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

Abstract

The present invention provides a reflective mask blank enabling production of a reflective mask with excellent reflectivity.　A reflective mask blank comprising a substrate, a multilayer reflective film that reflects EUV light, an intermediate film, a protective film, and an absorber film in the stated order, wherein the intermediate film contains silicon atoms and oxygen atoms, and the atomic ratio of the oxygen atom content to the silicon atom content is less than 0.070.

Description

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

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

[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. In addition, a protective film is often provided between the multilayer reflective film and the absorber film to protect the multilayer reflective film during patterning of the absorber 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] An example of a reflective mask blank that is a master plate for obtaining such a reflective mask is the reflective mask blank described in Patent Document 1. More specifically, Patent Document 1 discloses that the reflective mask blank has an intermediate film between a protective layer and a multilayer reflective film, and that the intermediate film contains silicon atoms and nitrogen atoms.

[0006] International Publication No. 2023 / 199888

[0007] In the reflective mask blank described in Patent Document 1, examples are disclosed in which the atomic weight ratio of the oxygen atom content to the silicon atom content in the intermediate film is changed. Here, a reflective mask obtained by processing the reflective mask blank is required to exhibit high reflectivity for EUV light at the opening of the absorber film. When the present inventors studied the reflective mask blank described in Patent Document 1, they found that the reflectivity for EUV light was insufficient and needed to be improved.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a reflective mask blank from which a reflective mask having excellent reflectance can be obtained. Another object of the present invention is to provide a method for manufacturing a reflective mask blank. Another object of the present invention is to provide a reflective mask and a method for manufacturing a reflective mask.

[0009] As a result of intensive research into the above-mentioned problems, the inventors of the present invention discovered that a reflective mask blank has an intermediate film between a multilayer reflective film and a protective film, and that adjusting the content of oxygen atoms relative to the content of silicon atoms in the intermediate film is important for improving reflectivity, leading to the completion of the present invention.

[0010] That is, the inventors have found that the above problems can be solved by the following configurations. [1] A reflective mask blank having, in this order, a substrate, a multilayer reflective film that reflects EUV light, an intermediate film, a protective film, and an absorber film, wherein the intermediate film contains silicon atoms and oxygen atoms, and the atomic weight ratio of the content of the oxygen atoms to the content of the silicon atoms is less than 0.070. [2] The reflective mask blank according to [1], wherein the protective film contains at least one element selected from the group consisting of ruthenium, rhodium, and silicon. [3] The reflective mask blank according to [1], wherein the protective film is a multilayer film having a lower layer and an upper layer, and the upper layer contains rhodium. [4] The reflective mask blank according to [2] or [3], wherein the protective film contains rhodium and one or more elements selected from the group consisting of boron, carbon, nitrogen, oxygen, silicon, titanium, zirconium, niobium, molybdenum, palladium, ruthenium, tantalum, and iridium. [5] The reflective mask blank according to any one of [1] to [4], wherein the intermediate film further contains nitrogen atoms, and the atomic weight ratio of the content of the nitrogen atoms to the content of the silicon atoms is 0.170 to 0.250. [6] The reflective mask blank according to any one of [1] to [5], wherein the film thickness of the intermediate film is 0.2 to 5.0 nm. [7] The reflective mask blank according to any one of [1] to [6], wherein the film thickness of the protective film is 1.0 to 10.0 nm. [8] The reflective mask blank according to any one of [1] to [7], wherein the root mean square roughness of the surface of the protective film opposite to the substrate side is 0.34 nm or less. [9] A method for manufacturing a reflective mask blank according to any one of [1] to [8], comprising the steps of forming the multilayer reflective film on the substrate, forming the intermediate film on the multilayer reflective film, forming the protective film on the intermediate film, and forming the absorber film on the protective film.

[10] The method for manufacturing a reflective mask blank according to [9], wherein the multilayer reflective film is formed by a sputtering method, the intermediate film is formed without exposing the formed multilayer reflective film to the atmosphere, and the protective film is formed by a sputtering method without exposing the formed intermediate film to the atmosphere.

[11] A reflective mask having an absorber film pattern formed by patterning the absorber film of the reflective mask blank according to any one of [1] to [8].

[12] A method for manufacturing a reflective mask, comprising the step of patterning the absorber film of the reflective mask blank according to any one of [1] to [8].

[0011] According to the present invention, a reflective mask blank from which a reflective mask excellent in reflectance can be obtained can be provided. Further, according to the present invention, a method for manufacturing a reflective mask blank can be provided. Further, according to the present invention, a reflective mask and a method for manufacturing a reflective mask can be provided.

[0012] 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.

[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 following represents the meaning of each description in this specification. In this specification, a numerical range expressed using "to" means a range including the lower limit and upper limit of the numerical values ​​written before and after "to". In this specification, elements such as hydrogen, boron, carbon, nitrogen, oxygen, silicon, titanium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tantalum, and iridium may be represented by the corresponding element symbol (H, B, C, N, O, Si, Ti, Zr, Nb, Mo, Ru, Rh, Pd, Ta, Ir, etc.).

[0015] <Reflective mask blank> The reflective mask blank of the present invention has a substrate, a multilayer reflective film that reflects EUV light, an intermediate film, a protective film, and an absorber film, in this order. In the reflective mask blank of the present invention, the intermediate film contains silicon (Si) atoms and oxygen (O) atoms, and the atomic weight ratio of the content of O atoms to the content of Si atoms is less than 0.070. The reflective mask blank of the present invention will be described with reference to the drawings.

[0016] Fig. 1 is a cross-sectional view showing one example of an embodiment of the reflective mask blank of the present invention. The reflective mask blank 10 shown in Fig. 1 has, in this order, a substrate 11, a multilayer reflective film 12, an intermediate film 13, a protective film 14, and an absorber film 15. As shown in Fig. 1, the reflective mask blank 10 may also have a back surface conductive film 16 on the surface of the substrate 11 opposite to the multilayer reflective film 12 side. The intermediate film 13 contains Si atoms and O atoms, and the atomic weight ratio of the O atom content to the Si atom content is less than 0.070.

[0017] Although the mechanism by which a reflective mask with excellent reflectance is obtained by using the reflective mask blank of the present invention is not entirely clear, the inventors speculate as follows. A reflective mask is obtained by processing a reflective mask blank. In a reflective mask, the portions exhibiting high reflectance are openings in the absorber film, and it is believed that the multilayer reflective film must have excellent reflectance. Here, the reflective mask blank of the present invention has an intermediate film, and the atomic weight ratio of the content of O atoms to Si atoms in the intermediate film is less than 0.070. It is believed that when such an intermediate film is present, absorption of EUV light in the intermediate film is reduced, and a multilayer reflective film with high reflectance can be obtained. As a result, it is believed that a reflective mask obtained by processing the reflective mask blank of the present invention has excellent reflectance.

[0018] The configuration of the reflective mask blank of the present invention will be described below. Note that, hereinafter, the fact that a reflective mask having excellent reflectance can be obtained from the reflective mask blank will also be simply referred to as "having excellent reflectance."

[0019] [Substrate] The substrate of the reflective mask blank of the present invention preferably has a small thermal expansion coefficient. A substrate with a small thermal expansion coefficient can suppress distortion of the 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 ２ However, the present invention is not limited to this, and substrates made of crystallized glass in which β-quartz solid solution is precipitated, quartz glass, metallic silicon, metal, and the like can also be used. ２ -TiO ２ The SiO-based glass ２ 90 to 95 mass% of TiO ２ It is preferable to use quartz glass containing 5 to 10 mass % of TiO ２ When the content of SiO is 5 to 10 mass %, the linear expansion coefficient is approximately zero at around room temperature, and there is almost no change in dimension at around room temperature. ２ -TiO ２ The SiO-based glass ２ and TiO ２ It may contain other minor components.

[0020] The surface of the substrate on which the multilayer reflective film is laminated (hereinafter also referred to as the "first principal surface") preferably has high surface smoothness. The surface smoothness of the first principal surface can be evaluated by surface roughness. The surface roughness of the first principal surface is preferably 0.15 nm or less in terms of root-mean-square roughness Rq. The surface roughness can be measured using an atomic force microscope and is described as the root-mean-square roughness Rq based on JIS B 0601. 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. The flatness of the substrate in a predetermined region of the first principal surface (e.g., a 132 mm × 132 mm region) is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less. The flatness can be measured using a flatness measuring instrument manufactured by Fujinon Corporation. The size and thickness of the substrate are appropriately determined 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.

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

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

[0023] The thickness of each layer constituting the multilayer reflective film and the number of 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.

[0024] 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.

[0025] [Interlayer Film] The reflective mask blank of the present invention has an intermediate film between the multilayer reflective film and the absorber film. The intermediate film of the reflective mask blank of the present invention contains Si atoms and O atoms, and the atomic weight ratio of the O atom content to the Si atom content is less than 0.070. Hereinafter, the "atomic weight ratio of the O atom content to the Si atom content" will also be referred to as "O / Si." The lower limit of O / Si is more than 0.000, preferably 0.010 or more, and more preferably 0.020 or more. The upper limit of O / Si is less than 0.070, preferably 0.060 or less, and more preferably 0.055 or less. By adjusting the O / Si ratio in the intermediate film to fall within the above range, a reflective mask with excellent reflectivity can be obtained, and adjusting the O / Si ratio to fall within the above range tends to reduce the occurrence of blisters. Blisters refer to a phenomenon in which a protective film lifts up and peels off at the interface with the multilayer reflective film. When a reflective mask obtained by processing a reflective mask blank is used for EUV exposure, hydrogen gas may be introduced into the exposure atmosphere. However, when hydrogen gas is introduced, the above-mentioned blisters are likely to occur.

[0026] The interlayer film may contain atoms other than Si atoms and O atoms. For example, the interlayer film may further contain N atoms. The atomic weight ratio of the N atom content to the Si atom content (hereinafter also referred to as "N / Si") is preferably 0.150 or more, more preferably 0.170 or more, and even more preferably 0.180 or more. N / Si is preferably 0.300 or less, more preferably 0.250 or less, and even more preferably 0.220 or less.

[0027] The thickness of the intermediate film is preferably 0.2 to 5.0 nm, more preferably 0.2 to 2.6 nm. The thickness of the intermediate film is determined by measuring the photoelectron intensity of each element while sputtering the outermost surface of the reflective mask blank with Ar ions using an X-ray photoelectron spectroscopy (XPS) device. Specifically, the thickness of the intermediate film is defined as the section from the interface between the intermediate film and the multilayer reflective film to the interface between the intermediate film and the protective film, and the film thickness is calculated from the sputtering time and sputtering rate in that section. The interface position between the intermediate film and the multilayer reflective film is determined as follows: The peak intensities of N1s and O1s are determined in each element profile in the thickness direction of the reflective mask blank obtained by XPS analysis. In the profile, the point where the intensity of either the N1s or O1s peak intensity of the element with the higher intensity begins to exceed half the peak intensity as viewed from the multilayer reflective film side is defined as the interface position between the intermediate film and the multilayer reflective film. The interface position between the intermediate film and the protective film is determined as follows. In the element profile in the thickness direction of the reflective mask blank obtained by XPS analysis, the peak intensity of the element contained in the protective film (for example, Ru3d ５／２ or Rh3d ５／２ The point on the profile where the intensity of the element contained in the protective film starts to become greater than half the peak intensity as viewed from the protective film side is determined to be the interface position between the intermediate film and the protective film.

[0028] In this specification, O / Si is determined by measuring the photoelectron intensity of each element while sputtering the outermost surface of the reflective mask blank with Ar ions using an XPS apparatus. Specifically, first, a section from the interface between the intermediate film and the multilayer reflective film to the interface between the intermediate film and the protective film is determined using the above procedure. Next, O / Si is calculated from the Si2p intensity at the depth position where the O1s intensity is maximum within the above section and the O1s intensity. Furthermore, when the intermediate film contains N atoms, N / Si is determined by measuring the photoelectron intensity of each element while sputtering the outermost surface of the reflective mask blank with Ar ions using an XPS apparatus. Specifically, first, a section from the interface between the intermediate film and the multilayer reflective film to the interface between the intermediate film and the protective film is determined using the above procedure. Next, N / Si is calculated from the Si2p intensity at the depth position where the N1s intensity is maximum within the above section and the N1s intensity.

[0029] The O atom content in the interlayer film is preferably 0.10 atomic % or more, more preferably 1.00 atomic % or more, and even more preferably 1.50 atomic % or more, based on the total atoms in the interlayer film. The O atom content in the interlayer film is preferably less than 7.00 atomic %, more preferably 6.00 atomic % or less, and even more preferably 5.00 atomic % or less, based on the total atoms in the interlayer film. The O atom content in the interlayer film is measured using the same method as for determining O / Si, and is determined from the intensity of each element at the depth position where the O1s intensity is maximum.

[0030] When the interlayer film contains N atoms, the content of N atoms in the interlayer film is preferably 3.00 atomic % or more, more preferably 5.00 atomic % or more, and even more preferably 10.00 atomic % or more, based on the total atoms in the interlayer film. Furthermore, the content of N atoms in the interlayer film is preferably 30.00 atomic % or less, more preferably 25.00 atomic % or less, and even more preferably 20.00 atomic % or less, based on the total atoms in the interlayer film. The content of N atoms in the interlayer film is measured using the same method as for determining N / Si above, and is determined from the intensity of each element at the depth position where the N1s intensity is maximum.

[0031] The Si atom content of the interlayer film is preferably 50.00 atomic % or more, more preferably 70.00 atomic % or more, and even more preferably 80.00 atomic % or more, based on the total atoms in the interlayer film. The Si atom content of the interlayer film is preferably 99.90 atomic % or less, more preferably 95.00 atomic % or less, and even more preferably 90.00 atomic % or less, based on the total atoms in the interlayer film. The Si atom content of the interlayer film is measured using the same method as for determining O / Si described above, and is determined from the intensity of each element at the depth position where the O1s intensity is maximum.

[0032] The interlayer film may contain elements other than Si, O, and N. Examples of the other elements include B, C, and elements that may be contained in the protective film described below. When the interlayer film contains other elements, the total content of the other elements, measured by the method for determining the O content described above, is preferably more than 0 atomic % and not more than 70 atomic %, and more preferably more than 0 atomic % and not more than 60 atomic %, relative to all atoms in the interlayer film.

[0033] The crystalline state of the interlayer film may be crystalline or amorphous, and is preferably amorphous.

[0034] The interlayer can be formed to a desired thickness using known film-forming methods such as magnetron sputtering and ion beam sputtering. For example, when forming the interlayer using ion beam sputtering, ion particles are supplied from an ion source to a Si target, and the film-forming atmosphere contains oxygen gas and nitrogen gas. Furthermore, the ratio of each element contained in the interlayer can be adjusted by changing the amount and ratio of gases contained in the film-forming atmosphere. Another method for forming the interlayer can be a method in which a Si layer is formed as the top layer of the multilayer reflective film, and then the surface of the Si layer is oxidized and nitrided to form the interlayer. An example of a method for oxidizing and nitriding is a method in which a plasma containing O and N (e.g., a high-frequency plasma) is irradiated. The following conditions are preferred for the method of irradiating the plasma containing O and N: Frequency of the high-frequency plasma device: 1.8 MHz Input power of the high-frequency plasma device: 300 to 1000 W Plasma irradiation atmosphere gas species: Ar gas and N ２ Mixture of Ar gas with N gas (Ar gas) ２ Gas volume ratio: 1.5 to 4.5) Vacuum degree of plasma irradiation atmosphere: 8.0 x 10 －３ Pa ~ 8.0 x 10 －２ Pa Nitrogen partial pressure in plasma irradiation atmosphere: 5.2 × 10 －３ ~3.0 x 10 －２ Pa Irradiation time: 100 to 1000 seconds (more preferably, 200 to 800 seconds) Exposure amount: 5.0 × 10 －１ ~4.8 x 10 １ Pa·s By adjusting the conditions for irradiating the plasma, the ratio of each element contained in the intermediate film can be adjusted.

[0035] After forming the multilayer reflective film, an intermediate film may be formed on the multilayer reflective film without exposing the formed multilayer reflective film to the atmosphere. Specifically, for example, the formation of the multilayer reflective film and the formation of the intermediate film may be carried out in the same film-forming chamber. Furthermore, after forming the multilayer reflective film, it is preferable to form the intermediate film without forming any other film or performing any surface treatment on the surface of the multilayer reflective film, such as surface treatment.

[0036] [Protective Film] The reflective mask blank of the present invention has a protective film between the multilayer reflective film and the absorber film. The protective film is provided for the purpose of protecting the multilayer reflective film from damage during an etching process (usually a dry etching process) to form a pattern on the absorber film. Examples of materials that can achieve the above purpose 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.

[0037] More specifically, the materials include Ru metal alone, Ru-containing materials containing Ru and one or more elements selected from the group consisting of B, C, N, O, Si, Ti, Zr, Nb, Mo, Rh, Y, Pd, Ta, and Ir, and Rh metal alone, Rh-containing materials containing Rh and one or more elements selected from the group consisting of B, C, N, O, Si, Ti, Zr, Nb, Mo, Ru, Y, Pd, Ta, and Ir. Ru-containing materials also include materials containing Y, and Rh-containing materials also include materials containing Y. Adding Ru, Nb, Mo, Zr, or Ti to Rh can reduce the extinction coefficient while suppressing an increase in the refractive index, thereby improving the reflectance to EUV light. Adding Ta, Ir, Pd, or Y to Rh can also improve resistance to etching processes. Furthermore, materials that can achieve the above object include Al nitrides containing Al and nitrogen, and Al ２ O ３ Among these, metal Ru alone, a material containing Ru, metal Rh alone, or a material containing Rh is preferred as a material that can achieve the above-mentioned object.

[0038] When the protective film contains Ru or Rh, it is also preferable that the protective film contains at least one element selected from the group consisting of B, C, N, and O. Addition of the above elements tends to reduce the crystallinity of the protective film and improve the smoothness of the surface of the protective film opposite the substrate. A protective film having 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. Note that 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.

[0039] 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 10.0 nm or less, more preferably 6.0 nm or less, even more preferably 5.0 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 1.0 nm or more, more preferably 1.5 nm or more, and even more preferably 2.0 nm or more. The thickness of the protective film is determined by X-ray reflectivity.

[0040] 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 selected from the group consisting of the above-mentioned preferred materials. It is also preferable that the total thickness of the multilayer film is within the above-mentioned preferred range. An example of an embodiment in which the protective film is a multilayer film is an embodiment in which the protective film is a multilayer film having a lower layer and an upper layer. The above-mentioned upper layer preferably contains Rh.

[0041] 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.

[0042] The surface roughness of the protective film, i.e., the surface roughness of the surface of the protective film opposite the substrate, is preferably 0.340 nm or less, more preferably 0.200 nm or less, and even more preferably 0.125 nm or less. The surface roughness is often 0.010 nm or more. When the surface roughness is within the above range, it is easy to form a smooth absorber film or the like on the protective film. Furthermore, scattering of EUV light can be suppressed, and the reflectance for EUV light is easily improved. The surface roughness can be measured using an atomic force microscope. The surface roughness is explained as the root-mean-square roughness Rq based on JIS B 0601.

[0043] 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.

[0044] After forming the interlayer film, a protective film may be formed on the interlayer film without exposing the formed interlayer film to the atmosphere. Specifically, for example, the formation of the interlayer film and the formation of the interlayer film may be performed in the same film-forming chamber. It is also preferable to form the protective film after forming the interlayer film without performing any treatment on the surface of the multilayer reflective film, such as forming another film or performing a surface treatment. It is particularly preferable to form the multilayer reflective film by a sputtering method, form the interlayer film without exposing the formed multilayer reflective film to the atmosphere, and then form the protective film by a sputtering method without exposing the formed interlayer film to the atmosphere.

[0045] [Absorber Film] The absorber film of the reflective mask blank of the present invention is required to have a high contrast between the EUV light reflected by the multilayer reflective film and the EUV light at the absorber film when the absorber film is patterned. The patterned absorber film (absorber film pattern) may function as a binary mask by absorbing EUV light, or may function as a phase shift mask that reflects EUV light and interferes with the EUV light from the multilayer reflective film to generate contrast.

[0046] When the absorber film pattern is used as a binary mask, the absorber film must absorb EUV light and have low reflectance for EUV light. Specifically, when EUV light is irradiated onto the surface of the absorber film, the maximum reflectance of EUV light at a wavelength of approximately 13.5 nm is preferably 2% or less. The absorber film may contain one or more metals selected from the group consisting of Ta, Ti, Sn, and Cr, as well as one or more components selected from the group consisting of O, N, B, Hf, and H. Among these, N or B is preferred. By including N or B, the crystalline state of the absorber film can be made amorphous or microcrystalline. The crystalline state of the absorber film is preferably amorphous. This improves the smoothness and flatness of the absorber film. Furthermore, improving the smoothness and flatness of the absorber film reduces the edge roughness of the absorber film pattern, thereby improving the dimensional accuracy of the absorber film pattern.

[0047] When the absorber film pattern is used as a phase shift mask, the reflectance of the absorber film to EUV light is preferably 2% or more. To obtain a sufficient phase shift effect, the reflectance of the absorber film is preferably 9 to 15%. Using the absorber film as a phase shift mask improves the contrast of the optical image on the wafer and increases the exposure margin. Examples of materials that can be used to form a phase shift mask include simple Ru metal, Ru alloys containing Ru and one or more metals selected from the group consisting of Cr, Au, Pt, Re, Hf, Ti, and Si, Ta and Nb alloys, oxides containing a Ru alloy or a TaNb alloy and oxygen, nitrides containing a Ru alloy or a TaNb alloy and nitrogen, and oxynitrides containing a Ru alloy or a TaNb alloy and oxygen and nitrogen.

[0048] The absorber film may be a single-layer film or a multilayer film made up of multiple films. When the absorber film is a single-layer film, the number of steps in manufacturing the mask blank can be reduced, thereby improving production efficiency. When the absorber film is a multilayer film, the layer disposed on the opposite side of the absorber film from the protective film side may be an anti-reflection film used when inspecting the absorber film pattern using inspection light (for example, wavelength 193 to 248 nm).

[0049] The absorber film can be formed by a known film formation method such as magnetron sputtering, ion beam sputtering, etc. For example, when a Ru oxide film is formed as the absorber film by magnetron sputtering, the absorber film can be formed by sputtering using a Ru target and supplying a gas containing Ar gas and oxygen gas.

[0050] The absorber film may be formed on the entire surface of the protective film, or the protective film may not be formed on a part of the protective film, so that the protective film is partially exposed.

[0051] [Back Surface Conductive Film] The reflective mask blank of the present invention may have a back surface conductive film on the surface (second main surface) opposite to the first main surface of the substrate. Providing a back surface conductive film enables the reflective mask blank to be handled using an electrostatic chuck. The back surface conductive film preferably has a low sheet resistance. The sheet resistance of the back surface conductive film is preferably, for example, 200 Ω / □ or less, more preferably 100 Ω / □ or less. The constituent material of the back surface conductive film can be selected from a wide range of materials described in known literature. For example, a high-dielectric-constant coating described in JP-A-2003-501823, specifically a coating made of Si, Mo, Cr, CrON, or TaSi, can be applied. Furthermore, the constituent material of the back surface conductive film may be a Cr compound containing Cr and one or more elements selected from the group consisting of B, N, O, and C, or a Ta compound containing Ta and one or more elements selected from the group consisting of B, N, O, and C. The thickness of the back surface conductive film is preferably 10 to 1,000 nm, more preferably 10 to 400 nm. The back surface conductive film may also have a function of adjusting stress on the second main surface side of the reflective mask blank. That is, the back surface conductive film can be adjusted to balance the stress from various films formed on the first main surface side and flatten the reflective mask blank. The back surface conductive film can be formed using a known film formation method, for example, a sputtering method such as magnetron sputtering or ion beam sputtering, a CVD method, a vacuum deposition method, or an electrolytic plating method.

[0052] [Other Films] The reflective mask blank of the present invention may have other films. Examples of the other films include a hard mask film. The hard mask film is preferably disposed on the side of the absorber film opposite to the protective film side. As the hard mask film, a material having high resistance to dry etching, such as a Cr-based film or a Si-based film, is preferably used. Examples of Cr-based films include materials containing Cr and one or more elements selected from the group consisting of O, N, C, and H. Specific examples include CrO and CrN. Examples of Si-based films include materials containing Si and one or more elements selected from the group consisting of O, N, C, and H. Specific examples include SiO ２ , SiON, SiN, SiO, Si, SiC, SiCO, SiCN, and SiCON. When a hard mask film is formed on the absorber film, dry etching can be performed even if the minimum line width of the absorber film pattern is small. Therefore, it is effective for miniaturizing the absorber film pattern.

[0053] <Method for manufacturing a reflective mask and a reflective mask> A reflective mask is obtained by patterning an absorber film of a reflective mask blank. An example of a method for manufacturing a reflective mask will be described with reference to FIG. 2. FIG. 2(a) shows a state in which a resist pattern 20 is formed on a reflective mask blank having, in this order, a backside conductive film 16, a substrate 11, a multilayer reflective film 12, an intermediate film 13, a protective film 14, and an absorber film 15. A known method can be used to form the resist pattern 20. For example, a resist is applied to the absorber film 15 of the reflective mask blank, and the resist pattern 20 is formed by exposure and development. The resist pattern 20 corresponds to a pattern formed on a wafer using a reflective mask. Then, using the resist pattern 20 of FIG. 2(a) as a mask, the absorber film 15 is etched and patterned, and the resist pattern 20 is removed to obtain a laminate having an absorber film pattern 15a shown in FIG. 2(b). Next, as shown in Fig. 2(c), a resist pattern 21 corresponding to the frame of the exposure region is formed on the laminate of Fig. 2(b), and dry etching is performed using the resist pattern 21 of Fig. 2(c) as a mask. Dry etching is performed until it reaches the substrate 11. After dry etching, the resist pattern 21 is removed, and a reflective mask shown in Fig. 2(d) is obtained.

[0054] Examples of dry etching used to form the absorber film pattern 15a include dry etching using a Cl-based gas and dry etching using an F-based gas. The resist pattern 20 or 21 can be removed by a known method, such as removal with a cleaning solution. Examples of cleaning solutions include a sulfuric acid-hydrogen peroxide solution (SPM), sulfuric acid, ammonia water, an ammonia-hydrogen peroxide solution (APM), OH radical cleaning water, and ozone water.

[0055] A reflective mask obtained by patterning the absorber film of the reflective mask blank of the present invention can be suitably used as a reflective mask used for exposure to EUV light. The reflective mask obtained using the reflective mask blank of the present invention has high reflectance and is suitable as a reflective mask.

[0056] 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 1 to 3 described below are examples, and Example 4 is a comparative example.

[0057] <Sample Preparation> Samples for confirming the composition were prepared according to the following procedure. The following describes the preparation procedure for the sample of Example 1 as a representative example. First, a silicon wafer (outer diameter: 4 inches, thickness: 0.5 mm, resistance: 1 to 100 Ω, orientation: (100)) was prepared as a substrate for film formation. Mo layers (2.3 nm) and Si layers (4.5 nm) were alternately deposited on the silicon wafer by ion beam sputtering to form a multilayer reflective film (272 nm). The number of Mo layers and Si layers was 40, and the Si layers were deposited so that the Si layers were the outermost layers. The deposition conditions for the Mo layers and Si layers were as follows. The film thickness of each layer was determined by fitting using the X-ray reflectivity (XRR) method with the film material and film thickness as parameters.

[0058] (Mo deposition conditions) Target: Mo target Sputtering gas: Ar gas (gas partial pressure: 0.02 Pa) Acceleration voltage: 700 V Deposition rate: 0.064 nm / sec (Si layer deposition conditions) Target: Si target (B doped) Sputtering gas: Ar gas (gas partial pressure: 0.02 Pa) Acceleration voltage: 700 V Deposition rate: 0.077 nm / sec

[0059] After forming the Si layer on the top surface of the multilayer reflective film, N ２ The intermediate film was formed in a gas-containing atmosphere. The formation of the intermediate film was carried out continuously in the same film-forming apparatus after the formation of the outermost Si layer. In other words, the intermediate film was formed without exposing the multilayer reflective film to the atmosphere. The formation conditions for the intermediate film were as follows:

[0060] (Conditions for forming intermediate film) Frequency of high frequency plasma device: 1.8 MHz Input power of high frequency plasma device: 500 W Carrier gas: Ar gas (gas partial pressure: 0.009 Pa, gas flow rate: 17 sccm) Exposure gas: N ２ Gas (gas partial pressure: 0.026 Pa, gas flow rate: 50 sccm) Exposure time: 300 seconds The intermediate film was formed by exposing the substrate to an oxygen partial pressure of 10×10 in the load lock chamber of the ion beam sputtering device. －６ After confirming that the pressure reached Pa, the sample after the formation of the multilayer reflective film was carried into a film formation chamber where ion beam sputtering was performed, and an intermediate film was formed. Note that "sccm" represents the flow rate under standard conditions, and is expressed in mL / min at 0°C and atmospheric pressure.

[0061] Immediately after the multilayer reflective film and the intermediate film were formed in the same film-forming chamber, a protective film (thickness: 2.5 nm) made of Ru was formed on the intermediate film by ion beam sputtering. The film-forming conditions for the protective film were as follows: Target: Ru target Sputtering gas: Ar gas (gas partial pressure: 0.02 Pa) Acceleration voltage: 700 V Film-forming rate: 0.052 nm / sec

[0062] For the samples of Examples 2 to 4, the film-forming conditions for the protective film or intermediate film were changed as follows.

[0063] In Example 2, a multilayer reflective film was formed under the same conditions as in Example 1, and then an intermediate film was formed under the same conditions as in Example 1 without exposing the multilayer reflective film to the atmosphere.

[0064] For the sample of Example 2, a protective film (thickness: 1.0 nm) made of Ru was formed as a protective film using an ion beam sputtering method, and then a protective film (thickness: 1.5 nm) made of Rh was further formed. The film formation conditions for the protective film made of Rh were as follows. (Film formation conditions for Ru film (lower layer)) Target: Ru target Sputtering gas: Ar gas Gas pressure: 0.027 Pa Ion acceleration voltage: 600 V Film formation rate: 0.056 nm / sec Film thickness: 1.0 nm (Film formation conditions for Rh film (upper layer)) Target: Rh target Sputtering gas: Ar gas Gas pressure: 0.027 Pa Ion acceleration voltage: 600 V Film formation rate: 0.077 nm / sec Film thickness: 1.5 nm

[0065] In Example 3, a multilayer reflective film was formed under the same conditions as in Example 1, and then an intermediate film was formed under the following conditions without exposing the multilayer reflective film to the atmosphere: (Interlayer film formation conditions) Frequency of high-frequency plasma device: 1.8 MHz Input power of high-frequency plasma device: 500 W Carrier gas: Ar gas (gas partial pressure: 0.009 Pa, gas flow rate: 17 sccm) Exposure gas: N ２ Gas (gas partial pressure: 0.026 Pa, gas flow rate: 50 sccm) Exposure time: 300 seconds The intermediate film was formed by exposing the substrate to an oxygen partial pressure of 10×10 in the load lock chamber of the ion beam sputtering device. －６ The sample after the formation of the multilayer reflective film was carried into a film formation chamber where ion beam sputtering was performed at a pressure exceeding Pa, and an intermediate film was formed. Note that "sccm" represents the flow rate under standard conditions, and is expressed in mL / min at 0°C and atmospheric pressure.

[0066] In Example 4, a multilayer reflective film was formed under the same conditions as in Example 1, and then an intermediate film was formed under the same conditions as in Example 1 without exposing the multilayer reflective film to the atmosphere. In Example 4, after the intermediate film was formed, it was removed from the film formation apparatus and exposed to the atmosphere. Then, in Example 4, a protective film (thickness 2.5 nm) selected from the group consisting of Ru was formed on the intermediate film by magnetron sputtering. The protective film formation conditions were as follows: Target: Ru target Sputtering gas: Ar gas (gas partial pressure: 0.15 Pa) Acceleration voltage: 180 V Film formation rate: 0.045 nm / sec

[0067] The thicknesses of the intermediate film and protective film in each sample were determined using the methods described in the sections on measuring the thickness of the intermediate film and the protective film. The structure of each sample is shown in the table below.

[0068] <Reflectance Simulation> A reflectance simulation was performed on each sample to determine the reflectance of EUV light. The optical constants of each layer in the EUV wavelength range were cited from a database provided by CXRO (The Center for X-Ray Optics). Furthermore, the thickness of each film was determined by XRR analysis for the multilayer reflective film, and by the method described above for the other films. The composition of the intermediate film was determined by determining the content of each element using the method for determining the O content of the intermediate film described above. The simulation results are shown in the table below.

[0069] <Results> The configuration and evaluation results of each sample are shown in the table. In the table, "Measurement method 1" indicates that the content of each element was determined by the method for determining the N content of the interlayer film. In the table, "Measurement method 2" indicates that the content of each element was determined by the method for determining the O content of the interlayer film. In the table, "at%" indicates atomic %. In the table, the "Surface roughness" column indicates the value measured by the above-mentioned method.

[0070]

[0071] In the above procedure, a silicon wafer was used as the substrate, but SiO ２ -TiO ２In addition, if the reflectance of the sample prepared by the above procedure is high, when a reflective mask is obtained by patterning the absorber film of a reflective mask blank obtained by forming an absorber film on the protective film of the above sample, it can be said that the reflective mask has excellent reflectance.

[0072] The results in Table 1 confirm that the samples of Examples 1 and 3, which have interlayer films with an O / Si ratio of less than 0.070, have higher reflectance for EUV light than the sample of Example 4, which has an O / Si ratio of 0.070 or more. The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2024-008680, filed on January 24, 2024, are incorporated herein by reference as part of the disclosure of the present invention.

[0073] REFERENCE SIGNS LIST 10 Reflective mask blank 11 Substrate 12 Multilayer reflective film 13 Intermediate film 14 Protective film 15 Absorber film 15a Absorber film pattern 16 Back surface conductive film 20, 21 Resist pattern

Claims

1. A reflective mask blank having a substrate, a multilayer reflective film that reflects EUV light, an intermediate film, a protective film, and an absorber film in this order, wherein the intermediate film contains silicon atoms and oxygen atoms, and the atomic weight ratio of the content of oxygen atoms to the content of silicon atoms is less than 0.

070.

2. The reflective mask blank according to claim 1, wherein the protective film contains at least one element selected from the group consisting of ruthenium, rhodium, and silicon.

3. The reflective mask blank according to claim 1, wherein the protective film is a multilayer film having a lower layer and an upper layer, and the upper layer contains rhodium.

4. The reflective mask blank according to claim 2 or 3, wherein the protective film contains rhodium and one or more elements selected from the group consisting of boron, carbon, nitrogen, oxygen, silicon, titanium, zirconium, niobium, molybdenum, palladium, ruthenium, tantalum, and iridium.

5. The reflective mask blank according to claim 1 or 2, wherein the intermediate film further contains nitrogen atoms, and the atomic weight ratio of the content of nitrogen atoms to the content of silicon atoms is 0.170 to 0.

250.

6. The reflective mask blank according to claim 1 or 2, wherein the film thickness of the intermediate film is 0.2 to 5.0 nm.

7. The reflective mask blank according to claim 1 or 2, wherein the film thickness of the protective film is 1.0 to 10.0 nm.

8. The reflective mask blank according to claim 1 or 2, wherein the root mean square roughness of the surface of the protective film on the side opposite to the substrate side is 0.340 nm or less.

9. A method for manufacturing the reflective mask blank according to claim 1 or 2, comprising forming the multilayer reflective film on the substrate, forming the intermediate film on the multilayer reflective film, forming the protective film on the intermediate film, and forming the absorber film on the protective film.

10. The method for manufacturing a reflective mask blank according to claim 9, wherein the formation of the multilayer reflective film is carried out by a sputtering method, the intermediate film is formed without exposing the formed multilayer reflective film to the atmosphere, and the formation of the protective film is carried out by a sputtering method without exposing the formed intermediate film to the atmosphere.

11. A reflective mask having an absorber film pattern formed by patterning the absorber film of the reflective mask blank according to claim 1 or 2.

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

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