Chemical solution, method for recycling film-coated substrate, method for manufacturing film-coated substrate, and method for manufacturing reflective mask blank

Abstract

A chemical agent according to one embodiment of the present invention contains a pH adjusting agent and at least one oxidant that is selected from the group consisting of metaperiodic acid, a metaperiodate salt, orthoperiodic acid, an orthoperiodate salt, permanganic acid, a permanganate salt and N-methylmorpholine N-oxide.

Description

[Technical Field]

[0001] The present invention relates to a chemical solution, a method for recycling a film-coated substrate, a method for manufacturing a film-coated substrate, and a method for manufacturing a reflective mask blank. [Background technology]

[0002] In recent years, with the miniaturization of semiconductor devices, EUV lithography (EUVL), an exposure technology using extreme ultraviolet (EUV), has been developed. EUV includes soft X-rays and vacuum ultraviolet light, and specifically refers to light with a wavelength of approximately 0.2 nm to 100 nm. At present, EUV with a wavelength of approximately 13.5 nm is mainly being considered.

[0003] In EUVL, the aperture pattern of a reflective mask is transferred to a semiconductor substrate. A reflective mask is obtained by forming an aperture pattern in the absorbing film of a reflective mask blank. A reflective mask blank includes a substrate such as a glass substrate, a multilayer reflective film formed on the substrate, and an absorbing film formed on the multilayer reflective film.

[0004] However, if there are irregularities near the aperture pattern in a reflective mask, the positional accuracy and contrast of the transferred pattern will be deteriorated, which will be a problem. The irregularities are caused by defects such as scratches and foreign particles.

[0005] Therefore, to ensure that no irregularities exist near the opening pattern, the film-coated substrate is inspected for surface defects and defects in the film for each process. If an unacceptable size defect is discovered as a result of the inspection, the defect is removed by cleaning or the like. On the other hand, if there is a defect that cannot be removed by cleaning or the like, at least the multilayer reflective film is peeled off and the substrate is recycled, or the substrate is discarded as a defective product.

[0006] Patent Document 1 discloses a method for recycling a multilayer film-coated substrate, which has a multilayer film having a reflective multilayer film formed on the substrate. In this recycling method, the multilayer film-coated substrate is brought into contact with a chemical solution consisting of an aqueous solution containing hydrogen peroxide and at least one selected from sodium hydroxide, potassium hydroxide, and ammonia, thereby peeling the multilayer film from the substrate and recycling the substrate. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2017-181733 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the method described in Patent Document 1 has the problem that the processing time required to peel the film from the film-coated substrate is long, and the damage to the peeled surface of the substrate is still significant.

[0009] An object of one aspect of the present invention is to shorten the processing time required to peel a film from a film-coated substrate, and to suppress damage to the peeled surface of the substrate. [Means for solving the problem]

[0010] The present invention includes the following [1] to

[12] .

[0011] [1] A chemical solution used to peel off at least a multilayer reflective film containing silicon and molybdenum from a glass substrate of a film-coated substrate having a multilayer reflective film formed on one surface of the glass substrate, the chemical solution comprising a pH adjuster and at least one oxidizing agent selected from the group consisting of metaperiodic acid, metaperiodate, orthoperiodic acid, orthoperiodate, permanganic acid, permanganate, and N-methylmorpholine N-oxide.

[0012] [2] The drug solution according to [1], having a pH of 10 or more and 16 or less.

[0013] [3] The chemical solution according to [1], wherein the pH adjuster is sodium hydroxide or potassium hydroxide.

[0014] [4] The chemical solution according to [1], wherein the oxidizing agent is metaperiodic acid, metaperiodate, orthoperiodic acid, or orthoperiodate.

[0015] [5] The chemical solution according to [1], wherein the oxidizing agent is permanganic acid or a permanganate.

[0016] [6] The chemical solution according to [1], further comprising at least one selected from the group consisting of metals and ions thereof having a redox potential higher than that of chromium (VI), in an amount of 0.0001 to 10 molar equivalents relative to the oxidizing agent.

[0017] [7] The chemical solution according to [1], further comprising an aminocarboxylic acid chelating agent, a hydroxy acid chelating agent, or a phosphonic acid chelating agent as a chelating agent.

[0018] [8] A method for regenerating a film-coated substrate, comprising contacting a film-coated substrate having a multilayer reflective film containing silicon and molybdenum formed on one surface of a glass substrate with a chemical solution containing a pH adjuster and at least one oxidizing agent selected from the group consisting of metaperiodic acid, metaperiodate, orthoperiodic acid, orthoperiodate, permanganic acid, permanganate, and N-methylmorpholine N-oxide, thereby peeling off at least the multilayer reflective film from the glass substrate and regenerating the surface of the glass substrate on which the multilayer reflective film was formed.

[0019] [9] The method for recycling a film-coated substrate according to [8], wherein the film-coated substrate has a protective film containing ruthenium on the multilayer reflective film.

[0020]

[10] The method for recycling a film-coated substrate described in [8], wherein the film-coated substrate has an absorbing film on the multilayer reflective film containing at least one selected from the group consisting of ruthenium, tantalum, niobium, and boron.

[0021]

[11] The method for recycling a film-coated substrate according to [8], wherein the film-coated substrate has a conductive film containing chromium or tantalum on the surface opposite to the surface on which the multilayer reflective film is formed.

[0022]

[12] A method for producing a film-coated substrate, comprising forming a multilayer reflective film containing at least silicon and molybdenum on one surface of the glass substrate recycled by the method for recycling a film-coated substrate described in any one of [8] to

[11] .

[0023]

[13] A method for producing a reflective mask blank, comprising: forming a multilayer reflective film containing silicon and molybdenum on one surface of the glass substrate recycled by the method for recycling a film-coated substrate according to any one of [8] to

[11] ; forming a protective film containing ruthenium or rhodium on the multilayer reflective film; forming an absorbing film containing at least one selected from the group consisting of ruthenium, tantalum, chromium, iridium, boron, niobium, rhenium, and palladium on the protective film; and forming a conductive film containing at least one selected from the group consisting of chromium, tantalum, and boron on the surface of the glass substrate opposite to the surface on which the reflective multilayer film is formed. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a flowchart showing a method for manufacturing a reflective mask blank according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing an example of a substrate. [Figure 3] FIG. 3 is a plan view of the substrate of FIG. [Figure 4] FIG. 4 is a cross-sectional view showing an example of a reflective mask blank. [Figure 5]FIG. 5 is a cross-sectional view showing an example of a reflective mask. [Figure 6] FIG. 6 shows the results of a reference experiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as the present embodiment) will be described with reference to the drawings. In the drawings, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Note that the dimensional ratios of the drawings are not limited to those shown. Furthermore, in the specification, the symbol "to" indicating a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits. The lower and upper limits include the range of rounding. Furthermore, "%", "ppm", and "ppb" represent mass fractions, and "equivalent" represents molar equivalents.

[0026] (Method of manufacturing a reflective mask blank) As shown in Fig. 1, the method for manufacturing a reflective mask blank has steps S1 to S7. To manufacture the reflective mask blank, for example, a substrate 2 shown in Figs. 2 and 3 is used. The substrate 2 includes a first main surface 21 and a second main surface 22 facing opposite to the first main surface 21. The first main surface 21 is rectangular. In this specification, a rectangular shape includes a shape with chamfered corners. The rectangle also includes a square. The second main surface 22 faces opposite to the first main surface 21. Like the first main surface 21, the second main surface 22 is also rectangular.

[0027] The substrate 2 also includes four end surfaces 23, four first chamfered surfaces 24, and four second chamfered surfaces 25. The end surfaces 23 are perpendicular to the first main surface 21 and the second main surface 22. The first chamfered surfaces 24 are formed at the boundaries between the first main surface 21 and the end surfaces 23. The second chamfered surfaces 25 are formed at the boundaries between the second main surface 22 and the end surfaces 23. In this embodiment, the first chamfered surfaces 24 and the second chamfered surfaces 25 are so-called C-chamfered surfaces, but may also be R-chamfered surfaces.

[0028] The substrate 2 is, for example, a glass substrate. The glass of the substrate 2 is preferably quartz glass containing titanium oxide (TiO2). Quartz glass has a smaller linear expansion coefficient and less dimensional change due to temperature changes than common soda-lime glass. The quartz glass may contain 80% to 95% silicon oxide (SiO2) and 4% to 17% TiO2. When the TiO2 content is 4% to 17%, the linear expansion coefficient is approximately zero near room temperature, and there is almost no dimensional change near room temperature. The quartz glass may contain a third component or impurities other than SiO2 and TiO2. As such quartz glass, for example, Corning's ULE (registered trademark) 7973 series may be used.

[0029] The size of the substrate 2 in plan view is, for example, 152 mm in length and 152 mm in width. The length and width may be greater than or equal to 152 mm.

[0030] The substrate 2 has a central region 27 and a peripheral region 28 on the first main surface 21. The central region 27 is a square region 142 mm long and 142 mm wide, excluding the rectangular frame-shaped peripheral region 28 surrounding the central region 27, and is an area processed to a desired flatness in steps S1 to S4, and is a quality assurance area. The vertical and horizontal dimensions of the quality assurance area may be 142 mm or more. The four sides of the central region 27 are parallel to the four end faces 23. The center of the central region 27 coincides with the center of the first main surface 21.

[0031] Although not shown, the second main surface 22 of the substrate 2 also has a central region and a peripheral region, similar to the first main surface 21. The central region of the second main surface 22, like the central region of the first main surface 21, is a square region measuring 142 mm in length and 142 mm in width, and is a region that is processed to a desired flatness by steps S1 to S4 of Fig. 1 and is a quality assurance region. The vertical and horizontal dimensions of the quality assurance region may be 142 mm or more.

[0032] First, in step S1, the first main surface 21 and the second main surface 22 of the substrate 2 are polished. In this embodiment, the first main surface 21 and the second main surface 22 are polished simultaneously using a double-sided polisher (not shown), but they may also be polished sequentially using a single-sided polisher (not shown). In step S1, the substrate 2 is polished while a polishing slurry is supplied between the polishing pad and the substrate 2.

[0033] Examples of polishing pads that can be used include urethane-based polishing pads, nonwoven fabric-based polishing pads, and suede-based polishing pads. The polishing slurry contains an abrasive and a dispersion medium. The abrasive is, for example, cerium oxide particles. The dispersion medium is, for example, water or an organic solvent. The first main surface 21 and the second main surface 22 may be polished multiple times using abrasives of different materials or particle sizes.

[0034] The abrasive used in step S1 is not limited to cerium oxide particles, but may be, for example, silicon oxide particles, aluminum oxide particles, zirconium oxide particles, titanium oxide particles, diamond particles, silicon carbide particles, or the like.

[0035] Next, in step S2, the surface shapes of the first main surface 21 and the second main surface 22 of the substrate 2 are measured. To measure the surface shape, for example, a non-contact measuring device such as a laser interference type is used to prevent the surface from being damaged. The measuring device measures the surface shape of the central region 27 of the first main surface 21 and the central region of the second main surface 22.

[0036] Next, in step S3, the measurement results of step S2 are referenced, and the first main surface 21 and the second main surface 22 of the substrate 2 are locally processed to improve flatness. The first main surface 21 and the second main surface 22 are locally processed in that order. The order is not particularly limited and does not matter which comes first. The local processing method is, for example, a GCIB (Gas Cluster Ion Beam) method or a PCVM (Plasma Chemical Vaporization Machining) method. The local processing method may also be a polishing method using a magnetic fluid, a polishing method using a rotary polishing tool, or a catalyst-based etching method. Note that if the flatness after step S1 is sufficient, the local processing of step S3 may not be necessary.

[0037] Next, in step S4, the first main surface 21 and the second main surface 22 of the substrate 2 are subjected to finish polishing. In this embodiment, the first main surface 21 and the second main surface 22 are polished simultaneously using a double-sided polisher (not shown), but they may also be polished sequentially using a single-sided polisher (not shown). In step S4, the substrate 2 is polished while a polishing slurry is supplied between the polishing pad and the substrate 2. The polishing slurry contains an abrasive. The abrasive is, for example, colloidal silica particles.

[0038] Next, in step S5, a conductive film 5 shown in FIG. 4 is formed in the central region 27 of the first main surface 21 of the substrate 2. The conductive film 5 is used to attach the reflective mask to an electrostatic chuck of an exposure tool. The conductive film 5 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 a conductive film 5 include a CrN film, a TaN film, a TaB film, a CrTaN film, a TiN film, and a ZrN film. The conductive film 5 may contain at least one element selected from the group consisting of chromium, tantalum, and boron.

[0039] Next, in step S6, a multilayer reflective film 3 shown in FIG. 4 is formed in the central region of the second main surface 22 of the substrate 2. The multilayer reflective film 3 reflects EUV light. The multilayer reflective film 3 is formed by alternately laminating high-refractive index layers and low-refractive index layers, for example. The high-refractive index layers are made of, for example, silicon (Si), and the low-refractive index layers are made of, for example, molybdenum (Mo). The multilayer reflective film 3 is formed by a sputtering method such as ion beam sputtering or magnetron sputtering.

[0040] Finally, in step S7, the absorber film 4 shown in FIG. 4 is formed on the multilayer reflective film 3 formed in step S6. The absorber film 4 absorbs EUV. The absorber film 4 is formed of a single metal, alloy, nitride, oxide, oxynitride, or the like containing at least one element selected from Ta, Cr, and palladium (Pd). The absorber film 4 can be formed by, for example, ion beam sputtering or sputtering. The absorber film 4 may contain at least one element selected from the group consisting of ruthenium, tantalum, chromium, iridium, boron, niobium, rhenium, and palladium. The absorber film 4 may contain at least one element selected from the group consisting of ruthenium, tantalum, niobium, and boron.

[0041] In this embodiment, steps S6 and S7 are performed after step S5, but may be performed before step S5.

[0042] The above steps S1 to S7 produce the reflective mask blank 1 shown in Fig. 4. The reflective mask blank 1 has a first main surface 11 and a second main surface 12 facing opposite to the first main surface 11, and has, from the first main surface 11 side to the second main surface 12 side, a conductive film 5, a substrate 2, a multilayer reflective film 3, and an absorbing film 4, in this order.

[0043] Although not shown, the reflective mask blank 1 has a central region and a peripheral region on the first main surface 11, similar to the substrate 2. The central region is a square region measuring 142 mm in length and 142 mm in width, excluding a rectangular frame-shaped peripheral region surrounding the central region, and is a quality assurance region. Similarly to the substrate 2, the reflective mask blank 1 also has a central region and a peripheral region on the second main surface 12. The central region is a square region measuring 142 mm in length and 142 mm in width, excluding a rectangular frame-shaped peripheral region surrounding the central region, and is a quality assurance region. The vertical and horizontal dimensions of the quality assurance region may be 142 mm or more.

[0044] The reflective mask blank 1 may include, in addition to the conductive film 5, the substrate 2, the multilayer reflective film 3, and the absorbing film 4, another film.

[0045] For example, the reflective mask blank 1 may further include a protective film. The protective film is formed between the multilayer reflective film 3 and the absorbing film 4. The protective film protects the multilayer reflective film 3 so that the multilayer reflective film 3 is not etched when the absorbing film 4 is etched to form the opening pattern 41 in the absorbing film 4. The protective film is formed of, for example, ruthenium (Ru), Si, or TiO2. The protective film may contain ruthenium or rhodium. The protective film may be formed by, for example, sputtering.

[0046] The reflective mask blank 1 may further include a low-reflection film. The low-reflection film is formed on the absorbing film 4. Then, an opening pattern 41 is formed in both the low-reflection film and the absorbing film 4. The low-reflection film is used to inspect the opening pattern 41, and has lower reflectivity to inspection light than the absorbing film 4. The low-reflection film is made of, for example, tantalum oxynitride (TaON) or tantalum oxide (TaO). The low-reflection film may be formed, for example, by sputtering.

[0047] 5, the reflective mask is obtained by forming an opening pattern 41 in an absorbing film 4. Photolithography and etching are used to form the opening pattern 41. Therefore, the resist film used to form the opening pattern 41 may be included in the reflective mask blank 1.

[0048] (Method for recycling film-coated substrates) Incidentally, in a reflective mask, if there are irregularities near the opening pattern 41, this will cause problems such as deterioration in the positional accuracy and contrast of the transferred pattern. The irregularities are caused by defects such as scratches and foreign matter.

[0049] Therefore, to ensure that no irregularities exist near the opening pattern 41, a surface defect inspection is carried out on the film-coated substrate after each process. If a defect of an unacceptable size is discovered as a result of the surface defect inspection, the defect is removed by cleaning. On the other hand, if there is a defect that cannot be removed by cleaning, at least the multilayer reflective film 3 is peeled off and the second main surface 22 of the substrate 2 is reclaimed, or the product is discarded as a defective product.

[0050] Here, the film-coated substrate refers to the substrate 2 on which at least the multilayer reflective film 3 is formed, which is obtained after step S6 in FIG. 1. Note that, if steps S6 and S7 are performed before step S5, the conductive film 5 does not have to be formed on the substrate 2. That is, the film-coated substrate may be a substrate 2 on which the multilayer reflective film 3 is formed, a substrate 2 on which the multilayer reflective film 3 and the absorbing film 4 are formed, a substrate 2 on which the conductive film 5 and the multilayer reflective film 3 are formed, or a substrate 2 (reflective mask blank 1) on which the conductive film 5, the multilayer reflective film 3, and the absorbing film 4 are formed. Furthermore, the film-coated substrate may include other films in addition to the conductive film 5, the multilayer reflective film 3, and the absorbing film 4, such as the protective film or low-reflection film described above. Furthermore, the film-coated substrate may be a reflective mask on which an opening pattern 41 is formed.

[0051] In this embodiment, the film-coated substrate is brought into contact with a chemical solution in order to peel at least the multilayer reflective film 3 from the substrate 2 of the film-coated substrate and regenerate the second main surface 22 of the substrate 2. At this time, if the film-coated substrate includes another film on the multilayer reflective film 3, it is necessary to peel that film at the same time. Furthermore, if the film-coated substrate includes a conductive film 5, it is preferable to peel the conductive film 5 at the same time as the multilayer reflective film 3. However, if it is not possible to peel the conductive film 5 at the same time, the conductive film 5 may be peeled by another method, such as using a chemical solution different from the chemical solution according to the present invention.

[0052] The method for contacting the film-coated substrate with the chemical solution is not particularly limited, but examples thereof include a method of immersing the film-coated substrate in a chemical solution stored in a treatment tank (hereinafter referred to as the immersion method), or a method of spraying the chemical solution onto the surface of the film-coated substrate. Of these methods, the immersion method is more preferable from the viewpoints of productivity and cost. In the immersion method, the chemical solution can be easily reused. It is preferable to replace the chemical solution when its performance has deteriorated.

[0053] From the viewpoint of productivity, the shorter the treatment time when the film-coated substrate is brought into contact with the chemical solution, the better. The treatment time is set to be longer than the time required to peel the multilayer reflective film 3 from the substrate 2 of the film-coated substrate (hereinafter referred to as T3). When the chemical solution can peel the conductive film 5 at the same time as the multilayer reflective film 3, the treatment time is set to be longer than either T3 or the time required to peel the conductive film 5 (hereinafter referred to as T5), whichever is longer. The shorter both T3 and T5 are, the shorter the treatment time will be, and therefore, it is preferable.

[0054] The temperature at which the film-coated substrate is brought into contact with the chemical solution is 20°C to 150°C, and preferably 40°C to 100°C. If the temperature is 20°C or higher, the treatment time can be sufficiently shortened. Also, if the temperature is 150°C or lower, there is little risk that the substrate 2 will be excessively damaged by the chemical solution.

[0055] 1 again to produce a reflective mask blank 1. At this time, steps S1 to S5 may be performed as necessary depending on the state of the substrate 2. For example, if the flatness of the substrate 2 from which all films have been removed is insufficient, local polishing or finish polishing may be performed before forming a film to achieve the desired flatness.

[0056] Furthermore, when the substrate 2 is recycled as described above to produce a reflective mask blank 1, if defects that cannot be removed by cleaning occur again, the above operations may be repeated until such defects no longer occur.

[0057] (medicinal solution) Next, the chemical solution according to this embodiment will be described in detail.

[0058] The chemical solution contains a solvent and additives, including at least a pH adjuster and an oxidizing agent, and may further contain optional additives, such as specific metals or chelating agents.

[0059] The solvent is water or an organic solvent, preferably water, and more preferably distilled water, ion-exchanged water, or ultrapure water.

[0060] The pH adjuster is an organic base or an inorganic base, with an inorganic base being preferred. When the pH adjuster is an inorganic base, the conductive film 5 containing Ta can be peeled off from the film-coated substrate. 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 in terms of basicity and water solubility, with NaOH or KOH being more preferred in terms of cost, and KOH being even more preferred in terms of its ability to shorten T5.

[0061] The concentration of the pH adjuster is adjusted within a range such that the pH of the chemical solution is 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, T3 can be made sufficiently short when the multilayer reflective film 3 contains Si and Mo. Furthermore, if the pH is 16 or lower, when the reflective mask blank 1 has a protective film containing Ru, the protective film can be stripped in a sufficiently short time.

[0062] The oxidizing agent is included at least for the purpose of peeling off the multilayer reflective coating 3. Therefore, the oxidizing agent has a redox potential higher than the redox potentials of at least the components constituting the multilayer reflective coating 3. For example, when the multilayer reflective coating 3 contains Si and Mo, the oxidizing agent preferably has a standard electrode potential of 0.8 V to 2.0 V, and specifically, the oxidizing agent is at least one selected from the group consisting of metaperiodic acid (HIO), metaperiodate, orthoperiodic acid (HIO), orthoperiodate, permanganic acid (HMnO), permanganate, and N-methylmorpholine N-oxide (abbreviated: NMO).

[0063] Among the above oxidizing agents, metaperiodic acid, metaperiodate, orthoperiodic acid, orthoperiodate, permanganic acid, or permanganate are preferred because they can shorten T3, and metaperiodic acid, metaperiodate, orthoperiodic acid, or orthoperiodate are more preferred because they exhibit high activity even at pH 10 to 16 and their by-products are water-soluble. Furthermore, when the film-coated substrate has a conductive film 5 containing Cr, permanganic acid or permanganate is also preferred because the conductive film 5 can be stripped off.

[0064] Furthermore, when the chemical solution contains an oxidizing agent, T5 can be shortened if the film-coated substrate has a conductive film 5 containing Ta.

[0065] The concentration of the oxidizing agent is 0.1 ppm to 40% of 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 more, the multilayer reflective film 3 can be peeled off. Furthermore, if the concentration of the oxidizing agent is 40% or less, there is little risk of precipitation of sparingly soluble by-products.

[0066] Optional additives are, for example, specific metals or chelating agents.

[0067] The specific metals are at least one selected from the group consisting of metals and ions thereof having a redox potential higher than that of Cr(VI). Specific examples of such metals include Ru and cerium (Ce). When the chemical solution contains the specific metals, the conductive film 5 can be stripped from the film-coated substrate if it contains a Cr-containing conductive film 5. The Ru ions or Ce ions may be added when preparing the chemical solution, or may be eluted from a stripped film (e.g., a protective film containing Ru).

[0068] The mechanism by which the conductive film 5 containing Cr is stripped by specific metals will be explained below, taking 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 chemical solution, and become RuO4 - These Ru oxide ions oxidize the Cr contained in the conductive film 5 to form water-soluble CrO4 2- As a result, the conductive film 5 containing Cr is peeled off.

[0069] The concentration of the specific metals is 0.0001 to 10 equivalents relative to the oxidizing agent, preferably 0.001 to 1 equivalent, and more preferably 0.01 to 0.1 equivalent. If the concentration of the specific metals is 0.0001 equivalent or more, peeling of the conductive film 5 containing Cr proceeds sufficiently. Furthermore, if the concentration of the specific metals is 10 equivalents or less, damage to the substrate can be sufficiently suppressed.

[0070] The chelating agent may be an aminocarboxylic acid chelating agent, a hydroxy acid chelating agent, or a phosphonic acid chelating agent. Examples of aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid (EDTA), triethylenetetraminehexaacetic acid (TTHA), nitrilotrismethylenephosphonic acid (NTPO), and N,N-bis(2-hydroxyethyl)glycine (Bicine). Examples of hydroxy acid chelating agents include tartaric acid. Examples of phosphonic acid chelating agents include hydroxyethylidene diphosphonic acid (HEDP) and phosphonoacetic acid. When the chemical solution contains the above chelating agents, the treatment time can be shortened.

[0071] Among the above chelating agents, EDTA or phosphonoacetic acid is more preferable in terms of shortening the treatment time, and TTHA is more preferable in terms of minimizing damage to the substrate 2.

[0072] The concentration of the chelating agent is 0.01% to 10%, preferably 0.1% to 5%, and more preferably 0.5% to 2% of the chemical solution. If the concentration of the chelating agent is 0.01% or more, the treatment time can be significantly shortened. Furthermore, if the concentration of the chelating agent is 10% or less, there is little risk of precipitation of poorly soluble by-products.

[0073] The above additives are mixed with a solvent to prepare a chemical solution. The additives are selected so that they dissolve in the solvent and do not precipitate poorly soluble by-products. One or more types of pH adjusters and oxidizing agents are included. Specific metals may be absent or may contain one or more types. Chelating agents may be absent or may contain one or more types. [Example]

[0074] Next, experimental data will be described with reference to Table 1. In Table 1, Examples 1 to 23 are working examples, and Examples 24 and 25 are comparative examples.

[0075] [Table 1] (Experimental Method) A conductive film 5 was formed by sputtering on the first main surface 21 of a substrate 2 made of quartz glass containing TiO2. The conductive film 5 was a CrN film or a film containing Ta as the main component (referred to as Ta-based in Table 1). Next, a multilayer reflective film 3 was formed by ion beam sputtering on the second main surface 22 of the substrate 2. The multilayer reflective film 3 was formed by alternately laminating 40 periods of Si films each about 4 nm thick and Mo films each about 3 nm thick, followed by a final Si film about 4 nm thick. Next, a protective film made of Ru was formed by sputtering on the multilayer reflective film 3 to a thickness of about 2.5 nm. A film-coated substrate was thus obtained. A small piece with a side length of about 10 mm was cut out of this film-coated substrate to serve as a test piece.

[0076] Next, a chemical solution was prepared and filled into a container. The container was then placed on a hot plate equipped with a stirrer and heated for approximately 30 minutes to maintain the specified temperature. The test specimen was then placed in the container and immersed in the chemical solution for up to 600 minutes while stirring, after which the test specimen was removed. However, if peeling of the multilayer reflective film 3 and the conductive film 5 was confirmed, the test specimen was removed at that point. Peeling of the multilayer reflective film 3 or the conductive film 5 was confirmed visually before removing the test specimen, and after removing the test specimen, it was confirmed again using a fluorescent X-ray analyzer (Rigaku Corporation: ZSX Primus II) that no film components remained. When the multilayer reflective film 3 was peeled, the protective film was also peeled at the same time.

[0077] (medicinal solution) Ultrapure water was used as the solvent.

[0078] As a pH adjuster, NaOH was used in Example 1, and KOH was used in Examples 2 to 25, each at a predetermined concentration.

[0079] As the oxidizing agent, sodium metaperiodate (NaIO4) was used in Examples 1 to 14, 18, and 19, H5IO6 in Examples 15 to 17 and 20, potassium permanganate (KMnO4) in Examples 21 and 22, NMO in Example 23, and hydrogen peroxide (HO2) in Examples 24 and 25, all at predetermined concentrations.

[0080] As the specific metal, RuCl3 was added in Examples 6 and 7, and Ru powder was added in Example 8 in a predetermined equivalent amount relative to the oxidizing agent.

[0081] As a chelating agent, 0.1% of EDTA was added in Example 9, 0.1% of TTHA in Example 10, 0.1% of NTPO in Example 11, 0.1% of bicine in Example 12, 0.1% of tartaric acid in Example 13, and 0.1% of phosphonoacetic acid in Example 14 were added.

[0082] The pH of the chemical solutions in Examples 1 to 25 was measured using a portable pH / ORP / ion meter (manufactured by Horiba Advanced Techno Co., Ltd.: D-73).

[0083] (Experimental results) In Table 1, the time (T3) from when the test piece was placed in the container until peeling of the multilayer reflective coating 3 was visually confirmed was marked "A" if it was within 30 minutes, "B" if it was more than 30 minutes and up to 45 minutes, "C" if it was more than 45 minutes and up to 60 minutes, "D" if it was more than 60 minutes and up to 120 minutes, "E" if it was more than 120 minutes and up to 600 minutes, and "X" if it had not peeled at 600 minutes. Note that when the multilayer reflective coating 3 was peeled, the protective coating was also peeled at the same time, so the time required for the protective coating to peel was not evaluated.

[0084] In Table 1, the time (T5) from when the test piece was placed in the container until peeling of the conductive film 5 was visually confirmed was evaluated in the same manner as T3.

[0085] In Table 1, the root mean square roughness (RMS) of the second main surface 22 of the substrate 2 measured with an atomic force microscope (Dimension Icon, manufactured by Bruker) was evaluated as "◎" when it was 0.15 nm or less after the experiment, and as "◯" when it was more than 0.15 nm and 0.5 nm or less, to evaluate substrate damage. If the RMS is 0.5 nm or less, the process load when re-polishing the substrate 2 after recycling can be sufficiently reduced.

[0086] As shown by the results of Examples 1 to 23, at least the multilayer reflective film 3 could be peeled off by the chemical solution according to the present invention.

[0087] From Examples 1 and 2, it was clear that the use of KOH as a pH adjuster can shorten T3 more than the use of NaOH.

[0088] A comparison of Example 3 with Examples 6 to 8 reveals that adding Ru or Ru ions as specific metals makes it possible to peel off not only the multilayer reflective film 3 but also the conductive film 5 made of CrN while suppressing substrate damage.

[0089] Comparison of Example 2 with Examples 9 to 14 revealed that the addition of a chelating agent can shorten T3.

[0090] On the other hand, when the oxidizing agent was H2O2 as in Example 24, the multilayer reflective film 3 could not be peeled even after 600 minutes. Also, when a chelating agent was added to the chemical solution of Example 24 as in Example 25, the multilayer reflective film 3 could be peeled, but the time required for peeling was longer than in Examples 1 to 22. Furthermore, Example 23 had the same T3 as Example 25, but was superior in terms of substrate damage.

[0091] Furthermore, when an attempt was made to peel off a Si wafer test piece on which a ruthenium-based, tantalum-based, niobium-based, or boron-based absorbing film had been formed using the above experimental method, it was found that these absorbing films could also be peeled off. Because the top layer of the multilayer reflective film on the glass substrate is a film containing silicon, these results show that a ruthenium-based, tantalum-based, niobium-based, or boron-based absorbing film on a multilayer reflective film formed on a glass substrate can also be peeled off.

[0092] (Reference experiment) A multilayer reflective film 3 was formed by sputtering on the second main surface 22 of a substrate 2 made of quartz glass containing TiO2. The multilayer reflective film 3 was formed by alternately laminating 40 periods of Si films of approximately 4 nm and Mo films of approximately 3 nm, followed by a final Si film of approximately 4 nm. Next, a protective film made of Ru was formed by sputtering on the multilayer reflective film 3 to a thickness of approximately 2.5 nm. In this manner, a substrate with a film was obtained.

[0093] Next, a reaction vessel was filled with 1 L of a chemical solution containing 22.4% KOH as a pH adjuster and 1% NaIO4 as an oxidizer, and the temperature was kept at 60-65°C. The reaction vessel was then stirred while the film-coated substrate was placed in the vessel. When peeling of the multilayer reflective film 3 was visually confirmed, the film-coated substrate was removed, and another film-coated substrate prepared in the same manner was placed in the vessel. This process was repeated eight times in succession.

[0094] The results of the above reference experiment are shown in Figure 6. As can be seen from Figure 1, T3 tended to increase slightly as the number of times the film-coated substrate was inserted increased, but the change was not so great that it was necessary to replace the chemical solution. This suggests that the chemical solution according to the present invention can be used repeatedly.

[0095] The chemical solution, the method for recycling a film-coated substrate, the method for manufacturing a film-coated substrate, and the method for manufacturing a reflective mask blank according to the present invention have been described above, but the present invention is not limited to the above-described embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure.

[0096] This application claims priority based on Patent Application No. 2021-094724, filed with the Japan Patent Office on June 4, 2021, and the entire contents of Patent Application No. 2021-094724 are incorporated herein by reference. [Explanation of symbols]

[0097] 1. Reflective mask blank 2 boards 3 Multilayer reflective film 4. Absorbent membrane 5 Conductive film 41 Opening Pattern

Claims

1. A chemical solution used to remove at least a multilayer reflective film containing silicon and molybdenum from a glass substrate of a film-coated substrate having a multilayer reflective film formed on one surface of the glass substrate, the chemical solution comprising: A pH adjuster; and at least one oxidizing agent selected from the group consisting of metaperiodic acid, metaperiodate, orthoperiodic acid, orthoperiodate, permanganic acid, permanganate, and N-methylmorpholine N-oxide.

2. The drug solution according to claim 1, having a pH of 10 or more and 16 or less.

3. The chemical solution according to claim 1 , wherein the pH adjuster is sodium hydroxide or potassium hydroxide.

4. 2. The chemical solution according to claim 1, wherein the oxidizing agent is metaperiodic acid, metaperiodate, orthoperiodic acid, or orthoperiodate.

5. The chemical solution according to claim 1 , wherein the oxidizing agent is permanganic acid or a permanganate.

6. 2. The chemical solution according to claim 1, further comprising at least one selected from the group consisting of a metal having a redox potential higher than the redox potential of chromium (VI) and an ion thereof, in an amount of 0.0001 to 10 molar equivalents relative to the oxidizing agent.

7. The chemical solution according to claim 1, further comprising an aminocarboxylic acid-based chelating agent, a hydroxy acid-based chelating agent, or a phosphonic acid-based chelating agent as a chelating agent.

8. A method for regenerating a film-coated substrate, comprising contacting a film-coated substrate, having a multilayer reflective film containing silicon and molybdenum formed on one surface of the glass substrate, with a chemical solution containing a pH adjuster and at least one oxidizing agent selected from the group consisting of metaperiodic acid, metaperiodate, orthoperiodic acid, orthoperiodate, permanganic acid, permanganate, and N-methylmorpholine N-oxide, to peel off at least the multilayer reflective film from the glass substrate, and regenerating the surface of the glass substrate on which the multilayer reflective film had been formed.

9. 9. The method for recycling a film-coated substrate according to claim 8, wherein the film-coated substrate has a protective film containing ruthenium on the multilayer reflective film.

10. 9. The method for recycling a film-coated substrate according to claim 8, wherein the film-coated substrate has an absorbing film on the multilayer reflective film, the absorbing film containing at least one selected from the group consisting of ruthenium, tantalum, niobium, and boron.

11. 9. The method for recycling a film-coated substrate according to claim 8, wherein the film-coated substrate has a conductive film containing chromium or tantalum on a surface opposite to the surface on which the multilayer reflective film is formed.

12. A method for producing a film-coated substrate, comprising forming a multilayer reflective film containing at least silicon and molybdenum on one surface of the glass substrate recycled by the method for recycling a film-coated substrate according to any one of claims 8 to 11.

13. forming a multilayer reflective film containing silicon and molybdenum on one surface of the glass substrate recycled by the method for recycling a film-coated substrate according to any one of claims 8 to 11; forming a protective film containing ruthenium or rhodium on the multilayer reflective film; forming an absorbing film containing at least one selected from the group consisting of ruthenium, tantalum, chromium, iridium, boron, niobium, rhenium, and palladium on the protective film; forming a conductive film containing at least one selected from the group consisting of chromium, tantalum, and boron on a surface of the glass substrate opposite to the surface on which the multilayer reflective film is formed; A method for producing a reflective mask blank, comprising:

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