer film consisting of multiple layers. When the protective film is a multilayer film, each layer constituting the multilayer film is preferably made of the above-mentioned preferred material. When the protective film is a multilayer film, it is also preferable that the total thickness of the multilayer film is within the above-mentioned preferred range. When the protective film is a multilayer film, it is also preferable that the layer in the protective film arranged closest to the buffer layer is a layer containing Rh. It is also preferable that the above-mentioned Rh-containing layer does not contain Ru.

[0029] The protective film can be formed by a known film formation method such as DC sputtering, magnetron sputtering, ion beam sputtering, etc. When forming a Rh film by magnetron sputtering, it is preferable to use a Rh target as the target and Ar gas as the sputtering gas.

[0030] [Buffer Layer] The reflective mask blank of the present invention has a buffer layer between the protective film and the phase shift film. The buffer layer contains Ru. As described above, the provision of the buffer layer can suppress the influence of the etching process (usually a dry etching process) of the phase shift film on the protective film and the multilayer reflective film.

[0031] The Ru content in the buffer layer is preferably 15 atomic % or more, more preferably 35 atomic % or more, even more preferably 50 atomic % or more, particularly preferably 70 atomic % or more, and most preferably 80 atomic % or more, based on the total atoms in the buffer layer. The upper limit of the Ru content in the buffer layer may be 100 atomic %. That is, the buffer layer may consist solely of Ru. The Ru content in the buffer layer may be 95 atomic % or less, 90 atomic % or less, or 85 atomic % or less, based on the total atoms in the buffer layer.

[0032] The buffer layer may contain a metal element other than Ru, which makes it less susceptible to etching relative to the phase shift film (hereinafter also referred to as having a "higher etching selectivity"). Examples of metal elements other than Ru include Group 4 elements, Group 5 elements, Group 6 elements, Group 7 elements, and Group 8 elements excluding Ru. In terms of increasing the etching selectivity, at least one element selected from the group consisting of Cr, Hf, Ta, W, Re, and Os is preferred, at least one element selected from the group consisting of Ta, Cr, and Hf is more preferred, at least one element selected from the group consisting of Ta and Cr is even more preferred, and Cr is particularly preferred. When the buffer layer contains a metal element other than Ru, the preferred range of the Ru content in the buffer layer is as described above. When the buffer layer contains a metal element other than Ru, the content of the metal element is preferably 1 atomic % or more, more preferably 10 atomic % or more, even more preferably 20 atomic % or more, and particularly preferably 30 atomic % or more, based on the total atoms in the buffer layer. The content of the metal element is preferably 85 atomic % or less, more preferably 80 atomic % or less, and even more preferably 60 atomic % or less, based on all atoms in the buffer layer.

[0033] When the buffer layer contains the metal element, the ratio of the metal element content to the total atoms of the buffer layer to the Ru content to the total atoms of the buffer layer (metal element content / Ru content) is preferably 0.02 or more, more preferably 0.10 or more, even more preferably 0.20 or more, and particularly preferably 0.50 or more. The ratio is often 9.00 or less, preferably 5.00 or less, more preferably 4.00 or less, even more preferably 3.00 or less, particularly preferably 2.00 or less, and most preferably 1.00 or less. It is also preferable that the metal element is Cr and that the ratio satisfies the above. That is, when the buffer layer contains Cr, the ratio of the Cr content to the total atoms of the buffer layer to the Ru content to the total atoms of the buffer layer (Cr content / Ru content) is also preferably within the above preferred range.

[0034] The buffer layer may further contain at least one element X1 selected from the group consisting of B, C, N, O, and Si. The buffer layer may contain only one element X1 or two or more elements. When the buffer layer contains the element X1, the content of the element X1 is preferably 1 atomic % or more, more preferably 3 atomic % or more, and even more preferably 5 atomic % or more, based on the total atoms of the buffer layer. When the buffer layer contains the element X1, the content of the element X1 is preferably 25 atomic % or less, more preferably 20 atomic % or less, and even more preferably 10 atomic % or less. When the buffer layer contains two or more elements X1, the content of the element X1 is the total content of the elements X1. The buffer layer does not necessarily need to contain the element X1.

[0035] The content of each element in the buffer layer is determined using analytical values ​​obtained by X-ray photoelectron spectroscopy (XPS). For XPS analysis, a PHI 5000 VersaProbe analyzer manufactured by ULVAC-PHI, Inc. is used. The analyzer is calibrated in accordance with JIS K 0145. First, a measurement sample approximately 1 cm square is cut out from a reflective mask blank. The obtained measurement sample is placed in a measurement holder so that the phase shift film side faces the measurement surface. After the measurement holder is loaded into the measurement holder, the phase shift film is removed with an argon ion beam to expose the buffer layer. After exposing the buffer layer, the buffer layer is removed from the outermost surface of the buffer layer by a thickness equal to half the thickness of the buffer layer. The sputtering rate during the removal can be measured using a separately prepared sample. After removing the outermost surface of the buffer layer, the removed portion is irradiated with X-rays (monochromated AlKα radiation) and analyzed at a photoelectron take-off angle (the angle between the surface of the measurement sample and the direction of the detector) of 45°. A neutralization gun is used during the analysis to suppress charge buildup. The analysis involves a wide scan in the binding energy range of 1000 to 0 eV to confirm the elements present, followed by a narrow scan depending on the elements present (e.g., Ru and the above-mentioned element X1). The narrow scan is performed, for example, with a pass energy of 58.7 eV, an energy step of 0.1 eV, a time / step of 50 ms, and 10 accumulations. The wide scan is performed with a pass energy of 58.7 eV, an energy step of 1 eV, a time / step of 50 ms, and 2 accumulations. The content of each element in the buffer layer is analyzed using the relative sensitivity coefficients specific to each element and each orbital from the spectrum obtained by narrow scan during XPS analysis according to the above procedure. Alternatively, a model sample formed under the same conditions as those for forming the buffer layer may be used to carry out the analysis in the same manner as above.

[0036] From the viewpoint of the optical properties of the resulting reflective mask, the thickness of the buffer layer is preferably 1 nm or more, more preferably 2 nm or more, and even more preferably 3 nm or more. From the viewpoint of etching resistance, the thickness of the buffer layer is preferably 20 nm or less, more preferably 15 nm or less, and even more preferably 10 nm or less. The film thickness of the buffer layer is determined by X-ray reflectivity.

[0037] The ratio of the thickness (dp) of the phase shift film to the thickness (db) of the buffer layer (thickness of phase shift film / thickness of buffer layer, dp / db) is, for example, 2.0 to 15.0. When dp / db is 2.0 or more, the influence of the buffer layer on exposure characteristics can be further reduced. When dp / db is 15.0 or less, the buffer layer easily protects the protective film from etching when etching the phase shift film, and the thickness of the protective film is less likely to change, so the influence on the multilayer reflective film can be further reduced. The ratio (dp / db) is preferably 3.5 to 12.0, more preferably 3.5 to 11.0, and even more preferably 3.5 to 8.0.

[0038] The crystallite diameter of the buffer layer is preferably 10 nm or less, more preferably 6.0 nm or less, and even more preferably 4.0 nm or less. The lower limit of the crystallite diameter is not particularly limited, but is often 0.1 nm or more. The buffer layer may also be amorphous. The method for measuring the crystallite diameter of the buffer layer is the same as the method for measuring the crystallite diameter of the protective film.

[0039] The buffer layer can be formed using known film formation methods such as DC sputtering, magnetron sputtering, and ion beam sputtering. When forming a RuCr film (a film containing Ru and Cr) by magnetron sputtering, it is preferable to use a RuCr target as the target and Ar gas as the sputtering gas. Furthermore, when forming a RuCr film, it may be formed using a dual sputtering method using a Ru target and a Cr target.

[0040] [Phase Shift Film] The phase shift film of the reflective mask blank of the present invention is required to have a high contrast between EUV light reflected by the openings in the phase shift film (multilayer reflective film) and EUV light reflected by the remaining portions of the phase shift film when the phase shift film is patterned to obtain a phase shift film pattern. In terms of using the phase shift film pattern as a phase shift mask, the reflectivity of the phase shift film for EUV light is preferably 2% or more. To obtain a sufficient phase shift effect, the reflectivity of the phase shift film is preferably 9 to 15%. Using a phase shift film as a phase shift mask improves the contrast of the optical image on the wafer, and the exposure margin is likely to increase.

[0041] The phase shift film of the present invention contains at least one element selected from the group consisting of Ir and Pt. When the phase shift film contains Ir, the Ir content is preferably 30 atomic % or more, more preferably 50 atomic % or more, and even more preferably 60 atomic % or more, based on the total atoms of the phase shift film. The Ir content may be 100 atomic % based on the total atoms of the phase shift film. That is, the phase shift film may consist solely of Ir. The Ir content may be 90 atomic % or less, or 80 atomic % or less, based on the total atoms of the phase shift film. When the phase shift film contains Pt, the Pt content is preferably 30 atomic % or more, more preferably 50 atomic % or more, and even more preferably 60 atomic % or more, based on the total atoms of the phase shift film. The Pt content may be 100 atomic % based on the total atoms of the phase shift film. That is, the phase shift film may consist solely of Pt. The Pt content may be 90 atomic % or less, or 80 atomic % or less, based on the total atoms of the phase shift film. The phase shift film may contain Ir and Pt.

[0042] The phase shift film may contain a metal element other than Ir and Pt. Examples of the metal element include elements from Group 4, Group 5, Group 6, and Group 7. In terms of the optical properties and processability of the phase shift film, at least one element selected from the group consisting of Si, Cr, Mo, Ta, W, Nb, and Re is preferred. When the phase shift film contains a metal element other than Ir and Pt, the preferred ranges for the Ir content and the Pt content in the phase shift film are as described above. When the phase shift film contains a metal element other than Ir and Pt, the content of the metal element is preferably 5 atomic % or more, more preferably 10 atomic % or more, and even more preferably 20 atomic % or more, based on the total atoms in the phase shift film. The content of the metal element is preferably 50 atomic % or less, more preferably 40 atomic % or less, and even more preferably 30 atomic % or less, based on the total atoms in the phase shift film.

[0043] The phase shift film preferably further contains at least one element selected from the group consisting of B, C, N, O, and Si (hereinafter also referred to as element X2). When the phase shift film contains element X2, the content of element X2 is preferably 1 atomic % or more, more preferably 3 atomic % or more, and even more preferably 5 atomic % or more, based on the total atoms of the phase shift film. When the phase shift film contains element X2, the content of element X2 is preferably 25 atomic % or less, more preferably 20 atomic % or less, and even more preferably 10 atomic % or less. When the phase shift film contains two or more elements X2, the content of element X2 is the total content of element X2. Note that the phase shift film does not necessarily contain element X2.

[0044] When the phase shift film contains Ir and Ta, the ratio of the Ir content (atomic %) in the phase shift film to the Ta content (atomic %) in the phase shift film (Ir content / Ta content) is, for example, 1 to 190. When this ratio is 1 or more, the optical properties of the phase shift film are easily adjusted to the range described below. When this ratio is 190 or less, the processability of the phase shift film is easily improved. The ratio is preferably 1 to 100, more preferably 1 to 40, even more preferably 2 to 30, particularly preferably 2 to 20, and most preferably 2 to 12.

[0045] When the phase shift film contains Ir and Cr, the ratio of the Ir content (atomic %) in the phase shift film to the Cr content (atomic %) in the phase shift film (Ir content / Cr content) is, for example, 1 to 105. When this ratio is 1 or more, the optical properties of the phase shift film are easily adjusted to the range described below. When this ratio is 105 or less, the processability of the phase shift film is easily improved. The ratio is preferably 2 to 105, more preferably 3 to 105, and even more preferably 4 to 105.

[0046] When the phase shift film contains Ir and W, the ratio of the Ir content (atomic %) in the phase shift film to the W content (atomic %) in the phase shift film (Ir content / W content) is, for example, 1 to 100. When this ratio is 1 or more, the optical properties of the phase shift film can be easily adjusted to the range described below. When this ratio is 100 or less, the processability of the phase shift film can be more easily improved. The ratio is preferably 1 to 90, more preferably 2 to 80, even more preferably 3 to 70, and particularly preferably 4 to 30.

[0047] When the phase shift film contains N as the element X2, the N content is preferably 1.0 to 10 atomic % based on the total atoms in the phase shift film. If the N content is 1.0 atomic % or more, the crystallinity of the phase shift film is likely to be reduced. From the viewpoint of optical properties, the N content is preferably 10 atomic % or less, and more preferably 5.0 atomic % or less.

[0048] When the phase shift film contains O as the element X2, the O content is preferably 1.0 to 15 atomic % based on the total atoms in the phase shift film. If the O content is 1.0 atomic % or more, the crystallinity of the phase shift film is likely to be reduced. From the viewpoints of optical properties and patterning properties, the O content is preferably 15 atomic % or less.

[0049] When the phase shift film contains Ir and O, the ratio of the Ir content (atomic %) in the phase shift film to the O content (atomic %) in the phase shift film (Ir content / O content) is, for example, 1 to 40. When the ratio is 1 or more, the hydrogen resistance of the phase shift film when exposed to hydrogen is easily improved. When the ratio is 40 or less, the crystallinity of the phase shift film is easily reduced, and the roughness of the sidewalls when the phase shift film is patterned is easily reduced. The ratio of the Ir content to the O content (Ir / O) is preferably 2 to 35, more preferably 2 to 30, even more preferably 2 to 25, and particularly preferably 3 to 20.

[0050] When the phase shift film contains Ir and N, the ratio of the Ir content (atomic %) in the phase shift film to the N content (atomic %) in the phase shift film (Ir content / N content) is, for example, 10 to 105. When this ratio is 10 or more, the hydrogen resistance of the phase shift film is easily improved. When this ratio is 105 or less, the crystallinity of the phase shift film is easily reduced, and the roughness of the sidewalls when the phase shift film is patterned is easily reduced. The ratio is preferably 10 to 70, more preferably 10 to 45, even more preferably 11 to 36, and particularly preferably 12 to 30.

[0051] When the phase shift film contains Ir, O, and N, the ratio of the Ir content (atomic %) in the phase shift film to the sum of the O content (atomic %) and N content (atomic %) in the phase shift film (Ir content / total content of O and N) is, for example, 1 to 45. If this ratio is 1 or more, the hydrogen resistance of the phase shift film is likely to be improved. If this ratio is 45 or less, the crystallinity of the phase shift film is likely to be reduced, and the roughness of the sidewalls when the phase shift film is patterned is likely to be reduced. The ratio is preferably 2 to 30, more preferably 2.5 to 20, even more preferably 4 to 17, and particularly preferably 6 to 16.

[0052] The thickness of the phase shift film is preferably 20 nm or more, more preferably 30 nm or more. In order to reduce the shadowing effect, the thickness of the phase shift film is preferably 60 nm or less, more preferably 55 nm or less, and even more preferably 50 nm or less. The thickness of the phase shift film is determined by X-ray reflectivity.

[0053] The refractive index n of the phase shift film is preferably 0.885 or more. The refractive index n of the phase shift film is preferably 0.935 or less, more preferably 0.920 or less, even more preferably 0.910 or less, and particularly preferably 0.900 or less, in order to enable the thickness of the phase shift film to be further reduced. The extinction coefficient k of the phase shift film is preferably 0.065 or less, more preferably 0.050 or less, and even more preferably 0.048 or less. The extinction coefficient k of the phase shift film is preferably 0.030 or more, more preferably 0.032 or more, even more preferably 0.035 or more, and particularly preferably 0.037 or more, in order to facilitate adjustment of the reflectance of the phase shift film to a lower value. The refractive index n and extinction coefficient k are determined by measuring the incidence angle dependence of reflectance using EUV light with a wavelength of 13.5 nm, and fitting the obtained profile using the refractive index n and extinction coefficient k as parameters.

[0054] The crystallite diameter of the phase shift film is preferably 10.0 nm or less, more preferably 6.0 nm or less, and even more preferably 4.0 nm or less. The lower limit of the crystallite diameter is not particularly limited, but is often 0.1 nm or more. The phase shift film of the present invention may also be amorphous. When the phase shift film contains the element X2, the crystallite diameter of the phase shift film is easily reduced. The method for measuring the crystallite diameter of the phase shift film is the same as the method for measuring the crystallite diameter of the protective film.

[0055] The phase shift film preferably has resistance to dissolution in cleaning solutions. When the phase shift film has resistance to dissolution in cleaning solutions, the phase shift film is less likely to be removed during the etching process of the etching mask film described later, making it easier to obtain a desired pattern. More specifically, it is preferable that the change in film thickness of the phase shift film is small when the phase shift film is brought into contact with a sulfuric acid-hydrogen peroxide aqueous solution (SPM). For example, when the phase shift film is etched with SPM at 100° C. for 20 minutes, the change in film thickness between before and after the etching process is preferably 1.0 nm or less, more preferably 0.5 nm or less, and even more preferably 0.2 nm or less. The lower limit of the change in film thickness is 0 nm or more.

[0056] The phase shift film may be a single layer film or a multilayer film made up of multiple films. When the phase shift film is a multilayer film made up of multiple films, the phase shift film may include a film that does not contain Ir or Pt.

[0057] The phase shift film can be formed by a known film formation method such as DC sputtering, magnetron sputtering, ion beam sputtering, etc. For example, when an IrTaN film is formed as the phase shift film by magnetron sputtering, the phase shift film can be formed by sputtering using a Ta target and an Ir target and supplying a gas containing Ar gas and nitrogen gas.

[0058] [Conductive Film] The reflective mask blank of the present invention may have a conductive film on the surface (second main surface) opposite to the first main surface of the substrate. By providing a conductive film, the reflective mask blank can be handled using an electrostatic chuck. The conductive film preferably has a low sheet resistance. The sheet resistance of the conductive film is preferably, for example, 200 Ω / sq. or less, more preferably 100 Ω / sq. or less. The conductive film may be made of a wide variety 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, may be used. The conductive film may also be made of 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. The thickness of the conductive film is preferably 10 to 1,000 nm, more preferably 10 to 400 nm. The conductive film may also have a function of adjusting stress on the second main surface side of the reflective mask blank. That is, the 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 conductive film can be formed using a known film formation method, for example, a sputtering method such as DC sputtering, magnetron sputtering, or ion beam sputtering, a CVD method, a vacuum deposition method, or an electrolytic plating method.

[0059] [Etching Mask Film] The reflective mask blank of the present invention may have an etching mask film on the side opposite to the substrate side of the phase shift film. The etching mask film is preferably made of a material that is highly resistant to dry etching. When an etching mask film is formed on the phase shift film, dry etching can be performed even if the minimum line width of the phase shift film pattern is small. Therefore, this is effective for miniaturizing the phase shift film pattern.

[0060] The etching mask film preferably contains one or more elements (hereinafter also referred to as "element X3") selected from the group consisting of Al, Si, Ti, Cr, Y, Nb, Mo, Ta, and Hf. That is, the material constituting the etching mask film preferably contains element X3. The etching mask film may further contain at least one element selected from the group consisting of B, N, and O. Examples of materials constituting the etching mask film include a simple substance of element X3, and oxides, nitrides, oxynitrides, carbides, carbonitrides, carbonates, fluorides, and oxyfluorides of element X3. Note that the material constituting the etching mask film may also be a composite compound (e.g., a composite oxide) containing two or more elements of element X3.

[0061] For example, Cr-based materials containing Cr as element X3 include materials containing Cr and one or more elements selected from the group consisting of O, N, C, and H, and more specifically, CrO, CrN, and CrON. The notation "CrON" represents a material containing Cr, O, and N, and the same notations below have the same meaning. Furthermore, Si-based materials containing Si as element X3 include materials containing Si and one or more elements selected from the group consisting of O, N, C, and H, and more specifically, SiO ２ , SiON, SiN, SiO, Si, SiC, SiCO, SiCN, and SiCON.

[0062] The thickness of the etching mask film is preferably 2 nm or more, and is preferably 30 nm or less, more preferably 25 nm or less, and even more preferably 10 nm or less.

[0063] The etching mask film can be formed by using a known film formation method such as DC sputtering, magnetron sputtering, or ion beam sputtering.

[0064] <Method for manufacturing a reflective mask and a reflective mask> The reflective mask of the present invention is obtained by patterning the phase shift film of the reflective mask blank of the present invention. One example of the method for manufacturing a reflective mask will be described with reference to FIG.

[0065] FIG. 2A shows a state in which a resist pattern 40 is formed on a reflective mask blank having, in this order, a conductive film 22, a substrate 12, a multilayer reflective film 14, a protective film 16, a buffer layer 18, a phase shift film 20, and an etching mask film 24. The resist pattern 40 can be formed by a known method, for example, by applying a resist to the etching mask film 24 of the reflective mask blank, followed by exposure and development 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. 2A as a mask, the etching mask film 24 is etched, and the etching mask film is patterned into a shape corresponding to the resist pattern 40 to obtain an etching mask film pattern 24pt. The resist pattern 40 is then removed to obtain the laminate shown in FIG. 2B. The etching mask film 24 can be etched by a known method, for example, by dry etching using a gas containing oxygen gas and a chlorine-based gas. Examples of chlorine-based gases include Cl. ２ , SiCl ４ , CHCl ３ , CCl ４ , and BCl ３ Examples of suitable 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. If necessary, an inert gas such as nitrogen gas, helium gas, or argon gas may be mixed. The resist pattern 40 may be removed by a known method, such as removal with a cleaning solution. Examples of suitable 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.

[0066] Next, the phase shift film 20 is etched and patterned using the etching mask film pattern 24pt of the pattern shown in Fig. 2(b) as a mask to obtain a laminate having a phase shift film pattern 20pt shown in Fig. 2(c). In the laminate shown in Fig. 2(c), the buffer layer 18 is exposed. Dry etching for forming the phase shift film pattern 20pt can be, for example, dry etching using a fluorine-based gas. Examples of fluorine-based gases include CF ４ , CHF ３ , C ２ F ６ , C ３ F ６ , C ４ F ６ , C ４ F ８ , C.H. ２ F ２ , C.H. ３ F, C ３ F ８ , F ２ , SF ６ , and NF ３ Examples of suitable gases include fluorine-based gases, and mixtures thereof. If necessary, active gases such as oxygen gas and chlorine gas, and inert gases such as nitrogen gas, helium gas, and argon gas may be mixed in addition to the fluorine-based gas. In the reflective mask blank of the present invention, the phase shift film contains at least one element selected from the group consisting of Ir and Pt, which facilitates improving the processability of the phase shift film 20 by dry etching using the fluorine-based gas. Furthermore, in the reflective mask blank of the present invention, the buffer layer 18 contains Ru, which makes it difficult to etch the phase shift film 20 during dry etching, thereby reducing the effects on the protective film 16 and the multilayer reflective film 14.

[0067] Next, the buffer layer 18 disposed in the opening is removed from the laminate shown in FIG. 2(c) using the etching mask film pattern 24pt and the phase shift film pattern 20pt as masks, thereby obtaining a buffer layer pattern 18pt. The buffer layer 18 can be removed, for example, by dry etching using a chlorine-based gas. Examples of chlorine-based gases are as described above. If necessary, an active gas such as oxygen gas and an inert gas such as nitrogen gas, helium gas, or argon gas may be mixed with the chlorine-based gas. The etching mask film pattern 24pt is then removed to obtain the laminate shown in FIG. 2(d). The laminate shown in FIG. 2(d) has a buffer layer pattern 18pt and a phase shift film pattern 20pt, in this order, on the side of the protective film 16 opposite the substrate 12 side. The etching mask film pattern 24pt can be removed by the same method as the etching method for the etching mask film 24. The process for obtaining the buffer layer pattern 18pt and the process for removing the etching mask film pattern 24pt may be performed simultaneously.

[0068] Next, as shown in Fig. 2(e), a resist pattern 42 corresponding to the frame of the exposure region is formed on the laminate of Fig. 2(d), and dry etching is performed using the resist pattern 42 of Fig. 2(e) as a mask. Dry etching is performed until it reaches the substrate 12. After dry etching, the resist pattern 42 is removed to obtain the reflective mask shown in Fig. 2(f).

[0069] The reflective mask obtained by patterning the phase shift film of the reflective mask blank of the present invention can be suitably used as a reflective mask used for exposure to EUV light. In the reflective mask of the present invention, the influence on the multilayer reflective film is suppressed in the process of obtaining the reflective mask from the reflective mask blank, so that the reflectance at the openings of the phase shift film pattern is high.

[0070] 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. Examples 3 to 11 described below are examples, and Examples 1 and 2 are comparative examples.

[0071] Example 4 First, the procedure for obtaining the substrate with a conductive film of Example 4 will be described as a representative example.

[0072] [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 a root-mean-square roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less. A 100 nm-thick Cr film was formed on the second main surface of the substrate using magnetron sputtering. The sheet resistance of the Cr film was 100 Ω / □.

[0073] [Multilayer Reflective Film] Next, a Mo / Si multilayer reflective film was formed on the first main 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 film (4.5 nm thick) and a Mo film (2.3 nm thick) using an ion beam sputtering method 40 times, and then forming an additional Si film (4.5 nm thick) after the 40th Mo film. The total thickness of the Mo / Si multilayer reflective film was 276.5 nm ((4.5 nm + 2.3 nm) × 40 + 4.5 nm).

[0074] [Protective Film] A Rh film (thickness: 2.5 nm) was formed as a protective film on the multilayer reflective film formed by the above procedure. The Rh film was formed by ion beam sputtering.

[0075] [Buffer Layer] A RuCr film (4 nm thick) was formed as a buffer layer on the protective film formed by the above procedure. The RuCr film was formed using a DC sputtering method. The element ratio in the buffer layer was analyzed using XPS as described above, and the ratio of the Ru content to the Cr content was Ru:Cr = 80:20 in atomic ratio.

[0076] [Phase Shift Film] An IrTaON film (32 nm thick) was formed as a phase shift film on the buffer layer formed by the above procedure. The IrTaON film was formed using a dual sputtering method. The elemental ratio of the IrTaON film was analyzed using XPS as described above, and the ratio of the Ir content, Ta content, O content, and N content was Ir:Ta:O:N = 69.1:22.9:3.1:4.9 in atomic ratio.

[0077] By the above procedure, a reflective mask blank of Example 4 was obtained.

[0078] <Evaluation> [Etching Rate] Etching rate measurement samples were prepared by forming only the buffer layer and phase shift film formed in the reflective mask blank of Example 4 on a substrate, and the etching rates of the buffer layer and the phase shift film were measured. Specifically, plasma was generated using an inductively coupled plasma (ICP) generator for the etching rate measurement sample, and etching was performed by irradiating the plasma to measure the etching rate of the phase shift film and the etching rate of the buffer layer. Specific etching conditions were as follows: Antenna RF power output: 720 W; Bias RF power output: 80 W; Etching gas pressure: 0.4 Pa; Etching gas flow rate: CF ４ 48 sccm, O ２ 12 sccm. Note that "sccm" is an abbreviation for "Standard Cubic Centimeter per Minute" and is the gas flow rate (cm) per minute converted into a volume value at 1 atmosphere (1013.25 hPa) and 0°C. ３The film thickness was measured by XRR before and after etching under the above conditions, and the change in film thickness was divided by the etching time to calculate the etching rate (unit: nm / min).

[0079] Examples 1 to 3 and 5 to 11: A reflective mask blank was obtained in the same manner as in Example 4, except that the film formation conditions for the buffer layer were adjusted so that the composition and film thickness were as shown in the table below. For buffer layers containing O or N, O was added to the sputtering atmosphere. ２ Gas or N ２ Gases were introduced and the amounts introduced were adjusted to obtain the compositions shown in the table below. In addition, samples for etching rate measurement were prepared in the same manner as in Example 4, and the etching rates of the buffer layer and the phase shift film in each example were measured.

[0080] <Results> The composition of the buffer layer and the measurement results of the etching rate are shown in Table 1 below. In Table 1, the column "Selectivity" indicates the ratio of the etching rate of the phase shift film to the etching rate of the buffer layer. The larger the selectivity, the more difficult it is for the buffer layer to be etched relative to the phase shift film, thereby improving the processing speed of the phase shift film and thereby improving the processability of the phase shift film. Furthermore, the larger the selectivity, the more difficult it is for the buffer layer to be etched relative to the phase shift film, thereby reducing the influence on the protective film and the multilayer reflective film, and suppressing a decrease in reflectivity in the resulting reflective mask. In Table 1, the notation "at %" means atomic percent. In Table 1, the column "Cr / Ru" indicates the ratio of the Cr content in the buffer layer to the Ru content in the buffer layer.

[0081]

[0082] The results shown in Table 1 confirm that the selectivity was low in Examples 1 and 2, in which the buffer layer did not contain Ru. A low selectivity reduces the processability of the phase shift film, and the reflectivity of the resulting reflective mask is likely to decrease. On the other hand, it was confirmed that the selectivity was high when the buffer layer contained Ru and the phase shift film contained at least one element selected from the group consisting of Ir and Pt. Thus, the reflective mask blank of the present invention provides excellent processability of the phase shift film and suppresses a decrease in reflectivity in the resulting reflective mask. Comparison of Example 3 with Examples 4 to 7, 10, and 11 confirmed that the selectivity was even better when the buffer layer further contained at least one element selected from the group consisting of Cr, Hf, Ta, W, Os, and Re. Comparison of Examples 4 and 8 with Examples 5 to 7 confirmed that the selectivity was even better when the ratio of the Cr content in the buffer layer to the Ru content in the buffer layer was 0.50 to 4.00. The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2024-000164, filed on January 4, 2024, are incorporated herein by reference as part of the disclosure of the present invention.

[0083] REFERENCE SIGNS LIST 10 reflective mask blank 12 substrate 14 multilayer reflective film 16 protective film 18 buffer layer 20 phase shift film 18pt buffer layer pattern 20pt phase shift film pattern 22 conductive film 24 etching mask film 24pt etching mask film pattern 40, 42 resist pattern

Claims

1. A reflective mask blank having, in this order, a substrate, a multilayer reflective film that reflects EUV light, a protective film, a buffer layer, and a phase shift film, wherein the buffer layer contains ruthenium, and the phase shift film contains at least one element selected from the group consisting of iridium and platinum.

2. The reflective mask blank according to claim 1, wherein the content of iridium in the phase shift film is 30 to 100 atomic % with respect to all the atoms of the phase shift film.

3. The reflective mask blank according to claim 1, wherein the content of platinum in the phase shift film is 30 to 100 atomic % with respect to all the atoms of the phase shift film.

4. The reflective mask blank according to any one of claims 1 to 3, wherein the phase shift film further contains at least one element selected from the group consisting of boron, carbon, nitrogen, oxygen, and silicon.

5. The reflective mask blank according to any one of claims 1 to 3, wherein the phase shift film contains at least one element selected from the group consisting of silicon, chromium, niobium, molybdenum, tantalum, tungsten, and rhenium.

6. The reflective mask blank according to claim 1, wherein the content of ruthenium in the buffer layer is 5 to 100 atomic % with respect to all the atoms of the buffer layer.

7. The reflective mask blank according to claim 6, wherein the content of ruthenium in the buffer layer is 50 to 100 atomic % with respect to all the atoms of the buffer layer.

8. The reflective mask blank according to any one of claims 1 to 3, 6, and 7, wherein the buffer layer further contains at least one element selected from the group consisting of chromium, hafnium, tantalum, tungsten, rhenium, and osmium.

9. The reflective mask blank according to claim 8, wherein the buffer layer further contains at least one element selected from the group consisting of chromium and tantalum.

10. The reflective mask blank according to claim 8, wherein the ratio of the content of chromium in the buffer layer to the content of ruthenium in the buffer layer with respect to all the atoms of the buffer layer is 0.10 to 9.

00.

11. The reflective mask blank according to claim 8, wherein in the buffer layer, the ratio of the content of chromium to the content of ruthenium with respect to all atoms of the buffer layer is 0.50 to 4.00 with respect to all atoms of the buffer layer.

12. The reflective mask blank according to any one of claims 1 to 3, 6, and 7, wherein the buffer layer further contains at least one element X1 selected from the group consisting of boron, carbon, nitrogen, oxygen, and silicon.

13. The reflective mask blank according to claim 12, wherein the content of the element X1 in the buffer layer is 1 to 20 atomic% with respect to all atoms of the buffer layer.

14. The reflective mask blank according to any one of claims 1 to 3, 6, and 7, wherein the protective film contains rhodium.

15. A reflective mask having a phase shift film pattern formed by patterning the phase shift film of the reflective mask blank according to any one of claims 1 to 3, 6, and 7.

16. A method for manufacturing a reflective mask for EUV lithography, comprising a step of patterning the phase shift film of the reflective mask blank according to any one of claims 1 to 3, 6, and 7.

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