Reflective mask blank

Abstract

SOLUTION: A reflective mask blank having a substrate, a multilayer reflective film formed on the substrate and configured to reflect exposure light, a protective film formed on the multilayer reflective film, and an absorber film formed in contact with the protective film and configured to absorb the exposure light, the reflective mask blank being a material of a reflective mask used in EUV lithography using EUV light as exposure light, the absorber film includes a main region occupying 94% or more of a thickness of the absorber film, and the main region is composed of multiple layers including one or more layers of each of a low degree of nitriding layer consisting of tantalum (Ta) and nitrogen (N) and containing nitrogen (N) at 20 atom% or less and a high degree of nitriding layer containing nitrogen (N) at 40 atom% or more and 60 atom% or less.EFFECT: Since the reflective mask blank of the present disclosure has low film stress of the absorber film and low surface roughness, it is possible to manufacture a reflective mask having good pattern transfer performance and good sensitivity in defect inspection of the pattern of the absorber film.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. [Background technology]

[0002] In the manufacturing process of semiconductor devices (semiconductor devices), 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 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, the formation of even finer patterns is becoming necessary. Therefore, extreme ultraviolet (EUV) lithography technology, which uses EUV light, which has an even shorter wavelength than ArF excimer laser light, as exposure light, has begun to be used. EUV light is light with a wavelength of approximately 0.2 to 100 nm, more specifically, light with a wavelength of approximately 13.5 nm. This EUV light has extremely low transmittance through materials, making conventional transmission-type projection optics and masks incompatible, so 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 an absorber film that absorbs EUV light formed in a pattern on the multilayer reflective film. On the other hand, a mask in the state before the absorber film is patterned (including a mask with a resist film formed thereon) is called a reflective mask blank, and this is used as the material for reflective masks. 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 absorber film that absorbs EUV light formed thereon.

[0005] The multilayer reflective film is usually formed by alternately stacking molybdenum (Mo) and silicon (Si) layers to obtain the required reflectivity for EUV light, while the absorber film is made of tantalum (Ta), which has a relatively large extinction coefficient for EUV light (Japanese Patent Laid-Open Publication No. 2002-246299 (Patent Document 1)).

[0006] Furthermore, as described in Japanese Patent Laid-Open Publication No. 2002-122981 (Patent Document 2), a ruthenium (Ru) film is formed on the multilayer reflective film as a protective film for protecting the multilayer reflective film. Also, a hard mask film containing chromium (Cr) may be formed on the absorber film as an etching mask when forming a pattern on the absorber film. Meanwhile, a backside conductive film is formed on the other main surface of the substrate. For electrostatic chucking, a metal nitride film is used as the backside conductive film, and examples thereof include films containing chromium (Cr) and tantalum (Ta). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-246299 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-122981 Summary of the Invention [Problem to be solved by the invention]

[0008] When manufacturing a reflective mask from a reflective mask blank, the absorber film is partially removed to form a pattern. Therefore, after forming the pattern on the absorber film, the stress in the film is released, causing changes in the surface shape of the substrate, such as warping. To transfer a fine pattern to a semiconductor substrate or the like with high precision using a reflective mask, it is necessary to minimize changes in the surface shape of the substrate, and to minimize deformation of the substrate due to film stress of the absorber film formed on the substrate before pattern formation. Furthermore, since high surface roughness reduces defect detection sensitivity, the surface roughness of the absorber film must be made smoother.

[0009] The present invention has been made to solve the above-mentioned problems, and aims to provide a reflective mask blank with low film stress and low surface roughness of the absorber film, which can be used to manufacture a reflective mask with good pattern transfer performance of the absorber film and good sensitivity in pattern defect inspection. [Means for solving the problem]

[0010] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that in a reflective mask blank having a substrate, a multilayer reflective film, a protective film, and an absorber film, by making the absorber film include a main region composed of multiple layers including one or more low-degree-nitridation layers made of tantalum (Ta) and nitrogen (N) and containing nitrogen (N) at 20 atomic % or less and one or more high-degree-nitridation layers containing nitrogen (N) at 40 atomic % or more and 60 atomic % or less, it is possible to achieve both good film stress and good surface roughness, leading to the present invention.

[0011] Therefore, the present invention provides the following reflective mask blank. 1. A reflective mask blank that serves as a material for a reflective mask used in EUV lithography using EUV light as the exposure light, comprising: a substrate; a multilayer reflective film formed on the substrate and reflecting exposure light; a protective film formed on the multilayer reflective film; and an absorber film formed in contact with the protective film and absorbing exposure light, the absorber film includes a main region that occupies 94% or more of the thickness of the absorber film; The main region is made of tantalum (Ta) and nitrogen (N), and is composed of multiple layers including at least one low-nitriding layer containing 20 atomic % or less of nitrogen (N) and at least one high-nitriding layer containing 40 atomic % or more and 60 atomic % or less of nitrogen (N). A reflective mask blank characterized by: 2. The reflective mask blank according to 1, wherein the absorber film is formed only in the main region. 3. The absorber film is The main region and a substrate side region that contacts the main region on the substrate side, from the main region and a surface side region in contact with the side of the main region away from the substrate, or The main region, a substrate side region that contacts the main region on the substrate side, and a surface side region that contacts the main region on the side away from the substrate And the substrate-side region contains tantalum (Ta), nitrogen (N), and an element contained in the protective film, and has a thickness of 1 nm or less; The surface-side region contains tantalum (Ta), nitrogen (N), and oxygen (O), and has a thickness of 2 nm or less. 2. The reflective mask blank according to claim 1. 4. The reflective mask blank according to 1, further comprising an etching mask film formed in contact with the absorber film. 5. The reflective mask blank according to 4, wherein the absorber film is formed only in the main region. 6. The absorber film is The main region and a substrate side region that contacts the main region on the substrate side, from the main region and a surface side region in contact with the side of the main region away from the substrate, or The main region, a substrate side region that contacts the main region on the substrate side, and a surface side region that contacts the main region on the side away from the substrate And the substrate-side region contains tantalum (Ta), nitrogen (N), and an element contained in the protective film, and has a thickness of 1 nm or less; The surface side region contains tantalum (Ta), nitrogen (N), and the elements contained in the etching mask film, and has a thickness of 1 nm or less. 5. The reflective mask blank according to 4. 7. The reflective mask blank according to 6, wherein the front side region further contains oxygen (O). 8. A reflective mask blank according to any one of 1 to 7, wherein the thickness of the absorber film is 50 nm or more and 80 nm or less. 9. A reflective mask blank according to any one of 1 to 7, wherein the layer of the main region farthest from the substrate is the high-nitridation layer. 10. The reflective mask blank according to 9, wherein the absorber film has a reflectance of 35% or less for light having a wavelength in the range of 193 to 260 nm. 11. A reflective mask blank according to any one of 1 to 7, wherein the main region comprises the low-nitridation layer and the high-nitridation layer. 12. A reflective mask blank as described in 11, characterized in that the layer of the main region closest to the substrate is the low-nitridation layer, the thickness of the low-nitridation layer is 0.3 nm or more and 2 nm or less, and the layers other than the layer closest to the substrate are the high-nitridation layers. 13. The reflective mask blank according to 12, wherein the absorber film has a reflectance of 35% or less for light having a wavelength in the range of 193 to 260 nm. 14. A reflective mask blank described in any one of 1 to 7, characterized in that the main region has a structure in which the low-nitridation layer and the high-nitridation layer are alternately stacked, and the thickness of each layer is 3 nm or more and 30 nm or less. 15. A reflective mask blank according to any one of 1 to 7, wherein the absorber film has a surface roughness Sq of 0.6 nm or less. 16. A reflective mask blank described in any one of 1 to 7, characterized in that the absorber film is a film that, when formed on the main surface of a substrate measuring 152 mm square and 6.35 mm thick, imparts to the substrate a warpage change ΔTIR ranging from +0.2 μm due to tensile stress to −0.5 μm due to compressive stress. 17. A reflective mask blank according to any one of 1 to 7, wherein the protective film contains ruthenium (Ru). [Effects of the Invention]

[0012] The reflective mask blank of the present invention has a small film stress in the absorber film and low surface roughness, and therefore can produce a reflective mask with good pattern transfer performance and good sensitivity in defect inspection of the absorber film pattern. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a reflective mask blank of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing another example of the reflective mask blank of the present invention. [Figure 3] FIG. 1 is a cross-sectional view showing an example of a main region of an absorber film in the present invention, which is composed of two layers, a low-nitridation layer and a high-nitridation layer, from the substrate side. [Figure 4] FIG. 10 is a cross-sectional view showing another example of the main region of the light absorbing film of the present invention, which shows an example in which the film is composed of four layers, from the substrate side, namely, a low-nitridation layer, a high-nitridation layer, a low-nitridation layer, and a high-nitridation layer, with the low-nitridation layer and the high-nitridation layer being alternately stacked. [Figure 5] 1 is a cross-sectional view showing an example of a reflective mask of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in more detail below. The reflective mask blank of the present invention comprises a substrate, a multilayer reflective film formed on the substrate and reflecting exposure light, a protective film formed on the multilayer reflective film, and an absorber film formed in contact with the protective film and absorbing exposure light.

[0015] The reflective mask blank of the present invention is suitable as a material for a reflective mask used in EUV lithography using EUV light as the exposure light. The wavelength of the EUV light used in EUV lithography using EUV light as the exposure light is 13 to 14 nm, and typically 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 an EUV mask blank and an EUV mask, respectively.

[0016] 1 is a cross-sectional view showing an example of a reflective mask blank of the present invention. This reflective mask blank 101 has a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1, a protective film 3 formed on the multilayer reflective film 2 in contact with the multilayer reflective film 2, and an absorber film 4 formed on the protective film 3.

[0017] The reflective mask blank of the present invention may further have another film, such as an etching mask film, formed in contact with the absorber film.

[0018] 2 is a cross-sectional view showing another example of a reflective mask blank of the present invention. This reflective mask blank 102 has a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1, a protective film 3 formed in contact with the multilayer reflective film 2, an absorber film 4 formed in contact with the protective film 3, and an etching mask film 5 formed in contact with the absorber film 4.

[0019] The substrate preferably has low thermal expansion characteristics for use in EUV light exposure, and for example, has a thermal expansion coefficient of ±2×10 -8 / ℃, preferably ±5×10 -9Preferably, the substrate is made of a material with a temperature within a range of 1 / °C. Examples of such materials include titania-doped quartz glass (SiO2-TiO2-based glass). Furthermore, it is preferable to use a substrate with a sufficiently flat surface, and the surface roughness of the main surface of the substrate is preferably 0.5 nm or less, more preferably 0.2 nm or less, in terms of RMS value. Such surface roughness can be achieved by polishing the substrate, for example. The substrate preferably has a main surface size of 152 mm square and a thickness of 6.35 mm. A substrate 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).

[0020] The multilayer reflective film is a film in a reflective mask that reflects exposure light. The multilayer reflective film is preferably formed on one main surface (front surface) of the substrate and is provided in contact with the one main surface of the substrate, but another film such as an undercoat film may be provided between the multilayer reflective film and the one main surface of the substrate. The multilayer reflective film has a periodic stacking structure in which high-refractive index layers, which have a relatively high refractive index for exposure light, and low-refractive index layers, which have a relatively low refractive index for exposure light, are alternately stacked.

[0021] 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 consisting 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.

[0022] The low refractive index layer is preferably formed of a material containing molybdenum (Mo). Alternatively, the low refractive index layer may 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), or 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.

[0023] The periodic stacking structure may include a high-refractive index layer and a low-refractive index layer, and each period may include one or more high-refractive index layers and one or more low-refractive index layers. The number of layers included in each period is two or more, and one period may be, for example, one high-refractive index layer and one low-refractive index layer. Furthermore, one period may include two or more high-refractive index layers with different compositions (e.g., different composition ratios, different compositions depending on the presence or absence of an additive element, etc.), or two or more low-refractive index layers with different compositions (e.g., different composition ratios, different compositions depending on the presence or absence of an additive element, etc.). In this case, the number of layers included in each period is three or more, and may be four or more, five or more, but preferably eight or less. The number of periods in the periodic stacking structure is preferably 30 or more, and preferably 50 or less, more preferably 40 or less. When the low-refractive index layer is formed of a material containing ruthenium (Ru), the layer farthest from the substrate (the uppermost layer) of the periodic stacking structure is preferably a high-refractive index layer.

[0024] The thickness of the multilayer reflective film having a periodic stacked structure is adjusted depending on the exposure wavelength and the incident 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.

[0025] Methods for forming multilayer reflective films include sputtering, which applies power to a target and ionizes the ambient gas to form plasma, and ion beam sputtering, which irradiates the target with an ion beam. Sputtering methods include DC sputtering, which applies a direct current voltage to the target, and RF sputtering, which applies a radio frequency voltage to the target. Sputtering involves applying a voltage to the target while the sputtering gas is introduced into the chamber, ionizing the gas and utilizing the sputtering phenomenon caused by the gas ions. Magnetron sputtering, in particular, is advantageous in terms of productivity. The power applied to the target can be either DC or RF. DC also includes pulse sputtering, which briefly reverses the negative bias applied to the target to prevent target charging.

[0026] The multilayer reflective film can be formed by a sputtering method using, for example, a sputtering device capable of mounting multiple 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 using a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as the sputtering gas.

[0027] Furthermore, when sputtering is reactive sputtering using a reactive gas, for example, a nitrogen-containing gas such as nitrogen (N2) gas may be used together with the noble gas when forming a film containing nitrogen (N); an oxygen-containing gas such as oxygen (O2) gas may be used when forming a film containing oxygen (O); a nitrogen oxide gas such as nitrous oxide (NO) gas, nitric oxide (NO) gas, or nitrogen dioxide (NO2) gas may be used when forming a film containing nitrogen (N) and oxygen (O); a carbon oxide gas such as carbon monoxide (CO) gas or carbon dioxide (CO2) gas may be used when forming a film containing carbon (C) and oxygen (O); a hydrogen-containing gas such as hydrogen (H2) gas when forming a film containing hydrogen (H); or a hydrocarbon gas such as methane (CH4) gas when forming a film containing carbon (C) and hydrogen (H).

[0028] Furthermore, when forming a layer containing boron (B), a molybdenum (Mo) target doped with boron (B) (molybdenum boride (MoB) target), a ruthenium (Ru) target doped with boron (B) (ruthenium boride (RuB) target), a silicon (Si) target doped with boron (B) (silicon boride (SiB) target), or the like can be used.

[0029] The protective film is also called a capping film. The protective film is a film for protecting the multilayer reflective film. The protective film is usually provided in contact with the multilayer reflective film. The protective film is preferably formed of a material containing ruthenium (Ru).

[0030] Examples of materials containing ruthenium (Ru) include ruthenium (Ru) alone and alloys containing ruthenium (Ru) and a metal or semimetal other than ruthenium (Ru). Examples of metals or semimetals other than ruthenium (Ru) include niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si). The protective film is preferably made of ruthenium (Ru) or ruthenium (Ru) and niobium (Nb). The content of the metal or semimetal other than ruthenium (Ru) in the protective film is preferably 30 atomic % or less, more preferably 20 atomic % or less, on average throughout the film. The lower limit of the content of the metal or semimetal other than ruthenium (Ru) in the protective film is not particularly limited, but is preferably 5 atomic % or more, more preferably 10 atomic % or more, on average throughout the film.

[0031] The protective film may have a single layer structure or a multilayer structure combining multiple layers with different compositions, and each of the single layer and 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 closest to the multilayer reflective film (in the case of a multilayer structure, the layer closest to the multilayer reflective film) and the side furthest from the multilayer reflective film (in the case of a multilayer structure, the layer furthest from the multilayer reflective film) may be made of ruthenium (Ru).

[0032] Furthermore, when the protective film 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 part or all of the thickness direction of the protective film. In particular, when niobium (Nb) is contained as the 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 part or all of the thickness direction of the protective film.

[0033] In the present invention, the dry etching using a gas containing chlorine (Cl) and oxygen (O) specifically includes dry etching using a gas containing chlorine (Cl2) gas and oxygen (O2) 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.

[0034] The thickness of the protective film is preferably 2 nm or more, more preferably 3 nm or more, and preferably 5 nm or less, more preferably 4 nm or less. If the thickness of the protective film is less than 2 nm, the function of protecting the multilayer reflective film may be insufficient. On the other hand, if the thickness of the protective film exceeds 5 nm, the reflection of EUV light from the multilayer reflective film may not be sufficient.

[0035] The protective film is formed by sputtering a target appropriately selected from a ruthenium (Ru) target, a target of a metal or semimetal 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, a target in which two or more selected from niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr) and silicon (Si) are mixed, or a target in which ruthenium (Ru) is mixed with 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 the like, using a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as the sputtering gas. The sputtering is preferably magnetron sputtering.

[0036] Heat treatment may be performed after the formation of the multilayer reflective film and / or after the formation of the protective film. By performing heat treatment, fluctuations in properties such as reflectance for EUV light can be suppressed even if the multilayer reflective film or the protective film is subsequently heated. If heat treatment is performed too many times, there is a concern that defects may be attached, and also from the viewpoint of productivity, it is preferable to perform heat treatment only after the formation of the protective film. The heat treatment temperature is preferably 120°C or higher and 150°C or lower. If the heat treatment temperature is higher than 150°C, there is a risk that the reflectance for EUV light will decrease.

[0037] Note that the surface of the protective film may be oxidized by oxygen in the atmosphere during heat treatment, forming an oxide layer. Furthermore, even without heat treatment, when the protective film is exposed after the absorber film pattern is formed, the surface of the protective film may be oxidized by oxygen in the atmosphere, forming an oxide layer. In this case, the surface of the protective film preferably contains ruthenium (Ru) and oxygen (O), or ruthenium (Ru), a metal or semimetal other than ruthenium (Ru), and oxygen (O), and more preferably consists of ruthenium (Ru) and oxygen (O), or ruthenium (Ru), a metal or semimetal other than ruthenium (Ru), and oxygen (O). In this case, the reflectance of the protective film with respect to light used for pattern inspection of the absorber film is preferably set to a reflectance assuming that the protective film will be oxidized.

[0038] In a reflective mask, the absorber film is a film that absorbs exposure light and reduces reflectance. In a reflective mask, a transfer pattern is formed by the difference in reflectance between a portion where the absorber film is formed and a portion where the absorber film is not formed. In the present invention, the absorber film contains tantalum (Ta) and nitrogen (N). Furthermore, the absorber film of the present invention is composed of multiple layers.

[0039] The absorber film of the present invention includes a main region. The main region is composed of tantalum (Ta) and nitrogen (N). The main region is a multilayer structure including at least one low-nitridation layer containing 20 atomic % or less of nitrogen (N) and at least one high-nitridation layer containing 40 atomic % to 60 atomic % of nitrogen (N). The thickness of the main region is preferably at least 94%, more preferably at least 96%, and even more preferably at least 98% of the thickness of the absorber film. It is particularly preferable that the absorber film consists only of the main region (i.e., the thickness of the main region is 100% of the thickness of the absorber film). It is difficult to simultaneously control both film stress and surface roughness with a single-layer absorber film. However, by forming the absorber film into a multilayer structure including a low-nitridation layer and a high-nitridation layer, it is possible to achieve both good film stress and good surface roughness while ensuring the necessary absorption performance (extinction coefficient k) of the absorber film for exposure light.

[0040] 3 is a cross-sectional view showing an example of the main region of the absorber film of the present invention, which is composed of two layers, a low-nitrided layer and a high-nitrided layer, from the substrate side. In this case, the main region 41 is composed of a low-nitrided layer 411 provided on the side closest to the substrate and a high-nitrided layer 412 provided on the side farthest from the substrate. When the absorber film is formed only by the main region, this main region 41 corresponds to the absorber film 4.

[0041] Because films made of tantalum (Ta) and nitrogen (N) tend to have large surface roughness and film stress due to grain formation (crystallization) within the film, it is common to add other elements such as boron (B), silicon (Si), germanium (Ge), hydrogen (H), oxygen (O), and carbon (C) to form amorphous or microcrystalline structures, thereby reducing surface roughness and film stress. However, adding other elements can easily cause defects during film formation and can also deteriorate etching properties, cleaning resistance, and exposure resistance.

[0042] The main region of the absorber film of the present invention is made of tantalum (Ta) and nitrogen (N), which makes it less likely to produce defects during film formation and has good etching properties, cleaning resistance, exposure resistance, etc. Furthermore, since it is made up of multiple layers including one or more low-nitrided layers and one or more high-nitrided layers, it can achieve good film stress and good surface roughness. Furthermore, the construction of low-nitrided layers and high-nitrided layers is advantageous in that it can obtain the required absorption performance (extinction coefficient k) with a thinner thickness than a film made up of only high-nitrided layers.

[0043] The main region of the absorber film may include a medium-nitrided layer containing more than 20 atomic % and less than 40 atomic % nitrogen (N), but in the medium-nitrided layer, crystal grains of various compositions are likely to be formed, and when formed by reactive sputtering, the sputtering is difficult to control, which tends to increase film stress and surface roughness. Therefore, it is preferable that the main region of the absorber film does not include a medium-nitrided layer containing more than 20 atomic % and less than 40 atomic % nitrogen (N), and it is also preferable that the main region of the absorber film consists of a low-nitrided layer and a high-nitrided layer.

[0044] The nitrogen (N) content of the low-nitridation layer is 20 atomic % or less, preferably 15 atomic % or less. The nitrogen (N) content of the low-nitridation layer is not particularly limited, but is preferably 5 atomic % or more, more preferably 10 atomic % or more. On the other hand, the nitrogen (N) content of the high-nitridation layer is 40 atomic % or more, preferably 50 atomic % or more, and 60 atomic % or less, preferably 55 atomic % or less. The tantalum (Ta) contents of both the low-nitridation layer and the high-nitridation layer are the remainder of the nitrogen (N) content.

[0045] The main region of the absorber film may contain at least one low-nitriding layer and at least one high-nitriding layer, but the upper limit of the number of low-nitriding layers is preferably 5 or less, and the upper limit of the number of high-nitriding layers is preferably 5 or less. The numbers of low-nitriding layers and high-nitriding layers included in the main region of the absorber film may be the same or different.

[0046] The thickness of each of the low-nitriding layers is preferably 0.3 nm or more, more preferably 1 nm or more, even more preferably 2 nm or more, particularly preferably 3 nm or more, and especially preferably 5 nm or more, and is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 10 nm or less. The thickness of each of the high-nitriding layers is preferably 3 nm or more, more preferably 5 nm or more, and is preferably 80 nm or less, more preferably 70 nm or less, and even more preferably 65 nm or less.

[0047] The thickness of all low-nitridation layers included in the main region of the absorber film (the thickness of the layer if there is one, or the total thickness of the layers if there are two or more) is preferably 0.3 nm or more, more preferably 1 nm or more, even more preferably 2 nm or more, and is preferably 30 nm or less, more preferably 20 nm or less, even more preferably 10 nm or less. The thickness of all high-nitridation layers included in the main region of the absorber film (the thickness of the layer if there is one, or the total thickness of the layers if there are two or more) is preferably 30 nm or more, more preferably 40 nm or more, even more preferably 50 nm or more, and is preferably 80 nm or less, more preferably 70 nm or less, even more preferably 65 nm or less.

[0048] In the inspection of an absorber film, specifically, in the inspection of an absorber film pattern on a reflective mask after the absorber film pattern is formed, light with a wavelength of 193 to 260 nm may be used. In this case, if the layer farthest from the substrate in the main region of the absorber film is a low-nitridation layer, the reflectance is high. From the viewpoint of reducing the reflectance in the inspection of such an absorber film and increasing the contrast at the inspection wavelength of the absorber film, it is preferable that the layer farthest from the substrate in the main region of the absorber film is a high-nitridation layer.

[0049] In the main region of the absorber film, if the layer farthest from the substrate has a high degree of nitridation, the reflectance of the absorber film for light with a wavelength of 193 to 260 nm, which is used for inspecting the absorber film, specifically, for inspecting the absorber film pattern on a reflective mask after the absorber film pattern has been formed, can be reduced. In this case, the reflectance of the absorber film for any light with a wavelength of 193 to 260 nm, preferably for light with a wavelength within the range of 193 to 260 nm (the maximum reflectance within the range of 193 to 260 nm), is preferably 35% or less, more preferably 32% or less. This ensures a good contrast between the light reflected from the multilayer reflective film and the protective film and the light reflected from the absorber film, improving inspection sensitivity.

[0050] In the main region of the absorber film, the layer closest to the substrate is preferably a low-nitridation layer. The low-nitridation layer may be formed on the side closest to the substrate or on a side other than the side closest to the substrate (for example, the center of the substrate in the thickness direction), but it is more preferable that the low-nitridation layer be formed only on the side closest to the substrate. When the layer closest to the substrate is a low-nitridation layer, the growth pattern of the fine crystal grains in the high-nitridation layer formed in contact with the low-nitridation layer differs from that when a high-nitridation layer is formed directly on the protective film, which is advantageous in terms of film stress and surface roughness, as it is possible to simultaneously obtain better film stress and better surface roughness.

[0051] In particular, if the low-nitridation layer is thin, preferably 2 nm or less, more preferably 1 nm or less, and the layers other than the layer closest to the substrate are high-nitridation layers, the low-nitridation layer, which has a different degree of nitridation from the high-nitridation layer, will only be present in the very thin portion in contact with the protective film, and the other portions will be high-nitridation layers, so that the etching characteristics of the absorber film can be made closer to that of a single-layer film over most of the absorber film, which is advantageous in terms of etching processability of the absorber film. In this case, the lower limit of the thickness of the low-nitridation layer is preferably 0.3 nm or more, more preferably 0.5 nm or more.

[0052] The main region of the absorber film may have a structure in which low-nitrided layers and high-nitrided layers are alternately stacked (alternate stack structure). By using a structure in which low-nitrided layers and high-nitrided layers are alternately stacked, the etching characteristics of the absorber film can be made closer to the etching characteristics of a single-layer film, which is advantageous in terms of the etching processability of the absorber film. In addition, the alternate stack structure is advantageous in that it can further reduce film stress.

[0053] 4 is a cross-sectional view showing another example of the main region of the absorber film of the present invention, which is an example composed of four layers, from the substrate side: a low-nitrided layer, a high-nitrided layer, another low-nitrided layer, and another high-nitrided layer. In this case, main region 41 consists of low-nitrided layer 411 provided closest to the substrate, high-nitrided layer 412 provided in contact with low-nitrided layer 411, low-nitrided layer 411 provided in contact with high-nitrided layer 412, and high-nitrided layer 412 provided in contact with low-nitrided layer 411 and farthest from the substrate. When the absorber film is formed only by the main region, main region 41 corresponds to absorber film 4.

[0054] When the main region of the absorber film has an alternating laminate structure, the thinner the layer thickness, the closer the etching characteristics of the absorber film can be to that of a single layer film, so the thickness of each layer is preferably 30 nm or less, more preferably 15 nm or less, and even more preferably 10 nm or less. On the other hand, in consideration of productivity, the thickness of each layer is preferably 3 nm or more, more preferably 5 nm or more. Furthermore, when the main region of the absorber film has an alternating laminate structure, the number of low-nitridation layers and high-nitridation layers is each 2 or more, and preferably 4 or less. The total number of layers included in the alternating laminate structure is 4 or more, and preferably 8 or less.

[0055] The absorber film and each layer constituting the absorber film, particularly the main region of the absorber film and each layer constituting the main region, can be formed by sputtering, preferably magnetron sputtering. Specifically, the absorber film can be formed by sputtering using a target appropriately selected from a tantalum (Ta) target and a target consisting of 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 by reactive sputtering using nitrogen (N2) gas as a reactive gas together with the rare gas.

[0056] The absorber film of the present invention preferably consists of only a main region, but may also include the main region and one or both of a substrate-side region that contacts the substrate side of the main region and a surface-side region that contacts the side of the main region away from the substrate. When the absorber film includes the main region and one or both of the substrate-side region and the surface-side region, the absorber film is preferably composed of the main region and the substrate-side region, the main region and the surface-side region, or the main region, the substrate-side region, and the surface-side region.

[0057] The substrate-side region may be a region formed in the absorber film in contact with the protective film by mixing the elements contained in the protective film with tantalum (Ta) and nitrogen (N), which are the elements constituting the main region. In this case, the substrate-side region preferably contains tantalum (Ta), nitrogen (N), and the elements contained in the protective film, and is composed of tantalum (Ta), nitrogen (N), and the elements contained in the protective film. Such a substrate-side region may be formed over time or by heat treatment while the film is in contact.

[0058] When the substrate-side region contains elements other than tantalum (Ta) and nitrogen (N), the etching characteristics differ from when it contains only tantalum (Ta) and nitrogen (N). Therefore, the thickness of the substrate-side region is preferably 1 nm or less, and more preferably 0.5 nm or less.

[0059] On the other hand, the surface-side region may be a region (surface oxide layer) formed by mixing oxygen (O) with tantalum (Ta) and nitrogen (N), which are elements constituting the main region. In this case, the surface-side region preferably contains tantalum (Ta), nitrogen (N), and oxygen (O), and is made of tantalum (Ta), nitrogen (N), and oxygen (O).

[0060] The surface-side region may be formed by mixing the elements constituting the main region, tantalum (Ta) and nitrogen (N), with elements contained in a film (e.g., an etching mask film) formed in contact with the absorber film. In this case, the surface-side region contains tantalum (Ta), nitrogen (N), and elements contained in the film formed in contact with the absorber film, and is preferably composed of tantalum (Ta), nitrogen (N), and elements contained in the film formed in contact with the absorber film. Such a surface-side region may be formed over time or by heat treatment while the film is in contact. In this case, the surface-side region may also contain oxygen (O).

[0061] The surface-side region containing oxygen (O) can be formed by natural oxidation in the air or by oxidation by heat treatment in an oxygen-containing atmosphere such as the air at a temperature of, for example, 200°C or less. When the surface-side region contains oxygen (O), the oxygen (O) content is preferably 20 atomic % or more and preferably 40 atomic % or less. Furthermore, the ratio of tantalum (Ta) to nitrogen (N) in the surface-side region is preferably the same as the ratio of tantalum (Ta) to nitrogen (N) in the portion of the main region that contacts the surface-side region.

[0062] When the surface-side region contains elements other than tantalum (Ta) and nitrogen (N), the etching characteristics will be different from when it contains only tantalum (Ta) and nitrogen (N). In particular, when the surface-side region contains oxygen (O), the processability may be reduced compared to when it contains only tantalum (Ta) and nitrogen (N). Therefore, the thickness of the surface-side region is preferably 2 nm or less, more preferably 1 nm or less, and even more preferably 0.5 nm or less.

[0063] The surface roughness Sq of the absorber film is preferably 0.6 nm or less, more preferably 0.5 nm or less. Furthermore, the absorber film is preferably a film that, when formed on the main surface of a 152 mm square, 6.35 mm thick substrate, imparts a warpage change ΔTIR to the substrate within the range of +0.2 μm due to tensile stress to −0.5 μm due to compressive stress.

[0064] From the viewpoint of obtaining the necessary optical properties of the absorber film against exposure light, the thickness of the absorber film (total thickness of the absorber film) is preferably 50 nm or more, more preferably 55 nm or more, and also preferably 81 nm or less, more preferably 80 nm or less, and even more preferably 70 nm or less. When the absorber film consists of only the main region, the thickness of the main region is the total thickness of the absorber film. When the absorber film consists of the main region and one or both of the substrate-side region and the surface-side region, the thickness of the main region is the thickness obtained by excluding the thicknesses of the substrate-side region and the surface-side region from the total thickness of the absorber film.

[0065] An etching mask film having etching characteristics different from those of the absorber film can be provided on the side of the absorber film that is away from the substrate as a hard mask for the absorber film. This etching mask film functions as a hard mask when dry etching the absorber film. The etching mask film is preferably provided in contact with the absorber film. The etching mask film may be a single layer or a multilayer.

[0066] The etching mask film preferably contains chromium (Cr), and is preferably formed from a material containing chromium (Cr). When processing an absorber film formed from a material containing tantalum (Ta), the material containing chromium (Cr) has different etching characteristics from the absorber film and functions as an etching mask when dry etching the absorber film. Therefore, the chromium (Cr)-containing material of the etching mask film preferably does not contain tantalum (Ta). Furthermore, the chromium (Cr)-containing material of the etching mask film preferably does not contain carbon (C). Examples of materials containing chromium (Cr) include simple Cr, CrO, CrN, and CrON.

[0067] The thickness of the etching mask film is not particularly limited, but if it is too thin, it may not function as a hard mask, and if it is too thick, processing characteristics may be deteriorated. 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.

[0068] The etching mask film can be formed by sputtering. Specifically, a chromium (Cr) target or a chromium (Cr) compound target (a target containing chromium (Cr), oxygen (O), nitrogen (N), or the like) is appropriately selected and used, and a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas is used as the sputtering gas. Alternatively, the etching mask film can be formed by reactive sputtering using a rare gas together with an oxygen-containing gas or a nitrogen-containing gas, specifically, oxygen (O) gas, nitrogen (N) gas, or nitrogen oxide (N0, NO, NO) gas. Magnetron sputtering is preferred for sputtering.

[0069] A conductive film (back surface conductive film) used for electrostatically chucking the reflective mask to an exposure device (e.g., an EUV scanner) may be provided on the other main surface (back surface), which is the surface opposite to the one main surface of the substrate, preferably in contact with the other main surface.

[0070] The backside conductive film preferably has a sheet resistance of 100 Ω / □ or less, and there are no particular limitations on the material. Examples of materials for the backside conductive film include materials containing tantalum (Ta) or chromium (Cr). Furthermore, materials containing tantalum (Ta) may contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc., while materials containing chromium (Cr) may contain oxygen (O), nitrogen (N), carbon (C), etc. Examples of materials containing tantalum (Ta) include elemental Ta and tantalum (Ta) compounds such as TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, and TaCONB. Specific examples of materials containing chromium (Cr) include elemental Cr and chromium (Cr) compounds such as CrO, CrN, CrON, CrC, CrCN, CrCO, and CrCON.

[0071] The thickness of the back surface conductive film 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 is preferably such that the film stress is balanced with the film and film pattern formed on one main surface (front surface) after it is formed as a reflective mask, i.e., after the absorber film pattern is formed. The back surface conductive film may be formed before forming the multilayer reflective film or after forming all of the films on the multilayer reflective film side of the substrate. Alternatively, the back surface conductive film may be formed after forming a portion of the films on the multilayer reflective film side of the substrate, and then the remaining films on the multilayer reflective film side of the substrate may be formed. The back surface conductive film may be formed, for example, by magnetron sputtering.

[0072] The reflective mask blank of the present invention may have a resist film formed on the side farthest from the substrate. The resist film is preferably an electron beam (EB) resist.

[0073] From the reflective mask blank, for example, a reflective mask can be manufactured which has a substrate, a multilayer reflective film formed on one main surface of the substrate, a protective film formed in contact with the multilayer reflective film, and an absorber film pattern (absorber film pattern) formed in contact with the protective film. In the reflective mask, a transfer pattern is formed due to the difference in reflectance between the part where the absorber film is formed and the part where the absorber film is not formed.

[0074] 5 is a cross-sectional view showing an example of a reflective mask of the present invention. This reflective mask 200 includes a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1, a protective film 3 formed in contact with the multilayer reflective film 2, and an absorber film pattern 4a formed in contact with the protective film 3.

[0075] The reflective mask of the present invention comprises: providing a reflective mask blank; If necessary, forming a resist film on the absorber film; forming a resist pattern from the resist film on the absorber film; a step of etching the absorber film using the resist pattern as an etching mask to form a pattern of the absorber film; a step of removing the resist pattern; It can be produced by a method comprising:

[0076] The reflective mask of the present invention further comprises: providing a reflective mask blank; If necessary, forming a resist film on the etching mask film; forming a resist pattern from the resist film on the etching mask film; a step of etching the etching mask film using the resist pattern as an etching mask to form a pattern of the etching mask film; a step of etching the absorber film using the pattern of the etching mask film as an etching mask to form a pattern of the absorber film; removing the resist pattern; a step of removing the pattern of the etching mask film; It can be produced by a method comprising:

[0077] The absorber film can be etched by dry etching using a gas containing chlorine (Cl) or a gas containing fluorine (F). An etching mask film containing chromium (Cr) can be etched by dry etching using a gas containing chlorine (Cl) and oxygen (O) to form an etching mask film pattern. After forming the absorber film pattern, the etching mask film pattern can be removed by dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0078] The resist pattern can be removed using sulfuric acid / hydrogen peroxide (SPM). [Example]

[0079] EXAMPLES The present invention will be specifically explained below by showing examples and comparative examples, but the present invention is not limited to the following examples.

[0080] [Example 1] A 284 nm thick multilayer reflective film was formed on the main surface of a 152 mm square, 6.35 mm thick low-thermal expansion glass substrate (SiO2-TiO2 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 while the substrate was rotating. Each target was attached to a sputtering device that can accommodate two targets and can discharge either one at a time or both targets simultaneously, and the substrate was then placed thereon.

[0081] First, while argon (Ar) gas was flowing into the chamber, power was applied to the silicon (Si) target to form a 4 nm thick silicon (Si) layer, and then the power application to the silicon (Si) target was stopped. Next, while argon (Ar) gas was flowing into the chamber, power was applied to the molybdenum (Mo) target to form a 3 nm thick molybdenum (Mo) layer, and then the power application to the molybdenum (Mo) target was stopped. This process of forming a silicon (Si) layer and a molybdenum (Mo) layer constitutes one cycle, and this was repeated 40 times. After the 40th cycle of the molybdenum (Mo) layer was formed, a 4 nm thick silicon (Si) layer was finally formed using the above method to form a multilayer reflective film.

[0082] Next, a protective film was formed on the multilayer reflective film 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 and the substrate rotating. Each target was mounted in a separate sputtering device that could accommodate two targets and discharge either one at a time or both targets simultaneously. After the formation of the multilayer reflective film, the substrate on which the multilayer reflective film had been formed was transferred from the sputtering device where the multilayer reflective film had been formed via a transport path maintained in a vacuum state without being taken out into the atmosphere.

[0083] First, while argon (Ar) gas was flowing into the chamber, power was applied simultaneously to a ruthenium (Ru) target and a niobium (Nb) target, and the power applied to the niobium (Nb) target was gradually increased over time to form a 3.9 nm thick film made of RuNb with a composition gradient in which niobium (Nb) increases in the thickness direction.

[0084] Next, the substrate on which the multilayer reflective film and the protective film 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 to oxidize the surface of the protective film.

[0085] Next, an absorber film was formed on the protective film by DC pulse magnetron sputtering using a tantalum (Ta) target, with the target facing the main surface of the substrate and the substrate rotating. The target was then installed in a separate sputtering device, and after the protective film was formed, the substrate with the multilayer reflective film and protective film formed thereon was transferred from the sputtering device that had formed the protective film to the substrate via a transport path maintained in a vacuum state, without being taken out into the atmosphere.

[0086] First, argon (Ar) gas (45 vol%), xenon (Xe) gas (18 vol%), and nitrogen (N2) gas (37 vol%) were flowed into the chamber, while power (1800 W) was applied to the tantalum (Ta) target, and the pressure inside the chamber was set to 0.13 Pa to form a 0.5 nm thick layer as a low-nitridation layer.

[0087] Next, while argon (Ar) gas (40 vol%) and nitrogen (N2) gas (60 vol%) were flowing into the chamber, power (1800 W) was applied to the tantalum (Ta) target, setting the pressure inside the chamber to 0.48 Pa and forming a 69.5 nm thick layer as a high-nitridation layer. A reflective mask blank was obtained as an absorber film 70 nm thick consisting of one low-nitridation layer (the layer closest to the substrate) and one high-nitridation layer (the layer furthest from the substrate).

[0088] The composition of the obtained absorber film was measured using an X-ray photoelectron spectroscopy (XPS) device (K-Alpha, manufactured by Thermo Fisher Scientific), and it was found that the low-nitridation layer was 85 atomic % tantalum (Ta) and 15 atomic % nitrogen (N), and the high-nitridation layer was 45 atomic % tantalum (Ta) and 55 atomic % nitrogen (N).

[0089] Before and after forming the absorber film, the warpage (TIR) ​​within a 142 mm square area at the center of the substrate surface was measured using a flatness tester (Tropel Ultra Flat 200 Mask, manufactured by CORNING), and the change in warpage before and after (ΔTIR) was calculated to be -0.32 μm (compressive stress).

[0090] The surface roughness Sq (root mean square height) of the obtained absorber film was measured with an atomic force microscope (AFM) and was found to be 0.40 nm.The reflectance of the obtained absorber film was also measured and found to have a maximum reflectance of 34.5% in the range of 193 to 260 nm.

[0091] [Example 2] A reflective mask blank was obtained in the same manner as in Example 1, except that the absorber film was a 60 nm thick absorber film formed by alternating stacking six layers in total, each consisting of three 10 nm thick low-nitridation layers formed in the same manner as in Example 1 and three 10 nm thick high-nitridation layers formed in the same manner as in Example 1, starting from the low-nitridation layers.

[0092] The change in warpage (ΔTIR), surface roughness Sq, and reflectance were evaluated in the same manner as in Example 1. The change in warpage (ΔTIR) was -0.35 μm (compressive stress), the surface roughness Sq was 0.32 nm, and the maximum reflectance in the range of 193 to 260 nm was 33.8%.

[0093] [Comparative Example 1] A reflective mask blank was obtained in the same manner as in Example 1, except that the absorber film was a single-layer absorber film consisting of a 70 nm thick highly nitrided layer formed in the same manner as in Example 1.

[0094] The change in warpage (ΔTIR), surface roughness Sq, and reflectance were evaluated in the same manner as in Example 1. The change in warpage (ΔTIR) was -0.61 μm (compressive stress), the surface roughness Sq was 0.62 nm, and the maximum reflectance in the range of 193 to 260 nm was 34.5%. This single-layer absorber film with a high degree of nitride had a high surface roughness Sq.

[0095] Comparative Example 2 A reflective mask blank was obtained in the same manner as in Example 1, except that the absorber film was a single-layer absorber film consisting of a 70 nm-thick low-nitridation layer formed in the same manner as in Example 1.

[0096] The change in warpage (ΔTIR), surface roughness Sq, and reflectance were evaluated in the same manner as in Example 1. The change in warpage (ΔTIR) was -0.62 μm (compressive stress), the surface roughness Sq was 0.26 nm, and the maximum reflectance in the range of 193 to 260 nm was 39.8%. This single-layer absorber film with a low degree of nitridation had a large film stress.

[0097] [Example 3] A multilayer reflective film was formed on the main surface of a 152 mm square, 6.35 mm thick low-thermal expansion glass substrate (SiO2-TiO2-based glass substrate) in the same manner as in Example 1, and a protective film was formed on the multilayer reflective film in the same manner as in Example 1.

[0098] Next, an absorber film was formed on the protective film by DC pulse magnetron sputtering using a tantalum (Ta) target, with the target facing the main surface of the substrate and the substrate rotating. The target was then installed in a separate sputtering device, and after the protective film was formed, the substrate with the multilayer reflective film and protective film formed thereon was transferred from the sputtering device that had formed the protective film to the substrate via a transport path maintained in a vacuum state, without being taken out into the atmosphere.

[0099] First, xenon (Xe) gas (32 vol%) and nitrogen (N2) gas (68 vol%) were flowed into the chamber, and power (1800 W) was applied to the tantalum (Ta) target, setting the pressure inside the chamber to 0.11 Pa, and a layer 31 nm thick was formed as a low-nitridation layer.

[0100] Next, while argon (Ar) gas (58 vol%) and nitrogen (N2) gas (42 vol%) were flowing into the chamber, power (1800 W) was applied to the tantalum (Ta) target, setting the pressure inside the chamber to 0.41 Pa and forming a 31 nm thick layer as a high-nitridation layer. A reflective mask blank was obtained as an absorber film 62 nm thick consisting of one low-nitridation layer (the layer closest to the substrate) and one high-nitridation layer (the layer furthest from the substrate).

[0101] The composition of the obtained absorber film was measured in the same manner as in Example 1, and it was found that the low-nitridation layer was 80 atomic % tantalum (Ta) and 20 atomic % nitrogen (N), and the high-nitridation layer was 55 atomic % tantalum (Ta) and 45 atomic % nitrogen (N).

[0102] The change in warpage (ΔTIR), surface roughness Sq, and reflectance were evaluated in the same manner as in Example 1. The change in warpage (ΔTIR) was -0.15 μm (compressive stress), the surface roughness Sq was 0.42 nm, and the maximum reflectance in the range of 193 to 260 nm was 31.9%.

[0103] [Example 4] A reflective mask blank was obtained in the same manner as in Example 3, except that the absorber film was a 60 nm thick absorber film formed by alternating low-nitridation layers of 15 nm thick formed in the same manner as in Example 3 and high-nitridation layers of 15 nm thick formed in the same manner as in Example 3, two of each for a total of four layers, starting from the low-nitridation layers.

[0104] The change in warpage (ΔTIR), surface roughness Sq, and reflectance were evaluated in the same manner as in Example 1. The change in warpage (ΔTIR) was -0.11 μm (compressive stress), the surface roughness Sq was 0.60 nm, and the maximum reflectance in the range of 193 to 260 nm was 30.4%.

[0105] Comparative Example 3 A reflective mask blank was obtained in the same manner as in Example 3, except that the absorber film was a single-layer absorber film consisting of a 60 nm thick highly nitrided layer formed in the same manner as in Example 3.

[0106] The change in warpage (ΔTIR), surface roughness Sq, and reflectance were evaluated in the same manner as in Example 1. The change in warpage (ΔTIR) was -0.86 μm (compressive stress), the surface roughness Sq was 0.42 nm, and the maximum reflectance in the range of 193 to 260 nm was 31.9%. This single-layer absorber film with a high degree of nitridation had a large film stress.

[0107] Comparative Example 4 A reflective mask blank was obtained in the same manner as in Example 3, except that the absorber film was a single-layer absorber film consisting of a low-nitridation layer having a thickness of 60 nm formed in the same manner as in Example 3.

[0108] The change in warpage (ΔTIR), surface roughness Sq, and reflectance were evaluated in the same manner as in Example 1. The change in warpage (ΔTIR) was +0.64 μm (tensile stress), the surface roughness Sq was 0.38 nm, and the maximum reflectance in the range of 193 to 260 nm was 37.0%. This single-layer absorber film with a low degree of nitridation had a large film stress and a high reflectance.

[0109] Comparative Example 5 A multilayer reflective film was formed on the main surface of a 152 mm square, 6.35 mm thick low-thermal expansion glass substrate (SiO2-TiO2-based glass substrate) in the same manner as in Example 1, and a protective film was formed on the multilayer reflective film in the same manner as in Example 1.

[0110] Next, an absorber film was formed on the protective film by DC pulse magnetron sputtering using a tantalum (Ta) target, with the target facing the main surface of the substrate and the substrate rotating. The target was then installed in a separate sputtering device, and after the protective film was formed, the substrate with the multilayer reflective film and protective film formed thereon was transferred from the sputtering device that had formed the protective film to the substrate via a transport path maintained in a vacuum state, without being taken out into the atmosphere.

[0111] Argon (Ar) gas (41 vol%), xenon (Xe) gas (12 vol%), and nitrogen (N) gas (47 vol%) were flowed into the chamber, while power (1800 W) was applied to the tantalum (Ta) target, and the pressure inside the chamber was set to 0.16 Pa. A single-layer absorber film with a thickness of 61 nm and a medium degree of nitridation was formed, and a reflective mask blank was obtained.

[0112] The composition of the obtained absorber film was measured in the same manner as in Example 1, and was found to be 75 atomic % tantalum (Ta) and 25 atomic % nitrogen (N).

[0113] The change in warpage (ΔTIR), surface roughness Sq, and reflectance were evaluated in the same manner as in Example 1. The change in warpage (ΔTIR) was -1.40 μm (compressive stress), the surface roughness Sq was 0.30 nm, and the maximum reflectance in the range of 193 to 260 nm was 33.8%. This single-layer absorber film with a medium degree of nitriding had an extremely large film stress. [Explanation of symbols]

[0114] 1 board 2 Multilayer reflective film 3 Protective film 4. Absorber membrane 4a Absorber film pattern 41 Main area 411 Low nitride layer 412 High nitridation layer 5 Etching mask film 101, 102 Reflective mask blanks 200 Reflective Mask

Claims

1. A reflective mask blank serving as a material for a reflective mask used in EUV lithography using EUV light as exposure light, comprising: a substrate; a multilayer reflective film formed on the substrate and reflecting exposure light; a protective film formed on the multilayer reflective film; and an absorber film formed in contact with the protective film and absorbing exposure light, the absorber film includes a main region that occupies 94% or more of the thickness of the absorber film; The main region is made of tantalum (Ta) and nitrogen (N), and is composed of multiple layers including at least one low-nitriding layer containing 20 atomic % or less of nitrogen (N) and at least one high-nitriding layer containing 40 atomic % or more and 60 atomic % or less of nitrogen (N). A reflective mask blank characterized by:

2. 2. The reflective mask blank according to claim 1, wherein the absorber film is formed only in the main region.

3. The absorber film is The main region and a substrate side region that contacts the main region on the substrate side, from the main region and a surface side region in contact with the side of the main region away from the substrate, or The main region, a substrate side region that contacts the main region on the substrate side, and a surface side region that contacts the main region on the side away from the substrate And the substrate-side region contains tantalum (Ta), nitrogen (N), and elements contained in the protective film, and has a thickness of 1 nm or less; The surface side region contains tantalum (Ta), nitrogen (N), and oxygen (O), and has a thickness of 2 nm or less.

2. The reflective mask blank according to claim 1.

4. 2. The reflective mask blank according to claim 1, further comprising an etching mask film formed in contact with the absorber film.

5. 5. The reflective mask blank according to claim 4, wherein the absorber film is formed only in the main region.

6. The absorber film is The main region and a substrate side region that contacts the main region on the substrate side, from the main region and a surface side region in contact with the side of the main region away from the substrate, or The main region, a substrate side region that contacts the main region on the substrate side, and a surface side region that contacts the main region on the side away from the substrate And the substrate-side region contains tantalum (Ta), nitrogen (N), and elements contained in the protective film, and has a thickness of 1 nm or less; The surface side region contains tantalum (Ta), nitrogen (N), and the elements contained in the etching mask film, and has a thickness of 1 nm or less.

5. The reflective mask blank according to claim 4.

7. 7. The reflective mask blank according to claim 6, wherein the front side region further contains oxygen (O).

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

9. 8. The reflective mask blank according to claim 1, wherein the layer of the main region farthest from the substrate is the high-degree-nitridation layer.

10. 10. The reflective mask blank according to claim 9, wherein the absorber film has a reflectance of 35% or less for light having a wavelength in the range of 193 to 260 nm.

11. 8. The reflective mask blank according to claim 1, wherein the main region comprises the low-degree-nitridation layer and the high-degree-nitridation layer.

12. The reflective mask blank according to claim 11, characterized in that the layer of the main region closest to the substrate is the low-degree-nitridation layer, the low-degree-nitridation layer has a thickness of 0.3 nm or more and 2 nm or less, and the layers other than the layer closest to the substrate are the high-degree-nitridation layers.

13. 13. The reflective mask blank according to claim 12, wherein the absorber film has a reflectance of 35% or less for light having a wavelength in the range of 193 to 260 nm.

14. 8. A reflective mask blank according to claim 1, wherein the main region has a structure in which the low-degree-nitridation layers and the high-degree-nitridation layers are alternately stacked, and the thickness of each layer is 3 nm or more and 30 nm or less.

15. 8. The reflective mask blank according to claim 1, wherein the absorber film has a surface roughness Sq of 0.6 nm or less.

16. 8. The reflective mask blank according to claim 1, wherein the absorber film is a film that, when the absorber film is formed on a main surface of a substrate that is 152 mm square and 6.35 mm thick, gives the substrate a warpage change ΔTIR in the range of +0.2 μm due to tensile stress to −0.5 μm due to compressive stress.

17. 8. The reflective mask blank according to claim 1, wherein the protective film contains ruthenium (Ru).

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