Manufacturing method of substrate with multilayer reflective film, reflective photomask substrate, reflective photomask, and semiconductor device

Abstract

This invention provides a substrate with a multilayer reflective film, which can significantly reduce the reflectivity of the multilayer reflective film to EUV exposure light and prevent surface bulging or peeling of the protective film on the multilayer reflective film. The substrate 110 of this invention has a multilayer reflective film 5 and a protective film 6 sequentially disposed on the main surface of a substrate 1. The substrate 1 is mainly composed of silicon, titanium, and oxygen, and further contains hydrogen. The multilayer reflective film 5 has a structure formed by alternating layers of low-refractive-index and high-refractive-index layers. The multilayer reflective film 5 contains hydrogen. The atomic number density of hydrogen in the multilayer reflective film 5 is less than 7.0 × 10⁻³ atoms / nm³.

Description

[Technical Field]

[0001] This invention relates to a reflective photomask used in the manufacture of semiconductor devices, and a substrate with a multilayer reflective film for manufacturing the reflective photomask and a reflective photomask substrate. Furthermore, this invention relates to a method for manufacturing a semiconductor device using the aforementioned reflective photomask. [Previous Technology]

[0002] Exposure apparatuses used in the manufacture of semiconductor devices have continuously evolved as the wavelength of the light source has gradually shortened. To achieve finer pattern transfer, EUV lithography, which uses extreme ultraviolet (EUV) light with a wavelength around 13.5 nm, has been developed. In EUV lithography, since there is less material transparent to EUV light, reflective photomasks are used. Representative reflective photomasks include binary reflective photomasks and phase-shifted reflective photomasks (halftone phase-shifted reflective photomasks). Binary reflective photomasks have a relatively thick absorber pattern that sufficiently absorbs EUV light. Phase-shifted reflective photomasks have a relatively thin absorber pattern (phase-shifted pattern) that reduces EUV light through light absorption and produces reflected light with a phase reversal of approximately 180 degrees relative to the reflected light from the multilayer reflective film.

[0003] Patent documents 1 to 3 describe technologies related to such reflective photomasks for EUV lithography and photomask substrates for manufacturing them.

[0004] Patent Document 1 describes a process in which a multilayer reflective film in the region outside the photomask pattern area is irradiated with laser light or an electron beam and heated. By performing this process, the high-refractive-index material and the low-refractive-index material of the multilayer reflective film diffuse, thereby reducing the reflectivity of the multilayer reflective film for EUV light.

[0005] Patent Document 2 describes the use of TiO2-SiO2 glass in photomasks and the like for EUV lithography. According to this document, the hydrogen content in the TiO2-SiO2 glass is preferably 5 × 10¹⁷ molecules / cm³ or higher. Furthermore, it is also described that OH groups are preferably added to the TiO2-SiO2 glass.

[0006] Patent Document 3 describes a method for creating a hydrogenated layer at the interface between a silicon layer and a molybdenum layer in a multilayer structure of a soft X-ray multilayer mirror. According to this document, by providing the hydrogenated layer, mutual reactions or diffusion at the interface between the silicon and molybdenum layers can be suppressed. [Prior Art Documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2010 / 026998 [Patent Document 2] Japanese Patent Application Publication No. 2011-162359 [Patent Document 3] Japanese Patent Application Publication No. Hei 5-297194 [Summary of the Invention]

[0008] [Problem to be Solved by the Invention] In EUV lithography, considering light transmittance, a projection optical system comprising multiple mirrors is used. Furthermore, the EUV light is incident obliquely relative to the reflective photomask, ensuring that the multiple mirrors do not block the projection light (exposure light). Regarding the incident angle, the current mainstream system sets it to 6 degrees relative to the vertical plane of the reflective photomask substrate.

[0009] In EUV lithography, due to the oblique incidence of the exposed light, an inherent problem known as the masking effect exists. The masking effect is the phenomenon where, because the exposed light is obliquely incident on the absorber pattern with a three-dimensional structure, a shadow is created, causing changes in the size or position of the transferred pattern. The three-dimensional structure of the absorber pattern acts as a wall, creating a shadow on the shaded side, thus altering the size or position of the transferred pattern. For example, when the orientation of the absorbed pattern is parallel to the direction of the obliquely incident light, and when it is perpendicular to the direction of the obliquely incident light, differences in the size and position of the transferred pattern occur, thereby reducing the transfer accuracy.

[0010] In reflective photomasks, the formation of ultra-fine and high-precision patterns is required, thus reducing the aforementioned shielding effect is necessary. Therefore, for reflective photomasks, research is underway to reduce the film thickness of the thin film patterns (absorber patterns, phase-shifting patterns). However, reducing the film thickness inevitably results in a higher reflectivity for EUV light compared to before.

[0011] Generally, pattern transfer in EUV lithography is performed by stepping through a reflective photomask to transfer the object. During this stepping scan, multiple identical transfer patterns are exposed and transferred onto the object by repeatedly performing exposure transfer and stepping. At this time, multiple transfer patterns are exposed onto the object with almost no gaps. Therefore, reflected light from the outer periphery of the area where the thin film transfer pattern is formed on the reflective photomask overlaps during exposure, resulting in what is known as overlapping exposure. If the reflectivity of the thin film pattern is higher than before, there is a risk of unnecessary light exposure in the area of ​​the object where this overlapping exposure occurs.

[0012] In order to reduce the reflectivity of the outer periphery of the area where the transfer pattern is formed on a reflective photomask to EUV light, the inventors attempted the method disclosed in Patent Document 1. Specifically, laser light irradiation was performed to induce diffusion between the constituent elements of the low-refractive-index layer and the constituent elements of the high-refractive-index layer of the multilayer reflective film. It was found that after this treatment, the surface of the protective film on the multilayer reflective film may bulge or peel off. It was also found that this phenomenon may occur when electron beam irradiation or heat treatment is performed. If such phenomena occur, it is impossible to continue the treatment to induce diffusion between the constituent elements of the low-refractive-index layer and the constituent elements of the high-refractive-index layer of the multilayer reflective film, thus failing to sufficiently reduce the reflectivity of the multilayer reflective film to EUV light exposure, and therefore a problem exists. Furthermore, the protective film cracking causes dust generation, resulting in frequent defects in the manufactured reflective photomask.

[0013] Therefore, the object of the present invention is to provide a substrate with a multilayer reflective film, which can sufficiently reduce the reflectivity of the multilayer reflective film to EUV exposure light, and can prevent the phenomenon of surface bulging or peeling of the protective film on the multilayer reflective film.

[0014] Furthermore, the object of the present invention is to provide a reflective photomask substrate and a reflective photomask manufactured using the aforementioned substrate with multilayer reflective films, and a method for manufacturing a semiconductor device using the reflective photomask. [Technical Means for Solving the Problem]

[0015] Through intensive research, the inventors have discovered that hydrogen present in the multilayer reflective film turns into gas due to heating caused by laser irradiation or other factors. This gas attempts to detach from the multilayer reflective film and accumulates at the interface between the multilayer reflective film and the protective film, resulting in the protective film bulging from the multilayer reflective film. Furthermore, it has been discovered that the temperature rise of the multilayer reflective film and the protective film causes the gaseous hydrogen trapped between them to thermally expand, thereby causing the protective film to rupture.

[0016] On the other hand, it is clear that the substrate of the photomask substrate used to manufacture the reflective photomask contains hydrogen and OH groups, and these cannot be eliminated. Furthermore, it is clear that hydrogen or OH groups can migrate from the substrate to the multilayer reflective film, and this phenomenon is difficult to prevent. Based on these observations, the inventors conducted further intensive research and concluded that the above-mentioned technical problems can be solved by using a substrate with a multilayer reflective film having the following configuration.

[0017] (Composition 1) A substrate with a multilayer reflective film, characterized in that a multilayer reflective film and a protective film are sequentially provided on the main surface of the substrate, and the substrate is mainly composed of silicon, titanium and oxygen, and contains hydrogen, the multilayer reflective film has a structure formed by alternating layers of low refractive index layer and high refractive index layer, the multilayer reflective film contains hydrogen, and the atomic number density of hydrogen in the multilayer reflective film is 7.0×10-3 atoms / nm3 or less.

[0018] (Structure 2) The substrate with a multilayer reflective film as described in Structure 1, wherein the high refractive index layer contains silicon and the low refractive index layer contains molybdenum.

[0019] (Content 3) The substrate with a multilayer reflective film as described in Constent 1 or 2, wherein the atomic number density of hydrogen in the substrate obtained by analysis of the substrate by secondary ion mass spectrometry is 1.0 × 10¹⁹ atoms / cm³ or more.

[0020] (Construction 4) A substrate with a multilayer reflective film as described in any one of Constructions 1 to 3, wherein the protective film contains ruthenium.

[0021] (Construction 5) A substrate with a multilayer reflective film as described in any one of Constructions 1 to 4, wherein the multilayer reflective film has a mixed region on the main surface formed by mixing the constituent elements of the low refractive index layer and the constituent elements of the high refractive index layer, and the surface reflectivity of the mixed region to EUV light is lower than that of other regions to EUV light.

[0022] (Composition 6) A photomask substrate, characterized in that it is provided sequentially on the main surface of a substrate with a multilayer reflective film, a protective film and a pattern forming film, wherein the substrate is mainly composed of silicon, titanium and oxygen, and contains hydrogen, wherein the multilayer reflective film has a structure formed by alternating layers of low refractive index layer and high refractive index layer, wherein the multilayer reflective film contains hydrogen, and the atomic number density of hydrogen in the multilayer reflective film is 7.0×10-3 atoms / nm3 or less.

[0023] (Structure 7) The photomask substrate as described in Structure 6, wherein the high refractive index layer contains silicon and the low refractive index layer contains molybdenum.

[0024] (Construction 8) The photomask substrate as described in Construction 6 or 7, wherein the atomic number density of hydrogen in the substrate obtained by analysis of the substrate using secondary ion mass spectrometry is 1.0 × 10¹⁹ atoms / cm³ or more.

[0025] (Construction 9) The photomask substrate as described in any one of Constructions 6 to 8, wherein the protective film contains ruthenium.

[0026] (Construction 10) The photomask substrate as described in any one of Constructions 6 to 9, wherein the multilayer reflective film has a mixed region on its main surface formed by mixing the constituent elements of the low refractive index layer and the constituent elements of the high refractive index layer, and the surface reflectivity of the mixed region to EUV light is lower than the surface reflectivity of the pattern forming film to EUV light.

[0027] (Composition 11) A reflective photomask, characterized in that it is provided sequentially on the main surface of a substrate with a multilayer reflective film, a protective film and a thin film pattern, wherein the substrate is mainly composed of silicon, titanium and oxygen, and contains hydrogen, the multilayer reflective film has a structure formed by alternating layers of low refractive index layer and high refractive index layer, the multilayer reflective film contains hydrogen, the atomic number density of hydrogen in the multilayer reflective film is less than 7.0×10-3 atoms / nm3, and the peripheral region of the multilayer reflective film on the main surface of which the thin film pattern is provided has a mixed region formed by mixing the constituent elements of the low refractive index layer and the constituent elements of the high refractive index layer, wherein the surface reflectivity of the mixed region to EUV light is lower than the surface reflectivity of the thin film pattern to EUV light.

[0028] (Structure 12) The reflective photomask as described in Structure 11, wherein the high refractive index layer contains silicon and the low refractive index layer contains molybdenum.

[0029] (Construction 13) The reflective photomask described in Construction 11 or 12, wherein the atomic number density of hydrogen in the substrate obtained by analysis of the substrate using secondary ion mass spectrometry is 1.0 × 10¹⁹ atoms / cm³ or more.

[0030] (Construction 14) A reflective photomask as described in any one of Constructions 11 to 13, wherein the protective film contains ruthenium.

[0031] (Configuration 15) A method for manufacturing a semiconductor device, characterized by comprising the step of exposing and transferring a transfer pattern onto a photoresist film on a semiconductor substrate using a reflective photomask as described in any one of Configurations 11 to 14. [Effects of the Invention]

[0032] According to the present invention, a substrate with a multilayer reflective film can be provided, which can sufficiently reduce the reflectivity of the multilayer reflective film to EUV exposure light, and can suppress the phenomenon of surface bulging of the protective film on the multilayer reflective film or the phenomenon of protective film peeling off.

[0033] Furthermore, according to the present invention, a method for manufacturing a reflective photomask substrate and a reflective photomask having a partially identical structure to the aforementioned substrate with a multilayer reflective film, and a semiconductor device using the reflective photomask, can be provided.

Implementation Method

[0035] Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. Furthermore, the following embodiments are for illustrative purposes only and do not limit the scope of the present invention.

[0036] FIG1 is a cross-sectional schematic diagram of the substrate 110 with a multilayer reflective film according to this embodiment. As shown in FIG1, the substrate 110 with a multilayer reflective film according to this embodiment has a multilayer reflective film 5 and a protective film 6 sequentially provided on the substrate 1. The multilayer reflective film 5 is a film used to reflect the light of exposure, and is composed of a multilayer film formed by alternately depositing low refractive index layers and high refractive index layers. The protective film 6 is a film used to protect the multilayer reflective film 5 from damage due to dry etching and cleaning during the manufacturing steps of the reflective photomask 200 described below. In addition, the protective film 6 can also protect the multilayer reflective film 5 when using electron beam (EB) to correct black spot defects in the photomask pattern. The substrate 110 with a multilayer reflective film according to this embodiment may also include a back conductive film 2 on the back side of the substrate 1 (the main surface opposite to the main surface on which the multilayer reflective film 5 is formed).

[0037] Using the substrate 110 with the multilayer reflective film of this embodiment, a reflective photomask substrate 100 can be manufactured. FIG2 is a cross-sectional schematic diagram of an example of the reflective photomask substrate 100. As shown in FIG2, the reflective photomask substrate 100 further includes an absorber film (patterning film) 7 on the protective film 6. By using the reflective photomask substrate 100 of this embodiment, a reflective photomask 200 having a multilayer reflective film 5 with high reflectivity for EUV light can be obtained.

[0038] In this specification, the phrase "having membrane B on membrane A" includes not only the case where membrane B and membrane A are connected in contact with each other, but also the case where there are other membranes between membrane A and membrane B. Furthermore, in this specification, "membrane B and membrane A are connected in contact with each other" means that membrane B is configured in contact with the surface of membrane A, and no other membrane is placed between membrane A and membrane B.

[0039] <Substrate 110 with Multilayer Reflective Film> Hereinafter, the substrate 110 with multilayer reflective film of this embodiment will be described in detail. The substrate 110 with multilayer reflective film includes a substrate 1, a multilayer reflective film 5, and a protective film 6.

[0040] <<Substrate 1>> Substrate 1 is mainly composed of silicon, titanium, and oxygen, and further contains hydrogen. In this case, the hydrogen also includes hydrogen present in the form of OH groups. As an example of substrate 1 mainly composed of silicon, titanium, and oxygen, SiO2-TiO2 glass can be cited. SiO2-TiO2 glass is a silicon dioxide glass containing TiO2, and is a low thermal expansion material with a smaller coefficient of thermal expansion than quartz glass. When substrate 1 is SiO2-TiO2 glass, substrate 1 contains hydrogen and OH groups.

[0041] For substrate 1, the atomic number density of hydrogen in substrate 1 obtained by analysis using secondary ion mass spectrometry (SIMS) is preferably 1.0 × 10¹⁹ atoms / cm³ or higher, more preferably 2.0 × 10¹⁹ atoms / cm³ or higher. On the other hand, the atomic number density of hydrogen in substrate 1 is preferably 5.0 × 10²¹ atoms / cm³ or lower, more preferably 3.0 × 10²¹ atoms / cm³ or lower. If the hydrogen content in substrate 1 is too high, the amount of hydrogen released from substrate 1 will increase, and more of this hydrogen will be absorbed into the multilayer reflective film 5. Furthermore, the hydrogen in substrate 1 detected by SIMS analysis includes states of bonding with Si, states of OH groups, states existing in ionic form, and states existing in molecular form. Therefore, the numerical value of the atomic number density of hydrogen in substrate 1 determined by SIMS analysis also includes the value of hydrogen in OH groups.

[0042] The concentration of OH groups in substrate 1 is preferably 50 ppm or more, and more preferably 60 ppm or more. The concentration of OH groups in substrate 1 can be measured by known methods, for example, by the method described in Japanese Patent No. 4792705.

[0043] From the viewpoint of improving the accuracy of pattern transfer, the first main surface of the substrate 1 on the side where the multilayer reflective film 5 is formed is preferably surface-processed to achieve a specific flatness. In the case of EUV exposure, the flatness in the 132 mm × 132 mm area of ​​the main surface of the substrate 1 on the side where the transfer pattern is formed is preferably 0.1 μm or less, more preferably 0.05 μm or less, and even more preferably 0.03 μm or less. Furthermore, when a reflective photomask is placed in the exposure apparatus, the second main surface (back side), which is opposite to the side where the multilayer reflective film 5 is formed, is adsorbed by an electrostatic chuck. The flatness of the second main surface in the 142 mm × 142 mm area is preferably 0.1 μm or less, more preferably 0.05 μm or less, and even more preferably 0.03 μm or less.

[0044] Furthermore, the smoothness of the surface of the substrate 1 is also important. The surface roughness of the first main surface of the substrate 1 is preferably less than 0.15 nm in terms of root mean square roughness (Rms), and more preferably less than 0.10 nm in terms of Rms. Moreover, the surface smoothness can be measured by atomic force microscopy.

[0045] Furthermore, in order to prevent the substrate 1 from deforming due to the film stress of the film (such as the multilayer reflective film 5) formed on the substrate 1, the substrate 1 preferably has high rigidity. The substrate 1 is particularly preferably a high Young's modulus of 65 GPa or higher.

[0046] <<Multilayer reflective film 5>> The multilayer reflective film 5 is used in the reflective photomask 200 to give it the function of reflecting EUV light. The multilayer reflective film 5 is a multilayer film formed by periodically stacking layers of elements with different refractive indices as the main components.

[0047] Generally speaking, as a multilayer reflective film 5, a multilayer film is formed by alternately depositing thin films (high refractive index layers) of light elements or their compounds as high refractive index materials and thin films (low refractive index layers) of heavy elements or their compounds as low refractive index materials for about 40 to 60 cycles (pairs).

[0048] The multilayer reflective film 5 comprises a stacked structure of "high refractive index layer / low refractive index layer" formed by sequentially stacking a high refractive index layer and a low refractive index layer from the substrate 1 side. Alternatively, this stacked structure can be stacked multiple times, with one "high refractive index layer / low refractive index layer" as one cycle. Alternatively, the multilayer reflective film 5 comprises a stacked structure of "low refractive index layer / high refractive index layer" formed by sequentially stacking a low refractive index layer and a high refractive index layer from the substrate 1 side. Alternatively, this stacked structure can be stacked multiple times, with one "low refractive index layer / high refractive index layer" as one cycle. Furthermore, the outermost layer of the multilayer reflective film 5, that is, the surface layer of the multilayer reflective film 5 on the side opposite to the substrate 1 side, is preferably a high refractive index layer. In the case where a high refractive index layer and a low refractive index layer are sequentially stacked from the substrate 1 side, the uppermost layer becomes a low refractive index layer. In this case, the low-refractive-index layer becomes the outermost surface of the multilayer reflective film 5, and therefore the outermost surface of the multilayer reflective film 5 is prone to oxidation, reducing the reflectivity of the reflective photomask 200. Therefore, it is preferable to form a high-refractive-index layer on top of the uppermost low-refractive-index layer. On the other hand, when a low-refractive-index layer and a high-refractive-index layer are sequentially deposited from the substrate 1 side, the uppermost layer becomes a high-refractive-index layer. In this case, it is not necessary to further form a high-refractive-index layer.

[0049] As a high refractive index layer, a material containing silicon (Si) can be used, for example. Besides elemental Si, Si compounds containing at least one element selected from boron (B), carbon (C), zirconium (Zr), nitrogen (N), and oxygen (O) can also be used as the Si-containing material. By using a high refractive index layer containing Si, a reflective photomask 200 with excellent EUV light reflectivity can be obtained.

[0050] As a low refractive index layer, for example, at least one elemental metal selected from molybdenum (Mo), ruthenium (Ru), rhodium (Rh) and platinum (Pt), or an alloy thereof, may be used.

[0051] In the substrate 110 with the multilayer reflective film of this embodiment, it is preferable that the low refractive index layer is a layer containing molybdenum (Mo) and the high refractive index layer is a layer containing silicon (Si). As the multilayer reflective film 5 for reflecting, for example, EUV light with a wavelength of 13 nm to 14 nm, it is preferable to use a Mo / Si periodic laminated film formed by alternatingly depositing Mo-containing layers and Si-containing layers for about 40 to 60 cycles.

[0052] Furthermore, when the uppermost high-refractive-index layer of the multilayer reflective film 5 is a silicon (Si) layer, a silicon oxide layer containing silicon and oxygen can also be formed between the uppermost layer (the Si layer) and the protective film 6. In this case, the photomask's resistance to cleaning can be improved.

[0053] In the substrate 110 with the multilayer reflective film of this embodiment, the multilayer reflective film 5 is characterized by containing hydrogen. The atomic number density of hydrogen in the multilayer reflective film 5 is 7.0 × 10⁻³ atoms / nm³ or less, preferably 6.5 × 10⁻³ atoms / nm³ or less, and more preferably 6.0 × 10⁻³ atoms / nm³ or less. On the other hand, the atomic number density of hydrogen in the multilayer reflective film 5 is preferably 1.0 × 10⁻⁴ atoms / nm³ or more, and more preferably 2.0 × 10⁻⁴ atoms / nm³ or more. The atomic number density of hydrogen in the multilayer reflective film 5 can be measured, for example, using secondary ion mass spectrometry (SIMS).

[0054] Generally, when the substrate 1 is made of SiO2-TiO2 glass, since SiO2-TiO2 glass necessarily contains a certain amount or more of hydrogen and OH groups, it is difficult to completely remove hydrogen and OH groups from the substrate 1. Therefore, hydrogen and OH groups released from the substrate 1 will also be absorbed into the multilayer reflective film 5 formed on the substrate 1. Especially when the high refractive index material in the multilayer reflective film 5 is silicon, this phenomenon will occur significantly because silicon easily absorbs hydrogen.

[0055] For the multilayer reflective film 5, it is difficult to achieve zero film stress during film formation. In order to reduce the film stress of the multilayer reflective film 5, heat treatment is usually performed. During this heat treatment, hydrogen and OH groups of the substrate 1 are easily absorbed into the multilayer reflective film 5. Furthermore, when forming the resist film 8 on the absorber film 7 of the photomask substrate 100, after applying the resist solution by spin coating or the like, a heat treatment (PAB: Pre-Applied bake) is performed to dry it. During this heat treatment, hydrogen and OH groups of the substrate 1 are easily absorbed into the multilayer reflective film 5. Furthermore, when the resist film 8 is a chemically amplified resist, after the transfer pattern is exposed and drawn onto the resist film 8 by an electron beam, a heat treatment (PEB: Post Exposure Bake) is performed. Furthermore, after developing the resist film 8, a heat treatment (Post Bake) is also performed. During these heat treatments, hydrogen and OH groups from substrate 1 are easily absorbed into the multilayer reflective film 5.

[0056] When hydrogen and OH groups are absorbed in the multilayer reflective film 5, during processes such as laser irradiation of the multilayer reflective film 5 to reduce reflectivity by interdiffusion of the constituent elements of the low-refractive-index layer and the constituent elements of the high-refractive-index layer, the hydrogen and OH groups absorbed in the multilayer reflective film 5 vaporize and accumulate between the multilayer reflective film 5 and the protective film 6. In this case, the following problem exists: due to the bulging of the protective film 6 on the multilayer reflective film 5 or the cracking of the protective film 6 itself, laser irradiation cannot be performed sufficiently, thereby failing to adequately reduce the reflectivity of specific areas of the multilayer reflective film 5 (such as the light-shielding area around the transfer pattern forming area) to EUV light.

[0057] According to the substrate 110 with a multilayer reflective film in this embodiment, the atomic density of hydrogen in the multilayer reflective film 5 is suppressed within the above-mentioned range. Therefore, when laser irradiation or other methods are performed to reduce the reflectivity of the multilayer reflective film 5, the phenomenon of hydrogen absorbed in the multilayer reflective film 5 vaporizing and accumulating between the multilayer reflective film 5 and the protective film 6 can be suppressed. As a result, the reflectivity of specific areas of the multilayer reflective film 5 (such as the light-shielding area around the transfer pattern forming area) to EUV light can be sufficiently reduced, thereby obtaining a substrate 110 with a multilayer reflective film and a reflective photomask substrate 100 capable of manufacturing a reflective photomask with high pattern transfer accuracy.

[0058] The reflectivity of the multilayer reflective film 5 in this embodiment for EUV light is preferably 65% ​​or higher. With a reflectivity of 65% or higher, the multilayer reflective film 5 can be better used to manufacture a reflective photomask 200 for a semiconductor device. The upper limit of reflectivity is typically 73%. Furthermore, the film thickness and logarithmic number of the low-refractive-index layer and the high-refractive-index layer constituting the multilayer reflective film 5 can be appropriately selected according to the exposure wavelength. Specifically, the film thickness and logarithmic number of the low-refractive-index layer and the high-refractive-index layer constituting the multilayer reflective film 5 can be selected in a manner that satisfies the Bourgue reflection law. In the multilayer reflective film 5, there are multiple high-refractive-index layers and multiple low-refractive-index layers, and the film thickness of the high-refractive-index layers or the film thickness of the low-refractive-index layers need not be the same. Also, the film thickness of the outermost surface (e.g., the Si layer) of the multilayer reflective film 5 can be adjusted within a range that does not reduce reflectivity. The thickness of the outermost high refractive index layer (e.g., Si layer) is, for example, 3 nm to 10 nm.

[0059] In the substrate 110 with a multilayer reflective film in this embodiment, the multilayer reflective film 5 has one period (pair) consisting of one pair of low-refractive-index layers and one pair of high-refractive-index layers. Preferably, it has 30 to 60 periods (pairs), more preferably 35 to 55 periods (pairs), and even more preferably 35 to 45 periods (pairs). The more periods (pairs) there are, the higher the reflectivity can be obtained, but the formation time of the multilayer reflective film 5 will be longer. By keeping the number of periods of the multilayer reflective film 5 within an appropriate range, a multilayer reflective film 5 with relatively high reflectivity can be obtained in a relatively short time.

[0060] The multilayer reflective film 5 of this embodiment can be formed by sputtering methods such as ion beam sputtering, DC (direct-current) sputtering, and RF (radio frequency) sputtering. In terms of the fact that impurities are less likely to be mixed into the multilayer reflective film 5, or that the ion source is independent and the conditions are relatively easy to set, it is preferable to form the multilayer reflective film 5 by ion beam sputtering.

[0061] The membrane stress of the multilayer reflective film 5 in this embodiment is preferably 0.42 GPa or less, and more preferably 0.25 GPa or less. It is difficult to achieve the above-mentioned membrane stress during the formation of the multilayer reflective film 5. In most cases, the membrane stress is reduced by performing heat treatment or the like as described above.

[0062] <<Protective Film 6>> To protect the multilayer reflective film 5 from the dry etching and cleaning processes during the manufacturing of the reflective photomask 200, a protective film 6 may be formed on or in contact with the surface of the multilayer reflective film 5. Furthermore, the protective film 6 also serves to protect the multilayer reflective film 5 when using electron beam (EB) to correct black spot defects in the thin film pattern. Here, Figures 1 and 2 show the case where the protective film 6 is a single layer, but the protective film 6 may also have a multilayer structure of two or more layers. The protective film 6 is formed from a material resistant to the etchant and cleaning solution used when patterning the absorber film 7. By forming the protective film 6 on the multilayer reflective film 5, damage to the surface of the multilayer reflective film 5 can be suppressed when manufacturing the reflective photomask 200 (EUV photomask) using a substrate 110 with the multilayer reflective film 5 and the protective film 6. Therefore, the reflectivity characteristics of the multilayer reflective film 5 for EUV light become excellent.

[0063] In the reflective photomask substrate 100 of this embodiment, a material that is resistant to the etching gas used in dry etching can be selected as the material of the protective film 6, wherein the dry etching is used to pattern the absorber film 7 formed on the protective film 6.

[0064] When the absorber film 7 in contact with the surface of the protective film 6 is a thin film of a material that can be etched by dry etching using fluorine-based gases or by dry etching using oxygen-free chlorine-based gases (e.g., a thin film containing tantalum (Ta)), the material of the protective film 6 may, for example, be a material containing ruthenium as the main component. Examples of materials containing ruthenium as the main component include: elemental Ru, Ru alloys containing at least one metal selected from titanium (Ti), niobium (Nb), molybdenum (Mo), zirconium (Zr), yttrium (Y), boron (B), lanthanum (La), cobalt (Co), rhenium (Re) and rhodium (Rh), and materials containing nitrogen.

[0065] When the absorber membrane 7 in contact with the surface of the protective membrane 6 is a thin film containing a material containing ruthenium (Ru) and chromium (Cr) (a specific RuCr-based material), the material used for the protective membrane 6 may be selected from the following materials: silicon (Si), materials containing silicon (Si) and oxygen (O), materials containing silicon (Si) and nitrogen (N), materials containing silicon (Si), oxygen (O) and nitrogen (N), and chromium-based materials such as chromium (Cr) or materials containing at least one element selected from chromium (Cr) and oxygen (O), nitrogen (N) and carbon (C).

[0066] When the protective film 6 is configured to contain ruthenium (Ru) and rhodium (Rh), the protective film 6 exhibits improved resistance to etching of chlorine-based gases and oxygen mixtures, resistance to etching of chlorine-based gases, resistance to etching of fluorine-based gases, and resistance to cleaning with a sulfuric acid-hydrogen peroxide mixture (SPM). If the rhodium content in the protective film 6 is too low, the additive effect will not be achieved; if it is too high, the extinction coefficient k of the protective film 6 for EUV light will increase, thus reducing the reflectivity of the reflective photomask 200. Therefore, the rhodium content in the protective film 6 is preferably 15 atomic% or more and not more than 50 atomic%, more preferably 20 atomic% or more and not more than 40 atomic%.

[0067] The protective film 6 may contain at least one element selected from N, C, O, H, and B. Preferably, the protective film 6 further contains nitrogen (N). By further containing nitrogen (N) in the protective film 6, the crystallinity can be reduced. As a result, the protective film 6 can be densified, thus further improving its resistance to etching gases and cleaning. The nitrogen content in the protective film 6 is preferably greater than 1 atomic% and less than 20 atomic%, and more preferably more than 3 atomic% and less than 10 atomic%.

[0068] The protective film 6 preferably further contains oxygen (O). By further containing oxygen (O) in the protective film 6, the crystallinity can be reduced. As a result, the protective film 6 can be densified, thereby further improving its resistance to etching gases and cleaning. The oxygen content of the protective film 6 is preferably greater than 1 atomic% and less than 20 atomic%, and more preferably more than 3 atomic% and less than 10 atomic%.

[0069] The thickness of the protective film 6 is not particularly limited as long as it can perform its function as the protective film 6. From the viewpoint of EUV light reflectivity, the thickness of the protective film 6 is preferably 1.0 nm to 8.0 nm, more preferably 1.5 nm to 6.0 nm. The extinction coefficient of the protective film 6 is preferably adjusted to be 0.030 or less, and more preferably to be 0.025 or less.

[0070] On the other hand, the protective film 6 may also be configured to include a first layer and a second layer from the substrate 1 side. In this case, the second layer may be a thin film containing ruthenium (Ru) and rhodium (Rh).

[0071] To suppress the diffusion of silicon (Si) from the multilayer reflective film 5 into the protective film 6, the first layer of the protective film 6 preferably comprises ruthenium (Ru) and at least one element selected from magnesium (Mg), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), germanium (Ge), zirconium (Zr), niobium (Nb), molybdenum (Mo), rhodium (Rh), hafnium (Hf), and tungsten (W). Especially when the first layer is a RuTi film, a RuZr film, or a RuAl film, the diffusion of silicon (Si) into the protective film 6 can be suppressed more reliably.

[0072] The Ru content of the first layer is preferably greater than 50 atomic% and less than 100 atomic%, more preferably greater than 80 atomic% and less than 100 atomic, and even more preferably greater than 95 atomic% and less than 100 atomic.

[0073] In the substrate 110 with a multilayer reflective film in this embodiment, the Ru content of the second layer is preferably less than the Ru content of the first layer. For example, when the first layer is a RuTi film and the second layer is a RuRh film, even if the Ti content of the RuTi film in the first layer is relatively low, silicon (Si) diffusion into the protective film 6 can be suppressed. Therefore, by having a lower Ru content in the second layer than in the first layer, the resistance to etching gases and cleaning can be further improved, and silicon (Si) diffusion into the protective film 6 can be suppressed.

[0074] The refractive index of the second layer of the protective film 6 is preferably less than that of the first layer. As a result, a substrate with a protective film (substrate 110 with a multilayer reflective film having a protective film 6) can be manufactured without reducing the reflectivity of EUV light from the multilayer reflective film 5, including the protective film 6. The refractive index of the second layer is preferably 0.920 or less, and more preferably 0.885 or less.

[0075] The thickness of the first layer of the protective film 6 is preferably 0.5 nm to 2.0 nm, more preferably 1.0 nm to 1.5 nm. Also, the thickness of the second layer of the protective film 6 is preferably 1.0 nm to 7.0 nm, more preferably 1.5 nm to 4.0 nm.

[0076] In EUV lithography, there is relatively little transparent material to the exposed light, making it technically difficult to implement an EUV photomask protective film to prevent foreign matter from adhering to the photomask pattern surface. Therefore, the use of a photomask without a protective film has become mainstream. Furthermore, in EUV lithography, EUV exposure can cause exposure contamination such as carbon film deposition or oxide film growth on the photomask. Therefore, during the manufacturing of semiconductor devices using the EUV exposure reflective photomask 200, multiple cleaning processes are required to remove foreign matter or contaminants from the photomask. Therefore, the EUV exposure reflective photomask 200 has much stricter requirements for washability compared to the photomask used in photolithography. The reflective photomask 200, with its protective film 6, improves its washability against cleaning solutions.

[0077] The method for forming the protective film 6 can be the same as known film forming methods, without any particular limitation. For specific examples, sputtering and ion beam sputtering can be cited.

[0078] In the substrate 110 with a multilayer reflective film in this embodiment, the multilayer reflective film 5 may have a mixed region on its first main surface formed by mixing the constituent elements of a low-refractive-index layer and the constituent elements of a high-refractive-index layer. For example, when the low-refractive-index layer is a layer containing molybdenum (Mo) and the high-refractive-index layer is a layer containing silicon (Si), a mixed region formed by mixing Mo and Si may be formed. This mixed region may be formed by locally heating the multilayer reflective film 5. For example, the mixed region may be formed by heating the multilayer reflective film 5 by irradiating it with laser light. In this case, the laser light may irradiate from the multilayer reflective film 5, or it may irradiate from the protective film 6 after a protective film 6 is formed on the multilayer reflective film 5. As the light source for the laser light, a CO2 laser or a solid-state laser may be used, for example. Furthermore, the mixed region may also be formed by irradiating the multilayer reflective film 5 with an electron beam.

[0079] The surface reflectivity of the mixed region to EUV light is lower than that of other regions to EUV light. For example, when manufacturing a reflective photomask 200 using a substrate 110 with a multilayer reflective film, if a mixed region is formed in the peripheral region of the area where the thin film pattern is to be formed, the reflectivity of the multilayer reflective film 5 in the peripheral region can be lower than that in other regions. Therefore, when the reflective photomask 200 is placed in an exposure apparatus and exposure transfer is performed by step scanning, unnecessary photosensitivity due to overlapping exposures can be prevented. As a result, patterns can be transferred with higher precision using photoresist films or the like formed on the surface of the semiconductor substrate. The surface reflectivity of the mixed region to EUV light is preferably 1.3% or less, more preferably 1% or less, and even more preferably 0.7% or less.

[0080] <Reflective Photomask Substrate 100> The reflective photomask substrate 100 of this embodiment will be described. By using the reflective photomask substrate 100 of this embodiment, a reflective photomask 200 having a multilayer reflective film 5 with a high reflectivity for exposed light can be manufactured.

[0081] <<Absorber Film (Pattern Forming Thin Film) 7>> The reflective photomask substrate 100 has an absorber film (pattern forming thin film) 7 on the substrate 110 with the aforementioned multilayer reflective film. That is, the absorber film 7 is formed on the uppermost layer of the substrate 110 with the multilayer reflective film, namely the protective film 6. The basic function of the absorber film 7 is to absorb EUV light. The absorber film 7 can be an absorber film 7 for the purpose of absorbing EUV light, or it can be an absorber film 7 with a phase shifting function that also takes into account the phase difference of EUV light. The absorber film 7 with the phase shifting function absorbs EUV light while reflecting a portion of the EUV light to shift the phase. That is, in the reflective photomask 200 obtained by patterning the absorber film 7 with the phase shifting function, in the part where the absorber film 7 is formed, EUV light is absorbed and light is reduced, and a portion of the light is reflected at a level that does not adversely affect the pattern transfer. Furthermore, in the region where the absorber film 7 is not formed (field region), EUV light is reflected from the multilayer reflective film 5 via the protective film 6. Therefore, the reflected light from the absorber film 7 with phase-shifting function has the desired phase difference with the reflected light from the field region. The absorber film 7 with phase-shifting function is formed such that the phase difference between the reflected light from the absorber film 7 and the reflected light from the multilayer reflective film 5 is 130 to 230 degrees. By the interference of the light with a phase difference of approximately 180 degrees at the edge of the pattern, the image contrast of the projected optical image is improved. As this image contrast is improved, the resolution increases, allowing for greater exposure margins, focus margins, and other exposure-related margins.

[0082] The absorber film 7 can be a single-layer film or a multilayer film comprising multiple films. In the case of a single-layer film, the number of steps in manufacturing the photomask substrate can be reduced, thus improving production efficiency. In the case of a multilayer film, the upper absorber film can function as an anti-reflective film when inspecting photomask patterns using light. In this case, the optical constants and film thickness of the upper absorber film need to be appropriately set. This improves the inspection sensitivity when inspecting photomask patterns using light. Furthermore, as the upper absorber film, films containing oxygen (O) and nitrogen (N) that can improve oxidation resistance can be used. This improves the long-term stability of the absorber film. Thus, by using the absorber film 7 composed of multilayer films, various functions can be added to the absorber film 7. When the absorber film 7 has a phase shift function, by using the absorber film 7 composed of multilayer films, the adjustment range of the optical surface can be increased. This makes it easier to obtain the desired reflectivity.

[0083] As the material for the absorber film 7, a material that has the function of absorbing EUV light and can be processed by etching (for example, by dry etching with chlorine (Cl) or fluorine (F) based gases) can be used. As a material with this function, elemental tantalum (Ta) or a tantalum compound containing Ta as the main component is preferred.

[0084] The absorber film 7 of tantalum and tantalum compounds described above can be formed by sputtering methods such as DC sputtering and RF sputtering. For example, a target containing tantalum and boron can be used, and the absorber film 7 can be formed by reactive sputtering using argon gas with added oxygen or nitrogen.

[0085] The tantalum compound used to form the absorber film 7 is an alloy containing Ta. When the absorber film 7 is an alloy of Ta, the crystal state of the absorber film 7 is preferably amorphous or microcrystalline in terms of smoothness and flatness. If the surface of the absorber film 7 is not smooth or flat, the edge roughness of the absorber pattern 7a will increase, and the dimensional accuracy of the pattern will deteriorate. The preferred surface roughness of the absorber film 7, in terms of root mean square roughness (RMS), is 0.5 nm or less, more preferably 0.4 nm or less, and even more preferably 0.3 nm or less.

[0086] As the tantalum compound used to form the absorber membrane 7, the following compounds may be used: compounds containing Ta and B; compounds containing Ta and N; compounds containing Ta, O and N; compounds containing Ta and B, and further containing at least one of O and N; compounds containing Ta and Si; compounds containing Ta, Si and N; compounds containing Ta and Ge; and compounds containing Ta, Ge and N, etc.

[0087] Ta has a relatively high absorption coefficient for EUV light. Furthermore, Ta is a material that can be easily dry-etched using chlorine-based or fluorine-based gases. Therefore, Ta can be considered a material for absorber film 7 with excellent processability. By further adding B, Si, and / or Ge to Ta, amorphous materials can be easily obtained. As a result, the smoothness of absorber film 7 can be improved. Moreover, if N and / or O are added to Ta, the oxidation resistance of absorber film 7 is improved, thus enhancing the long-term stability of absorber film 7.

[0088] Furthermore, as a material for the absorber membrane 7, in addition to tantalum or tantalum compounds, at least one metal selected from palladium (Pd), silver (Ag), platinum (Pt), gold (Au), iridium (Ir), tungsten (W), chromium (Cr), cobalt (Co), manganese (Mn), tin (Sn), vanadium (V), nickel (Ni), hafnium (Hf), iron (Fe), copper (Cu), tellurium (Te), zinc (Zn), magnesium (Mg), germanium (Ge), aluminum (Al), rhodium (Rh), ruthenium (Ru), molybdenum (Mo), niobium (Nb), titanium (Ti), zirconium (Zr), yttrium (Y), and silicon (Si), or compounds thereof, may be used.

[0089] <<Back Conductive Film 2>> A back conductive film 2 for electrostatic chucks is formed on the second main surface of the substrate 1 (on the surface opposite to the multilayer reflective film 5). The sheet resistance of the back conductive film 2 is typically 100 Ω / □ or less. The back conductive film 2 can be formed, for example, by DC sputtering, RF sputtering, or ion beam sputtering using a target made of metals such as chromium or tantalum, or alloys thereof. The chromium (Cr) material used to form the back conductive film 2 is preferably a Cr compound containing at least one of boron, nitrogen, oxygen, and carbon. Examples of Cr compounds include CrN, CrON, CrCN, CrCON, CrBN, CrBON, CrBCN, and CrBOCN. The tantalum (Ta) material used to form the back conductive film 2 is preferably Ta (tantalum), an alloy containing Ta, or any of these containing at least one Ta compound selected from boron, nitrogen, oxygen, and carbon. Examples of Ta compounds include: TaB, TaN, TaO, TaON, TaCON, TaBN, TaBO, TaBON, TaBCON, TaHf, TaHfO, TaHfN, TaHfON, TaHfCON, TaSi, TaSiO, TaSiN, TaSiON, and TaSiCON.

[0090] The thickness of the back conductive film 2 is not particularly limited, and is typically between 10 nm and 200 nm. The back conductive film 2 can adjust the stress on the second main surface side of the photomask substrate 100. That is, the back conductive film 2 can achieve a balance between the stress generated by the various films formed on the first main surface side and the stress on the second main surface side. By achieving a balance between the stress on the first main surface side and the second main surface side, the reflective photomask substrate 100 can be adjusted to become flat.

[0091] Furthermore, a back conductive film 2 may be formed on the substrate 110 with the multilayer reflective film before the absorption film 7 is formed. In this case, a substrate 110 with the back conductive film 2 and the multilayer reflective film, as shown in FIG1, can be obtained.

[0092] <Other Thin Films> The substrate 110 with multilayer reflective films and the reflective photomask substrate 100 manufactured by the manufacturing method of this embodiment can have an etching hard mask film (also called an "etching mask film") and / or a resist film 8 on the absorber film 7. Representative materials for the etching hard mask film include: silicon (Si), and materials in which at least one element selected from oxygen (O), nitrogen (N), carbon (C), and hydrogen (H) is added; or chromium (Cr), and materials in which at least one element selected from oxygen (O), nitrogen (N), carbon (C), and hydrogen (H) is added. Specific examples include: SiO2, SiON, SiN, SiO, Si, SiC, SiCO, SiCN, SiCON, Cr, CrN, CrO, CrON, CrC, CrCO, CrCN, and CrOCN. However, when the absorber film 7 is an oxygen-containing compound, it is advisable to avoid oxygen-containing materials (such as SiO2) from the viewpoint of etch resistance when using a hard mask for etching. When an etch hard mask is formed, the thickness of the resist film 8 can be reduced, which is beneficial for pattern miniaturization.

[0093] In the reflective photomask substrate 100 of this embodiment, the multilayer reflective film 5 may have a mixed region on its first main surface formed by mixing the constituent elements of a low-refractive-index layer and the constituent elements of a high-refractive-index layer. The mixed region may be formed, for example, by heating the multilayer reflective film 5 by irradiating it with laser light. In this case, laser light may irradiate from the multilayer reflective film 5, or it may irradiate from the protective film 6 after a protective film 6 has been formed on the multilayer reflective film 5. Alternatively, laser light may irradiate from the absorber film 7 after an absorber film 7 has been formed on the protective film 6. For example, a CO2 laser or a solid-state laser may be used as the light source for the laser light.

[0094] The surface reflectivity of the mixed region to EUV light is lower than that of the absorber film 7 to EUV light. For example, when manufacturing a reflective photomask 200 using a reflective photomask substrate 100, if a mixed region is formed in the peripheral region of the area where the thin film pattern is to be set, the reflectivity of the multilayer reflective film 5 in that peripheral region can be lower than the reflectivity of the absorber film 7 in the area where the thin film pattern is to be set. Therefore, when the reflective photomask 200 is placed in an exposure apparatus and exposure transfer is performed by step scanning, unnecessary photosensitivity due to overlapping exposures can be prevented. As a result, patterns can be transferred with higher precision using photoresist films or the like formed on the surface of a semiconductor substrate.

[0095] <Reflective Photomask 200> By patterning the absorber film 7 of the aforementioned reflective photomask substrate 100, a reflective photomask 200 having a protective film 6 on a multilayer reflective film 5 and an absorber pattern 7a on the protective film 6 can be obtained. By using the reflective photomask substrate 100 of this embodiment, a reflective photomask 200 having a multilayer reflective film 5 with a high reflectivity for exposed light can be obtained.

[0096] A method for manufacturing a reflective photomask 200 using the reflective photomask substrate 100 of this embodiment will be described. Only a brief description will be given here, and a detailed description will be provided later with reference to the drawings in the embodiments.

[0097] A reflective photomask substrate 100 is prepared, and a resist film 8 is formed on the outermost surface of its first main surface (as described in the following embodiments, on the absorber film 7). (This is not necessary when the reflective photomask substrate 100 has a resist film 8). A desired pattern, such as a circuit pattern, is drawn (exposed) on the resist film 8. At this time, a pattern for the outer peripheral region 204, where a thin film pattern that will become a transfer pattern is to be set, can also be drawn (exposed). This pattern is formed during a subsequent process where the multilayer reflective film 5 of the outer peripheral region 204 is processed to form a mixed region (processing performed using laser irradiation, electron beam irradiation, etc.). Then, the resist film 8 is developed and rinsed to form a specific resist pattern 8a.

[0098] Using the resist pattern 8a as a mask, the absorber film 7 is dry-etched to form the absorber pattern 7a. Furthermore, as the etching gas, gases selected from the following can be used: chlorine-based gases such as Cl2, SiCl4, and CHCl3; a mixture of chlorine-based gases and O2 in a specific ratio; a mixture of chlorine-based gases and He in a specific ratio; a mixture of chlorine-based gases and Ar in a specific ratio; fluorine-based gases such as CF4, CHF3, C2F6, C3F6, C4F6, C4F8, CH2F2, CH3F, C3F8, SF6, and F2; and a mixture of fluorine-based gases and O2 in a specific ratio.

[0099] Subsequently, the resist pattern 8a is removed by ashing or resist stripping solution, thereby manufacturing a reflective photomask 200.

[0100] In the reflective photomask 200 of this embodiment, the multilayer reflective film 5 may have a mixed region formed by mixing the constituent elements of a low-refractive-index layer and the constituent elements of a high-refractive-index layer on the first main surface. The mixed region may be formed, for example, by heating the multilayer reflective film 5 by irradiating it with laser light. In this case, laser light may be irradiated from the multilayer reflective film 5, or irradiated from the protective film 6 after a protective film 6 is formed on the multilayer reflective film 5. Alternatively, laser light may be irradiated from the absorber film 7 after an absorber pattern 7a is formed on the absorber film 7. Furthermore, laser light may be irradiated from the absorber film 7 in the peripheral region of the region where the absorber pattern 7a is formed after an absorber pattern 7a is formed on the absorber film 7. For example, a CO2 laser or a solid-state laser may be used as the light source for the laser light.

[0101] The surface reflectivity of the mixed region to EUV light is lower than that of the absorber pattern 7a to EUV light. For example, when a mixed region is formed in the peripheral region of the area where the absorber pattern 7a is provided, the reflectivity of the multilayer reflective film 5 in the peripheral region can be lower than that of the absorber pattern 7a. Therefore, when the reflective photomask 200 is placed in the exposure apparatus and exposure transfer is performed by step scanning, unnecessary photosensitivity due to overlapping exposures can be prevented. As a result, patterns can be transferred with higher precision using photoresist films or the like formed on the surface of the semiconductor substrate.

[0102] On the other hand, in the case of a reference mark formed on the multilayer reflective film 5 in the substrate 110 with the multilayer reflective film, the reflective photomask substrate 100, and the reflective photomask 200. Generally, this reference mark is set as a reference for the position coordinates of defects when there are defects in the first main surface of the substrate 1, the multilayer reflective film 5, the protective film 6, the absorber film 7, etc. Sometimes, by irradiating the protective film 6 and the multilayer reflective film 5 with high-energy light such as laser light, the protective film 6 and the multilayer reflective film 5 are shrunken to form a recess, and this recess is used as a reference mark. When a reference mark is formed by this method, hydrogen and OH groups absorbed into the multilayer reflective film 5 vaporize and accumulate between the multilayer reflective film 5 and the protective film 6. Also, the protective film 6 on the multilayer reflective film 5 may bulge out, or the protective film 6 itself may crack. By using the multilayer reflective film 5 described above, a reference mark can be formed without these phenomena.

[0103] <Semiconductor Device Manufacturing Method> The semiconductor device manufacturing method of this embodiment includes the following steps: using the above-mentioned reflective photomask 200, performing a photolithography process using an exposure apparatus to expose and transfer a transfer pattern to the transfer object.

[0104] By using the reflective photomask 200 of this embodiment for EUV exposure, the desired transfer pattern can be exposed and transferred onto the photoresist film on the semiconductor substrate. In addition to this photolithography step, various steps such as etching of the processed film, formation of insulating or conductive films, introduction of dopants, or annealing can be performed to manufacture semiconductor devices with the desired electronic circuitry with high yield. [Example]

[0105] Hereinafter, embodiments and comparative examples will be described with reference to the drawings. As shown in FIG1, the substrate 110 with a multilayer reflective film in the embodiment has a substrate 1, a multilayer reflective film 5 and a protective film 6.

[0106] First, four substrates 1, each 6025 in size (approximately 152 mm × 152 mm × 6.35 mm), were prepared, each cut from SiO2-TiO2 glass ingots of different compositions, with the first and second main surfaces ground. These substrates 1 are made of low thermal expansion glass (SiO2-TiO2 based glass). The main surfaces of the substrates 1 are ground by a coarse grinding process, a fine grinding process, a localized processing process, and a contact grinding process.

[0107] Next, a multilayer reflective film 5 is formed on the main surface (first main surface) of the four substrates 1. Regarding the multilayer reflective film 5 formed on the substrate 1, in order to make it suitable for EUV light with a wavelength of 13.5 nm, it is designed as a periodic multilayer reflective film 5 containing Mo and Si. The multilayer reflective film 5 is formed by alternately depositing Mo and Si films on the substrate 1 using a Mo target and a Si target, and by ion beam sputtering under a Kr gas atmosphere. First, a Si film is formed with a thickness of 4.2 nm, then a Mo film is formed with a thickness of 2.8 nm. This is considered one cycle, and 40 cycles are deposited in the same manner. Finally, a Si film is formed with a thickness of 4.0 nm, thereby forming the multilayer reflective film 5.

[0108] Subsequently, the substrate 1 after the formation of the four multilayer reflective films 5 is subjected to heat treatment using a heating plate to reduce the film stress of the multilayer reflective films 5. The conditions for each heat treatment (heating temperature is 200°C) are shown in Table 1.

[0109] Subsequently, a protective film 6 containing a Ru-containing material is formed on the multilayer reflective film 5 of the four substrates 1. The protective film 6 is formed in an Ar gas atmosphere by DC sputtering using a Ru target, with a film thickness of 2.5 nm. Through the above steps, four substrates 110 with multilayer reflective films are manufactured.

[0110] <<Atomic Number Density of Hydrogen in Multilayer Reflective Film 5>> The atomic number density [atoms / nm3] of hydrogen contained in the multilayer reflective film 5 of the four substrates 110 with multilayer reflective films manufactured in the manner described above was measured using a SIMS (quadrupole secondary ion mass spectrometer: PHI ADEPT-1010TM, manufactured by ULVAC-PHI Corporation). The measurement conditions were as follows: the primary ion species was Cs+, the primary accelerating voltage was 1.0 kV, the primary ion irradiation region was 90 μm square, the secondary ion polarity was positive, and the detected secondary ion species were [Cs-H]+, [Cs-D]+, or [Cs-He]+. Furthermore, the standard sample was Si. The measurement results are shown in Table 1 below.

[0111] <<Atomic Number Density of Hydrogen in Substrate 1>> The atomic number density [atoms / cm3] of hydrogen in substrate 1 of the four substrates 110 with multilayer reflective films described above was measured using a SIMS (quadrupole secondary ion mass spectrometer: PHI ADEPT-1010TM, manufactured by ULVAC-PHI Corporation) in the same procedure as for the multilayer reflective film 5. The measurement results are shown in Table 1.

[0112] <Reflective photomask substrate 100> Next, absorber films 7 containing TaBN are formed on the protective films 6 of the four substrates 110 with multilayer reflective films. The absorber films 7 are formed in a mixed gas atmosphere of Ar gas and N2 gas by DC sputtering using a TaB mixed sintering target, with a film thickness of 62 nm.

[0113] The elemental ratios of the TaBN film are as follows: Ta is 75 atomic%, B is 12 atomic%, and N is 13 atomic%. The refractive index n of the TaBN film at a wavelength of 13.5 nm is approximately 0.949, and the extinction coefficient k is approximately 0.030.

[0114] Subsequently, by means of DC sputtering (reactive sputtering), a back conductive film 2 containing CrN is formed on the second main surface (back side) of four substrates 110 with multilayer reflective films under the following conditions. The formation conditions of the back conductive film 2 are as follows: Cr target, mixed gas atmosphere of Ar and N2 (Ar: 90 atomic%, N: 10 atomic%), and film thickness of 20 nm.

[0115] In the manner described above, four reflective photomask substrates 100 having absorber films 7 on the protective film 6 are manufactured.

[0116] <Reflective Photomask 200> Next, using the above-mentioned four reflective photomask substrates 100, reflective photomasks 200 are manufactured respectively. Referring to FIG3, the manufacturing method of each reflective photomask 200 will be described.

[0117] First, as shown in FIG3(b), a resist film 8 is formed on the absorber film 7 of the reflective photomask substrate 100. Then, a desired pattern, such as a circuit pattern, is drawn (exposed) on the resist film 8. At the same time, the pattern of the peripheral region 204 to which laser light will irradiate the multilayer reflective film 5 in subsequent steps is also drawn (exposed). Next, the resist film 8 is developed and rinsed to form a specific resist pattern 8a (FIG3(c)). Then, using the resist pattern 8a as a mask, the absorber film 7 (TaBN film) is dry-etched using Cl2 gas to form the absorber pattern 7a (FIG3(d)). The protective film 6 containing Ru has extremely high resistance to dry etching with Cl2 gas, serving as a sufficient etch stop layer. Subsequently, the resist pattern 8a is removed by ashing or resist stripping solution. Next, the multilayer reflective film 5, after the peripheral region 204 of the absorber film 7 has been removed, is subjected to CO2 laser irradiation over the protective film 6, which mixes the constituent elements (Mo) of the low-refractive-index layer and (Si) of the high-refractive-index layer of the multilayer reflective film 5 to form a mixed region. Through the above steps, four reflective photomasks 200 are manufactured (Fig. 3(e)).

[0118] The four reflective photomasks 200 manufactured in the above manner have a 132 mm × 132 mm region 202 on the first main surface, which is provided with an absorber pattern 7a (thin film pattern), and an outer peripheral region 204 of the region 202. The outer peripheral region 204 is a region where the absorber pattern 7a is not provided, and the multilayer reflective film 5 in this region is a mixed region formed by mixing the constituent elements (Mo) of the low refractive index layer and the constituent elements (Si) of the high refractive index layer. The reflectivity of the multilayer reflective film 5 (with a protective film 6 deposited on it) of the outer peripheral region 204 of the four reflective photomasks 200 for EUV light with a wavelength of 13.5 nm was measured, and the results were all less than 0.7%. Furthermore, the reflectivity of the region 202 of the four reflective photomasks 200 where the absorber pattern 7a is provided for EUV light with a wavelength of 13.5 nm was measured, and the results were all greater than 67%.

[0119] [Table 1] The atomic density of hydrogen atoms in the multilayer reflective film [atoms / nm] 3 ] Annealing time (200℃) [min) for multilayer reflective films Hydrogen atomic number density in the substrate [atoms / cm] 3 ] The protective film bulges, peels, or cracks. Example 1 0.0059 10 1.2×10 19 none Example 2 0.0063 15 3.2×10 19 none Example 3 0.0068 30 4.1×10 19 none Comparative Example 1 0.0075 60 2.2×10 19 have

[0120] According to the results shown in Table 1, the reflectivity of the multilayer reflective film 5 in the outer peripheral region 204 is significantly lower than that of the absorber pattern 7a in the patterned region (region 202).

[0121] By observing the cross-section of the reflective photomask 200 with an electron microscope, it was found that no bulging or peeling was observed between the multilayer reflective film and the protective film in the reflective photomasks of Examples 1 to 3. Furthermore, no phenomenon such as cracking of the protective film itself was observed.

[0122] In contrast, in the reflective photomask of Comparative Example 1, it was confirmed that hydrogen accumulated between the multilayer reflective film and the protective film, causing bulging. Furthermore, it was also confirmed that the protective film itself was ruptured. [Simplified Explanation of the Diagram]

[0034] Figure 1 is a cross-sectional schematic diagram of an example of a substrate with a multilayer reflective film. Figure 2 is a cross-sectional schematic diagram of an example of a reflective photomask substrate. Figures 3(a) to (e) are step diagrams illustrating the manufacturing process of a reflective photomask.

Claims

1. A substrate with a multilayer reflective film, characterized in that a multilayer reflective film and a protective film are sequentially provided on the main surface of the substrate, and the multilayer reflective film has a structure formed by alternating layers of low refractive index layer and high refractive index layer, the multilayer reflective film contains hydrogen, the atomic number density of hydrogen in the multilayer reflective film is 7.0×10-3 atoms / nm3 or less, and the substrate has a reference mark formed by irradiating the multilayer reflective film and the protective film with high energy light.

2. A substrate with a multilayer reflective film, characterized in that a multilayer reflective film and a protective film are sequentially provided on the main surface of the substrate, and the multilayer reflective film has a structure formed by alternating layers of low refractive index layer and high refractive index layer, the multilayer reflective film contains hydrogen, the atomic number density of hydrogen in the multilayer reflective film is less than 7.0×10-3 atoms / nm3, and the multilayer reflective film and the protective film have reference marks including recesses.

3. The substrate with a multilayer reflective film as claimed in claim 1 or 2, wherein the substrate is mainly composed of silicon, titanium and oxygen, and further contains hydrogen.

4. The substrate with a multilayer reflective film as claimed in claim 1 or 2, wherein the high refractive index layer contains silicon and the low refractive index layer contains molybdenum.

5. The substrate with a multilayer reflective film as claimed in claim 1 or 2, wherein the atomic number density of hydrogen in the substrate obtained by secondary ion mass spectrometry analysis is 1.0 × 10¹⁹ atoms / cm³ or more.

6. The substrate with a multilayer reflective film as claimed in claim 1 or 2, wherein the protective film contains ruthenium.

7. The substrate with a multilayer reflective film as claimed in claim 1 or 2, wherein the multilayer reflective film has a mixed region on the main surface formed by mixing the constituent elements of the low refractive index layer and the constituent elements of the high refractive index layer, and the surface reflectivity of the mixed region to EUV light is lower than that of other regions to EUV light.

8. A photomask substrate, characterized in that it has a multilayer reflective film, a protective film and a pattern forming film sequentially disposed on the main surface of a substrate, wherein the multilayer reflective film has a structure formed by alternating layers of low refractive index layer and high refractive index layer, the multilayer reflective film contains hydrogen, the atomic number density of hydrogen in the multilayer reflective film is 7.0×10-3 atoms / nm3 or less, and the photomask substrate has a reference mark formed by irradiating the multilayer reflective film and the protective film with high energy light.

9. A photomask substrate, characterized in that it has a multilayer reflective film, a protective film and a pattern forming film sequentially disposed on the main surface of the substrate, wherein the multilayer reflective film has a structure formed by alternating layers of low refractive index layer and high refractive index layer, the multilayer reflective film contains hydrogen, the atomic number density of hydrogen in the multilayer reflective film is 7.0×10-3 atoms / nm3 or less, and the multilayer reflective film and the protective film have reference marks including recesses.

10. The photomask substrate of claim 8 or 9, wherein the substrate is mainly composed of silicon, titanium and oxygen, and further contains hydrogen.

11. The photomask substrate of claim 8 or 9, wherein the high refractive index layer contains silicon and the low refractive index layer contains molybdenum.

12. The photomask substrate of claim 8 or 9, wherein the atomic number density of hydrogen in the substrate obtained by secondary ion mass spectrometry analysis of the substrate is 1.0 × 10¹⁹ atoms / cm³ or more.

13. The photomask substrate of claim 8 or 9, wherein the protective film contains ruthenium.

14. The photomask substrate of claim 8 or 9, wherein the multilayer reflective film has a mixed region on the main surface formed by mixing the constituent elements of the low refractive index layer and the constituent elements of the high refractive index layer, and the surface reflectivity of the mixed region to EUV light is lower than the surface reflectivity of the pattern forming film to EUV light.

15. A reflective photomask, characterized in that a transfer pattern is formed on the thin film of the photomask substrate as claimed in any one of claims 8 to 14.

16. The reflective photomask of claim 15, wherein the multilayer reflective film is a mixed region formed by mixing the constituent elements of the low refractive index layer and the constituent elements of the high refractive index layer in the peripheral region of the area on the main surface where the thin film pattern is provided, and the surface reflectivity of the mixed region to EUV light is lower than that of the thin film pattern to EUV light.

17. A method for manufacturing a semiconductor device, characterized by comprising the step of using a reflective photomask as claimed in claim 15 or 16 to expose and transfer a transfer pattern onto a photoresist film on a semiconductor substrate.

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