Substrate with reflective film, mask blank, reflective mask, and method for manufacturing semiconductor device

Abstract

To provide a substrate with a reflection film capable of suppressing occurrence of a blister in a reflection film formed on an end face of the substrate.SOLUTION: A substrate with a reflection film comprises: a substrate which has an end face which is connected to outer edges of two main surfaces and facing two main surfaces; and a reflection film which is formed on the main surfaces and at least a part on the end face. The reflection film on the main surface has a structure in which a low refractive index layer and a high refractive index layer are alternately laminated. The reflection film on the end face has a single layer structure including: an element whose content is largest in the low refractive index layer; and an element whose content is largest in the high refractive index layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a substrate with a reflective film, a mask blank, a reflective mask, and a method for manufacturing a semiconductor device, which are used in EUV lithography. [Background technology]

[0002] In general, in the manufacturing process of semiconductor devices, fine patterns are formed using photolithography. Furthermore, to form these fine patterns, a number of transfer masks, also known as photomasks, are typically used. These transfer masks are generally formed by providing a fine pattern made of a metal thin film or the like on a light-transmitting glass substrate, and photolithography is also used to manufacture these transfer masks.

[0003] Furthermore, in recent years, with the increasing integration density of semiconductor devices in the semiconductor industry, there has been a demand for finer patterns that exceed the transfer limit of conventional photolithography methods using ultraviolet light. To enable the formation of such fine patterns, EUV lithography, an exposure technology using extreme ultraviolet (EUV) light, is seen as promising. Here, EUV light refers to light in the wavelength range of the soft X-ray region or the vacuum ultraviolet region, specifically light with a wavelength of approximately 0.2 to 100 nm. A reflective mask has been proposed as a mask for use in EUV lithography. Such a reflective mask has a multilayer reflective film that reflects exposure light formed on a substrate, and an absorber film that absorbs exposure light is formed in a pattern on the multilayer reflective film (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2009 / 116348 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, with the increasing demand for miniaturization in the lithography process, issues in the lithography process have become more prominent. One of these issues is the problem of contamination adhesion to the mirrors and masks of the exposure machine due to EUV light irradiation in the EUV lithography process.

[0006] To solve this problem, techniques that suppress the adhesion of contamination during EUV exposure by creating a hydrogen atmosphere, such as hydrogen radicals, inside the exposure chamber, and cleaning methods that remove contamination using hydrogen plasma are beginning to be used.

[0007] However, when the above technology is applied, a new problem arises: hydrogen penetrates the mask film, condenses, and causes swelling of the film, known as "blistering." When such a film swells and bursts, it generates dust, causing contamination inside the exposure chamber. It has been found that hydrogen that penetrates the film is likely to be captured at the interface with other films, depending on the film material, and blisters are likely to occur at the interface between two stacked films.

[0008] Meanwhile, a reflective mask used in EUV lithography has a reflective film formed on a substrate that reflects exposure light (EUV light). This reflective film is a multilayer film with a structure in which low-refractive index layers and high-refractive index layers are alternately stacked, and is formed on one main surface of the substrate using, for example, a sputtering method. In this case, the film is not only formed on one main surface of the substrate, but also extends around and is deposited on the edge surface of the substrate. If the film deposited on this edge surface has a multilayer film structure similar to that of the film formed on the main surface, there is a greater risk of blisters occurring at the interface of the multilayer film.

[0009] Therefore, the first object of the present invention is to provide a substrate with a reflective film and a mask blank that can suppress the occurrence of blisters, particularly in the reflective film formed on the edge face of the substrate, and second object of the present invention is to provide a reflective mask that uses this mask blank and can suppress the occurrence of blisters, particularly in the reflective film formed on the edge face of the substrate. Another object of the present invention is to provide a method for manufacturing a semiconductor device using this reflective mask. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the inventors of the present invention have pursued extensive research, focusing in particular on the structure of a film that extends and adheres to the edge faces of a substrate when a reflective film is formed on the main surface of the substrate, and as a result have completed the present invention. That is, in order to solve the above problems, the present invention has the following configuration.

[0011] (Configuration 1) A substrate with a reflective film, comprising: a substrate having two opposing main surfaces and end faces connected to the outer edges of the two main surfaces; and a reflective film formed on one of the main surfaces and on at least a part of the end face, wherein the reflective film on the main surface has a structure in which low-refractive index layers and high-refractive index layers are alternately laminated, and the reflective film on the end face has a single-layer structure containing the element that is most abundant in the low-refractive index layer and the element that is most abundant in the high-refractive index layer.

[0012] (Configuration 2) The substrate with a reflective film according to configuration 1, characterized in that the ratio of the content [atomic %] of the element with the highest content in the low refractive index layer to the total content [atomic %] of the element with the highest content in the low refractive index layer and the element with the highest content in the high refractive index layer contained in the reflective film formed on the end face is less than 0.4. (Configuration 3) 3. The substrate with a reflective film according to claim 1, wherein the thickness of the portion of the reflective film formed on the end face is thinner than the thickness of the portion of the reflective film formed on the main surface.

[0013] (Configuration 4) A substrate with a reflective film according to any one of structures 1 to 3, characterized in that the element most abundant in the low refractive index layer is molybdenum, and the element most abundant in the high refractive index layer is silicon. (Configuration 5) 5. The substrate with a reflective film according to any one of configurations 1 to 4, wherein the surface roughness (root mean square roughness) Rq of the reflective film formed on the end face is 1.5 nm or more.

[0014] (Configuration 6) 1. A mask blank comprising: a substrate having two opposing main surfaces and end faces connected to outer edges of the two main surfaces; a reflective film formed on one of the main surfaces and on at least a part of the end face; and a thin film for pattern formation formed on the reflective film, wherein the reflective film on the main surface has a structure in which low-refractive-index layers and high-refractive-index layers are alternately stacked, and the reflective film on the end face has a single-layer structure containing the element that is most abundant in the low-refractive-index layer and the element that is most abundant in the high-refractive-index layer.

[0015] (Configuration 7) The mask blank according to configuration 6, characterized in that the ratio of the content [atomic %] of the element with the highest content in the low refractive index layer to the total content [atomic %] of the element with the highest content in the low refractive index layer and the element with the highest content in the high refractive index layer contained in the reflective film formed on the end face is less than 0.4. (Configuration 8) 8. The mask blank according to claim 6, wherein the thickness of the portion of the reflective film formed on the end face is thinner than the thickness of the portion of the reflective film formed on the main surface.

[0016] (Configuration 9) 9. A mask blank according to any one of structures 6 to 8, wherein the element most abundant in the low refractive index layer is molybdenum, and the element most abundant in the high refractive index layer is silicon. (Configuration 10) 10. The mask blank according to any one of configurations 6 to 9, wherein the surface roughness (root mean square roughness) Rq of the reflective film formed on the end face is 1.5 nm or more.

[0017] (Configuration 11) A reflective mask comprising: a substrate having two opposing main surfaces and edge surfaces connected to the outer edges of the two main surfaces; a reflective film formed on one of the main surfaces and on at least a portion of the edge surface; and a thin film formed on the reflective film and having a transfer pattern, wherein the reflective film on the main surfaces has a structure in which low-refractive index layers and high-refractive index layers are alternately stacked, and the reflective film on the edge surface has a single-layer structure containing the element most abundant in the low-refractive index layer and the element most abundant in the high-refractive index layer.

[0018] (Configuration 12) A reflective mask according to configuration 11, characterized in that the ratio of the content [atomic %] of the element with the highest content in the low refractive index layer to the total content [atomic %] of the element with the highest content in the low refractive index layer and the element with the highest content in the high refractive index layer contained in the reflective film formed on the end surface is less than 0.4. (Configuration 13) 13. The reflective mask according to claim 11, wherein the thickness of the portion of the reflective film formed on the end face is thinner than the thickness of the portion of the reflective film formed on the main surface.

[0019] (Configuration 14) 14. A reflective mask according to any one of structures 11 to 13, wherein the element most abundant in the low refractive index layer is molybdenum, and the element most abundant in the high refractive index layer is silicon. (Configuration 15) 15. The reflective mask according to any one of structures 11 to 14, wherein the surface roughness (root mean square roughness) Rq of the reflective film formed on the end face is 1.5 nm or more.

[0020] (Configuration 16) 16. A method for manufacturing a semiconductor device, comprising the step of exposing and transferring a transfer pattern onto a resist film on a semiconductor substrate using the reflective mask according to any one of configurations 11 to 15. [Effects of the Invention]

[0021] According to the present invention, the reflective film on the end face has a single-layer structure containing the element that is most abundant in the low refractive index layer and the element that is most abundant in the high refractive index layer, and therefore it is possible to provide a substrate with a reflective film and a mask blank that can particularly suppress the occurrence of blisters in the reflective film formed on the end face of the substrate.

[0022] Furthermore, according to the present invention, by using this mask blank, it is possible to provide a reflective mask that can suppress the occurrence of blisters, particularly in the reflective film formed on the edge face of the substrate. Furthermore, the present invention can provide a method for manufacturing a semiconductor device using this reflective mask. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a cross-sectional view showing a configuration of an embodiment of a substrate with a reflective film of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing the film configuration of a reflective film. [Figure 3] 1 is a cross-sectional view showing a configuration of an embodiment of a mask blank of the present invention. [Figure 4] FIG. 1 is a cross-sectional view of a reflective mask manufactured using a mask blank of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described in detail. [Substrate with reflective film] First, the substrate with a reflective film according to the present invention will be described. FIG. 1 is a cross-sectional view showing the configuration of an embodiment of a substrate with a reflective film of the present invention. As shown in FIG. 1, a substrate 10 with a reflective film according to one embodiment of the present invention includes a substrate 1 and a reflective film 2. The substrate 1 has two opposing main surfaces 1a and 1b, and end surfaces 1c and 1d that connect to the outer edges of the two main surfaces 1a and 1b.

[0025] The substrate 1 used in the present invention is rectangular overall and has four end faces connected to the outer edges of the two main surfaces 1a and 1b. In the present invention, the term "end face" refers to these four end faces. The cross-sectional view of FIG. 1 shows two end faces 1c and 1d, which are opposite each other on the left and right sides of the substrate, but the substrate also has two other end faces, which are opposite each other on the front and back sides of the substrate. Therefore, the reflective film 2 is also formed on at least a portion of the other two end faces not shown in FIG. 1. In the following description of this embodiment, for convenience of explanation, the two end faces 1c and 1d will be described, but the same applies to the other two opposing end faces not shown in FIG. 1.

[0026] The reflective film 2 is formed on one main surface 1a and at least a part of the end faces 1c and 1d.

[0027] 2, the reflective film 2a formed on the main surface 1a has a multilayer structure in which low refractive index layers 21 and high refractive index layers 22 are alternately stacked. In this specification, the low refractive index and high refractive index are based on the refractive index at the wavelength of EUV light. In addition, the reflective films 2c and 2d formed on the end faces 1c and 1d have a single-layer structure containing the element with the highest content in the low-refractive-index layer 21 and the element with the highest content in the high-refractive-index layer 22.

[0028] Here, the content of the element having the highest content in the low refractive index layer 21 is preferably more than 50 atomic %, more preferably 70 atomic % or more, and even more preferably 90 atomic % or more. Similarly, the content of the element having the highest content in the high refractive index layer 22 is preferably more than 50 atomic %, more preferably 70 atomic % or more, and even more preferably 90 atomic % or more.

[0029] On the other hand, the reflective films 2c and 2d formed on the end faces 1c and 1d may have a single layer structure containing a material in which the main component elements of the low refractive index layer 21 and the main component elements of the high refractive index layer 22 are mixed.

[0030] Here, the "main constituent elements" of the low-refractive-index layer 21 (high-refractive-index layer 22) refer to the constituent elements excluding elements whose content in the low-refractive-index layer 21 (high-refractive-index layer 22) is less than 5 atomic %. That is, in this case, the total content of the "main constituent elements" in the low-refractive-index layer 21 (high-refractive-index layer 22) is 95 atomic % or more. Therefore, even if the formed reflective film contains impurity components contained in the target material or impurity components derived from structures such as shields in the film formation chamber, such components are not the main constituent elements of the low-refractive-index layer or high-refractive-index layer.

[0031] In the case of EUV exposure, the substrate 1 is set to a thickness of 0±1.0×10 in order to prevent distortion of the pattern due to heat during exposure. -7 / °C, more preferably 0±0.3×10 -7 Materials having a low thermal expansion coefficient within the range of 1 / °C are preferably used, and examples of materials having a low thermal expansion coefficient within this range include SiO2-TiO2 glass and multi-component glass ceramics.

[0032] When a glass substrate is used as the substrate 1, the main surface of the glass substrate on which the transfer pattern is formed is surface-processed to have a high degree of flatness in order to obtain at least pattern transfer accuracy and positional accuracy. In the case of EUV exposure, the main surface of the glass substrate on which the transfer pattern is formed preferably has a flatness of 0.1 μm or less, particularly preferably 0.05 μm or less, in a 132 mm × 132 mm area or a 142 mm × 142 mm area. Furthermore, the main surface opposite the side on which the transfer pattern is formed is the surface that is electrostatically chucked when set in an exposure tool, and has a flatness of 1 μm or less, preferably 0.5 μm or less, in a 142 mm × 142 mm area.

[0033] The reflective film 2 is a multilayer film in which low refractive index layers 21 and high refractive index layers 22 are alternately stacked, and generally, a multilayer film is used in which thin films of heavy elements or their compounds and thin films of light elements or their compounds are alternately stacked for about 40 to 60 periods. For example, a Mo / Si periodic laminated film, in which Mo films (low refractive index layers) and Si films (high refractive index layers) are alternately laminated in 40 or more periods, is preferably used as a reflective film for EUV light with a wavelength of 13 to 14 nm. Other multilayer reflective films used in the EUV light region include Ru / Si periodic multilayer films, Mo / Be periodic multilayer films, Mo compound / Si compound periodic multilayer films, Si / Nb periodic multilayer films, Si / Mo / Ru periodic multilayer films, Si / Mo / Ru / Mo periodic multilayer films, and Si / Ru / Mo / Ru periodic multilayer films. The material of the reflective film 2 may be appropriately selected depending on the exposure wavelength. The reflective film 2 can be formed by, for example, ion beam sputtering or atomic layer deposition (ALD).

[0034] In order to solve the above-mentioned problems, the present inventors conducted extensive research, focusing particularly on the structure of a film that extends around and adheres to the edge face of the substrate when forming a reflective film on the main surface of the substrate. As a result, they found that the reflective film adhered to the edge face of the substrate does not need to reflect exposure light at all, and therefore does not need to have a multilayer film structure like the reflective film formed on the main surface of the substrate. Furthermore, they found that a film with a single layer structure that does not have an interface within the film will lead to a solution to the problem, from the perspective of suppressing the occurrence of blisters.

[0035] In the reflective film-coated substrate 10 according to the present embodiment described above, when the reflective film 2 is formed on the main surface of the substrate 1, the reflective film 2c (or 2d) formed on the end face 1c (or 1d) of the substrate 1 has a single-layer structure containing the element (e.g., molybdenum) most abundant in the low-refractive-index layer 21 and the element (e.g., silicon) most abundant in the high-refractive-index layer 22. The reflective film 2c (or 2d) is formed by mixing and diffusing at least the element (e.g., molybdenum) most abundant in the low-refractive-index layer 21 and the element (e.g., silicon) most abundant in the high-refractive-index layer 22. The reflective film 2c (or 2d) has a single-layer structure without a clear interface. In addition, the reflective film 2c (or 2d) is a single-layer structure film having no interface, which is formed by mixing and diffusing the main constituent element (e.g., molybdenum) of the low refractive index layer 21, which is the film constituent material of the reflective film 2, and the main constituent element (e.g., silicon) of the high refractive index layer 22. Therefore, even if a technique for suppressing the adhesion of contamination due to hydrogen radicals or hydrogen plasma is applied during EUV exposure using a mask blank and a reflective mask described below that are fabricated using the reflective film-coated substrate 10 of this embodiment, it is possible to significantly reduce the risk of blisters occurring.

[0036] On the other hand, as described above, the reflective film 2c (or 2d) can also be a film with a single-layer structure having no interface, by mixing and diffusing a constituent element (e.g., molybdenum) of the main component of the low refractive index layer 21, which is the film-constituting material of the reflective film 2, with a constituent element (e.g., silicon) of the main component of the high refractive index layer 22. In this case, the reflective film-coated substrate 10 can also significantly reduce the risk of blisters occurring by applying a technique for suppressing adhesion of contamination by hydrogen radicals or hydrogen plasma during EUV exposure using a mask blank and a reflective mask, which will be described later, fabricated using the reflective film-coated substrate 10.

[0037] The film configuration of the substrate with a reflective film according to the present invention may be any configuration having at least a reflective film 2 that reflects exposure light (e.g., EUV light) on a substrate 1, as shown in FIG. 1, and may further have other films such as an underlayer (described later) and a protective film formed on the reflective film 2.

[0038] 1 according to this embodiment, the end faces connecting to the outer edges of the two opposing main surfaces 1a, 1b are surfaces that are substantially perpendicular to these two main surfaces, but the substrate end faces may also have chamfered surfaces. That is, when the end faces of the substrate have side faces that are substantially perpendicular to the two main surfaces and two chamfered surfaces that connect these side faces to the outer edges of the two main surfaces, and the reflective film 2 is formed on at least a portion of these side faces and chamfered surfaces, the "reflective film on the end faces" refers to the reflective film formed on at least a portion of these side faces and chamfered surfaces.

[0039] Similarly, in the reflective film-coated substrate 10 of the present embodiment, the ratio (hereinafter referred to as L / [L+H] ratio) of the content [atomic %] of the element most abundant in the low refractive index layer 21 (the main constituent element of the low refractive index layer 21, for example, molybdenum) contained in the reflective film 2c (or 2d) formed on the end face 1c (or 1d) to the total content [atomic %] of the element most abundant in the low refractive index layer 21 (the main constituent element of the low refractive index layer 21, for example, silicon) and the element most abundant in the high refractive index layer 22 (the main constituent element of the high refractive index layer 22, for example) is preferably less than 0.4. From the viewpoint of reflectivity, the reflective film 2a formed on the main surface 1a of the substrate 1 preferably has a thickness ratio of the low refractive index layer to the high refractive index layer of 4:6 (i.e., the L / [L+H] ratio of the entire reflective film 2a formed on the main surface 1a is 0.4).

[0040] In contrast, the reflective film 2c (or 2d) formed on the end face 1c (or 1d) of the present embodiment is a film with a single layer structure containing the element with the largest content in the low-refractive-index layer 21 and the element with the largest content in the high-refractive-index layer 22. Alternatively, the reflective film 2c (or 2d) is a film with a single layer structure in which a constituent element of the main component of the low-refractive-index layer 21 and a constituent element of the main component of the high-refractive-index layer 22 are mixed. In addition, the element with the largest content in the low-refractive-index layer 21 (the constituent element of the main component of the low-refractive-index layer 21) is often a transition metal (e.g., molybdenum). The element with the largest content in the low-refractive-index layer 21 (the constituent element of the main component of the low-refractive-index layer 21) has lower chemical resistance than the element with the largest content in the high-refractive-index layer 22 (the constituent element of the main component of the high-refractive-index layer 22) and is therefore more likely to dissolve from the single layer film. From this perspective, it can be said that the L / [L+H] ratio of the reflective film 2c (or 2d) formed on the end face 1c (or 1d) is preferably smaller than the L / [L+H] ratio of the entire reflective film 2a formed on the main surface 1a. The L / [L+H] ratio of the reflective film 2c (or 2d) formed on the end face 1c (or 1d) is preferably 0.33 or less, and more preferably 0.3 or less. In particular, when the element most abundant in the low-refractive-index layer 21 (the element constituting the main component of the low-refractive-index layer) is a transition metal and the element most abundant in the high-refractive-index layer 22 (the element constituting the main component of the high-refractive-index layer) is silicon, chemical resistance is improved when the transition metal content is lower than the stoichiometrically stable ratio of transition metal:silicon = 1:2 for transition-metal silicide-based materials.

[0041] Furthermore, it is desirable that the film thickness of the portion of the reflective film 2 formed on the end face (the film thickness of the reflective film 2c (or 2d)) is thinner than the film thickness of the portion of the reflective film 2 formed on the main surface (the film thickness of the reflective film 2a). If the film thickness of the portion of the reflective film 2 formed on the end face is thick, there is a higher risk of dust generation due to film peeling at the substrate end face. There is also a higher possibility of an interface being formed in the film. The ratio of the film thickness of the reflective film 2c (or 2d) to the film thickness of the reflective film 2a is preferably 0.4 or less, and more preferably 0.3 or less.

[0042] The surface roughness (root mean square roughness) Rq of the reflective film 2c (or 2d) formed on the end face 1c (or 1d) is, for example, 1.5 nm or more. The surface roughness (root mean square roughness) Rq of the reflective film 2c (or 2d) is preferably 2 nm or more. On the other hand, the surface roughness (root mean square roughness) Rq of the reflective film 2c (or 2d) is preferably 3 nm or less.

[0043] As described above, in the reflective film-coated substrate 10 according to the present embodiment, when the reflective film 2 is formed on the main surface of the substrate 1, the reflective film 2c (or 2d) formed on the end face 1c (or 1d) of the substrate 1 has a single-layer structure containing the element (e.g., molybdenum) most abundant in the low-refractive-index layer 21 and the element (e.g., silicon) most abundant in the high-refractive-index layer 22. The reflective film 2c (or 2d) is a single-layer film having no clear interface. Furthermore, according to the substrate 10 with a reflective film of this embodiment, when the reflective film 2 is formed on the main surface of the substrate 1, the reflective film 2c (or 2d) formed on the end face 1c (or 1d) of the substrate 1 is a single-layer structure film having no interface, in which the main component elements (e.g., molybdenum) of the low refractive index layer and the main component elements (e.g., silicon) of the high refractive index layer, which are the film constituent materials of the reflective film 2, are mixed and diffused. Therefore, even if a technique for suppressing the adhesion of contamination due to hydrogen radicals or hydrogen plasma is applied during EUV exposure using a reflective mask fabricated using the reflective film-coated substrate 10 of this embodiment, it is possible to significantly reduce the risk of blisters occurring.

[0044] [Mask blank] Next, a mask blank according to the present invention will be described. A mask blank according to the present invention comprises a substrate having two opposing main surfaces and end faces connected to outer edges of the two main surfaces, a reflective film formed on one of the main surfaces and on at least a part of the end face, and a pattern-forming thin film formed on the reflective film, wherein the reflective film on the main surfaces has a structure in which low-refractive-index layers and high-refractive-index layers are alternately laminated, and the reflective film on the end face has a single-layer structure containing the element most abundant in the low-refractive-index layer and the element most abundant in the high-refractive-index layer.

[0045] Alternatively, the present invention provides a mask blank comprising a substrate, a reflective film, and a pattern-forming thin film, wherein the substrate has two opposing main surfaces and end faces connecting to outer edges of the two main surfaces, the reflective film is formed on one of the main surfaces and on at least a part of the end face, the reflective film on the main surface has a structure in which low-refractive-index layers and high-refractive-index layers are alternately stacked, the reflective film on the end face has a single-layer structure containing a material in which a main component element of the low-refractive-index layer and a main component element of the high-refractive-index layer are mixed, and the pattern-forming thin film is formed on the reflective film.

[0046] The film configuration of the mask blank according to the present invention may be any configuration having at least a reflective film that reflects exposure light (e.g., EUV light) and a pattern-forming thin film on a substrate, and may also include other films such as an underlayer (described below), a protective film formed on the reflective film, or an etching mask film formed on the pattern-forming thin film. The pattern-forming thin film may be an absorber film that absorbs EUV light. The pattern-forming thin film may also be a phase shift film that has the function of transmitting EUV light at a predetermined transmittance and the function of generating a predetermined phase difference between EUV light that passes through the thin film, is reflected at the interface with the reflective film, and is then emitted again from the thin film, and EUV light that passes through a vacuum and is directly reflected by the reflective film.

[0047] The mask blank according to the present invention is also characterized in that the reflective film is formed on one of the main surfaces and on at least a part of the end faces, the reflective film on the main surface has a structure in which low-refractive-index layers and high-refractive-index layers are alternately laminated, and the reflective film on the end faces has a single-layer structure containing a material in which a main component element of the low-refractive-index layer and a main component element of the high-refractive-index layer are mixed. These features have been explained in detail in the above-mentioned "substrate with reflective film," and therefore will not be explained again here.

[0048] Furthermore, the following points regarding the mask blank according to the present invention are the same as those in the case of the above-mentioned "substrate with reflective film," and therefore will not be described here. (1) The ratio (L / [L+H] ratio) of the content [atomic %] of the element most abundant in the low refractive index layer (the constituent element of the main component of the low refractive index layer) to the total content [atomic %] of the element most abundant in the low refractive index layer (the constituent element of the main component of the low refractive index layer) and the element most abundant in the high refractive index layer (the constituent element of the main component of the high refractive index layer) contained in the reflective film formed on the end face is less than 0.4. (2) The thickness of the portion of the reflective film formed on the end face is thinner than the thickness of the portion of the reflective film formed on the main surface. (3) The low refractive index layer is made of, for example, a material containing molybdenum, and the high refractive index layer is made of, for example, a material containing silicon. (4) The surface roughness (root mean square roughness) Rq of the reflective film formed on the end face is 1.5 nm or more. (5) Any other matter related to (1) to (4).

[0049] Fig. 3 is a cross-sectional view showing the configuration of an embodiment of the mask blank of the present invention, in which the same reference numerals are used to designate the same parts as those in Fig. 1. 3 according to an embodiment of the present invention includes a substrate 1, a reflective film 2 that reflects, for example, EUV light, formed on the substrate 1, a protective film 3, and a pattern-forming thin film 4. In this embodiment, a case will be described in which the pattern-forming thin film 4 is an absorber film that absorbs exposure light (for example, EUV light).

[0050] The details of the substrate 1 and the reflective film 2 are as described above.

[0051] As described above, for EUV exposure, a glass substrate with a low thermal expansion coefficient, such as SiO2-TiO2-based glass, is preferably used as the substrate 1. However, it may be difficult to achieve high surface smoothness, such as a root-mean-square (RMS) surface roughness of 0.1 nm or less, through precision polishing of such a glass substrate. Therefore, it is preferable to form an underlayer (not shown) on the surface of the glass substrate (substrate 1) to reduce the surface roughness or defects on the glass substrate. The material for such an underlayer does not need to be transparent to the exposure light, and is preferably selected from materials that provide high smoothness and good defect quality when the underlayer surface is precision polished. For example, Si or silicon compounds containing Si (e.g., SiO2, SiON, etc.) are preferably used because they provide high smoothness and good defect quality when precision polished. Si is particularly preferred as the material for the underlayer.

[0052] The surface of such an underlayer is preferably precision-polished to a smoothness required for a mask blank substrate. The surface of the underlayer is desirably precision-polished to a root-mean-square roughness (Rq) of 0.15 nm or less, more preferably 0.1 nm or less. Furthermore, in consideration of the influence on the surface of the reflective film 2 formed on the underlayer, the surface of the underlayer is desirably precision-polished to a maximum surface roughness (Rmax) such that Rmax / Rq is 2 to 10, more preferably 2 to 8. The thickness of the underlayer is preferably in the range of, for example, 75 nm to 300 nm.

[0053] In general, it is desirable to provide a protective film 3 between the reflective film 2 and the pattern-forming thin film 4 as in this embodiment, in order to protect the reflective film 2 when patterning or correcting the pattern of the pattern-forming thin film 4.

[0054] The protective film 3 is formed on the reflective film 2 to protect the reflective film 2 from dry etching and cleaning during the manufacturing process of the reflective mask 30. The protective film 3 can also protect the reflective film 2 during opaque defect repair (EB defect repair) of a transfer pattern using an electron beam (EB). The protective film 3 can have a laminated structure of three or more layers. For example, the bottom and top layers of the protective film 3 can be layers made of a Ru-containing material, with a metal other than Ru or an alloy of a metal other than Ru interposed between the bottom and top layers. The protective film 3 can be made of, for example, a material containing ruthenium as a main component. Examples of materials containing ruthenium as a main component include Ru metal alone and Ru alloys containing Ru with metals such as titanium (Ti), niobium (Nb), molybdenum (Mo), zirconium (Zr), yttrium (Y), boron (B), lanthanum (La), cobalt (Co), and / or rhenium (Re). Furthermore, these materials for the protective film 3 may further contain nitrogen. The protective film 3 is effective when the pattern-forming thin film 4 is patterned by dry etching using a Cl-based gas.

[0055] The thickness of the protective film 3 is not particularly limited as long as it can function as the protective film 3. From the viewpoint of reflectance of EUV light, the thickness of the protective film 3 is preferably 1.0 nm to 8.0 nm, and more preferably 1.5 nm to 6.0 nm.

[0056] The protective film 3 may be provided on the reflective film 2c (or 2d) formed on the end face 1c (or 1d), but its provision is not essential. The reflective film 2c (or 2d) on the end face 1c (or 1d) often does not have a pattern-forming thin film 4 provided thereon, and is therefore less susceptible to dry etching and EB defect repair. Furthermore, the reflective film 2c (or 2d) is a single-layer film containing the element with the highest content in the low-refractive-index layer and the element with the highest content in the high-refractive-index layer, or a single-layer film formed from a material containing a mixture of the main constituent elements of the low-refractive-index layer and the main constituent elements of the high-refractive-index layer, and therefore has high resistance to these elements, including chemical resistance. For these reasons, there is little need to provide the protective film 3 on the reflective film 2c (or 2d). The surface layer of the reflective film 2c (or 2d) (e.g., a region 5 nm or less from the surface) may also contain the constituent elements of the protective film 3.

[0057] Furthermore, in the mask blank 20 of this embodiment, the pattern-forming thin film 4 may be a single-layer film or a multilayer film consisting of multiple films. A single-layer film has the advantage of reducing the number of steps in mask blank manufacturing, thereby improving production efficiency. In the case of a multilayer film, the optical constants and film thickness of the upper thin film can be appropriately set so that it serves as an anti-reflection film during optical mask pattern defect inspection. This improves the inspection sensitivity during optical mask pattern defect inspection. Furthermore, using a film containing oxygen (O) and nitrogen (N), which improve oxidation resistance, as the upper thin film improves stability over time.

[0058] The material of the pattern-forming thin film 4 is not particularly limited as long as it has the function of absorbing EUV light and can be processed by etching or the like (preferably by dry etching with a chlorine (Cl) and / or fluorine (F)-based gas). As a material having such a function, tantalum (Ta) alone or a material containing Ta can be preferably used.

[0059] Examples of materials containing Ta include materials containing Ta and B, materials containing Ta and N, materials containing Ta, B and at least one of O and N, materials containing Ta and Si, materials containing Ta, Si and N, materials containing Ta, Ge, materials containing Ta, Ge and N, materials containing Ta and Pd, materials containing Ta and Ru, and materials containing Ta and Ti.

[0060] The pattern-forming thin film 4 can be formed from a material containing at least one selected from the group consisting of, for example, Ni alone, a material containing Ni, Cr alone, a material containing Cr, Ru alone, a material containing Ru, Pd alone, a material containing Pd, Mo alone, and a material containing Mo.

[0061] The pattern-forming thin film 4 can be formed by, for example, sputtering. The thickness of the pattern-forming thin film 4 is preferably in the range of, for example, 25 nm to 70 nm.

[0062] An etching mask film may be provided on the pattern-forming thin film 4. By providing the etching mask film, the resist film formed on the absorber film can be made thinner when patterning the pattern-forming thin film 4, so that a fine pattern can be formed on the pattern-forming thin film 4 with high precision.

[0063] Such an etching mask film is formed of a material having etching selectivity with respect to the pattern-forming thin film 4. When the absorber film is formed of the tantalum-based material, the etching mask film is preferably formed of, for example, a chromium-based material. Examples of chromium-based materials include chromium (Cr) alone and chromium compounds (chromium oxide, chromium nitride, chromium oxynitride, chromium carbide, etc.). The etching mask film can be formed by, for example, sputtering, and the thickness of the etching mask film is preferably in the range of, for example, 5 nm to 15 nm.

[0064] The mask blank 20 according to the present embodiment as shown in Fig. 3 described above can be manufactured by sequentially forming the reflective film 2, the protective film 3, and the pattern-forming thin film 4 on the substrate 1. If necessary, an underlayer (not shown) can be formed between the substrate 1 and the reflective film 2. If necessary, an etching mask film (not shown) can be formed on the pattern-forming thin film 4.

[0065] In the mask blank 20 according to the present embodiment described above, when the reflective film 2 is formed on the main surface of the substrate 1, the film formed on the edge surface of the substrate 1 is a single-layer film in which the film constituent materials of the reflective film 2, for example, Si and Mo, are mixed and diffused, and which has no interface. Therefore, even if a technique for suppressing adhesion of contamination due to hydrogen radicals or hydrogen plasma is used during EUV exposure, it is possible to significantly reduce the risk of blisters occurring.

[0066] [Reflective mask] The present invention also provides a reflective mask. The reflective mask according to the present invention is a reflective mask characterized in that a transfer pattern is provided on the pattern-forming thin film of the mask blank having the above-described configuration. Fig. 4 is a cross-sectional view of a reflective mask manufactured using the mask blank of the present invention, in which the same reference numerals are used to designate parts that are the same as those in Fig. 1 or 3. FIG. 4 shows a reflective mask 30 having a transfer pattern 4a formed by patterning the pattern-forming thin film 4 in the mask blank 20 shown in FIG.

[0067] For example, photolithography is the most suitable method for patterning the pattern-forming thin film 4 in the aforementioned mask blank 20. That is, in order to obtain the reflective mask of the present invention, a manufacturing method is suitable that uses the aforementioned mask blank 20 and includes at least the steps of forming a resist film on the surface of the mask blank 20, forming a resist pattern on this resist film by electron beam lithography and development, and patterning the pattern-forming thin film 4 by dry etching using the formed resist pattern as a mask.

[0068] As described above, in the reflective mask 30 according to the present embodiment, when the reflective film 2 is formed on the main surface of the substrate 1, the film formed on the edge surface of the substrate 1 is a single-layer film in which the film constituent materials of the reflective film 2, for example, Si and Mo, are mixed and diffused, and have no interface. Therefore, even if a technique for suppressing adhesion of contamination due to hydrogen radicals or hydrogen plasma is applied during EUV exposure using this reflective mask 30, it is possible to suppress the occurrence of blisters and significantly reduce the risk of blister occurrence.

[0069] [Semiconductor device manufacturing method] The present invention also provides a method for manufacturing a semiconductor device, comprising the step of exposing and transferring a transfer pattern onto a resist film on a semiconductor substrate using the above-mentioned reflective mask. By using the reflective mask according to the present invention, it is possible to significantly reduce the risk of blisters occurring during EUV exposure, even when a technique for suppressing contamination adhesion due to hydrogen radicals or hydrogen plasma is used. Therefore, according to the present invention, good pattern transfer can be performed, and high-quality semiconductor devices on which highly accurate device patterns are formed can be manufactured. [Example]

[0070] Hereinafter, the embodiments of the present invention will be described more specifically with reference to examples. Example 1 A SiO2-TiO2 glass substrate (approximately 152.4 mm x 152.4 mm, approximately 6.35 mm thick) was prepared by polishing the substrate in stages using a double-sided polishing machine with cerium oxide abrasive grains and colloidal silica abrasive grains, followed by surface treatment with low-concentration hydrosilicofluoric acid. The surface roughness of the resulting glass substrate 1 was 0.20 nm in root-mean-square roughness (Rq). The surface roughness was measured using an atomic force microscope (AFM) over a 1 μm x 1 μm measurement area.

[0071] Next, a conductive backside film (not shown) having a laminated structure of a lower layer made of CrON and an upper layer made of CrN was formed on the main surface 1b of the glass substrate 1 (the main surface opposite the main surface 1a on which the reflective film 2 was to be formed). The lower layer (CrON layer) was deposited to a thickness of 15 nm by reactive sputtering (DC magnetron sputtering) using a Cr target in a mixed gas atmosphere of Ar gas, N2 gas, and O2 gas. The upper layer (CrN layer) was deposited to a thickness of 180 nm by reactive sputtering (DC magnetron sputtering) using a Cr target in a mixed gas atmosphere of Ar gas and N2 gas. The composition (atomic %) of the CrN layer was measured by X-ray photoelectron spectroscopy (XPS), and the atomic ratio was found to be 91 atomic % chromium (Cr) and 9 atomic % nitrogen (N).

[0072] Next, an ion beam sputtering apparatus was used to form a reflective film 2 (total thickness 280 nm) composed of a multilayer film on the main surface 1a of the glass substrate 1 by stacking 40 periods of a high-refractive-index Si film (thickness: 2.8 nm) and a low-refractive-index Mo film (thickness: 4.2 nm). Specifically, the conductive back surface film of the glass substrate 1 was fixed to the stage of the ion beam sputtering apparatus with an electrostatic chuck, and sputtered particles (Si particles and Mo particles) were incident obliquely onto the main surface 1a of the glass substrate, depositing them on the main surface 1a and the end faces 1c and 1d, respectively, to form the reflective film 2. During this film formation, the end faces 1c and 1d of the glass substrate were not masked with a shield or the like. Through the above processes, the substrate with a reflective film of Example 1 was obtained.

[0073] The reflective film was formed not only on the main surface 1a of the glass substrate but also on the edge surfaces (four edge surfaces including 1c and 1d) of the glass substrate. The reflective film on the edge surfaces of the glass substrate was analyzed using a transmission electron microscope (TEM). As a result, it was confirmed that the film thickness of the portion of the reflective film formed on the edge surfaces was thinner (approximately 40 nm) than that of the portion of the reflective film formed on the main surfaces. It was also confirmed that the reflective film on the edge surfaces of the glass substrate has a single-layer structure, not a multilayer structure. Therefore, the reflective film on the edge surfaces of the glass substrate does not have a reflecting function for exposure light. Furthermore, analysis of the composition of the reflective film on the edge surfaces of the glass substrate using an energy-dispersive transmission electron microscope (TEM-EDX) confirmed that it contains Si and Mo. That is, when the reflective film was formed on the main surfaces of the glass substrate, the film that was attached to the edge surfaces of the glass substrate and that extended around the edge surfaces of the glass substrate was a single-layer structure in which the Si and Mo film components of the reflective film were mixed and diffused, and had no interface.

[0074] The ratio of the content (atomic %) of Mo, a constituent element of the main component of the low refractive index layer included in the reflective film formed on the substrate end face, divided by the total content (atomic %) of Mo, a constituent element of the main component of the low refractive index layer, and Si, a constituent element of the main component of the high refractive index layer, was 0.25. The surface roughness (root mean square roughness) Rq of the reflective film formed on the end face was 2 nm or more.

[0075] Next, using the same method as above, a conductive back surface film was formed on the main surface 1b of the glass substrate 1, and a reflective film consisting of a multilayer film was formed on the main surface 1a by stacking 40 periods of Si films and Mo films, thereby obtaining a substrate with a reflective film. Next, using a DC magnetron sputtering system, a protective film made of Ru (thickness: 2.5 nm) and an absorber film consisting of a laminated film of a TaN film (thickness: 48 nm, composition Ta:N=70 at%:30 at%) and a TaO film (thickness: 11 nm, composition Ta:O=35 at%:65 at%) were formed on the reflective film of this reflective film-coated substrate. The compositions of each film were measured by X-ray photoelectron spectroscopy (XPS). In this manner, a mask blank (reflective mask blank) was produced.

[0076] Next, a reflective mask was fabricated using this mask blank. First, a positive resist film for electron beam writing was formed as a resist film on the surface of the absorber film of the mask blank to a thickness of 80 nm by spin coating using a spinner (spin coating device).

[0077] Next, a predetermined mask pattern was written on the resist film using an electron beam writing machine, and then development was carried out to form a resist pattern.

[0078] Next, using this resist pattern as a mask, the absorber film was etched away by a fluorine-based gas (CF4 gas) to remove the TaO film and a chlorine-based gas (Cl2 gas) to remove the TaN film, thereby forming an absorber film pattern. Furthermore, the resist pattern remaining on the absorber film pattern was removed with hot sulfuric acid to obtain the reflective mask for EUV lithography of Example 1. When the reflective films 2c and 2d on the end faces 1c and 1d of this reflective mask of Example 1 were observed, it was confirmed that there was no noticeable film loss.

[0079] When the reflective mask obtained as described above is set in an EUV exposure tool to transfer a pattern onto a semiconductor substrate on which a resist film has been formed, it is desirable to create a hydrogen atmosphere, such as hydrogen radicals, inside the exposure chamber, to suppress contamination adhesion to the mirror and mask of the exposure tool during EUV exposure, as described above. In the case of the reflective mask according to this embodiment, as described above, when the reflective film is formed on the main surface of the glass substrate, the film formed on the edge surface of the glass substrate does not have a multilayer structure, but rather a single-layer structure in which the Si and Mo film components of the reflective film are mixed and diffused, resulting in no interface. Therefore, even if a technique for suppressing contamination adhesion due to hydrogen radicals or hydrogen plasma is used during EUV exposure, the risk of blister formation can be significantly reduced. Therefore, according to the present invention, good pattern transfer can be achieved.

[0080] (Comparative Example) As in Example 1, a SiO2-TiO2-based glass substrate (approximately 152.4 mm x 152.4 mm, approximately 6.35 mm thick) was prepared by polishing the substrate in stages using a double-sided polishing machine with cerium oxide abrasive grains and colloidal silica abrasive grains, and then surface-treating the substrate with low-concentration hydrosilicofluoric acid. The surface roughness of the resulting glass substrate 1 was 0.25 nm in root-mean-square roughness (Rq). The surface roughness was measured using an atomic force microscope (AFM) over a 1 μm x 1 μm measurement area.

[0081] Next, using the same procedure as in Example 1, a conductive back surface film (not shown) having a laminated structure of a lower layer made of CrON and an upper layer made of CrN was formed on the main surface 1b of the glass substrate 1.

[0082] Next, using an ALD (Atomic Layer Deposition) apparatus (a film formation apparatus using atomic layer deposition), 40 periods of a high-refractive-index Si film (thickness: 2.8 nm) and a low-refractive-index Mo film (thickness: 4.2 nm) were stacked on the main surface 1a of the glass substrate 1 to form a reflective film (total thickness: 280 nm) consisting of a multilayer film. Si particles and Mo particles were incident on the main surface 1a of the glass substrate from an oblique direction, respectively, and deposited on the main surface 1a and the end faces 1c and 1d, respectively, to form the reflective film 2. During this film formation, the end faces 1c and 1d of the glass substrate were not masked with a shield or the like. Through the above processes, a comparative example of a substrate with a reflective film was obtained.

[0083] The reflective film was formed not only on the main surface of the glass substrate but also on the edge surface of the glass substrate. The structure of the reflective film on the edge surface of the glass substrate was analyzed using a transmission electron microscope (TEM). As a result, it was confirmed that the reflective film on the edge surface of the glass substrate had a multilayer structure in which Si films and Mo films were alternately stacked, similar to the reflective film formed on the main surface. In other words, when the reflective film was formed on the main surface of the glass substrate, the film that was attached to the edge surface of the glass substrate in a wraparound manner was a multilayer film structure having an interface.

[0084] Next, using the same method as above, a conductive back surface film was formed on the main surface 1b of the glass substrate 1, and a reflective film consisting of a multilayer film was formed on the main surface 1a by stacking 40 periods of Si films and Mo films, thereby obtaining a substrate with a reflective film. Next, in the same manner as in Example 1 described above, a protective film made of Ru and an absorber film made of a laminated film of a TaN film and a TaO film were formed on the reflective film of this reflective film-coated substrate, thereby producing a mask blank (reflective mask blank) of the comparative example.

[0085] Next, using this mask blank, a reflective mask for EUV lithography as a comparative example was produced in the same manner as in Example 1 above.

[0086] When the reflective mask obtained as described above is set in an EUV exposure tool to transfer a pattern onto a semiconductor substrate on which a resist film has been formed, it is desirable to apply a technique for suppressing the adhesion of contamination due to hydrogen radicals or hydrogen plasma during EUV exposure. However, in the case of the reflective mask according to this comparative example, as described above, the film formed on the edge face of the glass substrate has a multilayer film structure with interfaces between each layer. Therefore, if a technique for suppressing the adhesion of contamination due to hydrogen radicals or hydrogen plasma is used during EUV exposure, there is a high risk of blisters occurring in the film on the edge face of the substrate, which may cause contamination inside the exposure chamber, for example, making it difficult to perform good pattern transfer. [Explanation of symbols]

[0087] 1 board 1a, 1b main surface 1c, 1d end face 2 Reflective film 2a Reflective film on the main surface of the substrate 2c, 2d Reflective film on the edge of the substrate 21 Low refractive index layer 22 High refractive index layer 3 Protective film 4 Thin films for pattern formation 4a Transcription pattern 10. Substrate with reflective film 20 Mask Blanks 30 Reflective mask

Claims

1. A substrate with a reflective film, a substrate having two opposing main surfaces and an end surface connected to outer edges of the two main surfaces; a reflective film formed on one of the main surfaces and at least a part of the end surface, the reflective film on the main surface has a structure in which low refractive index layers and high refractive index layers are alternately laminated, the reflective film on the end surface has a single-layer structure containing the element with the highest content in the low-refractive-index layer and the element with the highest content in the high-refractive-index layer, a L / [L+H] ratio of the content [atomic %] of the element most abundant in the low refractive index layer to the total content [atomic %] of the element most abundant in the low refractive index layer and the element most abundant in the high refractive index layer, which are contained in the reflective film formed on the end face, is smaller than the L / [L+H] ratio of the entire reflective film on the main surface.

2. A substrate with a reflective film as described in Claim 1, characterized in that the film thickness of the portion formed on the end surface of the reflective film is thinner than the film thickness of the portion formed on the main surface of the reflective film.

3. A substrate with a reflective film as described in claim 1 or 2, characterized in that the ratio of the film thickness of the portion of the reflective film formed on the end surface to the film thickness of the portion of the reflective film formed on the main surface is 0.4 or less.

4. A substrate with a reflective film described in any one of claims 1 to 3, characterized in that the element most abundant in the low refractive index layer is molybdenum, and the element most abundant in the high refractive index layer is silicon.

5. A substrate with a reflective film described in any one of claims 1 to 4, characterized in that the surface roughness (root mean square roughness) Rq of the reflective film formed on the end face is 1.5 nm or more.

6. A mask blank characterized by having a substrate with a reflective film described in any one of claims 1 to 5 and a thin film for pattern formation formed on the reflective film of the substrate with a reflective film.

7. A reflective mask comprising a substrate with a reflective film according to any one of claims 1 to 5, and a thin film formed on the reflective film of the substrate with a reflective film and having a transfer pattern.

8. A method for manufacturing a semiconductor device, comprising a step of exposing and transferring a transfer pattern onto a resist film on a semiconductor substrate using the reflective mask described in claim 7.

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