Reflective mask blank and method for manufacturing reflective mask

Abstract

Provided is a reflective mask blank in which, when being etched by using an etching gas containing a fluorine-based gas and an oxygen-based gas, the ratio of the etching rate for an absorber film with respect to the etching rate for a hard mask film is high.　This reflective mask blank has a substrate (12), a multilayer reflective film (14) that reflects EUV light, an absorber film (18), and a hard mask film (20) in the stated order. The absorber film (18) contains a first element selected from the group consisting of ruthenium, tungsten, and tantalum. The hard mask film (20) contains a second element selected from the group consisting of tantalum, aluminum, and ruthenium, and a third element selected from the group consisting of nitrogen, oxygen, boron, and carbon. The ratio of the content of the third element in the hard mask film (20) with respect to the content of the first element in the absorber film (18) is 0.02-0.80.

Description

Reflective mask blank, method for manufacturing a reflective mask

[0001] The present invention relates to a reflective mask blank and a method for manufacturing a reflective mask.

[0002] In recent years, in order to further miniaturize semiconductor devices, EUV (Extreme Ultra Violet) lithography, which uses EUV light with a central wavelength of about 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] As a reflective mask blank having such an absorber film, for example, Patent Document 1 discloses a reflective mask blank that satisfies specific requirements.

[0006] International Publication No. 2023 / 026868

[0007] The present inventors have studied the reflective mask blank described in Patent Document 1 and have found that when the absorber film of the reflective mask blank is etched using an etching gas containing a fluorine-based gas and an oxygen-based gas, the ratio of the etching rate of the absorber film to the etching rate of the hard mask film (etching rate of absorber film / etching rate of hard mask film) is small, and there is room for improvement.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a reflective mask blank in which, when etched using an etching gas containing a fluorine-based gas and an oxygen-based gas, the ratio of the etching rate of the absorber film to the etching rate of the hard mask film is large. Another object of the present invention is to provide a method for manufacturing a reflective mask.

[0009] The present inventors have found that the above problems can be solved by the following configuration.

[0010] [1] A reflective mask blank having, in this order, a substrate, a multilayer reflective film that reflects EUV light, an absorber film, and a hard mask film, wherein the absorber film contains a first element selected from the group consisting of ruthenium and tungsten and tantalum, the hard mask film contains a second element selected from the group consisting of tantalum, aluminum, and ruthenium, and a third element selected from the group consisting of nitrogen, oxygen, boron, and carbon, and the ratio of the content of the third element in the hard mask film to the content of the first element in the absorber film is 0.02 to 0.80. [2] The reflective mask blank according to [1], wherein the third element is nitrogen. [3] The reflective mask blank according to [1] or [2], wherein the content of the first element in the absorber film is 50 to 80 atomic % with respect to all atoms in the absorber film. [4] The reflective mask blank according to any one of [1] to [3], wherein the hard mask film has a thickness of 2.0 to 40.0 nm. [5] The reflective mask blank according to any one of [1] to [4], wherein the ratio of the content of the third element in the hard mask film to the content of the first element in the absorber film is 0.02 to 0.70. [6] The reflective mask blank according to any one of [1] to [5], wherein the second element is selected from the group consisting of tantalum and ruthenium. [7] The reflective mask blank according to any one of [1] to [6], wherein the second element is tantalum, and the content of the third element in the hard mask film is 15 to 35 atomic % relative to all atoms in the hard mask film. [8] The reflective mask blank according to any one of [1] to [6], wherein the second element is aluminum, and the content of the third element in the hard mask film is 40 to 55 atomic % relative to all atoms in the hard mask film.[9] The reflective mask blank according to any one of [1] to [6], wherein the second element is ruthenium, the content of ruthenium in the absorber film is 27 atomic % or more relative to all atoms in the absorber film, and the content of the third element in the hard mask film is 1 to 10 atomic % relative to all atoms in the hard mask film.

[10] The reflective mask blank according to any one of [1] to [9], further comprising a protective film between the absorber film and the multilayer reflective film, the protective film containing at least one element selected from the group consisting of silicon, ruthenium, and rhodium.

[11] The reflective mask blank according to

[10] , wherein the protective film contains rhodium, and the content of rhodium in the protective film is 50 atomic % or more relative to all atoms in the protective film.

[12] The reflective mask blank according to

[10] or

[11] , further comprising a second absorber film between the protective film and the absorber film, wherein the second absorber film contains ruthenium and at least one element selected from the group consisting of nitrogen, oxygen, boron, and carbon.

[13] A method for manufacturing a reflective mask, comprising the steps of: patterning the hard mask film of the reflective mask blank according to any one of [1] to

[12] ; and patterning the absorber film with an etching gas containing a fluorine-based gas and an oxygen-based gas, using the patterned hard mask film as a mask, to manufacture a reflective mask.

[0011] According to the present invention, a reflective mask blank can be provided in which, when etched using an etching gas containing a fluorine-based gas and an oxygen-based gas, the ratio of the etching rate of the absorber film to the etching rate of the hard mask film is large. Also, according to the present invention, a method for manufacturing a reflective mask can be provided.

[0012] 1 is a schematic diagram showing an example of an embodiment of a reflective mask blank of the present invention. FIG. 2 is a schematic diagram showing an example of a manufacturing process of a reflective mask using the reflective mask blank of the present invention.

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

[0014] The meaning of each description in this specification is shown below. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In this specification, elements such as boron, carbon, nitrogen, oxygen, aluminum, 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, Al, Si, Ti, Cr, Zr, Nb, Mo, Ru, Rh, Pd, Ta, Re, Ir, and Pt, etc.).

[0015] <Reflective Mask Blank> The reflective mask blank of the present invention (hereinafter also simply referred to as "reflective mask blank") is a reflective mask blank having, in this order, a substrate, a multilayer reflective film that reflects EUV light (hereinafter also simply referred to as "multilayer reflective film"), an absorber film, and a hard mask film, wherein the absorber film contains Ru and a first element selected from the group consisting of W and Ta, the hard mask film contains a second element selected from the group consisting of Ta, Al and Ru, and a third element selected from the group consisting of N, O, B and C, and the ratio of the content of the third element in the hard mask film to the content of the first element in the absorber film (content of the third element in the hard mask film / content of the first element in the absorber film; hereinafter also referred to as "specific ratio") is 0.02 to 0.80.

[0016] The mechanism by which the ratio of the etching rate of the absorber film to the etching rate of the hard mask film (hereinafter also referred to as "selectivity") increases when a reflective mask blank is etched using an etching gas containing a fluorine-based gas and an oxygen-based gas is not entirely clear, but the present inventors speculate as follows. One of the characteristics of a reflective mask blank is that the absorber film and the hard mask film in the reflective mask blank each contain specific elements, and the specific ratio in the reflective mask blank is 0.02 to 0.80. In particular, when the absorber film and the hard mask film each contain specific elements and the specific ratio is within a predetermined range, it is speculated that the selectivity increases. For example, when the specific ratio exceeds 0.80, the etching rate of the hard mask film tends to increase, or the etching rate of the absorber film tends to decrease, resulting in a small selectivity. Furthermore, when the specific ratio is less than 0.20, there is a problem that the etching rate of the hard mask film tends to increase, and a sufficient selectivity may not be obtained.

[0017] The reflective mask blank of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a reflective mask blank. The reflective mask blank 10 shown in FIG. 1 has a substrate 12, a multilayer reflective film 14, a protective film 16, an absorber film 18, and a hard mask film 20, in this order. Although the reflective mask blank 10 has the protective film 16, the reflective mask blank does not necessarily have to have a protective film. Although not shown in FIG. 1, the reflective mask blank 10 may have a back surface conductive film, which will be described later, on the side of the substrate 12 opposite to the hard mask film side. The reflective mask blank 10 may also have an intermediate film, which will be described later, between the protective film 16 and the multilayer reflective film 14.

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

[0019] [Specific Ratio] The specific ratio in the reflective mask blank is 0.02 to 0.80, preferably 0.02 to 0.70. The specific ratio is the ratio of the content of the third element in the hard mask film to the content of the first element in the absorber film.

[0020] Regarding the specific ratio, the content of the first element in the absorber film is the content (atomic %) of the first element relative to all atoms in the absorber film, and the content of the first element in the absorber film is preferably 30 to 80 atomic %, more preferably 50 to 80 atomic %, relative to all atoms in the absorber film.

[0021] Regarding the specific ratio, the content of the third element in the hard mask film is the content (atomic %) of the third element relative to all atoms in the hard mask film, and the content of the third element in the hard mask film is preferably 1 to 60 atomic % and more preferably 1 to 50 atomic % relative to all atoms in the hard mask film.

[0022] The type and content of the first and third elements are measured by the same method as the method for measuring the content of elements contained in the absorber film, which will be described later.

[0023] [Substrate] The substrate of the reflective mask blank 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 −1.0×10 at 20° C. －７ ~1.0 x 10 －７ / °C is preferred, and -0.3 × 10 －７ ~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 such as crystallized glass in which β-quartz solid solution is precipitated, quartz glass, metallic silicon, and metal can also be used. ２ -TiO ２ The SiO-based glass ２ 90 to 95 mass% of TiO ２ It is preferable to use quartz glass containing 5 to 10 mass % of TiO ２When the content of SiO is 5 to 10 mass %, the linear expansion coefficient is approximately zero at around room temperature, and there is almost no change in dimension at around room temperature. ２ -TiO ２ The SiO-based glass ２ and TiO ２ It may contain other minor components.

[0024] 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 substrate preferably has a flatness of 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 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 in order to prevent deformation due to film stress of films (e.g., multilayer reflective films and absorber films) formed on the substrate. For example, the Young's modulus of the substrate is preferably 65 GPa or more.

[0025] [Multilayer reflective film] The multilayer reflective film of the reflective mask blank 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.

[0026] The multilayer reflective film is 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, in order to achieve a high reflectivity 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 at least one element 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, and Si / Ru / Mo / Ru multilayer reflective films can also be used.

[0027] The thickness of each layer constituting the multilayer reflective film and the number of repeating units of the layer can be appropriately selected depending on the film material used and the reflectivity of the reflective layer required for EUV light. Taking a Mo / Si multilayer reflective film as an example, to obtain a multilayer reflective film with a maximum reflectivity of 60% or more for EUV light, it is sufficient to laminate Mo films with a thickness of 2.2 to 2.4 nm and Si films with a thickness of 4.4 to 4.6 nm so that the number of repeating units is 30 to 60.

[0028] Each layer constituting the multilayer reflective film can be deposited to a desired thickness using known deposition methods such as magnetron sputtering and ion beam sputtering. For example, when a multilayer reflective film is fabricated 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 ion beam sputtering. Then, a Mo layer of a predetermined thickness is deposited using a Mo target. This Si layer and Mo layer constitute one cycle, and 30 to 60 cycles are stacked to form a Mo / Si multilayer reflective film.

[0029] [Intermediate film] The reflective mask blank may have an intermediate film between the multilayer reflective film and the protective film. The intermediate film is a layer separate from the protective film and is made of a material having a different composition from the protective film. The material constituting the intermediate film is preferably a material containing at least one element selected from the group consisting of Ru, Rh, Pd, Ir, and Pt, more preferably a material containing at least one element selected from the group consisting of Ru and Rh, and even more preferably a material containing Ru.

[0030] The interlayer film may consist solely of at least one element selected from the group consisting of Ru, Rh, Pd, Ir, and Pt, or may contain other elements. Examples of other elements include at least one element selected from the group consisting of Si, Ti, Cr, Zr, Nb, Mo, Pd, and Ta, as well as B, C, N, and O. When the interlayer film contains at least one element selected from the group consisting of Ru, Rh, Pd, Ir, and Pt, the total content of Ru, Rh, Pd, Ir, and Pt is preferably more than 50 atomic %, more preferably 60 atomic % or more, even more preferably 80 atomic % or more, and particularly preferably 90 atomic % or more, based on the total atoms of the interlayer film. The upper limit is preferably 100 atomic % or less.

[0031] The thickness of the interlayer is preferably 0.3 to 10.0 nm, more preferably 0.5 to 5.0 nm, even more preferably 0.5 to 2.5 nm, and particularly preferably 0.5 to 1.5 nm. It is also preferable to adjust the total thickness of the interlayer and protective layers so that it falls within the above-mentioned preferred range of the protective layer thickness.

[0032] The type and content of elements contained in the intermediate film, as well as the thickness of the intermediate film, are measured by the same method as for the absorber film.

[0033] [Protective Film] The reflective mask blank preferably further comprises a protective film between the absorber film and the reflective multilayer film. The protective film serves to protect the reflective multilayer film from damage during etching (usually a dry etching process) when a pattern is formed on the absorber film. It is also preferable that the protective film protects the reflective multilayer film during removal of the hard mask film.

[0034] The protective film is not particularly limited, but preferably contains at least one element X selected from the group consisting of Si, Ru, and Rh, and more preferably contains at least Rh. The protective film may also contain other elements. Examples of other elements include at least one element selected from the group consisting of B, C, N, O, Ti, Zr, Nb, Mo, and Ta. The content of element X (preferably Rh) in the protective film is preferably 50 atomic % or more, more preferably 70 atomic % or more, and even more preferably 90 atomic % or more, based on the total atoms in the protective film. The upper limit may be 100 atomic % or less, 99 atomic % or less, or 97 atomic % or less.

[0035] The type and content of elements contained in the protective film can be obtained by the same method as the method for obtaining the type and content of elements contained in the absorber film, which will be described later.

[0036] More specifically, examples of the material for the protective film include Ru metal alone; Ru alloys containing Ru and at least one element selected from the group consisting of Si, Y, Ti, Zr, Nb, Mo, Rh, Pd, Ta, and Ir; Rh metal alone; and Rh alloys containing Rh and at least one element 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 k while suppressing an increase in the refractive index, making it easy to improve the reflectance for EUV light. Adding Ta, Ir, Pd, or Y to Rh can make it easy to improve resistance to etching processes. Materials that can achieve the above objective include Al metal alone, nitrides containing Al and N, 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.

[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 0.5 to 10.0 nm, more preferably 1.0 to 5.0 nm, even more preferably 1.0 to 3.0 nm, and particularly preferably 1.0 to 2.5 nm. The thickness of the protective film is measured, for example, by the method for measuring the thickness of an absorber film described below.

[0038] The density of the protective film is 10.0 to 14.0 g / cm ３ The density of the protective film is preferably 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 When the density is equal to or less than this, it is easy to suppress a decrease in reflectance for EUV light. The density of the protective film is measured, for example, by the XRR method, which is a method for measuring the thickness of an absorber film, which will be described later.

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

[0040] [Absorber Film] The absorber film of the reflective mask blank is required to have a high contrast between the EUV light reflected by the multilayer reflective film and the EUV light in the absorber film when the absorber film is patterned.

[0041] The absorber film contains Ru and a first element. In other words, the absorber film contains Ru and a first element selected from the group consisting of W and Ta. W is preferable as the first element. Furthermore, the absorber film preferably contains only Ru and W, or only Ru and Ta. Furthermore, it is also preferable that the absorber film does not contain any element contained in the hard mask film described below.

[0042] The Ru content in the absorber film is preferably 10 atomic % or more, more preferably 15 atomic % or more, even more preferably 20 atomic % or more, and particularly preferably 25 atomic % or more, relative to all atoms in the absorber film. The upper limit is preferably 50 atomic % or less, more preferably 40 atomic % or less, and even more preferably 35 atomic % or less. The W content in the absorber film is preferably 30 atomic % or more, more preferably 40 atomic % or more, even more preferably 50 atomic % or more, and particularly preferably 65 atomic % or more, relative to all atoms in the absorber film. The upper limit is preferably 80 atomic % or less, and more preferably 75 atomic % or less. The Ta content in the absorber film is preferably 30 atomic % or more, more preferably 40 atomic % or more, and even more preferably 50 atomic % or more, relative to all atoms in the absorber film. The upper limit is preferably 80 atomic % or less, more preferably 75 atomic % or less, and even more preferably 65 atomic % or less. The total content of Ru, W, and Ta in the absorber film is preferably 95 to 100 atomic %, more preferably 99 to 100 atomic %, and even more preferably 99.9 to 100 atomic %, based on all atoms in the absorber film.

[0043] The reflective mask blank may have multiple types of absorber films. For example, when the reflective mask blank further has a protective film between the absorber film and the multilayer reflective film, the reflective mask blank may further have a second absorber film between the protective film and the absorber film. That is, the reflective mask blank may have a substrate, a multilayer reflective film, a protective film, a second absorber film, an absorber film, and a hard mask film in this order. Preferred embodiments of the absorber film are as described above. Moreover, unlike the absorber film, the second absorber film may or may not contain Ru. Moreover, it may or may not contain the first element. The second absorber film preferably contains Ru and at least one element Y selected from the group consisting of N, O, B, and C, more preferably contains Ru and N, and even more preferably contains only Ru and N.

[0044] The content of Ru in the second absorber film is preferably 10 atomic % or more, more preferably 15 atomic % or more, even more preferably 50 atomic % or more, particularly preferably 80 atomic % or more, and most preferably 90 atomic % or more, relative to all atoms in the second absorber film. The upper limit is preferably 99.9 atomic % or less, more preferably 99.5 atomic % or less, even more preferably 99 atomic % or less, particularly preferably 98 atomic % or less, and most preferably 97 atomic % or less. The content of the element Y (preferably N) in the second absorber film is preferably 0 to 20.0 atomic %, more preferably 0.1 to 15.0 atomic %, even more preferably 0.1 to 10.0 atomic %, particularly preferably 0.1 to 5.0 atomic %, and even more preferably 0.1 to 3.0 atomic % relative to all atoms in the second absorber film. The total content of Ru and the element Y (preferably N) in the second absorber film is preferably 95 to 100 atomic %, more preferably 99 to 100 atomic %, and even more preferably 99.9 to 100 atomic %, relative to all atoms in the second absorber film.

[0045] In this specification, the content of elements contained in the absorber film (or second absorber film) is determined by analysis using X-ray photoelectron spectroscopy (XPS). For the XPS analysis, an analytical instrument "PHI 5000 VersaProbe" manufactured by ULVAC-PHI, Inc. is used. The instrument 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 absorber film side faces the measurement surface. After the measurement holder is loaded into the instrument, if another layer is disposed on the side of the absorber film opposite the substrate side, the other layer is removed with an Ar ion beam to expose the absorber film. After exposing the absorber film, the phase shift film is removed from the outermost surface of the absorber film by a thickness equal to half the thickness of the absorber film. The sputtering rate during the removal can be measured using a separately prepared sample. After removing the outermost surface of the absorber film, 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°. During the analysis, a neutralization gun is used to suppress charge buildup. The analysis involves a wide scan in the binding energy range of 0 to 1000 eV to confirm the elements present, followed by a narrow scan depending on the elements present (e.g., Ru, W, and N). 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 five 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 two accumulations. The content of each element in the absorber film is analyzed using the relative sensitivity coefficient specific to each element and each orbital from the spectrum obtained by narrow scanning when XPS analysis is performed according to the above procedure. Note that analysis may also be performed according to the same procedure as above using a model sample formed under the same conditions as those for forming the absorber film.

[0046] The thickness of the absorber film (or second absorber film) is preferably 2.0 nm or more, more preferably 10.0 nm or more, even more preferably 20.0 nm or more, and particularly preferably 30.0 nm or more. In terms of reducing the shadowing effect, the thickness of the absorber film is preferably 60.0 nm or less, more preferably 55.0 nm or less, and even more preferably 50.0 nm or less. The thickness of the absorber film can be measured by X-ray reflectometry (XRR). For XRR measurement, a Smart Lab HTP from Rigaku Corporation is used. CuKα rays are used as the X-ray source, with a tube voltage of 40 kV and a tube current of 30 mA. The accompanying software (GlobalFit) is used for analysis.

[0047] The absorber film (or the second absorber film) is preferably a phase shift film. The absorber film pattern (patterned absorber film) 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.

[0048] The crystalline state of the absorber film (or the second absorber film) is preferably amorphous. This can provide excellent SPM resistance. Furthermore, the smoothness and flatness of the absorber film can also be improved. Higher smoothness and flatness of the absorber film reduces the edge roughness of the absorber film pattern, allowing for higher dimensional accuracy of the absorber film pattern.

[0049] The absorber film (or the second absorber film) can be formed using a known film formation method such as magnetron sputtering, ion beam sputtering, etc. For example, when a RuW film is formed as the absorber film using magnetron sputtering, the absorber film can be formed by sputtering using a Ru target and a W target.

[0050] [Hard Mask Film] The hard mask film of the reflective mask blank contains a second element and a third element. In other words, the hard mask film contains a second element selected from the group consisting of Ta, Al, and Ru, and a third element selected from the group consisting of N, O, B, and C. When a hard mask film is formed on an absorber film, dry etching can be performed even if the minimum line width of the absorber film pattern is small. Therefore, this is effective for miniaturizing the absorber film pattern.

[0051] The second element is preferably an element selected from the group consisting of Ta and Ru. The third element is preferably N. The hard mask film may contain elements other than the second element and the third element. Examples of such elements include Cr, Hf, O, B, C, and Y. The hard mask film preferably contains only the second element and the third element, and more preferably contains only Ta and N, only Al and N, or only Ru and N.

[0052] The content of the second element in the hard mask film is preferably 30 to 99 atomic %, more preferably 50 to 99 atomic %, based on all atoms in the hard mask film. The total content of the second element and the third element in the hard mask film is preferably 95 to 100 atomic %, more preferably 99 to 100 atomic %, and even more preferably 99.9 to 100 atomic %, based on all atoms in the hard mask film.

[0053] In terms of achieving a larger selectivity, the hard mask film is preferably one of the following modes 1 to 3. Mode 1: The second element is tantalum, and the content of the third element in the hard mask film is 15 to 35 atomic % relative to all atoms in the hard mask film. Mode 2: The second element is aluminum, and the content of the third element in the hard mask film is 40 to 55 atomic % relative to all atoms in the hard mask film. Mode 3: The second element is ruthenium, and the content of ruthenium in the absorber film is 27 atomic % or more relative to all atoms in the absorber film (the upper limit is preferably 50 atomic % or less), and the content of the third element in the hard mask film is 1 to 10 atomic % relative to all atoms in the hard mask film.

[0054] The thickness of the hard mask film is preferably 2.0 nm or more. The thickness of the hard mask film is preferably 40.0 nm or less, more preferably 35.0 nm or less, even more preferably 30.0 nm or less, particularly preferably 25.0 nm or less, and most preferably 10.0 nm or less. The thickness of the hard mask film is also preferably 2.0 to 40.0 nm. The thickness of the hard mask film is measured, for example, by a method for measuring the thickness of an absorber film.

[0055] The hard mask film can be formed by using a known film formation method such as DC sputtering, magnetron sputtering, or ion beam sputtering.

[0056] [Back Surface Conductive Film] The reflective mask blank 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 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. The constituent material of the back surface conductive film may also be a Cr compound containing Cr and at least one element selected from the group consisting of B, N, O, and C, or a Ta compound containing Ta and at least one element selected from the group consisting of B, N, O, and C.

[0057] The thickness of the back surface conductive film is preferably 10 to 1000 nm, more preferably 10 to 400 nm. The thickness of the back surface conductive film is measured, for example, by the method for measuring the thickness of the absorber film described above.

[0058] The back surface conductive film may also have a function of adjusting stress on the second main surface side of the reflective mask blank, i.e., the back surface conductive film can adjust the reflective mask blank to be flat by balancing with stresses from various films formed on the first main surface side.

[0059] The back surface conductive film can be formed by 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.

[0060] <Method for manufacturing a reflective mask blank> The method for forming each film of a reflective mask blank is as described above. A reflective mask blank can be manufactured by sequentially forming each of the above films on a substrate. Specifically, a method for manufacturing a reflective mask blank includes a method for forming a multilayer reflective film on a substrate, forming an absorber film on the multilayer reflective film, and forming a hard mask film on the absorber film. The method for manufacturing a reflective mask blank may also include a film manufacturing procedure other than the above. For example, after forming a multilayer reflective film, an intermediate film may be formed on the multilayer reflective film, and a protective film may be further formed on the intermediate film. Here, when forming a multilayer reflective film, an intermediate film is formed on the multilayer reflective film, and a protective film is formed on the intermediate film, it is preferable to perform the formation continuously without exposure to the atmosphere from the start of formation of the intermediate film to the end of formation of the protective film. It is also preferable to perform the formation continuously without exposure to the atmosphere from the start of formation of the multilayer reflective film to the end of formation of the protective film.

[0061] <Method for manufacturing a reflective mask> The method for manufacturing a reflective mask of the present invention is not particularly limited as long as it uses the reflective mask blank of the present invention. In particular, the method for manufacturing a reflective mask preferably includes the steps of patterning a hard mask film of a reflective mask blank and, using the patterned hard mask film as a mask, patterning an absorber film with an etching gas containing a fluorine-based gas and an oxygen-based gas to manufacture a reflective mask. Furthermore, the method for manufacturing a reflective mask more preferably includes the step of patterning the absorber film and then removing the patterned hard mask film to manufacture a reflective mask. Hereinafter, the above manufacturing method will be described with reference to FIG. 2. As mentioned above, the reflective mask blank does not necessarily have a protective film.

[0062] FIG. 2A shows a state in which a resist pattern 40 is formed on a reflective mask blank having a substrate 12, a multilayer reflective film 14, a protective film 16, an absorber film 18, and a hard mask film 20 in this order. The resist pattern 40 can be formed by a known method, for example, by applying a resist to the hard mask film 20 of the reflective mask blank, and then exposing and developing the resist pattern 40. The resist pattern 40 corresponds to a pattern formed on a wafer using a reflective mask. The hard mask film 20 is then etched using the resist pattern 40 in FIG. 2A as a mask, and the hard mask film 20 is patterned into a shape corresponding to the resist pattern 40. The resist pattern 40 is then removed to obtain the stacked structure shown in FIG. 2B. The hard mask film 20 can be etched by a known method, such as dry etching using an etching gas. The first etching gas used to etch the hard mask film 20 is not particularly limited, but examples thereof include a gas containing a chlorine-based gas. The chlorine-based gas may include Cl. ２ Gas, SiCl ４ Gas, CHCl ３ Gas, CCl ４ Gas and BCl ３ The first etching gas preferably contains at least one selected from the group consisting of chlorine-based gases, and may contain an active gas or an inert gas in addition to the chlorine-based gas. Examples of the active gas include O ２ Examples of inert gases include N ２ The first etching gas preferably contains a chlorine-based gas, more preferably a chlorine-based gas and an oxygen-based gas, and the second etching gas preferably contains at least one selected from the group consisting of a chlorine-based gas, a He gas, and an Ar gas. ２ Gas and O ２ It is more preferable that the chlorine-based gas contains Cl ２It is preferable that the first etching gas contains a gas. It is preferable that the first etching gas is plasmatized. The resist pattern 40 can be removed by a known method, for example, by using a cleaning liquid. Examples of cleaning liquids include sulfuric acid-hydrogen peroxide solution (SPM), sulfuric acid, ammonia water, ammonia-hydrogen peroxide solution (APM), OH radical cleaning water, and ozone water.

[0063] Next, the absorber film 18 is etched and patterned using the patterned hard mask film 20 shown in Fig. 2(b) as a mask to obtain a laminate having an absorber film pattern 18pt shown in Fig. 2(c). In the laminate shown in Fig. 2(c), the protective film 16 is exposed. The second etching gas used to etch the absorber film 18 is not particularly limited, but examples thereof include gases containing fluorine-based gases. Fluorine-based gases include CF ４ Gas, CHF ３ Gas, C ２ F ６ Gas, C ３ F ６ Gas, C ４ F ６ Gas, C ４ F ８ Gas, CH ２ F ２ Gas, CH ３ F gas, C ３ F ８ Gas, BF ３ Gas, XeF ２ Gas, F ２ Gas, SF ６ Gas and NF ３ The second etching gas may contain at least one selected from the group consisting of fluorine-based gas, active gas, and inert gas. ２ Examples of inert gases include N ２ The second etching gas preferably contains a fluorine-based gas, more preferably a fluorine-based gas and an oxygen-based gas, and more preferably contains CF. ４ Gas and O ２It is more preferable that the second etching gas contains a fluorine-based gas. The content of the fluorine-based gas is preferably 2 to 15% by volume, more preferably 2 to 7% by volume, based on the total volume of the second etching gas. Specifically, the etching may be performed under the etching conditions shown in the Examples section.

[0064] Next, the hard mask film 20 is removed from the stacked body shown in Fig. 2(c) to obtain the stacked body shown in Fig. 2(d). The method for removing the hard mask film 20 can be the same as the method for etching the hard mask film 20 described above.

[0065] Next, as shown in Fig. 2(e), a resist pattern 41 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 41 of Fig. 2(e) as a mask. Dry etching is performed until it reaches the substrate 12. After dry etching, the resist pattern 41 is removed to obtain the reflective mask shown in Fig. 2(f).

[0066] A reflective mask obtained by patterning the absorber film of a reflective mask blank can be suitably used as a reflective mask for exposure with EUV light.

[0067] The present invention will be described in more detail below based on examples. The materials, amounts used, ratios, treatment details, and treatment procedures 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 1 to 11 are examples, and Examples 12 to 16 are comparative examples.

[0068] Example 1 First, the procedure for obtaining the reflective mask blank of Example 1 will be described as a representative example.

[0069] [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 × 107 m ２ / s２ The quality assurance area of ​​the first main surface of the substrate was polished to a root mean square (RMS) roughness 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 / sq.

[0070] [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).

[0071] [Protective Film] On the multilayer reflective film formed by the above procedure, a Rh film (thickness: 2.5 nm) was formed as a protective film by ion beam sputtering.

[0072] [Absorber Film] A RuW film (thickness: 40.0 nm) was formed as an absorber film on the protective film formed by the above procedure. The RuW film was formed by reactive sputtering under the following conditions: Target: Ru target and W target Sputtering gas: Ar gas Input power density per Ru target area: 2.5 W / cm ２ Input power density per W target area: 7.3 W / cm ２ ・Film formation rate: 0.063nm / sec

[0073] [Hard Mask Film] A hard mask film (thickness: 30.0 nm) was formed on the absorber film formed by the above procedure by magnetron sputtering. The hard mask film was a TaN film, and the film formation conditions for the TaN film were as follows: Target: Ta target Sputtering gas: Ar and N ２ A mixed gas (Ar: 90% by volume, N ２ : 10% by volume) Input power density per Ta target area: 6.2 W / cm ２ Film formation rate: 0.0436nm / sec

[0074] By the above procedure, the reflective mask blank of Example 1 was obtained.

[0075] Examples 2 to 16 Reflective mask blanks were obtained in the same manner as in Example 1, except that the film formation conditions for the absorber film and the hard mask film were adjusted so as to have the compositions shown in the table below.

[0076] <Evaluation Method and Evaluation Criteria> [Composition and Thickness of Each Layer] The chemical compositions of the absorber film and the hard mask film were measured by the above-mentioned XPS using an X-ray photoelectron spectrometer (PHI 5000 VersaProbe) manufactured by ULVAC-PHI, Inc. The thickness of each film was measured by the above-mentioned XRR.

[0077] [Etching Rate (Selectivity)] For the reflective mask blanks of each example produced by the above procedure, measurement sample 1 was prepared in which only the respective absorber film was formed on a substrate, and measurement sample 2 was prepared in which only the respective hard mask film was formed on a substrate, and the etching rates of measurement sample 1 and measurement sample 2 were measured. Specifically, for the etching rate measurement samples 1 and 2, plasma was generated using an inductively coupled plasma (ICP) generator, and etching was performed by irradiating the plasma, and the etching rates of measurement samples 1 and 2 were measured. The etching conditions were as follows: Antenna RF power output: 1200 W Bias RF power output: 50 W Etching gas pressure: 0.4 Pa Etching gas flow rate: CF ４ Gas (3 sccm), O ２ Gas (57 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. ３ The thicknesses of measurement sample 1 and measurement sample 2 before and after etching under the above conditions were measured by XRR, and the amount of change in thickness was divided by the etching time to calculate the etching rate (unit: nm / min).

[0078] <Results> The configuration of each reflective mask blank, each measurement result, and evaluation result are shown in the table. "At%" means atomic % relative to all atoms in the absorber film or hard mask film. "Specific ratio (third / first)" indicates the ratio of the content (atomic %) of the third element in the hard mask film to the content (atomic %) of the first element in the absorber film. "Selectivity" indicates the ratio of the etching rate of the absorber film to the etching rate of the hard mask film measured at the above-mentioned etching rate.

[0079]

[0080] From the results shown in Table 1, it was confirmed that, with the reflective mask blank of the present invention, when the absorber film was etched using an etching gas containing a fluorine-based gas and an oxygen-based gas, the ratio of the etching rate of the absorber film to the etching rate of the hard mask film was large (Examples 1 to 11). Furthermore, it was confirmed that the ratio of the etching rate of the absorber film to the etching rate of the hard mask film was larger when the hard mask film was in the following Examples 1 to 3. Example 1: The second element was tantalum, and the content of the third element in the hard mask film was 15 to 35 atomic % relative to all atoms in the hard mask film (Examples 1, 2, 4, and 8). Example 2: The second element was aluminum, and the content of the third element in the hard mask film was 40 to 55 atomic % relative to all atoms in the hard mask film (Examples 7 and 11). Aspect 3: The second element is ruthenium, the content of ruthenium in the absorber film is 27 atomic % or more relative to all atoms in the absorber film, and the content of the third element in the hard mask film is 1 to 10 atomic % relative to all atoms in the hard mask film (Examples 6 and 9). The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2024-108744, filed on July 5, 2024, are incorporated herein by reference.

[0081] REFERENCE SIGNS LIST 10 Reflective mask blank 12 Substrate 14 Multilayer reflective film 16 Protective film 18 Absorber film 18pt Absorber film pattern 20 Hard mask film 40, 41 Resist pattern

Claims

A substrate; a multilayer reflective film that reflects EUV light; an absorber film; A reflective mask blank having, in this order, a hard mask film, the absorber film comprises ruthenium and a first element selected from the group consisting of tungsten and tantalum; the hard mask film includes a second element selected from the group consisting of tantalum, aluminum, and ruthenium, and a third element selected from the group consisting of nitrogen, oxygen, boron, and carbon; a ratio of the content of the third element in the hard mask film to the content of the first element in the absorber film is 0.02 to 0.

80. The reflective mask blank according to claim 1 , wherein the third element is nitrogen.

2. The reflective mask blank according to claim 1, wherein the content of said first element in said absorber film is 50 to 80 atomic % with respect to all atoms in said absorber film.

2. The reflective mask blank according to claim 1, wherein the hard mask film has a thickness of 2.0 to 40.0 nm.

2. The reflective mask blank according to claim 1, wherein a ratio of the content of said third element in said hard mask film to the content of said first element in said absorber film is 0.02 to 0.

70.

2. The reflective mask blank according to claim 1, wherein the second element is selected from the group consisting of tantalum and ruthenium. 　 the second element is tantalum, and 2. The reflective mask blank according to claim 1, wherein the content of said third element in said hard mask film is 15 to 35 atomic % based on all atoms in said hard mask film. 　 the second element is aluminum, and 2. The reflective mask blank according to claim 1, wherein the content of said third element in said hard mask film is 40 to 55 atomic % based on all atoms in said hard mask film. 　 the second element is ruthenium, The content of ruthenium in the absorber film is 27 atomic % or more with respect to all atoms in the absorber film, and 2. The reflective mask blank according to claim 1, wherein the content of said third element in said hard mask film is 1 to 10 atomic % based on all atoms in said hard mask film. 　 a protective film between the absorber film and the multilayer reflective film; 2. The reflective mask blank according to claim 1, wherein the protective film contains at least one element selected from the group consisting of silicon, ruthenium, and rhodium. 　 the protective film contains rhodium, 11. The reflective mask blank according to claim 10, wherein the rhodium content in the protective film is 50 atomic % or more based on all atoms in the protective film. 　 a second absorber film between the protective film and the absorber film; 11. The reflective mask blank according to claim 10, wherein the second absorber film contains ruthenium and at least one element selected from the group consisting of nitrogen, oxygen, boron, and carbon. 　 A step of patterning the hard mask film of the reflective mask blank according to any one of claims 1 to 12; and patterning the absorber film using the patterned hard mask film as a mask with an etching gas containing a fluorine-based gas and an oxygen-based gas, thereby manufacturing a reflective mask.

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