Reflective mask blank, reflective mask and producing method thereof, as well as producing method of semiconductor device

Abstract

To provide a reflective mask blank capable of preventing occurrence of electrostatic breakdown, while suppressing a CD change in a dry etching process, by reducing an oxygen concentration ratio of an etching mask membrane below a predetermined oxygen concentration.SOLUTION: A reflective mask blank 100 comprises a multilayer reflective film 2, an absorber film 4, and an etching mask film 6 in this order, wherein the absorber film includes a buffer layer 42 and an absorbent layer 44, and the etching mask film contains an element X and oxygen. In the etching mask membrane, when the oxygen concentration ratio obtained by dividing the oxygen content by a total content of element X and oxygen is defined, the oxygen concentration ratio on the absorbent layer side of the etching mask membrane is higher than the oxygen concentration ratio in the thickness center of the etching mask film, and the element X contains at least one selected from tantalum and silicon.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a reflective mask blank, which is an original plate for producing an exposure mask used in the manufacture of a semiconductor device, a reflective mask and a method for producing the same, and a method for producing a semiconductor device. [Background technology]

[0002] The types of light sources of exposure equipment in semiconductor device manufacturing have evolved with gradually shorter wavelengths, from g-line with a wavelength of 436 nm, i-line with a wavelength of 365 nm, KrF laser with a wavelength of 248 nm, and ArF laser with a wavelength of 193 nm. In order to realize finer pattern transfer, EUV lithography using extreme ultraviolet (EUV: Extreme Ultra Violet) with a wavelength of about 13.5 nm has been developed. In EUV lithography, a reflective mask is used because there are few materials transparent to EUV light. In this reflective mask, a multilayer reflective film that reflects exposure light is formed on a low-thermal expansion substrate, and a mask structure in which a desired transfer pattern is formed on a protective film for protecting the multilayer reflective film is used as a basic structure. In addition, in terms of the configuration of the transfer pattern, representative ones include a binary type reflective mask made of a relatively thick absorber pattern that sufficiently absorbs EUV light, and a phase shift type reflective mask (halftone phase shift type reflective mask) made of a relatively thin absorber pattern that attenuates EUV light by optical absorption and generates reflected light that is almost inverted in phase (about 180° phase inversion) with respect to the reflected light from the multilayer reflective film. This phase shift type reflective mask (halftone phase shift type reflective mask) has the effect of improving resolution because it can obtain a high transfer optical image contrast due to the phase shift effect, just like a transmission type optical phase shift mask. In addition, since the film thickness of the absorber pattern (phase shift pattern) of the phase shift type reflective mask is thin, a fine phase shift pattern can be formed with high accuracy.

[0003] A reflective mask blank, which is an original plate for manufacturing a reflective mask, typically has a multilayer reflective film for reflecting exposure light, a protective film for protecting the multilayer reflective film from dry etching or defect correction using an electron beam (EB), an absorber film for forming an absorber pattern, and an etching mask film that serves as a mask for pattern etching the absorber film, on a substrate. In addition, when the etching selectivity between the absorber film that absorbs / attenuates EUV light and the protective film is not sufficiently high, the absorber film mainly has a buffer layer that protects the underlying multilayer reflective film from damage during dry etching during pattern formation.

[0004] Meanwhile, EUV lithography uses a projection optical system consisting of multiple reflecting mirrors due to the light transmittance. In this type of projection optical system, EUV light is made incident on a reflective mask at an angle to prevent these multiple reflecting mirrors from blocking the projection light (exposure light). With the improvement of the numerical aperture (NA) of the projection optical system, the incidence angle of the exposure light is being studied to be larger (for example, 6° or more). However, a projection optical system in which the exposure light is made incident on the mask surface at an angle has a problem of a shadowing effect that reduces the accuracy of the dimensions and position of the pattern that is transferred and formed.

[0005] The shadowing effect is mainly caused by the three-dimensional structure of the absorber pattern. Therefore, the shadowing effect can be reduced by making the absorber film as thin as possible. However, if the absorber film is made thin, it will not be able to absorb the exposure light sufficiently, and undesirable reflected light from the absorber pattern may adversely affect the transfer accuracy, so there is a limit to how thin the absorber film can be.

[0006] In light of this background, for example, Patent Document 1 discloses a reflective mask blank in which an absorber film has a buffer layer and an absorbing layer provided on the buffer layer, the buffer layer is made of a material containing tantalum (Ta) or silicon (Si), and the absorbing layer is made of a material containing chromium (Cr) having a relatively large extinction coefficient for EUV light (for example, wavelength 13.5 nm). It has been confirmed that this configuration makes it possible to realize an absorber pattern with an EUV light reflectance of 2% or less even if the thickness of the absorber film is made thinner than before.

[0007] Furthermore, Patent Document 1 discloses that the etching mask film is made of a material containing tantalum (Ta) or silicon (Si), the same as the buffer layer, so that the etching mask film can be removed at the same time when the buffer layer is patterned.

[0008] For example, fluorine (F)-based gas is used when patterning an etching mask film containing tantalum (Ta). However, when fluorine (F)-based gas is used for dry etching of the etching mask film, the etching rate of the resist film is relatively high, so that it is difficult to finely and precisely pattern the etching mask film using only the resist film. In this regard, for example, Patent Document 2 describes a photomask that includes a hard mask layer as an etching mask film on an absorption layer containing chromium (Cr), and the hard mask layer includes a tantalum (Ta)-based first hard mask layer for patterning the absorption layer and a chromium (Cr)-based second hard mask layer for patterning the first hard mask layer. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2020 / 175354 [Patent Document 2] US Patent Application Publication No. 2021 / 0405519 Summary of the Invention [Problem to be solved by the invention]

[0010] In general, in order to suppress the change in CD (Critical Dimension) during the dry etching process using an etching gas containing oxygen, it is preferable that the etching mask film is an oxide. On the other hand, when the oxygen concentration in a tantalum-based etching mask film is high, the electrical resistivity increases, and excessive charging occurs during the manufacturing process of a reflective mask blank and a reflective mask, resulting in a problem that the frequency of occurrence of fatal defects due to electrostatic breakdown increases.

[0011] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a reflective mask blank which prevents electrostatic breakdown while suppressing CD changes during dry etching by reducing the oxygen concentration ratio at the center of the thickness of an etching mask film compared to the oxygen concentration ratio at least at the bottom of the etching mask film, as well as a reflective mask manufactured from the reflective mask blank, a method for manufacturing a reflective mask, and a method for manufacturing a semiconductor device using a reflective mask. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention has the following configuration.

[0013] (Configuration 1) Configuration 1 of the present invention is a reflective mask blank comprising a multilayer reflective film, an absorber film, and an etching mask film in this order, the absorber film includes a buffer layer and an absorber layer having etching resistance to the buffer layer; the etching mask film has etching resistance to the absorption layer and contains an element X and oxygen (O); Here, when the oxygen concentration ratio is defined as the content (atomic %) of oxygen (O) in the etching mask film divided by the total content (atomic %) of element X and oxygen (O), the oxygen concentration ratio on the absorption layer side of the etching mask film is higher than the oxygen concentration ratio at the thickness center of the etching mask film, The reflective mask blank is one in which the element X includes at least one selected from tantalum (Ta) and silicon (Si).

[0014] (Configuration 2) A second aspect of the present invention is the reflective mask blank according to the first aspect, wherein the oxygen concentration ratio on the surface side of the etching mask film opposite to the absorption layer is higher than the oxygen concentration ratio in the center of the thickness of the etching mask film.

[0015] (Configuration 3) A third aspect of the present invention is the reflective mask blank according to the first or second aspect, wherein the etching mask film has a thickness of 6 nm to 30 nm.

[0016] (Configuration 4) A fourth aspect of the present invention is the reflective mask blank according to any one of the first to third aspects, wherein a ratio of a thickness of the etching mask film to a thickness of the buffer layer is 0.1-15.

[0017] (Configuration 5) A fifth aspect of the present invention is the reflective mask blank according to any one of the first to fourth aspects, further comprising a second etching mask film on the first etching mask film, the second etching mask film containing chromium (Cr).

[0018] (Configuration 6) A sixth aspect of the present invention is the reflective mask blank according to any one of the first to fifth aspects, wherein the buffer layer contains at least one selected from tantalum (Ta) and silicon (Si).

[0019] (Configuration 7) A seventh aspect of the present invention is the reflective mask blank according to any one of the first to sixth aspects, wherein the absorbing layer contains at least one selected from the group consisting of chromium (Cr) and ruthenium (Ru).

[0020] (Configuration 8) An eighth aspect of the present invention is the reflective mask blank according to any one of the first to seventh aspects, further comprising a protective film between the multilayer reflective film and the absorber film.

[0021] (Configuration 9) A ninth aspect of the present invention is a reflective mask having an absorber pattern in which the absorber film in the reflective mask blank of any one of the first to eighth aspects is patterned.

[0022] (Configuration 10) Configuration 10 of the present invention is a method for producing a reflective mask from the reflective mask blank of any of configurations 1 to 8, comprising the steps of dry-etching the etching mask film to form an etching mask film pattern, and patterning the absorber film using the etching mask film pattern as a mask.

[0023] (Configuration 11) An eleventh aspect of the present invention is a method for manufacturing a semiconductor device, comprising the steps of setting the reflective mask according to the ninth aspect in an exposure tool and transferring a transfer pattern to a resist film formed on a transfer substrate. Effect of the Invention

[0024] According to the present invention, a manufacturing method of a reflective mask blank and a reflective mask can be provided, which can prevent the occurrence of fatal defects caused by electrostatic breakdown while suppressing the CD change during the dry etching process by reducing the oxygen concentration ratio at the center of the thickness of the etching mask film compared to the oxygen concentration ratio at least at the bottom of the etching mask film. According to the present invention, the etching mask film has a predetermined oxygen concentration ratio, so that the etching rate of the etching mask film can be adjusted according to the pattern etching of the absorber film. Therefore, a manufacturing method of a reflective mask blank and a reflective mask can be provided, which does not damage the absorber film surface or the protective film that protects the multilayer reflective film during the dry etching process. According to the present invention, a reflective mask having a fine and high-precision absorber pattern in which the CD change during the etching process is suppressed can be provided. According to the present invention, a semiconductor device having a fine and high-precision transfer pattern can be manufactured by using the reflective mask. [Brief description of the drawings]

[0025] [Figure 1] 1 is a schematic cross-sectional view for explaining a general configuration of a reflective mask blank according to one embodiment of the present invention. FIG. [Diagram 2] FIG. 2 is a schematic cross-sectional view for explaining an example of a layer structure of a reflective mask blank. [Diagram 3] FIG. 2 is a schematic cross-sectional view for explaining another example of a layer structure of a reflective mask blank. [Figure 4A] 1A to 1C are schematic cross-sectional views for explaining a process for producing a reflective mask from a reflective mask blank. [Figure 4B] 1A to 1C are further schematic cross-sectional views illustrating the process of producing a reflective mask from a reflective mask blank. [Figure 4C] 1A to 1C are further schematic cross-sectional views illustrating the process of producing a reflective mask from a reflective mask blank. [Figure 4D] 1A to 1C are further schematic cross-sectional views for explaining the process of producing a reflective mask from a reflective mask blank. [Figure 4E] 1A to 1C are further schematic cross-sectional views for explaining the process of producing a reflective mask from a reflective mask blank. [Figure 4F] 1A to 1C are further schematic cross-sectional views for explaining the process of producing a reflective mask from a reflective mask blank. [Figure 4G] 1A to 1C are further schematic cross-sectional views for explaining the process of producing a reflective mask from a reflective mask blank. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the following embodiment is one form for embodying the present invention, and does not limit the scope of the present invention. In addition, in the drawings, the same or corresponding parts are given the same reference numerals, and the description thereof may be simplified or omitted.

[0027] In this specification, "on" a substrate or a film includes not only the case where it is in contact with the upper surface of the substrate or film, but also the case where it is not in contact with the upper surface of the substrate or film. In other words, "on" a substrate or a film includes the case where a new film is formed above the substrate or film, or the case where another film is interposed between the substrate or film. In addition, "on" does not necessarily mean the upper side in the vertical direction, but merely indicates the relative positional relationship in the thickness direction of the substrate or film.

[0028] <Reflective mask blank configuration> 1 is a schematic cross-sectional view for explaining the configuration of a reflective mask blank 100 according to one embodiment of the present invention. As shown in the figure, the reflective mask blank 100 has a substrate 1, a multilayer reflective film 2 formed on a first main surface (front surface) side and reflecting EUV light as exposure light, a protective film 3 provided to protect the multilayer reflective film 2, an absorber film 4 absorbing EUV light, and an etching mask film 6, which are laminated in this order. In the reflective mask blank 100 of this embodiment, the absorber film 4 has a buffer layer 42 and an absorption layer 44 provided on the buffer layer 42. In addition, a back surface conductive film 5 for electrostatic chuck is formed on the second main surface (back surface) side of the substrate 1.

[0029] The reflective mask blank 100 may include a configuration in which no back surface conductive film 5 is formed. The reflective mask blank 100 may also include a configuration of a mask blank with a resist film in which a resist film 11 is formed on an etching mask film 6.

[0030] The structure of each layer of the reflective mask blank 100 according to one embodiment of the present invention will be specifically described below.

[0031] <<Substrate>> In order to prevent distortion of the transfer pattern (the absorber pattern described below) due to heat during exposure to EUV light, the substrate 1 is preferably one having a low thermal expansion coefficient within the range of 0±5 ppb / ° C. Examples of materials having a low thermal expansion coefficient within this range include SiO2-TiO2 glass and multi-component glass ceramics.

[0032] The first main surface of the substrate 1 on which the transfer pattern is formed is surface-processed to have a high flatness in order to obtain at least pattern transfer accuracy and positional accuracy. In the case of EUV exposure, the flatness is preferably 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.03 μm or less in a 132 mm×132 mm area of ​​the main surface of the substrate 1 on which the transfer pattern is formed. The second main surface on the opposite side to the side on which the absorber film 4 is formed is a surface that is electrostatically chucked when set in an exposure device, and the flatness is preferably 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.03 μm or less in a 142 mm×142 mm area.

[0033] Furthermore, the surface roughness (surface smoothness) of the first main surface of the substrate 1 on which the transfer pattern is formed is preferably 0.1 nm or less in terms of root mean square roughness (Rq). The surface roughness can be measured by an atomic force microscope.

[0034] Furthermore, the substrate 1 preferably has high rigidity to prevent deformation due to film stress of the films (such as the multilayer reflective film 2) formed thereon, and in particular, preferably has a high Young's modulus of 65 GPa or more.

[0035] <<Multilayer reflective film>> The multilayer reflective film 2 has a multilayer structure in which a plurality of layers mainly composed of elements with different refractive indexes are laminated periodically. In general, the multilayer reflective film 2 is made of a multilayer film in which thin films (high refractive index layers) of light elements or compounds thereof, which are high refractive index materials, and thin films (low refractive index layers) of heavy elements or compounds thereof, which are low refractive index materials, are alternately laminated for about 40 to 60 periods. To form the multilayer reflective film 2, high refractive index layers and low refractive index layers may be laminated in this order from the substrate 1 side for multiple periods. In this case, one laminate structure (high refractive index layer / low refractive index layer) constitutes one period.

[0036] The top layer of the multilayer reflective film 2, i.e., the surface layer of the multilayer reflective film 2 opposite to the substrate 1, is preferably a high refractive index layer. When a high refractive index layer and a low refractive index layer are laminated in this order from the substrate 1 side, the top layer is a low refractive index layer. However, when a low refractive index layer is the surface of the multilayer reflective film 2, the low refractive index layer is easily oxidized, which reduces the reflectance of the surface of the multilayer reflective film, so it is preferable to form a high refractive index layer on the low refractive index layer. On the other hand, when a low refractive index layer and a high refractive index layer are laminated in this order from the substrate 1 side, the top layer is a high refractive index layer. In that case, the topmost high refractive index layer is the surface of the multilayer reflective film 2.

[0037] The high refractive index layer included in the multilayer reflective film 2 is, for example, a layer made of a material containing silicon (Si). The high refractive index layer may contain simple Si or a Si compound. The Si compound may be a Si compound containing silicon (Si) and boron (B), carbon (C), nitrogen (N), oxygen (O) and hydrogen (H). By using a layer containing Si as the high refractive index layer, a reflective mask 200 for EUV lithography having excellent reflectance of EUV light can be obtained.

[0038] The low refractive index layer included in the multilayer reflective film 2 is a layer made of a material containing a transition metal. The transition metal contained in the low refractive index layer is, for example, a metal element selected from molybdenum (Mo), ruthenium (Ru), rhodium (Rh), and platinum (Pt), or an alloy thereof.

[0039] For example, as the multilayer reflective film 2 for EUV light with a wavelength of 13 to 14 nm, a Mo / Si multilayer film in which Mo films and Si films are alternately laminated in about 40 to 60 periods can be preferably used.

[0040] The reflectance of such a single multilayer reflective film 2 is, for example, 65% or more. The upper limit of the reflectance of the multilayer reflective film 2 is, for example, 73%. The thickness and period of the layers included in the multilayer reflective film 2 can be selected so as to satisfy Bragg's law. The thickness and period of each constituent layer of the multilayer reflective film 2 may be appropriately selected according to the exposure wavelength, and are selected so as to satisfy Bragg's law of reflection. The multilayer reflective film 2 has a plurality of high refractive index layers and a plurality of low refractive index layers, but the thicknesses of the high refractive index layers and the low refractive index layers do not have to be the same. The film thickness of the Si layer on the outermost surface of the multilayer reflective film 2 can be adjusted within a range that does not reduce the reflectance. The film thickness of the Si (high refractive index layer) on the outermost surface can be 3 nm to 10 nm.

[0041] The multilayer reflective film 2 can be formed by ion beam sputtering. For example, when the multilayer reflective film 2 is a Mo / Si multilayer film, a Mo film having a thickness of about 3 nm is formed on the substrate 1 by ion beam sputtering using a Mo target. Next, a Si film having a thickness of about 4 nm is formed using a Si target. By repeating such an operation, the multilayer reflective film 2 can be formed in which 40 to 60 periods of Mo / Si films are laminated. At this time, the surface layer of the multilayer reflective film 2 on the side opposite to the substrate 1 is a layer containing Si (Si film). The thickness of one period of Mo / Si film is 7 nm. In addition, when forming the multilayer reflective film 2, krypton (Kr) ion particles may be supplied from an ion source to perform ion beam sputtering to form the multilayer reflective film 2.

[0042] <<Protective film>> The reflective mask blank 100 preferably has a protective film 3 between the multilayer reflective film 2 and the absorber film 4. By forming the protective film 3 on the multilayer reflective film 2, damage to the surface of the multilayer reflective film 2 can be suppressed when a reflective mask 200 (EUV mask) is manufactured using the reflective mask blank 100, resulting in good reflectance characteristics for EUV light.

[0043] The protective film 3 is formed on the multilayer reflective film 2 to protect the multilayer reflective film 2 from dry etching and cleaning in the manufacturing process of the reflective mask 200, which will be described later. It also serves to protect the multilayer reflective film 2 when repairing black defects in the absorber pattern 4a using an electron beam (EB). The protective film 3 is made of a material that is resistant to etchants, cleaning solutions, and the like.

[0044] Here, while FIG. 1 shows the protective film 3 as a single layer, it may have a laminated structure of two or more layers.

[0045] For example, the protective film 3 can be made of a material containing Ru as a main component. That is, the material of the protective film 3 can be Ru metal alone, Rh metal alone, Ru alloys containing at least one metal selected from Ru, titanium (Ti), niobium (Nb), rhodium (Rh), molybdenum (Mo), zirconium (Zr), yttrium (Y), boron (B), lanthanum (La), cobalt (Co), rhenium (Re), and the like, and materials containing nitrogen (N) in these alloys.

[0046] Such a protective film 3 is particularly effective when the buffer layer 42 of the absorber film 4 is patterned by dry etching using an oxygen-free fluorine-based gas (F-based gas) or chlorine-based gas (Cl-based gas). The protective film 3 is preferably formed of a material that provides an etching selectivity ratio of the buffer layer 42 to the protective film 3 (etching rate of the buffer layer 42 / etching rate of the protective film 3) of 1.5 or more, preferably 3 or more, in dry etching using a fluorine-based gas or a chlorine-based gas.

[0047] The thickness of the protective film 3 is not particularly limited as long as it can function as the protective film 3. From the viewpoint of reflectance of EUV light, the thickness of the protective film 3 is preferably 1.0 nm to 8.0 nm, and more preferably 1.5 nm to 6.0 nm.

[0048] Examples of the method for forming the protective film 3 include ion beam sputtering, magnetron sputtering, reactive sputtering, chemical vapor deposition (CVD), and vacuum deposition. The protective film 3 may be formed by ion beam sputtering continuously after the formation of the multilayer reflective film 2.

[0049] <<Absorber film>> An absorber film 4 for absorbing or extinguishing EUV light is formed on the above-mentioned multilayer reflective film 2 or protective film 3. For example, in a reflective mask blank 100 for producing a binary type reflective mask, the thickness of the absorber film 4 is preferably as thin as possible in order to obtain a fine and highly accurate absorber pattern (transfer pattern). Therefore, the material of the absorber film 4 is preferably one having a high absorptivity (low reflectivity) for EUV light. Also, in a reflective mask blank 100 for producing a phase-shifting reflective mask, the absorber film 4 is preferably formed of a material having a high absorptivity in order to invert the phase of the EUV reflected light with a relatively thin absorber pattern.

[0050] Furthermore, in the reflective mask blank 100 according to this embodiment, the absorber film 4 has a buffer layer 42 and an absorber layer 44 provided on the buffer layer 42 (the side opposite to the substrate 1).

[0051] In the absorber film 4 of this embodiment, the material of the absorber layer 44 can be a material that has the function of absorbing EUV light, can be processed by etching or the like (preferably can be etched by dry etching with a chlorine (Cl)-based gas and / or a fluorine (F)-based gas), and has a high etching selectivity with respect to the protective film 3 and the etching mask film 6 described below. As a material having such a function, at least one metal selected from palladium (Pd), silver (Ag), platinum (Pt), gold (Au), iridium (Ir), tungsten (W), chromium (Cr), cobalt (Co), manganese (Mn), tin (Sn), tantalum (Ta), vanadium (V), nickel (Ni), hafnium (Hf), iron (Fe), copper (Cu), tellurium (Te), zinc (Zn), magnesium (Mg), germanium (Ge), aluminum (Al), rhodium (Rh), ruthenium (Ru), molybdenum (Mo), niobium (Nb), titanium (Ti), zirconium (Zr), yttrium (Y) and silicon (Si), an alloy containing two or more metals, or a compound thereof can be preferably used. The compound may contain oxygen (O), nitrogen (N), carbon (C) and / or boron (B) in said metal or alloy. The material of the absorption layer 44 preferably contains, for example, chromium (Cr) and / or ruthenium (Ru). When a thin film containing Cr or Ru is disposed in contact with the surface of the protective film 3 containing Ru as a main component, a problem occurs in that the etching selectivity between the absorption layer 44 and the protective film 3 is not high. For this reason, in the reflective mask blank 100 according to the present embodiment, a buffer layer 42 made of a material containing at least one selected from tantalum (Ta) and silicon (Si) is disposed between the absorption layer 44 and the protective film 3.

[0052] In one embodiment, the material of the buffer layer 42 contains tantalum (Ta). The material of the buffer layer 42 preferably contains tantalum (Ta) and one or more elements selected from oxygen (O), nitrogen (N), and boron (B). Specific examples of the material of the buffer layer 42 containing tantalum (Ta) include Ta, TaN, TaO, TaON, TaB, TaBN, TaBO, and TaBON. Furthermore, the material of the buffer layer 42 containing tantalum (Ta) may further contain at least one metal, or two or more metals selected from palladium (Pd), silver (Ag), platinum (Pt), gold (Au), iridium (Ir), tungsten (W), chromium (Cr), cobalt (Co), manganese (Mn), tin (Sn), vanadium (V), nickel (Ni), hafnium (Hf), iron (Fe), copper (Cu), tellurium (Te), zinc (Zn), magnesium (Mg), germanium (Ge), aluminum (Al), rhodium (Rh), ruthenium (Ru), molybdenum (Mo), niobium (Nb), titanium (Ti), zirconium (Zr), yttrium (Y), and silicon (Si).

[0053] When the material of the buffer layer 42 contains Ta and at least one element selected from N and B, the Ta content in the buffer layer 42 is 50 atomic % or more and can be 70 atomic % or more. The Ta content in the buffer layer 42 is 95 atomic % or less and can be 65 atomic % or less. The total content of N and B in the buffer layer 42 is 50 atomic % or less and can be 30 atomic % or less. The total content of N and B in the buffer layer 42 can be 5 atomic % or more. The N content is preferably smaller than the B content. This is because the smaller the N content, the faster the etching rate with chlorine gas becomes and the easier it is to remove the buffer layer 42.

[0054] Furthermore, when the material of the buffer layer 42 contains Ta and O, the Ta content in the buffer layer 42 is 50 atomic % or more and can be 70 atomic % or more. The Ta content in the buffer layer 42 is 95 atomic % or less and can be 65 atomic % or less. The O content in the buffer layer 42 is 70 atomic % or less and can be 60 atomic % or less. From the viewpoint of ease of etching, the O content in the buffer layer 42 is 10 atomic % or more and can be 20 atomic % or more.

[0055] In another embodiment, the buffer layer 42 may be formed of a material containing silicon (Si). The material of the buffer layer 42 preferably contains silicon (Si) and at least one element selected from oxygen (O), nitrogen (N), carbon (C), and hydrogen (H).

[0056] Specific examples of materials containing silicon (Si) include SiO, SiN, SiON, SiC, SiCO, SiCN, SiCON, MoSi, MoSiO, MoSiN, and MoSiON. As the material containing Si, it is preferable to use SiO, SiN, or SiON. Note that the material may contain a semimetal or metal other than Si within a range in which the effects of the present invention can be obtained. Also, molybdenum silicide may be used as the metal Si compound.

[0057] The thickness of the buffer layer 42 may be approximately the same as or thinner than the etching mask film 6 described below, within a range that does not damage the protective film 3 when etching the absorber film 4. Specifically, the thickness of the buffer layer 42 is preferably 2 nm to 50 nm, and can be 4 nm to 30 nm.

[0058] As described above, the buffer layer 42 is made of a material containing at least one selected from tantalum (Ta) and silicon (Si), and can be etched with, for example, an oxygen-free fluorine-based gas or chlorine-based gas. In addition, the buffer layer 42 made of such a material can have sufficient etching resistance against the protective film 3 containing Ru as a main component.

[0059] Next, the absorbing layer 44 disposed on and in contact with the buffer layer 42 can be made of a material containing at least one selected from chromium (Cr) and ruthenium (Ru), as described in detail below. This allows the absorbing layer 44 to have etching resistance against the buffer layer 42, and can satisfy the optical characteristics required for an absorber film (phase shift film) even if its film thickness is made thinner than before.

[0060] Here, the A layer having "etching resistance" to the B layer means that when the B layer is etched using the A layer as a mask, the etching rate of the B layer is sufficiently faster than the etching rate of the A layer. More specifically, the A layer can be said to have "etching resistance" to the B layer when the etching selectivity of the B layer to the A layer, defined by the formula: etching rate of the B layer / etching rate of the A layer, is 1.5 or more, preferably 3 or more.

[0061] In one embodiment, the material of the absorption layer 44 is chromium (Cr) alone or a Cr compound containing chromium (Cr) and at least one element selected from nitrogen (N), oxygen (O), and carbon (C). Examples of the Cr compound include CrN, CrC, CrON, CrCO, CrCN, CrCON, CrBN, CrBC, CrBON, CrBCN, and CrBOCN. In order to increase the extinction coefficient of the absorption layer 44, the material may be oxygen-free. In this case, it is also possible to increase the etching selectivity with respect to chlorine-based gas. Examples of the Cr compound that does not contain oxygen include CrN, CrC, CrCN, CrBN, CrBC, and CrBCN. The Cr content of the Cr compound is preferably 50 atomic % or more and less than 100 atomic %, and more preferably 80 atomic % or more and less than 100 atomic %. In this specification, "free of oxygen" or "substantially free of oxygen" refers to a compound that contains 10 atomic % or less, preferably 5 atomic % or less.

[0062] In another embodiment, the absorbing layer 44 may be formed of a material including ruthenium (Ru) alone or a Ru compound including ruthenium (Ru) and at least one element selected from nitrogen (N) and oxygen (O). Examples of the Ru compound include RuN, RuON, and RuO.

[0063] The material of the absorber layer 44 may be a RuCr-based compound containing ruthenium (Ru) and chromium (Cr). Ru-based compounds tend to have a crystallized structure, which adversely affects processing performance. That is, crystal grains of crystallized metal tend to have large sidewall roughness when forming an absorber pattern, so it is preferable that the absorber film 4 is amorphous. By adding chromium (Cr) to ruthenium (Ru) as the material of the absorber layer 44, the crystal structure can be made amorphous and processing characteristics can be improved. Furthermore, by further containing at least one element selected from nitrogen (N) and oxygen (O) in addition to ruthenium (Ru) and chromium (Cr), the crystal structure can be made more amorphous. Examples of RuCr-based compounds include RuCrN, RuCrON, and RuCrO. The composition range (atomic ratio) of Ru and Cr can be Ru:Cr=40:1 to 1:20, or 40:1 to 3:7. The material of the absorption layer 44 may be a RuTa-based compound or a RuPt-based compound containing ruthenium (Ru) and tantalum (Ta) or platinum (Pt). The RuTa-based compound or the RuPt-based compound may further contain at least one element selected from nitrogen (N), oxygen (O), and boron (B). Examples of the RuTa-based compound include RuTaN, RuTaON, RuTaO, RuTaB, RuTaBN, RuTaBO, and RuTaBNO. Examples of the RuPt-based compound include RuPtN, RuPtON, RuPtO, RuPtB, RuPtBN, RuPtBO, and RuPtBNO. The Ru content of the RuTa-based compound is preferably 30 atomic % or more and less than 100 atomic %, and more preferably 40 atomic % or more and less than 100 atomic %. The Ru content of the RuPt-based compound is preferably 30 atomic % or more and less than 100 atomic %, and more preferably 40 atomic % or more and less than 100 atomic %.

[0064] The absorbing layer 44 containing at least one element selected from chromium (Cr) and ruthenium (Ru) can be etched by a mixed gas of a chlorine-based gas and an oxygen gas. The absorbing layer 44 may also be etched by a mixed gas of a fluorine-based gas and an oxygen gas.

[0065] The thickness of the absorber layer 44 is preferably 10 nm to 70 nm, and more preferably 20 nm to 60 nm. The total thickness of the absorber film 4 including the buffer layer 42 and the absorber layer 44 is preferably 15 nm to 75 nm, and more preferably 25 nm to 65 nm.

[0066] Also, an oxide layer may be formed on the surface of the absorber film 4 (absorption layer 44). By forming an oxide layer on the surface of the absorber film 4 (absorption layer 44), the cleaning resistance of the absorber pattern 4a of the obtained reflective mask 200 can be improved. The thickness of the oxide layer is preferably 1.0 nm or more, and more preferably 1.5 nm or more. Also, the thickness of the oxide layer is preferably 5 nm or less, and more preferably 3 nm or less. If the thickness of the oxide layer is less than 1.0 nm, it is too thin to be effective, and if it exceeds 5 nm, it has a large effect on the surface reflectance for the mask inspection light, making it difficult to control to obtain a predetermined surface reflectance.

[0067] The method of forming the oxide layer includes performing hot water treatment, ozone water treatment, heat treatment in an oxygen-containing gas, ultraviolet irradiation treatment in an oxygen-containing gas, O2 plasma treatment, etc., on the mask blank after the absorber film 4 (absorption layer 44) is formed. In addition, when the surface of the absorber film 4 (absorption layer 44) is exposed to the atmosphere after the absorber film 4 (absorption layer 44) is formed, an oxide layer may be formed on the surface layer by natural oxidation. In particular, in some cases, an oxide layer with a thickness of 1 to 2 nm is formed.

[0068] <<Etching mask film>> In the reflective mask blank 100 of this embodiment, an etching mask film 6 is formed to serve as a mask (also referred to as a "hard mask") for patterning the absorber film 4. The etching mask film 6 is disposed in contact with the upper surface of the above-mentioned absorbing layer 44, and has an etching mask film 61 having etching resistance with respect to the absorbing layer 44. The reflective mask blank 100 may have the etching mask film 61 disposed in contact with the absorbing layer 44 as a first etching mask film, and further have a second etching mask film 62 having etching resistance with respect to the first etching mask film 61.

[0069] For example, as in Layer Configuration Example 1 shown in Fig. 2, the first etching mask film 61 is made of a composition gradient film containing a predetermined element X and oxygen (O). Furthermore, the first etching mask film 61 may partially include layers 64 and 65 containing a predetermined element X and oxygen (O) and a layer 66 containing substantially no oxygen (O), as in Layer Configuration Example 2 shown in Fig. 3.

[0070] In both of the above-described layer configuration examples 1 and 2, the predetermined element X contained in the first etching mask film 61 includes at least one element selected from tantalum (Ta) and silicon (Si). The material of the first etching mask film 61 preferably includes the above-described element X and at least one element selected from oxygen (O), nitrogen (N) and boron (B). Specific examples of the material include TaO, TaON, TaBO, TaBON, SiO, SiON, SiBO, and SiBON.

[0071] When the material of the first etching mask film 61 contains Ta and O, the Ta content in the first etching mask film 61 is 50 atomic % or more and can be 70 atomic % or more. The Ta content in the first etching mask film 61 is 95 atomic % or less and can be 65 atomic % or less. The O content in the first etching mask film 61 is 70 atomic % or less and can be 60 atomic % or less. The O content in the first etching mask film 61 is 2 atomic % or more and can be 6 atomic % or more.

[0072] When the material of the first etching mask film 61 contains Si and O, the Si content in the first etching mask film 61 is 25 atomic % or more and can be 40 atomic % or more. The Si content in the first etching mask film 61 is 80 atomic % or less and can be 60 atomic % or less. The O content in the first etching mask film 61 is 70 atomic % or less and can be 60 atomic % or less. The O content in the first etching mask film 61 is 10 atomic % or more and can be 20 atomic % or more.

[0073] As described above, the material of the etching mask film 61 preferably contains a predetermined element X and oxygen (O) with a predetermined concentration ratio profile in the film thickness direction. When the etching mask film 61 has a predetermined oxygen concentration ratio, damage to the protective film 3 (the multilayer reflective film 2 when the protective film 3 is not present) or the absorbing layer 44 can be prevented in the process of dry etching the buffer layer 42, as will be described later.

[0074] The first etching mask film 61 contains at least one element selected from tantalum (Ta) and silicon (Si), and can be etched and removed with a fluorine-based gas. Examples of the fluorine-based gas that can be used include CF4, CHF3, C2F6, C3F6, C4F6, C4F8, CH2F2, CH3F, C3F8, SF6, and F2. These etching gases may further contain an inert gas such as He and / or Ar, as necessary.

[0075] In this specification, the oxygen concentration ratio relative to the total content of the at least one element X in the etching mask film 61 is defined by the following formula (1).

number

[0076] The content of each component constituting the etching mask film 6 can be measured by energy dispersive X-ray analysis (EDX) using a scanning transmission electron microscope (STEM).

[0077] In the reflective mask blank 100 according to a preferred embodiment of the present invention, the oxygen concentration ratio on the side of the absorption layer 44 of the first etching mask film 61 is higher than the oxygen concentration ratio at the thickness center of the etching mask film 61. It is also preferable that the oxygen concentration ratio on the side of the first etching mask film 61 opposite to the absorption layer 44 is higher than the oxygen concentration ratio at the thickness center of the etching mask film. By making the surface and bottom of the first etching mask film 61 have an oxygen concentration ratio of a predetermined value or more and making the oxygen concentration ratio at the thickness center of the first etching mask film 61 have a predetermined value or less, it becomes easier to prevent electrostatic breakdown while suppressing CD changes during the dry etching process.

[0078] In addition, the oxygen concentration ratio on the side of the first etching mask film 61 facing the absorption layer 44 can be made equal to or higher than the oxygen concentration ratio on the opposite side of the etching mask film 61 facing the absorption layer 44. When the first etching mask film 61 is made of a material containing Ta, the selectivity between the first etching mask film 61 and the absorption layer 44 can be increased in etching with a fluorine-based gas.

[0079] In addition, the oxygen concentration ratio on the side of the first etching mask film 61 opposite to the absorption layer 44 can be made higher than the oxygen concentration ratio on the absorption layer 44 side of the etching mask film 61. In this case, it is possible to further suppress the oxidation expansion that occurs when the second etching mask film 62 is etched with a chlorine-based gas containing oxygen gas, and it is possible to suppress the CD change caused by the thickening of the first etching mask film 61.

[0080] These characteristics can be defined by the magnitude relationship between the oxygen concentration ratio at the interface position x1 between the first etching mask film 61 and the absorption layer 44, the oxygen concentration ratio at the interface position x2 between the first etching mask film 61 and the second etching mask film 62 or the surface position x2 of the etching mask film 61, and the oxygen concentration ratio at the center position x3 in the film thickness direction of the first etching mask film 61.

[0081] In other words, if we express these in a comparative formula, O / (X+O) ratio at the center of the thickness x3 < O / (X+O) ratio at the interface x1; O / (X+O) ratio at the center of the film thickness x3 < O / (X+O) ratio at the interface (surface) x2; It is preferable that: Moreover, the O / (X+O) ratio at the interface (surface) x2 can be set to be less than or equal to the O / (X+O) ratio at the interface x1 in order to increase the selectivity between the first etching mask film 61 and the absorption layer 44. Moreover, in order to suppress the CD change caused by the thickening of the first etching mask film 61, the O / (X+O) ratio at the interface x1 can be set to be less than the O / (X+O) ratio at the interface (surface) x2.

[0082] In a preferred embodiment of the reflective mask blank 100, the oxygen concentration ratio (O / (X+O) ratio) at the thickness center position x3 of the first etching mask film 61 is 70% or less, and can be set to 50% or less.

[0083] The oxygen concentration ratio (O / (X+O) ratio) at the interface position x1 between the first etching mask film 61 and the absorption layer 44 is not less than 5% and can be not less than 10%. The (O / (X+O) ratio) is not more than 90% and can be not more than 80%.

[0084] The difference between the oxygen concentration ratio (O / (X+O) ratio) at the interface position x1 with the absorption layer 44 and the oxygen concentration ratio (O / (X+O) ratio) at the center position x3 of the first etching mask film 61 is 5% or more and can be 10% or more. The difference in (O / (X+O) ratio) is 85% or less and can be 75% or less.

[0085] The oxygen concentration ratio (O / (X+O) ratio) at the interface position x2 between the first etching mask film 61 and the second etching mask film 62 or at the surface position x2 of the first etching mask film 61 is 1% or more and can be 5% or more. The (O / (X+O) ratio) is 85% or less and can be 75% or less.

[0086] Moreover, the difference between the oxygen concentration ratio (O / (X+O) ratio) at the interface position x2 between the first etching mask film 61 and the second etching mask film 62 or at the surface position x2 of the first etching mask film 61 and the oxygen concentration ratio (O / (X+O) ratio) at the center position x3 of the first etching mask film 61 is 1% or more and can be 5% or more. Moreover, the difference in the (O / (X+O) ratio) is 80% or less and can be 70% or less.

[0087] According to the reflective mask blank 100 of this embodiment, the oxygen concentration ratio (O / (X+O) ratio) at the center position x3 of the first etching mask film 61 is reduced to a predetermined value or less, so that it is possible to prevent the occurrence of fatal defects due to electrostatic breakdown while suppressing CD changes during the dry etching process. Furthermore, by specifying the oxygen concentration ratio of the etching mask film 61, it is possible to adjust the etching rate of the etching mask film 61 in accordance with the progress of the pattern etching of the buffer layer 42, and thus it is possible to suppress damage to the protective film 3 or the absorption layer 44 during the dry etching process of the buffer layer 42.

[0088] The magnitude relationship of the above-mentioned oxygen concentration ratio (O / (X+O) ratio) can be evaluated by X-ray photoelectron spectroscopy (XPS) in addition to EDX. It is also possible to evaluate by combining these analysis results with a transmission electron microscope (TEM). Furthermore, by fitting the data measured by these methods using a known approximation function, it is possible to determine the interface positions x1 and x2 between the above-mentioned layers and the center position x3 of the etching mask film 61. In this specification, the magnitude relationship of the oxygen concentration ratio (O / (X+O) ratio) of the etching mask film 61 is given as a value obtained by EDX, and the content of the elements constituting each film is given as a value obtained by XPS.

[0089] Usually, components (elements) of each layer are mutually diffused near the interface between the first etching mask film 61 and the absorbing layer 44. Here, in order to determine the interface position x1 between the first etching mask film 61 and the absorbing layer 44, a method is adopted in which an inflection point x1 at which the total content of metal elements contained in the absorbing layer 44 inflects in the film thickness direction x is determined as the interface position x1. Specifically, the interface position x1 between the first etching mask film 61 and the absorbing layer 44 can be measured as follows.

[0090] First, the total content (atomic %) of metal elements contained in the absorbing layer 44 is measured in the film thickness direction x from the first etching mask film 61 to the absorbing layer 44. Here, the total content of metal elements refers to the Cr content when the absorbing layer 44 is, for example, CrN, and refers to the RuCr content when the absorbing layer 44 is, for example, RuCrN. Next, a function y_abs(x) is obtained by curve fitting the measured data of the total content.

[0091] This curve fitting can employ a known approximation method using an S-shaped function. The S-shaped approximation function is generally used to approximate an S-shaped profile. As the S-shaped approximation function, an odd function selected from a third-order or higher polynomial function, a sigmoid function, an error function, an exponential function, a sine function, or the like can be used.

[0092] In order to determine the interface position x1 between the first etching mask film 61 and the absorption layer 44, the range x (x1a to x1b) in the film thickness direction x for curve fitting the content of the metal element contained in the absorption layer 44 can be determined as follows.

[0093] The start point (x=x1a) of the fitting range in the first etching mask film 61 is near the interface position x1 with the absorption layer 44, and can be set at a position where the total content (atomic %) of the element X constituting the first etching mask film 61 is maximum. Here, the total content of the element X is the Ta content when the etching mask film 61 is, for example, TaBO, the Si content when the etching mask film 61 is, for example, SiO, and the TaSi content when the etching mask film 61 is, for example, TaSiO.

[0094] The end point (x = x1b) of the fitting range within the absorption layer 44 can be set near the interface position x1 with the first etching mask film 61, at a position where the total content (atomic %) of the metal elements constituting the absorption layer 44 is at its maximum value.

[0095] An inflection point x1 of the total content of the metal elements constituting the absorbing layer 44 can be obtained as the solution of the following second derivative equation (2), in which the second derivative of y_abs(x) is zero.

[0096]

number

[0097] In addition, when there are two or more solutions (inflection points) that satisfy equation (2) obtained by approximation using a high-order S-shaped function, the measurement data of the metal content can be approximated by a cubic function, and the inflection point that is closest to the solution of the second derivative equation obtained by differentiating the cubic approximation function twice can be estimated to be the true interface position x1.

[0098] The inflection point x1 of the approximate content profile of the metal element obtained as described above means the position (depth in the film thickness direction) at which the component dominance of the first etching mask film 61 switches to the component dominance of the absorption layer 44. Therefore, the position x1 of the calculated inflection point can be regarded as the interface position x1 between the first etching mask film 61 and the absorption layer 44.

[0099] When the etching mask film 6 has the second etching mask film 62, the interface position x2 between the second etching mask film 62 and the first etching mask film 61 can also be determined based on the position of the inflection point where the dominant component switches, by applying the above-mentioned curve fitting method mutatis mutandis. That is, in order to determine the interface position x2 between the second etching mask film 62 and the first etching mask film 61, a fitting curve function y_em2(x) that approximates the total content of the metal elements constituting the second etching mask film 62 is calculated, and the position of the inflection point x2 obtained as the solution of the second derivative equation where the value obtained by second-order differentiation of y_em2(x) is zero can be regarded as the interface position x2.

[0100] The thickness of the first etching mask film 61 is 6 nm to 30 nm, and can be 8 nm to 20 nm. The ratio of the thickness of the first etching mask film 61 to the thickness of the buffer layer 42 is 0.1 to 15, and can be 0.3 to 10.

[0101] The first etching mask film 61 containing Ta and O can be formed by sputtering using a Ta target in an oxygen gas (O2) and rare gas atmosphere. The first etching mask film 61 containing Si and O can be formed by sputtering using a Si target in an oxygen gas (O2) and rare gas atmosphere. At this time, the etching mask film 61 having a predetermined gradient composition of the above-mentioned oxygen concentration ratio profile can be formed by controlling the supply amount of oxygen gas (O2) or by replacing the supplied oxygen gas with another gas (for example, layer configuration example 1 shown in FIG. 2). Also, the etching mask film 61 can be configured to have the above-mentioned oxygen concentration ratio profile by forming it into a two-layer structure or three-layer structure. For example, it is also possible to form a three-layer structure of layers 64, 65, and 66, in which layers 64 and 65 containing oxygen and layer 66 substantially not containing oxygen (for example, layer configuration example 2 shown in FIG. 3).

[0102] In addition, by adjusting the oxygen concentration in the surface layer of the absorption layer 44 in contact with the first etching mask film 61, it is possible to adjust the oxygen concentration ratio at the interface position x1 between the first etching mask film 61 and the absorption layer 44. By adjusting the oxygen concentration in the bottom part of the second etching mask film 62 in contact with the first etching mask film 61, it is possible to adjust the oxygen concentration ratio at the interface position x2 between the first etching mask film 61 and the second etching mask film 62.

[0103] As described above, the reflective mask blank 100 according to this embodiment may have the second etching mask film 62 formed on the first etching mask film 61. In this case, the material of the second etching mask film 62 is preferably chromium (Cr) or a Cr compound. Examples of Cr compounds include materials containing chromium (Cr) and at least one element selected from nitrogen (N), oxygen (O), carbon (C) and hydrogen (H). Specifically, the second etching mask film 62 preferably contains CrN, CrO, CrC, CrON, CrOC, CrCN or CrOCN.

[0104] The Cr content in the second etching mask film 62 is 30 atomic % or more and can be 40 atomic % or more. The Cr content in the first etching mask film 61 is 95 atomic % or less and can be 90 atomic % or less.

[0105] The thickness of the second etching mask film 62 is 3 nm to 20 nm, and can be set to 5 nm to 15 nm.

[0106] The second etching mask film 62 can be formed by sputtering using a Cr-based target. Since the second etching mask film 62 contains chromium, it can be etched and removed with a mixed gas of a chlorine-based gas and an oxygen gas.

[0107] <<Resist film>> The reflective mask blank 100 of this embodiment can have a resist film 11 on the etching mask film 6. That is, the reflective mask blank 100 of this embodiment also includes a form having a resist film 11. In the reflective mask blank 100 of this embodiment, the resist film 11 can also be made thin by selecting an appropriate material and / or an appropriate thickness of the absorber film 4 (the buffer layer 42 and the absorber layer 44) and an etching gas.

[0108] For example, a chemically amplified resist (CAR) can be used as the material of the resist film 11. The resist film 11 is patterned and the absorber film 4 (the buffer layer 42 and the absorption layer 44) is etched, thereby manufacturing a reflective mask 200 having a predetermined transfer pattern.

[0109] <<Backside conductive film>> A back surface conductive film 5 for an electrostatic chuck is generally formed on the second main surface (back surface) side of the substrate 1 (opposite the surface on which the multilayer reflective film 2 is formed). The electrical characteristics (sheet resistance) required for the back surface conductive film 5 for an electrostatic chuck are generally 100 Ω / □ (Ω / Square) or less. The back surface conductive film 5 can be formed, for example, by magnetron sputtering or ion beam sputtering using a target of a metal or alloy such as chromium (Cr) or tantalum (Ta).

[0110] The chromium (Cr)-containing material of the back surface conductive film 5 is preferably a Cr compound containing at least one element selected from boron (B), nitrogen (N), oxygen (O), and carbon (C) in Cr. Examples of the Cr compound include CrN, CrON, CrCN, CrCON, CrBN, CrBON, CrBCN, and CrBOCN.

[0111] The tantalum (Ta)-containing material of the back surface conductive film 5 is preferably Ta, an alloy containing Ta, or a Ta compound containing at least one of boron (B), nitrogen (N), oxygen (O), and carbon (C) in any of these. Examples of Ta compounds include TaB, TaN, TaO, TaON, TaCON, TaBN, TaBO, TaBON, TaBCON, TaHf, TaHfO, TaHfN, TaHfON, TaHfCON, TaSi, TaSiO, TaSiN, TaSiON, and TaSiCON.

[0112] It is preferable that the material containing tantalum (Ta) or chromium (Cr) has a small amount of nitrogen (N) present in its surface layer. Specifically, the nitrogen content in the surface layer of the back surface conductive film 5 made of a material containing tantalum (Ta) or chromium (Cr) is preferably less than 5 atomic %, and more preferably the surface layer does not substantially contain nitrogen. This is because the lower the nitrogen content in the surface layer of the back surface conductive film 5 made of a material containing tantalum (Ta) or chromium (Cr), the higher the wear resistance.

[0113] The back surface conductive film 5 is preferably made of a material containing tantalum (Ta) and boron (B). When the back surface conductive film 5 is made of a material containing Ta and B, a conductive film 23 having wear resistance and chemical resistance can be obtained. When the back surface conductive film 5 contains Ta and B, the B content is preferably 5 to 30 atomic %. The ratio of Ta and B (Ta:B) in the sputtering target used for forming the back surface conductive film 5 is preferably 95:5 to 70:30.

[0114] The thickness of the back surface conductive film 5 is not particularly limited as long as it satisfies the function for electrostatic chuck, but is usually 10 nm to 200 nm. The back surface conductive film 5 also functions to adjust the stress on the second main surface side of the mask blank 100, and is adjusted to obtain a flat reflective mask blank 100 by balancing with the stress from various films formed on the first main surface side.

[0115] <Reflection mask 200 and its manufacturing method> An outline of a method for manufacturing a reflective mask 200 using the reflective mask blank 100 of this embodiment will be described below.

[0116] First, a reflective mask blank 100 is prepared, and a resist film 11 is formed on an etching mask film 6 formed on an absorber film 4 on a first main surface of the reflective mask blank 100 (FIG. 4A). A chemically amplified resist (CAR) can be used to form the resist film 11.

[0117] A desired pattern is drawn (exposed) on this resist film 11, and then developed and rinsed to form a predetermined resist pattern 11a (FIG. 4B).

[0118] Next, the second etching mask film 62 is dry-etched using a mixed gas of a chlorine-based gas and an oxygen gas, with the resist pattern 11a as a mask, to form a mask pattern 62a (FIG. 4C).

[0119] After the resist pattern 11a is removed by oxygen ashing, the first etching mask film 61 is dry-etched using the mask pattern 62a as a mask and a fluorine-based gas to form a mask pattern 61a (FIG. 4D).

[0120] Next, the absorbing layer 44 is dry-etched using a mixed gas of a chlorine-based gas and an oxygen gas with the mask pattern 61a as a mask, thereby forming an absorbing layer pattern 44a (FIG. 4E). In this dry-etching process using a mixed gas of a chlorine-based gas and an oxygen gas, the mask pattern 62a of the second etching mask film 62 is removed.

[0121] Thereafter, the buffer layer 42 is patterned by dry etching using a fluorine-based gas, with the absorption layer pattern 44a as a mask. In the same process, the mask pattern 61a of the first etching mask film 61 is removed with a fluorine-based gas (FIG. 4F).

[0122] After removing the mask pattern 61a of the first etching mask film 61, if the buffer layer 42 in the absorber pattern 4a is not completely etched, the remaining portion can be completely removed using a chlorine-based gas (FIG. 4G).

[0123] Finally, wet cleaning is performed using pure water or an acidic or alkaline aqueous solution to manufacture the reflective mask 200 of this embodiment. After the wet cleaning, a mask defect inspection can be performed as necessary, and mask defect correction can be performed appropriately.

[0124] The reflective mask 200 thus manufactured has an absorber pattern 4a formed by patterning the absorber film 4 in the reflective mask blank 100. The absorber pattern 4a of the reflective mask 200 absorbs EUV light and can reflect the EUV light at the openings of the absorber pattern 4a, so that a predetermined fine transfer pattern can be transferred onto a transfer target by irradiating the reflective mask 200 with EUV light using a predetermined optical system.

[0125] According to the reflective mask 200 and its manufacturing method of the present embodiment, by defining the oxygen concentration ratio of the etching mask film 61 in the reflective mask blank 100, it is possible to adjust the etching rate of the etching mask film 61 in accordance with the progress of the pattern etching of the buffer layer 42. This makes it possible to suppress damage to the protective film 3 or the absorbing layer 44 during the dry etching process of the buffer layer 42 while suppressing CD changes. Therefore, it is possible to provide a reflective mask 200 having an absorber pattern 4a in which a fine transfer pattern is formed with high accuracy.

[0126] <Method of Manufacturing Semiconductor Device> The manufacturing method of the semiconductor device of this embodiment includes a step of setting the reflective mask 200 of this embodiment in an exposure apparatus having an exposure light source that emits EUV light, and transferring a transfer pattern to a resist film formed on a transfer substrate.

[0127] By performing EUV exposure using the reflective mask 200 of this embodiment, a desired transfer pattern based on the absorber pattern 4a on the reflective mask 200 can be formed on a semiconductor substrate while suppressing deterioration of transfer dimensional accuracy due to the shadowing effect. In addition, since the absorber pattern 4a is a fine and highly accurate pattern with little sidewall roughness, a desired pattern can be formed on a semiconductor substrate with high dimensional accuracy. In addition to this lithography process, various processes such as etching of the processed film, formation of an insulating film and a conductive film, introduction of a dopant, and annealing can be performed to manufacture a semiconductor device in which a desired electronic circuit is formed.

[0128] More specifically, the EUV exposure apparatus is composed of a laser plasma light source that generates EUV light, an illumination optical system, a mask stage system, a reduction projection optical system, a wafer stage system, and a vacuum facility. The light source is equipped with a debris trap function, a cut filter that cuts out long-wavelength light other than the exposure light, and a facility for vacuum differential pumping. The illumination optical system and reduction projection optical system are composed of reflective mirrors. The EUV exposure reflective mask 200 is electrostatically attracted by a conductive film formed on its second main surface and placed on the mask stage.

[0129] The light from the EUV light source is irradiated onto the reflective mask 200 at an angle of 6° to 8° with respect to the vertical plane of the reflective mask 200 via an illumination optical system. The light reflected from the reflective mask 200 in response to this incident light is reflected (specularly reflected) in the opposite direction to the incident direction and at the same angle as the incident angle, and is guided to a reflective projection optical system having a reduction ratio of usually 1 / 4, and exposure is performed on the resist on the wafer (semiconductor substrate) placed on the wafer stage. During this time, at least the area through which the EUV light passes is evacuated to a vacuum. In addition, for this exposure, scanning exposure is mainstream, in which the mask stage and the wafer stage are scanned in synchronization at a speed according to the reduction ratio of the reduction projection optical system, and exposure is performed through a slit. Then, a resist pattern can be formed on the semiconductor substrate by developing this exposed resist film. In the present invention, a mask is used that has a thin film with a small shadowing effect and a high-precision absorber pattern 4a with little sidewall roughness. Therefore, the resist pattern formed on the semiconductor substrate has a desired high dimensional accuracy. Then, by carrying out etching etc. using this resist pattern as a mask, a predetermined wiring pattern can be formed on, for example, a semiconductor substrate. A semiconductor device is manufactured through such exposure steps, a process for processing the film to be processed, a process for forming an insulating film or a conductive film, a dopant introduction process, an annealing process, and other necessary processes.

[0130] According to the method for manufacturing a semiconductor device of the present embodiment, the reflective mask 200 having a fine and highly accurate absorber pattern 4a formed thereon, which has a high absorptivity for EUV light while thinning the thickness of the absorber film 4, can be used for manufacturing a semiconductor device. Therefore, a semiconductor device having a fine and highly accurate transfer pattern can be manufactured. EXAMPLES

[0131] [Example 1] 1, the reflective mask blank 100 of Example 1 has a back surface conductive film 5, a substrate 1, a multilayer reflective film 2, a protective film 3, an absorber film 4, and an etching mask film 6. The absorber film 4 is composed of a buffer layer 42 and an absorber layer 44.

[0132] First, a reflective mask blank 100 of Example 1 will be described. In the following description, the elemental composition of the formed thin film was measured by X-ray photoelectron spectroscopy (XPS). The oxygen concentration ratio (O / (X+O) ratio) was measured by energy dispersive X-ray analysis (EDX) using a scanning transmission electron microscope (STEM) and determined by performing the above-mentioned fitting.

[0133] A SiO2-TiO2-based glass substrate, which is a low-thermal expansion glass substrate having a size of 6025 (approximately 152 mm × 152 mm × 6.35 mm) with both the first and second main surfaces polished, was prepared as substrate 1. In order to obtain a flat and smooth main surface, polishing was performed through a rough polishing process, a precision polishing process, a localized polishing process, and a touch polishing process. A back surface conductive film 5 made of a CrN film was formed under the following conditions by magnetron sputtering (reactive sputtering) on ​​the second main surface (back surface) of the SiO2-TiO2-based glass substrate 1. The back surface conductive film 5 was formed to a thickness of 20 nm using a Cr target in a mixed gas atmosphere of argon (Ar) gas and nitrogen (N2) gas.

[0134] Next, a multilayer reflective film 2 was formed on the main surface (first main surface) of the substrate 1 opposite to the side on which the back conductive film 5 was formed. The multilayer reflective film 2 formed on the substrate 1 was a periodic multilayer reflective film made of molybdenum (Mo) and silicon (Si) in order to make the multilayer reflective film 2 suitable for EUV light with a wavelength of 13.5 nm. The multilayer reflective film 2 was formed by alternately laminating Mo layers and Si layers on the substrate 1 by ion beam sputtering in a krypton (Kr) gas atmosphere using a Mo target and a Si target. First, a Si film was formed with a thickness of 4.2 nm, and then a Mo film was formed with a thickness of 2.8 nm. This constitutes one period, and 40 periods were laminated in the same manner, and finally a Si film was formed with a thickness of 4.0 nm to form the multilayer reflective film 2.

[0135] Subsequently, a protective film 3 made of a RuNb film was formed to a thickness of 3.5 nm by DC magnetron sputtering using a RuNb target (Ru:Nb=80 at %:20 at %) in an Ar gas atmosphere.

[0136] Next, an absorber film 4 consisting of a buffer layer 42 and an absorbing layer 44 was formed on the protective film 3. Table 1 shows the materials and film thicknesses of the buffer layer 42, the absorbing layer 44 and the etching mask film 6 in Example 1. Specifically, first, a buffer layer 42 made of a TaBN film was formed by DC magnetron sputtering. The TaBN film was formed to a thickness of 10 nm by reactive sputtering in a mixed gas atmosphere of Ar gas and N2 gas using a mixed sintered TaB target, as shown in Table 1. The element ratio of the TaBN film was 88 atomic % Ta, 5 atomic % B, and 7 atomic % N.

[0137] Next, an absorption layer 44 made of a CrN film was formed by magnetron sputtering. The CrN film was formed to a thickness of 36 nm by reactive sputtering using a Cr target in a mixed gas atmosphere of Ar gas and N2 gas, as shown in Table 1. The element ratio of the CrN film was 88 atomic % for Cr and 12 atomic % for N. Next, a first etching mask film 61 made of a TaBO film was formed on the absorbing layer 44 by DC magnetron sputtering. The TaBO film was formed to a thickness of 16 nm by reactive sputtering in a mixed gas atmosphere of Ar gas and O2 gas using a TaB mixed sintered target, as shown in Table 1. At this time, by changing the supply amount of O2 gas in the mixed gas atmosphere, a composition gradient film with different oxygen concentration ratios in the film thickness direction shown in Table 2 was obtained.

[0138] Next, a second etching mask film 62 made of a CrOCN film was formed on the first etching mask film 61. The CrOCN film was formed to a thickness of 6 nm by reactive sputtering using a Cr target in an atmosphere of Ar gas, CO2 gas, and N2 gas. The element ratio of the CrOCN film was 38 atomic % Cr, 39 atomic % O, 11 atomic % C, and 12 atomic % N.

[0139] In this manner, the reflective mask blank 100 of Example 1 was produced.

[0140] Next, the reflective mask 200 of Example 1 was manufactured using the reflective mask blank 100 of Example 1 described above. A resist film 11 was formed on the second etching mask film 62 of the reflective mask blank 100 to a thickness of 50 nm (FIG. 4A). A chemically amplified resist (CAR) was used to form the resist film 11. A desired pattern was drawn (exposed) on this resist film 11, and then developed and rinsed to form a predetermined resist pattern 11a (FIG. 4B). Next, using the resist pattern 11a as a mask, a CrOCN film (second etching mask film 62) was etched using a mixed gas of Cl2 gas and O2 gas to form a mask pattern 62a (FIG. 4C). Next, after removing the resist pattern 11a by oxygen ashing, the mask pattern 62a was used as a mask to perform dry etching of the TaBO film (first etching mask film 61) using a mixed gas of CF4 gas and He gas to form a mask pattern 61a (FIG. 4D). Using the mask pattern 61a as a mask, the CrN film (the absorption layer 44) was dry-etched using a mixture of Cl2 gas and O2 gas to form the absorption layer pattern 44a (FIG. 4E). At this time, the CrOCN film was also peeled off at the same time.

[0141] After that, the buffer layer 42 was patterned by dry etching using CF4 gas and He gas, using the absorption layer pattern 44a as a mask. At this time, the mask pattern 61a made of a TaBO film was also removed at the same time (FIG. 4F). The remaining part of the buffer layer 42 was removed with Cl2 gas (FIG. 4G). Finally, wet cleaning was performed using pure water (DIW), and the reflective mask 200 of Example 1 was manufactured.

[0142] In the reflective mask blank 100 used in the manufacture of the reflective mask 200 of Example 1, the first etching mask film 61 satisfied the following conditions: O / (X+O) ratio at the thickness center x3<O / (X+O) ratio at the interface x1, and O / (X+O) ratio at the thickness center x3<O / (X+O) ratio at the interface x2, as shown in Table 2. Therefore, it was possible to prevent the first etching mask film 61 from being excessively charged, and to prevent the occurrence of fatal defects due to electrostatic breakdown. In addition, it was possible to suppress the CD change of the first etching mask film 61, and it was possible to make the CD of the absorber pattern 4a within the design value ±6 nm or less.

[0143] The reflective mask 200 produced in Example 1 was set in an EUV scanner, and EUV exposure was performed on a wafer on which a film to be processed and a resist film were formed on a semiconductor substrate. The exposed resist film was then developed to form a resist pattern on the semiconductor substrate on which the film to be processed was formed. The resist pattern was transferred to the film to be processed by etching, and various processes such as the formation of an insulating film and a conductive film, the introduction of a dopant, and annealing were performed to manufacture a semiconductor device having desired characteristics.

[0144] [Example 2] In Example 2, except for the first etching mask film 61, a reflective mask blank 100 and a reflective mask 200 were manufactured with the same structure and method as in Example 1, and a semiconductor device was manufactured in the same method as in Example 1.

[0145] A first etching mask film 61 consisting of a laminated film in which a TaBO film, a TaBN film, and a TaBO film were laminated in this order was formed on the absorption layer 44 by DC magnetron sputtering. The TaBO film was formed by reactive sputtering in a mixed gas atmosphere of Ar gas and O2 gas using a TaB mixed sintered target. The TaBN film was formed by reactive sputtering in a mixed gas atmosphere of Ar gas and N2 gas using a TaB mixed sintered target. As a result, a laminated film having the oxygen concentration ratio shown in Table 2 was obtained.

[0146] In the reflective mask blank 100 used in the manufacture of the reflective mask 200 of Example 2, the first etching mask film 61 satisfied the following conditions: O / (X+O) ratio at the thickness center x3<O / (X+O) ratio at the interface x1, and O / (X+O) ratio at the thickness center x3<O / (X+O) ratio at the interface x2, as shown in Table 2. Therefore, it was possible to prevent the first etching mask film 61 from being excessively charged, and to prevent the occurrence of fatal defects due to electrostatic breakdown. In addition, it was possible to suppress the CD change of the first etching mask film 61, and it was possible to make the CD of the absorber pattern 4a within the design value ±6 nm or less.

[0147] [Example 3] In Example 3, except for the first etching mask film 61, a reflective mask blank 100 and a reflective mask 200 were manufactured with the same structure and method as in Example 1, and a semiconductor device was manufactured in the same method as in Example 1.

[0148] A first etching mask film 61 made of a SiO film was formed on the absorbing layer 44 by RF magnetron sputtering. The SiO film was formed to a thickness of 20 nm by reactive sputtering in a mixed gas atmosphere of Ar gas and O2 gas using a Si target, as shown in Table 1. At this time, by changing the supply amount of O2 gas in the mixed gas atmosphere, a composition gradient film with different oxygen concentration ratios in the film thickness direction, as shown in Table 2, was obtained.

[0149] In the reflective mask blank 100 used in the manufacture of the reflective mask 200 of Example 3, the first etching mask film 61 satisfied the following conditions: O / (X+O) ratio at the thickness center x3<O / (X+O) ratio at the interface x1, and O / (X+O) ratio at the thickness center x3<O / (X+O) ratio at the interface x2, as shown in Table 2. Therefore, it was possible to prevent the first etching mask film 61 from being excessively charged, and to prevent the occurrence of fatal defects due to electrostatic breakdown. In addition, it was possible to suppress the CD change of the first etching mask film 61, and it was possible to make the absorber pattern 4a have a CD of the design value ±6 nm or less.

[0150] [Comparative Example 1] In Comparative Example 1, a reflective mask blank 100 and a reflective mask 200 were manufactured with the same structure and method as in Example 1, except for the first etching mask film 61, and a semiconductor device was manufactured in the same method as in Example 1.

[0151] In the reflective mask blank 100 used in the manufacture of the reflective mask 200 of Comparative Example 1, the O / (X+O) ratios of the first etching mask film 61 at the thickness center x3, interface x1, and interface x2 were uniform at 65%. As a result, the first etching mask film 61 was excessively charged beyond its electrostatic breakdown voltage, resulting in a fatal defect that rendered the reflective mask defective. In addition, the CD change of the first etching mask film 61 could not be suppressed, and the absorber pattern 4a had a CD exceeding the design value ±6 nm.

[0152] [Table 1]

[0153] [Table 2] [Explanation of symbols]

[0154] 1 Board 2 Multilayer reflective film 3 Protective film 4. Absorber membrane 4a Absorber pattern 5 Backside conductive film 6 Etching mask film 11 Resist film 42 Buffer layer 44 Absorbing Layer 61 First etching mask film 62 Second etching mask film 100 Reflective mask blank 200 Reflective mask

Claims

1. A reflective mask blank comprising a multilayer reflective film, an absorber film, and an etching mask film in this order, The absorbent membrane includes an absorbent layer, The etching mask film is placed in contact with the absorption layer and contains element X and oxygen (O), The element X includes at least one selected from tantalum (Ta) and silicon (Si), A reflective mask blank in which, when the oxygen concentration ratio is defined by dividing the oxygen (O) content (atomic %) in the etching mask film by the total content (atomic %) of element X and oxygen (O), the oxygen concentration ratio at surface position x2 opposite to the absorption layer of the etching mask film is higher than the oxygen concentration ratio at the center position x3 of the etching mask film thickness.

2. The difference between the oxygen concentration ratio at the surface position x2 and the oxygen concentration ratio at the center position x3 of the etching mask film is 5% or more and 80% or less, according to Claim 1.

3. The reflective mask blank according to claim 1 or 2, wherein the oxygen concentration ratio at the center position x3 of the etching mask film is 70% or less.

4. The reflective mask blank according to claim 1 or 2, wherein the oxygen concentration ratio at the surface position x2 of the etching mask film is 5% or more and 85% or less.

5. The reflective mask blank according to claim 1 or 2, wherein the oxygen concentration ratio at the interface position x1 between the etching mask film and the absorption layer is 10% or more and 90% or less.

6. A second etching mask film is provided on top of the first etching mask film, wherein the second etching mask film contains chromium (Cr), The reflective mask blank according to claim 1 or 2, wherein the surface position x2 is the interface position between the first etching mask film and the second etching mask film.

7. The reflective mask blank according to claim 1 or 2, wherein the absorbent membrane includes a buffer layer, and the buffer layer includes at least one selected from tantalum (Ta) and silicon (Si).

8. The reflective mask blank according to claim 1 or 2, wherein the absorbing layer comprises at least one selected from chromium (Cr) and ruthenium (Ru).

9. A reflective mask blank according to claim 1 or 2, further comprising a protective film between the multilayer reflective film and the absorbent film.

10. A reflective mask having a patterned absorbent pattern in the absorbent film of the reflective mask blank according to claim 1 or 2.

11. A method for manufacturing a semiconductor device, comprising the steps of setting the reflective mask described in claim 10 in an exposure apparatus and transferring a transfer pattern to a resist film formed on a substrate to be transferred.

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