Reflective mask blank, reflective mask, reflective mask blank manufacturing method, and reflective mask manufacturing method

Abstract

This reflective mask blank has, in the following order, a substrate, a multilayer reflective film that reflects EUV light, and an absorption film that absorbs EUV light, and has a conductive film on the opposite side of the substrate from the multilayer reflective film. The conductive film has a Young's modulus of 250 GPa or less as measured by a nanoindenter.

Description

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

[0001] The present 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.

[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 includes soft X-rays and vacuum ultraviolet light, and specifically refers to light with a wavelength of approximately 0.2 nm to 100 nm. At present, EUV light with a wavelength of approximately 13.5 nm is mainly being considered.

[0003] In EUVL, a reflective mask is used. The reflective mask has, for example, a substrate, a multilayer reflective film, and an absorbing film, in that order. The multilayer reflective film reflects EUV light. The absorbing film 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. In EUVL, the opening pattern of the absorbing film is transferred onto a target substrate such as a semiconductor substrate. Transferring includes transferring with reduction.

[0004] The reflective mask has a conductive film on the opposite side of the substrate from the multilayer reflective film. The conductive film is used, for example, to attach the reflective mask to an electrostatic chuck of an exposure tool. The conductive film of the reflective mask described in Patent Document 1 has a static friction coefficient of 0.25 or more measured in the air. It is described that a static friction coefficient of 0.25 or more can suppress misalignment of the reflective mask even when the electrostatic chuck moves at high speed.

[0005] International Publication No. 2016 / 204051

[0006] The electrostatic chuck of an exposure apparatus repeatedly attracts and releases a reflective mask for purposes such as maintenance or replacement of the reflective mask. This causes wear on the electrostatic chuck. As a result, particles are sometimes generated. The particles get caught between the electrostatic chuck and the reflective mask and deform the reflective mask. As a result, the transfer accuracy of EUVL sometimes deteriorates.

[0007] One aspect of the present disclosure provides a technique for suppressing wear of an electrostatic chuck that electrostatically attracts a reflective mask.

[0008] A reflective mask blank according to one embodiment of the present disclosure comprises a substrate, a multilayer reflective film that reflects EUV light, and an absorbing film that absorbs EUV light, in this order, and a conductive film on the opposite side of the substrate from the multilayer reflective film, wherein the conductive film has a Young's modulus of 250 GPa or less as measured with a nanoindenter.

[0009] According to one aspect of the present disclosure, it is possible to suppress wear of an electrostatic chuck that electrostatically attracts a reflective mask.

[0010] FIG. 1 is a cross-sectional view showing a reflective mask blank according to an embodiment. FIG. 2 is a flowchart showing a method for manufacturing a reflective mask blank according to an embodiment. FIG. 3 is a cross-sectional view showing a reflective mask according to an embodiment. FIG. 4 is a flowchart showing a method for manufacturing a reflective mask according to an embodiment. FIG. 5A is a cross-sectional view showing an example of step S201, FIG. 5B is a cross-sectional view showing an example of step S202, and FIG. 5C is a cross-sectional view showing an example of step S203. FIG. 6 is a cross-sectional view showing an example of EUV light reflected by the reflective mask of FIG. 3. FIG. 7 is a cross-sectional view showing an example of a reflective mask and an electrostatic chuck. FIG. 8 is a cross-sectional view showing another example of a reflective mask and an electrostatic chuck. FIG. 9 is a cross-sectional view showing an example of an arrangement of electrodes used for measuring contact resistance. FIG. 10 is a diagram showing an example of the relationship between resistance, inter-electrode distance, and contact resistance.

[0011] 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 range of values ​​means that the values ​​before and after it are included as the lower and upper limits. The range of values ​​includes the range rounded up or down.

[0012] 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 Figure 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.

[0013] 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 on a 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 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 the first etching gas during processing of the absorbing film 13.

[0014] The reflective mask blank 1 has a conductive film 15 on the opposite side of the substrate 10 from the multilayer reflective film 11. 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.

[0015] 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 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.

[0016] 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 the first etching gas that forms the 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The second etching gas is selected depending on the combination of the material of the resist film 16 and the material of the hard mask film 14, and is not particularly limited, but may include, for example, a fluorine-based gas. The fluorine-based gas may be, for example, CF ４ Gas, CHF ３ Gas, C ２ F ６ Gas, C ３ F ６ Gas, C ４ F ６ Gas, C ４ F ８ Gas, CH ２ F ２ Gas, CH ３ F gas, C ３ F ８Gas, F ２ Gas, SF ６ Gas and NF ３ The second etching gas may contain at least one selected from the group consisting of a fluorine-based gas, an active gas, and an inert gas. The active gas may be, for example, O ２ Gas and O ３ The inert gas includes at least one selected from the group consisting of N ２ The second etching gas preferably contains at least one selected from the group consisting of a nitrogen gas, a He gas, and an Ar gas. The second etching gas is preferably a plasma.

[0023] 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.

[0024] 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, but includes, for example, a chlorine-based gas and an oxygen-based gas. The chlorine-based gas is, for example, Cl ２ Gas, SiCl ４ Gas, CHCl ３ Gas, CCl ４ Gas and BCl ３ The oxygen-based gas includes at least one selected from the group consisting of O ２ Gas and O ３ The first etching gas may contain at least one selected from the group consisting of a chlorine-based gas, an oxygen-based gas, and an inert gas. The inert gas may be, for example, N ２ The first etching gas preferably contains at least one selected from the group consisting of a nitrogen gas, a He gas, and an Ar gas. The first etching gas is preferably a plasma.

[0025] In step S204, although not shown, the hard mask film 14 is removed. A third etching gas, for example, is used to remove the hard mask film 14. The third etching gas, like the second etching gas, contains, for example, a fluorine-based gas. The third etching gas is preferably a plasma gas. A chemical solution may be used to remove the hard mask film 14.

[0026] 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.

[0027] The substrate 10 is, for example, a glass substrate. The material of the substrate 10 is TiO ２ The quartz glass has a smaller coefficient of linear expansion and a smaller change in dimension due to temperature changes than common soda lime glass. ２ 80% by mass to 95% by mass of TiO ２ It may contain 4% to 17% by mass of TiO ２ When the content is 4% by mass to 17% by mass, the linear expansion coefficient is approximately zero around room temperature, and there is almost no dimensional change around room temperature. ２ and TiO ２ The substrate 10 may contain a third component or impurities other than the above. The material of the substrate 10 may be crystallized glass in which a β-quartz solid solution is precipitated, silicon, a metal, or the like.

[0028] 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. In plan view (viewed in the Z-axis direction), the substrate 10 measures, for example, 152 mm long and 152 mm wide. The vertical and horizontal dimensions may be 152 mm or greater. The first major surface 10a and the second major surface 10b each have, for example, a square quality assurance area at their centers. The quality assurance area measures, for example, 142 mm long and 142 mm wide. The vertical and horizontal dimensions may be 142 mm or greater. The quality assurance area on the first major 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, the quality assurance area on the first major surface 10a preferably does not have defects that cause phase defects.

[0029] The multilayer reflective film 11 reflects EUV light. The multilayer reflective film 11 is formed by alternately stacking, for example, high-refractive-index layers and low-refractive-index layers. 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 that a Mo / Si multilayer reflective film is used. Note that other films that can be used as the multilayer reflective film 11 include a Ru / Si multilayer reflective film, a Mo / Be multilayer reflective film, a Mo compound / Si compound multilayer reflective film, a Si / Mo / Ru multilayer reflective film, a Si / Mo / Ru / Mo multilayer reflective film, a Si / Ru / Mo / Ru multilayer reflective film, and a Si / Ru / Mo multilayer reflective film.

[0030] The thickness of each layer constituting the multilayer reflective film 11 and the number of repeating units of the layers can be appropriately selected depending on the material of each layer and the reflectivity for 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 for EUV light at an incident angle θ (see FIG. 6 ) of 6°, Mo layers with a thickness of 2.3±0.1 nm and Si layers with a thickness of 4.5±0.1 nm can be stacked so that the number of repeating units is 30 to 60. The multilayer reflective film 11 preferably has a reflectivity of 60% or more for EUV light at an incident angle θ of 6°. The reflectivity is more preferably 65% ​​or more.

[0031] The method for forming each layer constituting the multilayer reflective film 11 is, for example, DC sputtering, magnetron sputtering, or ion beam sputtering. When the Mo / Si multilayer reflective film is formed using ion beam sputtering, an example of the film formation conditions for the Mo layer and the Si layer is as follows: <Si layer formation conditions> Target: Si target, Sputtering gas: Ar gas, Gas pressure: 1.3×10 －２ Pa ~ 2.7 x 10 －２ Pa, Ion acceleration voltage: 300 V to 1500 V, Film formation rate: 0.030 nm / sec to 0.300 nm / sec, 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 x 10 －２ Pa, ion acceleration voltage: 300 V to 1500 V, film formation rate: 0.030 nm / sec to 0.300 nm / sec, film thickness of Mo layer: 2.3±0.1 nm, <Repeating units of Si layer and Mo layer> Number of repeating units: 30 to 60 (preferably 40 to 50).

[0032] 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.

[0033] The protective film 12 contains at least one element selected from, for example, Ru, Rh, and Si. When the protective film 12 contains Rh, the protective film 12 may contain only Rh, or may contain an Rh compound. The Rh compound may contain, in addition to Rh, at least one element selected from the group consisting of Ru, Nb, Mo, Ta, Ir, Pd, Zr, Y, and Ti.

[0034] The Rh compound may contain, in addition to Rh, at least one element selected from the group consisting of N, O, C, and B. These 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 Rh compound has an amorphous structure or a microcrystalline structure, the X-ray diffraction profile of the Rh compound does not have a clear peak.

[0035] 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 protective film 12 as a whole multifunctional.

[0036] 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 a 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. Furthermore, in order to suppress the crystallinity of the protective film 12, the lower layer of the protective film 12 preferably contains at least one element selected from C, N, and B in addition to the at least one element described above. 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. A mixing layer formed by mixing the components contained in the multilayer reflective film 11 and the 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.

[0037] The thickness of the protective film 12 is preferably 1.0 nm to 4.0 nm, more preferably 2.0 nm to 3.5 nm, and even more preferably 2.5 nm to 3.0 nm. If the thickness of the protective film 12 is 1.0 nm or more, the etching resistance is good. Furthermore, if the thickness of the protective film 12 is 4.0 nm or less, the reflectance to EUV light is good.

[0038] 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 it is equal to or less than this, it is possible to suppress a decrease in reflectance for EUV light.

[0039] The protective film 12 can be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering. When the Rh film is formed by DC sputtering, an example of the film formation conditions is as follows: <Conditions for forming Rh film> Target: Rh target, Sputtering gas: Ar gas, Gas pressure: 1.0×10 －２ Pa ~ 1.0 x 10 ０ Pa, target power density: 1.0 W / cm ２ ~8.5 W / cm ２ , Film formation rate: 0.020 nm / sec to 1.000 nm / sec, Film thickness: 1 nm to 10 nm.

[0040] The absorbing film 13 absorbs EUV light. The absorbing film 13 is a film in 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 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 phase shift film shifts the phase of the second EUV light L2 relative to the first EUV light L1 shown in FIG. 6 .

[0041] The first EUV light L1 is light that passes through the opening pattern 13op of the absorbing film 13 without being absorbed by the absorbing film 13, is reflected by the multilayer reflective film 11, and passes through the opening pattern 13op of the absorbing film 13 without being absorbed again by the absorbing film 13. The second EUV light L2 is light that passes through the absorbing film 13 while being absorbed by the absorbing film 13, is reflected by the multilayer reflective film 11, and passes through the absorbing film 13 while being absorbed again by the absorbing film 13.

[0042] 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 of or behind the phase of the second EUV light L2. The absorbing film 13 improves the contrast of the transferred image by utilizing 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.

[0043] In EUVL, a so-called shadowing effect occurs. The shadowing effect refers to the occurrence of a region in the vicinity of 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.

[0044] 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, and 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.

[0045] In order to reduce the thickness of the absorbing film 13 so as to reduce the shadowing effect while ensuring 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.

[0046] The absorbing film 13 preferably contains at least one metal element selected from Cr, Ta, Nb, Ir, Pt, Pd, Os, Re, Au, and Ru. These metal elements have a relatively small refractive index, so the film thickness of the absorbing film 13 can be reduced while ensuring a 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 element selected from O, B, C, and N. By adding at least one element selected from O, B, C, and N, crystallization can be suppressed while suppressing deterioration of optical properties, and the roughness of the opening pattern 13op can be reduced.

[0047] In this embodiment, the absorbing 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 absorbing film 13 are formed on the protective film 12 in this order. The uppermost layer of the absorbing film 13 is the layer farthest from the protective film 12. The uppermost layer of the absorbing 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. When the absorbing film 13 is a multi-layer film, the thickness of the absorbing film 13 means the total film thickness of the multi-layer film.

[0048] The method for forming the absorbing film 13 is, for example, a DC sputtering method, a magnetron sputtering method, an ion beam sputtering method, or the like. ２ The nitrogen content of the absorbing film 13 can be controlled by adjusting the gas content.

[0049] When a TaN film is formed by reactive sputtering, an example of the film formation conditions is as follows: <TaN film formation conditions> Target: Ta target, Output density of Ta target: 1.0 W / cm ２ ~8.5 W / cm ２ , Sputtering gas: Ar gas and N ２ Gas mixture, N in sputtering gas ２ Gas volume ratio (N ２ / (Ar+N ２ )): 0.01 to 0.25, Gas pressure: 1.0 x 10 －２ Pa ~ 1.0 x 10 ０Pa, Ta target power density: 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.

[0050] The hard mask film 14 is formed on the opposite side of the protective film 12 with respect to the absorbing film 13, 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.

[0051] 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.

[0052] 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.

[0053] The hard mask film 14 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0054] 7, the conductive film 15 is formed on the opposite side of the substrate 10 from the multilayer reflective film 11, and is used to attract the reflective mask 2 to an electrostatic chuck 21 of an exposure tool 20. The electrostatic chuck 21 has an electrode 22 that generates an electrostatic attraction force, an insulating stage 23 in which the electrode 22 is embedded, and a plurality of insulating burls 24 that protrude from the stage 23. The plurality of burls 24 come into contact with the conductive film 15. In this embodiment, each of the plurality of burls 24 is cylindrical, but may also be tapered conical.

[0055] The electrostatic chuck 21 repeatedly attracts and releases the reflective mask 2 for the purpose of maintenance or replacement of the reflective mask 2. In this case, the Young's modulus of the conductive film 15 measured with a nanoindenter is preferably 250 GPa or less so that the burrs 24 of the electrostatic chuck 21 do not wear out.

[0056] The nanoindenter performs a quasi-static indentation test on the sample to obtain the mechanical properties of the sample. The nanoindenter is not particularly limited, but an example is the iMicro manufactured by KLA Corporation. The Young's modulus is calculated using, for example, the continuous stiffness measurement method (CSM). To minimize the influence of the substrate 10, the Young's modulus is calculated when the indentation depth is 1 / 3 of the film thickness of the conductive film 15.

[0057] In this embodiment, the conductive film 15 is a single-layer film made up of a single layer, but it may also be a multi-layer film having a lower layer 15A and an upper layer 15B as shown in Figure 8. The lower layer 15A and upper layer 15B that make up the conductive film 15 are formed in this order on the substrate 10. The lower layer 15A contacts the substrate 10. The upper layer 15B contacts a plurality of burls 24.

[0058] The lower layer 15A of the conductive film 15 does not need to be in contact with the substrate 10, and another functional film may be formed between the conductive film 15 and the substrate 10. The conductive film 15 may have an intermediate layer between the lower layer 15A and the upper layer 15B.

[0059] When the conductive film 15 is a multilayer film, the Young's modulus of the conductive film 15 is measured with a nanoindenter after all layers constituting the conductive film 15 are formed on the substrate 10. Even when the conductive film 15 is a multilayer film, the Young's modulus when the indentation depth is 1 / 3 of the film thickness of the conductive film 15 is used to eliminate the influence of the substrate 10 as much as possible.

[0060] If the Young's modulus of the conductive film 15 measured with a nanoindenter is 250 GPa or less, the conductive film 15 is sufficiently soft. Therefore, wear of the burrs 24 of the electrostatic chuck 21 can be suppressed, and the generation of particles can be suppressed. Particles can get caught between the electrostatic chuck 21 and the reflective mask 2 and deform the reflective mask 2. As a result, the transfer accuracy of EUVL can be deteriorated. According to this embodiment, the generation of particles can be suppressed, and the transfer accuracy of EUVL can be improved.

[0061] The Young's modulus of the conductive film 15 measured with a nanoindenter is preferably 250 GPa or less, more preferably 220 GPa or less, and even more preferably 200 GPa or less. The Young's modulus of the conductive film 15 measured with a nanoindenter is preferably 100 GPa or more, and more preferably 120 GPa or more.

[0062] When the conductive film 15 is a single layer film, from the viewpoint 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 total content of N, O, C, B, and Si in the compound is preferably 30 at % or less.

[0063] The content of each element in the conductive film 15 is a value obtained by analysis using X-ray photoelectron spectroscopy (XPS). A detailed content analysis method follows the method described in the examples below. When the conductive film 15 has a multilayer structure, analysis is performed while etching the conductive film 15 from the surface opposite the substrate 10 using, for example, ion sputtering with argon or the like, and the content of each element in each layer of the conductive film 15 is analyzed.

[0064] When the conductive film 15 is a single layer film containing Ta and N, the Ta content is preferably 70 at % or more, more preferably 75 at % or more, and is preferably 95 at % or less, more preferably 90 at % or less, and even more preferably 85 at % or less.

[0065] When the conductive film 15 is a single layer film containing Ta and B, the Ta content is preferably 70 at% or more, more preferably 75 at% or more, and even more preferably 80 at% or more. The Ta content is preferably 95 at% or less, more preferably 90 at% or less, and even more preferably 85 at% or less.

[0066] When the conductive film 15 is a single layer film containing Ta and B, the B content is preferably 5 at % or more, more preferably 10 at % or more, and even more preferably 15 at % or more. The B content is preferably 30 at % or less, more preferably 25 at % or less, and even more preferably 20 at % or less.

[0067] When the conductive film 15 is a multi-layer film, the lower layer 15A preferably contains at least one metal element selected from Cr and Ta from the viewpoints of conductivity and stability. The lower layer 15A preferably contains a compound of the above metal element. From the viewpoints of conductivity and film stress adjustment, the compound preferably contains at least one nonmetal element selected from N, C, B, and Si. Among these nonmetal elements, N is most preferable from the viewpoint of film stress adjustment. Adjusting the film stress can reduce warpage of the reflective mask 2. From the viewpoint of conductivity, the lower layer 15A preferably does not substantially contain O. The O content of the lower layer 15A is preferably 0.1 at% or less.

[0068] When the conductive film 15 is a multilayer film and the lower layer 15A contains Ta and N, the Ta content is preferably 60 at% or more, more preferably 65 at% or more, and even more preferably 70 at% or more. The Ta content is preferably 95 at% or less, more preferably 90 at% or less, even more preferably 85 at% or less, and particularly preferably 80 at% or less.

[0069] When the conductive film 15 is a multilayer film and the lower layer 15A contains Ta and N, the N content is preferably 5 at% or more, more preferably 10 at% or more, even more preferably 15 at% or more, and particularly preferably 20 at% or more. The N content is preferably 40 at% or less, more preferably 35 at% or less, and even more preferably 30 at% or less.

[0070] When the conductive film 15 is a multi-layer film and the lower layer 15A contains Cr and N, the Cr content is preferably 75 at% or more, more preferably 80 at% or more, and even more preferably 85 at% or more. The Cr content is preferably 95 at% or less, and more preferably 93 at% or less.

[0071] When the conductive film 15 is a multilayer film and the lower layer 15A contains Cr and N, the N content is preferably 3 at% or more, more preferably 5 at% or more, and even more preferably 7 at% or more. The N content is preferably 25 at% or less, more preferably 20 at% or less, even more preferably 15 at% or less, and particularly preferably 10 at% or less.

[0072] When the conductive film 15 is a multi-layer film, the upper layer 15B is preferably formed of a material softer than the lower layer 15A, and preferably contains a total of 5 at% or more of at least one non-metallic element selected from O, B, Si, and C to reduce hardness. Among these non-metallic elements, O is most preferable from the viewpoint of chemical stability. The total content of the above non-metallic elements is preferably 5 at% or more, more preferably 10 at% or more, and even more preferably 20 at% or more. The total content of the above non-metallic elements is preferably 60 at% or less, more preferably 55 at% or less. From the viewpoint of softness, the upper layer 15B preferably does not substantially contain N. The N content of the upper layer 15B is preferably 0.1 at% or less.

[0073] When the conductive film 15 is a multilayer film and the upper layer 15B contains Ta and O, the Ta content is preferably 45 at% or more, more preferably 50 at% or more, and even more preferably 55 at% or more. The Ta content is preferably 80 at% or less, more preferably 75 at% or less, even more preferably 70 at% or less, and particularly preferably 65 at% or less.

[0074] When the conductive film 15 is a multilayer film and the upper layer 15B contains Ta and O, the O content is preferably 20 at% or more, more preferably 25 at% or more, even more preferably 30 at% or more, and still more preferably 35 at% or more. The O content is preferably 55 at% or less, more preferably 50 at% or less, and still more preferably 45 at% or less.

[0075] When the conductive film 15 is a multilayer film and the upper layer 15B contains Cr and O, the Cr content is preferably 65 at% or more, more preferably 70 at% or more, and even more preferably 75 at% or more, and is preferably 95 at% or less, more preferably 90 at% or less, and even more preferably 85 at% or less.

[0076] When the conductive film 15 is a multilayer film and the upper layer 15B contains Cr and O, the O content is preferably 5 at% or more, more preferably 10 at% or more, and even more preferably 15 at% or more. The O content is preferably 35 at% or less, more preferably 30 at% or less, and even more preferably 25 at% or less.

[0077] When the conductive film 15 is a multi-layer film, the upper layer 15B preferably contains at least one metal element selected from Cr and Ta, from the viewpoint of adhesion between the upper layer 15B and the lower layer 15A. It is more preferable that the upper layer 15B and the lower layer 15A contain the same metal element. For example, it is more preferable that both the upper layer 15B and the lower layer 15A contain Cr. Alternatively, it is more preferable that both the upper layer 15B and the lower layer 15A contain Ta. It is also possible for both the upper layer 15B and the lower layer 15A to contain Cr and Ta.

[0078] When the conductive film 15 is a multi-layer film, the upper layer 15B preferably has a thickness of 4 nm or more. The thicker the upper layer 15B, which is softer than the lower layer 15A, the more the wear of the burl 24 of the electrostatic chuck 21 can be reduced. The thickness of the upper layer 15B is preferably 4 nm or more, and more preferably 6 nm or more. However, the upper layer 15B has lower conductivity than the lower layer 15A. Therefore, from the viewpoint of the conductivity of the conductive film 15, the thickness of the upper layer 15B is preferably 50 nm or less, and more preferably 30 nm or less.

[0079] The contact resistance of the conductive film 15 is preferably 1000×10 －３ Ω cm ２ or less, more preferably 500×10 －３ Ω cm ２ or less, and more preferably 300×10 －３ Ω cm ２ The following is the result.

[0080] As shown in FIG. 9, the contact resistance of the conductive film 15 is determined by arranging five disk electrodes 30A, 30B, 30C, 30D, and 30E, each 1.2 mm in diameter, in a line at a 2.0 mm pitch and measuring the resistance at each inter-electrode distance D1, D2, D3, and D4. D1 is 0.8 mm, D2 is 2.8 mm, D3 is 4.8 mm, and D4 is 6.8 mm. As shown in FIG. 10, a regression line is determined by the least squares method. The model formula of the regression line is as shown in FIG. 10. The intercept of the regression line (2×R Ｃ ) is divided by 2 and multiplied by the contact area (S) between one disk electrode and the conductive film 15 to obtain the contact resistance (ρ Ｃ ) is obtained (ρ Ｃ =R Ｃ ×S).

[0081] 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.

[0082] The conductive film 15 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0083] [Examples] Experimental data will be described below. In Examples 1 to 6, the conductive film 15 was formed on the substrate 10 under the film formation conditions shown in Table 1. Examples 1 to 3 are examples, and Examples 4 to 6 are comparative examples.

[0084] The substrate is SiO ２ -TiO ２ A glass substrate (6-inch (152 mm) square outer diameter, 6.3 mm thick) was prepared. This glass substrate had 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 rigidity is 3.07 × 10 ７ m ２ / s ２ It was.

[0085] In Example 1, as shown in Table 1, a TaN film was formed as a lower layer by magnetron sputtering, and then a TaO film was formed as an upper layer by magnetron sputtering. The film formation conditions for the TaN film and the TaO film were as follows: <TaN film formation conditions> Target: Ta target, Sputtering gas: 81% by volume of Ar gas, N ２ Mixed gas containing 19% by volume of gas, Gas pressure: 0.23 Pa, Input power density: 2.6 W / cm ２ <TaO film formation conditions> Target: Ta target, Sputtering gas: 40% by volume of Ar gas, O ２ Mixed gas containing 60% by volume of gas, Gas pressure: 0.05 Pa, Input power density: 2.7 W / cm ２ .

[0086] (Conductive Film Composition) The composition of the formed conductive film 15 was analyzed by XPS. For XPS, a "PHI 5000 VersaProbe" manufactured by ULVAC-PHI, Inc. The composition determined by analysis is shown in Table 1 below.

[0087] (Film Thickness) The film thickness of the conductive film 15 was measured by XRR (X-ray reflectivity). For the XRR measurement, a Smart Lab HTP manufactured by Rigaku Corporation was used. CuKα rays were used as the X-ray source, and the tube voltage was 40 kV and the tube current was 30 mA. For analysis, the accompanying software (GlobalFit) was used.

[0088] In Examples 2 to 6, the conductive film 15 was formed on the substrate 10 under the same conditions except that the film formation conditions were changed as shown in Table 1.

[0089]

[0090] After the conductive film 15 was formed, contamination was evaluated by an abrasion resistance test. In Table 1, a contamination rating of "Good" means that no particles or scratches were generated on the lens surface during the abrasion resistance test, and a contamination rating of "Poor" means that at least one of particles and scratches was generated on the lens surface during the abrasion resistance test. The abrasion resistance test was performed under vacuum as follows. First, a lens (curvature 0.18 cm, material BK-7) simulating a bar 24 was prepared. The lens had a TiN film on its surface. Next, the substrate 10 was placed on a vibration stage with the conductive film 15 facing upward. Next, the vibration stage was vibrated with the lens facing downward and the conductive film 15 in contact. The vibration conditions were a stroke of 0.1 mm, a frequency of 14 Hz, and a vibration time of 15 hours. The lens surface was then observed using an optical microscope for the presence or absence of particles and scratches, and the abrasion resistance was evaluated.

[0091] Unlike Examples 4 to 6, Examples 1 to 3 had conductive film 15 with a Young's modulus of 250 GPa or less, and therefore no particles or scratches were observed on the lens surface in the wear resistance test. This shows that Examples 1 to 3 can suppress wear of burrs 24 of electrostatic chuck 21 and suppress particle generation compared to Examples 4 to 6.

[0092] In Example 1, a soft upper TaO film was formed on a hard lower TaN film, and therefore the Young's modulus of the conductive film 15 was 250 GPa or less, unlike Example 5. In Example 3, a soft upper CrO film was formed on a hard lower CrN film, and therefore the Young's modulus of the conductive film 15 was 250 GPa or less, unlike Example 4.

[0093] In Example 2, the gas pressure during deposition of the conductive film 15 was higher than in Example 6, and therefore the Young's modulus of the conductive film 15 was 250 GPa or less. It was found that even when the film type is the same, the Young's modulus of the conductive film 15 can be made 250 GPa or less if the gas pressure during deposition is high.

[0094] In the present examples, the dynamic friction coefficient and the like were evaluated for a substrate with a conductive film formed on the substrate, but the evaluation results for the dynamic friction coefficient and the like are similar when the conductive film is formed as part of a reflective mask blank.

[0095] The reflective mask blank, reflective mask, reflective mask blank manufacturing method, and reflective mask manufacturing method according to the present disclosure have 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.

[0096] This application claims priority based on Japanese Patent Application No. 2023-201163 filed with the Japan Patent Office on November 29, 2023, the entire contents of which are incorporated herein by reference.

[0097] REFERENCE SIGNS LIST 1 reflective mask blank 2 reflective mask 10 substrate 11 multilayer reflective film 13 absorbing film 15 conductive film

Claims

1. A reflective mask blank having a substrate, a multilayer reflective film that reflects EUV light, and an absorbing film that absorbs EUV light, in that order, and a conductive film on the opposite side of the substrate to the multilayer reflective film, wherein the conductive film has a Young's modulus of 250 GPa or less as measured with a nanoindenter.

2. The reflective mask blank according to claim 1, wherein the conductive film has conductive lower and upper layers, the lower and upper layers being formed in that order on the substrate, the lower layer containing at least one metal element selected from Cr and Ta, and the upper layer containing at least one non-metal element selected from O, B, Si and C in a total amount of 5 at% or more.

3. The reflective mask blank according to claim 2, wherein the upper layer has a thickness of 4 nm or more.

4. A reflective mask blank according to claim 2 or 3, wherein the lower layer contains at least one nonmetallic element selected from the group consisting of N, B, Si and C.

5. The reflective mask blank according to claim 2, wherein the upper layer contains at least one metal element selected from the group consisting of Cr and Ta.

6. The contact resistance of the conductive film is 1000×10 －３ Ω cm ２ The reflective mask blank according to any one of claims 1 to 3, wherein:

7. A reflective mask blank according to any one of claims 1 to 3, wherein the conductive film has a thickness of 50 nm to 400 nm.

8. A reflective mask comprising the reflective mask blank according to any one of claims 1 to 3, and comprising an aperture pattern in the absorbing film.

9. A method for manufacturing a reflective mask blank, comprising: preparing a substrate having a first main surface and a second main surface facing opposite to the first main surface; forming a multilayer reflective film that reflects EUV light and an absorbing film that absorbs EUV light, in that order, on the first main surface of the substrate; and forming a conductive film on the second main surface of the substrate, wherein the conductive film has a Young's modulus of 250 GPa or less as measured with a nanoindenter.

10. A method for manufacturing a reflective mask, comprising the steps of: preparing a reflective mask blank according to any one of claims 1 to 3; and forming an opening pattern in the absorbing film, in this order.

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