Reflective mask blanks and reflective masks

Abstract

To provide a technology that improves the etching resistance of the protective film, suppresses mixing of the protective film and the multilayer reflective film, prevents surface roughening of the protective film, and suppresses elemental diffusion to the surface of the protective film. [Solution] The reflective mask blank comprises, in this order, a substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs the EUV light. The protective film contains Rh as its main component. The multilayer reflective film has an uppermost layer that is closest to the protective film and contains Si and N. The elemental ratio of N to Si (N / Si) of the uppermost layer is greater than 0.00 and less than 1.50, and the elemental ratio of O to Si (O / Si) is 0.00 or more and less than 0.44.

Description

[Technical Field]

[0001] This disclosure relates to reflective mask blanks and reflective masks. [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, a reflective mask is used. The reflective mask comprises, in this order, a substrate such as a glass substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs EUV light. The absorbing film may also be a phase-shifting film that shifts the phase of the EUV light. An aperture pattern is formed on the absorbing film. In EUVL, the aperture pattern of the absorbing film is transferred to a target substrate such as a semiconductor substrate. Transferring includes transferring at a reduced size.

[0004] The reflective mask described in Patent Document 1 comprises, in this order, a substrate, a multilayer reflective film, a reflectance reduction suppression film, a blocking film, an etching stopper film, and an absorption film. The reflectance reduction suppression film is made of Si or the like. The blocking film is made of Nb or the like and suppresses the diffusion of Si, which constitutes the reflectance reduction suppression film, into the etching stopper film. The etching stopper film is made of Ru or a Ru alloy. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-170931 [Overview of the project] [Problems that the invention aims to solve]

[0006] A reflective mask comprises, in this order, a substrate such as a glass substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs EUV light. The protective film protects the multilayer reflective film from etching gas when an aperture pattern is formed on the absorbing film using an etching gas. The etching gas is, for example, a halogen-based gas, an oxygen-based gas, or a mixture thereof.

[0007] The protective film remains on the multilayer reflective film even when exposed to etching gas. The protective film in Patent Document 1 is made of Ru or a Ru alloy. When the main component of the protective film is Ru, the etching resistance of the protective film was insufficient. In particular, when an oxygen-based gas is used as the etching gas (including when a mixed gas is used), the etching resistance of the protective film was insufficient.

[0008] One aspect of this disclosure provides a technology that improves the etching resistance of a protective film and suppresses mixing of the protective film and the multilayer reflective film, surface roughening of the protective film, and elemental diffusion to the surface of the protective film. [Means for solving the problem]

[0009] A reflective mask blank according to one aspect of the present disclosure comprises, in this order, a substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs the EUV light. The protective film contains Rh as its main component. The multilayer reflective film has an uppermost layer closest to the protective film that contains Si and N. The uppermost layer has an elemental ratio of N to Si (N / Si) greater than 0.00 and less than 1.50, and an elemental ratio of O to Si (O / Si) of 0.00 or more and less than 0.44. [Effects of the Invention]

[0010] According to one aspect of the present disclosure, by using a protective film containing Rh as a main component, the etching resistance of the protective film can be improved. Further, by keeping the element ratios (N / Si, O / Si) in the outermost layer of the multilayer reflective film within the above ranges, mixing of the protective film and the multilayer reflective film, roughening of the surface of the protective film, and element diffusion to the surface of the protective film can be suppressed.

Brief Description of Drawings

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing a reflective mask blank according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a reflective mask according to one embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing an example of EUV light reflected by the reflective mask of FIG. 2. [Figure 4] FIG. 4 is a flowchart showing a method for manufacturing a reflective mask blank according to one embodiment. [Figure 5] FIG. 5 is a flowchart showing a method for manufacturing a reflective mask according to one embodiment. [Figure 6] It is a cross-sectional view showing a reflective mask blank according to a modified example. [Figure 7] FIG. 7 is a diagram showing a STEM image and an elemental mapping image of a reflective mask blank according to Example 1. [Figure 8] FIG. 8 is a diagram showing a STEM image and an elemental mapping image of a reflective mask blank according to Example 4. [Figure 9] FIG. 9 is a diagram showing a STEM image and an elemental mapping image of a reflective mask blank according to Example 5. [Figure 10] FIG. 10 is a diagram showing a STEM image and an elemental mapping image of a reflective mask blank according to Example 8. [Figure 11] FIG. 11 is a distribution diagram of the elemental concentration of the reflective mask according to Example 8.

Embodiments for Carrying Out the Invention

[0012] The embodiments for implementing this disclosure will be described below with reference to the drawings. In each drawing, identical or corresponding components will be denoted by the same reference numeral, and their descriptions may be omitted. In the specification, the numeral "~" indicating a numerical range means that the numbers before and after it are included as the lower and upper limits, respectively.

[0013] In Figures 1 to 3, the X-axis, Y-axis, and Z-axis directions are mutually orthogonal. The Z-axis direction is perpendicular to the first main surface 10a of the substrate 10. The X-axis direction is perpendicular to the incident surface of EUV light (the surface containing the incident and reflected rays). As shown in Figure 3, the incident rays are tilted in the positive Y-axis direction as they move in the negative Z-axis direction, and the reflected rays are tilted in the positive Y-axis direction as they move in the positive Z-axis direction.

[0014] Referring to Figure 1, a reflective mask blank 1 according to one embodiment will be described. The reflective mask blank 1 has, for example, a substrate 10, a multilayer reflective film 11, a protective film 12, an absorption film 13, and an etching mask film 14 in this order. The multilayer reflective film 11, the protective film 12, the absorption film 13, and the etching mask film 14 are formed on the first main surface 10a of the substrate 10 in this order. Note that the reflective mask blank 1 only needs to have at least the substrate 10, the multilayer reflective film 11, the protective film 12, and the absorption film 13.

[0015] The reflective mask blank 1 may further have a functional film not shown in Figure 1. For example, the reflective mask blank 1 may have a conductive film on the side opposite to the multilayer reflective film 11, with respect to the substrate 10. The conductive film is formed on the second main surface 10b of the substrate 10. The second main surface 10b is the surface facing the opposite direction from the first main surface 10a. The conductive film is used, for example, to attract the reflective mask 2 to the electrostatic chuck of the exposure apparatus.

[0016] The reflective mask blank 1, although not shown, may have a buffer film between the protective film 12 and the absorption film 13. The buffer film protects the protective film 12 from etching gases that form an opening pattern 13a in the absorption film 13. The buffer film is etched more slowly than the absorption film 13. Unlike the protective film 12, the buffer film ultimately has the same opening pattern as the opening pattern 13a of the absorption film 13.

[0017] Next, a reflective mask 2 according to one embodiment will be described with reference to Figures 2 and 3. The reflective mask 2 is fabricated, for example, using the reflective mask blank 1 shown in Figure 1, and includes an opening pattern 13a in the absorption film 13. The etching mask film 14 shown in Figure 1 is removed after the opening pattern 13a is formed in the absorption film 13.

[0018] In EUVL, the aperture pattern 13a of the absorption film 13 is transferred to a target substrate such as a semiconductor substrate. Transfer includes transfer in a reduced size. The substrate 10, multilayer reflective film 11, protective film 12, absorption film 13, and etching mask film 14 will be described below in this order.

[0019] The substrate 10 is, for example, a glass substrate. The material of the substrate 10 is preferably quartz glass containing TiO2. Compared to general soda-lime glass, quartz glass has a smaller coefficient of linear expansion and less dimensional change due to temperature changes. The quartz glass may contain 80% to 95% by mass of SiO2 and 4% to 17% by mass of TiO2. When the TiO2 content is 4% to 17% by mass, the coefficient of linear expansion at room temperature is almost 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. The material of the substrate 10 may also be crystallized glass with a β-quartz solid solution precipitated, silicon, or metal, etc.

[0020] The substrate 10 has a first main surface 10a and a second main surface 10b facing the opposite direction from the first main surface 10a. A multilayer reflective film 11 or the like is formed on the first main surface 10a. In plan view (viewed along the Z-axis), the size of the substrate 10 is, for example, 152 mm in length and 152 mm in width. The length and width dimensions may be 152 mm or more. The first main surface 10a and the second main surface 10b each have, for example, a square quality assurance area in the center. The size of the quality assurance area is, for example, 142 mm in length and 142 mm in width. The quality assurance area of ​​the first main surface 10a preferably has a root mean square roughness Rq of 0.15 nm or less and a flatness of 100 nm or less. Furthermore, it is preferable that the quality assurance area of ​​the first main surface 10a does not have defects that cause phase defects.

[0021] The multilayer reflective film 11 reflects EUV light. The multilayer reflective film 11 is, for example, made by alternately stacking high refractive index layers and low refractive index layers. The material of the high refractive index layer is, for example, silicon (Si), and the material of the low refractive index layer is, for example, molybdenum (Mo), and a Mo / Si multilayer reflective film is used. In addition, Ru / Si multilayer reflective films, Mo / Be multilayer reflective films, Mo compound / Si compound multilayer reflective films, Si / Mo / Ru multilayer reflective films, Si / Mo / Ru / Mo multilayer reflective films, Si / Ru / Mo / Ru multilayer reflective films, and Si / Ru / Mo multilayer reflective films can also be used as the multilayer reflective film 11.

[0022] The film thickness of each layer constituting the multilayer reflective film 11 and the number of repeating units of the layer can be appropriately selected according to the material of each layer and its reflectance to EUV light. In the case of a Mo / Si multilayer reflective film 11, to achieve a reflectance of 60% or more for EUV light with an incident angle θ (see Figure 3) of 6°, a Mo layer with a film thickness of 2.3±0.1 nm and a Si layer with a film thickness of 4.5±0.1 nm should be stacked so that the number of repeating units is between 30 and 60. Preferably, the multilayer reflective film 11 has a reflectance of 60% or more for EUV light with an incident angle θ of 6°. More preferably, the reflectance is 65% or more.

[0023] The film formation method for each layer constituting the multilayer reflective film 11 is, for example, DC sputtering method, magnetron sputtering method, ion beam sputtering method, or the like. When forming a Mo / Si multilayer reflective film using the ion beam sputtering method, an example of the film formation conditions for each of the Mo layer and the Si layer is as follows. <Film formation conditions for Si layer> Target: Si target, Sputtering gas: Ar gas, Gas pressure: 0.013 Pa to 0.027 Pa, Ion acceleration voltage: 300 V to 1500 V, Film formation rate: 0.030 nm / sec to 0.300 nm / sec, Film thickness of Si layer: 4.5 ± 0.1 nm, <Film formation conditions for Mo layer> Target: Mo target, Sputtering gas: Ar gas, Gas pressure: 0.013 Pa to 0.027 Pa, Ion acceleration voltage: 300 V to 1500 V, Film formation rate: 0.030 nm / sec to 0.300 nm / sec, Film thickness of Mo layer: 2.3 ± 0.1 nm, <Repeating unit of Si layer and Mo layer> Number of repeating units: 30 to 60 (preferably 40 to 50).

[0024] The uppermost layer of the multilayer reflective film 11 is formed, for example, by at least nitriding the Si layer after forming the Si layer. The Si layer is nitrided, for example, by exposing it to a plasmaized nitrogen-containing gas. Hereinafter, the nitriding using a plasmaized nitrogen-containing gas is also referred to as radical nitriding. When radical nitriding is performed after forming the Si layer, the uppermost layer of the multilayer reflective film 11 means the layer that has been radical nitrided. After radical nitriding, the Si layer may be oxidized by exposing it to an air atmosphere. Hereinafter, the oxidation using an air atmosphere is also referred to as air oxidation.

[0025] Note that the uppermost layer of the multilayer reflective film 11 may be formed by a reactive sputtering method. The reactive sputtering method can control the element ratio (N / Si) of N and Si in the uppermost layer by the content rate of N2 gas in the sputtering gas. Also, the reactive sputtering method can control the element ratio (O / Si) of O and Si in the uppermost layer by the content rate of O2 gas in the sputtering gas.

[0026] The multilayer reflective film 11 has an uppermost layer that is closest to the protective film 12 and contains Si and N. The uppermost layer has an elemental ratio of N to Si (N / Si) greater than 0.00 and less than 1.50 (0.00 < (N / Si) < 1.50), and an elemental ratio of O to Si (O / Si) greater than or equal to 0.00 and less than 0.44 (0.00 ≤ (O / Si) < 0.44). In this specification, elemental ratio refers to molar ratio.

[0027] As will be explained in detail in the Examples section, by keeping the elemental ratio (N / Si, O / Si) of the uppermost layer of the multilayer reflective film 11 within the above range, mixing of the protective film 12 and the multilayer reflective film 11, surface roughness of the protective film 12, and elemental diffusion to the surface of the protective film 12 can be suppressed.

[0028] Here, the mixing of the protective film 12 and the multilayer reflective film 11 is a phenomenon that occurs when the protective film 12 is formed. On the other hand, elemental diffusion to the surface of the protective film 12 is a phenomenon in which easily oxidized elements (for example, Si contained in the uppermost layer) diffuse to the surface of the protective film 12 when the protective film 12 is exposed to the oxygen-based gas when an opening pattern 13a is formed in the absorption film 13 using an oxygen-based gas.

[0029] The elemental ratio (N / Si) in the uppermost layer of the multilayer reflective film 11 is greater than 0.00 and less than 1.50. A larger elemental ratio (N / Si) suppresses mixing between the protective film 12 and the multilayer reflective film 11, as well as elemental diffusion to the surface of the protective film 12. Furthermore, an elemental ratio (N / Si) of less than 1.50 suppresses a decrease in reflectivity to EUV light. The elemental ratio (N / Si) is preferably greater than 0.10 and less than 0.50, and more preferably greater than 0.10 and less than 0.30.

[0030] The elemental ratio (O / Si) in the uppermost layer of the multilayer reflective film 11 is 0.00 or more and less than 0.44. The larger the elemental ratio (O / Si), the more the mixing of the protective film 12 and the multilayer reflective film 11, and the more the diffusion of elements to the surface of the protective film 12 can be suppressed. Also, by having an elemental ratio (O / Si) of less than 0.44, surface roughness of the protective film 12 can be suppressed. The elemental ratio (O / Si) is preferably 0.00 or more and less than 0.40, more preferably 0.00 or more and less than 0.30, even more preferably 0.00 or more and less than 0.25, particularly preferably 0.00 or more and less than 0.10, and most preferably 0.00.

[0031] The protective film 12 is formed between the multilayer reflective film 11 and the absorption film 13, protecting the multilayer reflective film 11. The protective film 12 protects the multilayer reflective film 11 from etching gases that form an opening pattern 13a (see Figure 2) in the absorption film 13. The protective film 12 remains on the multilayer reflective film 11 even when exposed to etching gases and is not removed.

[0032] Etching gases are, for example, halogenated gases, oxygenated gases, or mixtures thereof. Examples of halogenated gases include chlorinated gases and fluorinated gases. Chlorinated gases include, for example, Cl2 gas, SiCl4 gas, CHCl3 gas, CCl4 gas, BCl3 gas, or mixtures thereof. Fluorinated gases include, for example, CF4 gas, CHF3 gas, SF6 gas, BF3 gas, XeF2 gas, or mixtures thereof. Oxygenated gases include O2 gas, O3 gas, or mixtures thereof.

[0033] The ratio (ER2 / ER1) of the etching rate ER2 of the absorption film 13 to the etching rate ER1 of the protective film 12 is also called the selectivity ratio (ER2 / ER1). The larger the selectivity ratio (ER2 / ER1), the better the processability of the absorption film 13. The selectivity ratio (ER2 / ER1) is preferably 5.0 or higher, more preferably 10 or higher, and even more preferably 30 or higher. The selectivity ratio (ER2 / ER1) is preferably 200 or lower, and more preferably 100 or lower.

[0034] The protective film 12 contains Rh as its main component. The protective film 12 contains Rh in an amount of 50 at% to 100 at%. By using Rh instead of Ru as the main component of the protective film 12, the etching resistance of the protective film 12 can be improved. In particular, the etching resistance of the protective film 12 can be improved when an oxygen-based gas is used as the etching gas (including when a mixed gas is used).

[0035] Rh is more readily interdiffused with Si than Ru. Therefore, when the protective film 12 contains Rh as its main component, the elemental ratio (N / Si, O / Si) in the uppermost layer of the multilayer reflective film 11 becomes more important than when the protective film 12 contains Ru as its main component. If the elemental ratio (N / Si, O / Si) in the uppermost layer of the multilayer reflective film 11 is within the above range, mixing between the uppermost layer of the multilayer reflective film 11 and the protective film 12 can be suppressed. By suppressing mixing, a decrease in etching resistance and a decrease in reflectivity to EUV light can be suppressed.

[0036] The protective film 12 may contain only Rh as a metallic element, but it is preferable that it contains an Rh compound. The Rh compound may contain, in addition to Rh, at least one element Z1 selected from the group consisting of Ru, Nb, Mo, Ta, Ir, Pd, Zr, Y, and Ti. Preferably, the protective film 12 contains only Rh as a metallic element, or contains Rh plus at least one of Ru and Pd.

[0037] By adding Ru, Nb, Mo, Zr, Y, or Ti to Rh, the extinction coefficient can be reduced while suppressing the increase in refractive index, thereby improving the reflectivity to EUV light. Furthermore, by adding Ta, Ir, Pd, or Y to Rh, the durability against etching gas and / or sulfuric acid peroxide can be improved. Sulfuric acid peroxide is used for removing the resist film or cleaning the reflective mask 2, as described later.

[0038] The elemental ratio of Z1 (all Z1) to Rh (Z1:Rh) is preferably 1:99 to 1:1. If the ratio value (Z1 / Rh) is 1 / 99 or greater, the reflectivity to EUV light is good. If the ratio value (Z1 / Rh) is 1 or less, the etching resistance of the protective film 12 is good. The elemental ratio of Z1 to Rh (Z1:Rh) is more preferably 3:10 to 1:1.

[0039] When Z1 is Ru, the elemental ratio of Ru to Rh (Ru / Rh) is preferably greater than 0.0 and less than 1.0 (0.0 < (Ru / Rh) < 1.0), and more preferably greater than 0.3 and less than 0.5 (0.3 < (Ru / Rh) < 0.5). If the elemental ratio (Ru / Rh) is greater than 0.0, the reflectivity to EUV light is good. If the elemental ratio (Ru / Rh) is less than 1.0, the etching resistance is good.

[0040] When Z1 is Pd, the elemental ratio of Pd to Rh (Pd / Rh) is preferably greater than 0.00 and less than 1.0 (0.00 < (Pd / Rh) < 1.0), and more preferably greater than 0.01 and less than 0.1 (0.01 < (Pd / Rh) < 0.1). If the elemental ratio (Ru / Rh) is greater than 0.00, etching resistance is good. If the elemental ratio (Ru / Rh) is less than 1.0, reflectivity to EUV light is good.

[0041] The Rh compound may contain, in addition to Rh, at least one element Z2 selected from the group consisting of N, O, C, and B. While element Z2 reduces the etching resistance of the protective film 12, it can suppress crystallization of the protective film 12, allowing for the formation of a smooth surface. Rh compounds containing element Z2 have an amorphous or microcrystalline structure. When the Rh compound has an amorphous or microcrystalline structure, the X-ray diffraction profile of the Rh compound does not have a distinct peak.

[0042] When the Rh compound contains Z2 in addition to Rh, the content of Rh (where the content of Z1 is 0 at%) or the total content of Rh and Z1 is preferably 40 at% to 99 at%, and the total content of Z2 is preferably 1.0 at% to 60 at%. When the Rh compound contains Z2 in addition to Rh, the content of Rh (where the content of Z1 is 0 at%) or the total content of Rh and Z1 is more preferably 80 at% to 99 at%, and the total content of Z2 is more preferably 1.0 at% to 20 at%.

[0043] The Rh compound contains 90 at% or more of Rh, contains at least one of Z1 and Z2, and has a film density of 10.0 g / cm 3 ~14.0 g / cm 3 has an amorphous structure or a microcrystalline structure. The film density of the protective film 12 is preferably 11.0 g / cm 3 ~13.0 g / cm 3 is. Incidentally, the protective film 12 contains 100 at% of Rh and has a film density of 11.0 g / cm 3 ~12.0 g / cm 3 has an amorphous structure or a microcrystalline structure. The film density of the protective film 12 is measured using the X-ray reflectivity method.

[0044] The thickness of the protective film 12 is preferably 1.0 nm to 4.0 nm, more preferably 2.0 nm to 3.5 nm, and even more preferably 2.5 nm to 3.0 nm. If the thickness of the protective film 12 is 1.0 nm or more, the etching resistance is good. Also, if the thickness of the protective film 12 is 4.0 nm or less, the reflectivity to EUV light is good.

[0045] The film density of the protective film 12 is preferably 10.0 g / cm 3 ~14.0 g / cm 3 is. If the film density of the protective film 12 is 10.0 g / cm 3 or more, the etching resistance is good. Also, if the film density of the protective film 12 is 14.0 g / cm 3 or less, the decrease in reflectivity to EUV light can be suppressed.

[0046] The upper surface of the protective film 12, that is, the surface on which the absorption film 13 of the protective film 12 is formed, preferably has a root mean square roughness Rq of 0.20 nm or less, more preferably 0.17 nm or less. If the root mean square roughness Rq is 0.20 nm or less, an absorption film 13 or the like can be smoothly formed on the protective film 12. Further, scattering of EUV light can be suppressed, and the reflectivity with respect to EUV light can be improved. The root mean square roughness Rq is preferably 0.05 nm or more.

[0047] The method for forming the protective film 12 is, for example, a DC sputtering method, a magnetron sputtering method, an ion beam sputtering method, or the like. When forming a Rh film using the DC sputtering method, an example of the film formation conditions is as follows. <Film formation conditions of Rh film> Target: Rh target, Sputtering gas: Ar gas, Gas pressure: 1.0×10 -2 Pa to 1.0×10 0 Pa, Output density of target: 1.0 W / cm 2 to 8.5 W / cm 2 , Film formation rate: 0.020 nm / sec to 1.000 nm / sec, Film thickness of Rh film: 1.0 nm to 4.0 nm.

[0048] When forming a Rh film, as the sputtering gas, N2 gas or a mixed gas of Ar gas and N2 may be used. The volume ratio of N2 gas in the sputtering gas (N2 / (Ar + N2)) is 0.05 or more and 1.0 or less.

[0049] When forming a RhO film using the DC sputtering method, an example of the film formation conditions is as follows. <Film formation conditions of RhO film> Target: Rh target, Sputtering gas: O2 gas or a mixed gas of Ar gas and O2, Volume ratio of O2 gas in the sputtering gas (O2 / (Ar + O2)): 0.05 to 1.0, Gas pressure: 1.0×10 -2 Pa to 1.0×10 0 Pa, Output density of target: 1.0 W / cm 2 to 8.5 W / cm 2 , Film formation rate: 0.020 nm / sec to 1.000 nm / sec, Film thickness of RhO film: 1.0 nm to 4.0 nm.

[0050] When forming a RhRu film using the DC sputtering method, an example of the film formation conditions is as follows. <Film formation conditions of RhRu film> Target: Rh target and Ru target (or RhRu target), Sputtering gas: Ar gas, Gas pressure: 1.0×10 -2 Pa to 1.0×10 0 Pa, Output density of target: 1.0 W / cm 2 to 8.5 W / cm 2 , Film formation rate: 0.020 nm / sec to 1.000 nm / sec, Film thickness of RhRu film: 1.0 nm to 4.0 nm.

[0051] The absorption film 13 absorbs EUV light. The absorption film 13 is a film on which the opening pattern 13a is formed. The opening pattern 13a is not formed in the manufacturing process of the reflective mask blank 1, but is formed in the manufacturing process of the reflective mask 2. The absorption film 13 may be a phase shift film that not only absorbs EUV light but also shifts the phase of EUV light. The absorption film 13 shifts the phase of the second EUV light L2 with respect to the first EUV light L1 shown in FIG. 3.

[0052] The first EUV light L1 passes through the opening pattern 13a without passing through the absorption film 13, is reflected by the multilayer reflective film 11, and passes through the opening pattern 13a again without passing through the absorption film 13. The second EUV light L2 passes through the absorption film 13 while being absorbed by the absorption film 13, is reflected by the multilayer reflective film 11, and passes through the absorption film 13 again while being absorbed by the absorption film 13.

[0053] The phase difference (≧0) between the first EUV light L1 and the second EUV light L2 is, for example, 170° to 250°. The phase of the first EUV light L1 may be ahead or behind the phase of the second EUV light L2. The absorption film 13 utilizes the interference between the first EUV light L1 and the second EUV light L2 to improve the contrast of the transferred image. The transferred image is an image obtained by transferring the opening pattern 13a of the absorption film 13 onto the target substrate.

[0054] In EUVL, a so-called projection effect (shadowing effect) occurs. The shadowing effect is caused by the fact that the incident angle θ of the EUV light is not 0° (for example, 6°), resulting in a region near the side wall of the aperture pattern 13a where the EUV light is blocked by the side wall, causing a positional or dimensional shift in the transferred image. To reduce the shadowing effect, it is effective to lower the height of the side wall of the aperture pattern 13a, and thus to thin the absorption film 13.

[0055] The thickness of the absorption film 13 is, for example, 60 nm or less, preferably 50 nm or less, in order to reduce the shadowing effect. The thickness of the absorption film 13 is preferably 20 nm or more, more preferably 30 nm or more, in order to ensure a phase difference between the first EUV light L1 and the second EUV light L2.

[0056] The absorption film 13 preferably contains at least one metallic element selected from Ru, Ta, Cr, Nb, Pt, Ir, Re, W, Mn, and Au. Since these metallic elements have relatively small refractive indices, the thickness of the phase-shift film can be reduced while ensuring a phase difference. Among the above metallic elements, the absorption film 13 preferably contains Ru.

[0057] The absorption film 13 preferably contains a compound of the above-mentioned metal element. In addition to the above-mentioned metal element, the compound contains at least one nonmetal element selected from O, N, C, and B. By adding a nonmetal element to the metal element, crystallization of the absorption film 13 can be suppressed and the roughness of the sidewall of the opening pattern 13a can be reduced. The absorption film 13 preferably contains oxygen as the nonmetal element, and more preferably contains oxygen and nitrogen.

[0058] The refractive index n of the absorption film 13 is preferably 0.930 or less, more preferably 0.920 or less, even more preferably 0.910 or less, and particularly preferably 0.90 or less. Furthermore, the refractive index n is preferably 0.885 or more. In this specification, the refractive index is the refractive index for light with a wavelength of 13.5 nm.

[0059] The extinction coefficient k of the absorption film 13 is preferably 0.015 or higher, and more preferably 0.020 or higher. Furthermore, the extinction coefficient k is preferably 0.065 or lower. In this specification, the extinction coefficient is the extinction coefficient for light with a wavelength of 13.5 nm.

[0060] The optical properties of the absorption film 13 (refractive index n and extinction coefficient k) are taken from the database of the Center for X-Ray Optics, Lawrence Berkeley National Laboratory, or from values ​​calculated from the "incident angle dependence" of the reflectance described later.

[0061] The incident angle θ of EUV light, the reflectance R for EUV light, the refractive index n of the absorption film 13, and the extinction coefficient k of the absorption film 13 satisfy the following equation (1): R = |(sinθ - ((n+ik)² - cos2θ)¹ / ²) / (sinθ + ((n+ik)² - cos2θ)¹ / ²)|···(1) Multiple combinations of incident angle θ and reflectance R are measured, and the refractive index n and extinction coefficient k are calculated using the least squares method so as to minimize the error between the multiple measurement data and equation (1).

[0062] Preferably, the absorption film 13 has an etching rate of 0 nm / min to 0.05 nm / min with sulfuric acid. If the etching rate of the absorption film 13 with sulfuric acid is 0.05 nm / min or less, damage to the absorption film 13 during cleaning can be suppressed.

[0063] The method for depositing the absorption film 13 can be, for example, DC sputtering, magnetron sputtering, ion beam sputtering, or reactive sputtering. With reactive sputtering, the oxygen content of the absorption film 13 can be controlled by the O2 gas content in the sputtering gas. Furthermore, with reactive sputtering, the nitrogen content of the absorption film 13 can be controlled by the N2 gas content in the sputtering gas.

[0064] When forming a RuN film as the absorption film 13 using the reactive sputtering method, an example of the film formation conditions is as follows. <Film formation conditions of RuN film> Target: Ru target, Sputtering gas: Mixed gas of Ar gas and N2 gas, Volume ratio of N2 gas in the sputtering gas (N2 / (Ar + N2)): 0.3 to 0.7, Gas pressure: 0.05 Pa to 0.40 Pa, Output density of the target: 1.0 W / cm 2 ~8.5 W / cm 2 , Film formation rate: 0.010 nm / sec to 0.030 nm / sec, Film thickness: 20 nm to 60 nm.

[0065] The etching mask film 14 is formed on the side opposite to the protective film 12 with respect to the absorption film 13 and is used to form the opening pattern 13a in the absorption film 13. A resist film (not shown) is provided on the etching mask film 14. In the manufacturing process of the reflective mask 2, first, a first opening pattern is formed in the resist film, then a second opening pattern is formed in the etching mask film 14 using the first opening pattern, and then a third opening pattern 13a is formed in the absorption film 13 using the second opening pattern. The first opening pattern, the second opening pattern, and the third opening pattern 13a have the same dimensions and the same shape in plan view (viewed in the Z-axis direction). The etching mask film 14 enables thinning of the resist film.

[0066] The etching mask film 14 preferably contains at least one element selected from Al, Hf, Y, Cr, Nb, Ti, Mo, Ta, and Si. The etching mask film 14 may further contain at least one element selected from O, N, and B.

[0067] The film thickness of the etching mask film 14 is preferably 2 nm or more and 30 nm or less, more preferably 2 nm or more and 25 nm or less, and still more preferably 2 nm or more and 10 nm or less.

[0068] The film formation method of the etching mask film 14 is, for example, a DC sputtering method, a magnetron sputtering method, or an ion beam sputtering method.

[0069] Next, with reference to Figure 4, a method for manufacturing a reflective mask blank 1 according to one embodiment will be described. The method for manufacturing a reflective mask blank 1 includes, for example, steps S101 to S105 shown in Figure 4. In step S101, a substrate 10 is prepared. In step S102, a multilayer reflective film 11 is formed on the first main surface 10a of the substrate 10. In step S103, a protective film 12 is formed on the multilayer reflective film 11. In step S104, an absorption film 13 is formed on the protective film 12. In step S105, an etching mask film 14 is formed on the absorption film 13.

[0070] The method for manufacturing the reflective mask blank 1 only needs to include at least steps S101 to S104. The method for manufacturing the reflective mask blank 1 may further include a step of forming a functional film, which is not shown in Figure 4.

[0071] Next, with reference to Figure 5, a method for manufacturing a reflective mask 2 according to one embodiment will be described. The method for manufacturing a reflective mask 2 has steps S201 to S204 shown in Figure 5. In step S201, a reflective mask blank 1 is prepared. In step S202, an etching mask film 14 is processed. A resist film (not shown) is provided on the etching mask film 14. First, a first opening pattern is formed on the resist film, and then a second opening pattern is formed on the etching mask film 14 using the first opening pattern. In step S203, a third opening pattern 13a is formed on the absorption film 13 using the second opening pattern. In step S203, the absorption film 13 is etched using an etching gas. In step S204, the resist film and the etching mask film 14 are removed. For example, sulfuric acid hydrochloride is used to remove the resist film. For example, an etching gas is used to remove the etching mask film 14. The etching gas used in step S204 (removal of etching mask film 14) may be the same type as the etching gas used in step S202 (processing of etching mask film 14). The manufacturing method for the reflective mask 2 only needs to include steps S201 and S203.

[0072] Next, referring to FIG. 6, the reflective mask blank 1 according to the modified example will be described. The reflective mask blank 1 may have a reflectivity adjusting film 15 containing Ru as a main component between the multilayer reflective film 11 and the protective film 12. Ru has a lower attenuation coefficient than Rh. By combining the protective film 12 containing Rh as a main component and the reflectivity adjusting film 15 containing Ru as a main component, it is possible to improve the etching resistance while improving the reflectivity with respect to EUV light.

[0073] The reflectivity adjusting film 15 contains 50 at% or more and 100 at% or less of Ru. The reflectivity adjusting film 15 may contain only Ru as a metal element, or may contain a Ru compound. The Ru compound may contain at least one element selected from the group consisting of Pd, Ir, Pt, Zr, Nb, Ta, and Ti in addition to Ru.

[0074] The Ru compound may contain at least one non-metal element selected from O, N, C, and B in addition to Ru. Although the non-metal element reduces the etching resistance, it can suppress the crystallization of the reflectivity adjusting film 15 and can form the surface of the reflectivity adjusting film 15 smoothly.

[0075] The film thickness of the reflectivity adjusting film 15 is preferably 0.1 nm to 2.0 nm, more preferably 0.5 nm to 2.0 nm, and even more preferably 1.0 nm to 1.5 nm. If the film thickness of the reflectivity adjusting film 15 is 0.1 nm or more, the reflectivity with respect to EUV light is good. If the film thickness of the reflectivity adjusting film 15 is 2.0 nm or less, the etching resistance is good.

[0076] When forming a Ru film as the reflectivity adjusting film 15 using the ion beam sputtering method, an example of the film forming conditions is as follows. <Film forming conditions for Ru film> Target: Ru target, Sputtering gas: Ar gas, Gas pressure: 0.010 Pa to 0.020 Pa, Ion acceleration voltage: 300 V to 1500 V, Film forming rate: 0.010 nm / sec to 0.100 nm / sec, Film thickness of Ru film: 0.1 nm to 2.0 nm.

Example

[0077] The experimental data is described below. In Examples 1 to 10, EUVL reflective mask blanks 1 were fabricated under the same conditions, except for the presence or absence and material of the top layer of the multilayer reflective film 11 and the reflectance adjustment film 15. Each reflective mask blank 1 consisted of a substrate 10, a multilayer reflective film 11, a protective film 12, and an absorption film 13. Examples 1 to 3 and Examples 9 to 10 are examples, and Examples 4 to 8 are comparative examples.

[0078] As substrate 10, a SiO2-TiO2 glass substrate (outer dimensions 6 inches (152 mm) square, thickness 6.3 mm) was prepared. This glass substrate has a thermal expansion coefficient of 0.02 × 10⁻¹⁰ at 20°C. -7 The temperature is / ℃, the Young's modulus is 67 GPa, the Poisson's ratio is 0.17, and the specific stiffness is 3.07 × 10⁻⁶. 7 m 2 / s 2 The quality assurance area of ​​the first main surface 10a of the substrate 10 had a root mean square roughness Rq of 0.15 nm or less and a flatness of 100 nm or less achieved by polishing. A 100 nm thick Cr film was deposited on the second main surface 10b of the substrate 10 using the magnetron sputtering method. The sheet resistance of the Cr film was 100 Ω / □.

[0079] A Mo / Si multilayer reflective film was formed as the multilayer reflective film 11. The Mo / Si multilayer reflective film was formed by repeating the process of depositing a Si layer (thickness 4.5 nm) and a Mo layer (thickness 2.3 nm) 40 times using the ion beam sputtering method. The total thickness of the Mo / Si multilayer reflective film was 272 nm ((4.5 nm + 2.3 nm) × 40).

[0080] Table 1 shows the deposition method for the uppermost layer of the multilayer reflective film 11. In Table 1, "IBD" represents ion beam sputtering, and "MS" represents magnetron sputtering. "MS (Formation of SiON layer)" means that a layer containing Si, O, and N was formed using reactive magnetron sputtering. The elemental ratios (N / Si) and (O / Si) shown in Table 1 were measured using an ULVAC-FI X-ray photoelectron spectrometer (PHI 5000 VersaProbe).

[0081] As the reflectance adjustment film 15, in Examples 3 and 6-7, the Ru film (thickness 1.0 nm) was formed by ion beam sputtering or DC sputtering, while in Example 8, the Nb film (thickness 1.0 nm) was formed by DC sputtering. In Examples 1, 2, 4, 5, 9, and 10, the reflectance adjustment film 15 was not formed.

[0082] A Rh film (thickness 2.5 nm) was formed as the protective film 12. The Rh film was formed using the DC sputtering method. The thickness T of the mixing layer shown in Table 1 was measured using TEM images. The mixing layer is a layer formed by interdiffusion between the protective film 12 and the uppermost layer of the multilayer reflective film 11 during the formation of the protective film 12. The thickness T of the mixing layer represents the degree of mixing. The more mixing progresses, the larger the thickness T of the mixing layer becomes.

[0083] After the formation of the protective film 12 and before the formation of the absorption film 13, the root mean square roughness Rq of the surface of the protective film 12 was measured. The measurement results are shown in Table 1. The root mean square roughness Rq of the surface of the protective film 12 shown in Table 1 was measured in accordance with JIS B0601:2013. Root mean square roughness Rq represents the degree of surface roughness.

[0084] A RuN film (thickness 35 nm) was formed as the absorption film 13. The RuN film was formed using a reactive sputtering method. Subsequently, the absorption film 13 was exposed to an oxygen-based gas used to form the aperture pattern 13a. At that time, the presence or absence of diffusion was investigated to determine whether easily oxidizable elements diffused onto the surface of the protective film 12. The easily oxidizable elements were Si, which is contained in the uppermost layer of the multilayer reflective film 11 in Examples 1 to 7 and Examples 9 to 10, and Nb, which is contained in the reflectance adjustment film 15 in Example 8. The presence or absence of diffusion is shown in Table 1. The presence or absence of diffusion was investigated using TEM-EDX.

[0085] Table 1 shows the film deposition conditions and evaluation results for the reflective mask blank 1 obtained in Examples 1 to 10.

[0086] [Table 1]

[0087] As shown in Table 1, in Examples 1-2 and 9-10, the elemental ratio (N / Si) in the uppermost layer of the multilayer reflective film 11 was greater than 0.00 and less than 1.50, and the elemental ratio (O / Si) was greater than or equal to 0.00 and less than 0.44. Therefore, according to Examples 1-2 and 9-10, the thickness T of the mixing layer was small, the root mean square roughness Rq of the surface of the protective film 12 was small, and no elemental diffusion to the surface of the protective film 12 was observed. In other words, according to Examples 1-2 and 9-10, even if the protective film 12 is an Rh film, mixing of the protective film 12 and the multilayer reflective film 11, surface roughness of the protective film 12, and elemental diffusion to the surface of the protective film 12 were suppressed. Furthermore, from Examples 1-2 and 9-10, it can be seen that the elemental ratio (N / Si, O / Si) is important regardless of the film formation method of the uppermost layer of the multilayer reflective film 11. Figure 7 shows the STEM image and elemental mapping image of the reflective mask blank according to Example 1. From Figure 7, it can be seen that the thickness T of the mixing layer is small according to Example 1.

[0088] On the other hand, in Example 4, both the elemental ratio (N / Si) and the elemental ratio (O / Si) were 0.00. Therefore, although the root mean square roughness Rq of the surface of the protective film 12 was good, the thickness T of the mixing layer of the protective film 12 was large, and elemental diffusion to the surface of the protective film 12 was observed. Figure 8 shows the STEM image and elemental mapping image of the reflective mask blank related to Example 4. From Figure 8, it can be seen that the thickness of the uppermost layer of the multilayer reflective film 11 has decreased, indicating that mixing between the uppermost layer of the multilayer reflective film 11 and the protective film 12 has progressed.

[0089] In Example 5, the elemental ratio (N / Si) was greater than 0.00 and less than 1.50, resulting in a small mixing layer thickness T and no elemental diffusion to the surface of the protective film 12. Figure 9 shows the STEM image and elemental mapping image of the reflective mask blank related to Example 5. Figure 9 also shows that the mixing layer thickness T is small in Example 5. However, as shown in Table 1, in Example 5, the elemental ratio (O / Si) exceeded 0.44, resulting in a large root mean square roughness Rq of the surface of the protective film 12.

[0090] As is clear from comparing Example 3 with Examples 6-7, when a reflectance adjustment film 15 is formed between the multilayer reflective film 11 and the protective film 12, the composition of the uppermost layer of the multilayer reflective film 11 is important, just as when the reflectance adjustment film 15 is not formed. If the elemental ratio (N / Si) in the uppermost layer of the multilayer reflective film 11 is greater than 0.00 and less than 1.50, and the elemental ratio (O / Si) is greater than or equal to 0.00 and less than 0.44, then even if the protective film 12 is a Rh film, mixing of the protective film 12 and the multilayer reflective film 11, surface roughness of the protective film 12, and elemental diffusion to the surface of the protective film 12 can be suppressed.

[0091] In Example 8, an Nb film was formed as a reflectivity adjustment film 15 between the Si layer, which is the uppermost layer of the multilayer reflective film 11, and the Rh film, which is the protective film 12. Figure 10 shows the STEM image and elemental mapping image of the reflective mask blank according to Example 5. From Figure 10, it can be seen that the mixing of the protective film 12 and the multilayer reflective film 11 can be suppressed by forming the Nb film. However, as shown in Table 1, elemental diffusion to the surface of the protective film 12 was observed in Example 8. Figure 11 shows the distribution of elemental concentrations after the reflective mask blank 1 according to Example 8 was exposed to an oxygen-based gas. As shown in Figure 11, there is an Nb peak to the left of the maximum Nb peak (at a position farther from the substrate 10). This indicates that Nb diffused to the surface of the protective film 12 when the protective film 12 was exposed to the oxygen-based gas.

[0092] The reflective mask blank, reflective mask, method for manufacturing a reflective mask blank, and method for manufacturing a reflective mask have been described above, but this disclosure is not limited to the embodiments described above. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims, and these also naturally fall within the technical scope of this disclosure.

[0093] This application claims priority based on Japanese Patent Application No. 2022-117803, filed with the Japan Patent Office on July 25, 2022, and the entire contents of Japanese Patent Application No. 2022-117803 are incorporated herein by reference. [Explanation of Symbols]

[0094] 1 Reflective Mask Blank 2 Reflective mask 10 circuit boards 11 Multilayer reflective film 12 Protective film 13 Absorption membrane

Claims

1. A reflective mask blank comprising, in this order, a substrate, a multilayer reflective film that reflects EUV light, a protective film that protects the multilayer reflective film, and an absorbing film that absorbs the EUV light, The protective film contains Rh as its main component, The multilayer reflective film has an uppermost layer that is closest to the protective film and contains Si and N. The uppermost layer is a reflective mask blank in which the elemental ratio of N to Si (N / Si) is greater than 0.00 and less than 1.50, and the elemental ratio of O to Si (O / Si) is 0.00 or greater and less than 0.

44.

2. The reflective mask blank according to claim 1, wherein the protective film contains, as a metallic element, Rh or, in addition to Rh, at least one element Z1 selected from the group consisting of Ru, Nb, Mo, Ta, Ir, Pd, Zr, Y, and Ti.

3. The reflective mask blank according to claim 2, wherein the protective film contains Rh or at least one of Ru and Pd in ​​addition to Rh as a metallic element.

4. The reflective mask blank according to claim 2 or 3, wherein the elemental ratio of Z1 (all Z1) to Rh (Z1:Rh) of the protective film is 1:99 to 1:

1.

5. The reflective mask blank according to claim 2 or 3, wherein the protective film contains, in addition to Rh, at least one element Z2 selected from the group consisting of N, O, C, and B.

6. The reflective mask blank according to claim 5, wherein the protective film has a Rh content (where the Z1 content is 0 at%) or a combined Rh and Z1 content of 80 at% to 99 at% and a total Z2 content of 1.0 at% to 20 at%.

7. The reflective mask blank according to any one of claims 1 to 3, wherein the uppermost layer has an elemental ratio of O to Si (O / Si) of 0.05 or more and less than 0.

44.

8. A reflective mask blank according to any one of claims 1 to 3, characterized in that the root mean square roughness Rq of the surface of the protective film is 0.05 nm or more and 0.20 nm or less.

9. A reflective mask blank according to any one of claims 1 to 3, wherein the thickness of the protective film is 1.0 nm to 4.0 nm.

10. The reflective mask blank according to any one of claims 1 to 3, wherein the reflective mask blank has a reflectance adjusting film containing 50 at% to 100 at% of Ru between the multilayer reflective film and the protective film.

11. The reflective mask blank according to claim 10, wherein the reflectance adjustment film includes, in addition to Ru, at least one element selected from the group consisting of Pd, Ir, Pt, Zr, Nb, Ta, and Ti.

12. The reflective mask blank according to claim 10, wherein the reflectance adjusting film contains at least one nonmetallic element selected from O, N, C, and B.

13. The reflective mask blank according to claim 10, wherein the thickness of the reflectance adjusting film is 0.1 nm to 2.0 nm.

14. The reflective mask blank according to any one of claims 1 to 3, wherein the absorption film contains at least one metallic element selected from Ru, Ta, Cr, Nb, Pt, Ir, Re, W, Mn, and Au.

15. The reflective mask blank according to claim 14, wherein the absorption film contains at least one metallic element selected from Ru, Ta, Cr, Pt, and W.

16. The reflective mask blank according to claim 14, wherein the absorption film contains at least one nonmetallic element selected from O, N, C, and B.

17. The reflective mask blank according to any one of claims 1 to 3, wherein the selectivity ratio (ER2 / ER1) of the etching rate ER2 of the absorption film to the etching rate ER1 of the protective film is 5.0 or more and 200 or less.

18. The aforementioned multilayer reflective film is formed by alternately stacking high refractive index layers and low refractive index layers. The aforementioned high refractive index layer contains silicon (Si), The low refractive index layer contains molybdenum (Mo), The reflective mask blank according to any one of claims 1 to 3, wherein the multilayer reflective film is a Mo / Si multilayer reflective film.

19. A reflective mask blank according to any one of claims 1 to 3, A reflective mask having an opening pattern in the aforementioned absorption membrane.

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