Film-attached substrate regeneration method, method for manufacturing glass substrate for mask blank, and method for manufacturing reflective mask blank

Abstract

Provided is a film-attached substrate regeneration method for regenerating a glass substrate from a film-attached substrate comprising said glass substrate, a multilayer reflective film that reflects EUV light, and a protective film that protects the multilayer reflective film. Said film-attached substrate regeneration method involving grinding and removing at least a portion of the protective film.

Description

Method for regenerating a film-coated substrate, method for manufacturing a glass substrate for mask blanks, and method for manufacturing a reflective mask blank

[0001] This disclosure relates to a method for regenerating a film-coated substrate, a method for manufacturing a glass substrate for mask blanks, and a method for manufacturing a reflective mask blank. This application claims priority under Japanese Patent Application No. 2024-164289, filed in Japan on September 20, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, with the miniaturization of semiconductor devices, EUV lithography (EUVL), a photolithography technique using extreme ultraviolet (EUV) light, has been developed. EUV includes soft X-rays and vacuum ultraviolet light, specifically light with wavelengths of approximately 0.2 nm to 100 nm. Currently, EUV with a wavelength of approximately 13.5 nm is being primarily studied.

[0003] In EUVL, the aperture pattern of the absorption film is transferred to a target substrate such as a semiconductor substrate. A reflective mask is obtained by forming an aperture pattern on the absorption film of a reflective mask blank. A reflective mask blank has, in this order, a substrate such as a glass substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorption film that absorbs EUV light. The absorption film may also be a phase-shifting film that shifts the phase of EUV light.

[0004] Incidentally, in reflective masks, the presence of irregularities near the aperture pattern can lead to problems because it degrades the positional accuracy and contrast of the transferred pattern. Irregularities are caused by defects such as scratches or foreign matter.

[0005] Therefore, to ensure that there are no irregularities near the aperture pattern, surface defect inspections and film defect inspections are performed on the film-coated substrate at each stage of the process. If defects of an unacceptable size are found as a result of the inspection, the defects are removed by cleaning or other means. On the other hand, if there are defects that cannot be removed by cleaning or other means, the substrate is either refurbished by stripping off the multilayer reflective film or discarded as a defective product.

[0006] In recent years, the competition in reducing the prices of electronic components such as semiconductor devices has been intensifying, and suppressing the manufacturing cost of transfer masks has also become an important issue. Against this backdrop, when a mask blank with surface defects is discovered after forming a thin film for pattern formation on a substrate, or when a pattern defect that is difficult to correct is discovered in a transfer mask manufactured using the mask blank, there is a demand for a method of regenerating a glass substrate by peeling off and removing the thin film from the substrate with the film instead of simply discarding these film-coated substrates with defects as defective products.

[0007] So far, for example, a method has been reported in which a substrate with a multilayer film is brought into contact with a stripping solution composed of an aqueous solution containing at least one selected from sodium hydroxide and potassium hydroxide and hydrogen peroxide, or a stripping solution obtained by mixing aqueous ammonia and hydrogen peroxide solution to strip and remove the multilayer film from the substrate and regenerate the substrate (see, for example, Patent Document 1).

[0008] Japanese Patent Application Laid-Open No. 2017-181733 (A)

[0009] However, in the method described in Patent Document 1 in which the substrate is brought into contact with the stripping solution, for example, when regenerating a film-coated substrate having a protective layer containing rhodium and excellent in etching resistance, since the corrosion resistance to the stripping solution is also high, there is a problem that the protective layer may not be stripped and removed by the treatment with the stripping solution.

[0010] An aspect of the present disclosure aims to provide a method for regenerating a film-coated substrate that can remove a protective film that is difficult to remove by chemical solution treatment and can regenerate a glass substrate when regenerating a film-coated substrate in which defective products may occur in a precise film formation process.

[0011] A method for regenerating a film-coated substrate according to an aspect of the present disclosure is a method for regenerating a film-coated substrate that regenerates the glass substrate from a film-coated substrate having a glass substrate, a multilayer reflective film that reflects EUV light, and a protective film that protects the multilayer reflective film, and includes polishing and removing at least a part of the protective film.

[0012] According to one aspect of this disclosure, when regenerating a film-coated substrate in which defects may occur during a precise film deposition process, it is possible to remove protective films that are difficult to remove by chemical treatment, and to provide a method for regenerating a film-coated substrate that can regenerate a glass substrate.

[0013] Figure 1 is a flowchart showing a method for regenerating a film-coated substrate according to one embodiment. Figure 2 is a cross-sectional view showing a film-coated substrate according to one embodiment. Figure 3 is a cross-sectional view showing a reflective mask blank, which is a film-coated substrate according to one embodiment. Figure 4 is a cross-sectional view showing a reflective mask blank, which is a film-coated substrate according to one embodiment. Figure 5 is a cross-sectional view showing a reflective mask, which is a film-coated substrate according to one embodiment. Figure 6 is a cross-sectional view showing an example of EUV light reflected by the reflective mask of Figure 5. Figure 7 is a flowchart showing a method for manufacturing a reflective mask blank according to one embodiment. Figure 8 is a flowchart showing a method for manufacturing a reflective mask according to one embodiment. Figure 9 is a diagram illustrating the measurement area of ​​the Rh X-ray intensity in a polished film-coated substrate according to Example 1.

[0014] The embodiments for implementing this disclosure will be described below with reference to the drawings. In each drawing, identical or corresponding components will be denoted by the same reference numeral, and their descriptions may be omitted. In the specification, the numeral "~" indicating a numerical range means that the numbers before and after it are included as the lower and upper limits, respectively.

[0015] (Method for regenerating a film-coated substrate) The method for regenerating a film-coated substrate according to the present disclosure is a method for regenerating a glass substrate from a film-coated substrate having a glass substrate, a multilayer reflective film that reflects EUV light, and a protective film that protects the multilayer reflective film, and preferably includes polishing and removing at least a part of the protective film (step S102), and bringing the polished film-coated substrate into contact with a chemical solution to remove the multilayer reflective film (step S103), and may further include other steps such as preparing the film-coated substrate (step S101) and cleaning (step S104) as needed.

[0016] Referring to Figure 1, a method for regenerating a film-coated substrate according to one embodiment will be described. The method for regenerating a film-coated substrate includes, for example, steps S101 to S104 shown in Figure 1. In step S101, the film-coated substrate is prepared. In step S102, at least a portion of the protective film 12 of the film-coated substrate is polished and removed. In step S103, the polished film-coated substrate is brought into contact with a chemical solution to remove the multilayer reflective film 11. In step S104, the regenerated glass substrate 10 is cleaned.

[0017] <Step S101: Preparation of film-coated substrate> - Film-coated substrate - In the method for regenerating film-coated substrates, the film-coated substrate to be regenerated is preferably a defective film-coated substrate that has become a defective product in the precise film deposition process of a reflective mask blank or reflective mask, but a reflective mask blank or reflective mask without defects may also be used.

[0018] The film-coated substrate comprises a glass substrate, a multilayer reflective film that reflects EUV light, and a protective film that protects the multilayer reflective film. It may also optionally have an absorption film and an etching mask film. Examples include the film-coated substrates 1 to 4 shown in Figures 2 to 5.

[0019] A film-coated substrate according to one embodiment will be described with reference to Figures 2 to 5. The film-coated substrate 1 shown in Figure 2 has a glass substrate 10, a multilayer reflective film 11, and a protective film 12 in that order. The film-coated substrate 2 shown in Figure 3 is a reflective mask blank having a glass substrate 10, a multilayer reflective film 11, a protective film 12, and an absorption film 13 in that order. The film-coated substrate 3 shown in Figure 4 is a reflective mask blank having a glass substrate 10, a multilayer reflective film 11, a protective film 12, an absorption film 13, and an etching mask film 14 in that order. Note that a reflective mask blank only needs to have at least a glass substrate 10, a multilayer reflective film 11, a protective film 12, and an absorption film 13.

[0020] The film-coated substrate 4 shown in Figure 5 is, for example, a reflective mask made using the reflective mask blank shown in Figure 4, and is a reflective mask having a glass substrate 10, a multilayer reflective film 11, a protective film 12, and an absorption film 13 in that order. The absorption film 13 has an opening pattern 13a. The etching mask film 14 shown in Figure 3 is removed after the opening pattern 13a is formed on the absorption film 13.

[0021] The film-coated substrates shown in Figures 2-5 may further have functional films not shown. For example, the film-coated substrate may have a conductive film on the side opposite to the multilayer reflective film 11, relative to the glass substrate 10. The conductive film is formed on the second main surface 10b of the glass substrate 10. The second main surface 10b is the surface facing the opposite direction from the first main surface 10a. The conductive film is used, for example, to attract the film-coated substrate to the electrostatic chuck of an exposure apparatus.

[0022] The film-coated substrates shown in Figures 2-5 may have a buffer film on the protective film 12 or between the protective film 12 and the absorption film 13, although these are not shown. The buffer film protects the protective film 12 from etching gases that form an opening pattern 13a in the absorption film 13. The buffer film is etched more slowly than the absorption film 13. Unlike the protective film 12, the buffer film ultimately has the same opening pattern as the opening pattern 13a of the absorption film 13.

[0023] In EUV lithography (EUVL), the aperture pattern 13a of the absorption film 13 is transferred to a target substrate such as a semiconductor substrate. Transfer includes transfer at a reduced size. The glass substrate 10, multilayer reflective film 11, protective film 12, absorption film 13, and etching mask film 14 will be described below in this order.

[0024] The material of the glass substrate 10 is TiO ２ Quartz glass containing SiO is preferred. Compared to general soda-lime glass, quartz glass has a smaller coefficient of linear expansion and less dimensional change due to temperature changes. Quartz glass contains SiO ２ 80% to 95% by mass, TiO ２ It may contain 4% to 17% by mass of TiO. ２When the content is between 4% by mass and 17% by mass, the coefficient of linear expansion at room temperature is approximately zero, and there is almost no dimensional change at room temperature. Quartz glass is composed of SiO ２ and TiO ２ It may also contain other third components or impurities. The material of the glass substrate 10 may be crystallized glass with a β-quartz solid solution precipitated, silicon, or metal, etc.

[0025] The glass substrate 10 has a first main surface 10a and a second main surface 10b facing the opposite direction from the first main surface 10a. A multilayer reflective film 11 or the like is formed on the first main surface 10a. In plan view (view in the stacking direction), the size of the glass substrate 10 is, for example, 152 mm in length and 152 mm in width. The length and width dimensions may be 152 mm or more. The first main surface 10a and the second main surface 10b each have, for example, a square quality assurance area in the center. The size of the quality assurance area is, for example, 142 mm in length and 142 mm in width. The quality assurance area of ​​the first main surface 10a preferably has a root mean square roughness Rq of 0.15 nm or less and a flatness of 100 nm or less. Furthermore, it is preferable that the quality assurance area of ​​the first main surface 10a does not have defects that cause phase defects.

[0026] The multilayer reflective film 11 reflects EUV light. The multilayer reflective film 11 is, for example, made by alternately stacking high refractive index layers and low refractive index layers. The material of the high refractive index layer is, for example, silicon (Si), and the material of the low refractive index layer is, for example, molybdenum (Mo), and a Mo / Si multilayer reflective film is used. In addition, Ru / Si multilayer reflective films, Mo / Be multilayer reflective films, Mo compound / Si compound multilayer reflective films, Si / Mo / Ru multilayer reflective films, Si / Mo / Ru / Mo multilayer reflective films, and Si / Ru / Mo / Ru multilayer reflective films can also be used as the multilayer reflective film 11.

[0027] The film thickness of each layer constituting the multilayer reflective film 11 and the number of repeating units of the layers can be appropriately selected according to the material of each layer and the reflectivity with respect to EUV light. When the multilayer reflective film 11 is a Mo / Si multilayer reflective film, in order to achieve a reflectivity of 60% or more with respect to EUV light with an incident angle θ (see FIG. 6) of 6°, a Mo layer with a film thickness of 2.3 ± 0.1 nm and a Si layer with a film thickness of 4.5 ± 0.1 nm may be laminated so that the number of repeating units is 30 or more and 60 or less. The multilayer reflective film 11 preferably has a reflectivity of 60% or more with respect to EUV light with an incident angle θ of 6°. More preferably, the reflectivity is 65% or more.

[0028] The protective film 12 is formed between the multilayer reflective film 11 and the absorption film 13 and protects the multilayer reflective film 11. The protective film 12 protects the multilayer reflective film 11 from an etching gas that forms an opening pattern 13a (see FIG. 5) in the absorption film 13. The protective film 12 remains on the multilayer reflective film 11 without being removed even when exposed to the etching gas.

[0029] The etching gas is, for example, a halogen-based gas, an oxygen-based gas, or a mixed gas thereof. Examples of the halogen-based gas include a chlorine-based gas and a fluorine-based gas. Examples of the chlorine-based gas include Cl ２ gas, SiCl ４ gas, CHCl ３ gas, CCl ４ gas, BCl ３ gas or a mixed gas thereof. Examples of the fluorine-based gas include CF ４ gas, CHF ３ gas, SF ６ gas, BF ３ gas, XeF ２ gas or a mixed gas thereof. Examples of the oxygen-based gas include O ２ gas, O ３ gas or a mixed gas thereof.

[0030] The ratio of the etching rate ER2 of the absorption film 13 to the etching rate ER1 of the protective film 12 (ER2 / ER1) is also called the selectivity ratio (ER2 / ER1). The larger the selectivity ratio (ER2 / ER1), the better the processability of the absorption film 13. The selectivity ratio (ER2 / ER1) is preferably 5.0 or higher, more preferably 10 or higher, and even more preferably 30 or higher. The selectivity ratio (ER2 / ER1) is preferably 200 or lower, and more preferably 100 or lower.

[0031] The protective film 12 preferably contains Rh as a metallic element, and more preferably contains 50 at% to 100 at% of Rh. The protective film 12 may further contain at least one element Z1 selected from the group consisting of Ru, Nb, Mo, Ta, Ir, Pd, Zr, Y, and Ti. In one embodiment, the protective film 12 preferably contains only Rh as a metallic element, or contains Rh plus at least one of Ru and Pd.

[0032] If the protective film 12 contains Rh, the etching resistance of the protective film 12 can be improved, especially when an oxygen-based gas is used as the etching gas (including when a mixed gas is used). When the protective film 12 has excellent etching resistance, its corrosion resistance is also improved, making it difficult to remove the protective film by chemical treatment alone when regenerating a film-coated substrate. Therefore, according to the method for regenerating a film-coated substrate, it is preferable that the protective film 12 contains Rh because it makes it possible to remove the protective film, which is difficult to remove by chemical treatment alone.

[0033] Rh is more readily interdiffused with Si than Ru. Therefore, when the protective film 12 contains Rh as its main component, the elemental ratio (N / Si, O / Si) in the uppermost layer of the multilayer reflective film 11 becomes more important than when the protective film 12 contains Ru as its main component. Preferably, the molar ratio of N to Si (N / Si) in the uppermost layer of the multilayer reflective film 11 is greater than 0.00 and less than 1.50 (0.00 < (N / Si) < 1.50), and the molar ratio of O to Si (O / Si) is 0.00 or greater and less than 0.25 (0.00 ≤ (O / Si) < 0.25). Within these ranges, mixing between the uppermost layer of the multilayer reflective film 11 and the protective film 12 can be suppressed. By suppressing mixing, a decrease in etching resistance and a decrease in reflectivity to EUV light can be suppressed.

[0034] By adding Ru, Nb, Mo, Zr, Y, or Ti to Rh, the extinction coefficient can be reduced while suppressing the increase in refractive index, thereby improving the reflectivity to EUV light. Furthermore, by adding Ta, Ir, Pd, or Y to Rh, the durability against etching gas and / or sulfuric acid peroxide can be improved. Sulfuric acid peroxide is used for removing the resist film or cleaning the reflective mask, as described later.

[0035] The elemental ratio of Z1 to Rh (Z1:Rh) is preferably 1:99 to 1:1. If the ratio (Z1 / Rh) is 1 / 99 or greater, the reflectivity to EUV light is good. If the ratio (Z1 / Rh) is 1 or less, the etching resistance of the protective film 12 is good. The elemental ratio of Z1 to Rh (Z1:Rh) is more preferably 3:10 to 1:1.

[0036] When Z1 is Ru, the elemental ratio of Ru to Rh (Ru / Rh) is preferably greater than 0.0 and less than 1.0 (0.0 < (Ru / Rh) < 1.0), and more preferably greater than 0.3 and less than 0.5 (0.3 < (Ru / Rh) < 0.5). If the elemental ratio (Ru / Rh) is greater than 0.0, the reflectivity to EUV light is good. If the elemental ratio (Ru / Rh) is less than 1.0, the etching resistance is good.

[0037] When Z1 is Pd, the elemental ratio of Pd to Rh (Pd / Rh) is preferably greater than 0.00 and less than 1.0 (0.00 < (Pd / Rh) < 1.0), and more preferably greater than 0.01 and less than 0.1 (0.01 < (Pd / Rh) < 0.1). If the elemental ratio (Ru / Rh) is greater than 0.00, etching resistance is good. If the elemental ratio (Ru / Rh) is less than 1.0, reflectivity to EUV light is good.

[0038] The protective film 12 may contain, in addition to Rh, at least one element Z2 selected from the group consisting of N, O, C, and B. While element Z2 reduces the etching resistance of the protective film 12, it can suppress crystallization of the protective film 12, allowing for the formation of a smooth surface. The protective film 12 containing element Z2 has an amorphous or microcrystalline structure. When the protective film 12 has an amorphous or microcrystalline structure, the X-ray diffraction profile of the protective film 12 does not have a clear peak.

[0039] When the protective film 12 contains Z2 in addition to Rh, it is preferable that the Rh content or the combined Rh and Z1 content be 40 at% to 99 at% and the total Z2 content be 1.0 at% to 60 at%. When the protective film 12 contains Z2 in addition to Rh, it is more preferable that the Rh content or the combined Rh and Z1 content be 80 at% to 99 at% and the total Z2 content be 1.0 at% to 20 at%.

[0040] The thickness of the protective film 12 is preferably 1.0 nm to 4.0 nm, more preferably 2.0 nm to 3.5 nm, and even more preferably 2.5 nm to 3.0 nm. If the thickness of the protective film 12 is 1.0 nm or more, etching resistance is good. Also, if the thickness of the protective film 12 is 4.0 nm or less, reflectivity to EUV light is good.

[0041] The film density of the protective film 12 is preferably 10.0 g / cm³. ３ ~14.0 g / cm ３ The film density of the protective film 12 is 10.0 g / cm³. ３ If the above conditions are met, the etching resistance is good. Also, the film density of the protective film 12 is 14.0 g / cm³. ３The following conditions can suppress the decrease in reflectivity to EUV light: The protective film 12 contains 100 at% Rh and 11.0 g / cm³ of Rh. ３ ~12.0 g / cm ３ If the film density is such that it has an amorphous or microcrystalline structure, the film density of the protective film 12 is measured using the X-ray reflectivity method.

[0042] The upper surface of the protective film 12, i.e., the surface on which the absorption film 13 of the protective film 12 is formed, preferably has a root mean square roughness Rq of 0.20 nm or less, and more preferably 0.17 nm or less. If the root mean square roughness Rq is 0.20 nm or less, the absorption film 13 and the like can be formed smoothly on the protective film 12. Furthermore, scattering of EUV light can be suppressed, and the reflectance to EUV light can be improved. The root mean square roughness Rq is preferably 0.05 nm or more.

[0043] The absorption film 13 absorbs EUV light. In the reflective mask (film-covered substrate 4) shown in Figure 5, the absorption film 13 is a film on which an aperture pattern 13a is formed. The aperture pattern 13a is not formed in the manufacturing process of the reflective mask blank, but is formed in the manufacturing process of the reflective mask. Therefore, the absorption film 13 in the reflective mask blanks (film-covered substrates 2-3) shown in Figures 3-4 does not have an aperture pattern 13a. The absorption film 13 may not only absorb EUV light, but also be a phase-shifting film that shifts the phase of EUV light. In the reflective mask, the absorption film 13 shifts the phase of the second EUV light L2 with respect to the first EUV light L1 shown in Figure 6.

[0044] The first EUV light L1 is light that passes through the aperture pattern 13a without passing through the absorption film 13, is reflected by the multilayer reflective film 11, and passes through the aperture pattern 13a again without passing through the absorption film 13. The second EUV light L2 is light that is absorbed by the absorption film 13, passes through the absorption film 13, is reflected by the multilayer reflective film 11, and is absorbed by the absorption film 13 again, while passing through the absorption film 13.

[0045] The phase difference (≧0) between the first EUV light L1 and the second EUV light L2 is, for example, 170° to 250°. The phase of the first EUV light L1 may lead or lag behind the phase of the second EUV light L2. The absorption film 13 improves the contrast of the transferred image by utilizing the interference between the first EUV light L1 and the second EUV light L2. The transferred image is an image obtained by transferring the aperture pattern 13a of the absorption film 13 onto the target substrate.

[0046] In EUVL, a so-called projection effect (shadowing effect) occurs. The shadowing effect is caused by the fact that the incident angle θ of EUV light is not 0° (for example, 6°), resulting in a region near the side wall of the aperture pattern 13a where the EUV light is blocked by the side wall, causing a positional or dimensional shift in the transferred image. To reduce the shadowing effect, it is effective to lower the height of the side wall of the aperture pattern 13a, and thinning the absorption film 13 is also effective.

[0047] The thickness of the absorption film 13 is, for example, 60 nm or less, preferably 50 nm or less, in order to reduce the shadowing effect. The thickness of the absorption film 13 is preferably 20 nm or more, more preferably 30 nm or more, in order to ensure a phase difference between the first EUV light L1 and the second EUV light L2.

[0048] The absorption film 13 preferably contains at least one metal element selected from Ru, Ta, Cr, Nb, Pt, Ir, Re, W, Mn, and Au. Since these metal elements have relatively small refractive indices, the thickness of the phase-shift film can be reduced while ensuring a phase difference. Among the above metal elements, the absorption film 13 preferably contains Ru.

[0049] The absorption film 13 contains, in addition to the above-mentioned metal elements, at least one nonmetal element selected from O, N, C, and B. By adding a nonmetal element to the metal element, crystallization of the absorption film 13 can be suppressed, and the roughness of the sidewalls of the opening pattern 13a can be reduced. The absorption film 13 preferably contains oxygen as the nonmetal element, and more preferably contains oxygen and nitrogen.

[0050] The refractive index n of the absorption film 13 is preferably 0.930 or less, more preferably 0.920 or less, even more preferably 0.910 or less, and particularly preferably 0.90 or less. Furthermore, the refractive index n is preferably 0.885 or more. In this specification, the refractive index is the refractive index for light with a wavelength of 13.5 nm.

[0051] The extinction coefficient k of the absorption film 13 is preferably 0.015 or higher, and more preferably 0.020 or higher. Furthermore, the extinction coefficient k is preferably 0.065 or lower. In this specification, the extinction coefficient is the extinction coefficient for light with a wavelength of 13.5 nm.

[0052] The optical properties of the absorption film 13 (refractive index n and extinction coefficient k) are obtained from the database of the Center for X-Ray Optics, Lawrence Berkeley National Laboratory, or from values ​​calculated from the "incident angle dependence" of the reflectance, as described later.

[0053] The incident angle θ of EUV light, the reflectance R for EUV light, the refractive index n of the absorption film 13, and the extinction coefficient k of the absorption film 13 satisfy the following equation (1): R = |(sinθ - ((n+ik)² - cos2θ)¹ / ²) / (sinθ + ((n+ik)² - cos2θ)¹ / ²)| ... (1) Multiple combinations of incident angle θ and reflectance R are measured, and the refractive index n and extinction coefficient k are calculated using the least squares method so as to minimize the error between the multiple measurement data and equation (1).

[0054] Preferably, the absorption film 13 has an etching rate of 0 nm / min to 0.05 nm / min with sulfuric acid hydrogen peroxide. If the etching rate of the absorption film 13 with sulfuric acid hydrogen peroxide is 0.05 nm / min or less, damage to the absorption film 13 during cleaning can be suppressed.

[0055] The etching mask film 14 is formed on the opposite side of the protective film 12 from the absorption film 13, and is used to form an opening pattern 13a in the absorption film 13. A resist film (not shown) is provided on top of the etching mask film 14. In the manufacturing process of the reflective mask, first an opening pattern is formed in the resist film, then a second opening pattern is formed in the etching mask film 14 using the first opening pattern, and then a third opening pattern (opening pattern 13a) is formed in the absorption film 13 using the second opening pattern. The first, second, and third opening patterns have the same dimensions and shape in a plan view (viewed in the Z-axis direction). The etching mask film 14 enables thinning of the resist film.

[0056] The etching mask film 14 preferably contains at least one element selected from Al, Hf, Y, Cr, Nb, Ti, Mo, Ta, and Si. The etching mask film 14 may further contain at least one element selected from O, N, and B.

[0057] The thickness of the etching mask film 14 is preferably 2 nm to 30 nm, more preferably 2 nm to 25 nm, and even more preferably 2 nm to 10 nm.

[0058] <Step S102: Polishing and Removal of Protective Film> In step S102, at least a portion of the protective layer of the film-coated substrate is polished and removed. Any physical polishing method can be appropriately selected. For example, it may be free abrasive particles polished using a polishing pad and slurry, or fixed abrasive particles polished using a polishing pad containing a grinding wheel.

[0059] If the subsequent step S103 is not performed, the entire surface of the film-coated substrate is polished to completely polish and remove the protective film 12 and the multilayer reflective film 11. If the glass substrate 10 has been polished, the glass substrate 10 is given a final polish. In this way, a glass substrate for mask blanks can be recycled and manufactured.

[0060] If the subsequent step S103 is included, at least a portion of the protective film 12 on the film-coated substrate is polished to remove the protective film 12 to the extent that a portion of the multilayer reflective film 11 is exposed. The removal rate of the protective film 12 on the film-coated substrate after polishing is preferably 10% or more, and more preferably 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, and 80% or more. If the removal rate is 10% or more, in the subsequent step S103, the chemical solution can sufficiently penetrate the multilayer reflective film 11 and remove the multilayer reflective film 11 together with the remaining protective film 12.

[0061] If the subsequent step S103 is included, it is preferable that at least a portion of the multilayer reflective film 11 is present on the surface of the polished film-coated substrate. This protects the glass substrate 10 from polishing by the multilayer reflective film 11 covering the surface, making the glass substrate easier to reuse because the surface of the glass substrate is not polished. Polishing of the glass substrate surface for reuse can be omitted, and glass substrates for mask blanks that meet quality and specifications can be recycled and manufactured. It also has the advantage of improving recycling efficiency.

[0062] <Step S103: Chemical Treatment> In step S103, the polished substrate with the film is brought into contact with a chemical solution to remove the multilayer reflective film 11. The remaining protective film 12 and other films on the protective film 12 can also be peeled off and removed.

[0063] There are no particular limitations on the method of bringing the film-coated substrate into contact with the chemical solution, but examples include immersing the film-coated substrate in the chemical solution stored in a treatment tank (hereinafter referred to as the immersion method); and spraying the chemical solution onto the surface of the film-coated substrate. Of these methods, the immersion method is more preferable from the viewpoint of productivity and cost. In the case of the immersion method, the chemical solution can be easily reused. It is preferable to replace the chemical solution when its performance has deteriorated.

[0064] From a productivity standpoint, the processing time when bringing the film-coated substrate into contact with the chemical solution should be as short as possible. The processing time should be set to be the same as or longer than the time required to peel off the multilayer reflective film 11 from the film-coated substrate. If the film-coated substrate has a conductive film and the chemical solution can peel off both the multilayer reflective film 11 and the conductive film simultaneously, the processing time should be set to be the same as or longer than the longer of the time required to peel off the multilayer reflective film 11 and the time required to peel off the conductive film.

[0065] The temperature at which the film-coated substrate and the chemical solution come into contact is 20°C to 150°C, preferably 40°C to 100°C. If the temperature is 20°C or higher, the processing time can be significantly shortened. Also, if the temperature is 150°C or lower, there is less risk of the glass substrate 10 being excessively damaged by the chemical solution.

[0066] -Pharmaceuticals- The aforementioned pharmaceuticals include a solvent, a pH adjuster, and an oxidizing agent, and may further include optional additives such as specific metals and chelating agents as needed.

[0067] The solvent is water or an organic solvent, with water being preferred. Preferred waters include distilled water, deionized water, pure water, and ultrapure water.

[0068] The pH adjusting agent is an organic base or an inorganic base, with an inorganic base being preferred. If the pH adjusting agent is one of these bases, the conductive film can be removed from the film-coated substrate if it has a conductive film containing Ta. Furthermore, examples of inorganic bases include hydroxides of alkali metals or alkaline earth metals. Among these, sodium hydroxide (NaOH), potassium hydroxide (KOH), or rubidium hydroxide (RbOH) are preferred from the viewpoint of basicity and water solubility, NaOH or KOH are more preferred from the viewpoint of cost, and KOH is even more preferred because it can shorten the time required to remove the conductive film.

[0069] The concentration of the pH adjusting agent is adjusted to a range such that the pH of the chemical solution reaches a desired value. The pH of the chemical solution is 10 to 16, preferably 12 to 15, and more preferably 13 to 15. If the pH is 10 or higher, the time required to peel off the conductive film can be sufficiently shortened when the multilayer reflective film 11 contains Si and Mo. Also, if the pH is 16 or lower, the protective film can be peeled off in a sufficiently short time when the reflective mask blank has a protective film containing Ru.

[0070] The oxidizing agent is included at least for the purpose of stripping the multilayer reflective film 11. Therefore, the oxidizing agent has a redox potential higher than that of at least the components constituting the multilayer reflective film 11. For example, when the multilayer reflective film 11 contains Si and Mo, the standard electrode potential of the oxidizing agent is preferably 0.8 V to 2.0 V, and specifically, metaperiodic acid (HIO) ４ ), metaperiodate, orthoperiodate (H ５ IO ６ ), orthoperiodate, permanganate (HMnO ４ It is at least one selected from the group consisting of ), permanganate, and N-methylmorpholine N-oxide (abbreviated as NMO). These may be used individually or in combination of two or more. Examples of metaiodates include sodium periodate (NaIO). ４ ) are some examples.

[0071] Among the oxidizing agents mentioned above, metaperiodic acid, metaperiodic acid salt, orthoperiodic acid, orthoperiodic acid salt, permanganic acid, or permanganate salt are preferred because they can shorten the time required to peel off the multilayer reflective film 11. Metaperiodic acid, metaperiodic acid salt, orthoperiodic acid, orthoperiodic acid salt are more preferred because they show high activity even at pH 10 to 16 and their by-products are water-soluble. Permanganic acid or permanganate salt are also preferred because they can peel off the conductive film when the film-coated substrate has a conductive film containing Cr. Furthermore, when the chemical solution contains an oxidizing agent, the time required to peel off the conductive film when the film-coated substrate has a conductive film containing Ta can be shortened.

[0072] The concentration of the oxidizing agent is 0.1 ppm to 40% relative to the chemical solution, preferably 0.1% to 10%, and more preferably 0.1% to 2%. If the concentration of the oxidizing agent is 0.1 ppm or higher, the multilayer reflective film 11 can be peeled off. Furthermore, if the concentration of the oxidizing agent is 40% or lower, there is little risk of poorly soluble by-products precipitation.

[0073] The term "specific metals" refers to at least one selected from the group consisting of metals and their ions having a redox potential higher than that of Cr(VI). Specific examples of such metals include Ru or cerium (Ce). These may be used individually or in combination of two or more. When the chemical solution contains specific metals, the conductive film on the film-coated substrate can be removed if the substrate has a conductive film containing Cr. Ru ions or Ce ions may be added during the preparation of the chemical solution, or they may be eluted from the film on the removed film-coated substrate (e.g., a protective film containing Ru).

[0074] The following explains the mechanism by which conductive films containing Cr are stripped by specific metals, using Ru as an example. Ru or Ru ions added to the chemical solution are oxidized to Ru(VII) or Ru(VIII) by the oxidizing agent in the solution, resulting in RuO ４ － or RuO ４ This is the state in which the Ru oxide ions oxidize the Cr contained in the conductive film, resulting in water-soluble CrO ４ ２－ This process removes the conductive film containing Cr.

[0075] The concentration of the specific metal is 0.0001 equivalents to 10 equivalents relative to the oxidizing agent, preferably 0.001 equivalents to 1 equivalent, and more preferably 0.01 equivalents to 0.1 equivalents. If the concentration of the specific metal is 0.0001 equivalents or more, the peeling of the conductive film containing Cr proceeds sufficiently. Furthermore, if the concentration of the specific metal is 10 equivalents or less, substrate damage can be sufficiently suppressed.

[0076] The chelating agent is an aminocarboxylic acid-based chelating agent, a hydroxy acid-based chelating agent, or a phosphonic acid-based chelating agent. Examples of aminocarboxylic acid-based chelating agents include ethylenediaminetetraacetic acid (EDTA), triethylenetetraminehexaacetic acid (TTHA), nitrilotrismethylenephosphonic acid (NTPO), or N,N-bis(2-hydroxyethyl)glycine (Bicine). These may be used individually or in combination of two or more. An example of a hydroxy acid-based chelating agent is tartaric acid. Examples of phosphonic acid-based chelating agents include hydroxyethylidenediphosphonic acid (HEDP) or phosphonoacetic acid. When the chemical solution contains the above-mentioned chelating agents, the processing time can be shortened.

[0077] Among the chelating agents mentioned above, EDTA or phosphonoacetic acid are more preferred because they shorten the processing time, and TTHA is more preferred because it causes less damage to the glass substrate 10.

[0078] The concentration of the chelating agent is 0.01% to 10% relative to the chemical solution, preferably 0.1% to 5%, and more preferably 0.5% to 2%. If the concentration of the chelating agent is 0.01% or higher, the processing time can be significantly shortened. Furthermore, if the concentration of the chelating agent is 10% or lower, there is little risk of precipitation of poorly soluble by-products.

[0079] A chemical solution is prepared by mixing a solvent, a pH adjuster, an oxidizing agent, and any additional additives as needed. At this time, each component is selected to be soluble in the solvent and to prevent the precipitation of poorly soluble by-products.

[0080] <Step S104: Cleaning> In step S104, the chemically treated glass substrate 10 is cleaned to remove any remaining film or chemical solution. Examples of cleaning solutions used for cleaning include water and solvents. Distilled water, deionized water, pure water, and ultrapure water are preferred as the water.

[0081] (Method for manufacturing a glass substrate for mask blanks) The method for manufacturing a glass substrate for mask blanks according to the present disclosure includes the method for regenerating a film-coated substrate according to the present disclosure as described above, and by regenerating the glass substrate 10, a glass substrate suitable for use as a mask blank can be manufactured. If the flatness of the glass substrate 10 from which all the films have been removed is not sufficient, local polishing or finish polishing may be performed to achieve the desired flatness, after which a film may be formed.

[0082] (Method for Manufacturing Reflective Mask Blanks) The method for manufacturing reflective mask blanks according to this disclosure is not particularly limited, except that it uses a glass substrate regenerated by the method for regenerating a film-coated substrate or the method for manufacturing a glass substrate for mask blanks according to this disclosure described above. A known manufacturing method can be appropriately selected depending on the purpose. Referring to Figure 7, a method for manufacturing a reflective mask blank according to one embodiment will be described. The method for manufacturing a reflective mask blank is a method for manufacturing a reflective mask blank shown in Figure 4, and for example, has steps S201 to S205 shown in Figure 7. In step S201, a regenerated glass substrate 10 is prepared. In step S202, a conductive film is formed. In step S203, a multilayer reflective film 11 is formed on the first main surface 10a of the glass substrate 10. In step S204, a protective film 12 is formed on the multilayer reflective film 11. In step S205, an absorption film 13 is formed on the protective film 12. In step S206, an etching mask film 14 is formed on the absorption film 13.

[0083] The method for manufacturing a reflective mask blank only needs to include at least steps S201 and S203 to S205, and may also include the formation of a conductive film in step S202, and any of these can be appropriately selected depending on the purpose. The method for manufacturing a reflective mask blank may further include a step of forming a functional film, which is not shown in Figure 7.

[0084] Furthermore, if defects that cannot be removed by cleaning occur again when a reflective mask blank is manufactured using the regenerated glass substrate 10 as described above, the glass substrate may be repeatedly regenerated using the film-coated substrate regeneration method until such defects no longer occur.

[0085] <Step S201: Preparation of the regenerated substrate> In step S201, the glass substrate is regenerated by the method for regenerating a film-coated substrate or the method for manufacturing a glass substrate for a mask blank described above, and this is prepared as a new glass substrate and can be used.

[0086] <Step S202: Formation of conductive film> In step S202, a conductive film (not shown) is formed on the second main surface 10b of the glass substrate 10. The conductive film is preferably formed of a metal nitride or metal boride containing one or more elements selected from the group consisting of chromium (Cr), tantalum (Ta), titanium (Ti), zirconium (Zr), and niobium (Nb). Specific examples of such conductive films include CrN film, TaN film, TaB film, CrTaN film, TiN film, and ZrN film.

[0087] <Step S203: Formation of Multilayer Reflective Film> In step S203, a multilayer reflective film 11 is formed. The multilayer reflective film 11 can be appropriately selected from the items described for the film-covered substrate. The film deposition method for each layer constituting the multilayer reflective film 11 can be, for example, DC sputtering, magnetron sputtering, or ion beam sputtering. When forming a Mo / Si multilayer reflective film using ion beam sputtering, an example of the film deposition conditions for the Mo layer and the Si layer is as follows.

[0088] - Si layer deposition conditions - Target: Si target Sputtering gas: Ar gas Gas pressure: 0.013 Pa to 0.027 Pa Ion acceleration voltage: 300 V to 1500 V Deposition rate: 0.030 nm / sec to 0.300 nm / sec Si layer thickness: 4.5 ± 0.1 nm

[0089] - Mo layer deposition conditions - Target: Mo target sputtering gas: Ar gas Gas pressure: 0.013 Pa to 0.027 Pa Ion acceleration voltage: 300 V to 1500 V Deposition rate: 0.030 nm / sec to 0.300 nm / sec Mo layer thickness: 2.3 ± 0.1 nm

[0090] - Repeating units of the Si layer and Mo layer - Number of repeating units: 30 to 60 (preferably 40 to 50).

[0091] The uppermost layer of the multilayer reflective film 11 is formed, for example, by nitriding the Si layer after forming the Si layer. The Si layer is nitrided, for example, by exposure to a plasma-activated nitrogen-containing gas. Hereinafter, nitriding using a plasma-activated nitrogen-containing gas will also be referred to as radical nitriding. After radical nitriding, the Si layer may be oxidized by exposure to an atmospheric environment. Hereinafter, oxidation using an atmospheric environment will also be referred to as atmospheric oxidation. When radical nitriding is performed after the formation of the Si layer, the uppermost layer of the multilayer reflective film 11 refers to the radically nitrided layer.

[0092] The uppermost layer of the multilayer reflective film 11 may be formed by reactive sputtering. In reactive sputtering, the elemental ratio of N to Si (N / Si) in the uppermost layer is determined by the N in the sputtering gas. ２ It can be controlled by the gas content. In addition, in the reactive sputtering method, the elemental ratio of O to Si (O / Si) in the uppermost layer is controlled by the O in the sputtering gas. ２ It can be controlled by adjusting the gas content.

[0093] The multilayer reflective film 11 may have an uppermost layer that is closest to the protective film 12 and contains Si and N. The uppermost layer has an elemental ratio of N to Si (N / Si) greater than 0.00 and less than 1.50 (0.00 < (N / Si) < 1.50), and an elemental ratio of O to Si (O / Si) greater than or equal to 0.00 and less than 0.25 (0.00 ≤ (O / Si) < 0.25). In this specification, elemental ratio refers to molar ratio.

[0094] By keeping the elemental ratio (N / Si, O / Si) in the uppermost layer of the multilayer reflective film 11 within the above range, mixing of the protective film 12 and the multilayer reflective film 11, surface roughness of the protective film 12, and elemental diffusion to the surface of the protective film 12 can be suppressed.

[0095] Here, the mixing of the protective film 12 and the multilayer reflective film 11 is a phenomenon that occurs when the protective film 12 is formed. On the other hand, elemental diffusion to the surface of the protective film 12 is a phenomenon in which easily oxidized elements (for example, Si contained in the uppermost layer) diffuse to the surface of the protective film 12 when the protective film 12 is exposed to the oxygen-based gas when an opening pattern 13a is formed in the absorption film 13 using an oxygen-based gas.

[0096] The elemental ratio (N / Si) in the uppermost layer of the multilayer reflective film 11 is greater than 0.00 and less than 1.50. The larger the elemental ratio (N / Si), the more the mixing of the protective film 12 and the multilayer reflective film 11, and the more the diffusion of elements to the surface of the protective film 12 can be suppressed. Furthermore, an elemental ratio (N / Si) of less than 1.50 can suppress the decrease in reflectivity to EUV light. The elemental ratio (N / Si) is preferably greater than 0.10 and less than 0.50, and more preferably greater than 0.10 and less than 0.30.

[0097] The elemental ratio (O / Si) in the uppermost layer of the multilayer reflective film 11 is 0.00 or more and less than 0.25. The larger the elemental ratio (O / Si), the more the mixing of the protective film 12 and the multilayer reflective film 11, and the more the diffusion of elements to the surface of the protective film 12 can be suppressed. Also, by having an elemental ratio (O / Si) of less than 0.25, surface roughness of the protective film 12 can be suppressed. The elemental ratio (O / Si) is preferably 0.00 or more and less than 0.10, and more preferably 0.

[0098] <Step S204: Formation of protective film> In step S204, a protective film 12 is formed. The protective film 12 can be appropriately selected from the items described in the section on the film-coated substrate.

[0099] The method for forming the protective film 12 is, for example, DC sputtering, magnetron sputtering, or ion beam sputtering. When forming the Rh film using DC sputtering, an example of the film formation conditions is as follows.

[0100] - Rh film deposition conditions - Target: Rh target Sputtering gas: Ar gas Gas pressure: 1.0 × 10 －２ Pa ~ 1.0 × 10 ０ Power density of the Pa target: 1.0 W / cm² ２ ~8.5 W / cm ２ Deposition rate: 0.020 nm / sec to 1.000 nm / sec. Rh film thickness: 1.0 nm to 4.0 nm.

[0101] Furthermore, when forming a Rh film, N is used as the sputtering gas. ２ Gas or Ar gas and N ２ A mixed gas may be used. N in sputtering gas ２Gas volume ratio (N ２ / (Ar+N ２ )) is between 0.05 and 1.0.

[0102] When forming a RhO film using the DC sputtering method, an example of the film formation conditions is as follows:

[0103] -Conditions for depositing RhO films- Target: Rh Target sputtering gas: O ２ Gas or Ar gas and O ２ O in mixed gas sputtering gas ２ Gas volume ratio (O ２ / (Ar+O ２ ): 0.05 to 1.0 Gas pressure: 1.0 x 10 －２ Pa ~ 1.0 × 10 ０ Power density of the Pa target: 1.0 W / cm² ２ ~8.5 W / cm ２ Deposition rate: 0.020 nm / sec to 1.000 nm / sec. RhO film thickness: 1.0 nm to 4.0 nm.

[0104] When forming a RhRu film using the DC sputtering method, an example of the film formation conditions is as follows:

[0105] -Conditions for depositing RhRu films- Target: Rh target and Ru target (or RhRu target) Sputtering gas: Ar gas Gas pressure: 1.0 × 10 －２ Pa ~ 1.0 × 10 ０ Power density of the Pa target: 1.0 W / cm² ２ ~8.5 W / cm ２ Deposition rate: 0.020 nm / sec to 1.000 nm / sec. Film thickness of Rh film and Ru film (or RhRu film): 1.0 nm to 4.0 nm.

[0106] <Step S205: Formation of Absorption Film> In step S205, an absorption film 13 is formed. The absorption film 13 can be appropriately selected from the items described in the section on the film-coated substrate.

[0107] The method for forming the absorption film 13 is, for example, DC sputtering, magnetron sputtering, ion beam sputtering, or reactive sputtering. In reactive sputtering, O in the sputtering gas ２ The oxygen content of the absorption film 13 can be controlled by the gas content. In addition, reactive sputtering uses N in the sputtering gas. ２ The nitrogen content of the absorption membrane 13 can be controlled by the gas content.

[0108] When forming a RuN film as an absorption film 13 using the reactive sputtering method, an example of the film formation conditions is as follows.

[0109] -Conditions for depositing RuN films- Target: Ru target sputtering gas: Ar gas and N ２ N in mixed gas sputter gas ２ Gas volume ratio (N ２ / (Ar+N ２ )): 0.3-0.7 Gas pressure: 0.05 Pa-0.40 Pa Target power density: 1.0 W / cm² ２ ~8.5 W / cm ２ Deposition rate: 0.010 nm / sec to 0.030 nm / sec. Film thickness: 20 nm to 60 nm.

[0110] <Step S206: Formation of etching mask film> In step S206, an etching mask film 14 is formed. The etching mask film 14 can be appropriately selected from the items described in the section on the film-covered substrate.

[0111] The method for forming the etching mask film 14 is, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0112] (Method for Manufacturing a Reflective Mask) Next, with reference to Figure 8, a method for manufacturing a reflective mask according to one embodiment will be described. The method for manufacturing a reflective mask is a method for manufacturing the reflective mask (film-coated substrate 4) shown in Figure 5, and includes steps S301 to S304 shown in Figure 8. Note that the method for manufacturing a reflective mask only needs to include steps S301 and S303.

[0113] <Step S301: Preparation of reflective mask blank> In step S301, a reflective mask blank is prepared. A reflective mask blank can be manufactured and used by the method for manufacturing a reflective mask blank described above in this disclosure.

[0114] <Step S302: Processing of Etching Mask Film> In step S302, the etching mask film 14 is processed. A resist film (not shown) is provided on the etching mask film 14. First, a first opening pattern is formed on the resist film, and then a second opening pattern is formed on the etching mask film 14 using the first opening pattern.

[0115] <Step S303: Etching of the absorption film> In step S303, a third opening pattern 13a is formed on the absorption film 13 using the second opening pattern. In step S303, the absorption film 13 is etched using an etching gas.

[0116] <Step S304: Removal of etching mask film> In step S304, the resist film and the etching mask film 14 are removed. For removing the resist film, for example, sulfuric acid peroxide is used. For removing the etching mask film 14, for example, an etching gas is used. The etching gas used in step S304 (removal of etching mask film 14) may be the same type of etching gas used in step S303 (etching of absorption film 13).

[0117] The experimental data is described below. Examples 1 and 4 are examples, and examples 2 and 3 are comparative examples.

[0118] (Example 1: Method for regenerating a film-coated substrate) <Preparation of film-coated substrate> Following the procedure below, a film-coated substrate 1 was prepared as the target of the film-coated substrate regeneration method (work-in-progress of a reflective mask blank), having a glass substrate 10, a multilayer reflective film 11, and a protective film 12 in that order, as shown in Figure 2.

[0119] The glass substrate 10 is SiO ２ -TiO ２A glass substrate (6 inches (152 mm) square, 6.3 mm thick) was prepared. This glass substrate has a coefficient of thermal expansion of 0.02 × 10⁻¹⁶ at 20°C. －７ The temperature is / °C, the Young's modulus is 67 GPa, the Poisson's ratio is 0.17, and the specific stiffness is 3.07 × 10⁻⁶. ７ I understand ２ / s ２ The quality assurance area of ​​the first main surface 10a of the glass substrate 10 had a root mean square roughness Rq of 0.15 nm or less and a flatness of 100 nm or less achieved by polishing.

[0120] A conductive film, a CrN film with a thickness of 360 nm, was deposited on the second main surface 10b of the glass substrate 10 using the magnetron sputtering method. The sheet resistance of the CrN film was 100 Ω / □.

[0121] A Mo / Si multilayer reflective film was formed as the multilayer reflective film 11. The Mo / Si multilayer reflective film was formed by repeatedly depositing a Si layer (thickness 4 nm) and a Mo layer (thickness 3 nm) 40 times using the ion beam sputtering method. The total thickness of the Mo / Si multilayer reflective film was 280 nm ((4 nm + 3 nm) × 40).

[0122] A protective film (thickness: 2.5 nm) consisting of a 1.0 nm thick Ru film and a 1.5 nm thick Rh film on the Ru film was formed on the multilayer reflective film 11 using a magnetron sputtering method under the Rh film and Ru film formation conditions described above.

[0123] <Polishing and Removal of Protective Film> The film-coated substrate obtained by the above procedure was subjected to free abrasive (physical polishing) using a polishing pad and slurry under the following conditions. -Free Abrasive Conditions- • Polishing amount: 67 nm • Polishing equipment: IRP-200 (manufactured by ZEEKO) • Polishing pad: Purelex QH-2014F (manufactured by Teijin Cordley Co., Ltd.) • Slurry: SHOROX NZ02(T) (manufactured by Resonac Co., Ltd.) • Polishing conditions: Constant speed machining

[0124] The removal rates of rhodium (Rh) and ruthenium (Ru) were evaluated using X-ray fluorescence analysis on physically polished substrates. Figure 9 is a diagram illustrating the measurement area of ​​Rh X-ray intensity on a polished film-coated substrate (length: 152 mm, width: 152 mm) according to Example 1. Specifically, as shown in Figure 9, when the coordinates of the center of the film-coated substrate viewed from above are set to (X axis, Y axis) = (0 mm, 0 mm), the X-ray intensity of Rh was measured in a 30 mm diameter area centered on each of five points: the center (0 mm, 0 mm), and four points on the periphery (-38 mm, 38 mm), (38 mm, 38 mm), (-38 mm, -38 mm), and (38 mm, -38 mm). The removal rate was calculated as the ratio (%) of the X-ray intensity of Rh after polishing to the X-ray intensity of Rh before polishing. The removal rate of Ru was calculated in the same manner. As a result, the removal rate of Rh from the protective film 12 before polishing was 83%, and the removal rate of Ru was 54%.

[0125] <Chemical Treatment> For the film-coated substrate after polishing, potassium hydroxide (KOH) is used as a pH adjuster, and 2% by mass of sodium periodate (NaIO) is used as an oxidizing agent. ４ An aqueous solution (pH 14) containing ) was used as the chemical solution, and the treatment was carried out by immersion at 65°C for 40 minutes.

[0126] <Cleaning and Evaluation> The substrate was cleaned with pure water and dried. The refurbished glass substrate was visually inspected under fluorescent light. No residual film was observed. Furthermore, when Rh and Ru were analyzed using X-ray fluorescence analysis, neither Rh peak nor Ru peak was detected.

[0127] (Example 2) The film-coated substrate regeneration method of Example 2 was carried out in the same manner as in Example 1, except that a film-coated substrate having a protective film containing Rh as in Example 1 was used, and the chemical treatment was performed without polishing off the protective film, and the method was evaluated.

[0128] As a result, it was found that in the recycled glass substrate of Example 2, a protective film containing Rh remained and could not be removed by chemical treatment alone.

[0129] (Example 3) <Preparation of film-coated substrate> In the same manner as in Example 1, a multilayer reflective film 11 was formed on a glass substrate 10, and then a protective film made of Ru (thickness: 2.5 nm) was formed on the multilayer reflective film 11 using the magnetron sputtering method to prepare a film-coated substrate having a protective film that does not contain Rh but contains Ru.

[0130] In Example 2, the film-coated substrate regeneration method of Example 3 was carried out and evaluated in the same manner as in Example 2, except that a film-coated substrate having a protective film containing Ru but not Rh was used instead of the film-coated substrate having a protective film containing Rh in Example 1.

[0131] As a result, no residual protective film containing Ru was observed in the recycled glass substrate of Example 3.

[0132] (Example 4: Method for manufacturing a reflective mask blank) Using a glass substrate recycled from Example 1, a multilayer reflective film 11 and a protective film 12 were formed on the glass substrate 10 in the same manner as in Example 1. Next, a RuN film (thickness 35 nm) was formed as an absorption film 13 using a reactive sputtering method. A reflective mask blank was then manufactured. As a result, no surface defects or defects in the film were observed, indicating that a reflective mask blank of good quality was manufactured. Therefore, it was confirmed that a glass substrate suitable for mask blank applications (glass substrate for mask blanks) can be manufactured using the film-coated substrate recycling method of Example 1.

[0133] The reflective mask blank, reflective mask, method for manufacturing a reflective mask blank, and method for manufacturing a reflective mask have been described above, but this disclosure is not limited to the embodiments described above. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims, and these also naturally fall within the technical scope of this disclosure.

[0134] The following appendices are disclosed with respect to the above embodiments, etc. [Appendix 1] A method for regenerating a film-covered substrate, comprising a glass substrate, a multilayer reflective film that reflects EUV light, and a protective film that protects the multilayer reflective film, the method comprising polishing and removing at least a portion of the protective film. [Appendix 2] The method for regenerating a film-covered substrate according to Appendix 1, wherein the protective film contains rhodium. [Appendix 3] The method for regenerating a film-covered substrate according to Appendix 1 or 2, wherein the polishing is carried out using at least one of free abrasive grains and fixed abrasive grains. [Appendix 4] The method for regenerating a film-covered substrate according to any one of Appendix 1 to 3, further comprising contacting the film-covered substrate after polishing with a chemical solution to remove the multilayer reflective film. [Appendix 5] The method for regenerating a film-covered substrate according to Appendix 4, wherein the removal rate of the protective film on the film-covered substrate after polishing is 10% or more. [Note 6] A method for regenerating a film-coated substrate according to Note 4 or 5, wherein the surface of the film-coated substrate after polishing has at least a portion of the multilayer reflective film. [Note 7] A method for regenerating a film-coated substrate according to any one of Notes 4 to 6, wherein the multilayer reflective film contains silicon and molybdenum, and the chemical solution contains a pH adjuster and at least one oxidizing agent selected from the group consisting of metaperiodic acid, metaperiodate salt, orthoperiodic acid, orthoperiodate salt, permanganic acid, permanganate salt, and N-methylmorpholine N-oxide. [Note 8] A method for manufacturing a glass substrate for mask blanks, comprising the method for regenerating a film-coated substrate according to any one of Notes 1 to 7. [Note 9] A method for manufacturing a reflective mask blank, comprising: forming a multilayer reflective film that reflects EUV light on one side of the glass substrate regenerated by the method for regenerating a film-coated substrate described in any one of Notes 1 to 7; forming a protective film on the multilayer reflective film to protect the multilayer reflective film; and forming an absorbing film that absorbs EUV light on the protective film. [Note 10] The method for manufacturing a reflective mask blank according to Note 9, further comprising forming a conductive film on the side of the glass substrate opposite to the side on which the absorbing film is formed.

[0135] According to the present invention, when regenerating a film-coated substrate in which defects may occur during a precise film deposition process, it is possible to remove protective films that are difficult to remove by chemical treatment, and to provide a method for regenerating a film-coated substrate that can regenerate a glass substrate.

[0136] 1, 2, 3, 4 Film-coated substrate 10 Glass substrate 11 Multilayer reflective film 12 Protective film 13 Absorbing film

Claims

1. A method for regenerating a film-coated substrate, comprising a glass substrate, a multilayer reflective film that reflects EUV light, and a protective film that protects the multilayer reflective film, the method comprising polishing and removing at least a portion of the protective film.

2. The method for regenerating a film-coated substrate according to claim 1, wherein the protective film contains rhodium.

3. The method for regenerating a film-coated substrate according to claim 1, wherein the polishing is carried out using at least one of free abrasive grains and fixed abrasive grains.

4. The method for regenerating a film-coated substrate according to claim 1, further comprising contacting the film-coated substrate after polishing with a chemical solution to remove the multilayer reflective film.

5. The method for regenerating a film-coated substrate according to claim 4, wherein the removal rate of the protective film on the film-coated substrate after polishing is 10% or more.

6. The method for regenerating a film-coated substrate according to claim 4, wherein at least a portion of the multilayer reflective film is present on the surface of the film-coated substrate after polishing.

7. The method for regenerating a film-coated substrate according to claim 4, wherein the multilayer reflective film contains silicon and molybdenum, and the chemical solution contains a pH adjuster and at least one oxidizing agent selected from the group consisting of metaperiodic acid, metaperiodate salt, orthoperiodic acid, orthoperiodate salt, permanganic acid, permanganate salt, and N-methylmorpholine N-oxide.

8. A method for manufacturing a glass substrate for mask blanks, comprising a method for regenerating a film-coated substrate according to any one of claims 1 to 7.

9. A method for manufacturing a reflective mask blank, comprising: forming a multilayer reflective film that reflects EUV light on one surface of a glass substrate regenerated by a method for regenerating a film-coated substrate according to any one of claims 1 to 7; forming a protective film on the multilayer reflective film to protect the multilayer reflective film; and forming an absorbing film that absorbs EUV light on the protective film.

10. The method for manufacturing a reflective mask blank according to claim 9, further comprising forming a conductive film on the surface of the glass substrate opposite to the surface on which the absorption film is formed.

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