Method for producing reflective mask blank

Abstract

To provide a technique that suppresses deterioration of a reference mark overtime.SOLUTION: A method for producing a reflective mask blank includes providing a substrate, a multilayer reflective film that reflects EUV light, and an absorptive film that absorbs EUV light, in this order, wherein the multilayer reflective film has repeated Si layers and Mo layers. The producing method includes, after forming the multilayer reflective film, before forming the absorptive film, partially removing the multilayer reflective film to form a recessed reference mark. By forming the reference mark, a mixing layer in which the Si layers and Mo layers are mixed is formed on the bottom surface of the reference mark. On the bottom surface of the reference mark, the layer immediately beneath the mixing layer is the Si layer. The producing method further includes, after forming the reference mark and before forming the absorptive film, irradiating the multilayer reflective film including the reference mark with ultraviolet light, and then cleaning the multilayer reflective film including the reference mark with a cleaning solution containing water, in this order.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a reflective mask blank. [Background technology]

[0002] In recent years, with the miniaturization of semiconductor devices, EUV lithography (EUVL), an exposure technology using extreme ultraviolet (EUV) light, has been developed. EUV has a wavelength of approximately 13.5 nm. EUVL uses a reflective mask. A reflective mask has, in this order, a substrate such as a glass substrate, a multilayer reflective film that reflects EUV light, and an absorbing film that absorbs EUV light. The absorbing film may not only absorb EUV light but also shift the phase of the EUV light. In other words, the absorbing film may be a phase shift film. An opening pattern is formed in the absorbing film. In EUVL, the opening pattern in the absorbing film is transferred to a target substrate such as a semiconductor substrate. Transferring includes reducing and transferring.

[0003] Patent Document 1 describes a technique for forming a fiducial mark to accurately detect the position of a defect in a multilayer reflective film. The fiducial mark is formed, for example, in the shape of a cross. The intersection of the center line of one straight line and the center line of the remaining straight lines becomes the reference point. An inspection device detects the position of the fiducial mark (more specifically, the position of the reference point). The inspection device also sets a coordinate system based on the position of the fiducial mark. The inspection device then detects the position of the defect in the set coordinate system.

[0004] The fiducial mark is formed by removing a portion of the multilayer reflective film. Laser processing or FIB (Focused Ion Beam) methods are used for the removal. A mixing layer is formed on the bottom surface of the fiducial mark by irradiating it with a laser beam or metal ions (e.g., Ga ions). The mixing layer is a mixture of the high-refractive index layer and the low-refractive index layer that make up the multilayer reflective film. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5935804 Summary of the Invention [Problem to be solved by the invention]

[0006] When a multilayer reflective film contains repeated Si and Mo layers, the mixing layer contains Si and Mo. The volume of Si hardly changes due to oxidation. The density of Si is approximately 2.3 g / cm. 3 whereas the density of SiO2 is about 2.2 g / cm 3 On the other hand, Mo's volume increases with oxidation. The density of Mo is approximately 10.3 g / cm 3 whereas the density of MoO3 is about 4.7 g / cm 3 is.

[0007] In the past, after forming a recessed fiducial mark, the bottom surface of the fiducial mark sometimes rose. The inventors of the present application investigated the cause of this and concluded that the main cause was natural oxidation of Mo contained in the mixing layer.

[0008] One embodiment of the present disclosure provides a technique for suppressing degradation of fiducial marks over time. [Means for solving the problem]

[0009] A method for manufacturing a reflective mask blank according to an embodiment of the present disclosure manufactures a reflective mask blank having, in this order, a substrate, a multilayer reflective film that reflects EUV light, and an absorbing film that absorbs EUV light, wherein the multilayer reflective film has alternating Si and Mo layers. The manufacturing method includes forming a concave fiducial mark by removing a portion of the multilayer reflective film after forming the multilayer reflective film and before forming the absorbing film. By forming the fiducial mark, a mixing layer in which the Si layer and the Mo layer are mixed is formed at the bottom surface of the fiducial mark. At the bottom surface of the fiducial mark, the layer immediately below the mixing layer is the Si layer. The manufacturing method includes, in this order, irradiating the multilayer reflective film including the fiducial mark with ultraviolet light and washing the multilayer reflective film including the fiducial mark with a cleaning solution containing water after forming the fiducial mark and before forming the absorbing film. [Effects of the Invention]

[0010] According to one embodiment of the present disclosure, the Mo content at the bottom surface of the fiducial mark can be reduced by UV irradiation and subsequent water rinsing, thereby suppressing deterioration of the fiducial mark over time. [Brief explanation of the 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 flowchart showing a method for manufacturing a reflective mask blank according to one 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. [Figure 7] FIG. 7 is a cross-sectional view showing an example of the positional relationship between the opening pattern of the absorbing film and the defect. [Figure 8] FIG. 8 is a flowchart showing an example of processing that is performed after S103 and before S105 shown in FIG. [Figure 9] FIG. 9 is a cross-sectional view showing an example of a reference mark. [Figure 10] FIG. 10 is a plan view showing an example of a reference mark. [Figure 11] FIG. 11 is a cross-sectional view showing an example of S302 shown in FIG. [Figure 12] FIG. 12 is a cross-sectional view showing an example of S303 shown in FIG. [Figure 13] FIG. 13 is a cross-sectional view showing an example of the relationship between D and H. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of 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 their description may be omitted. In the specification, the symbol "to" indicating a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits. The numerical range includes the range rounded up or down.

[0013] In each drawing, the X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to one another. The Z-axis direction is perpendicular to the first main surface 10a of the substrate 10. The X-axis direction is perpendicular to the plane of incidence of the EUV light (the plane including the incident light beam and the reflected light beam). As shown in FIG. 6, the incident light beam is tilted more in the positive Y-axis direction as it moves in the negative Z-axis direction, and the reflected light beam is tilted more in the positive Y-axis direction as it moves in the positive Z-axis direction.

[0014] A reflective mask blank 1 according to one embodiment will be described with reference to FIG. 1 . The reflective mask blank 1 includes, for example, a substrate 10, a multilayer reflective film 11, a protective film 12, an absorbing film 13, and a hard mask film 14, in this order. The multilayer reflective film 11, the protective film 12, the absorbing film 13, and the hard mask film 14 are formed in this order on a first main surface 10a of the substrate 10. The multilayer reflective film 11 reflects EUV light. The protective film 12 protects the multilayer reflective film 11 from a first etching gas during processing of the absorbing film 13. The absorbing film 13 absorbs EUV light. The absorbing film 13 may not only absorb EUV light but also shift the phase of the EUV light. In other words, the absorbing film 13 may be a phase shift film. The hard mask film 14 protects a portion of the absorbing film 13 from a first etching gas during processing of the absorbing film 13.

[0015] The reflective mask blank 1 has a conductive film 15 on the side opposite to the multilayer reflective film 11 with respect to the substrate 10. That is, the reflective mask blank 1 may have the conductive film 15, substrate 10, multilayer reflective film 11, protective film 12, absorbing film 13, and 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 opposite to the first main surface 10a. The conductive film 15 is used to attach the reflective mask 2 to an electrostatic chuck of an exposure tool.

[0016] The reflective mask blank 1 may further have a functional film not shown in FIG. 1 . For example, the reflective mask blank 1 may have an anti-reflection film not shown between the absorbing film 13 and the hard mask film 14. The anti-reflection film improves the optical contrast during inspection of the opening pattern 13op of the absorbing film 13. The reflective mask blank 1 may also have a diffusion barrier film not shown between the multilayer reflective film 11 and the protective film 12. The diffusion barrier film suppresses diffusion of metal elements contained in the protective film 12 into the multilayer reflective film 11.

[0017] Although not shown, the reflective mask blank 1 may have a buffer film between the protective film 12 and the absorbing film 13. The buffer film protects the protective film 12 from a first etching gas that forms an opening pattern 13op in the absorbing film 13. The buffer film is etched more slowly than the absorbing film 13. Unlike the protective film 12, the buffer film will ultimately have the same opening pattern as the opening pattern 13op of the absorbing film 13.

[0018] Next, a method for manufacturing a reflective mask blank 1 according to one embodiment will be described with reference to Fig. 2. The method for manufacturing a reflective mask blank 1 includes, for example, steps S101 to S106 shown in Fig. 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 absorbing film 13 is formed on the protective film 12. In step S106, a hard mask film 14 is formed on the absorbing film 13.

[0019] The order of steps S101 to S106 is not limited to the order shown in Fig. 2. For example, the order of step S102 and steps S103 to S106 may be reversed. Furthermore, 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 not shown in Fig. 2.

[0020] Next, a reflective mask 2 according to one embodiment will be described with reference to FIG. 3. The reflective mask 2 includes, for example, the reflective mask blank 1 shown in FIG. 1 and includes an opening pattern 13op in an absorbing film 13. In EUVL, the opening pattern 13op in the absorbing film 13 is transferred to a target substrate such as a semiconductor substrate. Transferring includes reducing and transferring. Note that the hard mask film 14 shown in FIG. 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 includes 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. An opening pattern to be transferred to the absorption film 13 is formed in the resist film 16.

[0022] In step S202, as shown in FIG. 5B, the hard mask film 14 is processed using the resist film 16 having an opening pattern. In 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 depending on the combination of the materials of the resist film 16 and the hard mask film 14, and is not particularly limited, and may include, for example, a fluorine-based gas. The fluorine-based gas may include, 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. The second etching gas may include, in addition to the fluorine-based gas, an active gas or an inert gas. The active gas may include, for example, at least one selected from O2 gas and O3 gas. The inert gas may include, for example, at least one selected from N2 gas, He gas, and Ar gas. The second etching gas is preferably a plasma-converted gas.

[0024] In step S203, as shown in FIG. 5C, the absorber film 13 is processed using the hard mask film 14 having an opening pattern. In the openings in the hard mask film 14, the absorber film 13 is exposed to a first etching gas, and the first etching gas etches the absorber film 13. The hard mask film 14 has higher resistance to the first etching gas than the absorber 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 absorber film 13.

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

[0026] In step S204, although not shown, the hard mask film 14 is removed. To remove the hard mask film 14, for example, a third etching gas is used. The third etching gas contains, for example, a fluorine-based gas, similar to the second etching gas. The third etching gas is preferably a plasma gas. To remove the hard mask film 14, a chemical solution may be used.

[0027] Next, referring back to FIG. 1, the substrate 10, the multilayer reflective film 11, the protective film 12, the absorbing film 13, the hard mask film 14, and the conductive film 15 will be described 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 common soda-lime glass, quartz glass has a smaller linear expansion coefficient and undergoes 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 linear expansion coefficient is approximately zero near room temperature, and there is almost no dimensional change near room temperature. The quartz glass may contain a third component or impurity other than SiO2 and TiO2. The material of the substrate 10 may also be crystallized glass in which a β-quartz solid solution is precipitated, silicon, metal, or the like.

[0029] The substrate 10 has a first major surface 10a and a second major surface 10b facing opposite to the first major surface 10a. A multilayer reflective film 11 and the like are formed on the first major surface 10a, and a conductive film 15 is formed on the second major surface 10b. In plan view (Z-axis direction), the substrate 10 measures, for example, 152 mm in length and 152 mm in width. The length and width may be 152 mm or greater. The first major surface 10a has a rectangular quality assurance area. The quality assurance area coincides with the exposure area in plan view. The exposure area is the area where the exposure device is intended to irradiate the absorber film 13 with EUV light. The size of the quality assurance area is appropriately selected depending on the size of the substrate 10; for example, the long side length is 132 mm and the short side length is 104 mm. The quality assurance area preferably has a root-mean-square roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less. It is also preferable that the quality assurance area does not have any defects that cause phase defects.

[0030] The multilayer reflective film 11 reflects EUV light. The multilayer reflective film 11 has, for example, high refractive index layers and low refractive index layers alternately. The high refractive index layers are made of, for example, silicon (Si), and the low refractive index layers are made of, for example, molybdenum (Mo), so a Mo / Si multilayer reflective film is used. Note that a Si / Mo / Ru multilayer reflective film, a Si / Mo / Ru / Mo multilayer reflective film, a Si / Ru / Mo / Ru multilayer reflective film, a Si / Ru / Mo multilayer reflective film, or a Si / Ru / Mo multilayer reflective film 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 layers 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 2.8 ± 0.1 nm and a Si layer with a film thickness of 4.0 ± 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 for 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: 4.0 ± 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: 2.8 ± 0.1 nm, <Repeating unit of Si layer and Mo layer> Number of repeating units: 30 to 60 (preferably 40 to 50).

[0033] The protective film 12 is formed between the multilayer reflective film 11 and the absorbing film 13 to protect the multilayer reflective film 11. The protective film 12 protects the multilayer reflective film 11 from the first etching gas when processing the absorbing film 13, i.e., in step S203. The protective film 12 is not removed even when exposed to the first etching gas, but remains on the multilayer reflective film 11.

[0034] The protective film 12 contains at least one element selected from, for example, Ru, Rh, and Si. The protective film 12 preferably contains ruthenium (Ru) as a main component. As described above, the protective film 12 containing Ru as a main component means that the Ru content in the protective film 12 is 40 at% or more. The Ru content in the protective film 12 is preferably 45 at% or more, and more preferably 50 at% or more. When the protective film 12 contains Ru, it may contain only Ru, or it may contain a Ru compound. The Ru compound may be a Ru alloy. The Ru alloy contains, in addition to Ru, at least one metal element selected from, for example, Rh, Nb, Mo, Ta, Ir, Pd, Zr, Y, and Ti.

[0035] The Ru compound may contain, in addition to Ru, at least one nonmetallic element selected from N, O, C, and B. These nonmetallic elements reduce the resistance of the protective film 12 to the first etching gas, but reduce the crystallinity of the protective film 12, thereby improving the smoothness of the protective film 12. When the Ru compound has a non-crystalline (amorphous) structure or a microcrystalline structure, the X-ray diffraction pattern of the Ru compound does not have a clear peak.

[0036] However, it is preferable that the protective film 12 does not contain at least one nonmetallic element selected from N, O, C, and B. In other words, it is preferable that the total content of N, O, C, and B is 0.1 at% or less. If the total content of N, O, C, and B is 0.1 at% or less, the protective film 12 is likely to crystallize, but the protective film 12 has good resistance to the first etching gas.

[0037] In this embodiment, the protective film 12 is a single-layer film made of a single layer, but it may also be a multi-layer 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 have such a multi-layer structure, materials with excellent predetermined functions can be used for each layer, thereby making the entire protective film 12 multifunctional.

[0038] The upper layer of the protective film 12 preferably contains at least one metal element selected from Ru and Rh, and more preferably contains Rh. The lower layer of the protective film 12 preferably contains at least one element selected from Ru, Rh, Nb, Mo, Zr, Y, and Si, and more preferably contains Ru. When 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. Note that a mixing layer formed by mixing components contained in the multilayer reflective film 11 and components contained in the lower layer of the protective film 12 may be formed between the multilayer reflective film 11 and the lower layer of the protective film 12.

[0039] The thickness of the protective film 12 is preferably 1.0 nm to 4.0 nm. If the thickness of the protective film 12 is 1.0 nm or more, the etching resistance is good. Furthermore, if the thickness of the protective film 12 is 4.0 nm or less, the reflectance to EUV light is good. The thickness of the protective film 12 is more preferably 2.0 nm to 3.5 nm, and even more preferably 2.5 nm to 3.0 nm.

[0040] The density of the protective film 12 is preferably 10.0 g / cm 3 ~14.0g / cm 3 The density of the protective film 12 is 10.0 g / cm 3 If the density of the protective film 12 is 14.0 g / cm or more, the etching resistance is good. 3 If the thickness is equal to or less than this, it is possible to suppress the absorption of EUV light by the protective film 12 (and hence the reduction in reflectance for EUV light).

[0041] 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 Ru film using the ion beam sputtering method, an example of the film formation conditions is as follows. <Film formation conditions of Ru film> Target: Ru target, Sputtering gas: Ar gas, Gas pressure: 0.010 Pa to 0.020 Pa, Output density of the target: 1.0 W / cm 2 ~8.5 W / cm 2 , Film formation rate: 0.01 nm / sec to 0.10 nm / sec, Film thickness: 1 nm to 10 nm.

[0042] The absorption film 13 absorbs EUV light. The absorption film 13 is a film on which an opening pattern 13op is to be formed. The opening pattern 13op 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. That is, the absorption film 13 may be a phase shift film. The phase shift film shifts the phase of the second EUV light L2 with respect to the first EUV light L1 shown in FIG. 6.

[0043] The first EUV light L1 passes through the opening pattern 13op of the absorption film 13 without being absorbed by the absorption film 13, is reflected by the multilayer reflective film 11, and passes through the opening pattern 13op of the absorption film 13 again without being absorbed by the absorption film 13. The second EUV light L2 is transmitted through the absorption film 13 while being absorbed by the absorption film 13, is reflected by the multilayer reflective film 11, and is transmitted through the absorption film 13 again while being absorbed by the absorption film 13.

[0044] 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 absorbing film 13 improves the contrast of the transferred image by utilizing the interference between the first EUV light L1 and the second EUV light L2. The transferred image is an image obtained by transferring the opening pattern 13op of the absorbing film 13 onto the target substrate.

[0045] In EUVL, a so-called projection effect (shadowing effect) occurs. The shadowing effect refers to the occurrence of an area near the sidewall of the opening pattern 13op where the sidewall blocks the EUV light due to the incident angle θ of the EUV light being not 0° (for example, 6°), resulting in a positional or dimensional deviation of the transferred image. In order to reduce the shadowing effect, it is effective to reduce the height of the sidewall of the opening pattern 13op, and it is also effective to thin the absorbing film 13.

[0046] The thickness of the absorbing film 13 is, for example, 60 nm or less, and preferably 50 nm or less, in order to reduce the shadowing effect. The thickness of the absorbing film 13 is preferably 20 nm or more, and 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.

[0047] In order to reduce the film thickness of the absorbing film 13 so as to reduce the shadowing effect while maintaining the phase difference between the first EUV light L1 and the second EUV light L2, it is effective to reduce the refractive index n of the absorbing film 13. Furthermore, in order to reduce the reflectance for the second EUV light L2, it is effective to increase the extinction coefficient k of the absorbing film 13. Thus, the absorbing film 13 is required to have excellent optical properties.

[0048] The absorbing film 13 preferably contains at least one metal element selected from Cr, Ta, Nb, Ir, Pt, Pd, Os, Re, W, Au, and Ru. These metal elements have a relatively small refractive index, so the thickness of the absorbing film 13 can be reduced while ensuring phase difference. The absorbing film 13 preferably contains a compound of a metal element. The compound of a metal element preferably contains at least one non-metal element selected from O, B, C, and N. Adding at least one of these non-metal elements can suppress crystallization while suppressing deterioration of optical properties.

[0049] The absorber film 13 more preferably contains Ta as a main component. The absorber film 13 containing Ta as a main component means that the Ta content in the absorber film 13 is 50 at % or more. The absorber film 13 may contain only Ta, but more preferably contains a Ta compound. The Ta compound more preferably contains N in addition to Ta. When the Ta compound contains N, crystallization of the absorber film 13 can be suppressed. Therefore, an increase in line edge roughness of the opening pattern 13op of the absorber film 13 due to crystallization of the absorber film 13 can be suppressed. Furthermore, surface roughness of the absorber film 13 due to crystallization of the absorber film 13 can be suppressed, and an increase in the detection rate of false defects can be suppressed. The Ta compound may contain at least one metal element selected from Cr, Nb, Ir, Pt, Pd, Os, Re, Au, and Ru in addition to Ta.

[0050] In this embodiment, the absorber film 13 is a single-layer film consisting of a single layer, but it may also be a multi-layer film having a lower layer and an upper layer. The lower layer and upper layer constituting the absorber film 13 are formed in this order on the protective film 12. The top layer of the absorber film 13 is the layer farthest from the protective film 12. The top layer of the absorber film 13 preferably contains at least one metal element selected from Cr, Ta, Nb, Ir, Pt, Pd, Os, Re, Au, and Ru, and more preferably contains a compound of the metal element. The top layer of the absorber film 13 more preferably contains Ta as a main component, and even more preferably contains a Ta compound. When the absorber film 13 is a multi-layer film, the thickness of the absorber film 13 means the total thickness of the multi-layer film.

[0051] When the Ta compound contains Ta and N, the content of N atoms in the Ta compound is preferably 10.0 at% to 35.0 at% for enhancing the etching selectivity, more preferably 10.0 at% to 25.0 at%, still more preferably 10.5 at% to 18.0 at%, and particularly preferably 11.0 at% to 16.0 at%.

[0052] 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.

[0053] The film formation method of the absorption film 13 is, for example, a DC sputtering method, a magnetron sputtering method, an ion beam sputtering method, or the like. The nitrogen content of the absorption film 13 can be controlled by the content of N2 gas in the sputtering gas.

[0054] When forming a TaN film using a reactive sputtering method, an example of the film formation conditions is as follows. <Film formation conditions of TaN film> Target: Ta target, Output density of Ta target: 1.0 W / cm 2 ~8.5 W / cm 2 、 Sputtering gas: Mixed gas of Ar gas and N2 gas, Volume ratio of N2 gas in sputtering gas (N2 / (Ar + N2)): 0.01 to 0.25, Gas pressure: 1.0×10 -2 Pa~1.0×10 0 Pa, Output density of Ta target: 1.0 W / cm 2 ~8.5 W / cm 2 、 Film formation rate: 0.020 nm / sec to 0.060 nm / sec, Film thickness: 20 nm to 60 nm.

[0055] The hard mask film 14 is formed on the opposite side of the absorbing film 13 from the protective film 12, and is used to form an opening pattern 13op in the absorbing film 13. The hard mask film 14 enables the resist film 16 to be made thinner.

[0056] The hard mask film 14 preferably contains at least one metal element or semi-metal 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 metal element or semi-metal element. The compound preferably contains at least one element selected from O, N, C, and B.

[0057] The thickness of the hard 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 further preferably 2 nm or more and 10 nm or less.

[0058] The hard mask film 14 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0059] The conductive film 15 is formed on the opposite side of the substrate 10 from the multilayer reflective film 11, and is used to attach the reflective mask 2 to an electrostatic chuck of an exposure device (not shown). In this embodiment, the conductive film 15 is a single-layer film, but it may also be a multi-layer film having a lower layer and an upper layer.

[0060] From the viewpoints of conductivity and stability, the conductive film 15 preferably contains at least one metal element selected from Cr and Ta. The conductive film 15 preferably contains a compound of the above metal element. The compound preferably contains at least one nonmetal element selected from N, O, C, B, and Si. The oxygen content of the compound is preferably 30 at% or less.

[0061] The thickness of the conductive film 15 is preferably 50 nm to 400 nm, and more preferably 70 nm to 350 nm. When the conductive film 15 is a multi-layer film, the thickness of the conductive film 15 is the total thickness of the multi-layer film.

[0062] The conductive film 15 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0063] Next, an example of the positional relationship between the opening pattern of the absorbing film and the defect will be described with reference to Fig. 7. As shown in Fig. 7, it is preferable to correct the position of the opening pattern 13op formed in the absorbing film 13 so that defects D1 and D2 present in the substrate 10, multilayer reflective film 11, protective film 12, or absorbing film 13 are covered by the absorbing film 13. This prevents the defects D1 and D2 from affecting the transfer accuracy of EUVL. This technique is called mitigation.

[0064] Defect D1 is a phase defect. The phase defect changes the phase of EUV light by disrupting the layer structure of the multilayer reflective film 11. The phase defect is formed, for example, on the first main surface 10a of the substrate 10 or inside the multilayer reflective film 11. On the other hand, defect D2 is an amplitude defect. The amplitude defect changes the amplitude of EUV light by absorbing the EUV light. The amplitude defect is formed, for example, on the surface 11a of the multilayer reflective film 11, on the surface 12a or inside the protective film 12, or on the surface 13a or inside the absorbing film 13.

[0065] 8, the method for manufacturing the reflective mask blank 1 includes steps S301 to S304. Steps S301 to S304 are performed after the formation of the multilayer reflective film 11 (step S103) and before the formation of the absorbing film 13 (step S105). Note that the order of steps S302 to S303 and step S304 may be reversed, and step S304 may be performed before steps S302 to S303.

[0066] 9, in step S301, at least a portion of the multilayer reflective coating 11 is removed to form a concave fiducial mark M. Step S301 may be performed after the formation of the multilayer reflective coating 11, or may be performed after the formation of the protective coating 12. For example, when the multilayer reflective coating 11 and the protective coating 12 are formed consecutively using the same film-forming apparatus, step S301 may be performed after the formation of the protective coating 12. In this case, in step S301, a portion of the protective coating 12 and a portion of the multilayer reflective coating 11 are removed to form a concave fiducial mark M.

[0067] As shown in Fig. 10, the reference marks M are formed, for example, one at each of the four corners of the surface 12a of the protective film 12. The reference marks M are used to inspect the defects D1 and D2 (step S304). The inspection device captures an image of the reference marks M and detects the positions of the reference marks M by image processing the captured image. The inspection device also sets a coordinate system based on the detected position of the reference marks M. The inspection device then detects the positions of the defects D1 and D2 in the set coordinate system.

[0068] The wavelength of the light used to capture the image is preferably 10 nm to 600 nm. The light used to capture the image is preferably EUV light (wavelength: 10 nm to 20 nm) or DUV light (wavelength: 200 nm to 360 nm). EUV light is suitable for detecting phase defects. On the other hand, DUV light is suitable for detecting amplitude defects. EUV light has a shorter wavelength than DUV light and can detect small defects.

[0069] The greater the number of reference marks M, the higher the reproducibility of the coordinate system set by the inspection device. The number of reference marks M is preferably 4 or more, and more preferably 8 or more. However, if the number of reference marks M is too large, it takes time and costs money to create the reference marks M. Therefore, the number of reference marks M is preferably 30 or less, and more preferably 20 or less.

[0070] The reference mark M is formed, for example, in the shape of a cross. The intersection of the center line of one straight line and the center line of the remaining straight lines is the reference point. The shape of the reference mark M is not limited to a cross, but may be rectangular. Rectangles include squares. The shape of the reference mark M may be a polygon other than a rectangle, such as a triangle, pentagon, or hexagon.

[0071] The reference mark M is formed by removing at least a portion of the multilayer reflective film 11. Examples of the removal method include laser processing and FIB (Focused Ion Beam) methods. A mixing layer 11C is formed on the bottom surface Ma of the reference mark M by irradiation with a laser beam or metal ions (e.g., Ga ions). The mixing layer 11C is a layer in which the high-refractive index layer and the low-refractive index layer that constitute the multilayer reflective film 11 are mixed. The mixing layer 11C may contain at least one of a component derived from the protective film 12, a component derived from the metal ions used in the FIB, and O due to natural oxidation.

[0072] When the multilayer reflective film 11 includes an Si layer 11A and an Mo layer 11B alternately as shown in FIG. 9, the mixing layer 11C includes Si and Mo. The volume of Si hardly changes due to oxidation. The density of Si is approximately 2.3 g / cm. 3 whereas the density of SiO2 is about 2.2 g / cm 3 On the other hand, Mo's volume increases with oxidation. The density of Mo is approximately 10.3 g / cm 3 whereas the density of MoO3 is about 4.7 g / cm 3 is.

[0073] The present inventors investigated the cause of the protrusion of the bottom surface Ma of the reference mark M after its formation, as shown by the dashed line in Figure 9, and concluded that the main cause was natural oxidation of Mo contained in the mixing layer 11C. Therefore, the present inventors considered implementing steps S302 and S303 as a countermeasure, and confirmed the effectiveness of this measure through experiments. The experimental data will be explained in the Examples section.

[0074] In step S302, ultraviolet light is irradiated onto the multilayer reflective film 11 including the reference mark M. The type of ultraviolet light is not particularly limited, but is preferably excimer ultraviolet light (wavelength: 172 nm, 185 nm, 254 nm, or 308 nm). The irradiation of ultraviolet light generates oxygen radicals. As a result, organic matter adhering to the surface of the mixing layer 11C can be decomposed and removed, and the oxidation of Mo contained in the mixing layer 11C can be promoted. Therefore, the bottom surface Ma of the reference mark M rises as shown in FIG. 11.

[0075] The irradiation energy E of the ultraviolet light is preferably 0.045 J / cm 2 The ultraviolet irradiation energy E is 0.045 J / cm 2 If the energy E is equal to or greater than this, the oxidation of Mo contained in the mixing layer 11C can be promoted, and Mo can be transformed into MoO3. The higher the ultraviolet irradiation energy E, the more preferable. The ultraviolet irradiation energy E is more preferably 0.050 J / cm 2 However, from the viewpoint of the effect on the irradiation time, the irradiation energy E of ultraviolet light is set to 2.00 J / cm 2 It may be less than 1.50 J / cm 2 It may be the following:

[0076] In step S303, the multilayer reflective film 11 including the fiducial mark M is cleaned with a cleaning solution containing water. The water contained in the cleaning solution dissolves MoO3 generated by the ultraviolet irradiation (step S302). Unlike Mo, MoO3 can be dissolved from the mixing layer 11C into water. As a result, the following effects (A) and (B) are obtained.

[0077] (A) As shown in FIG. 12, the protrusion on the bottom surface Ma of the reference mark M can be removed, and the bottom surface Ma of the reference mark M can be returned to a flat state. (B) The Mo content in the bottom surface Ma of the reference mark M can be reduced, and the bottom surface Ma can be prevented from protruding again due to natural oxidation. This enables long-term storage. Therefore, it becomes possible to form the absorption film 13 even after 7 days or more have passed since the formation of the reference mark M.

[0078] To achieve the effect (B) above, it is important that the layer immediately below the mixing layer 11C on the bottom surface Ma of the reference mark M is the Si layer 11A. If the Mo layer 11B exists instead of the Si layer 11A, the contact area between the Mo layer 11B and the mixing layer 11C is too large. Therefore, even if steps S302 and S303 are performed, the Mo content on the bottom surface Ma of the reference mark M cannot be sufficiently reduced, and the bottom surface Ma will rise again due to natural oxidation.

[0079] Therefore, in step S301, the depth D of the reference mark M is set so that the layer immediately below the mixing layer 11C is the Si layer 11A at the bottom surface Ma of the reference mark M. The depth D of the reference mark M can be controlled, for example, by the irradiation time of a laser beam or metal ions (e.g., Ga ions).

[0080] An example of the relationship between D and H will be described with reference to FIG. 13. In the following description, H is the height of the protrusion on the bottom surface Ma of the reference mark M (see FIG. 9). In FIG. 13, H was measured 60 days after steps S301, S302, and S303 were performed. Note that in FIG. 13, steps S301, S302, and S303 were performed on the same day.

[0081] As shown in Figure 13, the range of D where H is 10 nm or less has a lower limit (e.g., 89.0 nm) and an upper limit (93.6 nm). The difference between the upper and lower limits (4.6 nm) is similar to the thickness of the Si layer 11A (4.0 nm). In Figure 13, the thickness of the Mo layer 11B is 2.8 nm.

[0082] 13, it can be seen that in order to obtain the effect (B) above, it is important that the layer immediately below the mixing layer 11C on the bottom surface Ma of the reference mark M is the Si layer 11A. If the Mo layer 11B exists instead of the Si layer 11A, it can be seen that even if steps S302 and S303 are performed, the bottom surface Ma will rise again due to natural oxidation thereafter.

[0083] The thickness of the Si layer 11A directly below the mixing layer 11C is preferably as large as possible to obtain the effect (B) described above. The thickness of the Si layer 11A directly below the mixing layer 11C is preferably 0.1 nm or more, more preferably 0.5 nm or more, even more preferably 1.5 nm or more, and most preferably 2.0 nm or more. The thickness of the Si layer 11A directly below the mixing layer 11C may be 4.2 nm or less from the viewpoint of the reflection efficiency of EUV light.

[0084] The mixing layer 11C is formed not only on the bottom surface Ma of the reference mark M but also on the side surface Mb of the reference mark M. On the side surface Mb of the reference mark M, Si layers 11A and Mo layers 11B are alternately arranged directly below the mixing layer 11C. On the side surface Mb of the reference mark M, the contact area between the Mo layer 11B and the mixing layer 11C is small, so the side surface Mb does not swell due to natural oxidation.

[0085] After step S303, the bottom surface Ma of the reference mark M preferably has a Mo content of less than 8.6 at%. If the Mo content is less than 8.6 at%, re-protrusion can be suppressed. The Mo content is more preferably 5.0 at% or less, even more preferably 2.0 at% or less, and particularly preferably 1.0 at% or less. Note that the Mo content may be 0.1 at% or more from the viewpoint of the elution efficiency of MoO3.

[0086] After step S303, the bottom surface Ma of the reference mark M preferably has a Si content of 30.0 at% or more. If the Si content is 30.0 at% or more, the Mo content is low and re-protrusion can be suppressed. The Si content is more preferably 32.0 at% or less, and even more preferably 34.0 at% or more. Note that the Si content may be 40.0 at% or less from the viewpoint of promoting oxidation (i.e., from the viewpoint of increasing the O content).

[0087] The cleaning liquid used in step S303 only needs to contain water, and may further contain a chemical solution (acid or alkali). That is, the cleaning liquid may be an aqueous solution. However, the cleaning liquid is preferably pure water to prevent unintended damage to the substrate 10, the multilayer reflective film 11, or the protective film 12. Furthermore, in step S303, ultrasonic waves may be applied to the cleaning liquid to improve cleaning efficiency.

[0088] The temperature of the cleaning solution may be room temperature, but is preferably 50°C or higher, and more preferably 70°C or higher. The higher the temperature of the cleaning solution, the higher the solubility of MoO3 in the cleaning solution. For example, the solubility of MoO3 in pure water is 0.107g / 100mL at 18°C, 0.490g / 100mL at 28°C, and 2.055g / 100mL at 70°C. The temperature of the cleaning solution may be 200°C or lower to prevent unintended damage to the substrate 10, multilayer reflective film 11, or protective film 12.

[0089] Note that oxidation of Mo proceeds not only in step S302 (irradiation with ultraviolet light) but also in step S303 (cleaning with a cleaning solution). However, to sufficiently oxidize Mo, it is important to remove organic matter in advance in step S302. Therefore, in this embodiment, both steps S302 and S303 are performed.

[0090] Step S302 (irradiation with ultraviolet light) and step S303 (cleaning with a cleaning liquid) may be performed after step S301 (formation of a fiducial mark), and although there are no particular limitations on the timing of their performance, they are preferably performed within 60 days, more preferably within 30 days, and even more preferably within 7 days after step S301. It is preferable to perform step S302 (irradiation with ultraviolet light) and step S303 (cleaning with a cleaning liquid) before natural oxidation of Mo progresses.

[0091] In step S304, the positions of defects D1 and D2 are inspected based on the position of fiducial mark M. For example, the inspection device captures an image of fiducial mark M and detects the position of fiducial mark M by performing image processing on the captured image. The inspection device also sets a coordinate system based on the detected position of fiducial mark M. The inspection device then detects the positions of defects D1 and D2 in the set coordinate system.

[0092] [Example] The experimental data will be explained below. In Examples 1 to 5, a film-coated substrate consisting of a substrate 10, a multilayer reflective film 11, and a protective film was prepared, and the film-coated substrate was processed under the same conditions except for the conditions shown in Table 1. Examples 1 and 2 are working examples, and Examples 3 to 5 are comparative examples.

[0093] A SiO2-TiO2-based glass substrate (6-inch (152 mm) square outer diameter, 6.3 mm thick) was prepared as the substrate 10. This glass substrate has a thermal expansion coefficient of 0.02 × 10 at 20 °C. -7 / °C, Young's modulus is 67 GPa, Poisson's ratio is 0.17, and specific stiffness is 3.07 × 10 7 m 2 / s 2 It was.

[0094] 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 (4.0 nm thick) and a Mo layer (2.8 nm thick) using an ion beam sputtering method 40 times, and then depositing one more Si layer (8.0 nm thick). The total thickness of the Mo / Si multilayer reflective film was 280 nm ((4.0 nm + 2.8 nm) × 40 + 8.0).

[0095] The protective film 12 was a Ru film (2.5 nm thick) formed by ion beam sputtering. In Examples 1 to 5, the multilayer reflective film 11 and the protective film 12 were formed consecutively using the same film formation apparatus, and therefore the fiducial marks M were formed after the formation of the protective film 12. The fiducial marks M were formed by the FIB method. The fiducial marks M were formed in the shape of a cross in plan view. The depth D of the fiducial marks M was controlled by the irradiation time of metal ions (Ga ions).

[0096] The composition of the bottom surface Ma of the fiducial mark M was measured using a Hitachi High-Tech transmission electron microscope (model: HD-2700) and an Oxford Instruments energy dispersive X-ray analyzer (model: AZtec Energy TEM Advanced Ultim Max TLE). The bottom surface Ma contained Ga, which was used in the FIB method.

[0097] The height H of the protrusion of the bottom surface Ma of the fiducial mark M was measured 60 days after step S301 (forming the fiducial mark) using an atomic force microscope (model number: L-trace II) manufactured by Hitachi High-Technologies Corporation. It is preferable that the height H after 60 days is 10 nm or less.

[0098] Whether or not the reference mark M could be detected was checked 60 days after step S301 (forming the reference mark) using an inspection device manufactured by Lasertec Corporation (model number: ABICS E120). After 60 days, it was checked whether or not the center point of the cross-shaped reference mark M could be detected.

[0099] The experimental conditions and results of Examples 1 to 5 are shown in Table 1.

[0100] [Table 1]

[0101] As shown in Table 1, in Examples 1 to 4, step S302 (irradiation with ultraviolet light) was performed after step S301 (formation of reference marks) (more specifically, within 24 hours). In addition, in Examples 1 to 3 and 5, step S302 (cleaning with a cleaning liquid) was performed after step S301 (formation of reference marks) (more specifically, within 24 hours).

[0102] As shown in Table 1, in Examples 1 and 2, steps S302 and S303 were performed after step S301, unlike Examples 3 to 5. Also, in Examples 1 and 2, the layer immediately below the mixing layer 11C on the bottom surface Ma of the reference mark M was the Si layer 11A, unlike Examples 3 to 5. Therefore, in Examples 1 and 2, the Mo content on the bottom surface Ma of the reference mark M could be sufficiently reduced.

[0103] Table 2 shows the composition of the bottom surface Ma of the reference mark M in Example 2. In Table 1, the total content of all elements was taken as 100%, whereas in Table 2, the total content of metal elements was taken as 100%.

[0104] [Table 2]

[0105] It can be seen from Table 2 that the Mo content of the bottom surface Ma of the reference mark M can be sufficiently reduced by performing steps S302 and S303.

[0106] As shown in Table 1, in Examples 1 and 2, the Mo content of the bottom surface Ma of the reference mark M was sufficiently reduced, so that even 60 days after the formation of the reference mark M, the height H of the protrusion of the bottom surface Ma was 10 nm or less, making it possible to detect the reference mark M.

[0107] The method for manufacturing a reflective mask blank according to the present disclosure has been described above, but the present disclosure is not limited to the above-described embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure. [Explanation of symbols]

[0108] 1. Reflective mask blank 2 Reflective mask 10 Substrate 11 Multilayer reflective film 11A Si layer 11B Mo layer 11C Mixing layer 13 Absorbent membrane M fiducial mark Ma Bottom

Claims

1. A method for producing a reflective mask blank, the method comprising the steps of: producing a reflective mask blank having, in this order, a substrate, a multilayer reflective film that reflects EUV light, and an absorbing film that absorbs EUV light, the multilayer reflective film having Si layers and Mo layers alternately, the method comprising the steps of: forming a recessed reference mark by removing a part of the multilayer reflective film after forming the multilayer reflective film and before forming the absorbing film; By forming the reference mark, a mixing layer in which the Si layer and the Mo layer are mixed is formed on the bottom surface of the reference mark, At the bottom surface of the reference mark, the layer immediately below the mixing layer is the Si layer, The manufacturing method for a reflective mask blank includes, in this order, irradiating the multilayer reflective film including the reference mark with ultraviolet light after forming the reference mark and before forming the absorbing film, and cleaning the multilayer reflective film including the reference mark with a cleaning liquid including water.

2. 2. The method for producing a reflective mask blank according to claim 1, wherein after the cleaning, the bottom surface of the reference mark has a Si content of 30.0 at % or more and a Mo content of less than 8.6 at %.

3. The method for producing a reflective mask blank according to claim 1 or 2, further comprising forming the absorbing film seven days or more after the fiducial marks are formed.

4. The irradiation energy of the ultraviolet light is 0.045 J / cm ２ The method for producing a reflective mask blank according to claim 1 or 2, wherein the method is as described above.

5. The method for producing a reflective mask blank according to claim 1 or 2, wherein the cleaning liquid is pure water.

6. 3. The method for manufacturing a reflective mask blank according to claim 1, further comprising inspecting the position of a defect based on the position of the fiducial mark after forming the fiducial mark and before forming the absorbing film.

Images