Reflective mask blank and method for manufacturing reflective mask

Abstract

To provide a reflective mask blank capable of producing a reflective mask having an absorbing film with a good cross-sectional shape, and a method for manufacturing the reflective mask using the reflective mask blank.SOLUTION: A reflective mask blank serving as a material of a reflective mask used in EUV lithography using EUV light as exposure light includes: a substrate 10; a reflective multilayer film 20 that is formed on one main surface of the substrate 10 and reflects the exposure light; a protective film 50 formed in contact with the reflective multilayer film 20; and an absorbing film 70 that is formed on the protective film 50 and absorbs the exposure light. The protective film 50 is formed using a film containing ruthenium (Ru). The absorbing film 70 is formed using a single-layer film containing tantalum (Ta) and nitrogen (N), and has a content of nitrogen of 30 atom% or more and less than 60 atom%. Contrast between light reflected from a surface of the protective film 50 and light reflected on a surface of the absorbing film 70 with respect to light having a wavelength of 193 nm to 248 nm is 20% or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a reflective mask blank, which is a material for a reflective mask used in the manufacture of semiconductor devices such as LSIs, and a method for manufacturing a reflective mask from the reflective mask blank. [Background technology]

[0002] In the manufacturing process of semiconductor devices (semiconductor device), photolithography technology is repeatedly used, in which exposure light is irradiated onto a transfer mask, and the circuit pattern formed on the mask is transferred onto a semiconductor substrate (semiconductor wafer) via a reduced projection optical system. Conventionally, the wavelength of the exposure light has mainly been 193 nm using argon fluoride (ArF) excimer laser light, and a process called multi-patterning, which combines exposure processes and processing processes multiple times, has been used to ultimately form patterns with dimensions smaller than the exposure wavelength.

[0003] However, as device patterns continue to become finer, there is a need to form even finer patterns, and so EUV lithography technology, which uses extreme ultraviolet (EUV) light with an even shorter wavelength than ArF excimer laser light as exposure light, has come to be used. EUV light is light with a wavelength of about 0.2 to 100 nm, more specifically, a wavelength of about 13.5 nm. EUV light has extremely low transparency to materials, so that conventional transmission type projection optical systems and masks cannot be used, and therefore reflective optical elements are used. Therefore, reflective masks are also used for pattern transfer.

[0004] A reflective mask has a multilayer reflective film that reflects EUV light formed on a substrate, and a pattern of an absorbing film that absorbs EUV light formed on the multilayer reflective film. On the other hand, a mask in a state before the absorbing film is patterned (including a mask in a state where a resist film is formed) is called a reflective mask blank, and this is used as the material for a reflective mask. A reflective mask blank generally has a basic structure including a low thermal expansion substrate, a multilayer reflective film that reflects EUV light formed on one of the two main surfaces of the substrate, and an absorbing film that absorbs EUV light formed thereon.

[0005] The multilayer reflective film is usually made by alternately stacking molybdenum (Mo) and silicon (Si) layers to obtain the necessary reflectance for EUV light. On the other hand, the absorbing film is made of tantalum (Ta), which has a relatively large extinction coefficient for EUV light (JP Patent Publication 2002-246299 (Patent Document 1)).

[0006] Furthermore, as a protective film (capping film) for protecting the multilayer reflective film, a ruthenium (Ru) film as disclosed in JP-A-2002-122981 (Patent Document 2) is formed on the multilayer reflective film. Also, as an etching mask when forming a pattern on the absorbing film, an etching mask film containing chromium (Cr) may be formed on the absorbing film. Meanwhile, a backside conductive film is formed on the other main surface of the substrate. As the backside conductive film, a metal nitride film has been proposed for electrostatic chucking, and a film containing mainly chromium (Cr) or tantalum (Ta) is mentioned. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2002-246299 A [Patent Document 2] JP 2002-122981 A Summary of the Invention [Problem to be solved by the invention]

[0008] A reflective mask can be used as a mask for lithography by forming a pattern on an absorbing film, where the absorber pattern is located, and by reflecting the EUV light at the other exposed parts of the protective film. After forming a pattern on the absorbing film, an inspection is carried out to check whether the absorber pattern is formed as designed. The wavelength of light used for the inspection is about 190 nm to 260 nm, and the reflected image is inspected. For this reason, in pattern inspection of an absorbing film, the contrast between the reflected light from the absorbing film and the reflected light from a portion of the protective film exposed after the absorbing film has been removed is important.

[0009] In order to increase the contrast, it is effective to form an oxide layer as a reflectance reducing layer on the surface of the absorbing film, and by forming a film with an intentionally increased oxygen content, the reflectance to the inspection light is reduced, and the reflectance contrast can be increased. However, when a film containing a large amount of oxygen is formed on the surface, the etching rate of the oxide film during processing is slower than that of the layer containing no oxygen on the substrate side of the reflectance reducing layer of the absorbing film, and the cross-sectional shape of the formed pattern is likely to deteriorate.

[0010] An object of the present invention is to provide a reflective mask blank capable of producing a reflective mask having an absorbing film with a good cross-sectional shape, and a method for producing a reflective mask using the reflective mask blank. [Means for solving the problem]

[0011] The present invention has been made to solve the above-mentioned problems. The present inventors have found that in an EUV mask blank in which a multilayer reflective film, a protective film containing Ru, and an absorbing film consisting of Ta and N are successively formed on a substrate, by making the absorbing film a single-layer film containing 30 atm% or more of nitrogen, the cross-sectional shape of the formed pattern can be improved while maintaining the reflectance contrast of pattern inspection light at 20% or more, and have thus achieved the present invention.

[0012] Accordingly, the present invention provides the following reflective mask blank and method for producing a reflective mask.

[0013] [Concept 1] The reflective mask blank according to the present invention comprises: A reflective mask blank that is a material for a reflective mask used in EUV lithography using EUV light as exposure light, A substrate; a reflective multilayer film formed on one main surface of the substrate and reflecting exposure light; a protective film formed in contact with the reflective multilayer film; an absorbing film formed on the protective film for absorbing exposure light; Equipped with The protective film is formed of a film containing ruthenium (Ru), The absorption film is formed of a single layer film made of tantalum (Ta) and nitrogen (N), and the nitrogen content is 30 atomic % or more and less than 60 atomic %, The contrast between light reflected from the surface of the protective film and light reflected from the surface of the absorbing film for light with a wavelength of 193 nm to 248 nm may be 20% or more.

[0014] [Concept 2] In the reflective mask blank according to concept 1, The absorbing film may have a thickness of 50 nm or more and 80 nm or less.

[0015] [Concept 3] In the reflective mask blank according to concept 1 or 2, The protective film may be made of ruthenium (Ru), or ruthenium (Ru) and niobium (Nb).

[0016] [Concept 4] A reflective mask blank according to any one of concepts 1 to 3, The protective film may be 2 nm or more and 5 nm or less.

[0017] [Concept 5] A reflective mask blank according to any one of concepts 1 to 4, The optical fiber may further include an etching mask film containing Cr, which is used as an etching mask when processing the absorbing film.

[0018] [Concept 6] A reflective mask blank according to any one of concepts 1 to 5 may be manufactured by sputter deposition.

[0019] [Concept 7] 7. The method for producing a reflective mask blank according to claim 6, further comprising the steps of: After the absorbing film is formed on the surface away from the substrate, it may be exposed to the atmosphere or heat-treated at a temperature of 150° C. or less in the atmosphere to form an oxide layer having a thickness of 2 nm or less.

[0020] [Concept 8] 8. The method for producing a reflective mask blank according to Concept 6 or 7, The protective film may be made of ruthenium (Ru) or ruthenium (Ru) and niobium (Nb), and after the protective film is formed, a heat treatment may be performed at 150° C. or less in the atmosphere. Effect of the Invention

[0021] According to the present invention, it is possible to provide a reflective mask blank which enables the production of a reflective mask having an absorbing film with an excellent cross-sectional shape. [Brief description of the drawings]

[0022] [Figure 1]FIG. 1 is a vertical sectional view showing an example of a reflective mask blank according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a longitudinal sectional view showing an aspect in which an absorbing film pattern is formed in a reflective mask blank according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a longitudinal sectional view showing an aspect in which an etching mask film is provided in a reflective mask blank according to an embodiment of the present invention. [Figure 4] FIG. 2 is a longitudinal sectional view showing an aspect in which an etching mask film and a resist film are provided in a reflective mask blank according to an embodiment of the present invention. [Diagram 5] FIG. 2 is a longitudinal sectional view showing an aspect in which an etching mask film pattern is formed using a resist pattern as an etching mask in a reflective mask blank according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The embodiments of the present invention will be described in further detail below. 1, the reflective mask blank of this embodiment has a multilayer reflective film 20 that reflects exposure light, a protective film 50, and an absorbing film 70 formed on one main surface (front surface) of a substrate 10, and may further have an etching mask film 170 (see FIGS. 3 and 4) that functions as an etching mask when processing the absorbing film 70. In addition, a back surface conductive film 30 may be provided on the other main surface of the substrate.

[0024] The reflective mask is suitable as a material for a reflective mask used in EUV lithography using EUV light as the exposure light. The wavelength of EUV light used in EUV lithography using EUV light as the exposure light is 13 to 14 nm, and is usually light with a wavelength of about 13.5 nm. A reflective mask blank and a reflective mask using EUV light as the exposure light are also called EUV mask blank and EUV mask, respectively.

[0025] The substrate 10 preferably has low thermal expansion characteristics for use in EUV light exposure, and has a thermal expansion coefficient of, for example, ±2×10 -8 / ℃, preferably within ±5×10 -9 It is preferable that the material is made of a material having a temperature within a range of 100°C / °F. Such a material is titania-doped quartz glass (SiO 2 -TiO 2 Glass-based glass, etc. The substrate 10 preferably has a sufficiently flat surface, and the surface roughness of the main surface of the substrate 10 is preferably 0.5 nm or less, more preferably 0.2 nm or less, in terms of RMS value. Such a surface roughness can be obtained by polishing the substrate 10, etc. The size of the main surface of the substrate 10 is preferably 152 mm square, and the thickness of the substrate 10 is preferably 6.35 mm. The substrate 10 of this size is a so-called 6025 substrate (a substrate with a main surface size of 6 inches square and a thickness of 0.25 inches).

[0026] The multilayer reflective film 20 is a film that reflects exposure light in a reflective mask. The multilayer reflective film 20 is preferably provided in contact with one main surface of the substrate 10, but another film such as an undercoat film may be provided between the multilayer reflective film 20 and the one main surface of the substrate 10. The multilayer reflective film 20 has a periodic laminate structure in which high refractive index layers having a relatively high refractive index to the exposure light and low refractive index layers having a relatively low refractive index to the exposure light are alternately laminated.

[0027] The high refractive index layer is preferably formed of a material containing silicon (Si). The high refractive index layer may contain one or more additive elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B) and hydrogen (H), or may be composed of a multilayer structure of a layer containing an additive element and a layer not containing an additive element. The thickness of the high refractive index layer is preferably 3.5 nm or more, more preferably 4 nm or more, and is preferably 4.9 nm or less, more preferably 4.4 nm or less.

[0028] The low refractive index layer is preferably formed of a material containing molybdenum (Mo). The low refractive index layer can also be formed of a material containing ruthenium (Ru). The low refractive index layer may contain one or more additive elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B) and hydrogen (H), and may be composed of a multilayer structure including a layer containing an additive element and a layer not containing an additive element. The thickness of the low refractive index layer is preferably 2.1 nm or more, more preferably 2.6 nm or more, and is preferably 3.5 nm or less, more preferably 3 nm or less.

[0029] The periodic stacking structure may include a high refractive index layer and a low refractive index layer, and one or more high refractive index layers and one or more low refractive index layers may be included in one period. The number of layers included in the periodic stacking structure is two or more, and the periodic stacking structure may be composed of, for example, one high refractive index layer and one low refractive index layer. In addition, two or more high refractive index layers having different compositions (for example, different composition ratios, different compositions depending on the presence or absence of an additive element, etc.) may be included, and two or more low refractive index layers having different compositions (for example, different composition ratios, different compositions depending on the presence or absence of an additive element, etc.) may be included. In this case, the number of layers included in the periodic stacking structure is three or more, and may be four or more or five or more, but is preferably eight or less. The number of periods is preferably 30 or more, and is preferably 50 or less, more preferably 40 or less. When the low refractive index layer is formed of a material containing ruthenium (Ru), it is preferable that the layer (uppermost layer) farthest from the substrate 10 in the periodic stacking structure is a high refractive index layer.

[0030] The thickness of the multilayer reflective film 20 having a periodic stacked structure is adjusted according to the exposure wavelength and the incidence angle of the exposure light, but is preferably 200 nm or more, more preferably 270 nm or more, and is preferably 400 nm or less, more preferably 290 nm or less.

[0031] The method for forming the multilayer reflective film 20 includes a sputtering method in which power is supplied to a target, the atmospheric gas is turned into plasma (ionized) by the supplied power, and sputtering is performed, and an ion beam sputtering method in which an ion beam is irradiated onto the target. Examples of the sputtering method include a DC sputtering method in which a direct current voltage is applied to the target, and an RF sputtering method in which a high frequency voltage is applied to the target. The sputtering method is a film formation method in which a voltage is applied to the target with a sputtering gas introduced into a chamber, the gas is ionized, and the sputtering phenomenon caused by the gas ions is utilized, and the magnetron sputtering method is particularly advantageous in terms of productivity. The power applied to the target may be DC or RF, and DC also includes pulse sputtering in which a negative bias applied to the target is reversed for a short period of time to prevent the target from being charged up.

[0032] The multilayer reflective film 20 can be formed by a sputtering method using, for example, a sputtering device capable of mounting a plurality of targets. Specifically, the target can be appropriately selected from a molybdenum (Mo) target for forming a layer containing molybdenum (Mo), a ruthenium (Ru) target for forming a layer containing ruthenium (Ru), a silicon (Si) target for forming a layer containing silicon (Si), and the like, and can be formed by using a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as the sputtering gas.

[0033] In addition, when sputtering is reactive sputtering using a reactive gas, for example, when forming a film containing nitrogen (N), nitrogen (N 2 When forming a film containing oxygen (O), a nitrogen-containing gas such as oxygen (O 2 When forming a film containing nitrogen (N) and oxygen (O), nitrous oxide (N 2 O) gas, nitric oxide (NO) gas, nitrogen dioxide (NO 2 When forming a film containing carbon (C) and oxygen (O), carbon monoxide (CO) gas, carbon dioxide (CO2 When forming a film containing carbon oxide gas such as SiO2 gas, or hydrogen (H2O), 2 ) gas, and methane (CH 4 ) gas may be used in conjunction with a rare gas.

[0034] Furthermore, when forming a layer containing boron (B), a molybdenum (Mo) target with boron (B) added (molybdenum boride (MoB) target), a silicon (Si) target with boron (B) added (silicon boride (SiB) target), or the like can be used.

[0035] The protective film 50 is also called a capping film. The protective film 50 is a film for protecting the multilayer reflective film 20. The protective film 50 is usually provided in contact with the multilayer reflective film 20. The protective film 50 is made of a material containing ruthenium (Ru).

[0036] Examples of materials containing ruthenium (Ru) include ruthenium (Ru) alone and alloys made of ruthenium (Ru) and metals or metalloids different from ruthenium (Ru). Examples of metals or metalloids different from ruthenium (Ru) include niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si). The content of metals or metalloids different from ruthenium (Ru) in the protective film 50 is preferably 30 atomic % or less, and more preferably 20 atomic % or less. The lower limit of the content of metals or metalloids different from ruthenium (Ru) in the protective film 50 is not particularly limited, but is preferably 5 atomic % or more, and more preferably 10 atomic % or more.

[0037] The protective film 50 may have a single layer structure or a multilayer structure in which multiple layers with different compositions are combined, and each layer constituting the single layer or multiple layers may have a gradient composition structure in which the composition changes continuously in the thickness direction. In particular, one or both of the side of the protective film 50 closest to the multilayer reflective film 20 (in the case of a multilayer structure, the layer closest to the multilayer reflective film 20) and the side furthest from the multilayer reflective film 20 (in the case of a multilayer structure, the layer furthest from the multilayer reflective film 20) may be made of ruthenium (Ru).

[0038] In addition, when the protective film 50 has a multilayer structure or a gradient composition structure, it is preferable that the content of a metal or metalloid other than ruthenium (Ru) increases from the multilayer reflective film side toward the side away from the multilayer reflective film in a part or all of the thickness direction of the protective film 50. In particular, when niobium (Nb) is contained as a metal or metalloid other than ruthenium (Ru), the inclusion of niobium (Nb) is also effective in improving resistance to dry etching using a gas containing chlorine (Cl) and oxygen (O), so it is preferable that the content of niobium (Nb) increases from the multilayer reflective film side toward the side away from the multilayer reflective film in a part or all of the thickness direction of the protective film 50.

[0039] In this embodiment, the dry etching using a gas containing chlorine (Cl) and oxygen (O) is specifically a chlorine (Cl 2 ) gas and oxygen (O 2 ) gas. The gas containing chlorine (Cl) and oxygen (O) may contain a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas.

[0040] The thickness of the protective film 50 is preferably 2 nm or more, more preferably 3 nm or more, and is preferably 5 nm or less, more preferably 4 nm or less. If the thickness of the protective film 50 is less than 2 nm, the function of protecting the multilayer reflective film becomes insufficient, and if the thickness exceeds 5 nm, the reflectance of EUV light decreases.

[0041] The protective film 50 is formed on a target that is a ruthenium (Ru) target, a metal or semimetal target different from ruthenium (Ru), specifically, a niobium (Nb) target, a rhenium (Re) target, a zirconium (Zr) target, a titanium (Ti) target, a chromium (Cr) target, a silicon (Si) target, or a target in which two or more types selected from niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr) and silicon (Si) are mixed. The target is a mixture of ruthenium (Ru) and one or more metals or semimetals different from ruthenium (Ru), selected from niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr) and silicon (Si), and is sputtered using a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as the sputtering gas. Magnetron sputtering is preferably used for sputtering.

[0042] A heat treatment may be performed after the formation of the multilayer reflective film 20 or the protective film 50. The heat treatment can suppress fluctuations in characteristics such as the reflectance to EUV light when heat is applied during the formation of the mask pattern. The heat treatment temperature is generally preferably 120° C. or higher and 150° C. or lower. Temperatures higher than 150° C. are not preferred because they reduce the reflectance to EUV light.

[0043] The heat treatment may be performed after the formation of either the multilayer reflective film 20 or the protective film 50, or both. However, from the standpoint of concerns about defect adhesion and productivity, it is better to perform the heat treatment as few times as possible, and it is preferable to perform the heat treatment after the formation of the protective film 50.

[0044] On the other hand, when a heat treatment is performed after the formation of the protective film 50, an oxide film may be formed on the surface of the protective film 50, and the reflectance to the pattern inspection light may decrease. Even if a heat treatment is not performed after the formation of the protective film 50, the surface layer of the protective film 50 may be oxidized after the pattern is formed. Therefore, the reflectance of the absorbing film 70 to the pattern inspection light needs to be set to a reflectance that assumes that the protective film 50 will be oxidized.

[0045] The absorbing film 70 has a single layer structure made of Ta and N, and may have a natural oxide layer formed by exposing the absorbing film 70 to the atmosphere after the formation of the absorbing film 70. Also, after the formation of the absorbing film 70, a heat treatment at 150° C. may be performed for the purpose of adjusting the film stress, and an oxide film may be formed by the heat treatment. In this case, it is preferable that the oxide film formed on the surface layer is as thin as possible, 2 nm or less, and more preferably 1 nm or less. If the oxide film on the surface layer is formed thick, the oxide film has a slower etch rate than a layer that is not oxidized, which is a cause of deterioration of the pattern shape, and is therefore undesirable.

[0046] The absorbing film 70 preferably contains 30% to 60% nitrogen, more preferably 40% to 55% nitrogen. If the nitrogen content is less than 30%, the reflected light relative to the pattern inspection light becomes too high, resulting in low reflectance contrast. On the other hand, if the nitrogen content is more than 60%, it is not preferable because it causes problems such as the EUV light being less absorbed and the sheet resistance of the absorbing film 70 becoming too high.

[0047] The contrast is defined as follows. Contrast(%)=((Rc)-(Ra)) / (Rc+Ra))×100 Rc: Reflectance of the protective film 50 to the inspection light Ra: Reflectance of the absorbing film 70 to the inspection light The higher the contrast against the pattern inspection light, the better. Specifically, 20% or more is preferable, and 25% or more is more preferable. If it is 15% or less, there is a high possibility that the edge of the pattern or an abnormal part cannot be detected.

[0048] The thickness of the absorbing film 70 containing Ta is preferably 50 nm to 80 nm, more preferably 55 nm to 70 nm, including all layers. The sheet resistance of the absorbing film 70 is preferably 10^6 Ω / □ or less, more preferably 10^5 Ω / □ or less. The surface roughness Sq of the absorbing film 70 is preferably 0.8 nm or less, more preferably 0.6 nm or less. If the absorbing film 70 formed of a single layer film made of tantalum (Ta) and nitrogen (N) is less than 50 nm, the reflectance of the absorber film part to EUV light does not decrease sufficiently during mask creation, making it difficult to obtain sufficient contrast with the opening, and if it exceeds 80 nm, the wafer transfer performance deteriorates due to the influence of the three-dimensional effect during exposure.

[0049] The absorbing film 70 can be formed by sputtering, and magnetron sputtering is preferable. Sputtering using a tantalum (Ta) target or a target containing tantalum (Ta) and nitrogen (N) and a rare gas such as helium (He) gas, neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as a sputtering gas, or a rare gas together with nitrogen (N 2 ) gas, by reactive sputtering.

[0050] As shown in FIG. 3, an etching mask film 170 having different etching characteristics from the absorbing film 70 can be provided on the side of the absorbing film 70 away from the substrate 10 as an etching mask film 170 of the absorbing film 70. This etching mask film 170 functions as an etching mask when the absorbing film 70 is dry-etched. The etching mask film 170 is preferably provided in contact with the absorbing film 70. The etching mask film 170 may be a single layer or a multilayer. The etching mask film 170 is preferably a film containing Cr, and examples of the etching mask film 170 include CrN, CrO, CrON, and CrCON. The thickness of the etching mask film 170 is not particularly limited, but if it is too thin, it may not function as an etching mask, and if it is too thick, processing characteristics may deteriorate. Therefore, the thickness is preferably 1 nm or more, more preferably 2 nm or more, and even more preferably 5 nm or more, and is preferably 20 nm or less, and more preferably 10 nm or less.

[0051] The etching mask film 170 can be formed by sputtering. Specifically, when a material containing chromium (Cr) is used, a target is appropriately selected from a chromium (Cr) target or a chromium (Cr) compound target (a target containing chromium (Cr) and oxygen (O), nitrogen (N), carbon (C), etc.), and when a material containing tantalum (Ta) is used, a target is appropriately selected from a tantalum (Ta) target or a tantalum (Ta) compound target (a target containing tantalum (Ta) and oxygen (O), nitrogen (N), carbon (C), boron (B), etc.), depending on the composition. Sputtering is performed using a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as a sputtering gas, or a rare gas containing an oxygen-containing gas, a nitrogen-containing gas, or a carbon-containing gas, specifically, oxygen (O 2 ) gas, nitrogen (N 2 ) gas, nitrogen oxide (N 2 O, NO, NO 2 ) gas, carbon oxide (CO, CO 2 ) gas, hydrogen (H 2) gas, hydrocarbon gas (e.g., methane CH 4 The layer can be formed by reactive sputtering using a reactive gas such as a ferroelectric gas, etc. The sputtering is preferably magnetron sputtering.

[0052] A conductive film (rear surface conductive film 30) used for electrostatically chucking the reflective mask to an exposure tool (e.g., an EUV scanner) may be provided on the other main surface (rear surface), which is the surface opposite to the one main surface of the substrate 10, preferably in contact with the other main surface.

[0053] The back conductive film 30 preferably has a sheet resistance of 100Ω / □ or less, and there is no particular restriction on the material. Examples of the material of the back conductive film 30 include materials containing tantalum (Ta) or chromium (Cr). The material containing tantalum (Ta) may contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc., and the material containing chromium (Cr) may contain oxygen (O), nitrogen (N), carbon (C), etc. Examples of the material containing tantalum (Ta) include Ta alone and tantalum (Ta) compounds such as TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, and TaCONB. Examples of the material containing chromium (Cr) include Cr alone and chromium (Cr) compounds such as CrO, CrN, CrON, CrC, CrCN, CrCO, and CrCON.

[0054] The thickness of the back surface conductive film 30 is not particularly limited as long as it functions as an electrostatic chuck, but is usually about 20 to 300 nm. The thickness of the back surface conductive film 30 is preferably formed so that the film stress is balanced with the film and the film pattern formed on one main surface (front surface) side after forming it as a reflective mask, that is, after forming the pattern of the absorbing film 70 (see FIG. 2). The back surface conductive film 30 may be formed before forming the multilayer reflective film 20, or after forming all the films on the multilayer reflective film side of the substrate 10. Also, the back surface conductive film 30 may be formed after forming a part of the films on the multilayer reflective film side of the substrate 10, and then the remaining films on the multilayer reflective film side of the substrate 10 may be formed. The back surface conductive film 30 can be formed, for example, by magnetron sputtering.

[0055] 4, the reflective mask blank may have a resist film 190 formed on the side furthest from the substrate 10. The resist film 190 is preferably an electron beam (EB) resist.

[0056] From the reflective mask blank, for example, a reflective mask having a substrate 10, a multilayer reflective film 20 formed on one main surface of the substrate 10, a protective film 50 formed in contact with the multilayer reflective film 20, and a pattern of an absorbing film 70 (absorbing film pattern) can be manufactured. In the reflective mask, a transfer pattern is formed due to the difference in reflectance between a portion where the absorbing film 70 is formed and a portion where the absorbing film 70 is not formed.

[0057] The reflective mask is providing a reflective mask blank; If necessary, a step of forming a resist film 190 on the absorbing film 70; forming a resist pattern from the resist film 190 on the absorbing film 70; a step of etching the absorbing film 70 using the resist pattern as an etching mask to form a pattern of the absorbing film 70; and removing the resist pattern.

[0058] The absorbing film 70 formed of a material containing tantalum (Ta) and nitrogen (N) can be etched by dry etching using a gas containing chlorine (Cl) or a gas containing fluorine (F).

[0059] In addition, the reflective mask is providing a reflective mask blank; If necessary, a step of forming a resist film 190 on the etching mask film 170; forming a resist pattern from a resist film 190 on the etching mask film 170; A process of forming a pattern of the etching mask film 170 by etching the etching mask film 170 using the resist pattern as an etching mask (see FIG. 5 ); a step of etching the absorbing film 70 using the pattern of the etching mask film 170 as an etching mask to form a pattern of the absorbing film 70 (see FIG. 2); removing the resist pattern; removing the pattern of the etching mask film 170; The method can be produced by a method comprising the steps of:

[0060] The etching mask film 170 is a film containing chromium (Cr), and the etching mask film 170 is patterned by dry etching using a gas containing chlorine (Cl) and oxygen (O) to form a pattern of the etching mask film 170. After the absorption film 70 is patterned using the pattern of the etching mask film 170 as an etching mask, the etching mask film 170 can be removed by dry etching using a gas containing chlorine (Cl) and oxygen (O). EXAMPLES

[0061] The present embodiment will be specifically described below with reference to examples and comparative examples, but the present embodiment is not limited to the following examples.

[0062] [Example 1] A 152 mm square, 6.35 mm thick low thermal expansion glass substrate (SiO 2 -TiO 2 A multilayer reflective film 20 having a thickness of 284 nm was formed on the main surface of a fluorine-based glass substrate (a fluorine-based glass substrate) by DC pulse magnetron sputtering using a molybdenum (Mo) target and a silicon (Si) target, with both targets facing the main surface of the substrate 10 and the substrate 10 rotating. Each target was attached to a sputtering device capable of mounting two targets and discharging the targets one by one or both simultaneously, and the substrate 10 was then placed thereon.

[0063] First, while argon (Ar) gas was flowing in the chamber, power was applied to the silicon (Si) target to form a silicon (Si) layer with a thickness of 4 nm, and the application of power to the silicon (Si) target was stopped. Next, while argon (Ar) gas was flowing in the chamber, power was applied to the molybdenum (Mo) target to form a molybdenum (Mo) layer with a thickness of 3 nm, and the application of power to the molybdenum (Mo) target was stopped. The operation of forming these silicon (Si) layer and molybdenum (Mo) layer was regarded as one cycle, and this was repeated 40 times to form the molybdenum (Mo) layer in the 40th cycle. Finally, a silicon (Si) layer with a thickness of 3 nm was formed by the above method, and a molybdenum (Mo) layer with a thickness of 0.5 nm was further formed thereon to form the multilayer reflective film 20.

[0064] A target was attached to another sputtering device, and after the formation of the multilayer reflective film 20, the substrate 10 on which the multilayer reflective film 20 was formed was placed from the sputtering device on which the multilayer reflective film 20 was formed via a transport path maintained in a vacuum state, without being taken out into the atmosphere. Next, a protective film 50 was formed on the multilayer reflective film 20 by DC pulse magnetron sputtering using a ruthenium (Ru) target, with the target facing the main surface of the substrate 10 and the substrate 10 rotating. At this time, power was applied to the ruthenium (Ru) target while argon (Ar) gas was flowing in the chamber, and a film of Ru having a thickness of 3.0 nm was formed.

[0065] Next, the substrate 10 on which the multilayer reflective film 20 and the protective film 50 were formed was subjected to a heat treatment in an air atmosphere at 150° C. for 15 minutes using a hot plate type heating device, thereby oxidizing the surface portion of the protective film 50.

[0066] The reflectance of the film obtained after the heat treatment was measured in the wavelength range of 193 nm to 248 nm using a UV-Vis-NIR spectrophotometer (SolidSpec3700, Shimadzu Corporation).

[0067] Next, an absorbing film 70 was formed on the heat-treated film by DC pulse magnetron sputtering using a tantalum (Ta) target, with the target facing the main surface of the substrate 10 and the substrate 10 rotating. At this time, power was applied to the tantalum (Ta) target while argon (Ar) gas and nitrogen (N) gas were flowing into the chamber, and a TaN film with a thickness of 70 nm was formed.

[0068] The reflectance of the obtained film was measured at wavelengths of 193 nm to 248 nm using the same UV-Vis-NIR spectrophotometer as above. The reflectance contrast was calculated from the reflectance before and after forming the absorbing film 70, and was 27.4% at wavelengths of 193 nm and 30.6% at 248 nm, indicating sufficient contrast against the pattern inspection light.

[0069] Next, the composition of the absorbing film 70 was measured using an X-ray photoelectron spectroscopy (XPS) device (K-Alpha, manufactured by Thermo Fisher Scientific), and it was found that tantalum (Ta) was 57 atomic % and nitrogen (N) was 43 atomic % of the total of tantalum (Ta) and nitrogen (N). In this case, a surface oxide layer was formed by natural oxidation in the atmosphere (thickness 1 nm). The oxygen content of the surface oxide layer was 20 atomic % of the total of tantalum (Ta), nitrogen (N) and oxygen (O) on the side of the surface oxide layer farthest from the substrate 10.

[0070] [Example 2] A multilayer reflective film 20 was formed in the same manner as in Example 1. A protective film 50 was formed on this multilayer reflective film 20 by DC pulse magnetron sputtering using a ruthenium (Ru) target and a niobium (Nb) target, with both targets facing the main surface of the substrate 10 and the substrate 10 being rotated.

[0071] Specifically, each target was mounted in a separate sputtering device capable of mounting two targets and discharging the targets one by one or both simultaneously, and after the formation of the multilayer reflective film 20, the substrate 10 on which the multilayer reflective film 20 was formed was placed from the sputtering device on which the multilayer reflective film 20 was formed via a transport path maintained in a vacuum state without being taken out into the atmosphere. Next, while flowing argon (Ar) gas into the chamber, power was applied simultaneously to the ruthenium (Ru) target and the niobium (Nb) target, and a film having a thickness of 3.9 nm and made of RuNb with a composition ratio of 88 atomic % of ruthenium (Ru) and 12 atomic % of niobium (Nb) was formed as the protective film 50.

[0072] Thereafter, similarly to Example 1, heat treatment was carried out at 150° C. for 15 minutes, and then the reflectance at wavelengths from 193 nm to 248 nm was measured using an ultraviolet-visible-near infrared spectrophotometer.

[0073] Furthermore, a film similar to that in Example 1 was formed on the protective film 50 as an absorbing film 70, that is, a film in which tantalum (Ta) was 57 atomic % and nitrogen (N) was 43 atomic % relative to the total of tantalum (Ta) and nitrogen (N). The reflectance was measured at wavelengths from 193 nm to 248 nm using an ultraviolet-visible-near infrared spectrophotometer. The reflectance contrast was calculated from the reflectance before and after the formation of the absorbing film 70, and was 24.9% at a wavelength of 193 nm and 26.0% at 248 nm, indicating sufficient contrast for the pattern inspection light.

[0074] [Example 3] A multilayer reflective film 20 was formed in the same manner as in Example 1. A protective film 50 was formed on this multilayer reflective film 20 by DC pulse magnetron sputtering using a ruthenium (Ru) target and a niobium (Nb) target, with both targets facing the main surface of the substrate 10 and the substrate 10 rotating. A film having a thickness of 3.6 nm and made of RuNb with a composition ratio of 85 atomic % of ruthenium (Ru) and 15 atomic % of niobium (Nb) was formed as the protective film 50 in the same manner as in Example 2, except for the power applied to each target when power is applied simultaneously to the ruthenium (Ru) target and the niobium (Nb) target.

[0075] Next, similarly to Example 1, heat treatment was carried out at 150° C. for 15 minutes, and thereafter, the reflectance at wavelengths from 193 nm to 248 nm was measured using an ultraviolet-visible-near infrared spectrophotometer.

[0076] Furthermore, an absorbing film 70 was formed on the protective film 50. In this case, the absorbing film 70 was formed with a thickness of 70 nm, containing 60 atomic % tantalum (Ta) and 40 atomic % nitrogen (N), in the same manner as in Example 1, except that the ratio of argon (Ar) gas and nitrogen (N) gas introduced into the chamber was changed. A surface oxide layer was formed (thickness 1 nm) by natural oxidation of this absorbing film 70 in the atmosphere. The oxygen content of the surface oxide layer was 22 atomic % with respect to the total of tantalum (Ta), nitrogen (N) and oxygen (O) on the side of the surface oxide layer farthest from the substrate 10.

[0077] Thereafter, the reflectance was measured from wavelengths of 193 nm to 248 nm using an ultraviolet-visible-near infrared spectrophotometer. The reflectance contrast was calculated from the reflectance before and after forming the absorbing film 70, and was found to be 22.1% at wavelengths of 193 nm and 27.3% at wavelengths of 248 nm, indicating sufficient contrast for the pattern inspection light.

[0078] [Example 4] A multilayer reflective film 20 was formed in the same manner as in Example 1. A protective film 50 was formed on this multilayer reflective film 20 by DC pulse magnetron sputtering using a ruthenium (Ru) target and a niobium (Nb) target, with both targets facing the main surface of the substrate 10 and the substrate 10 rotating. A film having a thickness of 3.9 nm and made of RuNb with a composition ratio of 82 atomic % of ruthenium (Ru) and 18 atomic % of niobium (Nb) was formed as the protective film 50 in the same manner as in Example 2, except for the power applied to each target when power is applied simultaneously to the ruthenium (Ru) target and the niobium (Nb) target.

[0079] Next, similarly to Example 1, heat treatment was carried out at 150° C. for 15 minutes, and thereafter, the reflectance at wavelengths from 193 nm to 248 nm was measured using an ultraviolet-visible-near infrared spectrophotometer.

[0080] Furthermore, an absorbing film 70 having a thickness of 70 nm and containing 70 atomic % tantalum (Ta) and 30 atomic % nitrogen (N) was formed on the protective film 50 in the same manner as in Example 1, except that the ratio of argon (Ar) gas and nitrogen (N) gas introduced into the chamber was changed. A surface oxide layer was formed by natural oxidation of this absorbing film 70 in the atmosphere (thickness 1.3 nm). The oxygen content of the surface oxide layer was 30 atomic % relative to the total of tantalum (Ta), nitrogen (N) and oxygen (O) on the side of the surface oxide layer farthest from the substrate 10.

[0081] Thereafter, the reflectance was measured from wavelengths of 193 nm to 248 nm using an ultraviolet-visible-near infrared spectrophotometer. The reflectance contrast was calculated from the reflectance before and after forming the absorbing film 70, and was 21.1% at wavelengths of 193 nm and 28.0% at wavelengths of 248 nm, indicating sufficient contrast for the pattern inspection light.

[0082] [Example 5] A multilayer reflective film 20 and a protective film 50 were formed in the same manner as in Example 3, and a heat treatment was carried out at 150° C. for 15 minutes in the same manner as in Example 1. Thereafter, the reflectance at wavelengths from 193 nm to 248 nm was measured using an ultraviolet-visible-near infrared spectrophotometer.

[0083] The absorbing film 70 was formed in the same manner as in Example 1, except that the film thickness was 61 nm (tantalum (Ta) was 57 atomic % and nitrogen (N) was 43 atomic % relative to the total of tantalum (Ta) and nitrogen (N)), and then the reflectance was measured at wavelengths of 193 nm to 248 nm using an ultraviolet-visible-near infrared spectrophotometer. The reflectance contrast was calculated from the reflectance before and after forming the absorbing film 70, and was 22.5% at a wavelength of 193 nm and 26.5% at 248 nm, indicating sufficient contrast for the pattern inspection light.

[0084] [Comparative Example 1] A multilayer reflective film 20 and a protective film 50 were formed in the same manner as in Example 2, and a heat treatment was carried out at 150°C for 15 minutes in the same manner as in Example 1. Thereafter, the reflectance at wavelengths from 193 nm to 248 nm was measured using an ultraviolet-visible-near infrared spectrophotometer.

[0085] Next, the absorbing film 70 was formed. When forming the absorbing film 70, nitrogen (N) gas was not introduced into the chamber, but only argon (Ar) gas was introduced, and power was applied to the tantalum (Ta) target to form a Ta film with a thickness of 70 nm. A surface oxide layer was formed by natural oxidation of this absorbing film 70 in the atmosphere (thickness 1.5 nm). The oxygen content of the surface oxide layer was 50 atomic % with respect to the total of tantalum (Ta), nitrogen (N) and oxygen (O) on the side of the surface oxide layer farthest from the substrate 10.

[0086] Thereafter, the reflectance was measured from wavelengths of 193 nm to 248 nm using an ultraviolet-visible-near infrared spectrophotometer. The reflectance contrast was calculated from the reflectance before and after forming the absorbing film 70, and was 8.2% at wavelengths of 193 nm and 17.1% at 248 nm, indicating that sufficient contrast was not obtained for the pattern inspection light.

[0087] [Comparative Example 2] A multilayer reflective film 20 and a protective film 50 were formed in the same manner as in Example 2, and a heat treatment was carried out at 150°C for 15 minutes in the same manner as in Example 1. Thereafter, the reflectance at wavelengths from 193 nm to 248 nm was measured using an ultraviolet-visible-near infrared spectrophotometer.

[0088] Next, the absorbing film 70 was formed in the same manner as in Example 1 except that the ratio of argon (Ar) gas and nitrogen (N) gas introduced into the chamber was changed, and the absorbing film 70 was formed to a thickness of 70 nm with 80 atomic % tantalum (Ta) and 20 atomic % nitrogen (N). A surface oxide layer was formed by natural oxidation of this absorbing film 70 in the atmosphere (thickness 1.5 nm). The oxygen content of the surface oxide layer was 45 atomic % with respect to the total of tantalum (Ta), nitrogen (N) and oxygen (O) on the side of the surface oxide layer farthest from the substrate 10.

[0089] Thereafter, the reflectance was measured from wavelengths of 193 nm to 248 nm using an ultraviolet-visible-near infrared spectrophotometer. The reflectance contrast was calculated from the reflectance before and after forming the absorbing film 70, and was found to be 17.0% at wavelengths of 193 nm and 20.2% at wavelengths of 248 nm, indicating that sufficient contrast was not obtained for the pattern inspection light.

[0090] [Comparative Example 3] A multilayer reflective film 20 and a protective film 50 were formed in the same manner as in Example 2, and a heat treatment was carried out at 150°C for 15 minutes in the same manner as in Example 1. Thereafter, the reflectance at wavelengths from 193 nm to 248 nm was measured using an ultraviolet-visible-near infrared spectrophotometer.

[0091] Next, the absorbing film 70 was formed. In this case, similarly to Comparative Example 2, a film having a thickness of 66 nm and containing 80 atomic % tantalum (Ta) and 20 atomic % nitrogen (N) was formed, and then argon (Ar) gas and oxygen (O) were introduced into the same chamber to form an oxide film having a thickness of 4 nm and containing 40 atomic % tantalum (Ta) and 60 atomic % oxygen (O), thereby forming the absorbing film 70 with a total thickness of 70 nm.

[0092] Thereafter, the reflectance was measured from wavelengths of 193 nm to 248 nm using an ultraviolet-visible-near infrared spectrophotometer. The reflectance contrast was calculated from the reflectance before and after forming the absorbing film 70, and was 27.8% at wavelengths of 193 nm and 39.8% at 248 nm, indicating sufficient contrast against the pattern inspection light.

[0093] On the other hand, since the oxide film portion is thick and has a high degree of oxidation, the etching rate during processing of the oxidized portion is slower than that of the non-oxidized portion, which raises concerns about deterioration of the cross-sectional shape of the pattern. [Explanation of symbols]

[0094] 10 Substrate 20 Reflective multilayer film 50 Protective film 70 Absorbing Membrane 170 Etching mask film

Claims

1. A reflective mask blank serving as a material for a reflective mask used in EUV lithography using EUV light as exposure light, A substrate; a reflective multilayer film formed on one main surface of the substrate and reflecting exposure light; a protective film formed in contact with the reflective multilayer film; an absorbing film formed on the protective film for absorbing exposure light; Equipped with The protective film is formed of a film containing ruthenium (Ru), The absorbing film is formed of a single layer film made of tantalum (Ta) and nitrogen (N), and the nitrogen content is 30 atomic % or more and less than 60 atomic %, A mask blank, characterized in that the contrast between light reflected from the surface of the protective film and light reflected from the surface of the absorbing film for light having a wavelength of 193 nm to 248 nm is 20% or more.

2. 2. The reflective mask blank according to claim 1, wherein the absorbing film has a thickness of 50 nm or more and 80 nm or less.

3. 2. The reflective mask blank according to claim 1, wherein the protective film is made of ruthenium (Ru) or ruthenium (Ru) and niobium (Nb).

4. 3. The reflective mask blank according to claim 1, wherein the protective film has a thickness of 2 nm or more and 5 nm or less.

5. 3. The reflective mask blank according to claim 1, further comprising an etching mask film containing Cr used as an etching mask when processing the absorbing film.

6. A method for producing a reflective mask blank, comprising the steps of: producing the reflective mask blank according to claim 1 or 2 by sputtering deposition.

7. 7. The method for producing a reflective mask blank according to claim 6, characterized in that after the absorption film is formed on the surface away from the substrate, an oxide layer having a thickness of 2 nm or less is formed by exposing the absorption film to the atmosphere or by performing a heat treatment at a temperature of 150° C. or less in an atmospheric air.

8. 8. The method for producing a reflective mask blank according to claim 6, wherein the protective film is made of ruthenium (Ru) or ruthenium (Ru) and niobium (Nb), and after the protective film is formed, a heat treatment is performed at 150° C. or less in the atmosphere.

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