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

Abstract

According to the present invention, a fine and good pattern of an absorbing film can be formed from a reflective mask blank from an absorbing film which can be patterned by dry etching using a gas containing oxygen (O). The reflective mask blank includes a substrate, a multilayer reflective film formed on one main surface of the substrate to reflect exposure light, an absorption film formed on the multilayer reflective film to absorb the exposure light, and an etching mask film containing niobium (Nb) on the absorption film.

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] 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 by reducing the shadowing effect in exposure using a reflective mask, that is, to reduce the thickness of the absorber film, thereby improving the accuracy of pattern transfer to the wafer. Therefore, attention is paid to chromium (Cr) absorber films that can be made thinner than tantalum (Ta) absorber films.

[0011] It is possible to etch an absorption film such as a chromium (Cr) film by dry etching using a gas containing chlorine (Cl) and oxygen (O). However, when etching the absorption film by forming a resist film, forming a resist pattern from the resist film, and dry etching using the resist pattern as an etching mask, it is necessary to form a thicker resist pattern (resist film) because the resist pattern is also etched in the dry etching using a gas containing oxygen (O). On the other hand, when trying to form a fine resist pattern from a thick resist film, the resist pattern collapses due to its high aspect ratio. Therefore, a fine resist pattern cannot be formed, and a fine pattern of the absorption film cannot be formed.

[0012] 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, which includes an absorption film that can be patterned by dry etching using a gas containing oxygen (O), and is suitable for forming a fine pattern of the absorption film, and to provide a method for manufacturing a reflective mask using the reflective mask blank.

[0013] The inventors have conducted intensive research to solve the above-mentioned problem. As a result, the inventors have found that the problem can be solved by providing an etching mask film containing niobium (Nb) on an absorption film composed of a material that can be dry-etched with a gas containing oxygen (O), particularly a gas containing chlorine (Cl) and oxygen (O).

[0014] 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; and an absorption film formed on the multilayer reflective film to absorb the exposure light, wherein the absorption film is composed of a material that can be dry-etched with a gas containing oxygen (O), and the reflective mask blank includes an etching mask film containing niobium (Nb) on the absorption film.

[0015] Preferably, the etching mask film containing niobium (Nb) is composed of niobium (Nb) alone, or a niobium (Nb) compound containing niobium (Nb) and oxygen (O).

[0016] Preferably, the absorption film contains chromium (Cr) or ruthenium (Ru).

[0017] In another aspect, the present invention provides a method for manufacturing a reflective mask, comprising the step of patterning the absorption film of the reflective mask blank according to any one of claims 1 to 4 by dry etching using a gas containing oxygen (O).

[0018] Preferably, the method includes the steps of: patterning the etching mask film using the resist pattern as an etching mask to form a pattern of the etching mask film; and patterning the absorption film by dry etching using a gas containing oxygen (O) using the pattern of the etching mask film as an etching mask.

[0019] Preferably, the method includes the step of removing the pattern of the etching mask film using a sulfuric acid-hydrogen peroxide mixture (SPM) after forming the pattern of the absorption film.

[0020] Advantageous Effects of the Invention

[0021] According to the present invention, a fine and good absorption film pattern can be formed from the absorption film that can be patterned by dry etching using a gas containing oxygen (O). BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1 is a cross-sectional view showing an example of the reflective mask blank of the present invention.

[0024] Figure 2 It is a cross-sectional view showing an example of the reflective mask of the present invention. DETAILED DESCRIPTION

[0025] 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, and an absorption film formed on the multilayer reflective film to absorb exposure light. In addition, the reflective mask blank of the present invention comprises an etching mask film on the absorption film.

[0026] 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.

[0027] Figure 1 The sectional view of an example of a reflective mask blank of the present invention is shown. 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, an absorption film 3 formed in contact with the multilayer reflective film 2, and an etching mask film 4 formed in contact with the absorption film 3.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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 a period. A period 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, a period may include at least two high refractive index layers (such as 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 (such as different composition ratios, or different compositions with or without added elements) that are different from each other. In this case, a period includes at least three layers and may include four, five or more layers, but is preferably no more than eight layers. The number of periods of the periodic stacked structure is preferably no less than 30 periods, and is preferably no more than 50 periods, more preferably no more than 40 periods. In the case where the low refractive index layer includes a material containing ruthenium (Ru), the layer (uppermost layer) farthest from the substrate in the periodic stacked structure is preferably a high refractive index layer. In addition, when the absorption film is in contact with a multilayer reflective film and the absorption film is an absorption film containing chromium (Cr) as described later, it is preferred that the layer farthest from the substrate (the top layer) in the periodic stacked structure is a silicon (Si) layer because the etching selectivity is high in the dry etching of the absorption film.

[0033] The thickness of the multilayer reflective film having a periodic stacking structure is adjusted according to the exposure wavelength 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.

[0034] 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 on 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 that utilizes the sputtering phenomenon of gas ions generated by applying a voltage to a target and introducing 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.

[0035] 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.

[0036] 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.

[0037] 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).

[0038] The reflective mask blank of the present invention may include a protective film for protecting the multilayer reflective film between the multilayer reflective film and the absorbent film. The protective film is also called a capping film. The protective film is a film for protecting the multilayer reflective film. The protective film is usually formed in contact with the multilayer reflective film. In addition, the protective film may be formed in contact with the absorbent film, or in contact with another film (such as an etching stopper film described later) in contact with the absorbent film.

[0039] The protective film contains a ruthenium (Ru)-containing material. Examples of ruthenium (Ru)-containing materials include a simple substance of ruthenium (Ru), and an alloy containing ruthenium (Ru) and another metal or metalloid 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. Among the ruthenium (Ru)-containing materials, a simple substance of ruthenium (Ru) or an alloy containing ruthenium (Ru) and niobium (Nb) is particularly preferred. In addition, in the case of contacting with the protective film to form an absorption film composed of a chromium (Cr)-containing material described later, it is preferred that the protective film is a film containing ruthenium (Ru) and niobium (Nb) because the etching selectivity is high in the dry etching of the absorption film. 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 % on an average basis of the entire film. The lower limit of the content of other metals or metalloids other than ruthenium (Ru) in the protective film is preferably not less than 5 atomic %, more preferably not less than 10 atomic % on an average basis over the entire film, but is not particularly limited thereto.

[0040] 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).

[0041] 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.

[0042] 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.

[0043] 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.

[0044] The protective film can be formed by using a target appropriately selected from the following targets as a target: 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 two or more mixed targets of niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr) and silicon (Si), and a target of ruthenium (Ru) and at least one other metal or metalloid other than ruthenium (Ru) selected from niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr) and silicon (Si), 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.

[0045] 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.

[0046] The absorption film is composed of a material that can be dry-etched by a gas containing oxygen (O). 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 chromium (Cr) or ruthenium (Ru).

[0047] As dry etching using a gas containing oxygen (O), the present invention exemplifies dry etching using a gas containing oxygen (O2) gas. In particular, dry etching using a gas containing oxygen (O) and not containing other gases except rare gases, or dry etching using a gas containing halogen and a gas containing oxygen (O) (specifically, oxygen (O2) gas) is preferred. Examples of halogens include chlorine (Cl) and fluorine (F). Examples of gases containing chlorine (Cl) include chlorine (Cl2) gas and hydrogen chloride (HCl) gas, and examples of gases containing fluorine (F) include carbon tetrafluoride (CF4) gas or sulfur hexafluoride (SF6) gas. The gas containing oxygen (O) may contain rare gases such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas and xenon (Xe) gas.

[0048] The chromium (Cr)-containing material may contain oxygen (O), nitrogen (N), carbon (C) or other elements. Examples of chromium (Cr)-containing materials include simple substances of Cr, and chromium (Cr) compounds such as CrO, CrN, CrON, CrC, CrCO, CrCN and CrCON. In addition, the chromium (Cr)-containing material may contain another element as long as the material can be dry-etched by an oxygen (O)-containing gas. In addition, the description of the chemical formula of the metal or metalloid compound indicates the constituent elements of the compound and does not mean their composition ratio (the same applies below).

[0049] The ruthenium (Ru)-containing material may contain oxygen (O), nitrogen (N), carbon (C), boron (B) or other elements. Examples of the ruthenium (Ru)-containing material include simple substance of Ru, and ruthenium (Ru) compounds such as RuO, RuN, RuON, RuC, RuCO, RuCN, RuCON, RuB, RuOB, RuNB, RuONB, RuCB, RuCOB, RuCNB and RuCONB. In addition, the ruthenium (Ru)-containing material may contain another element as long as the material can be dry-etched by oxygen (O) gas.

[0050] The etching selectivity of the absorption film relative to the protective film is preferably not less than 3, more preferably not less than 5. The sheet resistance of the absorption film is preferably not more 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.

[0051] 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 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 ruthenium (Ru)-containing material, a ruthenium (Ru) target, and a ruthenium (Ru) compound target (a target containing ruthenium (Ru) and oxygen (O), nitrogen (N), carbon (C), boron (B) or other elements) The target is an element) and can be formed by 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 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.

[0052] An etching mask film having different etching characteristics from the absorption film can be provided on the absorption film on the side away from the substrate as a hard mask for the absorption film. The etching mask film of the present invention contains niobium (Nb). Niobium oxide (NbO) is formed from niobium (Nb) in dry etching using oxygen (O)-containing gas. Niobium oxide (NbO) is resistant to dry etching using oxygen (O)-containing gas.

[0053] The etching mask film acts as a hard mask in the dry etching of the absorption film using an oxygen (O)-containing gas. Therefore, the etching mask film preferably does not contain the metal or metalloid elements contained in the absorption film, particularly chromium (Cr) and ruthenium (Ru). The etching mask film is preferably formed in contact with the absorption film. The etching mask film can be composed of a single layer or a multilayer.

[0054] The etching mask 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, in the niobium (Nb) compound containing niobium (Nb) and oxygen (O), the content of niobium (Nb) 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.

[0055] 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.

[0056] The etching mask film containing niobium (Nb) 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 mask 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 a niobium (Nb) compound 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).

[0057] 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. As dry etching using a gas containing fluorine (F), specifically, the present invention exemplifies dry etching using a gas containing carbon tetrafluoride (CF4) gas or sulfur hexafluoride (SF6) gas. The gas containing chlorine (Cl) preferably does not contain a gas containing (O). The gas containing chlorine (Cl) and the gas containing fluorine (F) may contain rare gases such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas.

[0058] 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.

[0059] 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, and preferably not more than 20 nm, more preferably not more than 10 nm, but is not particularly limited thereto.

[0060] The etching mask film can be formed by sputtering. The etching mask film can be formed by sputtering using a niobium (Nb) target and an optional niobium (Nb) compound target (a target containing niobium (Nb) and oxygen (O), nitrogen (N), carbon (C), boron (B) or other elements) as a sputtering 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 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 and rare gas as sputtering gas. Sputtering is preferably performed by a magnetron sputtering method.

[0061] In the case where the etching mask film contains oxygen (O), niobium (Nb) is easily naturally oxidized, and therefore, an etching mask 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 the separate niobium (Nb), the film may be heat-treated.

[0062] In addition, another etching mask film (second etching mask film) that serves as a hard mask in etching the etching mask film (first etching mask film) containing niobium (Nb) may be formed on the etching mask film containing niobium (Nb), preferably in contact with the etching mask film containing niobium (Nb). As the second etching mask film, an etching mask film containing chromium (Cr) is exemplified.

[0063] The reflective mask blank of the present invention may include an etching stopper film between the protective film and the absorption film. The etching stopper film is a film for protecting the protective film and preventing the etching of the protective film in dry etching using a gas containing oxygen (O), particularly a gas containing chlorine (Cl) and oxygen (O). Therefore, the etching stopper film acts as an etching stopper layer for dry etching using a gas containing oxygen (O), particularly a gas containing chlorine (Cl) and oxygen (O). The etching stopper film preferably contains niobium (Nb) or tantalum (Ta). The etching stopper film containing niobium (Nb) or tantalum (Ta) is not etched by etching using a gas containing oxygen (O), particularly a gas containing chlorine (Cl) and oxygen (O). Therefore, damage to the protective film can be prevented.

[0064] 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.

[0065] 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.

[0066] 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 have 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.

[0067] 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.

[0068] 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, and a pattern of an absorbent film (absorbent film pattern) formed in contact with the multilayer reflective film. In the reflective mask, a transfer pattern is formed by a reflectivity difference between a portion where the absorbent film is formed and a portion where the absorbent film is not formed.

[0069] Figure 2 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 a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1 and a pattern 31 of an absorption film formed in contact with the reflective film 2.

[0070] The reflective mask of the present invention can be manufactured by a method comprising the following steps:

[0071] preparing a reflective mask blank,

[0072] optionally forming a resist film on the etching mask film,

[0073] forming a resist pattern from the resist film on the etching mask film,

[0074] forming a pattern of the etching mask film by etching the etching mask film using the resist pattern as an etching mask,

[0075] The absorption film is etched by using the pattern of the etching mask film as an etching mask to form a pattern of the absorption film,

[0076] removing the resist pattern, and

[0077] The pattern of the etching mask film is removed.

[0078] The etching mask film containing niobium (Nb) can be etched by dry etching using a gas containing chlorine (Cl) or a gas containing fluorine (F).

[0079] The absorption film is patterned by dry etching using a gas containing oxygen (O), and since the etching mask film containing niobium (Nb) is not etched by the dry etching using a gas containing oxygen (O), in the dry etching of the absorption film using the gas containing oxygen (O), the pattern of the etching mask film serves as an etching mask in the dry etching using the gas containing oxygen (O).

[0080] In the case of forming another etching mask film (second etching mask film) that acts as a hard mask in the etching of an etching mask film (first etching mask film) containing niobium (Nb), the pattern of the second etching mask film can be formed by etching the second etching mask film using the resist pattern as an etching mask, and the pattern of the first etching mask film can be formed by etching the first etching mask film using the pattern of the second etching mask film as an etching mask.

[0081] In the case where the second etching mask film is an etching mask film containing chromium (Cr), the pattern of the second etching mask film can be formed by dry etching using a gas containing chlorine (Cl) and oxygen (O). In this case, when the absorption film contains a chromium (Cr)-containing material, while the absorption film is patterned by dry etching using a gas containing chlorine (Cl) and oxygen (O), the pattern of the second etching mask film can be removed by dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0082] An absorption film containing a chromium (Cr) material can be etched by dry etching using a gas containing chlorine (Cl) and oxygen (O). An absorption film containing a ruthenium (Ru) material can be etched by dry etching using a gas containing oxygen (O), specifically dry etching using a gas containing oxygen (O) and not containing any gas other than a rare gas, or by dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0083] The etching mask film is etched using the resist pattern as an etching mask to form a pattern of the etching mask film, and the absorption film is patterned by dry etching using a gas containing oxygen (O) using the pattern of the etching mask film as an etching mask to form a pattern of the absorption film. Compared with the case where the resist pattern is directly formed on the absorption film and then the absorption film is patterned by dry etching using a gas containing oxygen (O) using the resist pattern as an etching mask to form a pattern of the absorption film, the resist pattern (resist film) can be thinned and a fine and good pattern can be formed.

[0084] The resist pattern and the pattern of the etching mask film containing niobium (Nb) can be removed using a sulfuric acid-hydrogen peroxide mixture (SPM).

[0085] In addition, the pattern of the etching mask film containing niobium (Nb) 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), and therefore, the pattern of the etching mask film containing niobium (Nb) is preferably removed with a sulfuric acid-hydrogen peroxide mixture (SPM). In this case, the pattern of the etching mask film containing niobium (Nb) can be removed continuously with the removal of the resist pattern.

[0086] 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).

[0087] Example

[0088] In the following, examples of the invention are given by way of illustration and not by way of limitation.

[0089] Example 1

[0090] 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 (cycles) 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), and the silicon (Si) layer is the uppermost layer. 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.

[0091] Next, a 45 nm thick chromium nitride (CrN) film (Cr:N=4:1 (atomic ratio)) was formed on the protective film as an absorption film. The chromium nitride (CrN) film was 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.

[0092] Next, a niobium (NbO) oxide film (Nb:O=2:5 (atomic ratio)) with a thickness of 2 nm was formed on the absorption film as an etching mask film. The niobium (Nb) film was first formed by sputtering a niobium (Nb) target while adding argon (Ar) gas at 12 SCCM at a power of 750 W, and then the niobium (Nb) oxide film was heat-treated at 150°C for 10 minutes in air to form a niobium (NbO) film.

[0093] 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.

[0094] A reflective mask was manufactured from the obtained reflective mask blank. First, a resist film having a thickness of 90 nm was formed on the etching mask film by coating an electron beam (EB) resist, and a resist pattern having a line-space (L / S) pattern having a line width of 50 nm was formed by drawing a pattern using an electron (EB) beam and developing.

[0095] Next, the resist pattern is used as an etching mask, and the etching mask film is patterned to form a pattern of the etching mask film using dry etching of a gas containing sulfur hexafluoride (SF6) gas. Dry etching is performed by an inductively coupled plasma (ICP) method under the following conditions: SF6 flow rate: 18 SCCM, He flow rate: 130 SCCM, pressure: 5 mTorr (0.67 Pa), ICP power: 325 W, and RIE voltage: 190 V.

[0096] Next, 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, using the pattern of the etching mask film as an etching mask. The dry etching is performed by an inductively coupled plasma (ICP) method under the following conditions: Cl2 flow rate: 185 SCCM, O2 flow rate: 55 SCCM, He flow rate: 9.25 SCCM, pressure: 6 mTorr (0.8 Pa), ICP power: 400 W, and RIE voltage: 700 V.

[0097] Next, the remaining resist pattern and the pattern of the etching mask film were removed by using a sulfuric acid-hydrogen peroxide mixture (SPM) to obtain a reflective mask. A fine and good absorption film pattern with a line width of 50 nm was formed in the obtained reflective mask.

[0098] Comparative Example 1

[0099] A reflective mask blank was obtained in the same manner as in Example 1, except that an etching mask film was not formed. Next, a resist pattern was formed directly on the absorption film in the same manner as in Example 1. Next, the absorption film was patterned by dry etching using a gas containing chlorine (Cl2) gas and oxygen (O2) gas in the same manner as in Example 1, except that the resist pattern was used as an etching mask, thereby attempting to form a pattern of the absorption film. However, the resist pattern disappeared before the pattern of the absorption film was formed, and thus the pattern of the absorption film could not be formed.

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; and An absorption film formed on the multilayer reflective film to absorb exposure light, wherein the absorption film is composed of a material capable of being dry-etched with a gas containing oxygen (O), and The reflective mask blank includes an etching mask film including niobium (Nb) on an absorption film. 2 . The reflective mask blank according to claim 1 , wherein the etching mask film containing niobium (Nb) is composed of niobium (Nb) alone or a niobium (Nb) compound containing niobium (Nb) and oxygen (O). 3 . The reflective mask blank of claim 1 , wherein the absorption film comprises chromium (Cr). The reflective mask blank of claim 1 , wherein the absorption film comprises ruthenium (Ru).

5. A method for manufacturing a reflective mask, comprising the following steps: The absorption film of the reflective mask blank according to any one of claims 1 to 4 is patterned by dry etching using a gas containing oxygen (O).

6. The manufacturing method according to claim 5, comprising the following steps: patterning the etching mask film using the resist pattern as an etching mask to form a pattern of the etching mask film; as well as Using the pattern of the etching mask film as an etching mask, the absorption film is patterned by dry etching using a gas containing oxygen (O).

7. The manufacturing method according to claim 6, comprising the following steps: After the pattern of the absorption film is formed, the pattern of the etching mask film is removed using a sulfuric acid-hydrogen peroxide mixture (SPM).

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