JP7475154B2 - Reflective mask blank, reflective mask, substrate with conductive film, and method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a reflective mask blank, a reflective mask, and a substrate with a conductive film. The present invention also relates to a method for manufacturing a semiconductor device using a reflective mask.

The types of light sources used in exposure equipment for semiconductor device manufacturing have evolved with gradually shorter wavelengths, from g-line with a wavelength of 436 nm, i-line with a wavelength of 365 nm, KrF laser with a wavelength of 248 nm, and ArF laser with a wavelength of 193 nm. In order to achieve finer pattern transfer, extreme ultraviolet (EUV) lithography with a wavelength of around 13.5 nm has been developed. In EUV lithography, a reflective mask is used because there are few materials transparent to EUV light. In this reflective mask, a multilayer reflective film that reflects exposure light is formed on a low-thermal expansion substrate, and the mask structure has a desired transfer pattern formed on a protective film to protect the multilayer reflective film. In addition, in terms of the configuration of the transfer pattern, representative examples include a binary type reflective mask made of a relatively thick absorber pattern that sufficiently absorbs EUV light, and a phase shift type reflective mask (halftone phase shift type reflective mask) made of a relatively thin absorber pattern that attenuates EUV light by optical absorption and generates reflected light that is almost inverted in phase (about 180° phase inversion) with respect to the reflected light from the multilayer reflective film. This phase shift type reflective mask, like the transmission type optical phase shift mask, has the effect of improving resolution because a high transfer optical image contrast can be obtained by the phase shift effect. In addition, since the film thickness of the absorber pattern (phase shift pattern) of the phase shift type reflective mask is thin, a fine phase shift pattern can be formed with high precision.

Technologies relating to such reflective masks for EUV lithography and mask blanks for producing them are disclosed in Patent Documents 1 to 3.

Patent Document 1 describes a reflective mask blank for EUV lithography in which at least a reflective layer that reflects EUV light and an absorber layer that absorbs EUV light are formed in this order on a substrate. Specifically, Patent Document 1 describes that the reflective mask blank in Patent Document 1 has an absorber layer that contains tantalum (Ta), nitrogen (N) and hydrogen (H), and that the total content of Ta and N in the absorber layer is 50 to 99.9 at %, and the content of H is 0.1 to 50 at %. Patent Document 1 describes that the reflective mask blank in Patent Document 1 has an amorphous crystalline state in the film of the absorber layer, and that stress and surface roughness are also reduced.

Patent Document 2 describes a reflective mask blank for EUV lithography in which a reflective layer that reflects EUV light and an absorber layer that absorbs EUV light are formed in this order on a substrate. Specifically, the reflective mask blank of Patent Document 2 describes that the absorber layer contains at least tantalum (Ta), boron (B), nitrogen (N) and hydrogen (H), and that in the absorber layer, the content of B is 1 at% or more and less than 5 at%, the content of H is 0.1 to 5 at%, the total content of Ta and N is 90 to 98.9 at%, and the composition ratio of Ta to N (Ta:N) is 8:1 to 1:1. As a result, the reflective mask blank of Patent Document 2 describes that the crystalline state of the film of the absorber layer becomes amorphous, and stress and surface roughness are also reduced.

Patent Document 3 describes a reflective mask blank for EUV lithography in which a multilayer reflective film that reflects EUV light and a pattern film that is partially etched during mask processing are formed in this order on a substrate. Specifically, Patent Document 3 describes a reflective mask blank in which the pattern film is composed of an absorber film that absorbs EUV light and a surface-reinforced reflective film formed on the absorber film, and the reflective mask blank satisfies the condition ((n-1) 2 +k 2 ) 1/2 > ((n ABS -1) ² +k ^{ABS 2} ) ^1/2 +0.03) when the refractive index of the absorber film is _{n ABS} and ^the absorption coefficient is k _ABS , and the refractive index of the surface-reinforced reflective film is ⁿ and the absorption coefficient _is k, at a wavelength of 13.53 nm. According to the reflective mask blank of Patent Document 3, the amplitude of the EUV light reflected on the surface of the pattern film is increased by the surface-reinforced reflective film formed on the absorber film, and the interference effect with the EUV light reflected on the multilayer reflective film is increased. It is described that by utilizing this interference effect, it is possible to make the pattern film thickness thinner than before so that the reflectance becomes 2% or less.

International Publication No. 2009/116348 International Publication No. 2010/050518 JP 2018-180544 A

The reflective mask blank of Patent Document 3 has a surface reflection enhancing film on the top layer of the absorber film (pattern film). It is described that Ag, Pt, Pd, Au, Ru, and Ni are used as the constituent materials of the surface reflection enhancing film. Thus, when the top layer of the absorber film is a thin metal film, it was found that the film quality of the metal film is likely to change over time depending on the film formation conditions. In particular, it was found that even for metal films that are thought to be relatively stable from the viewpoint of redox potential, the film quality of the metal film is likely to change over time when the film thickness is thin. When the film quality of the metal film changes over time, a problem occurs in that the deviation from the design value of optical properties such as reflectance becomes large, especially when the film thickness is thin.

In addition, when an etching mask film is laminated on the top layer of the absorber film, depending on the combination of materials between the top layer and the etching mask film, a diffusion layer may be formed at the interface, causing the same problem as above of a large deviation from the design values of the optical properties.

The present invention aims to provide a reflective mask blank, a reflective mask, a substrate with a conductive film, and a method for manufacturing a semiconductor device that can suppress changes in the quality of a thin metal film over time.

In order to solve the above problems, the present invention has the following configuration.
(Configuration 1)
A reflective mask blank comprising a substrate, a multilayer reflective film on the substrate, and a laminated film on the multilayer reflective film,
The laminated film includes a top layer and other underlying layers,
The thickness of the uppermost layer is 0.5 nm or more and less than 5 nm,
The uppermost layer contains at least one metal element selected from rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), ruthenium (Ru), gold (Au), iridium (Ir), cobalt (Co), tin (Sn), nickel (Ni), rhenium (Re), molybdenum (Mo), and niobium (Nb), and at least one additive element selected from hydrogen (H) and deuterium (D);
A reflective mask blank, characterized in that the total content of metal elements in the uppermost layer is 95 atomic % or more.

(Configuration 2)
The reflective mask blank according to structure 1, wherein the metal element contained in the uppermost layer is at least one selected from rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), ruthenium (Ru), and gold (Au).

(Configuration 3)
3. The reflective mask blank according to claim 1, wherein the uppermost layer has at least one of an amorphous structure and a microcrystalline structure.

(Configuration 4)
the laminated film is composed of an absorber film including a first layer and a second layer from the substrate side,
the second layer contains at least one metal element selected from rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), ruthenium (Ru), gold (Au), iridium (Ir), cobalt (Co), tin (Sn), nickel (Ni), rhenium (Re), molybdenum (Mo), and niobium (Nb);
4. The reflective mask blank according to any one of structures 1 to 3, wherein the uppermost layer is a layer forming a surface layer of the second layer.

(Configuration 5)
an etching mask film provided in contact with the uppermost layer;
the etching mask film is made of a material containing silicon (Si);
5. The reflective mask blank according to any one of structures 1 to 4, wherein the metal element of the uppermost layer is ruthenium (Ru).

(Configuration 6)
an etching mask film provided in contact with the uppermost layer;
The etching mask film is made of a material containing chromium (Cr),
5. The reflective mask blank according to any one of structures 1 to 4, wherein the metal element of the uppermost layer is at least one selected from platinum (Pt), ruthenium (Ru), and palladium (Pd).

(Configuration 7)
7. The reflective mask blank according to any one of structures 4 to 6, wherein the first layer is made of a material containing at least one selected from the group consisting of tantalum (Ta) and chromium (Cr).

(Configuration 8)
8. A reflective mask having an absorber pattern formed by patterning the absorber film in the reflective mask blank according to any one of configurations 4 to 7.

(Configuration 9)
9. A method for manufacturing a semiconductor device, comprising the steps of: setting the reflective mask according to configuration 8 in an exposure apparatus having an exposure light source that emits EUV light; and transferring a transfer pattern to a resist film formed on a transfer substrate.

(Configuration 10)
A substrate with a conductive film comprising a substrate and a back surface conductive film on the substrate,
The back surface conductive film includes a top layer and other underlying layers,
The thickness of the uppermost layer is 0.5 nm or more and less than 5 nm,
The uppermost layer contains at least one metal element selected from platinum (Pt), gold (Au), aluminum (Al), copper (Cu), nickel (Ni), chromium (Cr), silver (Ag), titanium (Ti), tungsten (W), indium (In), molybdenum (Mo), rhodium (Rh) and zinc (Zn), and at least one additive element selected from hydrogen (H) and deuterium (D);
A substrate with a conductive film, wherein the total content of metal elements in the uppermost layer is 95 atomic % or more.

(Configuration 11)
The conductive film-attached substrate according to structure 10, wherein the metal element contained in the uppermost layer is at least one selected from platinum (Pt), gold (Au), copper (Cu), silver (Ag) and rhodium (Rh).

(Configuration 12)
12. A reflective mask blank comprising a multilayer reflective film and an absorber film on a main surface opposite to the main surface on which the back conductive film is formed in the substrate with a conductive film according to Structure 10 or 11.

(Configuration 13)
13. A reflective mask having an absorber pattern formed by patterning the absorber film in the reflective mask blank according to configuration 12.

(Configuration 14)
14. A method for manufacturing a semiconductor device, comprising the steps of: setting the reflective mask according to Structure 13 in an exposure apparatus having an exposure light source that emits EUV light; and transferring a transfer pattern to a resist film formed on a transfer substrate.

The present invention provides a reflective mask blank, a reflective mask, a substrate with a conductive film, and a method for manufacturing a semiconductor device that can suppress changes in the quality of a thin metal film over time.

FIG. 2 is a schematic cross-sectional view of a reflective mask blank. FIG. 2 is a schematic cross-sectional view of a reflective mask blank according to another embodiment. FIG. 2 is a schematic cross-sectional view of a reflective mask blank according to another embodiment. FIG. 2 is a schematic cross-sectional view of a substrate with a conductive film. 1A to 1C are schematic diagrams showing a method for manufacturing a reflective mask. 1 shows a pattern transfer device. The figures show the results of a simulation of the EUV light reflectivity versus absorber film thickness when the lower and uppermost layers are a TaBN film and a Ru film, a TaBN film and a Pt film, and a CrN film and a Pt film, respectively, and the film thickness of the uppermost layer is fixed at 3 nm.

The following describes in detail the embodiments of the present invention with reference to the drawings. Note that the following embodiments do not limit the scope of the present invention in any way.

Figure 1 is a schematic cross-sectional view of a main part of a reflective mask blank 100 of this embodiment. As shown in Figure 1, the reflective mask blank 100 includes a substrate 10, a multilayer reflective film 12 formed on the substrate 10, and a laminate film 16 formed on the multilayer reflective film 12. The laminate film 16 includes a lower layer 18 and a top layer 20 formed on and in contact with the lower layer 18. A protective film 14 may be included between the multilayer reflective film 12 and the laminate film 16.

In this specification, "on" a substrate or film includes not only the case of contacting the top surface of the substrate or film, but also the case of not contacting the top surface of the substrate or film. In other words, "on" a substrate or film includes the case of a new film being formed above the substrate or film, or the case of another film being interposed between the substrate or film. Also, "on" does not necessarily mean the upper side in the vertical direction. "On" merely indicates the relative positional relationship of the substrate, film, etc. Also, in this specification, for example, "film A is disposed in contact with film B" means that film A and film B are disposed so as to be in direct contact with each other, without another film being interposed between film A and film B.

<Substrate>
To prevent distortion of the transferred pattern due to heat during exposure to EUV light, the substrate 10 is preferably one having a low thermal expansion coefficient within the range of 0±5 ppb/° C. Examples of materials having a low thermal expansion coefficient within this range include SiO ₂ —TiO ₂ glass and multi-component glass ceramics.

The main surface of the substrate 10 on which the transfer pattern (the absorber film pattern described later) is formed is preferably processed to increase its flatness. By increasing the flatness of the main surface of the substrate 10, the positional accuracy and transfer accuracy of the pattern can be increased. For example, in the case of EUV exposure, in a 132 mm x 132 mm area of the main surface of the substrate 10 on which the transfer pattern is formed, the flatness is preferably 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.03 μm or less. In addition, the main surface (back surface) on the opposite side to the side on which the transfer pattern is formed is a surface fixed by an electrostatic chuck to the exposure device, and in the 142 mm x 142 mm area, the flatness is 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.03 μm or less. In this specification, flatness is a value that represents the surface warpage (amount of deformation) indicated by TIR (Total Indicated Reading), and is the absolute value of the difference in height between the highest point on the substrate surface above the focal plane and the lowest point on the substrate surface below the focal plane, where the focal plane is a plane determined by the least squares method with the substrate surface as the reference.

In the case of EUV exposure, the surface roughness of the main surface of the substrate 10 on which the transfer pattern is formed is preferably 0.1 nm or less in terms of root-mean-square roughness (Rq). The surface roughness can be measured with an atomic force microscope.

It is preferable that the substrate 10 has high rigidity to prevent deformation due to film stress of the film (such as the multilayer reflective film 12) formed thereon. In particular, it is preferable that the substrate 10 has a high Young's modulus of 65 GPa or more.

<Multilayer reflective film>
The multilayer reflective film 12 has a structure in which a plurality of layers each mainly composed of elements having different refractive indices are laminated periodically. In general, the multilayer reflective film 12 is made of a multilayer film in which thin films (high refractive index layers) of a light element or its compound, which is a high refractive index material, and thin films (low refractive index layers) of a heavy element or its compound, which is a low refractive index material, are alternately laminated for about 40 to 60 periods.
To form the multilayer reflective film 12, a high refractive index layer and a low refractive index layer may be laminated in this order multiple times from the substrate 10 side. In this case, one laminate structure (high refractive index layer/low refractive index layer) corresponds to one period.

The top layer of the multilayer reflective film 12, i.e., the surface layer of the multilayer reflective film 12 on the side opposite the substrate 10, is preferably a high refractive index layer. When a high refractive index layer and a low refractive index layer are stacked in this order from the substrate 10 side, the top layer is a low refractive index layer. However, when the low refractive index layer is the surface of the multilayer reflective film 12, the reflectance of the surface of the multilayer reflective film is reduced by the low refractive index layer being easily oxidized, so it is preferable to form a high refractive index layer on the low refractive index layer. On the other hand, when a low refractive index layer and a high refractive index layer are stacked in this order from the substrate 10 side, the top layer is a high refractive index layer. In that case, the topmost high refractive index layer is the surface of the multilayer reflective film 12.

In this embodiment, the high refractive index layer may be a layer containing Si. The high refractive index layer may contain simple Si or may contain a Si compound. The Si compound may contain Si and at least one element selected from the group consisting of B, C, N, O, and H. By using a layer containing Si as the high refractive index layer, a multilayer reflective film with excellent reflectance for EUV light can be obtained.

In this embodiment, the low refractive index layer may be a layer containing at least one element selected from the group consisting of Mo, Ru, Rh, and Pt, or a layer containing an alloy containing at least one element selected from the group consisting of Mo, Ru, Rh, and Pt.

For example, as the multilayer reflective film 12 for EUV light with a wavelength of 13 to 14 nm, a Mo/Si multilayer film in which Mo films and Si films are alternately stacked for about 40 to 60 periods can be preferably used. Other multilayer reflective films that can be used in the EUV light region include, for example, Ru/Si periodic multilayer films, Mo/Be periodic multilayer films, Mo compound/Si compound periodic multilayer films, Si/Nb periodic multilayer films, Si/Mo/Ru periodic multilayer films, Si/Mo/Ru/Mo periodic multilayer films, and Si/Ru/Mo/Ru periodic multilayer films. The material of the multilayer reflective film can be selected taking into consideration the exposure wavelength.

The reflectance of such a multilayer reflective film 12 alone is, for example, 65% or more. The upper limit of the reflectance of the multilayer reflective film 12 is, for example, 73%. The thickness and period of the layers contained in the multilayer reflective film 12 can be selected so as to satisfy Bragg's law.

The multilayer reflective film 12 can be formed by a known method. For example, the multilayer reflective film 12 can be formed by an ion beam sputtering method.

For example, if the multilayer reflective film 12 is a Mo/Si multilayer film, a Mo film with a thickness of about 3 nm is formed on the substrate 10 using a Mo target by ion beam sputtering. Next, a Si film with a thickness of about 4 nm is formed using a Si target. By repeating such operations, a multilayer reflective film 12 can be formed in which 40 to 60 periods of Mo/Si films are stacked. At this time, the surface layer of the multilayer reflective film 12 on the side opposite the substrate 10 is a layer containing Si (Si film). The thickness of one period of Mo/Si film is 7 nm.

<Protective film>
In order to protect the multilayer reflective film 12 from dry etching and cleaning in the manufacturing process of the reflective mask 200 described later, a protective film 14 can be formed on the multilayer reflective film 12 or in contact with the surface of the multilayer reflective film 12. The protective film 14 also has a function of protecting the multilayer reflective film 12 when correcting black defects in a transfer pattern using an electron beam (EB). Here, FIG. 1 shows a case where the protective film 14 is a single layer, but the protective film 14 may have a laminated structure of two or more layers. The protective film 14 is preferably formed of a material that is resistant to an etchant or cleaning solution used when patterning the lower layer 18. By forming the protective film 14 on the multilayer reflective film 12, damage to the surface of the multilayer reflective film 12 during the manufacturing of the reflective mask 200 can be suppressed. As a result, the reflectance characteristic of the multilayer reflective film 12 for EUV light is improved.

In the reflective mask blank 100 of this embodiment, a material that is resistant to the etching gas used in the dry etching for patterning the lower layer 18 formed on the protective film 14 can be used as the material of the protective film 14. When the lower layer 18 is formed of multiple layers, a material that is resistant to the etching gas used in the dry etching for patterning the bottom layer (the layer in contact with the protective film 14) of the lower layer 18 can be used as the material of the protective film 14 that contacts the lower layer 18 (when the protective film 14 includes multiple layers, the top layer of the protective film 14). It is preferable that the material of the protective film 14 is a material that has an etching selectivity ratio of the bottom layer of the lower layer 18 to the protective film 14 (etching rate of the bottom layer of the lower layer 18/etching rate of the protective film 14) of 1.5 or more, preferably 3 or more.

For example, if the bottom layer of the underlayer 18 in contact with the surface of the protective film 14 is a thin film made of a material containing tantalum (Ta), the bottom layer of the underlayer 18 can be etched by dry etching using a halogen-based gas that does not contain oxygen gas. A material containing ruthenium (Ru) as a main component can be used as a material for the protective film 14 that is resistant to this etching gas.

In addition, if the bottom layer of the lower layer 18 in contact with the surface of the protective film 14 is a thin film made of a material containing chromium (Cr), the bottom layer of the lower layer 18 can be etched by dry etching using a mixed gas of oxygen gas and a chlorine-based gas. As a material for the protective film 14 that is resistant to this etching gas, a material containing ruthenium (Ru) as a main component and containing an element (Zr, Y, Rh, etc.) that is resistant to etching by oxygen gas can be used.

When the bottom layer of the lower layer 18 is a material containing at least one selected from tantalum (Ta) and chromium (Cr), the material of the protective film 14 that can be used is a material containing ruthenium as a main component, as described above. Specific examples of materials containing ruthenium as a main component include Ru metal alone, Ru alloys containing at least one metal selected from titanium (Ti), niobium (Nb), molybdenum (Mo), zirconium (Zr), yttrium (Y), boron (B), lanthanum (La), cobalt (Co), rhenium (Re), and rhodium (Rh), and materials containing nitrogen in these metals or alloys.

In addition, when the bottom layer of the lower layer 18 is formed of a material containing at least one selected from tantalum (Ta) and chromium (Cr), the bottom layer and the top layer of the protective film 14 can be formed of a material containing ruthenium as a main component. The layer between the bottom layer and the top layer can be formed of a metal other than Ru or an alloy containing it.

The Ru content of the Ru alloy is 50 atomic % or more and less than 100 atomic %, preferably 80 atomic % or more and less than 100 atomic %, and more preferably 95 atomic % or more and less than 100 atomic %. In particular, when the Ru content of the Ru alloy is 95 atomic % or more and less than 100 atomic %, the element (silicon) constituting the multilayer reflective film 12 can be suppressed from diffusing into the protective film 14. In addition, the cleaning resistance of the mask can be improved while ensuring sufficient reflectance of EUV light. Furthermore, the protective film 14 can function as an etching stopper when etching the lower layer 18. In addition, the protective film 14 can prevent the multilayer reflective film 12 from changing over time.

The thickness of the protective film 14 is not particularly limited as long as the protective film 14 can function to protect the multilayer reflective film 12. From the viewpoint of the reflectance of EUV light, the thickness of the protective film 14 is preferably 1.0 nm to 8.0 nm, and more preferably 1.5 nm to 6.0 nm.

A known method can be used to form the protective film 14. Examples of methods for forming the protective film 14 include sputtering and ion beam sputtering.

The reflective mask blank 100 may further have a back surface conductive film 22 on the main surface opposite to the side of the substrate 10 on which the multilayer reflective film 12 is formed. The back surface conductive film 22 is used when the reflective mask blank 100 is attracted by an electrostatic chuck.

The reflective mask blank 100 may include an undercoat film formed between the substrate 10 and the multilayer reflective film 12. The undercoat film is formed, for example, for the purpose of improving the smoothness of the surface of the substrate 10. The undercoat film is formed, for example, for the purpose of reducing defects, improving the reflectance of the multilayer reflective film, correcting stress in the multilayer reflective film, etc.

<Laminated Film>
The reflective mask blank 100 of this embodiment has a laminated film 16 formed on a multilayer reflective film 12 (or a multilayer reflective film 12 with a protective film 14). The laminated film 16 includes a top layer 20 and a lower layer 18, which is the other layer. The lower layer 18 is formed on and in contact with the multilayer reflective film 12 (or the multilayer reflective film 12 with a protective film 14). The top layer 20 is formed on and in contact with the lower layer 18.

In the reflective mask blank 100 of this embodiment, the laminated film 16 is made of an absorber film 17 for absorbing EUV light. In this case, the absorber film 17 includes an absorber layer as a lower layer 18 and a top layer 20. The absorber layer (lower layer 18) is a layer for absorbing EUV light. The top layer 20 is a layer for increasing the amplitude of the EUV light reflected on the surface of the absorber film 17. By increasing the amplitude of the EUV light reflected on the surface of the absorber film 17, the interference effect with the EUV light reflected by the multilayer reflective film 12 is increased. By utilizing this interference effect, the thickness of the absorber film 17 at which the reflectance is a predetermined value or less (e.g., 2.5% or less) can be made thinner than before.

When the lower layer 18 is an absorbing layer, the material of the lower layer 18 may be, for example, a material containing at least one selected from tantalum (Ta) and chromium (Cr).

Examples of materials containing tantalum (Ta) include materials containing tantalum (Ta) and at least one element selected from oxygen (O), nitrogen (N), carbon (C), boron (B) and hydrogen (H). Among these, materials containing tantalum (Ta) and nitrogen (N) are preferred. Specific examples of such materials include tantalum nitride (TaN), tantalum oxynitride (TaON), tantalum boride nitride (TaBN), and tantalum boride oxynitride (TaBON).

Examples of materials containing chromium (Cr) include materials containing chromium (Cr) and at least one element selected from oxygen (O), nitrogen (N), carbon (C), boron (B) and hydrogen (H). Among these, materials containing chromium (Cr) and nitrogen (N) and/or carbon (C) are preferred. Specific examples of such materials include chromium nitride (CrN), chromium oxide nitride (CrON), chromium carbide (CrC), chromium oxide carbide (CrOC), chromium carbonitride (CrCN), and chromium oxide carbonitride (CrOCN).

The lower layer 18 (absorption layer) made of the above-mentioned materials can be formed by magnetron sputtering methods such as DC sputtering and RF sputtering. For example, the lower layer 18 (absorption layer) can be formed by a reactive sputtering method using a target containing tantalum and boron and a rare gas such as argon (Ar) gas, krypton (Kr) gas, and/or xenon (Xe) gas to which nitrogen gas has been added.

The material of the lower layer 18 is not particularly limited as long as it has the function of absorbing EUV light, has etching selectivity with respect to the top layer 20, and has etching selectivity with respect to the protective film 14. As such a material, at least one metal selected from palladium (Pd), silver (Ag), platinum (Pt), gold (Au), iridium (Ir), tungsten (W), chromium (Cr), cobalt (Co), manganese (Mn), tin (Sn), tantalum (Ta), vanadium (V), nickel (Ni), hafnium (Hf), iron (Fe), copper (Cu), tellurium (Te), zinc (Zn), magnesium (Mg), germanium (Ge), aluminum (Al), and rhodium (Rh), or a compound thereof, can be preferably used.

In the reflective mask blank 100 of this embodiment, the film thickness of the top layer 20 is 0.5 nm or more and less than 5 nm, and preferably 0.5 nm or more and 4 nm or less.

In the reflective mask blank 100 of this embodiment, the top layer 20 contains a metal element and at least one additive element selected from hydrogen (H) and deuterium (D).

The metal element contained in the top layer 20 is at least one selected from rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), ruthenium (Ru), gold (Au), iridium (Ir), cobalt (Co), tin (Sn), nickel (Ni), rhenium (Re), molybdenum (Mo), and niobium (Nb).

The total content of the metal elements in the top layer 20 is 95 atomic % or more, preferably 97 atomic % or more, and less than 100 atomic %. When the top layer 20 contains one metal element, the total content is the content of the metal alone. When the top layer 20 contains multiple metal elements, the total content is the total content of the multiple metal elements.

The total content of the above-mentioned additive elements in the top layer 20 is 0.1 atomic % or more, and preferably 0.3 atomic % or more. The total content of the additive elements is 5 atomic % or less, and more preferably 3 atomic % or less.

When the refractive index of the lower layer 18 (absorption layer) is n ₁ and the refractive index of the top layer 20 is n ₂ , the lower layer 18 (absorption layer) and the top layer 20 are preferably made of materials that satisfy the relationship n ₁ > n _2. By satisfying the relationship n ₁ > n ₂ , the amplitude of the EUV light reflected on the surface of the absorber film 17 can be increased. As a result, the thickness of the absorber film 17 that provides a reflectance of, for example, 2.5% or less can be made thinner than in the past. The thickness of the absorber film 17 is preferably 55 nm or less, and more preferably 45 nm or less.

Figure 7 shows the simulation results of the EUV light reflectance versus the thickness of the absorber film 17 when the lower layer 18 and the top layer 20 are respectively a TaBN film and a Ru film, a TaBN film and a Pt film, and a CrN film and a Pt film, and the thickness of the top layer 20 is fixed at 3 nm. For reference, the simulation results are also shown when the absorber film 17 is a single layer of TaBN film. As can be seen from Figure 7, when the top layer 20 is provided on the lower layer 18, it is possible to make the thickness of the absorber film 17 thinner than when the top layer 20 is not provided.

The refractive index _n1 of the lower layer 18 (the absorbing layer) is preferably 0.92 to 1.0 inclusive. The refractive index _n2 of the uppermost layer 20 is preferably 0.87 to 0.95 inclusive.

As described above, the top layer 20 is a thin metal film with a thickness of 0.5 nm or more and less than 5 nm. Thus, it was found that when the top layer 20 of the absorber film 17 is a thin metal film, the film quality of the metal film is likely to change over time depending on the film formation conditions. When the film quality of the metal film changes over time, a problem occurs in that the optical properties such as reflectance deviate significantly from the design values, particularly when the film thickness is thin.

In order to solve such problems, in the reflective mask blank 100 of this embodiment, the top layer 20 contains at least one additive element selected from hydrogen (H) and deuterium (D). By containing the above additive element in the top layer 20, it is possible to suppress the film quality of the top layer 20 from changing over time. The reason why such an effect is obtained is not clear, but it is thought that this is because the thin metal film constituting the top layer 20 has a microcrystalline structure or an amorphous structure due to the above additive element, and the intrusion of oxygen and the like into the crystal grain boundaries is suppressed. Since it is possible to reduce the crystallinity with the same amount of addition as hydrogen (H), it is more preferable that the above additive element contained in the top layer 20 is deuterium (D).

The content (atomic %) of the additive element contained in the top layer 20 is preferably higher than the content (atomic %) of the additive element contained in the lower layer 18 (absorption layer). By having the content of the additive element contained in the top layer 20 higher than that of the lower layer 18, it becomes possible to more effectively suppress changes in the film quality of the top layer 20 over time.

The metal element contained in the top layer 20 is preferably at least one selected from rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), ruthenium (Ru) and gold (Au). These metal elements have an oxidation-reduction potential (standard electrode potential) of +0.4 V or more and have been considered to be relatively stable. In addition, the metal element contained in the top layer 20 is more preferably at least one selected from palladium (Pd), platinum (Pt) and gold (Au). These metal elements have an oxidation-reduction potential (standard electrode potential) of +0.9 V or more and have been considered to be more stable. However, it has become clear that even in metal films containing these metal elements, when the film thickness of the metal film is thin (film thickness is 0.5 nm or more and 5 nm), the film quality of the metal film is likely to change over time. In other words, it has become clear that even in films made of these metals that have been considered to be relatively stable, when the film thickness of the metal film is thin, there is a high need to suppress the film quality of the metal film from changing over time. For this reason, when these metal elements are included in the top layer 20, the effect of suppressing changes in film quality due to the above-mentioned added elements is more pronounced.

The top layer 20 can be formed by magnetron sputtering methods such as DC sputtering and RF sputtering. The above-mentioned additive elements can be added to the top layer 20 by reactive sputtering using a metal target made of the metal elements contained in the top layer 20 and a rare gas (Ar gas, Kr gas, and/or Xe gas) and hydrogen gas and/or deuterium gas.

In the reflective mask blank 100 of this embodiment, a resist film 26 may be formed on the laminate film 16 (absorber film 17). This aspect is shown in FIG. 1. A pattern is drawn and exposed on the resist film 26 by an electron beam lithography device, and then a development process is performed to form a resist pattern. A pattern (absorber pattern) can be formed in the laminate film 16 by dry etching the laminate film 16 (absorber film 17) using this resist pattern as a mask. As a material for the resist film 26, for example, a chemically amplified resist (CAR) can be used.

In another embodiment of the reflective mask blank 100, the laminated film 16 is made of an absorber film 17 for absorbing EUV light. In this case, as shown in FIG. 2, the absorber film 17 includes a first layer 62 and a second layer 64 from the substrate 10 side. The top layer 20 is a layer that forms the surface layer of the second layer 64 on the opposite side to the first layer 62, and has a film thickness of 0.5 nm or more and less than 5 nm. The first layer 62 is a layer for absorbing EUV light. The second layer 64 including the top layer 20 is a layer for absorbing EUV light and increasing the amplitude of the EUV light reflected on the surface of the absorber film 17. By increasing the amplitude of the EUV light reflected on the surface of the absorber film 17, the interference effect with the EUV light reflected by the multilayer reflective film 12 is increased. By utilizing this interference effect, the film thickness of the absorber film 17 at which the reflectance is a predetermined value or less (for example, 2.5% or less) can be made thin, as in the above embodiment.

The material for the first layer 62 can be the same as the material for the absorbent layer (lower layer 18) described above.

The second layer 64 and the top layer 20 may be made of at least one metal selected from rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), ruthenium (Ru), gold (Au), iridium (Ir), cobalt (Co), tin (Sn), nickel (Ni), rhenium (Re), molybdenum (Mo) and niobium (Nb), or a compound of these metals containing at least one selected from nitrogen (N), oxygen (O), carbon (C) and boron (B).

The total content of the metal elements contained in the second layer 64 and the top layer 20 is 95 atomic % or more, preferably 97 atomic % or more, and less than 100 atomic %. When the second layer 64 and the top layer 20 contain one metal element, the total content is the content of the metal alone. When the second layer 64 contains multiple metal elements, the total content is the total content of the multiple metal elements.

The additive element and film thickness of the top layer 20 are the same as those of the above-described embodiment. The second layer 64 may contain at least one additive element selected from hydrogen (H) and deuterium (D) throughout the entire thickness direction. The content of the additive element in the second layer 64 may decrease from the top layer 20 toward the first layer 62.

The thickness of the first layer 62 is preferably 20 nm or more, more preferably 25 nm or more, and preferably 60 nm or less, more preferably 55 nm or less. The thickness of the second layer 64 is preferably 1 nm or more, more preferably 1.5 nm or more, and preferably 25 nm or less, more preferably 20 nm or less.

When the refractive index of the first layer 62 is _n1 and the refractive index of the second layer 64 is _n2 , the first layer 62 and the second layer 64 are preferably made of a material that satisfies the relationship _n1 > _n2 . By satisfying the relationship _n1 > _n2 , it is possible to increase the amplitude of the EUV light reflected on the surface of the absorber film 17. As a result, the thickness of the absorber film 17 that provides a reflectance of, for example, 2.5% or less can be made thin, as in the above-described embodiment.

The refractive index _n1 of the first layer 62 is preferably 0.92 or more and 1.0 or less, and the refractive index _n2 of the second layer 64 is preferably 0.87 or more and 0.95 or less.

In yet another embodiment of the reflective mask blank 100, a phase shift film having a phase shift function provided in an absorber film may be used.
In the portion where the phase shift film (phase shift pattern) is formed, the EUV light is absorbed and reduced while a part of the light is reflected at a level that does not adversely affect the pattern transfer. On the other hand, in the opening (the portion where the phase shift film is not formed), the EUV light is reflected from the multilayer reflective film 12 through the protective film 14. The reflected light from the portion where the phase shift film is formed forms a desired phase difference with the reflected light from the opening. The phase shift film is formed so that the phase difference between the reflected light from the phase shift film and the reflected light from the multilayer reflective film 12 is 160° to 200°. The light with the inverted phase difference of about 180° interferes with each other at the pattern edge portion, thereby improving the image contrast of the projected optical image. With the improvement in the image contrast, the resolution increases, and various tolerances related to exposure such as the exposure dose tolerance and the focus tolerance are expanded. Although it depends on the pattern and the exposure conditions, the target reflectance of the phase shift film to obtain this phase shift effect is generally 2% or more in terms of relative reflectance. In order to obtain a sufficient phase shift effect, the reflectance of the phase shift film is preferably 6% or more in terms of relative reflectance. Here, the relative reflectance of the phase shift film (phase shift pattern) is the reflectance of the EUV light reflected from the phase shift pattern when the reflectance of the EUV light reflected from the multilayer reflective film 12 (including the multilayer reflective film 12 with the protective film 14) in a portion without the phase shift pattern is taken as 100%. In this specification, the relative reflectance may be simply referred to as "reflectance".

To further improve resolution and throughput when manufacturing semiconductor devices, the relative reflectance of the phase shift pattern is required to be 6% to 35%, and more preferably 15% to 35%.

The material for the first layer 62 can be the same as the material for the absorbent layer (lower layer 18) described above.

The material for the second layer 64 and the top layer 20 can be ruthenium (Ru) and at least one metal selected from chromium (Cr), nickel (Ni), cobalt (Co), vanadium (V), niobium (Nb), molybdenum (Mo), tungsten (W) and rhenium (Re), or a Ru-based compound containing these metals and at least one selected from nitrogen (N), oxygen (O) and carbon (C).

The material for the second layer 64 and the top layer 20 can be a Ru-based compound containing ruthenium (Ru) and at least one selected from nitrogen (N), oxygen (O) and carbon (C).

The total content of metal elements contained in the second layer 64 and the top layer 20 is the same as above. The added elements and film thickness of the top layer 20 are also the same as above.

When the refractive index of the first layer 62 is _n3 and the refractive index of the second layer 64 is _n4 , the first layer 62 and the second layer 64 are preferably made of a material that satisfies the relationship _n3 > _n4 . Furthermore, when the extinction coefficient of the first layer 62 is _k3 and the extinction coefficient of the second layer 64 is _k4 , the first layer 62 and the second layer 64 are preferably made of a material that satisfies the relationship _k3 > _k4 .
The first layer 62 preferably has a refractive index _n3 of 0.93 to 0.96 and an extinction coefficient _k3 of 0.02 to 0.04. The second layer 64 preferably has a refractive index _n4 of 0.86 to 0.95 and an extinction coefficient _k4 of 0.008 to 0.035.

By including the above-mentioned additive element in the top layer 20 of the second layer 64, it is possible to suppress the film quality of the top layer 20 from changing over time. This makes it possible to suppress deviations from the design values of the optical properties such as the reflectance and phase difference of the absorber film or phase shift film.

<Etching mask film>
The laminated film 16 may further include an etching mask film formed on the absorber film 17 (phase shift film). A resist film may further be formed on the etching mask film. In this case, the top layer 20 is an etching mask film or a layer forming a surface layer of the etching mask film. When the laminated film 16 includes an etching mask film, the top layer 20 may be a metal film having a thickness of less than 0.5 to 5 nm so that the contrast is improved in an inspection using a defect inspection device. In this case, the top layer 20 of the laminated film 16 may contain the above-mentioned metal element and at least one additive element selected from hydrogen (H) and deuterium (D), similar to the top layer 20 of the absorber film 17 described above. The top layer 20 of the laminated film 16 is formed of a thin metal film containing the above-mentioned additive element, so that the top layer 20 has a microcrystalline structure or an amorphous structure. This makes it possible to detect defects on the surface of the etching mask film with higher accuracy when the surface of the etching mask film is inspected by a defect inspection device.

Figure 3 shows a reflective mask blank 100 according to another embodiment. As shown in Figure 3, an etching mask film 24 may be formed in contact with the top layer 20 of the laminated film 16 (absorber film 17). A resist film 26 may further be formed on the etching mask film 24.

When the absorber film 17 (particularly the top layer 20) is etched with a fluorine-based gas, a material containing chromium (Cr) can be used as the material of the etching mask film 24. By forming the etching mask film 24 from a material containing chromium (Cr), the etching selectivity of the top layer 20 relative to the etching mask film 24 can be increased. Examples of materials containing chromium include materials containing chromium (Cr) and at least one selected from nitrogen (N), oxygen (O), carbon (C) and boron (B). Examples of such materials include CrN, CrC, CrO, CrON, CrOC, CrCN, CrCON, CrBN, CrBC, CrBO, CrBC, CrBON, CrBCN and CrBOCN. When the etching mask film 24 is made of a material containing chromium, the chromium (Cr) content is preferably 50 atomic % or more and less than 100 atomic %, and more preferably 80 atomic % or more and less than 100 atomic %.

When the absorber film 17 (particularly the top layer 20) is etched with a chlorine-based gas containing oxygen, a material containing silicon (Si) can be used as the material of the etching mask film 24. By forming the etching mask film 24 from a material containing silicon (Si), the etching selectivity of the top layer 20 relative to the etching mask film 24 can be increased. Examples of materials containing silicon (Si) include materials containing silicon (Si) and at least one selected from nitrogen (N), oxygen (O), carbon (C) and hydrogen (H). Examples of materials containing silicon (Si) include metal silicon (metal silicide) containing silicon (Si) and a metal, or metal silicon compounds (metal silicide compounds). Examples of metal silicon compounds include materials containing metal and Si and at least one selected from N, O, C and H.

When the etching mask film 24 is formed, it is possible to reduce the thickness of the resist film 26, making it possible to form a finer pattern on the absorber film 17 (particularly the top layer 20). The thickness of the etching mask film 24 is preferably 3 nm or more. By making the thickness of the etching mask film 24 3 nm or more, it is possible to form a finer pattern on the top layer 20 with high precision. In addition, from the viewpoint of reducing the thickness of the resist film 26, the thickness of the etching mask film 24 is preferably 15 nm or less, and more preferably 10 nm or less.

When the etching mask film 24 is formed, a diffusion layer may be formed at the interface between the etching mask film 24 and the top layer 20. This diffusion layer is formed when elements contained in one layer diffuse into the other layer. If such a diffusion layer is formed, a problem occurs in that when the etching mask film 24 is removed to form an absorber pattern, the optical properties (reflectance, etc.) of the absorber pattern deviate significantly from the design values. For this reason, it is preferable to suppress the formation of the diffusion layer as much as possible.

According to the reflective mask blank 100 of this embodiment, the top layer 20 contains a metal element and at least one additive element selected from hydrogen (H) and deuterium (D). This allows the thin metal film constituting the top layer 20 to have a microcrystalline structure or an amorphous structure due to the additive element, making it possible to prevent the elements contained in the top layer 20 from diffusing into the etching mask film 24. Alternatively, it becomes possible to prevent the elements contained in the etching mask film 24 from diffusing into the top layer 20. As a result, it becomes possible to prevent the formation of a diffusion layer at the interface between the etching mask film 24 and the top layer 20.

When the metal element contained in the top layer 20 is ruthenium (Ru), the top layer 20 can be etched with a chlorine-based gas containing oxygen. In this case, therefore, the material containing silicon (Si) described above can be used as the material for the etching mask film 24. In this case, it is possible to prevent the formation of a diffusion layer containing RuSi.

When the metal element contained in the top layer 20 is at least one selected from platinum (Pt), ruthenium (Ru), and palladium (Pd), the top layer 20 can be etched with a fluorine-based gas. Therefore, in this case, the material containing chromium (Cr) described above can be used as the material for the etching mask film 24. In this case, it is possible to prevent the formation of a diffusion layer containing PtCr, RuCr, or PdCr.

_{Examples of the fluorine-based gas include CF4, CHF3, C2F6, C3F6, C4F6, C4F8, CH2F2 , CH3F , C3F8 , SF6 , and F2 . Examples of} the chlorine-based gas include _Cl2 , _{SiCl4 , CHCl3 , CCl4} , and _BCl3 . Also, a mixed gas containing a fluorine-based gas and/or a chlorine-based gas and _O2 at a predetermined ratio can be used. Also, these etching gases can further contain an inert gas such as _He and/or Ar, as necessary.

<Backside conductive film>
As described above, the back surface conductive film 22 is formed on the main surface of the substrate 10 opposite to the side on which the multilayer reflective film 12 is formed. The back surface conductive film 22 is used when the reflective mask blank 100 is attracted by an electrostatic chuck.

The electrical characteristics (sheet resistance) required for the back surface conductive film 22 for an electrostatic chuck are typically 100 Ω/□ (Ω/Square) or less. The back surface conductive film 22 can be formed, for example, by magnetron sputtering or ion beam sputtering.

The back surface conductive film 22 can be formed using a material that has a transmittance of 20% or more for light with a wavelength of 532 nm or 470 nm, for example. This makes it possible to correct the positional deviation of the reflective mask from the back surface using a laser beam or the like.

The material of the back conductive film 22 (transparent conductive film) having high transmittance preferably contains one or more metal elements selected from platinum (Pt), gold (Au), aluminum (Al), copper (Cu), nickel (Ni), chromium (Cr), silver (Ag), titanium (Ti), tungsten (W), indium (In), molybdenum (Mo), rhodium (Rh) and zinc (Zn). In addition, a metal compound containing at least one selected from boron, nitrogen, oxygen and carbon in the metal element can be used within a range that satisfies the desired transmittance and electrical characteristics. Since metal films containing these metal elements have high electrical conductivity, when these metal films are used as the back conductive film 22, the back conductive film 22 can be made thin. From the viewpoint of transmittance, the thickness of the metal film is preferably 50 nm or less, and more preferably 20 nm or less. In addition, the thickness of the metal film is preferably 2 nm or more because the sheet resistance tends to increase rapidly if the film thickness is too thin, and from the viewpoint of stability during film formation.

A surface layer (uppermost layer) of the back surface conductive film 22 having a thickness of 0.5 nm or more and less than 5 nm from the surface thereof may contain the above metal element and at least one additive element selected from hydrogen (H) and deuterium (D).
The back surface conductive film 22 may be a laminated film made up of a plurality of layers. 1 to 3 show an example in which the back surface conductive film 22 is a laminated film.

When the back surface conductive film 22 is a laminated film, the back surface conductive film 22 may include a top layer 30 and a lower layer 28. The lower layer 28 is a layer formed in contact with the main surface (back surface) of the substrate 10. The top layer 30 is a layer formed in contact with the lower layer 28. In Figs. 1 to 3, the top layer 30 is located at the bottom.

The top layer 30 of the back surface conductive film 22 may be formed of a thin metal film containing the above-mentioned additive element. That is, the top layer 30 of the back surface conductive film 22 (stacked film) may contain one or more metal elements selected from platinum (Pt), gold (Au), aluminum (Al), copper (Cu), nickel (Ni), chromium (Cr), silver (Ag), titanium (Ti), tungsten (W), indium (In), molybdenum (Mo), rhodium (Rh), and zinc (Zn), and at least one additive element selected from hydrogen (H) and deuterium (D).
By forming the top layer 30 (or the top layer as the surface layer) of the back surface conductive film 22 from a thin metal film containing the above-mentioned additive element, the top layer 30 of the back surface conductive film 22 has a microcrystalline structure or an amorphous structure. This makes it possible to suppress changes in the film quality of the back surface conductive film 22 and thus changes in its conductivity, etc. As a result, it becomes possible to hold the reflective mask blank 100 more stably by the electrostatic chuck.

It is more preferable that the metal element contained in the top layer 30 (or the top layer as a surface layer) is at least one selected from platinum (Pt), gold (Au), copper (Cu), silver (Ag), and rhodium (Rh). These metal elements have an oxidation-reduction potential (standard electrode potential) of +0.5 V or more and are considered to be more stable. It is also more preferable that the metal element contained in the top layer 30 is at least one selected from platinum (Pt) and gold (Au). These metal elements have an oxidation-reduction potential (standard electrode potential) of +1.0 V or more and are considered to be more stable. As in the case of the top layer 20 described above, when the top layer 30 contains these metal elements, the effect of suppressing changes in film quality due to the above-mentioned added elements is more pronounced.

The lower layer 28 of the back conductive film 22 can be a film having a stress adjustment function for adjusting the stress between the first main surface side of the substrate 10 on which the multilayer reflective film 12 is formed and the second main surface side of the substrate 10 on which the back conductive film 22 is formed. In this case, examples of the material of the lower layer 28 include Si ₃ N ₄ and SiO _2. Since Si ₃ N ₄ has a high transmittance for wavelengths of 532 nm or 470 nm, there are fewer limitations on the film thickness compared to other materials. For example, in the case of the lower layer 28 of Si ₃ N ₄ , it is possible to adjust the stress in the film thickness range of 1 to 100 nm. When the material of the lower layer 28 is Si ₃ N ₄ and SiO ₂ , the film thickness of the top layer 30 made of a metal film is preferably 2 nm or more and less than 5 nm from the viewpoint of ensuring conductivity and transmittance. In addition, the film thickness of the laminated film of the lower layer 28 and the top layer 30 is preferably 6 nm or more and 110 nm or less, more preferably 15 nm or more and 70 nm or less.

In addition, a Ta-based oxide film or a Cr-based oxide film with a small extinction coefficient can be used as the material of the lower layer 28 of the back conductive film 22. The material of the lower layer 28 preferably has an extinction coefficient of 1.3 or less at a wavelength of 532 nm or 470 nm. Examples of Ta-based oxide films include TaO, TaON, TaCON, TaBO, TaBON, and TaBCON. When the lower layer 28 is a Ta-based oxide film, the oxygen (O) content is preferably 20 to 70 atomic %. Examples of Cr-based oxide films include CrO, CrON, CrCON, CrBO, CrBON, and CrBOCN. When the lower layer 28 is a Cr-based oxide film, the oxygen (O) content is preferably 25 to 75 atomic %. Furthermore, the material of the lower layer 28 may be an oxide film of the metal film of the uppermost layer 30, i.e., PtO, AuO, AlO, CuO, NiO, CrO, AgO, TiO, WO, InO, MoO, RhO, or ZnO.

When the material of the lower layer 28 is a metal oxide film such as a Ta-based oxide film or a Cr-based oxide film, the thickness of the top layer 30 made of a metal film is preferably 2 nm or more and less than 5 nm from the viewpoint of ensuring conductivity and transmittance. In addition, the thickness of the laminated film of the lower layer 28 containing a Ta-based oxide film and the top layer 30 is preferably 3 nm or more and 200 nm or less, more preferably 10 nm or more and 60 nm or less. The thickness of the laminated film of the lower layer 28 containing a Cr-based oxide film and the top layer 30 is preferably 3 nm or more and 250 nm or less, more preferably 10 nm or more and 100 nm or less.

The lower layer 28 can also have a function of improving the adhesion between the substrate 10 and the back conductive film 22 and suppressing the intrusion of hydrogen from the substrate 10 into the back conductive film 22. The lower layer 28 can also have a function of suppressing the transmission of vacuum ultraviolet light and ultraviolet light (wavelength: 130 to 400 nm), which are called out-of-band light when EUV light is used as an exposure source, through the substrate 10 and being reflected by the back conductive film 22. Examples of materials for the lower layer 28 include Si, SiO ₂ , SiON, SiCO, SiCON, SiBO, SiBON, Cr, CrN, CrON, CrC, CrCN, CrCO, CrCON, Mo, MoSi, MoSiN, MoSiO, MoSiCO, MoSiON, MoSiCON, TaO, and TaON. The thickness of the lower layer 28 is preferably 1 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. The material and thickness of the lower layer 28 are selected so that the laminated film formed by laminating the lower layer 28 and the top layer 30 has a transmittance of 20% or more.

<Substrate with conductive film>
Fig. 4 is a schematic cross-sectional view of a conductive film-attached substrate 110 according to this embodiment. As shown in Fig. 4, the conductive film-attached substrate 110 includes a substrate 10 and a back surface conductive film 22 formed on the substrate 10. The back surface conductive film 22 includes a top layer 30 and a lower layer 28 other than the top layer 30. The substrate 10, the back surface conductive film 22, the top layer 30 and the lower layer 28 of the conductive film-attached substrate 110 are similar to the substrate 10, the back surface conductive film 22, the top layer 30 and the lower layer 28 of the reflective mask blank 100 described above.

<Reflection mask and its manufacturing method>
The reflective mask of this embodiment can be manufactured by using the reflective mask blank 100 of this embodiment. An example of a method for manufacturing a reflective mask will be described below.

FIG. 5 is a schematic diagram showing a method for manufacturing the reflective mask 200. As shown in FIG.
As shown in Fig. 5, first, a reflective mask blank 100 is prepared, which includes a substrate 10, a multilayer reflective film 12 formed on the substrate 10, a protective film 14 formed on the multilayer reflective film 12, and a laminated film 16 (lower layer 18 and uppermost layer 20) formed on the protective film 14 (Fig. 5(a)). Next, a resist film 26 is formed on the laminated film 16 (Fig. 5(b)). A pattern is written on the resist film 26 by an electron beam lithography device, and a developing and rinsing process is performed to form a resist pattern 26a (Fig. 5(c)).

The laminated film 16 (lower layer 18 and uppermost layer 20) is dry-etched using the resist pattern 26a as a mask. The lower layer 18 and the uppermost layer 20 are etched in two stages using etching gases that have etching selectivity between them. As a result, the parts of the laminated film 16 that are not covered by the resist pattern 26a are etched, and a laminated film pattern 40 (absorber pattern) is formed (Figure 5(d)).

The etching gas for the lower layer 18 and the uppermost layer 20 may be a fluorine-based gas and/or a chlorine-based gas depending on the material of the lower layer 18 and the uppermost layer _20. The fluorine-based gas may be _CF4 , _CHF3 , _C2F6 , _C3F6 , _{C4F6 , C4F8} , _CH2F2 , _{CH3F , C3F8} , _{SF6 ,} or _F2 . The chlorine-based gas may be _Cl2 , _SiCl4 , _CHCl3 , _CCl4 , or _BCl3 . A mixed gas containing a fluorine-based gas and/or a chlorine-based gas and _O2 at a predetermined ratio may be used. These etching gases may _further contain an inert gas such as He and/or Ar as necessary.
As an etching gas for dry etching the lower layer 18, an etching gas having etching selectivity with respect to the protective film 14 may be used.

After the laminated film pattern 40 is formed, the resist pattern 26a is removed with a resist remover. After removing the resist pattern 26a, a wet cleaning process is performed using an acidic or alkaline aqueous solution to obtain the reflective mask 200 of this embodiment (FIG. 5(e)).

When using a reflective mask blank 100 in which an etching mask film 24 is formed on the top layer 20, an additional process is performed in which a pattern (etching mask pattern) is formed in the etching mask film 24 using the resist pattern 26a as a mask, and then a pattern is formed in the laminate film 16 using the etching mask pattern as a mask.

The reflective mask 200 obtained in this manner has a structure in which a multilayer reflective film 12, a protective film 14, and a laminated film pattern 40 (absorber pattern) are layered on a substrate 10.

The region 44 where the multilayer reflective film 12 (including the protective film 14) is exposed has the function of reflecting EUV light. The region 46 where the multilayer reflective film 12 (including the protective film 14) is covered by the laminated film pattern 40 (absorber pattern) has the function of absorbing EUV light. According to the reflective mask 200 of this embodiment, the thickness of the absorber pattern that has a reflectance of, for example, 2.5% or less can be made thinner than in the past, so that a finer pattern can be transferred to the transfer target.

<Method of Manufacturing Semiconductor Device>
A transfer pattern can be formed on a semiconductor substrate by lithography using the reflective mask 200 of this embodiment. This transfer pattern has a shape that is a result of transferring the pattern of the reflective mask 200. By forming a transfer pattern on a semiconductor substrate using the reflective mask 200, a semiconductor device can be manufactured.

Using Figure 6, we will explain the method of transferring a pattern to a semiconductor substrate 56 with a resist using EUV light.

Figure 6 shows a pattern transfer device 50. The pattern transfer device 50 includes a laser plasma X-ray source 52, a reflective mask 200, and a reduction optical system 54. An X-ray reflection mirror is used as the reduction optical system 54.

The pattern reflected by the reflective mask 200 is reduced, usually to about 1/4, by the reduction optical system 54. For example, a wavelength band of 13 to 14 nm is used as the exposure wavelength, and the optical path is preset to be in a vacuum. Under these conditions, the EUV light generated by the laser plasma X-ray source 52 is made to enter the reflective mask 200. The light reflected by the reflective mask 200 is transferred onto the semiconductor substrate 56 with resist via the reduction optical system 54.

The light reflected by the reflective mask 200 enters the reduction optical system 54. The light that enters the reduction optical system 54 forms a transfer pattern in the resist layer on the resist-coated semiconductor substrate 56. By developing the exposed resist layer, a resist pattern can be formed on the resist-coated semiconductor substrate 56. By etching the semiconductor substrate 56 using the resist pattern as a mask, for example, a predetermined wiring pattern can be formed on the semiconductor substrate. Through these steps and other necessary steps, a semiconductor device is manufactured.

In order to confirm the change in reflectance over time when hydrogen (H) or deuterium (D) is not added to the top layer 20 of the absorber film, the following experiment was carried out.
The reflective mask blanks of samples 1 to 6 for the experiment were prepared as follows.
A _SiO2 - _TiO2- based glass substrate was prepared, which was a low-thermal expansion glass substrate having a size of 6025 (approximately 152 mm x 152 mm x 6.35 mm) with both the first and second main surfaces polished. To obtain a flat and smooth main surface, the substrate was polished through a rough polishing process, a precision polishing process, a localized polishing process, and a touch polishing process.

A multilayer reflective film was formed by periodically stacking Mo films/Si films on the main surface of a glass substrate.

Specifically, using a Mo target and a Si target, Mo films and Si films were alternately laminated on a substrate by ion beam sputtering (using Kr). The thickness of the Mo film was 2.8 nm. The thickness of the Si film was 4.2 nm. The thickness of one period of the Mo/Si film was 7.0 nm. 40 periods of such Mo/Si films were laminated, and finally a Si film was deposited to a thickness of 4.0 nm to form a multilayer reflective film.

A protective film containing a Ru compound was formed on the multilayer reflective film. Specifically, a RuNb target (Ru: 80 atomic %, Nb: 20 atomic %) was used to form a protective film made of a RuNb film on the multilayer reflective film by DC magnetron sputtering in an Ar gas atmosphere. The thickness of the protective film was 3.5 nm.

Next, an absorption layer (lower layer) or a first layer made of a TaBN film was formed on the protective film by DC magnetron sputtering. The TaBN film was formed by reactive sputtering in a mixed gas atmosphere of Xe gas and _N2 gas using a TaB mixed sintered target. The composition ratio (Ta:B:N) of the TaBN film was measured by X-ray photoelectron spectroscopy (XPS) to be 75:12:13. The refractive index of the TaBN film at a wavelength of 13.5 nm was 0.949. The film thicknesses of the absorption layer (lower layer) or the first layer in samples 1 to 6 are as shown in Table 1 below.

Next, a top layer or a second layer including the top layer, made of a metal film, was formed on the absorber layer (lower layer) or the first layer by DC magnetron sputtering. The top layer or the second layer including the top layer was formed by DC magnetron sputtering in a Kr gas atmosphere using a metal target made of Pt, Ru, or Ni, which is contained in the top layer. For example, for sample 1, a Pt film was formed by sputtering using a Pt target and Kr gas. The thickness of the top layer was set to a thickness that increases the amplitude of the EUV light reflected on the surface of the absorber film, as shown in Figure 7.

The metal elements contained in the top layer and the film thickness of the top layer or the second layer are as shown in Table 1 below. The content of the metal elements in the formed film was confirmed to be 95 atomic % or more by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The content of the metal elements in the top layer formed on the second layer was measured at a depth of 2 nm from the surface.

As a result, reflective mask blanks of samples 1 to 6 were obtained, in which a multilayer reflective film, a protective film, an absorbing layer (lower layer) or a first layer, and a top layer or a second layer including the top layer were laminated on a substrate. The reflectance (first time) of the obtained samples 1 to 6 at a wavelength of 13.5 nm was measured.

Next, samples 1 to 6 were left in an atmosphere with a temperature of 22°C and a relative humidity of 50% for 4 days, after which the reflectance of samples 1 to 6 at a wavelength of 13.5 nm was measured (for the second time).

The amount of change in reflectance between the first and second passes was calculated using the following formula for the reflective mask blanks of Samples 1 to 6. The results are shown in Table 1.
Fluctuation amount = 2nd reflectance - 1st reflectance [%]

As can be seen from the results shown in Table 1, the reflectance fluctuation amount exceeded 0.2% for the reflective mask blanks of samples 1 to 6. This is considered to be because the film quality of the entire uppermost layer made of a metal film changed over time, resulting in a large fluctuation amount of the reflectance.
Furthermore, when the crystal structures of Samples 1 to 6 were measured by an X-ray diffractometer (XRD) and an electron diffraction method (ED), they were found to have crystallinity.

Next, to confirm the change in reflectance over time when hydrogen (H) or deuterium (D) is added to the top layer 20, reflective mask blanks of samples 7 to 13 were fabricated and the following experiment was carried out.

A substrate similar to that of sample 1 was prepared, and a multilayer reflective film, a protective film, and an absorbing layer (lower layer) or a first layer were formed on the substrate in the same manner as in sample 1. The film thicknesses of the absorbing layer (lower layer) or the first layer in samples 7 to 13 are as shown in Table 2 below.

Next, a top layer or a second layer including a top layer made of a metal film was formed on the absorbing layer (lower layer) or the first layer by DC magnetron sputtering. The top layer was formed by reactive sputtering using Kr gas and hydrogen gas or deuterium gas, using a metal target made of Pt, Ru, or Ni contained in the top layer. For example, in the preparation of sample 7, a Pt film doped with H was formed by reactive sputtering using a Pt target, Kr gas, and hydrogen gas.

The metal elements contained in the top layer, their contents, deposition gas flow rate ratio, and film thickness of the top layer or the second layer including the top layer are as shown in Table 2 below. The metal element contents in the deposited film were measured by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). Dynamic secondary ion mass spectrometry (SIMS) also confirmed that H or D was present at a depth of 2 nm from the surface of the top layer or the second layer.

As a result, reflective mask blanks samples 7 to 13 were obtained, in which a multilayer reflective film, a protective film, an absorbing layer (lower layer) or a first layer, and a top layer or a second layer including the top layer were laminated on a substrate. The reflectance of the obtained samples 7 to 13 was measured in the same manner as sample 1, and the amount of change in reflectance was calculated.

As can be seen from the results shown in Table 2, in the reflective mask blanks of samples 7 to 13, changes in the film quality of the uppermost layer made of a metal film were suppressed, and the fluctuation in reflectance was within 0.2%.
Furthermore, when the crystal structures of Samples 7 to 13 were measured by an X-ray diffractometer (XRD) and an electron diffraction method (ED), they were found to have a microcrystalline structure or an amorphous structure.

Example 1
A reflective mask blank and a reflective mask according to a first embodiment will be described.
The reflective mask blank of Example 1 was produced under the same production conditions as those for the above-mentioned Sample 8. An etching mask film made of a CrN film was formed on the uppermost layer of the produced reflective mask blank to produce a reflective mask blank having an etching mask film.

The etching mask film was formed to the thickness shown in Table 3 by magnetron sputtering (reactive sputtering) using a Cr target in a mixed gas atmosphere of Ar and _N2 (Ar: 90%, N: 10%).

A back conductive film made of CrN was formed on the back surface of the above glass substrate by magnetron sputtering. The back conductive film was formed to a thickness of 20 nm by magnetron sputtering (reactive sputtering) using a Cr target in a mixed gas atmosphere of Ar and _N2 (Ar: 90%, N: 10%).

In this manner, the reflective mask blank of Example 1 was manufactured.

Next, the reflective mask of Example 1 was manufactured using the reflective mask blank of Example 1. No diffusion layer was formed between the etching mask film and the top layer.

The reflective mask was manufactured by forming an etching mask pattern and a laminated film pattern (a second layer pattern and a first layer pattern) using the etching gas in Table 3 according to the manufacturing method of the reflective mask described above, and removing the etching mask pattern with a mixed gas of _Cl2 gas and _O2 gas.

The reflectance of the reflective mask of Example 1 at a wavelength of 13.5 nm was measured in the same manner as for Sample 8, and the amount of variation in reflectance was calculated. It was found to be within 0.1%, confirming that there was little deviation from the design value.

Example 2
A reflective mask blank and a reflective mask according to a second embodiment will be described.
The reflective mask blank of Example 2 was prepared under the same preparation conditions as those of Sample 10. An etching mask film made of a _SiO2 film was formed on the uppermost layer of the prepared reflective mask blank to prepare a reflective mask blank having an etching mask film.

The etching mask film was formed to a thickness shown in Table 4 by RF sputtering using a SiO ₂ target in an Ar gas atmosphere.

A back conductive film was formed in the same manner as in Example 1, and a reflective mask blank of Example 2 was produced. No diffusion layer was formed between the etching mask film and the top layer.

Next, the reflective mask of Example 2 was manufactured using the reflective mask blank of Example 2 above.

The reflective mask was manufactured by forming an etching mask pattern and a laminated film pattern (upper layer pattern and lower layer pattern) using the etching gas in Table 4 according to the manufacturing method of the reflective mask described above, and removing the etching mask pattern with _CF4 gas.

The reflectance of the reflective mask of Example 2 at a wavelength of 13.5 nm was measured in the same manner as for Sample 10, and the amount of variation in reflectance was calculated. It was found to be within 0.2%, confirming that there was little deviation from the design value.

Example 3
A substrate with a conductive film according to a third embodiment will be described.
The substrate with a conductive film of Example 3 was obtained by preparing a glass substrate similar to that of Sample 1 and forming a back conductive film on the main surface of the glass substrate opposite to the main surface on which the multilayer reflective film was formed.

Specifically, a back conductive film (including the top layer) consisting of a Pt film containing H was formed by DC magnetron sputtering using a Pt target in the deposition gas atmosphere shown in Table 5. The metal elements contained in the back conductive film and their contents, deposition gas flow rate ratio, and film thickness of the back conductive film are as shown in Table 5 below. The contents of metal elements in the deposited film were measured by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS).

As a result, a substrate with a conductive film was obtained in which a back conductive film including a top layer was laminated on the substrate. The obtained substrate with a conductive film was left for 4 days in an atmosphere at a temperature of 22°C and a relative humidity of 50%, and then the sheet resistance and transmittance were measured. The results are shown in Table 5, with almost no deviation from the design values. The transmittance was measured by irradiating the back surface of the substrate with a conductive film with light having a wavelength of 470 nm. The sheet resistance was measured using a four-terminal measurement method.

REFERENCE SIGNS LIST 10 Substrate 12 Multilayer reflective film 14 Protective film 16 Laminated film 17 Absorber film 18, 28 Lower layer 20, 30 Top layer 22 Back conductive film 24 Etching mask film 26 Resist film 40 Laminated film pattern 62 First layer 64 Second layer 100 Reflective mask blank 110 Substrate with conductive film 200 Reflective mask

Claims (9)

A reflective mask blank comprising a substrate, a multilayer reflective film on the substrate, and a laminated film on the multilayer reflective film,
The laminated film includes a top layer and other underlying layers,
The uppermost layer contains at least one metal element selected from rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), ruthenium (Ru), gold (Au), iridium (Ir), cobalt (Co), tin (Sn), nickel (Ni), rhenium (Re), molybdenum (Mo), and niobium (Nb), and at least one additive element selected from hydrogen (H) and deuterium (D);
The total content of metal elements in the uppermost layer is 95 atomic % or more ,
A reflective mask blank, characterized in that the film thickness of the uppermost layer is 0.5 nm or more and less than 5 nm . A reflective mask blank comprising a substrate, a multilayer reflective film on the substrate, and a laminated film on the multilayer reflective film,
The laminated film includes a top layer and other underlying layers,
The uppermost layer contains at least one metal element selected from rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), ruthenium (Ru), gold (Au), iridium (Ir), cobalt (Co), tin (Sn), nickel (Ni), rhenium (Re), molybdenum (Mo), and niobium (Nb), and at least one additive element selected from hydrogen (H) and deuterium (D);
The total content of metal elements in the uppermost layer is 95 atomic % or more,
the laminated film is composed of an absorber film including a first layer and a second layer from the substrate side,
the second layer contains at least one metal element selected from rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), ruthenium (Ru), gold (Au), iridium (Ir), cobalt (Co), tin (Sn), nickel (Ni), rhenium (Re), molybdenum (Mo), and niobium (Nb);
A reflective mask blank, wherein the uppermost layer is a layer that forms a surface layer of the second layer. 3. The reflective mask blank according to claim 2 , wherein the first layer is made of a material containing at least one selected from the group consisting of tantalum (Ta) and chromium (Cr). 4. The reflective mask blank according to claim 1, wherein the metal element contained in the uppermost layer is at least one selected from the group consisting of rhodium (Rh), palladium (Pd), silver (Ag), platinum (Pt), ruthenium (Ru) and gold (Au). 5. The reflective mask blank according to claim 1 , wherein the uppermost layer has at least one of an amorphous structure and a microcrystalline structure. an etching mask film provided in contact with the uppermost layer;
the etching mask film is made of a material containing silicon (Si);
6. The reflective mask blank according to claim 1, wherein the metal element of the uppermost layer is ruthenium (Ru). an etching mask film provided in contact with the uppermost layer;
The etching mask film is made of a material containing chromium (Cr),
6. The reflective mask blank according to claim 1, wherein the metal element of the uppermost layer is at least one selected from platinum (Pt), ruthenium (Ru), and palladium (Pd). A reflective mask comprising the patterned laminated film in the reflective mask blank according to claim 1 . 9. A method for manufacturing a semiconductor device, comprising the steps of: setting the reflective mask according to claim 8 in an exposure apparatus having an exposure light source that emits EUV light; and transferring a transfer pattern to a resist film formed on a transfer substrate.