Reflection-type mask blank and method for manufacturing reflection-type mask

Abstract

As a reflective mask blank including a protective film containing ruthenium (Ru), the reflective mask blank is provided by including a substrate, a multilayer reflective film, a protective film, an absorption film, and an etching prevention film containing niobium (Nb) and not containing ruthenium (Ru) between the protective film and the absorption film, in which the protective film is difficult to damage and a reduction in thickness can be suppressed.

Description

Technical Field

[0001] The present invention relates to a reflective mask blank which is a material for a reflective mask used for manufacturing a semiconductor device such as an LSI, and a method for manufacturing a reflective mask from the reflective mask blank. Background Art

[0002] In the manufacturing process of semiconductor devices, photolithography technology is repeatedly used, in which a transfer mask is irradiated with exposure light, and the circuit pattern formed on the transfer mask is transferred to a semiconductor substrate (semiconductor wafer) through a reduced projection optical system. In the past, the mainstream wavelength of exposure light was 193nm using argon fluoride (ArF) excimer laser. By adopting a method called multiple patterning that combines the exposure process and the processing process multiple times, a pattern with a size smaller than the exposure wavelength is finally formed.

[0003] However, due to the need to form finer patterns under the continuous miniaturization of device patterns, extreme ultraviolet lithography technology using extreme ultraviolet (hereinafter referred to as "EUV") light with a wavelength shorter than that of ArF excimer laser as exposure light is used. EUV light has a wavelength of about 0.2 to 100 nm, and in particular, light with a wavelength of about 13.5 nm. EUV light has very low transmittance to matter and cannot be used in previous transmissive projection optical systems or masks, so a reflective type optical element device is applied. Therefore, a reflective mask is also used as a mask for pattern transfer.

[0004] In a reflective mask, a multilayer reflective film that reflects EUV light is formed on a substrate, and a pattern of an absorption film that absorbs EUV light is formed on the multilayer reflective film. On the other hand, the material before the absorption film is patterned (including the material forming the resist layer) is called a reflective mask blank, and is used as a material for a reflective mask. The reflective mask blank generally has a basic structure including a low thermal expansion substrate, a multilayer reflective film that reflects EUV light formed on either of the two main surfaces of the substrate, and an absorption film that absorbs EUV light formed thereon.

[0005] As a multilayer reflective film, a multilayer reflective film in which molybdenum (Mo) layers and silicon (Si) layers are alternately stacked to have a necessary reflectivity for EUV light is generally used. On the other hand, as an absorption film, tantalum (Ta) or the like having a relatively large extinction coefficient with respect to EUV light is used (Patent Document 1: JP-A 2002-246299).

[0006] In addition, as a protective film (capping film) for protecting the multilayer reflective film in, for example, cleaning a reflective mask, a ruthenium (Ru) film as disclosed in Patent Document 2 (JP-A 2002-122981) is formed on the multilayer reflective film. In some cases, a hard mask film containing chromium (Cr) is formed on the absorption film as an etching mask in patterning the absorption film. On the other hand, a conductive film is formed on the other main surface of the substrate. As the conductive film, a metal nitride film has been proposed for electrostatic clamping, and a film mainly containing chromium (Cr) or tantalum (Ta) is exemplified.

[0007] Reference List

[0008] Patent Document 1: JP-A 2002-246299

[0009] Patent Document 2: JP-A 2002-122981 Summary of the invention

[0010] The protective film needs to have the function of protecting the multilayer reflective film. Specifically, examples of the function include a function for protecting the multilayer reflective film from being exposed to etching gas or cleaning liquid during patterning of the absorption film, and a function for suppressing a decrease in reflectivity caused by repeated exposure in exposure using a reflective mask.

[0011] In the process of manufacturing a reflective mask using a reflective mask blank as a material, in forming a pattern on an absorption film by dry etching, a certain amount of overetching is generally performed in order to control the pattern shape. The protective film is exposed to etching and damaged by overetching. In the case where the absorption film includes a tantalum (Ta)-containing material, since a gas containing chlorine (Cl) and not containing oxygen (O) is preferably used as an etching gas, the protective film is required to be resistant to dry etching using a gas containing chlorine (Cl) and not containing oxygen (O).

[0012] In addition, in the case where the pattern of the hard mask film obtained by patterning the hard mask film made of a material containing chromium (Cr) is used as an etching mask when the absorption film is patterned, the pattern of the hard mask film is usually removed by dry etching using a gas containing chlorine (Cl) and oxygen (O) after the absorption film is patterned. At this time, the protective film is also exposed to dry etching using a gas containing chlorine (Cl) and oxygen (O). Therefore, the protective film is required to have resistance to dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0013] In addition, cleaning using a sulfuric acid-hydrogen peroxide mixture (SPM) is performed to remove the residue of the resist used in manufacturing the reflective mask or to remove contaminants caused by repeated use of the reflective mask. Therefore, the protective film is also required to be resistant to the sulfuric acid-hydrogen peroxide mixture (SPM).

[0014] During dry etching in the manufacture of a reflective mask, if the protective film is damaged and the film quality and film thickness change, problems such as loss of function for protecting the multilayer reflective film are caused. Therefore, it is proposed to add an additive element such as niobium (Nb) to a protective film containing ruthenium (Ru) to improve resistance to dry etching and enhance the function of the protective film for protecting the multilayer reflective film.

[0015] However, even if the resistance of the protective film containing ruthenium (Ru) to dry etching is enhanced by adding an additive element such as (Nb), in the dry etching of the protective film containing a tantalum (Ta) material, the protective film becomes thinner when the protective film is exposed to a gas containing chlorine (Cl) and no oxygen (O). In addition, in the pattern of removing the hard mask film, the protective film also becomes thinner when the protective film is exposed to a gas containing chlorine (Cl) and oxygen (O). In addition, the protective film also becomes thinner in the cleaning using a sulfuric acid-hydrogen peroxide mixture (SPM).

[0016] Therefore, chemical damage to the protective film is inevitable, and the protective film also becomes thinner due to physical damage, so it is necessary to suppress functional degradation of the protective film for protecting the multilayer reflective film due to thickness reduction.

[0017] Tantalum (Ta) films are generally used for absorber films. However, it is necessary to reduce the pattern height corresponding to the film thickness of the absorber film to improve the accuracy of pattern transfer to the wafer, so attention is paid to chromium (Cr) absorber films that can be made thinner than tantalum (Ta) absorber films.

[0018] However, when a chromium (Cr)-based absorption film is formed on a ruthenium (Ru)-based protective film that is generally used as a protective film for a multilayer reflective film, the ruthenium (Ru)-based film is etched by dry etching using a gas containing chlorine (Cl) and oxygen (O) used in dry etching of the chromium (Cr)-based film, and the (Ru)-based protective film is damaged and thinned.

[0019] The present invention is proposed to solve the above-mentioned problems, and an object of the present invention is to provide a reflective mask blank including a protective film, wherein when an absorption film formed on a protective film including a ruthenium (Ru)-containing material is etched by dry etching using a gas containing chlorine (Cl) and oxygen (O), the protective film is difficult to be damaged and a reduction in thickness can be suppressed, and to provide a method for manufacturing a reflective mask using the reflective mask blank.

[0020] The inventors have conducted intensive research to solve the above-mentioned problem. As a result, the inventors have found that in a reflective mask blank in which an absorption film is formed on a protective film containing ruthenium (Ru), the problem can be solved by providing an etching stopper film containing niobium (Nb) and no ruthenium (Ru) between the protective film and the absorption film.

[0021] In one aspect, the present invention provides a reflective mask blank, which is a reflective mask material used in EUV lithography using EUV light as exposure light, comprising: a substrate; a multilayer reflective film formed on one main surface of the substrate to reflect the exposure light; a protective film formed on the multilayer reflective film to protect the multilayer reflective film; and an absorption film formed on the protective film to absorb the exposure light, wherein the protective film contains ruthenium (Ru), and the reflective mask blank also includes an etching stopper film containing niobium (Nb) and no ruthenium (Ru) between the protective film and the absorption film.

[0022] Preferably, the etch stopper film is composed of niobium (Nb) alone, or a niobium (Nb) compound containing niobium (Nb) and oxygen (O).

[0023] Preferably, the protective film is composed of ruthenium (Ru).

[0024] Preferably, the absorber film contains chromium (Cr).

[0025] Preferably, the absorption film contains tantalum (Ta), and the reflective mask blank further includes an etching mask film containing chromium (Cr) on the absorption film.

[0026] On the other hand, the present invention provides a method for manufacturing a reflective mask, comprising the following steps: patterning an absorption film of a reflective mask blank by dry etching using a gas containing chlorine (Cl) and oxygen (O); or after patterning the absorption film of the reflective mask blank, removing the etching mask film by dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0027] In other aspects, the present invention provides a method of manufacturing a reflective mask from a reflective mask blank, comprising the steps of: after forming a pattern of an absorption film, removing an etching stopper film at a portion exposed by removing the absorption film.

[0028] Preferably, the etching stopper film at the portion exposed by removing the absorber film is removed using a sulfuric acid-hydrogen peroxide mixture (SPM).

[0029] Advantageous Effects of the Invention

[0030] According to the present invention, a reflective mask blank including a protective film can be provided, in which, when an absorption film formed on a protective film including a ruthenium (Ru)-containing material is etched by dry etching using a gas containing chlorine (Cl) and oxygen (O), the protective film is hardly damaged and a reduction in thickness can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a cross-sectional view showing an example (first embodiment) of the reflective mask blank of the present invention.

[0033] Figure 2 It is a cross-sectional view showing an example (second embodiment) of the reflective mask blank of the present invention.

[0034] Figure 3 It is a cross-sectional view showing an example of the reflective mask of the present invention. DETAILED DESCRIPTION

[0035] The reflective mask blank of the present invention comprises a substrate, a multilayer reflective film formed on one main surface (front surface) of the substrate to reflect exposure light, a protective film formed on the multilayer reflective film, and an absorption film formed on the protective film to absorb exposure light. In addition, the reflective mask blank of the present invention comprises an etching stopper film between the protective film and the absorption film.

[0036] The reflective mask blank of the present invention is suitable for a reflective mask material used in EUV lithography using EUV light as exposure light. The wavelength of EUV light used in EUV lithography using EUV light as exposure light is 13 to 14 nm, usually about 13.5 nm. The reflective mask blank and the reflective mask using EUV light as exposure light are also referred to as EUV mask blank and EUV mask, respectively.

[0037] Figure 1 The sectional view is a diagram showing an example (first embodiment) of a reflective mask blank of the present invention. The reflective mask blank 11 includes: a substrate 1; and on the substrate 1, a multilayer reflective film 2 formed in contact with the substrate 1, a protective film 3 formed in contact with the multilayer reflective film 2, an etching stopper film 4 formed in contact with the protective film 3, and an absorption film 5 formed in contact with the etching stopper film 4.

[0038] In the case of EUV light exposure, the substrate preferably has low thermal expansion properties. For example, the substrate preferably comprises a thermal expansion coefficient within ±2×10 -8 / ℃, preferably within ±5×10 -9 / ℃ within the material. As such a material, titanium dioxide doped quartz glass (SiO2-TiO2 glass) is exemplified. In addition, it is preferred to use a substrate with a very flat surface. The surface roughness of the main surface of the substrate is preferably not more than 0.5nm, more preferably not more than 0.2nm in RMS value. Such surface roughness can be obtained by polishing the substrate, etc. The substrate preferably has a main surface size of 152mm square and a thickness of 6.35mm. A substrate with this size is called a 6025 substrate, which has a main surface size of 6 inches square and a thickness of 0.25 inches.

[0039] The multilayer reflective film is a film that reflects exposure light in a reflective mask. The multilayer reflective film is preferably formed in contact with one main surface of the substrate, but may be formed via another film such as an underlying film on one main surface of the substrate. The multilayer reflective film has a periodic stacked structure in which a high refractive index layer having a relatively high refractive index with respect to the exposure light and a low refractive index layer having a relatively low refractive index with respect to the exposure light are alternately stacked.

[0040] The high refractive index layer preferably comprises a silicon-containing (Si) material. The high refractive index layer may contain at least one additive element selected from oxygen (O), nitrogen (N), carbon (C), boron (B) and hydrogen (H). In addition, the high refractive index layer may be configured as a multilayer, comprising a layer containing additive elements and a layer not containing additive elements. The thickness of the high refractive index layer is preferably not less than 3.5 nm, more preferably not less than 4 nm, and preferably not more than 4.9 nm, more preferably not more than 4.4 nm.

[0041] The low refractive index layer preferably comprises a material containing molybdenum (Mo). The low refractive index layer may comprise a material containing ruthenium (Ru). The low refractive index layer may contain at least one additive element selected from oxygen (O), nitrogen (N), carbon (C), boron (B) and hydrogen (H). In addition, the low refractive index layer may be configured as a multilayer, the multilayer comprising a layer containing additive elements and a layer not containing additive elements. The thickness of the low refractive index layer is preferably not less than 2.1nm, more preferably not less than 2.6nm, and preferably not more than 3.5nm, more preferably not more than 3nm.

[0042] The periodic stacked structure may include a high refractive index layer and a low refractive index layer, and may include at least one high refractive index layer and at least one low refractive index layer in one cycle. One cycle includes at least two layers and may be configured as, for example, a high refractive index layer and a low refractive index layer. In addition, one cycle may include at least two high refractive index layers (e.g., different composition ratios, or different compositions with or without added elements) that are different from each other, and may include at least two low refractive index layers (e.g., different composition ratios, or different compositions with or without added elements) that are different from each other. In this case, one cycle includes at least three layers and may include four, five or more layers, but is preferably no more than eight layers. The number of cycles of the periodic stacked structure is preferably not less than 30 cycles, and is preferably no more than 50 cycles, more preferably no more than 40 cycles. In the case where the low refractive index layer includes a ruthenium (Ru) material, the layer (uppermost layer) farthest from the substrate in the periodic stacked structure is preferably a high refractive index layer.

[0043] The thickness of the multilayer reflective film having a periodic stacking structure is adjusted according to the exposure light and the incident angle of the exposure light, and the thickness is preferably not less than 200nm, more preferably not less than 270nm, and preferably not more than 400nm, more preferably not more than 290nm.

[0044] Examples of methods for forming a multilayer reflective film include a sputtering method in which power is supplied to a target and a plasma of an atmosphere gas is formed by the supplied power (the atmosphere gas is ionized) for sputtering, and an ion beam sputtering method in which an ion beam is irradiated to a target. Sputtering methods include a DC sputtering method in which a DC voltage is applied to a target and an RF sputtering method in which a high-frequency voltage is applied to a target. The sputtering method is a film forming method utilizing the sputtering phenomenon of gas ions generated by applying a voltage to a target and supplying a sputtering gas into a chamber to ionize the gas. In particular, the magnetron sputtering method has advantages in terms of productivity. Power can be applied to the target by a DC system or an RF system. The DC system also includes a pulse sputtering in which a negative bias voltage applied to a target is reversed for a short time to prevent charge-up of the target.

[0045] The multilayer reflective film can be formed by, for example, a sputtering method using a sputtering device capable of mounting a plurality of targets. In particular, the multilayer reflective film can be formed by using a target appropriately selected from the following: a molybdenum (Mo) target for forming a molybdenum (Mo)-containing layer, a ruthenium (Ru) target for forming a ruthenium (Ru)-containing layer, a silicon (Si) target for forming a silicon (Si)-containing layer, and other targets as targets, and using a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas as a sputtering gas.

[0046] In addition, in the case where the sputtering is reactive sputtering using a reactive gas, a nitrogen-containing gas such as nitrogen (N2) gas to form a nitrogen (N)-containing film, an oxygen-containing gas such as oxygen (O2) gas to form an oxygen (O)-containing film, a nitrogen oxide gas such as nitrous oxide (N2O) gas, nitric oxide (NO) gas and nitrogen dioxide (NO2) gas to form a nitrogen (N) and oxygen (O)-containing film, a carbon oxide gas such as carbon monoxide (CO) gas and carbon dioxide (CO2) gas to form a carbon (C) and (O)-containing film, a hydrogen-containing gas such as hydrogen (H2) gas to form a hydrogen (H)-containing film or a hydrocarbon gas such as methane (CH4) gas to form a carbon (C) and hydrogen (H)-containing film can be used together with a rare gas.

[0047] In addition, a molybdenum (Mo) target to which boron (B) is added (molybdenum boride (MoB) target) or a silicon (Si) target to which boron (B) is added (silicon boride (SiB) target) may be used to form a layer containing boron (B).

[0048] The protective film is also called a capping film. The protective film is a film used to protect the multilayer reflective film. The protective film is usually formed in contact with the multilayer reflective film. The protective film contains a ruthenium (Ru)-containing material.

[0049] Examples of ruthenium (Ru)-containing materials include simple substances of ruthenium (Ru), and alloys composed of ruthenium (Ru) and other metals or metalloids different from ruthenium (Ru). Examples of other metals or metalloids different from ruthenium (Ru) include niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), silicon (Si), etc. In ruthenium (Ru)-containing materials, simple substances of ruthenium (Ru) are particularly preferred, and the protective film is preferably composed of ruthenium (Ru). The content of other metals or metalloids different from ruthenium (Ru) in the protective film is preferably not more than 30 atomic %, more preferably not more than 20 atomic % based on the average of the entire film. The lower limit of the content of other metals or metalloids different from ruthenium (Ru) in the protective film is preferably not less than 5 atomic %, more preferably not less than 10 atomic % based on the average of the entire film, but is not particularly limited thereto.

[0050] The protective film may have a single-layer structure or a multilayer structure in which a plurality of layers having different compositions are combined. In addition, each layer constituting the single layer or the multilayer may have a composition gradient structure in which the composition changes continuously along the thickness direction. In particular, in the protective film, either or both of the side close to the multilayer reflective film (the layer close to the multilayer reflective film in the case of the multilayer structure) and the side farthest from the multilayer reflective film (the layer farthest from the multilayer reflective film in the case of the multilayer structure) may be composed of ruthenium (Ru).

[0051] In the case where the protective film has a multilayer structure or a composition gradient structure, in a part or all of the thickness direction of the protective film, the content of the metal or metalloid other than ruthenium (Ru) is preferably increased from the multilayer reflective film side to the side away from the multilayer reflective film. In particular, in the case where niobium (Nb) is contained as the metal or metalloid other than ruthenium (Ru), niobium (Nb) is effective in improving the resistance to dry etching using a gas containing chlorine (Cl) and oxygen (O). Therefore, in a part or all of the thickness direction of the protective film, the content of niobium (Nb) is preferably increased from the multilayer reflective film side to the side away from the multilayer reflective film.

[0052] As dry etching using a gas containing chlorine (Cl) and oxygen (O), specifically, the present invention exemplifies dry etching using a gas containing chlorine (Cl2) and oxygen (O2). The gas containing chlorine (Cl) and oxygen (O) may contain a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas.

[0053] The thickness of the protective film is preferably not less than 2 nm, more preferably not less than 3 nm, and is preferably not more than 5 nm, more preferably not more than 4 nm.

[0054] The protective film can be formed by using a target appropriately selected from the following: a ruthenium (Ru) target, a target of other metals or metalloids other than ruthenium (Ru), in particular a niobium (Nb) target, a rhenium (Re) target, a zirconium (Zr) target, a titanium (Ti) target, a chromium (Cr) target, a silicon (Si) target, a target selected from niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr) and silicon (Si) A target of a mixture of two or more, and a target of ruthenium (Ru) and at least one metal or metalloid other than ruthenium (Ru) selected from niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr) and silicon (Si) as a target, and using a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas and xenon (Xe) gas as a sputtering gas, sputtering. Sputtering is preferably performed by a magnetron sputtering method.

[0055] In a reflective mask, the absorption film is a film that absorbs exposure light and reduces reflectivity. In a reflective mask, a transfer pattern is formed by a reflectivity difference between a portion where the absorption film is formed and a portion where the absorption film is not formed. The absorption film may be composed of a single layer or multiple layers, and an anti-reflection layer may be formed on the surface of the absorption film.

[0056] The absorption film preferably contains tantalum (Ta) or chromium (Cr). The absorption film is a film that can absorb EUV light and contains a material that can be processed into a pattern. The absorption film preferably contains a material containing tantalum (Ta) or chromium (Cr).

[0057] The tantalum (Ta)-containing material may contain oxygen (O), nitrogen (N), carbon (C), boron (B) or other elements. Examples of the tantalum (Ta)-containing material include simple substance of Ta and tantalum (Ta) compounds such as TaO, TaN, TaON, TaC, TaCO, TaCN, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCOB, TaCNB and TaCONB. In addition, the description of the chemical formula of the metal or metalloid compound indicates the constituent elements of the compound, but does not mean their composition ratio (the same applies below).

[0058] In the case where the material containing tantalum (Ta) does not contain oxygen (O), the material containing tantalum (Ta) can be etched by dry etching using a gas containing chlorine (Cl). In this case, when the material containing tantalum (Ta) contains nitrogen (N), the etching rate increases in the dry etching using a gas containing chlorine (Cl). In addition, when the material containing tantalum (Ta) contains nitrogen (N) and does not contain oxygen (O), the etching selectivity for the etching stop film increases in the dry etching using a gas containing chlorine (Cl). Therefore, in the absorption film containing tantalum (Ta), the portion in contact with the etching stop film preferably does not contain oxygen (O) and preferably contains a large amount of nitrogen (N).

[0059] As dry etching using a gas containing chlorine (Cl), specifically, the present invention exemplifies dry etching using a gas containing chlorine (Cl2) gas, hydrogen chloride (HCl) gas, etc. The gas containing chlorine (Cl) preferably does not contain a gas containing (O). The gas containing chlorine (Cl) may contain a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas.

[0060] The chromium (Cr)-containing material may contain oxygen (O), nitrogen (N), carbon (C) or other elements. Examples of the chromium (Cr)-containing material include simple substance of Cr, and chromium (Cr) compounds such as CrO, CrN, CrON, CrC, CrCO, CrCN and CrCON.

[0061] The sheet resistance of the absorber film is preferably not greater than 1×10 6 Ω / square, more preferably not more than 1×10 5 Ω / square The surface roughness Sq of the absorption film is preferably not more than 0.8 nm, more preferably not more than 0.6 nm.

[0062] The absorption film (each layer constituting the absorption film) can be formed by sputtering, and the sputtering is preferably performed by a magnetron sputtering method. In particular, the absorption film can be formed according to the composition by using a target appropriately selected from the following: in the case of being formed by a tantalum (Ta)-containing material, a tantalum (Ta) target, and a tantalum (Ta) compound target (a target containing tantalum (Ta) and oxygen (O), nitrogen (N), carbon (C), boron (B) or other elements), or in the case of being formed by a chromium (Cr)-containing material, a chromium (Cr) target, and a chromium (Cr) compound target (a target containing chromium (Cr) and oxygen (O), nitrogen (N), carbon (C) or other elements), and sputtering using a rare gas such as helium (He) gas, neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas and xenon (Xe) gas as a sputtering gas; or it can be formed by reactive sputtering using a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas and a carbon-containing gas, specifically, oxygen (O2) gas, nitrogen (N2) gas, nitrogen oxide (N2O, NO, NO2) gas and carbon oxide (CO, CO2) gas with a rare gas as a sputtering gas.

[0063] An etching mask film having different etching characteristics from the absorbing film may be provided on the side of the absorbing film away from the substrate as a hard mask for the absorbing film. The etching mask film acts as a hard mask in the dry etching of the absorbing film. The etching mask film is preferably formed in contact with the absorbing film. The etching mask film may be composed of a single layer or multiple layers.

[0064] Figure 2The sectional view is a diagram showing an example (second embodiment) of a reflective mask blank of the present invention. The reflective mask blank 12 includes: a substrate 1; and on the substrate 1, a multilayer reflective film 2 formed in contact with the substrate 1, a protective film 3 formed in contact with the multilayer reflective film 2, an etching stopper film 4 formed in contact with the protective film 3, an absorption film 5 formed in contact with the etching stopper film 4, and an etching mask film 6 formed in contact with the absorption film 5.

[0065] In the case where the absorption film contains tantalum (Ta), the etching mask film preferably contains chromium (Cr) and the etching mask film preferably contains a chromium (Cr)-containing material. The chromium (Cr)-containing material has different etching characteristics from the absorption film in processing the absorption film containing tantalum (Ta) material. The etching mask film containing chromium (Cr) material acts as an etching mask in the dry etching of the absorption film containing tantalum (Ta) material, and is suitable. Therefore, the etching mask film preferably does not contain tantalum (Ta) with a chromium (Cr)-containing material. Examples of chromium (Cr)-containing materials include simple substances of Cr, CrO, CrN, CrON, CrC, CrOC, CrNC and CrONC.

[0066] In the case where the absorption film contains chromium (Cr), the etching mask film preferably contains tantalum (Ta) and the etching mask film preferably contains a tantalum (Ta) material. The tantalum (Ta) material has different etching characteristics from the absorption film in processing the absorption film containing the chromium (Cr) material. The etching mask film containing the tantalum (Ta) material acts as an etching mask in the dry etching of the absorption film containing the chromium (Cr) material, and is suitable. Therefore, the etching mask film preferably contains no chromium (Cr) with the tantalum (Ta) material. Examples of tantalum (Ta) materials include simple substances of Ta, TaO, TaN, TaON, TaC, TaOC, TaNC and TaONC. The tantalum (Ta) material may also contain boron (B) or hydrogen (H).

[0067] After patterning the absorption film, the etching mask film may remain in the reflective mask, for example as a reflectivity reducing film for reducing reflectivity at the wavelength of light used in inspection such as pattern inspection, or may be removed so as not to remain on the reflective mask.

[0068] When the hard mask film is too thin, the hard mask film cannot function as an etching mask, but when the hard mask film is too thick, the processing properties may deteriorate. Therefore, the thickness of the hard mask film is preferably not less than 1 nm, more preferably not less than 2 nm, further preferably not less than 5 nm, and preferably not more than 20 nm, more preferably not more than 10 nm, but is not particularly limited thereto.

[0069] The etching mask film can be formed by sputtering. In particular, the etching mask film can be formed by using a target appropriately selected from the following according to the composition: in the case of being formed by a chromium (Cr)-containing material, a chromium (Cr) target, and a chromium (Cr) compound target (a target containing chromium (Cr) and oxygen (O), nitrogen (N), carbon (C) or other elements), or in the case of being formed by a tantalum (Ta)-containing material, a tantalum (Ta) target, and a tantalum (Ta) compound target (a target containing tantalum (Ta) and oxygen (O), nitrogen (N), carbon (C), boron (B) or other elements), and using It can be formed by sputtering with rare gases such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas and xenon (Xe) gas as sputtering gas; or it can be formed by reactive sputtering with reactive gases such as oxygen-containing gas, nitrogen-containing gas and carbon-containing gas, specifically, oxygen (O2) gas, nitrogen (N2) gas, nitrogen oxide (N2O, NO, NO2) gas, carbon oxide (CO, CO2) gas, hydrogen (H2) gas and hydrocarbon gas (e.g. methane (CH4) gas) and rare gas as sputtering gas. Sputtering is preferably performed by a magnetron sputtering method.

[0070] The etching stopper film is a film for protecting the protective film and preventing the protective film from being etched in dry etching using a gas containing chlorine (Cl) and oxygen (O). Therefore, the etching stopper film acts as an etching stopper for dry etching using a gas containing chlorine (Cl) and oxygen (O). The etching stopper film is a film containing niobium (Nb) and not containing ruthenium (Ru).

[0071] The film containing niobium (Nb) has resistance to dry etching using a gas containing chlorine (Cl) and oxygen (O), which is used to etch a chromium (Cr)-based film, and acts as a film for protecting the protective film. Therefore, in patterning an absorption film containing chromium (Cr) by dry etching using a gas containing chlorine (Cl) and oxygen (O), or in removing the etching mask film containing chromium (Cr) by dry etching using a gas containing chlorine (Cl) and oxygen (O) after patterning an absorption film containing tantalum (Ta) using a pattern of an etching mask film containing chromium (Cr), the etching stopper film containing niobium (Nb) can prevent the protective film from being damaged.

[0072] The etching stopper film is preferably composed of a single substance of niobium (Nb), but may contain a niobium (Nb) compound containing niobium (Nb) and oxygen (O) such as niobium oxide (NbO). The niobium (Nb) compound containing niobium (Nb) and oxygen (O) preferably contains niobium (Nb) and oxygen (O) as main components, and the total content of niobium (Nb) and oxygen (O) is preferably not less than 70 atomic %, more preferably not less than 80 atomic %, further preferably 91 atomic %, and particularly preferably 100 atomic % on an average basis of the entire film. In addition, the content of niobium (Nb) in the niobium (Nb) compound containing niobium (Nb) and oxygen (O) is preferably not less than 20 atomic %, more preferably not less than 28 atomic %, and further preferably not less than 29 atomic % on an average basis of the entire film.

[0073] The niobium (Nb) compound containing oxygen (O) may further contain an element or compound that can be etched by dry etching using a gas containing chlorine (Cl) or a gas containing fluorine (F), and may contain, for example, elements such as silicon (Si), nitrogen (N), carbon (C) and other elements, or compounds of the elements. The content of elements other than niobium (Nb) and oxygen (O) is preferably not more than 30 atomic %, more preferably not more than 20 atomic % on an average basis of the entire film. In this case, the total content of oxygen (O), nitrogen (N) and carbon (C) is preferably not more than 72 atomic % on an average basis of the entire film.

[0074] The etching stopper film may be composed of a single layer or a multilayer. Examples of multilayers include a combination of layers containing niobium (Nb) having different compositions or composition ratios, such as a combination of a layer containing a niobium (Nb) compound containing oxygen (O) and a layer containing niobium (Nb), and a combination of layers containing a niobium (Nb) compound containing (O) having different composition ratios. Each layer may be a single composition layer or a layer having a composition gradient with a gradient composition. When the etching stopper film contains oxygen (O), it is preferred that the oxygen (O) content is high on the surface side (the side away from the substrate); or the layer on the surface side is a layer containing niobium (Nb) oxide containing oxygen (O), and the layer on the substrate side is a layer composed of niobium (Nb) or a layer containing niobium (Nb) and no oxygen (O).

[0075] As dry etching using a gas containing fluorine (F), the present invention exemplifies dry etching using a gas containing carbon tetrafluoride (CF4) gas or sulfur hexafluoride (SF6) gas. The gas containing fluorine (F) may contain a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas.

[0076] The thickness of the etching stopper film is preferably not less than 0.5 nm, more preferably not less than 1 nm, and is preferably not more than 10 nm, more preferably not more than 5 nm.

[0077] The etching stop film can be formed by sputtering. The etching stop film can be formed by sputtering using a niobium (Nb) target and an optional target of a metal or metalloid other than niobium (Nb), specifically, a silicon (Si) target or other target as a target, and using a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas and xenon (Xe) gas as a sputtering gas; or can be formed by reactive sputtering using a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas and a carbon-containing gas, specifically, oxygen (O2) gas, nitrogen (N2) gas, nitrogen oxide (N2O, NO, NO2) gas and carbon oxide (CO, CO2) gas with a rare gas as a sputtering gas. Sputtering is preferably performed by a magnetron sputtering method.

[0078] In the case where the etching stopper film contains oxygen (O), niobium (Nb) is easily naturally oxidized, and therefore, an etching stopper film containing a niobium (Nb) compound containing oxygen (O) can be formed by forming a separate niobium (Nb) film and exposing it to an atmosphere containing oxygen (O), such as air, for oxidation. In order to oxidize separate niobium (Nb), the film may be heat-treated.

[0079] A conductive film (conductive film) for electrostatically clamping a reflective mask to an exposure device (eg, EUV scanner) may be formed on the other main surface (back side surface) which is a surface opposite to one main surface in the substrate, preferably in contact with the other main surface.

[0080] The sheet resistance of the conductive film is preferably not more than 100Ω / square, and there is no particular limitation on the material for the conductive film. Examples of materials for the conductive film include, for example, materials containing tantalum (Ta) or chromium (Cr). Tantalum (Ta)-containing materials may contain oxygen (O), nitrogen (N), carbon (C), boron (B) or other elements, and chromium (Cr)-containing materials may contain oxygen (O), nitrogen (N), carbon (C) or other elements. Examples of tantalum (Ta)-containing materials include, for example, simple substances of Ta and tantalum (Ta) compounds such as TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB and TaCONB. Examples of chromium (Cr)-containing materials include, for example, simple substances of Cr, and chromium (Cr) compounds such as CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON.

[0081] The thickness of the conductive film is generally about 20 to 300 nm, but is not particularly limited thereto as long as the thickness is sufficient for electrostatic clamping purposes. The conductive film is preferably formed to a thickness such that after obtaining a reflective mask, that is, after forming a pattern of an absorption film, the film stress between the conductive film and the film (s) formed at one main surface (front surface) and the pattern (s) of the film (s) is balanced. The conductive film may be formed before forming the multilayer reflective film, or after forming all the films on the multilayer reflective film side of the substrate. After forming a portion of the film on the multilayer reflective film side of the substrate, the conductive film may be formed, and then the remaining film may be formed on the multilayer reflective film side of the substrate. The conductive film can be formed by, for example, a magnetron sputtering method.

[0082] The reflective mask blank may include a resist film formed on a side farthest from the substrate. The resist film is preferably an electron beam (EB) resist.

[0083] From a reflective mask blank, for example, a reflective mask includes a substrate, a multilayer reflective film formed on one main surface of the substrate, a protective film formed in contact with the multilayer reflective film, a pattern of an etching stopper film formed in contact with the protective film, and a pattern of an absorption film (absorption film pattern) formed in contact with the pattern of the etching stopper film. In the reflective mask, a transfer pattern is formed by a reflectivity difference between a portion where the absorption film is formed and a portion where the absorption film is not formed.

[0084] Figure 3 1 is a cross-sectional view showing an example of a reflective mask of the present invention. The reflective mask 10 includes: a substrate 1; and on the substrate 1, a multilayer reflective film 2 formed in contact with the substrate 1, a protective film 3 formed in contact with the multilayer reflective film 2, a pattern 41 of an etching stopper film formed in contact with the protective film 3, and a pattern 51 of an absorption film formed in contact with the pattern 41 of the etching stopper film. In this case of the reflective mask 10, the pattern 51 of the absorption film is formed on the protective film 3 via the pattern 41 of the etching stopper film.

[0085] The reflective mask of the present invention can be manufactured by a method comprising the following steps:

[0086] preparing a reflective mask blank;

[0087] optionally forming a resist film on the absorber film;

[0088] forming a resist pattern from the resist film on the absorption film;

[0089] forming a pattern of the absorption film by etching the absorption film using the resist pattern as an etching mask;

[0090] removing the resist pattern; and

[0091] The etching stopper film is removed at the portion exposed by removing the absorption film.

[0092] The absorption film including a material containing chromium (Cr) can be etched by dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0093] In this case, the etching stopper film containing niobium (Nb) is not etched by dry etching using a gas containing chlorine (Cl) and oxygen (O). Therefore, damage to the protective film can be prevented.

[0094] The absorption film including the material including tantalum (Ta) can be etched by dry etching using a gas including chlorine (Cl) or a gas including fluorine (F).

[0095] In the dry etching of an absorption film containing a tantalum (Ta) material, dry etching using a gas containing fluorine (F) is suitable for etching an oxygen (O) portion formed by natural oxidation or other means, and dry etching using a gas containing chlorine (Cl) is suitable for etching a portion that does not contain oxygen (O). Therefore, it is preferred to pattern the absorption film containing tantalum (Ta) by initially performing dry etching using a gas containing fluorine (F) and then switching to dry etching using a gas containing chlorine (Cl) midway. In this case, since the etching stop film has low resistance to dry etching using a gas containing chlorine (Cl), it is preferred to perform etching so that the etching stop film does not disappear. In order to perform etching so that, for example, the etching stop film does not disappear, an endpoint detector connected to the etching equipment can be used.

[0096] Furthermore, the reflective mask of the present invention can be manufactured by a method comprising the following steps:

[0097] preparing a reflective mask blank;

[0098] optionally forming a resist film on the etching mask film;

[0099] forming a resist pattern from the resist film on the etching mask film;

[0100] forming a pattern of the etching mask film by etching the etching mask film using the resist pattern as an etching mask;

[0101] forming a pattern of the absorption film by etching the absorption film using the pattern of the etching mask film as an etching mask;

[0102] removing the resist pattern;

[0103] removing the pattern of the etching mask film; and

[0104] The etching stopper film is removed at the portion exposed by removing the absorption film.

[0105] After forming the pattern of the absorption film, when the etching mask film is a film containing a tantalum (Ta) material, the pattern of the etching mask film can be removed by dry etching using a gas containing chlorine (Cl) or a gas containing fluorine (F). When the etching mask film is a film containing a chromium (Cr) material, the pattern of the etching mask film can be removed by dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0106] In the case where the absorption film contains tantalum (Ta), a film containing chromium (Cr) is used as an etching mask film, and the etching mask film can be patterned by dry etching using a gas containing chlorine (Cl) and oxygen (O) to form a pattern of the etching mask film. After the absorption film is patterned using the pattern of the etching mask film as an etching mask, the etching mask film can be removed by dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0107] In this case, the etching stopper film containing niobium (Nb) is not etched by dry etching using a gas containing chlorine (Cl) and oxygen (O). Therefore, damage to the protective film can be prevented.

[0108] The resist pattern and the etching stopper film at the portion exposed by removing the absorption film may be removed with a sulfuric acid-hydrogen peroxide mixture (SPM).

[0109] In addition, the etching stopper film at the portion exposed by removing the absorption film can be removed by dry etching using a gas containing chlorine (Cl) or a gas containing fluorine (F). However, when niobium (Nb) is exposed to a gas containing oxygen (O), niobium (Nb) is oxidized to form niobium oxide (NbO). Niobium oxide (NbO) is difficult to remove by dry etching using a gas containing chlorine (Cl) or a gas containing fluorine (F), so it is preferable to remove the etching stopper film with a sulfuric acid-hydrogen peroxide mixture (SPM). In this case, the etching stopper film can be removed simultaneously with the removal of the resist pattern.

[0110] The pattern of the absorber film and the exposed protective film may be subjected to treatment in contact with a sulfuric acid-hydrogen peroxide mixture (SPM), such as cleaning using a sulfuric acid-hydrogen peroxide mixture (SPM).

[0111] Example

[0112] In the following, examples of the invention are given by way of illustration and not by way of limitation.

[0113] Examples 1 and 2

[0114] On one main surface of a precision-polished low thermal expansion substrate made of SiO2 doped with titanium oxide, a multilayer reflective film is formed by sputtering, in which 40 pairs of molybdenum (Mo) layers with a thickness of 3nm and silicon (Si) layers with a thickness of 4nm are alternately stacked as a pair (cycle). Next, a ruthenium (Ru) film with a thickness of 3nm is formed as a protective film by sputtering on the multilayer reflective film. The multilayer reflective film and the protective film have a reflectivity of 64% at an incident angle of 6° with respect to EUV light with a wavelength of 13.5nm.

[0115] Next, a niobium (NbO) oxide film (Nb:O=2:5 (atomic ratio)) with a thickness of 2 nm was formed on the protective film as an etching stopper film. The niobium (Nb) film was first formed by sputtering with a power of 750 W applied to a niobium (Nb) target while adding argon (Ar) gas at 12 SCCM, and then the niobium (Nb) oxide film was heat-treated at 150°C for 10 minutes in air to form a niobium (NbO) film.

[0116] Next, a chromium nitride (CrN) film (Cr:N=4:1 (atomic ratio)) with a thickness of 45 nm is formed on the etching stopper film as an absorption film. The chromium nitride (CrN) film is formed by applying a power of 1000 W to the chromium (Cr) target while adding argon (Ar) gas at 20 SCCM and nitrogen (N2) gas at 10 SCCM.

[0117] Furthermore, on the other main surface of the substrate, a tantalum nitride (TaN) film was formed as a conductive film with a thickness of 70 nm by sputtering, thereby obtaining a reflective mask blank.

[0118] A reflective mask was manufactured from the obtained reflective mask blank. First, a resist film was formed on the absorption film by coating an electron beam (EB) resist, and a resist pattern having a line-space (L / S) pattern with a line width of 200 nm was formed by drawing a pattern using an electron (EB) beam and developing.

[0119] Next, the resist pattern is used as an etching mask, and the absorption film is patterned to form a pattern of the absorption film using dry etching of a gas containing chlorine (Cl2) gas and oxygen (O2) gas. Dry etching is performed by an inductively coupled plasma (ICP) method under the following conditions: Cl2 flow rate: 185SCCM, O2 flow rate: 55SCCM, He flow rate: 9.25SCCM, pressure: 6mTorr (0.8Pa), ICP power: 400W, RIE voltage: 700V, and overetching: 227 seconds (in Example 1) and 454 seconds (in Example 2). At this stage, a cross section of the etched portion of the absorption film is observed by a transmission electron microscope (TEM). As a result, each of the etching stop films maintains a thickness of 2nm without loss.

[0120] Next, while removing the resist pattern with a sulfuric acid-hydrogen peroxide mixture (SPM), the etching stopper film at the portion of the etching stopper film exposed by removing the absorption film was removed to obtain a reflective mask. The cross section of the etched portion of the absorption film was observed by a transmission electron microscope (TEM). As a result, each of the absorption films maintained a thickness of 3 nm without damage. In addition, a good pattern of the absorption film was obtained.

[0121] Comparative Example 1

[0122] A reflective mask blank was obtained in the same manner as in Example 1 except that the etching stopper film was not formed. Next, a resist pattern was formed in the same manner as in Example 1. Next, in the same manner as in Example 1, the resist pattern was used as an etching mask, and dry etching using a gas containing chlorine (Cl2) gas and oxygen (O2) gas was used to pattern the absorption film to form a pattern of the absorption film. The cross section of the etched portion of the absorption film was observed by a transmission electron microscope (TEM). As a result, the protective film disappeared.

[0123] Comparative Example 2

[0124] A reflective mask blank was obtained in the same manner as in Example 1, except that the etching stop film was not formed. Next, a resist pattern was formed in the same manner as in Example 1. Next, the resist pattern was used as an etching mask, and the absorption film was patterned to form a pattern of the absorption film using dry etching with a gas containing chlorine (Cl2) gas and oxygen (O2) gas in the same manner as in Example 1, except that the overetching was 0 seconds. The cross-section of the etched portion of the absorption film was observed by a transmission electron microscope (TEM). As a result, it was confirmed that the absorption film remained on the protective film and the portion of the absorption film that should be removed was confirmed. In addition, a good pattern of the absorption film was not obtained because the line width dimension was not controlled by overetching.

Claims

1. A reflective mask blank, which is a reflective mask material used in EUV lithography using EUV light as exposure light, comprising: substrate; a multilayer reflective film formed on one main surface of the substrate and reflecting exposure light; a protective film formed on the multilayer reflective film for protecting the multilayer reflective film; and An absorption film formed on the protective film to absorb exposure light, Wherein, the protective film contains ruthenium (Ru), and The reflective mask blank further includes an etch stopper film containing niobium (Nb) and not containing ruthenium (Ru) between the protective film and the absorption film.

2. The reflective mask blank according to claim 1, wherein the etch stop film is composed of niobium (Nb) alone or a niobium (Nb) compound containing niobium (Nb) and oxygen (O).

3. The reflective mask blank according to claim 1, wherein the protective film is composed of ruthenium (Ru). The reflective mask blank of claim 1 , wherein the absorption film comprises chromium (Cr). 5 . The reflective mask blank according to claim 1 , wherein the absorption film contains tantalum (Ta), and the reflective mask blank further comprises an etching mask film containing chromium (Cr) on the absorption film.

6. A method for manufacturing a reflective mask, comprising the following steps: The absorption film of the reflective mask blank of claim 4 is patterned by dry etching using a gas containing chlorine (Cl) and oxygen (O).

7. A method for manufacturing a reflective mask, comprising the following steps: After the absorption film of the reflective mask blank of claim 5 is patterned, the etching mask film is removed by dry etching using a gas containing chlorine (Cl) and oxygen (O).

8. A method for preparing a reflective mask from a reflective mask blank according to any one of claims 1 to 5, comprising the steps of: After the absorption film is patterned, the etching stopper film is removed from the portion exposed by removing the absorption film.

9. The manufacturing method according to claim 8, wherein the etching stopper film at the portion exposed by removing the absorption film is removed using a sulfuric acid-hydrogen peroxide mixture (SPM).

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