Reflective mask blank

Abstract

SOLUTION: Provided is a reflection-type mask blank which is a material for a reflection-type mask used for UV lithography using EUV light as exposure light, has a periodical layer structure formed on one of the main surfaces of a substrate, in which a layer having a relatively low refractive index to the exposure light and a layer having relatively high refractive index to the exposure light are alternately laminated, and comprises: a reflective multilayer film which reflects the exposure light; a protective film formed abutting the reflective multilayer film; and an absorber film formed abutting the protective film, which absorbs the exposure light. The membrane stress of the absorber film is equal to or less than the membrane stress of the absorber film when the absorber film is formed directly on the substrate.EFFECT: To provide a reflection-type mask blank which has secured necessary characteristics for an absorber film and has reduced film stress.SELECTED DRAWING: Figure 2

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. 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 have been proposed as masks for pattern transfer.

[0004] A reflective mask generally has a reflective multilayer film that reflects EUV light formed on one main surface of a low-thermal expansion glass substrate, and an absorber film that absorbs EUV light formed in a pattern on the reflective multilayer film. On the other hand, a mask in a state before the absorber 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 has a reflective multilayer film that reflects EUV light formed on one main surface of a low-thermal expansion glass substrate, and an absorber film that absorbs EUV light formed on the reflective multilayer film, and has a basic structure including a reflective multilayer film and an absorber film.

[0005] The reflective multilayer film typically uses a Mo / Si reflective multilayer film, which ensures EUV light reflectivity by alternately stacking molybdenum (Mo) and silicon (Si) layers. The absorber film is typically made of a material primarily composed of tantalum (Ta), which has a relatively large extinction coefficient for EUV light (see Japanese Patent Laid-Open Publication No. 2002-246299 (Patent Document 1)). On the other main surface of the substrate, a backside conductive film, such as a metal film, is formed for electrostatic chucking when the reflective mask is held in an exposure tool. The backside conductive film typically contains chromium (Cr) and tantalum (Ta).

[0006] In addition, a protective film for protecting the reflective multilayer film is usually formed between the reflective multilayer film and the absorber film. The protective film is provided to protect the reflective multilayer film when it is exposed to etching gas during etching performed to form a mask pattern on the absorber film or when it is exposed to cleaning liquid during cleaning after mask pattern formation, and also to prevent the reflective multilayer film from being damaged during pattern correction processing when defects are detected after mask pattern formation. Ruthenium (Ru), for example, is used as a material for the protective film (Japanese Patent Laid-Open Publication No. 2002-122981 (Patent Document 2)). When the protective film is further required to have the function of suppressing a decrease in the reflectance of the reflective multilayer film when exposed to EUV light, it has been proposed to use a material obtained by adding niobium (Nb), rhodium (Rh), zirconium (Zr), or the like to ruthenium (Ru). [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] In the manufacturing process of a reflective mask blank, after the formation of a reflective multilayer film, a mark serving as a reference for defect coordinate positions is formed, and then an actinic blank inspection (ABI) using EUV light is performed to detect defects known as phase defects. During reflective mask processing, so-called mitigation (defect mitigation) is performed based on the defect coordinate information obtained during the ABI inspection to prevent the defects from being transferred during the pattern writing process on the reflective mask, and ultimately, the desired pattern is formed in the absorber film. To prevent misalignment during mitigation and changes in the substrate shape after patterning, it is necessary to keep the film stress of the absorber film as low as possible.

[0009] The absorber film of a reflective mask blank requires removal of a portion of the film to form a pattern, and if the film stress is large, the amount of warpage of the substrate will change as the pattern is formed. Therefore, to maintain the positional accuracy of the pattern, it is preferable that the film stress is small. However, in addition to the film stress, the absorber film must have a sufficiently low reflectance at a specified thickness, a microcrystalline structure and low surface roughness to keep the LER (Line Edge Roughness) of the pattern low, a high etching rate to ensure processability, and a sheet resistance of 10 to prevent the substrate from becoming charged during EB (Electron Beam) writing. 7 It is required that the film stress of the absorber film be kept below Ω / □. The film stress of the absorber film can be adjusted to some extent by changing the film formation conditions, but changing the film formation conditions will significantly change not only the film stress but also other properties such as film quality. In particular, with films with a high degree of nitride, the film stress cannot be adjusted by simply changing the film formation conditions, and it is difficult to reduce the film stress.

[0010] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a reflective mask blank having an absorber film with low film stress, in particular an absorber film that ensures the properties required for an absorber film and has low film stress. [Means for solving the problem]

[0011] As a result of extensive investigations into solving the above problems, the present inventors have found that by forming a protective film in contact with an absorber film from a material consisting of ruthenium (Ru), niobium (Nb) and oxygen (O), with the composition of the side close to the reflective multilayer film containing ruthenium (Ru) but not containing oxygen (O) and the composition of the side in contact with the absorber film consisting of ruthenium (Ru), niobium (Nb) and oxygen (O) or niobium (Nb) and oxygen (O), and forming an absorber film in contact with this protective film, it is possible to obtain a reflective mask blank having an absorber film that ensures the properties required for an absorber film and has low film stress, particularly an absorber film in contact with the protective film whose film stress is equal to or less than the film stress when the absorber film is formed directly on a substrate, and have thereby completed the present invention.

[0012] Therefore, the present invention provides the following reflective mask blank. 1. It is a material for reflective masks used in EUV lithography, which uses EUV light as the exposure light. A reflective mask blank comprising: a substrate; a reflective multilayer film formed on one main surface of the substrate, the reflective multilayer film having a periodic stacking structure in which layers having a relatively low refractive index for exposure light and layers having a relatively high refractive index for exposure light are alternately stacked, the reflective multilayer film reflecting the exposure light; a protective film formed in contact with the reflective multilayer film; and an absorber film formed in contact with the protective film and absorbing the exposure light, The protective film is consisting of ruthenium (Ru), niobium (Nb) and oxygen (O), the composition of the side adjacent to the reflective multilayer film contains ruthenium (Ru) and does not contain oxygen (O); The composition of the side in contact with the absorber film is composed of ruthenium (Ru), niobium (Nb), and oxygen (O), and the total content of niobium (Nb) and oxygen (O) is 60 atomic % or more, or is composed of niobium (Nb) and oxygen (O), The absorber film is Contains tantalum (Ta) and nitrogen (N), The nitrogen (N) content is 35 atomic % or more and 45 atomic % or less, The ratio of tantalum (Ta) to nitrogen (N) is Ta / N in an atomic ratio of 55 / 45 to 65 / 35, Thickness: 50nm to 80nm is A reflective mask blank characterized by: 2 The protective film is characterized in that the composition of the side adjacent to the reflective multilayer film is made of ruthenium (Ru) or ruthenium (Ru) and niobium (Nb). 1 The reflective mask blank according to claim 1. 3 The composition of the protective film on the side adjacent to the reflective multilayer film is characterized in that the content of niobium (Nb) is 60 atomic % or less. 2 The reflective mask blank according to claim 1. 4 The protective film is characterized in that the content of niobium (Nb) increases stepwise and / or continuously in the thickness direction from the side close to the reflective multilayer film to the side in contact with the absorber film. 2 The reflective mask blank according to claim 1. 5The protective film is characterized in that the content of oxygen (O) increases stepwise and / or continuously in the thickness direction from the side close to the reflective multilayer film to the side in contact with the absorber film. 1 The reflective mask blank according to claim 1. 6. The reflective mask blank according to 1, wherein the composition of the side in contact with the absorber film consists of niobium (Nb) and oxygen (O). 7. The reflective mask blank according to 1, wherein the absorber film is a single layer made of tantalum (Ta) and nitrogen (N). 8. The reflective mask blank according to 1, wherein the protective film includes a stress relaxation layer formed in contact with the absorber film. 9. The protective film is (A) a layer containing ruthenium (Ru) and not containing oxygen (O), the layer being adjacent to the reflective multilayer film; The stress relaxation layer, (B) a layer having a composition consisting of ruthenium (Ru), niobium (Nb) and oxygen (O), or niobium (Nb) and oxygen (O), and in contact with the absorber film 9. The reflective mask blank according to 8, characterized in that it consists of two layers: 10. The reflective mask blank according to 9, wherein the layer (A) is made of ruthenium (Ru) or ruthenium (Ru) and niobium (Nb). 11. The reflective mask blank according to 10, wherein the niobium (Nb) content of the layer (A) on the side closest to the reflective multilayer film is 60 atomic % or less. 12. A reflective mask blank according to claim 10, characterized in that the (A) layer is composed of two or more sublayers having different compositions, or a compositionally gradient layer, and the niobium (Nb) content increases stepwise and / or continuously in the thickness direction from the side closest to the reflective multilayer film to the side in contact with the (B) layer. 13 .The reflective mask blank described in 9, characterized in that the (B) layer is composed of two or more sub-layers having different compositions, or a compositionally gradient layer, and the oxygen (O) content increases stepwise and / or continuously in the thickness direction from the side in contact with the (A) layer toward the side in contact with the absorber film. 149. A reflective mask blank as described in 9, characterized in that the thickness of the protective film is 2 nm or more and 5 nm or less, and the thickness of the (B) layer is 10% or more and 50% or less of the thickness of the protective film. 15 The absorber film further contains one or more additive elements selected from hydrogen (H), boron (B), carbon (C), silicon (Si), molybdenum (Mo), zirconium (Zr), chromium (Cr), germanium (Ge) and aluminum (Al), and the total content of the additive elements is 20 atomic % or less. 9 The reflective mask blank according to claim 1. 16 . before The absorber film ,Ta It consists of a substrate-side layer made of tantalum (Ta) and nitrogen (N) and a surface layer made of tantalum (Ta), nitrogen (N) and oxygen (O). 、 before the ratio of tantalum (Ta) to nitrogen (N) in the substrate-side layer and the surface layer is 55 / 45 to 65 / 35 in atomic ratio, and the oxygen (O) content in the surface layer on the side farthest from the substrate is 20 atomic % or more and 40 atomic % or less; The thickness of the surface layer is 2 nm or less Characterized by 9 The reflective mask blank according to claim 1. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a reflective mask blank in which the characteristics required for the absorber film are ensured and the film stress is reduced. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a first embodiment of a reflective mask blank of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing an example of a second embodiment of the reflective mask blank of the present invention. [Figure 3] FIG. 2 is a cross-sectional view showing an example of a third embodiment of the reflective mask blank of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in more detail below. The reflective mask of the present invention is used in EUV lithography using EUV light as exposure light. The reflective mask blank of the present invention is a material for the reflective mask. The EUV light used in EUV lithography using EUV light as exposure light has a wavelength of 13 to 14 nm, and is usually light with a wavelength of about 13.5 nm (e.g., 13.4 to 13.6 nm). A reflective mask blank and a reflective mask using EUV light as exposure light are also called EUV mask blank and EUV mask, respectively.

[0016] The reflective mask blank of the present invention comprises a substrate, a reflective multilayer film formed on (upper side of) one main surface (front surface) of the substrate and reflecting exposure light, a protective film formed in contact with the reflective multilayer film, and an absorber film formed in contact with the protective film and absorbing the exposure light (reducing the reflectance of the exposure light). The reflective multilayer film is preferably provided in contact with one main surface of the substrate, but another film such as an underlayer may be provided between the reflective multilayer film and the one main surface of the substrate.

[0017] In the present invention, one main surface of the substrate is defined as the front and upper side, and the other main surface on which a back surface conductive film (described later) can be provided is defined as the back surface and lower side, but the terms "front and back" and "top and bottom" are defined for convenience. The one main surface and the other main surface are either of the two main surfaces (film formation surfaces) of the substrate, and the terms "front and back" and "top and bottom" are interchangeable.

[0018] The substrate preferably has low thermal expansion characteristics for use in EUV light exposure, and for example, the thermal expansion coefficient is preferably ±2×10 -8 / ℃, more preferably ±5×10 -9The substrate is preferably made of a material within the temperature range of 100°C / °F. Examples of such materials include titania-doped SiO2-TiO2 glass. Furthermore, it is preferable to use a substrate with a sufficiently flat surface, with the surface roughness of the main surface of the substrate preferably being 0.5 nm or less, more preferably 0.2 nm or less, in terms of RMS value. Such a surface roughness can be achieved by polishing the substrate. A suitable substrate is, for example, a 6-inch square, 0.25-inch thick substrate known as a 6025 substrate, as specified by the SEMI standard. In the SI unit system, a 6025 substrate is usually expressed as a 152 mm square, 6.35 mm thick substrate.

[0019] The reflective multilayer film has a periodic stacking structure in which layers with a relatively low refractive index to the exposure light (layers formed from materials with a relatively low refractive index to the exposure light (low refractive index materials)) and layers with a relatively high refractive index to the exposure light (layers formed from materials with a relatively high refractive index to the exposure light (high refractive index materials)) are alternately stacked. An example of the periodic stacking structure is a Si / Mo periodic stacking structure consisting of multiple layers in which layers (Si layers) formed from silicon (Si), a material with a relatively high refractive index to the exposure light, and layers (Mo layers) formed from molybdenum (Mo), a material with a relatively low refractive index to the exposure light, are alternately stacked.

[0020] The Si layer and the Mo layer are preferably layers formed of simple Si and simple Mo, respectively, but may contain other elements as long as the content is less than 10 atomic %. The number of stacked Si layers and Mo layers is preferably 40 or more cycles (40 or more layers for each) and preferably 60 or less cycles (60 or less layers for each).

[0021] The thicknesses of the Si layer and the Mo layer are appropriately set according to the exposure wavelength, with the Si layer preferably being 5 nm or less and the Mo layer preferably being 4 nm or less. The lower limits of the thicknesses of the Si layer and the Mo layer are not particularly limited, but are typically 1 nm or more. The thicknesses of the Si layer and the Mo layer may be set so as to obtain high reflectivity for the exposure light. The thickness of each Si layer and each Mo layer may be constant or may vary from layer to layer. The total thickness of the Si / Mo periodic stacked structure (the thickness of the reflective multilayer film when the reflective multilayer film is composed only of the Si / Mo periodic stacked structure) is typically about 250 to 450 nm.

[0022] In the Si / Mo periodic stacked structure, a layer containing silicon (Si) and nitrogen (N) may be formed between one or more of the Si layers and the Mo layers, in contact with both the Si layer and the Mo layer. The layer containing silicon (Si) and nitrogen (N) preferably does not contain oxygen (O). A specific example of the layer containing silicon (Si) and nitrogen (N) is a SiN layer (here, SiN indicates that the constituent elements are silicon (Si) and nitrogen (N), but does not indicate the composition ratio). The nitrogen (N) content of the layer containing silicon (Si) and nitrogen (N) is preferably 1 atomic % or more, more preferably 5 atomic % or more, and preferably 60 atomic % or less, more preferably 57 atomic % or less. The thickness of the layer containing silicon (Si) and nitrogen (N) is preferably 2 nm or less, more preferably 1 nm or less. The lower limit of the thickness of the layer containing silicon (Si) and nitrogen (N) is not particularly limited, but is preferably 0.1 nm or more.

[0023] Methods for forming reflective multilayer 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 charge-up.

[0024] The Si / Mo periodic stacked layer structure can be formed by sputtering using, for example, a sputtering apparatus capable of mounting multiple targets. Specifically, a silicon (Si) target for forming a silicon (Si)-containing layer such as a Si layer or a SiN layer, and a molybdenum (Mo) target for forming a molybdenum (Mo)-containing layer such as a Mo layer are used. When forming the Si and Mo layers, a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas is used as a sputtering gas. When forming the SiN layer, nitrogen (N) gas is used as a reactive gas together with the rare gas. The Si target and the Mo target are sequentially sputtered to form each layer.

[0025] The protective film is a film for protecting the reflective multilayer film. The protective film is provided to protect the reflective multilayer film, for example, during cleaning in the processing of a reflective mask or during repair of the reflective mask. The stress of the absorber film formed on the protective film depends on the film composition and film deposition conditions. However, there is a limit to how much stress can be reduced by simply changing the film composition and film deposition conditions, for example, in the case of an absorber film containing tantalum (Ta) and nitrogen (N) with a high degree of nitridation. Furthermore, changing the film composition and film deposition conditions to reduce the stress of the absorber film changes other properties required for the absorber film, such as reflectivity, film quality, etching rate, and sheet resistance. Since there is usually a trade-off between film stress and other properties, there is also a limit to how much stress can be reduced in the absorber film while maintaining the required properties.

[0026] When an absorber film is formed in contact with the protective film of the present invention, the protective film of the present invention has the effect of alleviating the stress of the absorber film, resulting in a reflective mask blank having an absorber film with low film stress while ensuring the necessary properties of the absorber film. Furthermore, the protective film of the present invention can reduce the film stress of the absorber film to less than the film stress of the absorber film when it is formed directly on the substrate. The film stress of the absorber film when it is formed directly on the substrate (ΔTIR, which is the difference between the TIR of the substrate before the absorber film is formed and the TIR of the substrate after the absorber film is formed) can be said to be the film stress of the absorber film that is not affected by other films. However, the protective film of the present invention can reduce the film stress of the absorber film when a reflective multilayer film, a protective film, and an absorber film are sequentially formed on the substrate (ΔTIR, which is the difference between the TIR of the substrate with the reflective multilayer film and protective film formed before the absorber film is formed and the TIR of the substrate after the absorber film is formed) to less than the film stress of the absorber film that is not affected by other films.

[0027] In the present invention, the protective film is made of a material consisting of ruthenium (Ru), niobium (Nb), and oxygen (O). The protective film is configured so that the composition of the side close to the reflective multilayer film, specifically, the composition at the interface or interface portion close to the reflective multilayer film, is different from the composition of the side in contact with the absorber film, specifically, the composition at the interface or interface portion in contact with the absorber film.

[0028] The composition of the protective film on the side closest to the reflective multilayer film contains ruthenium (Ru) but does not contain oxygen (O). The composition of the protective film on the side closest to the reflective multilayer film may contain niobium (Nb). By setting the composition of the side closest to the reflective multilayer film in this way, it is possible to suppress a decrease in reflectance due to the formation of the protective film, and to ensure sufficient reflectance for exposure light of a reflective mask obtained from the reflective mask blank. The composition of the protective film on the side closest to the reflective multilayer film is preferably made of ruthenium (Ru) or ruthenium (Ru) and niobium (Nb).

[0029] When the composition of the protective film on the side closest to the reflective multilayer film consists of ruthenium (Ru) and niobium (Nb), the niobium (Nb) content is preferably 60 atomic % or less, more preferably 50 atomic % or less, even more preferably 40 atomic % or less, and is greater than 0 atomic %, preferably 5 atomic % or more, more preferably 10 atomic % or more, and even more preferably 20 atomic % or more. If the niobium (Nb) content is too high, the resistance to chlorine-based etching decreases during etching of the absorber film, and if the protective film is damaged, the reflectivity of the reflective multilayer film may decrease, and the SPM cleaning resistance may also decrease.

[0030] On the other hand, the composition of the side of the protective film that contacts the absorber film is made of ruthenium (Ru), niobium (Nb) and oxygen (O), or niobium (Nb) and oxygen (O). By making the composition of the side that contacts the absorber film like this, it is possible to alleviate the stress of the absorber film that is formed in contact with the protective film. Furthermore, it is possible to increase the resistance of the absorber film to chlorine-based etching when etching the absorber film.

[0031] The composition of the protective film on the side in contact with the absorber film preferably has a high total content of niobium (Nb) and oxygen (O), and the total content of niobium (Nb) and oxygen (O) is preferably 60 atomic % or more, more preferably 70 atomic % or more, and even more preferably 80 atomic % or more.

[0032] The thickness of the protective film 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.

[0033] The protective film may have a composition in which the niobium (Nb) content increases or decreases stepwise and / or continuously in the thickness direction from the side closest to the reflective multilayer film to the side closest to the absorber film, and the protective film may have a composition in which the oxygen (O) content increases stepwise and / or continuously in the thickness direction from the side closest to the reflective multilayer film to the side closest to the absorber film.

[0034] The composition of the protective film on the side closest to the reflective multilayer film is a composition containing ruthenium (Ru) but not oxygen (O), preferably a composition containing ruthenium (Ru) and niobium (Nb) but not oxygen (O), more preferably a composition consisting of ruthenium (Ru) or ruthenium (Ru) and niobium (Nb), and the composition of the protective film on the side in contact with the absorber film is a composition consisting of ruthenium (Ru), niobium (Nb) and oxygen (O), or niobium (Nb) and oxygen (O), thereby making it possible to suppress a decrease in reflectivity due to the formation of the protective film, relieve stress in the absorber film formed in contact with the protective film, and ensure resistance to chlorine-based etching when etching the absorber film.

[0035] A method for forming a protective film in which the composition of the side closest to the reflective multilayer film contains ruthenium (Ru) but does not contain oxygen (O), and the composition of the side of the protective film in contact with the absorber film is a composition consisting of ruthenium (Ru), niobium (Nb) and oxygen (O), or niobium (Nb) and oxygen (O) can be exemplified by first forming the side closest to the reflective multilayer film by sputtering using a ruthenium (Ru) target and, if necessary, a niobium (Nb) target as targets and a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as the sputtering gas, and then forming the side in contact with the absorber film by reactive sputtering using a rare gas as the sputtering gas together with oxygen (O2) gas as the reactive gas. In sputtering, the ratio of ruthenium (Ru) to niobium (Nb) can be changed by changing the ratio of power applied to the ruthenium (Ru) target and the niobium (Nb) target. Also, the oxygen gas content can be changed by changing the amount of oxygen (O2) gas introduced.

[0036] Another method is to use a ruthenium (Ru) target and, if necessary, a niobium (Nb) target as the target, and a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as the sputtering gas to form a protective film with a composition that does not contain oxygen (O), and then perform an ashing process using oxygen plasma or a heat treatment in the presence of oxygen gas, such as in the atmosphere, to make the composition of the side of the protective film that comes into contact with the absorber film a composition that contains oxygen (O).

[0037] In particular, a method of heat-treating the protective film to have a composition containing oxygen (O) on the side in contact with the absorber film is preferred because it is easy and has a low risk of defects. Although a higher heat-treating temperature facilitates oxidation, it is preferable to set the heat-treating temperature at 150°C or less, taking into consideration the decrease in reflectance. Furthermore, when the heat-treating temperature is set at 150°C or less, in order to facilitate oxidation, when forming a film with a composition not containing oxygen (O) before the heat-treating, it is preferable to increase the niobium (Nb) content of the protective film on the side in contact with the absorber film, or to use a composition that does not contain ruthenium (Ru). Furthermore, when heat-treating the protective film to have a composition containing oxygen (O) on the side in contact with the absorber film, it is preferable to set the change rate of reflectance for exposure light (EUV light) before and after the heat-treating in the state where the reflective multilayer film and the protective film are stacked, to 0.5% or less.

[0038] The protective film can be constructed of a single layer, in which case the protective film is a compositionally graded film whose composition changes in the thickness direction. Fig. 1 is a cross-sectional view showing an example of a first embodiment of the reflective mask blank of the present invention. This reflective mask blank 101 comprises a substrate 1, a reflective multilayer film 2 formed on the substrate 1 in contact with the substrate 1, a protective film 3 formed in contact with the reflective multilayer film 2, and an absorber film 4 formed in contact with the protective film 3. In this case, the protective film 3 has a single-layer structure, and it is sufficient that it has a compositional gradient whose composition changes intermittently and / or continuously in the thickness direction.

[0039] The protective film is preferably constructed of two or three layers. Fig. 2 is a cross-sectional view showing an example of the second embodiment of the reflective mask blank of the present invention. This reflective mask blank 102 comprises a substrate 1, a reflective multilayer film 2 formed on the substrate 1 in contact with the substrate 1, a protective film 3 formed in contact with the reflective multilayer film 2, and an absorber film 4 formed in contact with the protective film 3. In this case, the protective film 3 has a two-layer structure consisting of an (A) layer 31 formed in contact with the reflective multilayer film 2 and a (B) layer 32 formed in contact with the absorber film 4. The protective film may be constructed of four or more layers.

[0040] When the protective film is composed of two layers, the layer adjacent to the reflective multilayer film can be composed of a layer ((A) layer) having a composition containing ruthenium (Ru) but not oxygen (O), and the layer in contact with the absorber film can be composed of a layer ((B) layer) having a composition consisting of ruthenium (Ru), niobium (Nb) and oxygen (O), or niobium (Nb) and oxygen (O).

[0041] The (A) layer contains ruthenium (Ru) but does not contain oxygen (O). The (A) layer may contain niobium (Nb). By configuring the (A) layer in this manner, it is possible to suppress a decrease in reflectance due to the formation of a protective film, and to ensure sufficient reflectance for exposure light of a reflective mask obtained from the reflective mask blank. The (A) layer is preferably a layer made of ruthenium (Ru) or a layer made of ruthenium (Ru) and niobium (Nb).

[0042] When the composition of the (A) layer is composed of ruthenium (Ru) and niobium (Nb), the niobium (Nb) content on the side of the (A) layer closest to the reflective multilayer film is preferably 60 atomic % or less, more preferably 50 atomic % or less, even more preferably 40 atomic % or less, and is greater than 0 atomic %, preferably 5 atomic % or more, more preferably 10 atomic % or more, and even more preferably 20 atomic % or more. If the niobium (Nb) content is too high, the resistance to chlorine-based etching during etching of the absorber film will decrease, and if the protective film is damaged, the reflectivity of the reflective multilayer film may decrease, and the SPM cleaning resistance may also decrease.

[0043] On the other hand, the (B) layer is a layer made of ruthenium (Ru), niobium (Nb) and oxygen (O), or a layer made of niobium (Nb) and oxygen (O). By configuring the (B) layer in this way, it can be used as a layer (stress relaxation layer) that relieves stress in the absorber film formed in contact with the protective film. Furthermore, it can be used as a layer that is highly resistant to chlorine-based etching when etching the absorber film.

[0044] The (B) layer preferably has a high total content of niobium (Nb) and oxygen (O), and on the side of the (B) layer that contacts the absorber film, the total content of niobium (Nb) and oxygen (O) is preferably 60 atomic % or more, more preferably 70 atomic % or more, and even more preferably 80 atomic % or more.

[0045] The thickness of the protective film (if the protective film is multilayered, the total thickness of all layers constituting the multilayered 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. When the protective film is composed of layer (A) and layer (B), the thickness of layer (B) is preferably 10% or more, more preferably 15% or more, and preferably 50% or less, more preferably 30% or less of the thickness of the protective film. If layer (B) is too thick, the reflectance may be significantly reduced due to the formation of the protective film, and SPM cleaning resistance may also be reduced. Specifically, the thickness of layer (B) is preferably 0.5 nm or more, more preferably 0.6 nm or more, and preferably 2 nm or less, more preferably 1.5 nm or less.

[0046] The composition of one or both of the (A) layer and the (B) layer may be such that the niobium (Nb) content increases or decreases stepwise and / or continuously in the thickness direction from the reflective multilayer film side to the absorber film side. In the case of the (A) layer, the niobium (Nb) content may increase or decrease stepwise and / or continuously from the side close to the reflective multilayer film to the side in contact with the (B) layer, and in the case of the (B) layer, the niobium (Nb) content may increase or decrease stepwise and / or continuously from the side in contact with the (A) layer to the side in contact with the absorber film. In this case, the (A) layer and the (B) layer may be composed of two or more sublayers having different compositions, or a compositionally graded layer.

[0047] (B) Layer Group ofThe (B) layer may be configured such that the oxygen (O) content increases stepwise and / or continuously from the reflective multilayer film side toward the absorber film side in the thickness direction. The (B) layer may be configured such that the niobium (Nb) content increases stepwise and / or continuously from the side in contact with the (A) layer toward the side in contact with the absorber film. In this case, the (B) layer may be configured with two or more sub-layers having different compositions, or a compositionally graded layer.

[0048] 3 is a cross-sectional view showing an example of a third embodiment of the reflective mask blank of the present invention. This reflective mask blank 103 comprises a substrate 1, a reflective multilayer film 2 formed on the substrate 1 in contact with the substrate 1, a protective film 3 formed in contact with the reflective multilayer film 2, and an absorber film 4 formed in contact with the protective film 3. The protective film 3 is composed of an (A) layer 31 formed in contact with the reflective multilayer film 2 and a (B) layer 32 formed in contact with the absorber film 4, and the (B) layer 32 is composed of two layers: a first sublayer 32a formed in contact with the (A) layer 31 and a second sublayer 32b formed in contact with the absorber film 4. In this case, the protective film 3 has a three-layer structure consisting of the (A) layer 31, the first sublayer 32a, and the second sublayer 32b.

[0049] A method for forming a protective film in which layer (A) contains ruthenium (Ru) but does not contain oxygen (O), and layer (B) is a layer consisting of ruthenium (Ru), niobium (Nb) and oxygen (O), or niobium (Nb) and oxygen (O) can be described as follows: First, layer (A) is formed by sputtering using a ruthenium (Ru) target and, optionally, a niobium (Nb) target, and a rare gas such as helium (He), argon (Ar), krypton (Kr), or xenon (Xe) as the sputtering gas. Then, layer (B) is formed by reactive sputtering using oxygen (O) as the reactive gas together with the rare gas as the sputtering gas. During sputtering, the ratio of ruthenium (Ru) to niobium (Nb) can be changed by changing the ratio of power applied to the ruthenium (Ru) target and the niobium (Nb) target. Moreover, by changing the amount of oxygen (O2) gas introduced, the oxygen gas content can be changed.

[0050] Another example is a method in which a protective film having a composition that does not contain oxygen (O) is formed using a ruthenium (Ru) target and, if necessary, a niobium (Nb) target as the target and a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as the sputtering gas, and then ashing treatment using oxygen plasma or heat treatment in the presence of oxygen gas, such as in the atmosphere, is performed to form layers (A) and (B) with a composition that contains oxygen (O) on the side of the protective film that comes into contact with the absorber film.

[0051] In particular, a method of heat-treating the protective film to have a composition containing oxygen (O) on the side in contact with the absorber film is preferred because it is easy and has a low risk of defects. Higher heat-treating temperatures facilitate oxidation, but considering the decrease in reflectivity, it is preferable to set the heat-treating temperature at 150°C or less. Furthermore, when the heat-treating temperature is set at 150°C or less, in order to facilitate oxidation, when a film with a composition not containing oxygen (O) is formed before the heat-treating, it is preferable to increase the niobium (Nb) content of the protective film on the side in contact with the absorber film, or to use a composition that does not contain ruthenium (Ru). Furthermore, when the protective film on the side in contact with the absorber film is heat-treated to have a composition containing oxygen (O), it is preferable to set the change rate of reflectivity for exposure light (EUV light) before and after the heat-treating when the reflective multilayer film and the protective film are stacked together to 0.5% or less.

[0052] The absorber film may be formed of any material that can absorb exposure light and be patterned, and is not particularly limited thereto. However, for example, it preferably contains tantalum (Ta). From the viewpoints of processing shape and durability, it is preferable that the absorber film contains tantalum (Ta) and nitrogen (N). Furthermore, the absorber film can reduce stress in the absorber film by having a microcrystalline structure or an amorphous structure rather than a highly crystalline structure (a structure with many metal bonds such that a high intensity peak is detected in XRD). The inclusion of nitrogen (N) is effective in forming an absorber film with a microcrystalline structure or an amorphous structure. Therefore, the nitrogen (N) content of the absorber film is preferably 35 atomic % or more. The upper limit of the nitrogen (N) content of the absorber film is not particularly limited, but is preferably 45 atomic % or less. The absorber film preferably has a tantalum (Ta) to nitrogen (N) ratio, Ta / N, of 55 / 45 to 65 / 35 in atomic ratio.

[0053] The absorber film may be composed of tantalum (Ta) and nitrogen (N), and may further contain one or more additive elements selected from hydrogen (H), boron (B), carbon (C), silicon (Si), molybdenum (Mo), zirconium (Zr), chromium (Cr), germanium (Ge), and aluminum (Al). The addition of additive elements is effective in forming an absorber film having a microcrystalline structure or an amorphous structure. In this case, the total content of additive elements is preferably 20 atomic % or less.

[0054] The lower the film stress of the absorber film, the more preferable. In the present invention, a reflective mask blank can be provided in which the absolute value of ΔTIR (the difference between the TIR of the substrate before the formation of the absorber film and the TIR of the substrate after the formation of the absorber film), calculated from the TIR values ​​measured before and after the formation of the absorber film, is preferably 0.5 μm or less, more preferably 0.3 μm or less.

[0055] The absorber film is preferably composed of a single layer, but the surface of the absorber film is usually naturally oxidized. In this case, the absorber film contains oxygen (O), but it is preferable that the oxygen (O) is contained only in the surface layer (surface oxidation layer) of the absorber film on the side farthest from the substrate. In this case, the absorber film is composed of a layer on the substrate side and a surface layer, and the thickness of the surface layer containing oxygen (O) is preferably 2 nm or less. Furthermore, the oxygen (O) content of the surface layer containing oxygen (O) is preferably 20 atomic % or more and 40 atomic % or less on the side farthest from the substrate. If the surface layer is too thick or the oxygen (O) content of the surface layer is too high, the absorber film may have difficulty absorbing exposure light.

[0056] The thickness of the absorber film is preferably 50 nm or more, more preferably 55 nm or more, and is preferably 80 nm or less, more preferably 70 nm or less. The sheet resistance of the absorber film is preferably 1×10 6 Ω / □ or less, more preferably 1×10 5 The surface roughness Sq of the absorber film is preferably 0.8 nm or less, and more preferably 0.6 nm or less.

[0057] The absorber film can be formed by sputtering, preferably magnetron sputtering. Specifically, the target can be a tantalum (Ta) target, or a metal target of the additive element if the additive element is a metal, or a tantalum (Ta) nitrogen target, or a metal compound target such as a target containing tantalum (Ta) and the additive element if the additive element is a nonmetal. Furthermore, a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas can be used as the sputtering gas. The absorber film can also be formed by reactive sputtering using a rare gas together with a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas, or a carbon-containing gas. Specific examples of reactive gases include nitrogen oxide gases such as oxygen (O) gas, nitrogen (N) gas, nitrous oxide (N0) gas, nitric oxide (NO) gas, and nitrogen dioxide (NO) gas, and carbon oxide gases such as carbon monoxide (CO) gas and carbon dioxide (CO) gas.

[0058] A hard mask film (an etching mask film for the absorber film) having etching characteristics different from those of the absorber film may be provided on the absorber film, preferably in contact with the absorber film, on the side away from the substrate. This hard mask film functions as an etching mask when dry etching the absorber film. After forming a pattern on the absorber film, this hard mask film may be left as a reflectance-reducing layer for reducing the reflectance at wavelengths of light used in inspections such as pattern inspection, or may be removed so that it does not remain on the reflective mask. Materials for the hard mask film include materials containing chromium (Cr). A hard mask film formed from a material containing chromium (Cr) is particularly suitable when the absorber film is formed from a material containing tantalum (Ta) but not chromium (Cr). When a layer (reflectance-reducing layer) mainly serving the function of reducing the reflectance at wavelengths of light used in inspections such as pattern inspection is formed as part of the absorber film, the hard mask film can be formed on the reflectance-reducing layer of the absorber film. The hard mask film can be formed, for example, by magnetron sputtering. The thickness of the hard mask film is not particularly limited, but is usually about 5 to 20 nm.

[0059] A back surface conductive film may be provided on (under) 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, and used to electrostatically chuck the reflective mask to an exposure device.

[0060] 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) or chromium (Cr) may contain oxygen (O), nitrogen (N), carbon (C), boron (B), 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. Examples of materials containing chromium (Cr) include elemental Cr and chromium (Cr) compounds such as CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, CrB, CrOB, CrNB, CrCNB, CrCOB, and CrCONB.

[0061] The thickness of the back surface conductive film is not particularly limited as long as it functions for electrostatic chucking, but is usually about 5 to 100 nm. The thickness of the back surface conductive film is preferably formed after forming the reflective mask, i.e., after forming the absorber film pattern, so that the film stress is balanced with the reflective multilayer film, protective film, and absorber film patterns. The back surface conductive film may be formed before forming the reflective multilayer film, or after forming all of the films on the reflective multilayer film side of the substrate. Alternatively, the back surface conductive film may be formed after forming part of the films on the reflective multilayer film side of the substrate, and then the remaining films on the reflective multilayer film side of the substrate may be formed. The back surface conductive film can be formed, for example, by magnetron sputtering.

[0062] 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.

[0063] From the reflective mask blank, for example, a reflective mask can be obtained that has a substrate, a reflective multilayer film formed on one main surface of the substrate, a protective film formed in contact with the reflective multilayer film, and an absorber film pattern (circuit pattern or mask 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.

[0064] Specifically, first, a resist film is formed on a reflective mask blank, or a reflective mask blank on which a resist film has been formed is used, and pattern writing and resist pattern formation are performed on the resist film by electron beam lithography. Next, the absorber film is removed using the resist pattern as an etching mask, or a hard mask film pattern is formed using the resist pattern as an etching mask, and the absorber film is removed using the hard mask film pattern as an etching mask, thereby forming the remaining portion of the absorber film as the absorber film pattern. Thereafter, the resist pattern is removed, and the hard mask film pattern is removed as necessary, thereby obtaining a reflective mask. [Example]

[0065] The present invention will be specifically explained below with reference to Reference Examples, Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0066] [Reference example 1] A 59-nm-thick TaN 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). The TaN film was deposited by DC pulse magnetron sputtering while the substrate was rotated. The low-thermal expansion glass substrate was placed in a chamber, and Ar gas (40 vol%) and N2 gas (60 vol%) were introduced. The chamber pressure was set to 0.48 Pa, and 1,800 W of power was applied to the tantalum (Ta) target.

[0067] The obtained TaN film was taken out into the atmosphere at room temperature, and its composition was measured using an X-ray photoelectron spectroscopy (XPS) device (K-Alpha, manufactured by Thermo Fisher Scientific). The composition was found to be 57 atomic % of tantalum (Ta) and 43 atomic % of nitrogen (N) relative to the total of tantalum (Ta) and nitrogen (N). In this case, a surface oxide layer (1 nm thick) was formed due to natural oxidation in the atmosphere. The oxygen content of the surface oxide layer, on the side farthest from the substrate, was 25 atomic % relative to the total of tantalum (Ta), nitrogen (N), and oxygen (O). The obtained film was used as the absorber film.

[0068] X-ray diffraction (XRD) measurements of the obtained film were performed using an X-ray diffractometer (Rigaku Corporation, SmartLab) to confirm the crystalline phase contained in the film, and none of the β-Ta crystalline phase, α-Ta crystalline phase, and cubic TaN crystalline phase were detected. In addition, the warpage (TIR) ​​within a 142 mm square area at the center of the substrate surface was measured before and after forming the absorber film using a flatness tester (Corning Incorporated, Tropel Ultra Flat 200 Mask) (the same applies to the warpage (TIR) ​​measurements below). The change in warpage before and after forming the absorber film (ΔTIR) was calculated and found to be 0.39 μm in absolute value.

[0069] [Example 1] A 284-nm-thick reflective multilayer 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) 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 and the substrate rotating. Each target was mounted on 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.

[0070] 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 then 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 layer with a thickness of 3 nm. De After forming the silicon (Si) layer and the molybdenum (Mo) layer, the application of power to the molybdenum (Mo) target was stopped. This process of forming the silicon (Si) layer and the molybdenum (Mo) layer constituted one cycle, and this was repeated 40 times to form the molybdenum (Mo) layer in the 40th cycle. Finally, a silicon (Si) layer of 4 nm was formed by the above method to form a reflective multilayer film.

[0071] Next, a film made of RuNb was formed on the reflective multilayer 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 mount two targets and discharge the targets one by one or both simultaneously. After the reflective multilayer film was formed, the substrate on which the reflective multilayer film had been formed was placed via a transport path maintained in a vacuum state from the sputtering device where the reflective multilayer film had been formed, without being taken out into the atmosphere.

[0072] 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 film made of RuNb with a composition gradient in which niobium (Nb) increased in the thickness direction.

[0073] Next, the substrate on which the reflective multilayer film and the RuNb film were formed was heat-treated in an air atmosphere at 150°C for 15 minutes using a hot plate heating device to oxidize the surface of the RuNb film. The thickness of the formed oxide layer was 1.5 nm, and the total content of niobium (Nb) and oxygen (O) relative to the total of ruthenium (Ru), niobium (Nb), and oxygen (O) was 70 atomic % on the side on which the absorber film was formed.

[0074] The film obtained by the heat treatment was a protective film consisting of a 2.4 nm thick layer (A) made of RuNb with a composition gradient in which the niobium (Nb) content relative to the total of ruthenium (Ru) and niobium (Nb) increases from 10 atomic % to 20 atomic % along the thickness, and a 1.5 nm thick layer (B) made of RuNbO. The total thickness of the protective film was 3.9 nm.

[0075] Next, an absorber film was formed on the protective film in the same manner as in Reference Example 1. The warpage (TIR) ​​within a 142 mm square area at the center of the substrate surface was measured before and after forming the absorber film, and the change in warpage before and after (ΔTIR) was calculated to be 0.27 μm in absolute value.

[0076] [Example 2] A reflective multilayer film was formed in the same manner as in Example 1 on the main surface of a low-thermal expansion glass substrate (SiO2-TiO2-based glass substrate) measuring 152 mm square and 6.35 mm thick.

[0077] Next, a film made of RuNb was formed on the reflective multilayer 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 mount two targets and discharge the targets one by one or both simultaneously. After the reflective multilayer film was formed, the substrate on which the reflective multilayer film had been formed was placed via a transport path maintained in a vacuum state from the sputtering device where the reflective multilayer film had been formed, without being taken out into the atmosphere.

[0078] 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 film made of RuNb with a composition gradient in which niobium (Nb) increased in the thickness direction.

[0079] Next, the substrate on which the reflective multilayer film and the RuNb film were formed was heat-treated in an air atmosphere at 150°C for 15 minutes using a hotplate heating device to oxidize the surface of the RuNb film. The thickness of the formed oxide layer was 1.5 nm, and the total content of niobium (Nb) and oxygen (O) relative to the total of ruthenium (Ru), niobium (Nb), and oxygen (O) was 88 atomic % on the side on which the absorber film was formed.

[0080] The film obtained by the heat treatment was a protective film consisting of a 2.4 nm thick layer (A) made of RuNb with a composition gradient in which the niobium (Nb) content relative to the total of ruthenium (Ru) and niobium (Nb) increases from 15 atomic % to 25 atomic % along the thickness direction, and a 1.5 nm thick layer (B) made of RuNbO. The total thickness of the protective film was 3.9 nm.

[0081] Next, an absorber film was formed on the protective film in the same manner as in Reference Example 1. The warpage (TIR) ​​within a 142 mm square area at the center of the substrate surface was measured before and after forming the absorber film, and the change in warpage before and after (ΔTIR) was calculated to be 0.23 μm in absolute value.

[0082] [Example 3] A reflective multilayer film was formed in the same manner as in Example 1 on the main surface of a low-thermal expansion glass substrate (SiO2-TiO2-based glass substrate) measuring 152 mm square and 6.35 mm thick.

[0083] Next, a ruthenium (Ru) target and a niobium (Nb) target were used to form a film composed of a layer of RuNb and a layer of Nb on the reflective multilayer film by DC pulse magnetron sputtering while rotating the substrate, with both targets facing the main surface of the substrate. Each target was mounted in a separate sputtering device that could mount two targets and discharge the targets one by one or both simultaneously. After the reflective multilayer film was formed, the substrate on which the reflective multilayer film had been formed was placed via a transport path maintained in a vacuum state from the sputtering device where the reflective multilayer film had been formed, without being taken out into the atmosphere.

[0084] 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 layer made of RuNb with a composition gradient in which niobium (Nb) increased in the thickness direction.Furthermore, power was applied only to the niobium (Nb) target to form a layer made of Nb, thereby forming a film made of a layer made of RuNb and a layer made of Nb.

[0085] Next, the substrate on which the reflective multilayer film and the film consisting of the layer made of RuNb and the layer made of Nb 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 film consisting of the layer made of RuNb and the layer made of Nb. The thickness of the formed oxide layer was 1.5 nm, and the total content of niobium (Nb) and oxygen (O) relative to the total of ruthenium (Ru), niobium (Nb), and oxygen (O) was 100 atomic % on the side on which the absorber film was formed.

[0086] The film obtained by the heat treatment was a protective film consisting of (A) layer, 2.4 nm thick, made of RuNb, with a composition gradient in which the niobium (Nb) content relative to the total of ruthenium (Ru) and niobium (Nb) increases from 10 atomic % to 20 atomic % along the thickness, and (B) layer, consisting of a first sublayer made of RuNbO, 1 nm thick, on the reflective multilayer side, and a second sublayer made of NbO, 0.5 nm thick, on the absorber side. The total thickness of the protective film was 3.9 nm.

[0087] Next, an absorber film was formed on the protective film in the same manner as in Reference Example 1. The warpage (TIR) ​​within a 142 mm square area at the center of the substrate surface was measured before and after forming the absorber film, and the change in warpage before and after (ΔTIR) was calculated to be 0.23 μm in absolute value.

[0088] [Comparative Example 1] A reflective multilayer film was formed in the same manner as in Example 1 on the main surface of a low-thermal expansion glass substrate (SiO2-TiO2-based glass substrate) measuring 152 mm square and 6.35 mm thick.

[0089] Next, a ruthenium (Ru) target was used on the reflective multilayer film, and a film made of Ru was formed by DC pulse magnetron sputtering while the target and the main surface of the substrate were opposed to each other and the substrate was rotated. The sputtering was performed in a separate sputtering device that can accommodate two targets and can discharge the targets one by one or both simultaneously. ,Ta After the target was attached and the reflective multilayer film was formed, the substrate on which the reflective multilayer film had been formed was placed via a transport path maintained in a vacuum state from the sputtering device where the reflective multilayer film had been formed, without being taken out into the atmosphere.

[0090] While argon (Ar) gas was flowing into the chamber, power was applied to the ruthenium (Ru) target to form a film made of Ru, which served as the protective film. In this example, no heat treatment was performed. The total thickness of the protective film was 3.9 nm.

[0091] Next, an absorber film was formed on the protective film in the same manner as in Reference Example 1. The warpage (TIR) ​​within a 142 mm square area at the center of the substrate surface was measured before and after forming the absorber film, and the change in warpage before and after (ΔTIR) was calculated to be 0.53 μm in absolute value.

[0092] [Example 4] A reflective multilayer film was formed in the same manner as in Example 1 on the main surface of a low-thermal expansion glass substrate (SiO2-TiO2-based glass substrate) measuring 152 mm square and 6.35 mm thick.

[0093] Next, a film made of RuNb was formed on the reflective multilayer 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 mount two targets and discharge the targets one by one or both simultaneously. After the reflective multilayer film was formed, the substrate on which the reflective multilayer film had been formed was placed via a transport path maintained in a vacuum state from the sputtering device where the reflective multilayer film had been formed, without being taken out into the atmosphere.

[0094] 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 film made of RuNb with a composition gradient in which niobium (Nb) increased in the thickness direction.

[0095] Next, the substrate on which the reflective multilayer film and the RuNb film were formed was heat-treated in an air atmosphere at 150°C for 15 minutes using a hotplate heating device to oxidize the surface of the RuNb film. The thickness of the formed oxide layer was 1.5 nm, and the total content of niobium (Nb) and oxygen (O) relative to the total of ruthenium (Ru), niobium (Nb), and oxygen (O) was 60 atomic % on the side on which the absorber film was formed.

[0096] The film obtained by the heat treatment was a protective film consisting of a 2.4 nm thick (A) layer made of RuNb with a composition gradient in which the niobium (Nb) content relative to the total of ruthenium (Ru) and niobium (Nb) increases from 5 atomic % to 10 atomic % along the thickness direction, and a 1.5 nm thick (B) layer made of RuNbO. The total thickness of the protective film was 3.9 nm.

[0097] Next, an absorber film was formed on the protective film in the same manner as in Reference Example 1. The warpage (TIR) ​​within a 142 mm square area at the center of the substrate surface was measured before and after forming the absorber film, and the change in warpage before and after (ΔTIR) was calculated to be 0.39 μm in absolute value.

[0098] Comparative Example 2 A reflective multilayer film was formed in the same manner as in Example 1 on the main surface of a low-thermal expansion glass substrate (SiO2-TiO2-based glass substrate) measuring 152 mm square and 6.35 mm thick.

[0099] Next, a film made of RuNb was formed on the reflective multilayer 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 mount two targets and discharge the targets one by one or both simultaneously. After the reflective multilayer film was formed, the substrate on which the reflective multilayer film had been formed was placed via a transport path maintained in a vacuum state from the sputtering device where the reflective multilayer film had been formed, without being taken out into the atmosphere.

[0100] First, while argon (Ar) gas was flowing into the chamber, power was simultaneously applied to a ruthenium (Ru) target and a niobium (Nb) target. Over time, the power applied to the niobium (Nb) target was gradually increased, forming a RuNb film with a composition gradient in which niobium (Nb) increased in the thickness direction, forming a protective film. In this example, no heat treatment was performed. The total thickness of the protective film was 3.9 nm.

[0101] Next, an absorber film was formed on the protective film in the same manner as in Reference Example 1. The warpage (TIR) ​​within a 142 mm square area at the center of the substrate surface was measured before and after forming the absorber film, and the change in warpage before and after (ΔTIR) was calculated to be 0.53 μm in absolute value.

[0102] [Reference example 2] A 59-nm-thick TaSiN 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). The TaSiN film was deposited by DC pulse magnetron sputtering while the substrate was rotated. The low-thermal expansion glass substrate was placed in a chamber, and Ar gas (67 vol%) and N2 gas (33 vol%) were introduced. The chamber pressure was set to 0.27 Pa, and a power of 1,620 W was applied to the tantalum (Ta) target and 180 W to the silicon (Si) target.

[0103] The obtained TaSiN film was taken out into the air at room temperature, and its composition was measured using an X-ray photoelectron spectroscopy (XPS) device (K-Alpha, manufactured by Thermo Fisher Scientific Co., Ltd.). The composition was found to be 55 atomic % of tantalum (Ta), 10 atomic % of silicon (Si), and 35 atomic % of nitrogen (N) relative to the total of tantalum (Ta), silicon (Si), and nitrogen (N). The obtained film was used as the absorber film.

[0104] X-ray diffraction (XRD) measurements of the obtained film were performed using an X-ray diffractometer (Rigaku Corporation, SmartLab) to confirm the crystalline phase contained in the film, and none of the β-Ta crystalline phase, α-Ta crystalline phase, or cubic TaN crystalline phase was detected. In addition, the warpage (TIR) ​​within a 142 mm square area at the center of the substrate surface was measured before and after forming the absorber film, and the change in warpage before and after (ΔTIR) was calculated, and the absolute value was 0.41 μm.

[0105] [Example 5] A reflective multilayer 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. Next, a protective film was formed on the reflective multilayer film in the same manner as in Example 1.

[0106] Next, an absorber film was formed on the protective film in the same manner as in Reference Example 2. The warpage (TIR) ​​within a 142 mm square area at the center of the substrate surface was measured before and after forming the absorber film, and the change in warpage before and after (ΔTIR) was calculated to be 0.37 μm in absolute value. [Explanation of symbols]

[0107] 1 board 2 Reflective multilayer film 3 Protective film 31 (A) layer 32 (B) layer 32a First Sublayer 32b Second Sublayer 4. Absorber membrane 101, 102, 103 Reflective mask blanks

Claims

1. It is a material for reflective masks used in EUV lithography, which uses EUV light as exposure light. A reflective mask blank comprising: a substrate; a reflective multilayer film formed on one main surface of the substrate, the reflective multilayer film having a periodic stacking structure in which layers having a relatively low refractive index for exposure light and layers having a relatively high refractive index for exposure light are alternately stacked, the reflective multilayer film reflecting the exposure light; a protective film formed in contact with the reflective multilayer film; and an absorber film formed in contact with the protective film and absorbing the exposure light, The protective film is consisting of ruthenium (Ru), niobium (Nb) and oxygen (O); the composition of the side close to the reflective multilayer film contains ruthenium (Ru) and does not contain oxygen (O); the composition of the side in contact with the absorber film is composed of ruthenium (Ru), niobium (Nb) and oxygen (O), and the total content of niobium (Nb) and oxygen (O) is 60 atomic % or more, or is composed of niobium (Nb) and oxygen (O); The absorber film is Contains tantalum (Ta) and nitrogen (N), The nitrogen (N) content is 35 atomic % or more and 45 atomic % or less, The ratio of tantalum (Ta) to nitrogen (N), Ta / N, is 55 / 45 to 65 / 35 in atomic ratio; The thickness is 50 nm or more and 80 nm or less. A reflective mask blank characterized by:

2. 2. The reflective mask blank according to claim 1, wherein the protective film has a composition on the side closest to the reflective multilayer film consisting of ruthenium (Ru) or ruthenium (Ru) and niobium (Nb).

3. 3. The reflective mask blank according to claim 2, wherein the niobium (Nb) content in the composition of the protective film on the side adjacent to the reflective multilayer film is 60 atomic % or less.

4. 3. The reflective mask blank according to claim 2, wherein the niobium (Nb) content of the protective film increases stepwise and / or continuously in the thickness direction from the side close to the reflective multilayer film toward the side in contact with the absorber film.

5. 2. The reflective mask blank according to claim 1, wherein the protective film has an oxygen (O) content that increases stepwise and / or continuously in the thickness direction from the side closest to the reflective multilayer film toward the side in contact with the absorber film.

6. A reflective mask blank as described in claim 1, characterized in that the composition of the side in contact with the absorber film consists of niobium (Nb) and oxygen (O).

7. A reflective mask blank as described in claim 1, characterized in that the absorber film consists of a single layer made of tantalum (Ta) and nitrogen (N).

8. 2. The reflective mask blank according to claim 1, wherein the protective film includes a stress relaxation layer formed in contact with the absorber film.

9. The protective film is (A) a layer containing ruthenium (Ru) and not containing oxygen (O), the layer being adjacent to the reflective multilayer film; (B) a layer which is the stress relaxation layer and has a composition consisting of ruthenium (Ru), niobium (Nb) and oxygen (O), or niobium (Nb) and oxygen (O), and is in contact with the absorber film; 9. The reflective mask blank according to claim 8, comprising two layers:

10. 10. The reflective mask blank according to claim 9, wherein the layer (A) is made of ruthenium (Ru) or ruthenium (Ru) and niobium (Nb).

11. 11. The reflective mask blank according to claim 10, wherein the niobium (Nb) content of the layer (A) on the side closest to the reflective multilayer film is 60 atomic % or less.

12. 11. The reflective mask blank according to claim 10, wherein the (A) layer is composed of two or more sub-layers having different compositions or a composition gradient layer, and the niobium (Nb) content increases stepwise and / or continuously in the thickness direction from the side close to the reflective multilayer film toward the side in contact with the (B) layer.

13. 10. The reflective mask blank according to claim 9, wherein the (B) layer is composed of two or more sub-layers having different compositions, or a composition gradient layer, and the oxygen (O) content increases stepwise and / or continuously in the thickness direction from the side in contact with the (A) layer toward the side in contact with the absorber film.

14. 10. The reflective mask blank according to claim 9, wherein the thickness of the protective film is 2 nm or more and 5 nm or less, and the thickness of the (B) layer is 10% or more and 50% or less of the thickness of the protective film.

15. 10. The reflective mask blank according to claim 9, wherein the absorber film further contains one or more additive elements selected from hydrogen (H), boron (B), carbon (C), silicon (Si), molybdenum (Mo), zirconium (Zr), chromium (Cr), germanium (Ge), and aluminum (Al), and the total content of the additive elements is 20 atomic % or less.

16. The absorber film comprises a substrate-side layer made of tantalum (Ta) and nitrogen (N) and a surface layer made of tantalum (Ta), nitrogen (N) and oxygen (O), a ratio of tantalum (Ta) to nitrogen (N), Ta / N, in the substrate-side layer and the surface layer is 55 / 45 to 65 / 35 in atomic ratio, and an oxygen (O) content is 20 atomic % or more and 40 atomic % or less on the side of the surface layer farthest from the substrate, The thickness of the surface layer is 2 nm or less.

10. The reflective mask blank according to claim 9.

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