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

Abstract

The purpose of the present invention is to provide a technique for improving an etching selection ratio and suppressing the surface roughness of a hard mask film.　A reflective mask blank (1) has, in the following order, a substrate (10), a multilayer reflective film (11) that reflects EUV light, a protective film (12) that protects the multilayer reflective film (11) from a first etching gas during processing of an absorbent film, an absorbent film (13) that absorbs EUV light, and a hard mask film (14). The hard mask film (14) protects part of the absorbent film (13) from the first etching gas during processing of the absorbent film (13). The hard mask film (14) has a compound containing Al and N, and said compound contains 40 at% or more of Al and 40 at% or more of N.

Description

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

[0001] This disclosure relates to a reflective mask blank, a method for manufacturing a reflective mask blank, and a method for manufacturing a reflective mask. This application claims priority to Japanese Patent Application No. 2024-068960, filed on April 22, 2024, the contents of which are incorporated herein by reference.

[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 light has a wavelength of approximately 13.5 nm. A reflective mask is used in EUVL. The reflective mask includes a substrate, a multilayer reflective film, a protective film, and an absorbing film, in that order. The multilayer reflective film reflects EUV light. The protective film protects the multilayer reflective film from a first etching gas during processing of the absorbing film. 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. 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] The reflective mask blank described in Patent Document 1 comprises a substrate, a multilayer reflective film, a protective film, an absorbing film, an etching mask film, and a resist film, in this order. The absorbing film contains iridium (Ir) and an additive element. The etching mask film contains chromium (Cr) and an additive element. The additive element to Cr is at least one selected from O, N, C, B, and H. Examples of materials for the etching mask film include CrN, CrO, CrC, CrON, CrOC, CrCN, and CrOCN. The etching mask film is a hard mask film.

[0004] WO 2022 / 138360 (A)

[0005] The method for manufacturing a reflective mask includes transferring an opening pattern of a hard mask film to an absorber film using a first etching gas. The first etching gas is selected depending on the combination of the material of the hard mask film and the material of the absorber film. The higher the ratio (ER2 / ER1) of the etching rate (ER2) of the absorber film to the etching rate (ER1) of the hard mask film, the better the processability of the absorber film. (ER2 / ER1) is also called the selectivity.

[0006] When the absorbing film contains Ir or the like, it is preferable to use a fluorine-based gas as the first etching gas. However, as described in Patent Document 1, when the hard mask film contains Cr as a main component, the etching resistance of the hard mask film against the fluorine-based gas is insufficient, and the selectivity (ER2 / ER1) is small. Therefore, it is considered to use a film containing Al as a main component as the hard mask film so as to increase the selectivity (ER2 / ER1).

[0007] Al has a higher boiling point of fluoride than Cr. Therefore, if a film containing Al as a main component is used as the hard mask film, the selectivity (ER2 / ER1) will be higher than if a film containing Cr as a main component is used as the hard mask film. However, the oxidation of Al may cause the surface of the hard mask film 14 to become rough.

[0008] An embodiment of the present disclosure provides a technique for improving the selectivity (ER2 / ER1) and suppressing surface roughness of a hard mask film.

[0009] A reflective mask blank according to an embodiment of the present disclosure comprises a substrate, a multilayer reflective film, a protective film, an absorbing film, and a hard mask film, in this order. The multilayer reflective film reflects EUV light. The protective film protects the multilayer reflective film from a first etching gas during processing of the absorbing film. The absorbing film absorbs the EUV light. The hard mask film protects a portion of the absorbing film from a first etching gas during processing of the absorbing film. The hard mask film comprises a compound containing Al and N. The compound contains 40 at% or more of Al and 40 at% or more of N.

[0010] According to an embodiment of the present disclosure, the selectivity (ER2 / ER1) can be improved and the surface roughness of the hard mask film can be suppressed.

[0011] 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. 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.

[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 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.

[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 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.

[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 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.

[0015] 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.

[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 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.

[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 Fig. 4 and Fig. 5A to Fig. 5C. The method for manufacturing a reflective mask 2 includes steps S201 to S204 shown in Fig. 4. In step S201, a reflective mask blank 1 is prepared, as shown in Fig. 5A. The reflective mask blank 1 includes a resist film 16, as shown in Fig. 5A. 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] 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 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 chlorine-based gas. The chlorine-based gas may be, for example, Cl ２ Gas, SiCl ４ Gas, CHCl ３ Gas, CCl ４ Gas and BCl ３ The second etching gas contains at least one selected from the group consisting of argon, argon, argon-based gases, and argon-based gases. As will be described in detail later, the hard mask film 14 contains Al, and chlorine-based gases tend to etch Al. Al is easily oxidized, and an oxide film is easily formed. Therefore, the second etching gas may contain Ar gas in addition to the chlorine-based gas. Ar gas is more easily converted into plasma than chlorine-based gases, and is therefore more likely to etch the oxide film of the hard mask film 14. The second etching gas is preferably a plasma-converted gas. The second etching gas preferably does not substantially contain an oxygen-based gas in order to suppress oxidation of the hard mask film 14. The oxygen-based gas is preferably O ２ Gas, O ３ The content of the oxygen-based gas in the second etching gas is preferably 0.5% by volume or less.

[0024] An example of processing conditions for the hard mask film 14 is shown below. <Processing conditions for hard mask film> Etching gas: Cl plasma ２ Gas, source power: 150W to 1000W, bias: 50W to 150W, pressure: 0.2Pa to 1.0Pa.

[0025] 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.

[0026] The first etching gas is selected depending on the combination of the material of the hard mask film 14 and the material of the absorbing film 13, and is not particularly limited, but includes, for example, a fluorine-based gas. The fluorine-based gas is, 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 ８ Gas, F ２ Gas, SF ６ Gas and NF ３ The first 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 The inert gas includes, 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.

[0027] An example of processing conditions for the absorbing film 13 is shown below. <Processing conditions for absorbing film> Etching gas: CF ４ Gas and O ２ A plasma-contained mixed gas containing a gas, source power: 150 W to 2000 W, bias: 20 W to 150 W, pressure: 0.2 Pa to 1.0 Pa.

[0028] In step S204, although not shown, the hard mask film 14 is removed. For example, a third etching gas is used to remove the hard mask film 14. The third etching gas contains a chlorine-based gas, similar to the second etching gas. The third etching gas may contain Ar gas in addition to the chlorine-based gas. The third etching gas is preferably a plasma. The third etching gas preferably does not substantially contain an oxygen-based gas in order to suppress oxidation of the hard mask film 14. The content of the oxygen-based gas in the third etching gas is preferably 0.5 vol % or less. A chemical solution may be used to remove the hard mask film 14.

[0029] As described above, step S203 involves transferring the opening pattern of the hard mask film 14 to the absorber film 13 using a first etching gas. The first etching gas is selected depending on the combination of the material of the hard mask film 14 and the material of the absorber film 13. In step S203, the higher the ratio (ER2 / ER1) of the etching rate (ER2) of the absorber film 13 to the etching rate (ER1) of the hard mask film 14, the better the processability of the absorber film 13. (ER2 / ER1) is also called the selectivity.

[0030] As will be described in detail later, the absorbing film 13 preferably contains at least one element selected from Ir, Pt, Pd, Co, Ni, Os, and Ru. These metal elements have a relatively small refractive index, so that the thickness of the absorbing film 13 can be reduced while ensuring a phase difference. When the absorbing film 13 contains these metal elements, it is preferable to use a fluorine-based gas as the first etching gas.

[0031] When the hard mask film 14 contains Cr as a main component as described in Patent Document 1, the etching resistance of the hard mask film 14 to fluorine-based gases is insufficient, and the selectivity (ER2 / ER1) is small. Therefore, in order to improve the selectivity (ER2 / ER1), it is conceivable to use a film containing Al as a main component as the hard mask film 14.

[0032] Al has a higher boiling point of fluoride than Cr. Therefore, if a film containing Al as a main component is used as the hard mask film, the selectivity (ER2 / ER1) will be higher than if a film containing Cr as a main component is used as the hard mask film. However, the oxidation of Al may cause the surface of the hard mask film 14 to become rough.

[0033] The hard mask film 14 of this embodiment has a compound containing Al and N. The compound contains 40 at % or more of Al and 40 at % or more of N. When the hard mask film 14 contains 40 at % or more of Al, the selectivity (ER2 / ER1) can be improved. Furthermore, when the hard mask film 14 contains 40 at % or more of N, oxidation of Al can be suppressed, and surface roughness of the hard mask film 14 can be suppressed.

[0034] If the oxidation of Al can be suppressed, the etching rate (ER3) of the hard mask film 14 is high in step S202. In step S202, the ratio (ER3 / ER4) of the etching rate (ER3) of the hard mask film 14 to the etching rate (ER4) of the resist film 16 is large, and the processability of the hard mask film 14 is good. This improves the processing accuracy of the hard mask film 14, and ultimately improves the processing accuracy of the absorption film 13.

[0035] The Al content of the hard mask film 14 may be 40 at % or more as described above, but is preferably 45 at % or more, and more preferably 50 at % or more. Since the N content of the hard mask film 14 is 40 at % or more, the Al content of the hard mask film 14 may be 60 at % or less.

[0036] The N content of the hard mask film 14 may be 40 at % or more as described above, but is preferably 45 at % or more, and more preferably 50 at % or more. Since the Al content of the hard mask film 14 is 40 at % or more, the N content of the hard mask film 14 may be 60 at % or less.

[0037] The compound constituting the hard mask film 14 preferably has a ratio (N content / Al content) of the N content (at %) to the Al content (at %) of 0.6 or more. If the ratio (N content / Al content) is 0.6 or more, oxidation of Al can be further suppressed, and surface roughness of the hard mask film 14 can be further suppressed. The ratio (N content / Al content) is more preferably 0.7 or more, even more preferably 0.8 or more, and particularly preferably 1.0 or more. The ratio (N content / Al content) may be 1.2 or less.

[0038] The compound constituting the hard mask film 14 may contain O in addition to Al and N. O is contained in the hard mask film 14 by, for example, natural oxidation. However, the lower the O content, the more preferable. Since the total content of Al and N is 80 at % or more, the O content is 20 at % or less.

[0039] The content of each element in the hard mask film 14 is measured using analytical values ​​obtained by X-ray photoelectron spectroscopy (XPS). For the XPS analysis, an analytical device "PHI 5000 VersaProbe" manufactured by ULVAC-PHI, Inc. is used. The device is pre-calibrated in accordance with JIS K 0145:2002. First, a measurement sample approximately 1 cm square is cut out from the reflective mask blank 1. The obtained measurement sample is placed in a measurement holder so that the hard mask film 14 side faces the measurement surface. The hard mask film 14 is irradiated with X-rays (monochromated AlKα rays), and the analysis is performed with a photoelectron take-off angle (the angle between the surface of the measurement sample and the direction of the detector) of 45°. During the analysis, a neutralization gun is used to suppress charge buildup. The analysis involves a wide scan in the binding energy range of 1000 eV to 0 eV to confirm the elements present, followed by a narrow scan depending on the elements present (e.g., Al and N). The narrow scan is performed, for example, with a pass energy of 58.7 eV, an energy step of 0.1 eV, a time / step of 50 ms, and 10 integrations. The wide scan is performed with a pass energy of 58.7 eV, an energy step of 1 eV, a time / step of 50 ms, and 2 integrations. The content of each element in the hard mask film 14 is calculated by analyzing the spectrum obtained by the narrow scan when XPS analysis is performed using the above procedure, using relative sensitivity coefficients specific to each element and each orbital, and analyzing the region where the spectral intensity becomes constant. Note that analysis may also be performed using a model sample formed under the same conditions as those for forming the hard mask film 14, following the same procedure as above.

[0040] In step S201, the root mean square roughness (Rq) of the surface of the hard mask film 14 opposite to the absorber film 13 (hereinafter simply referred to as the "surface of the hard mask film 14") is preferably 1.5 nm or less. If the root mean square roughness (Rq) of the surface of the hard mask film 14 is 1.5 nm or less, the processing accuracy of the opening pattern of the hard mask film 14 is good, and therefore the processing accuracy of the opening pattern of the absorber film 13 is also good.

[0041] The root mean square roughness (Rq) of the surface of the hard mask film 14 is more preferably 1.0 nm or less. The smaller the root mean square roughness (Rq) of the surface of the hard mask film 14, the more preferable, but it may be 0.5 nm or more.

[0042] The root mean square roughness (Rq) of the surface of the hard mask film 14 is measured in accordance with JIS B0601:2013 before the formation of the resist film 16. The root mean square roughness (Rq) of the surface of the hard mask film 14 may be measured in a region where an opening pattern is to be formed, for example, in the quality assurance region described below. The quality assurance region is a region that coincides with the exposure region in a plan view. The exposure region is a region where the exposure tool is scheduled to irradiate the absorber film 13 with EUV light.

[0043] In step S201, the thickness t of the hard mask film 14 is preferably 20 nm or less. If the thickness of the hard mask film 14 is 20 nm or less, the processing time during processing of the hard mask film 14 can be shortened and the side surfaces of the openings in the hard mask film 14 can be prevented from being inclined. The thickness of the hard mask film 14 is preferably 15 nm or less, and more preferably 10 nm or less.

[0044] Furthermore, in step S201, the film thickness of the hard mask film 14 is preferably 0.1 nm or more. If the film thickness of the hard mask film 14 is 0.1 nm or more, a sufficient amount of the hard mask film 14 remains when processing of the absorption film 13 is completed. The film thickness of the hard mask film 14 is more preferably 0.5 nm or more.

[0045] 1, the substrate 10, the multilayer reflective film 11, the protective film 12, the absorbing film 13, and the conductive film 15 will be described in this order. The hard mask film 14 is as described above.

[0046] 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 TiO２ 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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, Si layer thickness: 4.5±0.1 nm. 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, Mo layer thickness: 2.3±0.1 nm. <Repeating units of Si layer and Mo layer> Number of repeating units: 30 to 60 (preferably 40 to 50).

[0051] 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.

[0052] The protective film 12 preferably contains 50 at % or more of 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 Z1 selected from Ru, Nb, Mo, Ta, Ir, Pd, Zr, Y, and Ti. By adding Ru, Nb, Mo, Zr, Y, or Ti to Rh, it is possible to reduce the extinction coefficient while suppressing an increase in the refractive index, and to improve the reflectance to EUV light. Furthermore, by adding Ta, Ir, Pd, or Y to Rh, it is possible to improve resistance to the first etching gas.

[0053] The Rh compound may contain, in addition to Rh, at least one element Z2 selected from N, O, C, and B. The element Z2 reduces the resistance of the protective film 12 to the first etching gas, but improves the smoothness of the protective film 12 by reducing the crystallinity of the protective film 12. The Rh compound containing the element Z2 has an amorphous structure or a microcrystalline structure. 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.

[0054] In this embodiment, the protective film 12 is a single-layer film made of a single layer, but it may be a multi-layer film having a lower layer and an upper layer. The lower layer of the protective film 12 is in contact with the multilayer reflective film 11. The upper layer of the protective film 12 is in contact with 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.

[0055] The upper layer of the protective film 12 preferably contains Rh, and more preferably contains a Rh compound. The lower layer of the protective film 12 preferably contains at least one element selected from Ru, Nb, Mo, Zr, Y, C, and B, and more preferably contains Ru. When the protective film 12 is a multilayer film, the Rh content of the entire protective film 12 is preferably 50 at% or more, more preferably more than 50 at%, and even more preferably 90 at% or more. Furthermore, when the protective film 12 is a multilayer film, the thickness of the protective film 12 below refers to the total thickness of the multilayer film.

[0056] 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.

[0057] 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 thus the reduction in reflectance for EUV light).

[0058] 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: 1.0 nm to 4.0 nm.

[0059] 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 .

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] The refractive index n of the absorbing film 13 is preferably 0.940 or less, more preferably 0.930 or less, even more preferably 0.929 or less, particularly preferably 0.925 or less, even more particularly preferably 0.920 or less, even more particularly preferably 0.918 or less, still more preferably 0.910 or less, and most preferably 0.900 or less. The smaller the refractive index n of the absorbing film 13, the thinner the absorbing film 13 can be. The refractive index n of the absorbing film 13 is preferably 0.885 or more. In this specification, the refractive index refers to the refractive index for EUV light (for example, light with a wavelength of 13.5 nm).

[0066] The extinction coefficient k of the absorbing film 13 is preferably 0.020 or more, more preferably 0.025 or more, even more preferably 0.030 or more, particularly preferably 0.034 or more, still more particularly preferably 0.036 or more, even more particularly preferably 0.038 or more, and still more preferably 0.042 or more. The larger the extinction coefficient k of the absorbing film 13, the easier it is to obtain a desired reflectance with a thin film thickness. The extinction coefficient k of the absorbing film 13 is preferably 0.065 or less. In this specification, the extinction coefficient is the extinction coefficient for EUV light (for example, light with a wavelength of 13.5 nm).

[0067] The optical properties (refractive index n and extinction coefficient k) of the absorbing film 13 are values ​​taken from the database of the Center for X-Ray Optics, Lawrence Berkeley National Laboratory, or values ​​calculated from the "incident angle dependence" of reflectance described below.

[0068] The incident angle θ of the EUV light, the reflectance R for the EUV light, the refractive index n of the absorbing film 13, and the extinction coefficient k of the absorbing film 13 satisfy the following formula (1): R=|(sin θ−((n+ik) ２ -cos ２ θ) １／２ ) / (sinθ+((n+ik) ２ -cos ２ θ) １／２) | ... (1) A plurality of combinations of the incident angle θ and the reflectance R are measured, and the refractive index n and the extinction coefficient k are calculated by the least squares method so that the error between the plurality of measurement data and the equation (1) is minimized.

[0069] The absorbing film 13 preferably contains at least one element X1 selected from Ir, Pt, Pd, Co, Ni, Os, and Ru. The total content of the element X1 is preferably 25 at% or more, more preferably 30 at% or more, even more preferably 40 at% or more, and particularly preferably 50 at% or more. The element X1 has a relatively small refractive index, so that the thickness of the absorbing film 13 can be reduced while ensuring a phase difference. When the absorbing film 13 contains the element X1, it is preferable to use a fluorine-based gas as the first etching gas.

[0070] The absorbing film 13 may contain only the element X1, or may contain a compound of the element X1. The compound of the element X1 preferably contains at least one element X2 selected from O, B, C, and N. Adding the element X2 to the element X1 can suppress crystallization while suppressing deterioration in optical properties, and can reduce roughness on the side surfaces of the opening pattern 13op. The compound of the element X1 preferably contains O, and more preferably contains O and N.

[0071] The absorbing film 13 may contain only the element X1, or may contain a compound of the element X1. The compound of the element X1 preferably contains at least one element X3 selected from Ta, Cr, Mo, W, Re, and Si. Adding the element X3 to the element X1 can improve hydrogen resistance. Among these elements, Ta, Cr, W, and Re can improve hydrogen resistance while suppressing deterioration of optical properties. Furthermore, Mo and Si can further improve hydrogen resistance.

[0072] The absorbing film 13 is formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering. ２ The oxygen content of the absorbing film 13 can be controlled by adjusting the gas content. ２ The nitrogen content of the absorbing film 13 can be controlled by adjusting the gas content.

[0073] When an IrTaON film is formed by reactive sputtering, an example of the film formation conditions is as follows: <Conditions for forming an IrTaON film> Target: Ir target and Ta target (or IrTa target), power density of Ir target: 1.0 W / cm ２ ~8.5 W / cm ２ , power density of Ta target: 1.0 W / cm ２ ~8.5 W / cm ２ , sputtering gas: Ar gas and O ２ Gas and N ２ O in gas mixtures and sputtering gases ２ Gas volume ratio (O ２ / (Ar + O ２ +N ２ )): 0.01 to 0.25, N in sputtering gas ２ Gas volume ratio (N ２ / (Ar + O ２ +N ２ )): 0.01 to 0.25, film formation rate: 0.020 nm / sec to 0.060 nm / sec, film thickness: 20 nm to 60 nm.

[0074] 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 tool. 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.

[0075] 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.

[0076] 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.

[0077] The conductive film 15 may be formed by, for example, DC sputtering, magnetron sputtering, or ion beam sputtering.

[0078] [Examples] Experimental data will be described below. In Examples 1 to 8, hard mask films having the compositions shown in Table 1 were formed on glass substrates, and the root-mean-square roughness Rq of the surface of the hard mask films and the etching rates ER1 and ER3 of the hard mask films were measured. Examples 1 to 4 are Examples, and Examples 5 to 8 are Comparative Examples.

[0079]

[0080] The conditions for measuring the etching rates ER1 and ER3 were as follows: <Measurement conditions for ER1> Etching gas: CF ４ Gas and O ２ A plasma-formed mixed gas containing CF ４ Gas flow rate: 48 sccm, O ２ Gas flow rate: 12 sccm, Source power: 720 W, Bias: 80 W, Pressure: 0.4 Pa. <ER3 measurement conditions> Etching gas: Cl ２ Gas, Cl ２ Gas flow rate: 90 sccm, source power: 1200 W, bias: 80 W, pressure: 1.0 Pa.

[0081] As shown in Table 1, the hard mask films of Examples 1 to 4 had an Al content of 40 at % or more and an N content of 40 at % or more. Therefore, the hard mask films of Examples 1 to 4 had a small root-mean-square roughness Rq, a small etching rate ER1, and a large etching rate ER3.

[0082] The reflective mask blank, the method for manufacturing a reflective mask blank, and the method for manufacturing a reflective mask 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.

[0083] According to the present invention, it is possible to provide a technique for improving the selectivity (ER2 / ER1) and suppressing surface roughness of the hard mask film.

[0084] REFERENCE SIGNS LIST 1 reflective mask blank 2 reflective mask 10 substrate 11 multilayer reflective film 12 protective film 13 absorbing film 14 hard mask film

Claims

1. A reflective mask blank having a substrate, a multilayer reflective film, a protective film, an absorbing film, and a hard mask film in this order, wherein the multilayer reflective film reflects EUV light, the protective film protects the multilayer reflective film from a first etching gas when processing the absorbing film, the absorbing film absorbs the EUV light, and the hard mask film protects a part of the absorbing film from the first etching gas when processing the absorbing film, wherein the hard mask film has a compound containing Al and N, and the compound contains 40 at% or more of Al and 40 at% or more of N.

2. The reflective mask blank according to claim 1, wherein the root mean square roughness (Rq) of the surface of the hard mask film opposite to the absorbing film is 1.5 nm or less.

3. The reflective mask blank according to claim 1 or 2, wherein the thickness of the hard mask film is 20 nm or less.

4. The reflective mask blank according to claim 1 or 2, wherein the absorbing film contains at least one element selected from Ir, Pt, Pd, Co, Ni, Os and Ru.

5. The reflective mask blank according to claim 1 or 2, wherein the protective film contains 50 at % or more of Rh.

6. A method for manufacturing a reflective mask blank having a substrate, a multilayer reflective film, a protective film, an absorbing film, and a hard mask film in this order, wherein the multilayer reflective film reflects EUV light, the protective film protects the multilayer reflective film from a first etching gas when processing the absorbing film, the absorbing film absorbs the EUV light, and the hard mask film protects a part of the absorbing film from a first etching gas when processing the absorbing film, the method comprising: forming the multilayer reflective film, the protective film, the absorbing film, and the hard mask film in this order on the substrate, the hard mask film having a compound containing Al and N, and the compound containing 40 at% or more of Al and 40 at% or more of N.

7. A method for manufacturing a reflective mask, comprising, in this order: preparing a reflective mask blank according to claim 1 or 2; transferring an opening pattern of a resist film to the hard mask film using a second etching gas different from the first etching gas; and transferring the opening pattern of the hard mask film to the absorbing film using the first etching gas.

8. The method for manufacturing a reflective mask according to claim 7, wherein the first etching gas contains a fluorine-based gas, and the second etching gas contains a chlorine-based gas.

Images