Glass substrate for reflective mask blanks, and method for manufacturing the same.

Abstract

To provide a technique that improves the cleaning efficiency of a glass substrate for reflective mask blanks.SOLUTION: A glass substrate for reflective mask blanks comprises a quartz glass substrate. The surface of the quartz glass substrate includes at least partly a modified region doped with iodine (I). In the modified region, the ratio of the intensity of monovalent I ions (II) to the intensity of monovalent Si ions (ISi), (II / ISi), is 5.0×10-3 to 1.0×102, as measured by secondary ion mass spectrometry.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] This disclosure relates to a glass substrate for reflective mask blanks and a method for manufacturing the same. [Background technology]

[0002] In recent years, with the miniaturization of semiconductor devices, EUV lithography (EUVL), a lithography 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 (External Ultraviolet Lapping), the aperture pattern of a reflective mask is transferred to a semiconductor substrate. The reflective mask is obtained by forming an aperture pattern on the absorption film of a reflective mask blank. The reflective mask blank includes a substrate such as a glass substrate, a multilayer reflective film formed on the substrate, and an absorption film formed on the multilayer reflective film.

[0004] Incidentally, in reflective masks, the presence of irregularities near the aperture pattern can cause problems as 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 removing at least the multilayer reflective film or discarded as a defective product.

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

Prior Art Document

Patent Document

[0007]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0008] In the manufacturing process of a reflective mask blank, a glass substrate may be washed with an aqueous detergent. When the water wettability to the surface of the glass substrate is poor, the affinity of the aqueous detergent to the surface of the glass substrate is poor, resulting in low washing efficiency.

[0009] One aspect of the present disclosure provides a technique that improves the washing efficiency with an aqueous detergent.

Means for Solving the Problem

[0010] The glass substrate for a reflective mask blank is made of a quartz glass substrate, and has a modified region doped with iodine (I) on at least a part of the surface of the quartz glass substrate. The modified region has the intensity of monovalent Si ions measured by secondary ion mass spectrometry (I Si ) intensity of monovalent I ions relative to (I I ) intensity ratio (I I / I Si ) is 5.0×10 -3 to 1.0×10 2 .

Effect of the Invention

[0011] According to one aspect of this disclosure, the cleaning efficiency of water-based detergents can be improved. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a flowchart showing a method for manufacturing a reflective mask blank according to one embodiment. [Figure 2] Figure 2 is a cross-sectional view showing an example of a substrate. [Figure 3] Figure 3 is a plan view of the substrate shown in Figure 2. [Figure 4] Figure 4 is a cross-sectional view showing an example of a reflective mask blank. [Figure 5] Figure 5 is a cross-sectional view showing an example of a reflective mask. [Figure 6] Figure 6 shows an example of the intensity ratio (II / ISi) of a quartz glass substrate. [Figure 7] Figure 7 is a box plot showing an example of the water contact angle of a quartz glass substrate. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments for carrying out the present invention (hereinafter simply referred to as "this embodiment") will be described with reference to the drawings. In the drawings, positional relationships such as up, down, left, and right shall be based on the positional relationships shown in the drawings unless otherwise specified. Note that the dimensional ratios in the drawings are not limited to the ratios shown. In addition, in the specification, "~" indicating a numerical range means that the numbers written before and after it are included as the lower limit and upper limit. The lower limit and upper limit include the range of rounding. Furthermore, "%", "ppm", and "ppb" represent mass fraction, and "equivalent" represents molar equivalent.

[0014] (Method of manufacturing a reflective mask blank) As shown in Figure 1, the method for manufacturing a reflective mask blank comprises steps S1 to S7. For manufacturing the reflective mask blank, for example, a substrate 2 shown in Figures 2 and 3 is used. The substrate 2 includes a first main surface 21 and a second main surface 22 facing the opposite direction 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. A rectangle also includes a square. The second main surface 22 faces the opposite direction to the first main surface 21. The second main surface 22 is also rectangular, similar to the first main surface 21.

[0015] Furthermore, the substrate 2 includes four end faces 23, four first chamfered surfaces 24, and four second chamfered surfaces 25. The end faces 23 are perpendicular to the first main surface 21 and the second main surface 22. The first chamfered surfaces 24 are formed at the boundary between the first main surface 21 and the end face 23. The second chamfered surfaces 25 are formed at the boundary between the second main surface 22 and the end face 23. In this embodiment, the first chamfered surfaces 24 and the second chamfered surfaces 25 are so-called C-chamfered surfaces, but they may also be R-chamfered surfaces.

[0016] Substrate 2 is, for example, a quartz glass substrate. The quartz glass substrate preferably contains titanium oxide (TiO2). Compared to general soda-lime glass, quartz glass has a smaller coefficient of thermal expansion and less dimensional change due to temperature changes. 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 coefficient of thermal expansion at room temperature is approximately zero, and there is almost no dimensional change at room temperature. The quartz glass may also contain third components or impurities other than SiO2 and TiO2. For example, Corning's ULE® 7973 series may be used as such a quartz glass.

[0017] In a plan view, the dimensions of the substrate 2 are, for example, 152 mm in length and 152 mm in width. The length and width dimensions may be greater than or equal to 152 mm.

[0018] The substrate 2 has a central region 27 and a peripheral region 28 on its first main surface 21. The central region 27 is a square area measuring 142 mm in length and 142 mm in width, excluding the rectangular frame-shaped peripheral region 28 that surrounds the central region 27. This area is processed to the desired flatness by steps S1 to S4 and is the quality assurance region. The length and width dimensions of the quality assurance region 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.

[0019] Although not shown in the figures, 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 is a square area with dimensions of 142 mm in length and 142 mm in width, similar to the central region of the first main surface 21, and is the region that is processed to the desired flatness by steps S1 to S4 in Figure 1, and is the quality assurance region. The length and width dimensions of the quality assurance region may be 142 mm or more.

[0020] 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 polishing machine (not shown), but they may also be polished sequentially using a single-sided polishing machine (not shown). In step S1, the substrate 2 is polished while supplying polishing slurry between the polishing pad and the substrate 2.

[0021] As polishing pads, for example, urethane-based polishing pads, nonwoven fabric-based polishing pads, or suede-based polishing pads can be used. 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 with abrasives of different materials or particle sizes.

[0022] The abrasive used in step S1 is not limited to cerium oxide particles. For example, the abrasive used in step S1 may be silicon oxide particles, aluminum oxide particles, zirconium oxide particles, titanium oxide particles, diamond particles, or silicon carbide particles.

[0023] 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. For measuring the surface shapes, a non-contact measuring instrument such as a laser interferometry instrument is used to avoid damaging the surface. The measuring instrument measures the surface shapes of the central region 27 of the first main surface 21 and the central region of the second main surface 22.

[0024] Next, in step S3, the measurement results from 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 sequence. The order in which they are processed does not matter and is not particularly limited. The local processing method may be, for example, the GCIB (Gas Cluster Ion Beam) method or the PCVM (Plasma Chemical Vaporization Machining) method. The local processing method may also be polishing with magnetic fluid, polishing with a rotary polishing tool, or catalyst-based etching. Note that if the flatness after step S1 is sufficient, the local processing in step S3 may not be necessary.

[0025] Next, in step S4, the first main surface 21 and the second main surface 22 of the substrate 2 are polished to a finish. In this embodiment, the first main surface 21 and the second main surface 22 are polished simultaneously using a double-sided polishing machine (not shown), but they may also be polished sequentially using a single-sided polishing machine (not shown). In step S4, the substrate 2 is polished while supplying polishing slurry between the polishing pad and the substrate 2. The polishing slurry contains an abrasive. The abrasive is, for example, colloidal silica particles.

[0026] Next, in step S5, a conductive film 5, as shown in Figure 4, is formed on the central region 27 of the first main surface 21 of the substrate 2. The conductive film 5 is used to attract the reflective mask to the electrostatic chuck of the exposure apparatus. Preferably, the conductive film 5 is 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 5 include CrN films, TaN films, TaB films, CrTaN films, TiN films, and ZrN films. The conductive film 5 may also contain at least one selected from the group consisting of chromium, tantalum, and boron.

[0027] Next, in step S6, a multilayer reflective film 3, as shown in Figure 4, is formed on 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 stacking high refractive index layers and low refractive index layers. The high refractive index layers are formed from silicon (Si), for example, and the low refractive index layers are formed from molybdenum (Mo), for example. As a method for depositing the multilayer reflective film 3, sputtering methods such as ion beam sputtering and magnetron sputtering are used.

[0028] Finally, in step S7, an absorption film 4, as shown in Figure 4, is formed on the multilayer reflective film 3 formed in step S6. The absorption film 4 absorbs EUV. The absorption film 4 is formed from a single metal, alloy, nitride, oxide, oxynitride, etc., containing at least one element selected from, for example, Ta, Cr, and palladium (Pd). As a method for forming the absorption film 4, for example, ion beam sputtering or sputtering can be used. The absorption film 4 may contain at least one selected from the group consisting of ruthenium, tantalum, chromium, iridium, boron, niobium, rhenium, and palladium. The absorption film 4 may contain at least one selected from the group consisting of ruthenium, tantalum, niobium, and boron.

[0029] In this embodiment, steps S6 and S7 are performed after step S5, but they may also be performed before step S5.

[0030] By following the steps S1 to S7 described above, a reflective mask blank 1 shown in Figure 4 is obtained. The reflective mask blank 1 has a first main surface 11 and a second main surface 12 facing the opposite direction from the first main surface 11, and has a conductive film 5, a substrate 2, a multilayer reflective film 3, and an absorbing film 4 in this order, from the side of the first main surface 11 to the side of the second main surface 12.

[0031] The reflective mask blank 1, although not shown in the figure, has a central region and a peripheral region on its first main surface 11, similar to the substrate 2. The central region is a square area measuring 142 mm vertically and 142 mm horizontally, excluding the rectangular frame-shaped peripheral region surrounding it, and is the quality assurance region. Similarly, the reflective mask blank 1 also has a central region and a peripheral region on its second main surface 12, similar to the substrate 2. The central region is a square area measuring 142 mm vertically and 142 mm horizontally, excluding the rectangular frame-shaped peripheral region surrounding it, and is the quality assurance region. The vertical and horizontal dimensions of the quality assurance region may be 142 mm or more.

[0032] In addition to the conductive film 5, the substrate 2, the multilayer reflective film 3, and the absorbing film 4, the reflective mask blank 1 may also include another film.

[0033] 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 absorption film 4. The protective film protects the multilayer reflective film 3 from being etched when the absorption film 4 is etched to form an aperture pattern 41 in the absorption film 4. The protective film is formed of, for example, ruthenium (Ru), Si, or TiO2. The protective film may also contain ruthenium or rhodium. For example, sputtering can be used as a method for forming the protective film.

[0034] Furthermore, the reflective mask blank 1 may also include a low-reflection film. The low-reflection film is formed on the absorption film 4. Subsequently, an aperture pattern 41 is formed on both the low-reflection film and the absorption film 4. The low-reflection film is used to inspect the aperture pattern 41 and has lower reflectivity than the absorption film 4 with respect to inspection light. The low-reflection film is formed of, for example, tantalum oxynitride (TaON) or tantalum oxide (TaO). As a method for depositing the low-reflection film, for example, sputtering can be used.

[0035] As shown in Figure 5, the reflective mask is obtained by forming an aperture pattern 41 in the absorption film 4. Photolithography and etching methods are used to form the aperture pattern 41. Therefore, the resist film used to form the aperture pattern 41 may be included in the reflective mask blank 1.

[0036] (Method for regenerating film-coated substrates) Incidentally, in reflective masks, the presence of irregularities near the aperture pattern 41 can lead to problems as it degrades the positional accuracy and contrast of the transferred pattern. Irregularities are caused by defects such as scratches or foreign matter.

[0037] Therefore, surface defect inspection is performed on the coated substrate at each stage of the process to ensure that no irregularities exist near the aperture pattern 41. If defects of an unacceptable size are found as a result of the surface defect inspection, the defects are removed by cleaning. On the other hand, if there are defects that cannot be removed by cleaning, at least the multilayer reflective film 3 is removed and the second main surface 22 of the substrate 2 is restored.

[0038] Here, "film-coated substrate" refers to the substrate 2 obtained from step S6 onwards in Figure 1, on which at least the multilayer reflective film 3 is formed. Note that if steps S6 to S7 are performed before step S5, the conductive film 5 does not need to be formed on the substrate 2. That is, the film-coated substrate is a substrate 2 on which the multilayer reflective film 3 is formed, a substrate 2 on which the multilayer reflective film 3 and the absorption 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 absorption film 4 are formed. Furthermore, the film-coated substrate may also contain other films besides the conductive film 5, the multilayer reflective film 3 and the absorption film 4, such as the protective film or the low-reflection film mentioned above. In addition, the film-coated substrate may also be a reflective mask on which the aperture pattern 41 is formed.

[0039] In this embodiment, the coated substrate is brought into contact with a chemical solution to remove at least the multilayer reflective film 3 from the substrate 2 of the coated substrate and to regenerate the second main surface 22 of the substrate 2. The chemical solution removes the multilayer reflective film 3 by dissolving it. At this time, if the coated substrate contains other films on top of the multilayer reflective film 3, those films must also be removed at the same time. Furthermore, if the coated substrate contains a conductive film 5, it is preferable to remove the conductive film 5 at the same time as the multilayer reflective film 3, but if it is not possible to remove the conductive film 5 at the same time, the conductive film 5 may be removed by another method, such as using a chemical solution different from the chemical solution according to the present invention.

[0040] There are no particular limitations on the method of bringing the film-coated substrate into contact with the chemical solution, but for example, a method of immersing the film-coated substrate in the chemical solution accumulated 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 can be used. 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.

[0041] 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 longer than the time required to remove the multilayer reflective film 3 from the substrate 2 of the film-coated substrate (hereinafter referred to as T3). If the chemical solution can remove the conductive film 5 at the same time as the multilayer reflective film 3, the processing time should be set to be longer than the longer of T3 and the time required to remove the conductive film 5 (hereinafter referred to as T5). It is preferable that both T3 and T5 be as short as possible, as this will result in a shorter processing time.

[0042] 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 substrate 2 being excessively damaged by the chemical solution.

[0043] The refurbished substrate 2 is subjected to at least steps S6 to S7 in Figure 1 again to manufacture a reflective mask blank 1. At this time, steps S1 to S5 may be performed as needed depending on the condition 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 to achieve the desired flatness before forming the film.

[0044] Furthermore, if defects that cannot be removed by cleaning reappear when the substrate 2 is regenerated and the reflective mask blank 1 is manufactured as described above, the above operations may be repeated until such defects no longer occur.

[0045] (Medicinal solution) Next, the chemical solution according to this embodiment will be described in detail.

[0046] The chemical solution contains a solvent and additives. The additives include at least a pH adjuster and an oxidizing agent, and may also include optional additives. Optional additives include, for example, specific metals or chelating agents.

[0047] The solvent is water or an organic solvent, with water being preferred. Distilled water, deionized water, or ultrapure water are preferred as the water.

[0048] The pH adjuster is an organic base or an inorganic base, with an inorganic base being preferred. If the pH adjuster is an inorganic base, the conductive film 5 containing Ta can be removed if the film-coated substrate has such a film. 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 T5.

[0049] The concentration of the pH adjuster is adjusted to a range such that the pH of the chemical solution reaches the 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 shortened sufficiently when the multilayer reflective film 3 contains Si and Mo. Also, if the pH is 16 or lower, the protective film can be removed in a sufficiently short time when the reflective mask blank 1 has a protective film containing Ru.

[0050] The oxidizing agent is included, for example, for the purpose of removing the multilayer reflective film 3. Therefore, the oxidizing agent has a redox potential higher than at least the redox potential of the components constituting the multilayer reflective film 3. For example, when the multilayer reflective film 3 contains Si and Mo, the standard electrode potential of the oxidizing agent is preferably 0.8V to 2.0V, and specifically, it is preferable to include at least one selected from the first group consisting of metaperiodic acid (HIO4), metaperiodate salt, orthoperiodic acid (H5IO6), and orthoperiodate salt.

[0051] Metaperiodic acid, metaperiodate salts, orthoperiodic acid, and orthoperiodate salts can shorten T3, exhibit high activity even at pH 10-16, and produce water-soluble byproducts. Furthermore, metaperiodic acid, metaperiodate salts, orthoperiodic acid, and orthoperiodate salts can dopage iodine onto substrate surfaces, improving the wettability of the substrate surface with water.

[0052] Furthermore, the oxidizing agent may further include at least one selected from the second group consisting of permanganic acid (HMnO4), permanganate salts, and N-methylmorpholine N-oxide (abbreviated as NMO). Among the second group, permanganic acid or permanganate salts are preferred because they can remove the conductive film 5 if the film-coated substrate has a conductive film 5 containing Cr.

[0053] 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.

[0054] 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 3 can be removed. Furthermore, if the concentration of the oxidizing agent is 40% or lower, there is little risk of precipitation of poorly soluble by-products.

[0055] Optional additives include, for example, specific metals or chelating agents.

[0056] The term "specific metals" refers to at least one selected from the group consisting of metals and their ions that have a redox potential higher than that of Cr(VI). Specific examples of such metals include Ru or cerium (Ce). When the chemical solution contains specific metals, the conductive film 5 can be removed if the substrate with the film has a conductive film 5 containing Cr. Note that Ru ions or Ce ions may be added during the preparation of the chemical solution, or they may be eluted from the removed film (e.g., a protective film containing Ru).

[0057] The mechanism by which a conductive film 5 containing Cr is removed by specific metals is explained below, 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 RuO4. - Alternatively, it becomes RuO4. These Ru oxide ions oxidize the Cr contained in the conductive film 5, forming water-soluble CrO4. 2- This removes the conductive film 5 containing Cr.

[0058] The concentration of the specific metal 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 equivalents. If the concentration of the specific metal is 0.0001 equivalents or more, the removal of the conductive film 5 containing Cr proceeds sufficiently. Furthermore, if the concentration of the specific metal is 10 equivalents or less, substrate damage can be sufficiently suppressed.

[0059] 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). 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.

[0060] Among the chelating agents mentioned above, EDTA or phosphonoacetic acid are preferred because they shorten the processing time, and TTHA is preferred because it causes less damage to the substrate 2.

[0061] 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 reduced. Furthermore, if the concentration of the chelating agent is 10% or lower, the risk of precipitation of poorly soluble by-products is small.

[0062] The above additives are mixed with a solvent to prepare the chemical solution. The additives are selected to be soluble in the solvent and to prevent the precipitation of poorly soluble by-products. One or more pH adjusters and oxidizing agents are included. Specific metals may or may not be included, or one or more may be included. Chelating agents may or may not be included, or one or more may be included.

[0063] The chemical solution is used, for example, for the purpose of regenerating the substrate 2 (for the purpose of removing the film formed on the substrate 2), as well as for the purpose of improving the wettability of water to at least a portion of the surface of the substrate 2. Hereinafter, the surface of the substrate 2 includes a first main surface 21, a second main surface 22, an end face 23, a first chamfered surface 24, and a second chamfered surface 25. Hereinafter, the surface of the substrate 2 may be simply referred to as the substrate surface.

[0064] As described above, the chemical solution contains at least one oxidizing agent selected from Group 1, which consists of metaperiodic acid, metaperiodate salt, orthoperiodic acid, and orthoperiodate salt. Metaperiodic acid, metaperiodate salt, orthoperiodic acid, and orthoperiodate salt can dopage the substrate surface with iodine and improve the wettability of the substrate surface with water.

[0065] Furthermore, the chemical solution does not need to be used for the purpose of regenerating substrate 2 (for the purpose of removing the film formed on substrate 2). The chemical solution should only be used for the purpose of improving the wettability of water to the substrate surface. In other words, the chemical solution may be supplied to substrate 2 even if no film has been formed on it. In any case, by improving the wettability of water to the substrate surface, the affinity of water-based detergents to the substrate surface can be improved, and the cleaning efficiency of water-based detergents can be improved.

[0066] Aqueous cleaning agents include, for example, pure water, acidic aqueous solutions, or alkaline aqueous solutions. Aqueous cleaning agents are used, for example, during the manufacturing process of EUVL mask blanks and in the cleaning process. The cleaning process is performed, for example, immediately before step S1 shown in Figure 1, between steps S1 and S2, between steps S3 and S4, between steps S4 and S5, between steps S5 and S6, between steps S6 and S7, or immediately after step S7.

[0067] The cleaning process is carried out by utilizing chemical reactions with acids or alkalis, cleaning using physical actions, or a combination of these. Examples of cleaning using physical actions include scrubbing, ultrasonic cleaning, and two-fluid cleaning, which involves mixing N2 gas and a cleaning solution and spraying it. Water-based cleaning agents are used in these cleaning processes.

[0068] The cleaning process includes, for example, RCA cleaning. RCA cleaning includes, for example, SC-1 cleaning, dilute hydrofluoric acid cleaning, and SC-2 cleaning in this order. In SC-1 cleaning, a mixed aqueous solution of ammonium hydroxide (NH4OH) and hydrogen peroxide (H2O2) is used as the aqueous detergent. In dilute hydrofluoric acid cleaning, dilute hydrofluoric acid is used as the aqueous detergent. In SC-2 cleaning, a mixed aqueous solution of hydrochloric acid (HCl) and hydrogen peroxide is used as the aqueous detergent. RCA cleaning may further include SPM cleaning. In SPM cleaning, a mixed aqueous solution of sulfuric acid (H2SO4) and hydrogen peroxide is used as the aqueous detergent. The cleaning process may also include SPM cleaning alone.

[0069] Water-based detergents may include pure water, a mixture of pure water and X, a mixture of pure water and Y, a mixture of pure water and Z, a mixture of pure water, X, and Z, or a mixture of pure water, Y, and Z. X is at least one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, formic acid, and acetic acid. Y is at least one selected from the group consisting of ammonia, tetramethylammonium hydroxide, triethanolamine, choline, sodium hydroxide, potassium hydroxide, and cesium hydroxide. Z is at least one selected from the group consisting of hydrogen peroxide, perchlorate ions, and periodate ions.

[0070] The aqueous detergent may, in addition to pure water, a mixture of pure water and X, a mixture of pure water and Y, a mixture of pure water and Z, a mixture of pure water, X and Z, or a mixture of pure water, Y and Z, have dissolved therein at least one gas selected from the group consisting of hydrogen (H₂), carbon dioxide (CO₂), nitrogen (N₂), oxygen (O₂), ozone (O₃), and argon (Ar). By having these gases dissolved therein, the aqueous detergent can control the generation amount of cavitation, thereby enabling control of particle removal performance. Among these gases, H₂, CO₂ or N₂ is preferred, and CO₂ is more preferred.

[0071] (Characteristics of Substrate Treated with Chemical Solution) The substrate 2 is formed of a quartz glass substrate, and has a modified region doped with iodine (I) on at least a part of the surface of the quartz glass substrate. The modified region has an intensity of monovalent Si ions (I Si ) measured by secondary ion mass spectrometry, and the intensity ratio of the intensity of monovalent I ions (I I ) to said intensity (I I / I Si ) is 5.0×10 -3 to 1.0×10 2 .

[0072] When the intensity ratio (I I / I Si ) is 5.0×10 -3 or higher, the water wettability to the modified region is favorable. Accordingly, the affinity of the aqueous detergent for the substrate surface can be improved, and the cleaning efficiency of the substrate surface by the aqueous detergent can be improved. The intensity ratio (I I / I Si ) is preferably 1.0×10 -2 or higher, more preferably 5.0×10 -2 or higher. From the viewpoint of the treatment time of the chemical solution, the intensity ratio (I I / I Si ) may be 1.0×10 1 or lower, and may also be 1.0×10 0 or lower.

[0073] The modified region preferably has an average water contact angle of 5° to 35°. The water contact angle is measured in accordance with JIS R3257:1999. If the average water contact angle is 35° or less, the water wettability is good. The average water contact angle is more preferably 30° or less. From the viewpoint of feasibility, the average water contact angle may be 5° or more.

[0074] The quartz glass substrate preferably has a modified region at least on its end face 23. Unlike the first main surface 21 and the second main surface 22, the end face 23 is not processed in steps S1, S3, and S4. Therefore, the modified region formed on the end face 23 is not removed in steps S1, S3, and S4. Thus, the cleaning efficiency of the end face 23 with a water-based cleaning agent can be improved even after steps S1, S3, or S4.

[0075] To form a modified region on the end face 23, the quartz glass substrate can be immersed in a chemical solution. By immersing the quartz glass substrate in the chemical solution, it is possible to remove the multilayer reflective film 3 that has been pre-formed on the second main surface 22, and at the same time, to form a modified region on both the second main surface 22 and the end face 23. By immersing the quartz glass substrate in the chemical solution, the removal of the multilayer reflective film 3 and the formation of the modified region can be carried out in a single process. [Examples]

[0076] Next, I will explain the experimental data.

[0077] (Experimental method) A conductive film 5 was formed on the first main surface 21 of a substrate 2 made of quartz glass containing TiO2 by sputtering. The conductive film 5 was a CrN film. Subsequently, a multilayer reflective film 3 was formed on the second main surface 22 of the substrate 2 by ion beam sputtering. The multilayer reflective film 3 consisted of 40 alternating layers of approximately 4 nm Si films and approximately 3 nm Mo films, followed by a final layer of approximately 4 nm Si film. Subsequently, a protective film of Ru, approximately 2.5 nm thick, was formed on the multilayer reflective film 3 by sputtering. A film-coated substrate was thus obtained. Small pieces with a side length of approximately 10 mm were cut from this film-coated substrate and used as test specimens.

[0078] Next, the chemical solution was prepared and filled into a container. The chemical solution was an aqueous solution containing 20% ​​by mass of KOH as a pH adjuster and 1% by mass of sodium metaperiodate (NaIO4) as an oxidizing agent. The chemical solution did not contain any specific metals or chelating agents. The pH of the chemical solution was 13.9. The pH of the chemical solution was measured using a portable pH / ORP / ion meter (Horiba Advanced Technology Co., Ltd.: D-73).

[0079] Next, the container holding the chemical solution was placed on a hot plate with a stirrer function, and the temperature of the chemical solution was adjusted to 60°C. Then, the test specimen was placed in the container, and while stirring the chemical solution, the test specimen was immersed in the 60°C solution for 20 minutes, after which the test specimen was removed. The removal of the multilayer reflective film 3 and the protective film was visually confirmed. Subsequently, fluorescence X-ray analysis (Rigaku Corporation: ZSX PrimusII) was used to confirm again that no film components remained. On the other hand, the conductive film 5 was visually confirmed to remain and not have been removed.

[0080] Next, the intensity of monovalent Si ions (I) on the quartz glass surface (second main surface 22) from which the multilayer reflective film 3 was removed with a chemical solution was measured by secondary ion mass spectrometry. Si The intensity of monovalent I ions against (I I ) intensity ratio (I I / I Si The intensity ratio (I) was measured. I / I Si For the measurement of ), a time-of-flight secondary ion mass spectrometry (TOF-SIMS) instrument (manufactured by ION-TOF, trade name TOF.SIMS 5) was used.

[0081] The measurement conditions were as follows: Irradiated primary ions: 209 Bi1 + Measurement range (area): Approximately 250 x 250 μm 2 Detected secondary ions: I - and Si - Sputter ions: Cs+ Sputtering area: Approximately 500 x 500 μm 2 .

[0082] Intensity ratio (I I / I Si The measurement results are shown in Figure 6. As shown in Figure 6, the iodine was immersed to a depth of approximately 3 nm from the surface of the quartz glass. At the surface of the quartz glass (depth 0 nm), the intensity ratio (I I / I Si ) is approximately 1.0 × 10 -1 The results were as follows. Figure 6 shows the measurement results for the second main surface 22, but the measurement results for the end face 23 were the same as those shown in Figure 6.

[0083] Furthermore, the water contact angle was measured on the quartz glass surface (second main surface 22) from which the multilayer reflective film 3 was removed using a chemical solution. A contact angle meter (Kyowa Interface Science Co., Ltd., product name: Portable Contact Angle Meter PCA-11) was used to measure the water contact angle. In addition to the water contact angle after treatment with the chemical solution, the water contact angle before treatment with the chemical solution (before the multilayer reflective film was formed) was also measured. The measurement results of the water contact angle are shown in Figure 7.

[0084] As shown in Figure 7, the average water contact angle of the quartz glass surface after treatment with the chemical solution was approximately 23°. On the other hand, the average water contact angle of the quartz glass surface before treatment with the chemical solution was approximately 42°. These results indicate that doping the quartz glass surface with iodine can improve the water wettability of the quartz glass surface.

[0085] The following additional information is disclosed regarding the above embodiments, etc. [Note 1] A glass substrate for a reflective mask blank, made of a quartz glass substrate, The quartz glass substrate has a modified region on at least a portion of its surface that is doped with iodine(I), The modified region is determined by the intensity of monovalent Si ions (I) measured by secondary ion mass spectrometry. Si The intensity of monovalent I ions against (I I ) intensity ratio (I I / ISi ) is 5.0 × 10 -3 ~1.0×10 2 This is a glass substrate for reflective mask blanks. [Note 2] The modified region is a glass substrate for a reflective mask blank as described in Appendix 1, wherein the average water contact angle is 5° to 35°. [Note 3] The glass substrate for a reflective mask blank according to Appendix 1 or 2, wherein the surface of the quartz glass substrate has a first main surface, a second main surface facing the opposite direction to the first main surface, and an end face perpendicular to the first main surface and the second main surface, and at least the end face has the modified region. [Note 4] The quartz glass substrate is a glass substrate for reflective mask blanks as described in any one of the appendices 1 to 3, containing 80% to 95% SiO2 and 4% to 17% TiO2, expressed in mass percent based on oxides. [Note 5] A manufacturing method for producing a glass substrate for a reflective mask blank as described in any one of the appendices 1 to 4, This includes supplying a chemical solution to at least a portion of the surface of the quartz glass substrate, A method for manufacturing a glass substrate for a reflective mask blank, comprising the above-mentioned chemical solution comprising a pH adjuster and at least one oxidizing agent selected from the group consisting of metaperiodic acid, metaperiodate salt, orthoperiodic acid, and orthoperiodate salt. [Note 6] The surface of the quartz glass substrate has a first main surface, a second main surface facing the opposite direction to the first main surface, and an end face perpendicular to the first and second main surfaces. The method for manufacturing a glass substrate for a reflective mask blank, as described in Appendix 5, comprising immersing the quartz glass substrate in the chemical solution to form the modified region at least on the end face. [Note 7] A method for manufacturing a glass substrate for a reflective mask blank according to Appendix 6, comprising immersing the quartz glass substrate in the chemical solution to remove a multilayer reflective film previously formed on the second main surface and to form the modified region on the second main surface and the end face. [Note 8] A method for manufacturing a glass substrate for a reflective mask blank, as described in any one of the appendices 5 to 7, wherein the pH of the chemical solution is 10 or more and 16 or less. [Note 9] The method for manufacturing a glass substrate for a reflective mask blank, as described in any one of appendices 5 to 8, wherein the pH adjusting agent is sodium hydroxide or potassium hydroxide. [Note 10] The method for manufacturing a glass substrate for a reflective mask blank according to any one of the appendices 5 to 9, wherein the chemical solution further comprises, in an amount of 0.0001 molar equivalent to 10 molar equivalent, at least one selected from the group consisting of metals and ions having a redox potential higher than that of chromium(VI), relative to the oxidizing agent. [Note 11] A method for manufacturing a glass substrate for a reflective mask blank, as described in any one of appendices 5 to 10, wherein the chemical solution further comprises an aminocarboxylic acid-based chelating agent, a hydroxy acid-based chelating agent, or a phosphonic acid-based chelating agent.

[0086] The glass substrate for reflective mask blanks and its manufacturing method described above have been explained, but the present invention is not limited to the embodiments described above. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These also naturally fall within the technical scope of this disclosure. [Explanation of symbols]

[0087] 1 Reflective Mask Blank 2. Substrate (quartz glass substrate) 21 1st main surface 22 Second main surface 23 End face

Claims

1. A glass substrate for a reflective mask blank, made of a quartz glass substrate, The quartz glass substrate has a modified region on at least a portion of its surface that is doped with iodine (I), The modified region is determined by the intensity of monovalent Si ions (I) measured by secondary ion mass spectrometry. Ｓｉ The intensity of monovalent I ions against (I Ｉ ) intensity ratio (I Ｉ / I Ｓｉ ) is 5.0 x 10 －３ ~1.0 x 10 ２ This is a glass substrate for reflective mask blanks.

2. The glass substrate for a reflective mask blank according to claim 1, wherein the modified region has an average water contact angle of 5° to 35°.

3. The surface of the quartz glass substrate has a first main surface, a second main surface facing the opposite direction to the first main surface, and an end face perpendicular to the first main surface and the second main surface, and at least the end face has the modified region, as described in claim 1 or 2.

4. The quartz glass substrate is expressed as SiO2 by mass percentage based on oxide. ２ It contains 80% to 95% of TiO ２ A glass substrate for a reflective mask blank according to claim 1 or 2, containing 4% to 17% of the above.

5. A manufacturing method for producing a glass substrate for a reflective mask blank according to claim 1 or 2, This includes supplying a chemical solution to at least a portion of the surface of the quartz glass substrate, A method for manufacturing a glass substrate for a reflective mask blank, comprising the above-mentioned chemical solution comprising a pH adjusting agent and at least one oxidizing agent selected from the group consisting of metaperiodic acid, metaperiodate salt, orthoperiodic acid, and orthoperiodate salt.

6. The surface of the quartz glass substrate has a first main surface, a second main surface facing the opposite direction to the first main surface, and an end face perpendicular to the first and second main surfaces. The method for manufacturing a glass substrate for a reflective mask blank according to claim 5, comprising immersing the quartz glass substrate in the chemical solution to form the modified region at least on the end face.

7. A method for manufacturing a glass substrate for a reflective mask blank according to claim 6, comprising immersing the quartz glass substrate in the chemical solution to remove a multilayer reflective film previously formed on the second main surface and to form the modified region on the second main surface and the end face.

8. The method for manufacturing a glass substrate for a reflective mask blank according to claim 5, wherein the pH of the chemical solution is 10 or more and 16 or less.

9. The method for manufacturing a glass substrate for a reflective mask blank according to claim 5, wherein the pH adjusting agent is sodium hydroxide or potassium hydroxide.

10. The method for manufacturing a glass substrate for a reflective mask blank according to claim 5, wherein the chemical solution further comprises, in an amount of 0.0001 molar equivalent to 10 molar equivalent, at least one selected from the group consisting of metals and ions having a redox potential higher than that of chromium (VI), relative to the oxidizing agent.

11. The method for manufacturing a glass substrate for a reflective mask blank according to claim 5, wherein the chemical solution further comprises an aminocarboxylic acid-based chelating agent, a hydroxy acid-based chelating agent, or a phosphonic acid-based chelating agent as a chelating agent.

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