Reflective mask blank, reflective mask, method for manufacturing a reflective mask blank, and method for manufacturing a reflective mask.

Abstract

This invention provides a technology for suppressing crystallization of the protective film when the protective film of a reflective mask blank contains Ru. [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 EUV light. The protective film contains a Ru compound, and the Ru compound contains Ru, Si, and O.

Description

[Technical Field]

[0001] This disclosure relates to a reflective mask blank, a reflective mask, a method for manufacturing a reflective mask blank, and a method for manufacturing a reflective mask. [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. A reflective mask, for example, has a glass substrate, a multilayer reflective film, a protective film, and an absorption film in that order. The multilayer reflective film reflects EUV light. The protective film protects the multilayer reflective film from etching gases during the processing of the absorption film. The absorption film absorbs EUV light. The absorption film may not only absorb EUV light but also shift its phase. In other words, the absorption film may be a phase-shifting film. In EUVL, the aperture pattern of the absorption film is transferred to a target substrate such as a semiconductor substrate. This transfer includes reducing the size of the pattern during transfer.

[0004] The reflective mask blank described in Patent Document 1 consists of a protective film made of a Ru compound containing Ru and X (where X is at least one selected from Nb and Zr). This protective film has an oxide layer mainly composed of X on the surface layer opposite the substrate of the protective film, in order to improve resistance to ozonated water and to etching gas (containing 70% or more oxygen and including chlorine-based gases).

[0005] The reflective mask blank described in Patent Document 2 has a protective film made of a Ru-based material and a phase-shift film made of a Ta-based material. A diffusion-blocking layer is formed on the surface of the protective film (the surface in contact with the phase-shift film). The diffusion-blocking layer contains Ru and O and suppresses interdiffusion between the protective film and the phase-shift film. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2010-092947 [Patent Document 2] Japanese Patent Publication No. 2015-122468 [Overview of the project] [Problems that the invention aims to solve]

[0007] The protective film on a reflective mask blank may contain Ru. If the Ru-containing protective film crystallizes, the absorption film may inherit the crystal structure of the protective film and crystallize itself. As a result, an opening pattern is formed along the grain boundaries of the absorption film, resulting in a coarser opening pattern.

[0008] One aspect of this disclosure provides a technique for suppressing crystallization of a protective film when the protective film of a reflective mask blank contains Ru. [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 EUV light. The protective film contains a Ru compound, and the Ru compound contains Ru, Si, and O. [Effects of the Invention]

[0010] According to one aspect of this disclosure, when the protective film of a reflective mask blank contains Ru, crystallization of the protective film can be suppressed.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing a reflective mask blank according to an embodiment. [Figure 2] FIG. 2 is a flowchart showing a method for manufacturing a reflective mask blank according to an embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing a reflective mask according to an embodiment. [Figure 4] FIG. 4 is a flowchart showing a method for manufacturing a reflective mask according to an embodiment. [Figure 5] FIG. 5(A) is a cross-sectional view showing an example of S201, FIG. 5(B) is a cross-sectional view showing an example of S202, and FIG. 5(C) is a cross-sectional view showing an example of S203. [Figure 6] FIG. 6 is a cross-sectional view showing an example of EUV light reflected by the reflective mask of FIG. 3. [Figure 7] FIG. 7 is a diagram showing a TEM image of a reflective mask blank according to Example 1 and the distribution of each element measured by TEM-EDX. [Figure 8] FIG. 8 is a diagram showing a TEM image of a reflective mask blank according to Example 5 and the distribution of each element measured by TEM-EDX.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments for implementing the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and the description may be omitted. In the specification, "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value. The numerical range includes the rounded range.

[0013] In each drawing, 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 6, 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 includes, for example, a substrate 10, a multilayer reflective film 11, a protective film 12, an absorption film 13, and a hard mask film 14 in this order. The multilayer reflective film 11, the protective film 12, the absorption film 13, and the hard mask film 14 are formed on the first main surface 10a of the substrate 10 in this order. The multilayer reflective film 11 reflects EUV light. The protective film 12 protects the multilayer reflective film 11 from the first etching gas during processing of the absorption film 13. The absorption film 13 absorbs EUV light. The absorption film 13 may not only absorb EUV light but also shift the phase of the EUV light. In other words, the absorption film 13 may be a phase-shifting film. The hard mask film 14 protects a portion of the absorption film 13 from the first etching gas during processing of the absorption film 13.

[0015] The reflective mask blank 1 may have a conductive film 15 on the side opposite to the multilayer reflective film 11 with respect to the substrate 10. In other words, the reflective mask blank 1 may have the conductive film 15, the substrate 10, the multilayer reflective film 11, the protective film 12, the absorption film 13, and the hard mask film 14 in this order. The conductive film 15 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 15 is used, for example, to attract the reflective mask 2 to the electrostatic chuck of the exposure apparatus.

[0016] 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 diffusion barrier film (not shown) between the multilayer reflective film 11 and the protective film 12. The diffusion barrier film suppresses the diffusion of metal elements contained in the protective film 12 into the multilayer reflective film 11.

[0017] 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 the first etching gas that forms the 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.

[0018] Next, with reference to Figure 2, 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 S106 shown in Figure 2. In step S101, a substrate 10 is prepared. In step S102, a conductive film 15 is formed on the second main surface 10b of the substrate 10. In step S103, a multilayer reflective film 11 is formed on the first main surface 10a of the substrate 10. In step S104, a protective film 12 is formed on the multilayer reflective film 11. In step S105, an absorption film 13 is formed on the protective film 12. In step S106, a hard mask film 14 is formed on the absorption film 13.

[0019] The order of steps S101 to S106 is not limited to the order shown in Figure 2. For example, the order of steps S102 and S103 to S106 may be reversed. Also, the method for manufacturing the reflective mask blank 1 does not have to include all of steps S101 to S106. 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 2.

[0020] Next, with reference to Figure 3, a reflective mask 2 according to one embodiment will be described. The reflective mask 2 is fabricated, for example, using the reflective mask blank 1 shown in Figure 1, and includes an aperture pattern 13a in the absorption film 13. 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 with reduction. Note that the hard mask film 14 shown in Figure 1 is not included in the reflective mask 2.

[0021] Next, a method for manufacturing a reflective mask 2 according to one embodiment will be described with reference to Figures 4 and 5. The method for manufacturing a reflective mask 2 has steps S201 to S204 shown in Figure 4. In step S201, a reflective mask blank 1 is prepared as shown in Figure 5(A). The reflective mask blank 1 includes a resist film 16 as shown in Figure 5(A). The resist film 16 is formed on a hard mask film 14. The resist film 16 has an opening pattern formed on it that is to be transferred to the absorption film 13.

[0022] In step S202, as shown in Figure 5(B), the hard mask film 14 is processed using a resist film 16 having an opening pattern. At the openings in the resist film 16, the hard mask film 14 is exposed to a second etching gas, and the second etching gas etches the hard mask film 14. At the end of step S202, the resist film 16 remains. As a result, the opening pattern of the resist film 16 is transferred to the hard mask film 14.

[0023] The second etching gas is selected according to the combination of the materials of the resist film 16 and the hard mask film 14, and is not particularly limited, but includes, for example, a fluorine-based gas. The fluorine-based gas includes, for example, at least one selected from CF4 gas, CHF3 gas, C2F6 gas, C3F6 gas, C4F6 gas, C4F8 gas, CH2F2 gas, CH3F gas, C3F8 gas, F2 gas, SF6 gas, and NF3 gas. In addition to the fluorine-based gas, the second etching gas may also include an active gas or an inert gas. The active gas includes, for example, O2 gas. The inert gas includes, for example, at least one selected from N2 gas, He gas, and Ar gas. The second etching gas is preferably plasma-generated.

[0024] In step S203, the absorption film 13 is processed using a hard mask film 14 having an opening pattern, as shown in Figure 5(C). At the openings of the hard mask film 14, the absorption film 13 is exposed to a first etching gas, and the first etching gas etches the absorption film 13. The hard mask film 14 has higher resistance to the first etching gas than the absorption film 13. At the end of step S203, the hard mask film 14 remains. As a result, the opening pattern of the hard mask film 14 is transferred to the absorption film 13.

[0025] The first etching gas is selected according to the combination of the material of the hard mask film 14 and the material of the absorption film 13, and is not particularly limited, but includes, for example, a chlorine-based gas and an oxygen-based gas. The chlorine-based gas includes, for example, at least one selected from Cl2 gas, SiCl4 gas, CHCl3 gas, CCl4 gas, and BCl3 gas. The oxygen-based gas includes, for example, at least one selected from O2 gas and O3 gas. In addition to the chlorine-based gas and oxygen-based gas, the first etching gas may also include an inert gas. The inert gas includes, for example, at least one selected from N2 gas, He gas, and Ar gas. The first etching gas is preferably plasma-generated.

[0026] In step S204, although not shown, the hard mask film 14 is removed. For example, a third etching gas is used to remove the hard mask film 14. The third etching gas, like the second etching gas, includes, for example, a fluorine-based gas. Preferably, the third etching gas is plasma-generated. Chemical solutions may also be used to remove the hard mask film 14.

[0027] Next, referring again to Figure 1, the substrate 10, multilayer reflective film 11, protective film 12, absorption film 13, hard mask film 14, and conductive film 15 will be explained in this order.

[0028] 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 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.

[0029] 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 length and width dimensions may be 142 mm or more. 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.

[0030] 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.

[0031] 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 the reflectivity with respect to EUV light. When the multilayer reflective film 11 is a Mo / Si multilayer reflective film, in order to achieve a reflectivity of 60% or more with respect to EUV light with an incident angle θ (see FIG. 6) of 6°, a Mo layer with a film thickness of 2.3 ± 0.1 nm and a Si layer with a film thickness of 4.5 ± 0.1 nm may be laminated so that the number of repeating units is 30 or more and 60 or less. The multilayer reflective film 11 preferably has a reflectivity of 60% or more with respect to EUV light with an incident angle θ of 6°. More preferably, the reflectivity is 65% or more.

[0032] The film formation method of each layer constituting the multilayer reflective film 11 is, for example, a DC sputtering method, a magnetron sputtering method, an 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: 1.3×10 -2 Pa~2.7×10 -2 Pa, Ion acceleration voltage: 300V~1500V, Film formation rate: 0.030 nm / sec~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: 1.3×10 -2 Pa~2.7×10 -2 Pa, Ion acceleration voltage: 300V~1500V, Film formation rate: 0.030 nm / sec~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: 30~60 (preferably 40~50).

[0033] 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 the first etching gas during the processing of the absorption film 13, i.e., in step S203. The protective film 12 remains on the multilayer reflective film 11 without being removed even when exposed to the first etching gas.

[0034] If the protective film 12 contains Ru, it may exhibit crystalline properties. If the protective film 12 crystallizes, the absorption film 13 may take over the crystalline structure of the protective film 12, and the absorption film 13 may crystallize as well. As a result, an opening pattern 13a is formed along the grain boundaries of the absorption film 13, and the opening pattern 13a becomes rough.

[0035] The protective film 12 in this embodiment contains a Ru compound, which contains Ru, Si, and O. Si is more easily oxidized than Ru, which can increase the O concentration in the Ru compound. O suppresses the crystallization of Ru. Therefore, the crystallization of the protective film 12 can be suppressed, and consequently, the crystallization of the absorption film 13 can be suppressed.

[0036] The Ru compound constituting the protective film 12 more preferably has an average Si concentration of 9.0 at% or higher. An average Si concentration of 9.0 at% or higher makes it easier to increase the O concentration of the Ru compound and suppress Ru crystallization. The average Si concentration is more preferably 9.5 at% or higher, even more preferably 10.0 at% or higher, and particularly preferably 15.0 at% or higher.

[0037] The Ru compound constituting the protective film 12 preferably has an average Si concentration of less than 37.9 at%. If the average Si concentration is less than 37.9 at%, the O concentration is not too high, and the formation of defects containing SiO can be suppressed. The formation of defects containing SiO causes surface roughness of the protective film 12. The average Si concentration is more preferably 37.0 at% or less, even more preferably 35.0 at% or less, and particularly preferably 25.0 at% or less.

[0038] The Ru compound constituting the protective film 12 preferably has an average O concentration of 3.0 at% or higher. An average O concentration of 3.0 at% or higher makes it easier for O to suppress the crystallization of Ru. The average O concentration is more preferably 3.5 at% or higher, and even more preferably 5.0 at% or higher.

[0039] The Ru compound constituting the protective film 12 preferably has an average O concentration of less than 12.6 at%. An average O concentration of less than 12.6 at% prevents excessive O concentration and suppresses the formation of defects containing SiO. The formation of defects containing SiO causes surface roughness of the protective film 12. The average O concentration is more preferably 10.0 at% or less, and even more preferably 8.0 at% or less.

[0040] The protective film 12 includes, for example, a RuSiO film. The RuSiO film can be obtained, for example, by first depositing a RuSi film and then oxidizing the RuSi film. The oxidation of the RuSi film begins from the surface of the RuSi film. Therefore, the oxygen concentration decreases as the depth from the surface of the RuSiO film increases. The oxygen concentration also depends on the elemental ratio of Ru and Si. Si is more easily oxidized than Ru, and the higher the Si concentration, the higher the oxygen concentration.

[0041] RuSi films are deposited, for example, by binary sputtering. The elemental ratio of Ru to Si can be adjusted by controlling the power density of the Ru target and the Si target. It is also possible to keep the elemental ratio of Ru to Si constant regardless of depth, to gradient the elemental ratio of Ru to Si, or to increase the Si concentration only in the outermost layer. Oxidation of the RuSi film includes, for example, irradiating the RuSi film with oxygen plasma or implanting oxygen ions into the RuSi film.

[0042] Furthermore, RuSiO films can also be deposited using reactive sputtering. In this case, the elemental ratio of Ru to Si can be adjusted by controlling the power density of the Ru target and the Si target. Additionally, the oxygen concentration can be adjusted by controlling the volume ratio of O2 gas in the sputtering gas (O2 / (Ar+O2)). The oxygen concentration remains constant regardless of the depth from the surface of the RuSiO film. It is also possible to gradient the oxygen concentration in the depth direction or to oxidize only the outermost layer.

[0043] In this embodiment, the protective film 12 is a single-layer film, but it may be a multilayer film having a lower layer and an upper layer. The lower layer of the protective film 12 is a layer formed in contact with the uppermost surface of the multilayer reflective film 11. The upper layer of the protective film 12 is in contact with the lowermost surface of the absorbing film 13. By making the protective film 12 a multilayer structure in this way, materials with superior properties for a given function can be used in each layer, thereby making the entire protective film 12 multifunctional.

[0044] The upper layer of the protective film 12 preferably contains at least one element selected from Ru and Rh, more preferably Rh, and even more preferably an Rh compound. The lower layer of the protective film 12 preferably contains at least one element selected from Ru, Rh, Nb, Mo, Zr, Y, and Si, more preferably Ru, and even more preferably an above-mentioned Ru compound. If the protective film 12 is a multilayer film, the thickness of the protective film 12 below refers to the total film thickness of the multilayer film. A mixing layer may be formed between the multilayer reflective film 11 and the lower layer of the protective film 12 by mixing the components contained in the multilayer reflective film 11 and the components contained in the lower layer of the protective film 12.

[0045] The thickness of the protective film 12 is preferably 1.0 nm to 7.0 nm, more preferably 2.0 nm to 6.5 nm, and even more preferably 2.5 nm to 6.5 nm. If the thickness of the protective film 12 is 1.0 nm or more, etching resistance is good. Also, if the thickness of the protective film 12 is 7.0 nm or less, reflectivity to EUV light is good.

[0046] The density of the protective film 12 is preferably 10.0 g / cm 3 ~14.0 g / cm 3 . If the density of the protective film 12 is 10.0 g / cm 3 or more, the etching resistance is good. Also, if the density of the protective film 12 is 14.0 g / cm 3 or less, a decrease in the reflectivity with respect to EUV light can be suppressed.

[0047] 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. Also, 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.

[0048] 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 RuSi film using the DC sputtering method and then oxidizing the RuSi film, an example of the film formation conditions is as follows. <Film formation conditions of RuSi film> Targets: Ru target and Si target, Sputtering gas: Ar gas, Gas pressure: 1.0×10 -2 Pa~1.0×10 0 Pa, Output density of the target: 1.0 W / cm 2 ~8.5 W / cm 2 , Film formation rate: 0.020 nm / sec~1.000 nm / sec, Film thickness: 1 nm~10 nm. <Oxidation conditions of RuSi film (plasma treatment conditions)> Flow rate of O2 gas: 200 sccm~3000 sccm Flow rate of Ar gas: 100 sccm~6000 sccm Percentage of O2 gas in a mixed gas of O2 and Ar gas: 0% to 90% by volume Power supply frequency for plasma generation: 10MHz~60MHz Power for plasma generation: 50W~600W Processing time: 2 sec to 120 sec Processing temperature: 80℃~350℃ Processing pressure: 50 Pa to 1200 Pa.

[0049] The absorption film 13 absorbs EUV light. The absorption film 13 is a film on which an aperture pattern 13a is to be formed. The aperture 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 not only absorb EUV light, but also shift the phase of the EUV light. In other words, the absorption film 13 may be a phase-shifting film. A phase-shifting film shifts the phase of the second EUV light L2 with respect to the first EUV light L1 shown in Figure 6.

[0050] The first EUV light L1 is light that passes through the aperture pattern 13a without passing through the absorption film 13, is reflected by the multilayer reflective film 11, and passes through the aperture pattern 13a again without passing through the absorption film 13. The second EUV light L2 is light that is absorbed by the absorption film 13, passes through the absorption film 13, is reflected by the multilayer reflective film 11, and is absorbed by the absorption film 13 again, while passing through the absorption film 13.

[0051] The phase difference (≧0) between the first EUV light L1 and the second EUV light L2 is, for example, 170° to 250°. The phase of the first EUV light L1 may lead or lag behind the phase of the second EUV light L2. The absorption film 13 improves the contrast of the transferred image by utilizing the interference of the first EUV light L1 and the second EUV light L2. The transferred image is an image obtained by transferring the aperture pattern 13a of the absorption film 13 onto the target substrate.

[0052] 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.

[0053] 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.

[0054] To reduce the shadowing effect while maintaining a phase difference between the first EUV light L1 and the second EUV light L2, it is effective to reduce the thickness of the absorption film 13 by decreasing the refractive index n of the absorption film 13. Furthermore, to reduce the reflectance to EUV light, it is effective to increase the extinction coefficient k of the absorption film 13. Thus, the absorption film 13 is required to have excellent optical properties.

[0055] The absorption film 13 preferably contains at least one metallic element selected from Cr, Ta, Nb, Ir, Pt, Pd, Au, and Ru. Since these metallic elements have relatively small refractive indices, the thickness of the absorption film 13 can be reduced while ensuring a phase difference. The absorption film 13 preferably contains a compound of a metallic element. The compound of a metallic element preferably contains at least one element selected from O, B, C, Si, and N. By adding at least one element selected from O, B, C, Si, and N, crystallization can be suppressed while suppressing a decrease in optical properties, and the roughness of the aperture pattern 13a can be reduced. The absorption film 13 more preferably contains a Ta compound. The Ta compound more preferably contains N. This is because the inclusion of N can suppress the crystallization of the Ta compound and prevent surface roughness due to crystallization. The absorption film 13 preferably contains TaN.

[0056] In this embodiment, the absorption film 13 is a film composed of a single layer, but it may also be a multilayer film having a lower layer and an upper layer. The lower layer and the upper layer constituting the absorption film 13 are formed on the protective film 12 in this order. The uppermost layer of the absorption film 13 is the layer farthest from the protective film 12. The uppermost layer of the absorption film 13 preferably contains at least one metal element selected from Cr, Ta, Nb, Ir, Pt, Pd, Au, and Ru, and more preferably contains a compound of the metal element. The uppermost layer of the absorption film 13 more preferably contains a Ta compound. The Ta compound is more preferable because it contains N to suppress the crystallization of Ta and can prevent the crystals from growing and the surface roughness from increasing. That is, the absorption film 13 preferably contains TaN. When the absorption film 13 is a multilayer film, the thickness of the absorption film 13 means the total film thickness of the multilayer film.

[0057] When the Ta compound contains Ta and N, the content of N atoms in the Ta compound is preferably 10.0 to 35.0 at% for increasing the etching selectivity ratio, more preferably 10.0 to 25.0 at%, still more preferably 10.5 to 18.0 at%, and particularly preferably 11.0 to 16.0 at%.

[0058] When the Ta compound contains N, it may further contain at least one element selected from hafnium (Hf), silicon (Si), zirconium (Zr), titanium (Ti), germanium (Ge), boron (B), tin (Sn), nickel (Ni), cobalt (Co), and hydrogen (H). The total content of these elements is preferably 10 at% or less.

[0059] Examples of the film formation method of the absorption film 13 include, for example, the DC sputtering method, the magnetron sputtering method, or the ion beam sputtering method. The nitrogen content of the absorption film 13 can be controlled by the content of N2 gas in the sputtering gas.

[0060] When forming a TaN film using the reactive sputtering method, an example of the film formation conditions is as follows. <Film Formation Conditions of TaN Film> Target: Ta target, Power density of Ta target: 1.0 W / cm² 2 ~8.5W / cm 2 , Sputtering gas: A mixture of Ar gas and N2 gas. Volume ratio of N2 gas in sputtering gas (N2 / (Ar+N2)): 0.01~0.25, Gas pressure: 1.0 × 10 -2 Pa~1.0×10 0 Pa, Power density of Ta target: 1.0 W / cm² 2 ~8.5W / cm 2 , Deposition rate: 0.020nm / sec~0.060nm / sec, Film thickness: 20nm to 60nm.

[0061] The absorption film 13 preferably has an extremely low reflectivity to EUV light. Specifically, the absorption film 13 preferably has a reflectivity of 2.0% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and particularly preferably 0.1% or less, to light with a wavelength of 13.5 nm. The absorption film 13 has a reflectivity of 0.0% or more to light with a wavelength of 13.5 nm.

[0062] The hard mask film 14 is formed on the opposite side of the protective film 12 from the absorption film 13, and is used to form an opening pattern 13a in the absorption film 13. The hard mask film 14 enables the thinning of the resist film 16.

[0063] The hard mask film 14 preferably contains at least one metallic or metalloid element selected from Al, Hf, Y, Cr, Nb, Ti, Mo, Ta, and Si. The hard mask film 14 preferably contains a compound of the above metallic or metalloid element. The compound preferably contains at least one element selected from O, N, C, and B.

[0064] The thickness of the hard mask film 14 is preferably 2 nm to 30 nm, more preferably 2 nm to 25 nm, and even more preferably 2 nm to 10 nm.

[0065] The hard mask film 14 can be deposited using methods such as DC sputtering, magnetron sputtering, or ion beam sputtering.

[0066] The conductive film 15 is formed on the side opposite to the multilayer reflective film 11 with respect to the substrate 10 and is used to adsorb the reflective mask 2 to the electrostatic chuck of the exposure apparatus. The conductive film 15 preferably contains at least one metallic element selected from Cr and Ta. The conductive film 15 preferably contains a compound of the above metallic elements. The compound preferably contains at least one element selected from O, N, C and B.

[0067] In this embodiment, the conductive film 15 is a single-layer film, but it may also be a multilayer film having a lower layer and an upper layer. The lower and upper layers constituting the conductive film 15 are formed on the substrate 10 in this order. The uppermost layer of the conductive film 15 is the layer furthest from the substrate 10. The uppermost layer of the conductive film 15 preferably contains at least one metal element selected from Cr and Ta, and more preferably contains a compound of the above metal element. If the conductive film 15 is a multilayer film, the thickness of the conductive film 15 means the total thickness of the multilayer film.

[0068] The thickness of the conductive film 15 is preferably 5 nm to 500 nm, more preferably 10 nm to 450 nm, and even more preferably 20 nm to 400 nm.

[0069] The method for depositing the conductive film 15 is, for example, DC sputtering, magnetron sputtering, or ion beam sputtering. [Examples]

[0070] The experimental data is described below. In Examples 1 to 5, a reflective mask blank 1 was fabricated having a substrate 10, a multilayer reflective film 11, a protective film 12, and an absorption film 13 in that order. In Examples 1 to 5, a reflective mask blank 1 with the same configuration was fabricated, except for the configuration of the protective film 12. Examples 1 to 5 are examples of actual cases.

[0071] 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 / □.

[0072] 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). The uppermost layer of the Mo / Si multilayer reflective film was the Si layer.

[0073] As the protective film 12, a RuSiO film (thickness 4 nm to 6 nm) with the composition shown in Table 1 was formed. The RuSiO film was formed by first forming a RuSi film using a binary sputtering method, and then oxidizing the RuSi film with an O plasma. The elemental ratio of Ru to Si in the RuSiO film was adjusted by the power density of the Ru target and the Si target, respectively. The O concentration in the RuSiO film was also proportional to the Si concentration. Si is more easily oxidized than Ru, and the higher the Si concentration, the higher the O concentration.

[0074] A TaN film (40 nm) was formed as the absorption film 13. The TaN film was formed by reactive sputtering.

[0075] Table 1 shows the experimental conditions and results for Examples 1 to 5. The concentrations of each element constituting the RuSiO film were analyzed using TEM (Transmission Electron Microscope)-EDX (Energy Dispersive X-ray Spectroscopy). The presence or absence of SiO-containing defects was confirmed by observing the surface of the TaN film with SEM (Scanning Electron Microscope). If SiO-containing defects exist at the interface between the RuSiO film and the TaN film, minute defects caused by these defects appear on the surface of the TaN film. The amorphous nature of the TaN film, i.e., the degree of crystallization, was confirmed by XRD (X-ray Diffraction).

[0076] [Table 1]

[0077] In Table 1, an "A" rating for the amorphous nature of the TaN film indicates that the full width at half maximum of the peak with the highest intensity in the 2θ range of 20° to 50° was 1.0° or greater in the XRD method using CuKα radiation, meaning that crystallization of the TaN film was suppressed. Also in Table 1, an "A" rating for the presence or absence of SiO-containing defects indicates that no minute defects caused by SiO-containing defects were observed on the surface of the TaN film by SEM, while a "B" rating indicates that minute defects caused by SiO-containing defects were observed on the surface of the TaN film by SEM.

[0078] As shown in Table 1, in Examples 1 to 5, since the protective film 12 was a RuSiO film, the crystallization of the TaN film, which is the absorption film 13, was suppressed. It has also been confirmed that even when the material of the absorption film 13 is a Nb-based material or an Ir-based material, the crystallization of the absorption film 13 can be suppressed if the protective film 12 is a RuSiO film. Furthermore, as shown in Table 1, in Examples 1 to 4, unlike Example 5, the Si concentration of the RuSiO film was less than 37.9 at%, so no minute defects caused by defects containing SiO were observed on the surface of the TaN film by SEM.

[0079] Figure 7 shows the TEM image of the reflective mask blank for Example 1 and the distribution of each element measured by TEM-EDX. Figure 8 shows the TEM image of the reflective mask blank for Example 5 and the distribution of each element measured by TEM-EDX. As shown in Figure 8, in Example 5, defects containing SiO were observed at the interface between the RuSiO film and the TaN film, but in Example 1, no defects containing SiO were observed at the interface between the RuSiO film and the TaN film.

[0080] 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. These also naturally fall within the technical scope of this disclosure.

[0081] This application claims priority based on Japanese Patent Application No. 2023-174933, filed with the Japan Patent Office on October 10, 2023, and the entire contents of Japanese Patent Application No. 2023-174933 are incorporated herein by reference. [Explanation of Symbols]

[0082] 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 EUV light, The protective film comprises a Ru compound, and the Ru compound comprises Ru, Si, and O, in a reflective mask blank.

2. The reflective mask blank according to claim 1, wherein the Ru compound has an average Si concentration of less than 37.9 at%.

3. The reflective mask blank according to claim 1, wherein the Ru compound has an average Si concentration of 9.0 at% or more.

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

5. The absorption film contains a compound of the metal element, The reflective mask blank according to claim 4, wherein the compound of the metal element comprises at least one element selected from O, B, C, Si, and N.

6. The reflective mask blank according to claim 5, wherein the absorption film contains a Ta compound, and the Ta compound contains N.

7. The reflective mask blank according to claim 6, wherein the content of N atoms in the Ta compound is 10.0 at% or more and 35.0 at% or less.

8. 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.

9. The method involves forming 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 on a substrate in this order. A method for manufacturing a reflective mask blank, wherein the protective film contains a Ru compound, and the Ru compound contains Ru, Si, and O.

10. Prepare a reflective mask blank according to any one of claims 1 to 3, Forming an opening pattern in the aforementioned absorption film, A method for manufacturing a reflective mask having the following elements in this order.

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