Method for manufacturing reflective mask blanks and reflective masks

Abstract

The present invention provides a reflective mask blank and a method for manufacturing a reflective mask that can improve wafer transfer characteristics. [Solution] The reflective mask blank comprises at least a substrate 10 and a multilayer reflective film 50 formed on one main surface of the substrate 10 that reflects exposure light. The multilayer reflective film 50 has a periodic stacked structure 51 in which a low refractive index layer 20 and a high refractive index layer 30 are alternately stacked. When one set of the low refractive index layer 20 and the high refractive index layer 30 is considered as one cycle, the periodic stacked structure 51 has 25 cycles or less.

Description

TECHNICAL FIELD

[0001] The present invention relates to a reflective mask blank which is a material for a reflective mask used in the manufacture of semiconductor devices such as LSIs, and a method for manufacturing the reflective mask.

BACKGROUND ART

[0002] In the manufacturing process of semiconductor devices (semiconductor apparatuses), a photolithography technique is repeatedly used, in which a transfer mask is irradiated with exposure light, and a circuit pattern formed on the mask is transferred onto a semiconductor substrate (semiconductor wafer) via a reduction projection optical system. Conventionally, the wavelength of exposure light has been mainly 193 nm using argon fluoride (ArF) excimer laser light, and by adopting a process called multi-patterning that combines an exposure process and a processing process multiple times, patterns with dimensions smaller than the exposure wavelength have been finally formed.

[0003] However, with the continuous miniaturization of device patterns, the formation of even finer patterns has been required, and thus EUV lithography technology using extreme ultraviolet (hereinafter referred to as "EUV") light, which has a shorter wavelength than ArF excimer laser light, has come into use. EUV light is light with a wavelength of about 0.2 to 100 nm, and more specifically, light with a wavelength around 13.5 nm. EUV light has extremely low transmittance to substances, and conventional transmission-type projection optical systems and masks cannot be used, so reflective optical elements are used. Therefore, a reflective mask has also been proposed as a mask for pattern transfer.

[0004] A general reflective mask has a multilayer reflective film that reflects EUV light formed on a substrate, and an absorber film that absorbs EUV light is formed in a pattern on the multilayer reflective film. On the other hand, in general, the state before patterning the absorber film (including the state where a resist film is formed) is called a reflective mask blank, which is used as a material for the reflective mask.

[0005] A reflective mask blank has a basic structure comprising a substrate with low thermal expansion and a multilayer reflective film formed thereon that reflects EUV light, and generally further comprising an absorber film that absorbs EUV light formed on the multilayer reflective film.

[0006] As a multilayer reflective film, a multilayer reflective film is typically used that obtains the required reflectivity for EUV light by alternately stacking molybdenum (Mo) films and silicon (Si) films. Furthermore, a ruthenium (Ru) film is formed on the outermost layer of the multilayer reflective film as a protective layer. On the other hand, as an absorber film, tantalum (Ta) or similar material with a relatively large extinction coefficient for EUV light is used.

[0007] Generally, multilayer reflective films have a periodic stacked structure in which low-refractive-index layers and high-refractive-index layers are alternately stacked, and films made of alternating layers of molybdenum (Mo) and silicon (Si) are used.

[0008] A higher cycle count in the reflective film results in higher reflectivity and a greater contrast with the low-reflectivity areas where the absorber film is formed. For this reason, a Mo / Si periodic multilayer film (see, for example, Patent Document 1: Japanese Patent Application Publication No. 2017-116931) is commonly used as a multilayer reflective layer, in which Mo films and Si films are stacked alternately for about 40 to 60 cycles. However, further improvement of wafer transfer characteristics is required to achieve miniaturization. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2017-116931 [Overview of the project] [Problems that the invention aims to solve]

[0010] The present invention provides a reflective mask blank and a method for manufacturing a reflective mask that can improve wafer transfer characteristics. [Means for solving the problem]

[0011] Wafer transfer characteristics can be measured using NILS as an indicator. NILS (Normalized Image Log Slope) is, NILS = (dI / dx) / (W×Ith) (W is the desired pattern dimension, Ith is the threshold light intensity that gives W, and dI / dx is the gradient of the spatial image) The value shown is NILS, and the larger the NILS value, the steeper the optical image becomes, improving the dimensional controllability of the resist pattern on the wafer. Therefore, a larger NILS value is effective for forming finer patterns on the wafer.

[0012] One of the causes of worsening NILS is the shadowing effect of the light-shielding film. In EUV lithography, the shadowing effect occurs because the exposure light is not directly incident on the reflective mask; therefore, a portion of the incident exposure light is blocked by the sidewalls of the absorber pattern. This effect improves as the thickness of the absorber pattern decreases, but further improvements in transfer characteristics are needed.

[0013] The inventors of this invention discovered that one of the causes of NILS deterioration is that the reflective film is formed from numerous reflective surfaces, and the position of the image on the wafer differs depending on where the absorber film pattern is reflected from the reflective surface. Because the reflected image is formed by this overlap, increasing the number of cycles degrades the transfer characteristics despite the increase in reflectivity. The further away from the substrate side, i.e., the pattern formation surface, the greater the discrepancy between the reflected image and the image on the side closer to the absorber film, which has higher reflectivity. The inventors discovered that the substrate-side layer of the multilayer reflective film has little effect on increasing reflectivity but is a cause of the deterioration of transfer characteristics, and that the transfer characteristics can be improved by limiting the number of cycles to 25 or less, leading to the present invention.

[0014] [Concept 1] The reflective mask blank according to the present invention is circuit board and a multilayer reflective film formed on one main surface of the substrate and configured to reflect exposure light, at least comprising, the multilayer reflective film has a periodic laminated structure in which low refractive index layers and high refractive index layers are alternately laminated, when one set of the low refractive index layer and the high refractive index layer is defined as one cycle, the periodic laminated structure may have 25 cycles or less.

[0015] [Concept 2] In the reflective mask blank according to Concept 1, the number of cycles of the periodic laminated structure may be 20 or less.

[0016] [Concept 3] In the reflective mask blank according to Concept 1, the number of cycles of the periodic laminated structure may be 15 or less.

[0017] [Concept 4] In the reflective mask blank according to any one of Concepts 1 to 3, the high refractive index layer contains silicon (Si), the low refractive index layer may contain either molybdenum (Mo) or ruthenium (Ru).

[0018] [Concept 5] In the reflective mask blank according to any one of Concepts 1 to 4, a protective layer disposed above the multilayer reflective film may be further comprised.

[0019] [Concept 6] In the reflective mask blank according to any one of Concepts 1 to 5, an absorber film disposed above the multilayer reflective film may be further comprised.

[0020] [Concept 7] A method for manufacturing a reflective mask according to the present invention, the reflective mask blank described in any one of Concepts 1 to 6 may be used. [Advantageous Effects of the Invention]

[0021] The present invention provides a reflective mask blank that reduces the 3D effect by eliminating reflective interfaces far from the surface of the reflective multilayer film by setting the number of cycles to 25 or less, and that can produce a mask with high transfer characteristics during pattern transfer, as well as a method for manufacturing a reflective mask using the reflective mask blank. [Brief explanation of the drawing]

[0022] [Figure 1] A longitudinal cross-sectional view showing a reflective mask blank according to an embodiment of the present invention. [Figure 2] A longitudinal cross-sectional view showing a reflective mask blank according to an embodiment of the present invention. [Figure 3] A longitudinal cross-sectional view showing a patterned absorbent film in a reflective mask blank according to an embodiment of the present invention. [Figure 4] A longitudinal cross-sectional view showing a reflective mask blank according to an embodiment of the present invention, in which a resist film is provided. [Figure 5] A longitudinal cross-sectional view showing a reflective mask blank according to an embodiment of the present invention, in which a patterned resist film is used as an etching mask to form a pattern on a hard mask film. [Figure 6] A longitudinal cross-sectional view showing a reflective mask blank according to an embodiment of the present invention, in which a patterned hard mask film is used as an etching mask to form a pattern on an absorber film. [Modes for carrying out the invention]

[0023] The embodiments of the present invention will be described in more detail below.

[0024] As shown in Figure 1, the reflective mask blank of this embodiment has a substrate 10 and a multilayer reflective film 50 that reflects exposure light, formed on the substrate 10 (on one of the main surfaces (front surface) of the substrate 10). The reflective mask blank of this embodiment is suitable as a material (EUV mask blank) for a reflective mask (EUV mask) used in EUV lithography, which uses EUV light as the exposure light. The wavelength of EUV light used in EUV lithography, which uses EUV light as the exposure light, is 13 to 14 nm, and is usually light with a wavelength of about 13.5 nm.

[0025] The substrate 10 preferably has low thermal expansion characteristics for use with EUV light exposure, for example, a thermal expansion coefficient of ±2 × 10 -8 Within / ℃, preferably ±5 × 10 -9 It is preferable that the substrate is made of a material within the range of / ℃. Examples of such materials include titania-doped quartz glass (SiO2-TiO2 glass). Furthermore, it is preferable that the substrate 10 has a sufficiently flattened surface, and the surface roughness of the main surface of the substrate 10 is preferably 0.5 nm or less, more preferably 0.2 nm or less, in RMS value. Such surface roughness can be obtained by polishing the substrate 10. The size of the substrate 10 is preferably 152 mm square for the main surface and 6.35 mm thick. A substrate 10 of this size is a so-called 6025 substrate (a substrate with a main surface size of 6 inches square and a thickness of 0.25 inches).

[0026] The multilayer reflective film 50 is a film that reflects EUV light, which is the exposure light, in a reflective mask. The multilayer reflective film 50 may be provided in contact with one main surface of the substrate 10, or an underlayer may be provided between the substrate 10 and the multilayer reflective film 50. The multilayer reflective film 50 is a film that reflects EUV light, which is the exposure light, in a reflective mask.

[0027] The multilayer reflective film 50 is generally a multilayer film in which low refractive index materials and high refractive index materials are alternately stacked, and in this case, it is a film that reflects EUV light, which is exposure light. The multilayer reflective film 50 has a laminated portion composed of multiple layers in which layers with a relatively high refractive index with respect to EUV light and layers with a relatively low refractive index with respect to EUV light are alternately stacked. In this laminated portion, a material with a small extinction coefficient is preferred for the layer having a relatively high refractive index with respect to EUV light, for example, Si (silicon) is used, and a material with a relatively small extinction coefficient is preferred for the layer having a relatively low refractive index with respect to EUV light, for example, Mo (molybdenum) is preferably used in a periodically stacked manner. Here, the Si layer and the Mo layer may be layers formed of pure silicon and pure molybdenum, respectively, or they may contain other components. Furthermore, a diffusion prevention layer may be provided between the Si layer and the Mo layer. The diffusion prevention layer may be provided all between the Si layer and the Mo layer, or only in part.

[0028] Furthermore, the multilayer reflective film 50 may be a Si / Ru multilayer in which a Si (silicon) layer is alternately stacked as a high refractive index layer with a relatively high refractive index for EUV light, and a Ru (ruthenium) layer is alternately stacked as a low refractive index layer with a relatively low refractive index for EUV light.

[0029] The multilayer reflective film 50 has a periodic stacked structure 51 in which a high refractive index layer 30 with a relatively high refractive index for EUV light and a low refractive index layer 20 with a relatively low refractive index for EUV light are alternately stacked. The number of cycles of the periodic stacked structure 51 is preferably 25 cycles or less, particularly 20 cycles or less, or 15 cycles or less, because a smaller number of cycles improves NILS, which is an indicator of pattern accuracy. However, if the number of cycles is too small, the amount of light required for exposure becomes excessive, so the number of cycles is preferably 10 or more. NILS (Normalized Image Log Slope) is, NILS = (dI / dx) / (W×Ith) (W is the desired pattern dimension, Ith is the threshold light intensity that gives W, and dI / dx is the gradient of the spatial image) The value shown is NILS, and the larger the NILS value, the steeper the optical image becomes, improving the dimensional controllability of the resist pattern on the wafer. Therefore, a larger NILS value is effective for forming finer patterns on the wafer.

[0030] The high refractive index layer 30 contains silicon (Si) and may also contain at least one additive element selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H). It may also be composed of a multilayer structure consisting of a layer containing the additive element and a layer not containing the additive element. The thickness of the high refractive index layer 30 is preferably 2.5 nm or more and 5.5 nm or less, and more preferably 3 nm or more and 5 nm or less.

[0031] The low refractive index layer 20 consists of a material containing molybdenum (Mo), a material containing ruthenium (Ru), etc., and can be pure molybdenum, pure ruthenium (Ru), or an alloy of molybdenum (Ru) and molybdenum (Mo). The content of metals such as molybdenum and ruthenium in the low refractive index layer 20 is preferably 70 atomic percent or more, and more preferably 80 atomic percent or more. The thickness of the low refractive index layer 20 is preferably 1 nm or more and 4 nm or less, and more preferably 1.5 nm or more and 3.5 nm or less.

[0032] Furthermore, the thickness of the high refractive index layer 30 and the low refractive index layer 20 may be constant or may differ in each individual layer. The overall thickness of the periodic laminated structure 51 consisting of the high refractive index layer 30 / low refractive index laminate 20 is preferably 190 nm or less, more preferably 160 nm or less, even more preferably 120 nm or less, and preferably 50 nm or more.

[0033] Methods for forming the multilayer reflective film 50 include sputtering, which involves supplying power to a target to plasmaize (ionize) the atmospheric gas and perform sputtering, and ion beam sputtering, which involves irradiating the target with an ion beam. Sputtering methods include DC sputtering, which applies a DC voltage to the target, and RF sputtering, which applies a high-frequency voltage to the target. Sputtering is a film deposition method that utilizes the sputtering phenomenon caused by gas ions, by applying a voltage to the target while sputtering gas is introduced into a chamber, thereby ionizing the gas. Magnetron sputtering, in particular, offers advantages in terms of productivity. The power applied to the target can be DC or RF, and DC sputtering also includes pulse sputtering, where the negative bias applied to the target is briefly reversed to prevent charge-up of the target.

[0034] The multilayer reflective film 50 can be formed by sputtering using, for example, a sputtering apparatus capable of mounting multiple targets. Specifically, when silicon is used as the high refractive index layer 30, a silicon (Si) target is used to form a silicon (Si)-containing layer; when a molybdenum-containing layer is formed as the low refractive index layer 20, a molybdenum (Mo) target is used to form a molybdenum-containing layer; and when a ruthenium-containing layer is formed as the low refractive index layer 20, a ruthenium (Ru) target is used to form a ruthenium-containing layer. The sputtering gas can be a rare gas such as neon (Ne), argon (Ar), krypton (Kr), or xenon (Xe).

[0035] In the multilayer reflective film 50, the periodic stacked structure 51 may have either a high refractive index layer 30 or a low refractive index layer 20 on the substrate 10 side. Furthermore, another film, such as a diffusion prevention layer, may be formed between the periodic stacked structure 51 and the protective film 110 described later. Also, when the uppermost layer of the periodic stacked structure 51 is the low refractive index layer 20, a silicon-containing layer may be provided between the periodic stacked structure 51 and the protective film 110 described later.

[0036] In the multilayer reflective film 50, a carbide layer may be provided in addition to the periodic stacked structure 51. In this case, the carbide layer may be provided between the periodic stacked structure 51 and the protective film 110. Alternatively, the carbide layer may be provided between the protective film 110 and the absorber film 120, or the carbide layer may be provided on the upper surface of the absorber film 120. When providing the carbide layer, it can also be formed by reactive sputtering using a hydrocarbon gas such as methane (CH4) gas as a carbon source together with a noble gas.

[0037] In the multilayer reflective film 50, a nitride layer may be provided in addition to the periodic stacked structure 51. In this case, the nitride layer may be provided between the periodic stacked structure 51 and the protective film 110. Alternatively, the nitride layer may be provided between the protective film 110 and the absorber film 120, or the nitride layer may be provided on the upper surface of the absorber film 120. When providing the nitride layer, it can be formed by reactive sputtering using a nitrogen-containing gas such as nitrogen gas simultaneously with a noble gas.

[0038] In the multilayer reflective film 50, in addition to the periodic stacked structure 51, a layer containing boron(B) may be provided. In this case, the layer containing boron(B) may be provided between the periodic stacked structure 51 and the protective film 110. Alternatively, a layer containing boron(B) may be provided between the protective film 110 and the absorber film 120, or a layer containing boron(B) may be provided on the upper surface of the absorber film 120. When forming the layer containing boron(B), a target doped with boron(B) can be used.

[0039] As shown in Figure 1, a protective film 110 may be provided on the multilayer reflective film 50 to protect the multilayer reflective film 50. A material containing ruthenium (Ru) is preferably used as the material for the protective film 110. The protective film 110 is required to protect the multilayer reflective film 50 from various dry etching and cleaning processes in the reflective mask manufacturing process, the exposure environment when using the reflective mask, and cleaning processes in the regeneration process after use. A material containing additive elements such as niobium (Nb), zirconium (Zr), titanium (Ti), and rhodium (Rh) to provide resistance to various processes is preferably used, and a multilayer structure made of these materials may also be used.

[0040] The protective film 110 may be formed between it and the multilayer reflective film 50 via another film, but it is usually formed in contact with the multilayer reflective film 50.

[0041] The protective film 110 can be formed, for example, by sputtering. As a target, a ruthenium (Ru) target or a ruthenium (Ru) alloy target can be used to form a film or layer containing ruthenium (Ru). A niobium (Nb) target or a niobium (Nb) alloy target can be used to form a film or layer containing niobium (Nb). Specifically, a ruthenium (Ru) target, a niobium (Nb) target, or an alloy target of ruthenium (Ru) and niobium (Nb) can be appropriately selected and used. The protective film 110 (each layer constituting the protective film 110) can be formed by sputtering using a noble gas such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as the sputtering gas, or by reactive sputtering using a noble gas together with a reactive gas such as an oxygen-containing gas, nitrogen-containing gas, or carbon-containing gas. Examples of reactive gases include nitrogen oxides such as oxygen (O2), nitrogen (N2), nitrous oxide (N2O), nitric oxide (NO), and nitrogen dioxide (NO2), as well as carbon oxides such as carbon monoxide (CO) and carbon dioxide (CO2). There are no particular restrictions on the thickness of the protective film 110, but it is usually around 2 to 5 nm.

[0042] As shown in Figure 1, the reflective mask blank of this embodiment may further have an absorber film 120 on the protective film 110 that absorbs exposure light and functions as a pattern-forming film. It is common to manufacture a reflective mask (EUV mask) by forming a pattern on the absorber film 120 using a reflective mask blank (EUV mask blank) having a substrate 10, a multilayer reflective film 50, a protective film 110, and an absorber film 120 (see Figure 3).

[0043] Specific examples of such reflective mask blanks include one having a substrate 10, a multilayer reflective film 50 formed on one main surface of the substrate 10 that reflects exposure light, a protective film 110 formed on the multilayer reflective film 50, and an absorber film 120 formed on the protective film 110 that absorbs exposure light. A reflective mask can be manufactured from a reflective mask blank having a substrate 10, a multilayer reflective film 50 formed on one main surface of the substrate 10 that reflects exposure light, a protective film 110 formed on the multilayer reflective film 50, and a pattern (absorber pattern) of the absorber film 120 formed on the protective film 110 that absorbs exposure light. The absorber film 120 is a film that absorbs exposure light, specifically EUV light, and reduces its reflectivity.

[0044] The material of the absorber film 120 is not limited as long as it is a material that absorbs EUV light and can be patterned. Examples of materials for the absorber film 120 include materials containing tantalum (Ta) or chromium (Cr). Furthermore, materials containing Ta or Cr may also contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Examples of materials containing Ta include elemental Ta, TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, and TaCONB, which are tantalum compounds. Specific examples of materials containing Cr include elemental Cr, CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCNB, CrCOB, and CrCONB, which are chromium compounds.

[0045] The absorber film 120 can be formed by sputtering, and magnetron sputtering is preferred. Specifically, it can be formed by sputtering using metal targets such as chromium (Cr) targets and tantalum (Ta) targets, or metal compound targets such as chromium compound targets and tantalum compound targets (targets containing metals such as Cr and Ta, and oxygen (O), nitrogen (N), carbon (C), boron (B), etc.), and noble gases such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas as the sputtering gas, or by reactive sputtering using reactive gases such as oxygen-containing gas, nitrogen-containing gas, and carbon-containing gas together with the noble gas. There are no particular restrictions on the thickness of the absorber film 120, but it is usually around 40 to 80 nm.

[0046] On the side of the absorber film 120 that is separated from the substrate 10, preferably a hard mask film (etching mask film for the absorber film 120) 130 may be provided in contact with the absorber film 120 and have different etching characteristics from the absorber film 120 (see Figure 4). This hard mask film 130 is a film that functions as an etching mask when dry etching the absorber film 120. After the absorber pattern is formed, the hard mask film 130 may be left as part of the absorber film 120, for example, as a reflectance reduction layer to reduce the reflectance at wavelengths of light used in inspections such as pattern inspection, or it may be removed so that it does not remain on the reflective mask. Examples of materials for the hard mask film 130 include materials containing chromium (Cr). A hard mask film 130 formed from a Cr-containing material is particularly suitable when the absorber film 120 is formed from a material containing Ta but not Cr. When forming a layer (reflectance reduction layer) on the absorber film 120 that primarily functions to reduce the reflectance at wavelengths of light used in inspections such as pattern inspection, the hard mask film 130 can be formed on the reflectance reduction layer of the absorber film 120. The hard mask film 130 can be formed, for example, by magnetron sputtering. There are no particular restrictions on the thickness of the hard mask film 130, but it is usually around 5 to 20 nm.

[0047] As shown in Figures 1 to 5, the reflective mask blank may further have a conductive film 150 provided on another main surface (back surface) of the substrate 10, which is the surface opposite to one of the main surfaces, preferably in contact with the other main surface, for electrostatically chucking the reflective mask to the exposure apparatus.

[0048] The conductive film 150 preferably has a sheet resistance of 100 Ω / □ or less, and there are no particular restrictions on the material. Examples of materials for the conductive film 150 include materials containing tantalum (Ta) or chromium (Cr). Furthermore, materials containing tantalum (Ta) or chromium (Cr) may also contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Examples of materials containing tantalum (Ta) include elemental Ta, TaO, TaN, TaON, TaC, TaCO, TaCN, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCOB, TaCNB, and TaCONB. Specific examples of materials containing chromium (Cr) include elemental Cr, CrO, CrN, CrON, CrC, CrCO, CrCN, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCOB, CrCNB, and CrCONB.

[0049] The thickness of the conductive film 150 is not particularly limited, as long as it functions for electrostatic chucks, but it is usually around 20 to 300 nm. The thickness of the conductive film 150 is preferably formed after it has been formed as a reflective mask, and especially after the pattern (absorber pattern) of the absorber film 120 has been formed, so that the film stress is balanced with the pattern (absorber pattern) of the multilayer reflective film 50 and the absorber film 120. The conductive film 150 may be formed before forming the multilayer reflective film 50, or after all the films on the multilayer reflective film 50 side of the substrate 10 have been formed, or a portion of the films on the multilayer reflective film 50 side of the substrate 10 may be formed first, then the conductive film 150 may be formed, and then the remaining films on the multilayer reflective film 50 side of the substrate 10 may be formed. The conductive film 150 can be formed, for example, by magnetron sputtering.

[0050] As shown in Figure 4, the reflective mask blank may further have a resist film 140 formed on the side furthest from the substrate 10. In this embodiment, the resist film 140 is preferably an electron beam (EB) resist. Furthermore, it is preferable that the resist film 140 can be removed by SPM cleaning.

[0051] A reflective mask comprising a substrate 10, a multilayer reflective film 50, a protective film 110, and a pattern of an absorber film 120 can be manufactured from the reflective mask blank of the present invention. The reflective mask can be manufactured by conventional methods.

[0052] For example, if a hard mask film 130 is not formed on the absorber film 120, a resist film 140 is formed in contact with the film furthest from the substrate 10 of the reflective photomask blank, for example, the side of the absorber film 120 that is furthest from the substrate 10. Then, a reflective photomask can be manufactured by patterning the absorber film 120 using a resist pattern obtained by patterning the resist film 140 as an etching mask, and then patterning the absorber film using a gas that can etch the absorber film 120, such as a chlorine-based gas or a fluorine-based gas. In the manufacture of a reflective photomask, the resist pattern can be removed with sulfuric acid peroxide (SPM).

[0053] When a hard mask film 130 is formed on an absorber film 120, a resist film 140 is formed in contact with the film furthest from the substrate 10 of the reflective photomask blank, for example, the hard mask film 130 on the side furthest from the substrate 10. Then, using the resist pattern obtained by patterning the resist film 140 as an etching mask, a pattern is formed on the hard mask film 130 by dry etching using a gas that can etch the hard mask film 130, such as a chlorine-based gas or a fluorine-based gas (see Figure 5). After that, the hard mask film 130 is used as an etching mask with a gas that does not easily etch the hard mask film 130 but easily etches the absorber film 120, and the absorber film 120 is patterned to manufacture a reflective photomask (see Figure 6). In the manufacture of a reflective photomask, the resist pattern can be removed with sulfuric acid peroxide (SPM). The hard mask may be removed or left in place and used as part of the absorber film 120. [Examples]

[0054] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0055] The NILS and reflectivity were calculated when a Mo layer and a Si layer were laminated on a glass substrate 10.

[0056] [Example 1] On a glass substrate 10, 3 nm Mo and 4 nm Si were alternately stacked as a multilayer reflective film 50, and the number of cycles of the periodic stacked structure 51 was set to 25. In Example 1, the periodic stacked structure 51 constitutes the multilayer reflective film 50. A 2 nm Ru was provided as a protective film 110 on the multilayer reflective film 50, and a 60 nm TaN was provided as an absorber film 120 on the protective film 110. A pattern with a wafer pitch of 32 nm and a line of 16 nm L / S (line and space) was formed on the absorber film 120 of the reflective mask blank obtained in this way, and the NILS was calculated with an exposure light of 13.53 nm, a reduction ratio of 4 times, an incident angle of 6 degrees, and an NA of 0.33, resulting in a value of 2.761.

[0057] [Example 2] On a glass substrate 10, 3 nm Mo and 4 nm Si were alternately stacked as a multilayer reflective film 50, and the number of cycles of the periodic stacked structure 51 was set to 20. In Example 2 as well, the periodic stacked structure 51 constitutes the multilayer reflective film 50. A 2 nm Ru was provided as a protective film 110 on the multilayer reflective film 50, and a 60 nm TaN was provided as an absorber film 120 on the protective film 110. A pattern with a wafer pitch of 32 nm and a line of 16 nm L / S (line and space) was formed on the absorber film 120 of the reflective mask blank obtained in this way, and the NILS was calculated with an exposure light of 13.53 nm, a reduction ratio of 4 times, an incident angle of 6 degrees, and an NA of 0.33, resulting in a value of 2.771.

[0058] [Example 3] On a glass substrate 10, 3 nm Mo and 4 nm Si were alternately stacked as a multilayer reflective film 50, and the number of cycles of the periodic stacked structure 51 was set to 15. In Example 3 as well, the periodic stacked structure 51 constitutes the multilayer reflective film 50. A 2 nm Ru was provided as a protective film 110 on the multilayer reflective film 50, and a 60 nm TaN was provided as an absorber film 120 on the protective film 110. A pattern with a wafer pitch of 32 nm and a line of 16 nm L / S (line and space) was formed on the absorber film 120 of the reflective mask blank obtained in this way, and the NILS was calculated with an exposure light of 13.53 nm, a reduction ratio of 4 times, an incident angle of 6 degrees, and an NA of 0.33, resulting in a value of 2.785.

[0059] [Example 4] On a glass substrate 10, 3 nm Mo and 4 nm Si were alternately stacked as a multilayer reflective film 50, and the number of cycles of the periodic stacked structure 51 was set to 10. In Example 4 as well, the periodic stacked structure 51 constitutes the multilayer reflective film 50. A 2 nm Ru was provided as a protective film 110 on the multilayer reflective film 50, and a 60 nm TaN was provided as an absorber film 120 on the protective film 110. Assuming that a pattern with a wafer pitch of 32 nm and a line of 16 nm L / S (line and space) was formed on the absorber film 120 of the reflective mask blank obtained in this way, the NILS was calculated to be 2.821 with an exposure light of 13.53 nm, a reduction ratio of 4 times, an incident angle of 6 degrees, and an NA of 0.33.

[0060] [Comparative Example 1] On a glass substrate 10, 3 nm Mo and 4 nm Si were alternately stacked as a multilayer reflective film 50, and the number of cycles of the periodic stacked structure 51 was set to 40. In Comparative Example 1, the periodic stacked structure 51 also constitutes the multilayer reflective film 50. A 2 nm Ru was provided as a protective film 110 on the multilayer reflective film 50, and a 60 nm TaN was provided as an absorber film 120 on the protective film 110. Assuming that a pattern with a wafer pitch of 32 nm and a line of 16 nm L / S (line and space) was formed on the absorber film 120 of the reflective mask blank obtained in this way, the NILS was calculated to be 2.744 with an exposure light of 13.53 nm, a reduction ratio of 4 times, an incident angle of 6 degrees, and an NA of 0.33. [Explanation of Symbols]

[0061] 10 circuit boards 20 Low refractive index layer 30 High refractive index layer 50 Multilayer reflective coating 51 Periodic layered structure

Claims

1. circuit board and A multilayer reflective film that reflects exposure light is formed on one of the main surfaces of the substrate, It has at least the following features: The multilayer reflective film has a periodic stacked structure in which low refractive index layers and high refractive index layers are alternately stacked. A reflective mask blank in which the periodic stacked structure consists of 25 cycles or less, with one pair of low-refractive-index layers and one high-refractive-index layer considered as one cycle.

2. The reflective mask blank according to claim 1, wherein the number of cycles of the periodic stacked structure is 20 or less.

3. The reflective mask blank according to claim 1, wherein the number of cycles of the periodic stacked structure is 15 or less.

4. The high refractive index layer contains silicon (Si), A reflective mask blank according to any one of claims 1 to 3, wherein the low refractive index layer comprises either molybdenum (Mo) or ruthenium (Ru).

5. A reflective mask blank according to any one of claims 1 to 3, further comprising a protective layer provided above the multilayer reflective film.

6. A reflective mask blank according to any one of claims 1 to 3, further comprising an absorbent film provided above the multilayer reflective film.

7. A method for manufacturing a reflective mask, characterized by using a reflective mask blank according to any one of claims 1 to 3.

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