Reflective mask blank and manufacturing method thereof

Abstract

The present invention provides a multilayer reflective film including a substrate, which is formed on one main surface of the substrate and reflects exposure light. The multilayer reflective film has a periodic stacked structure in which repeating units are stacked a plurality of times, each repeating unit including one of a high refractive index layer, a low refractive index layer, and a medium refractive index layer having a refractive index lower than a refractive index of the high refractive index layer and higher than a refractive index of the low refractive index layer, and in the repeating unit, the high refractive index layer and the medium refractive index layer are disposed on the substrate side and the side away from the substrate, respectively, with respect to the low refractive index layer.

Description

Technical Field

[0001] The present invention relates to a reflective mask blank as a material for a reflective mask used in manufacturing semiconductor devices such as LSIs, and a method for manufacturing the same. Background Art

[0002] In the manufacturing process of semiconductor devices, lithography technology is repeatedly used, in which exposure light is irradiated onto a transfer mask through a reduction projection optical system, and the circuit pattern formed on the transfer mask is transferred onto a semiconductor substrate (semiconductor wafer). Conventionally, the mainstream wavelength of the exposure light has been 193 nm by an argon fluoride (ArF) excimer laser. By adopting a process called multi-patterning in which the exposure process and the processing process are combined multiple times, a pattern having a size smaller than the exposure wavelength is finally formed.

[0003] However, because it is necessary to form a finer pattern under continuous miniaturization of device patterns, extreme ultraviolet lithography technology is used, which uses extreme ultraviolet (hereinafter referred to as "EUV") light having a wavelength shorter than that of the ArF excimer laser as the exposure light. EUV light is light having a wavelength of about 0.2 to 100 nm, particularly light having a wavelength of about 13.5 nm. EUV light has very low permeability to substances and cannot be used in a conventional transmission projection optical system or mask. Therefore, a reflective optical element device is applied. Accordingly, a reflective mask has also been proposed as a mask for pattern transfer.

[0004] In a normal reflective mask, a multilayer reflective film that reflects EUV light is formed on a substrate, and a patterned absorber film that absorbs EUV light is formed on the multilayer reflective film. On the other hand, generally, the material before patterning the absorber film (including the material for forming a resist film) is called a reflective mask blank and is used as the material for a reflective mask. The reflective mask blank has a basic structure including a substrate and a multilayer reflective film formed on the substrate and reflecting EUV light, and in many cases, also includes an absorber film formed on the multilayer reflective film and absorbing EUV light.

[0005] Citation List

[0006] Patent Document 1: JP-A 2007-109971 Summary of the Invention

[0007] In EUV lithography, EUV light as exposure light is incident on a reflective mask at a certain angle, and is mainly incident at an angle of 6 degrees with respect to the normal of the main surface of the reflective mask. A part of the exposure light incident at a certain angle is blocked by the sidewall of the absorber pattern, thereby generating a so-called 3D effect (three-dimensional effect or shadow effect). The 3D effect causes deviations in the position and size of the transferred pattern. Therefore, it is preferable to reduce the 3D effect to minimize the absorber pattern. The 3D effect can be reduced by a thinner absorber pattern. Therefore, it is desirable to reduce the thickness of the absorber pattern.

[0008] On the other hand, in addition to the thickness of the absorber pattern, the 3D effect also varies according to the structure of the multilayer reflective film. Reflection of EUV light as exposure light is caused by the overlap of reflections occurring at each interface of the layers inside the multilayer reflective film. However, when the reflection at a position deeper than the surface of the multilayer reflective film mainly contributes to the reflection of the exposure light by the multilayer reflective film, the 3D effect increases. Therefore, in order to reduce the 3D effect, it is advantageous for the multilayer reflective film to relatively increase the contribution to reflection at a position closer to the surface.

[0009] Generally, the multilayer reflective film has a periodic laminated structure in which a low refractive index layer and a high refractive index layer are alternately laminated. For example, a multilayer reflective film (Mo / Si multilayer reflective film) in which 40 cycles of molybdenum (Mo) layers and silicon (Si) layers are alternately laminated is known as a film that effectively reflects EUV light, and is currently used as the mainstream multilayer reflective film in EUV mask blanks.

[0010] The present invention has been completed to solve the above problems, and an object of the present invention is to provide a reflective mask blank including a multilayer reflective film having a reduced 3D effect and a high reflectivity, and a method for manufacturing the reflective mask blank.

[0011] Compared with molybdenum (Mo), ruthenium (Ru) is a material having a lower refractive index and a higher extinction coefficient with respect to EUV light having a wavelength of 13.5 nm as exposure light. Therefore, in the case of having an ideal interface (an interface without interdiffusion or roughness) with a high refractive index layer using silicon (Si) or the like, the low refractive index layer of ruthenium (Ru) has a higher reflection coefficient than the low refractive index layer of molybdenum (Mo).

[0012] Therefore, in a multi-layer reflective film having fewer layers, a multi-layer reflective film (Ru / Si multi-layer reflective film) using ruthenium (Ru) as a low refractive index layer provides a higher reflectivity compared to a Mo / Si multi-layer reflective film. Additionally, when comparing the same number of layers, the contribution to reflection at a position closer to the surface of the Ru / Si multi-layer reflective film is relatively large, and the Ru / Si multi-layer reflective film is advantageous in reducing the 3D effect. On the other hand, since ruthenium (Ru) has a relatively large extinction coefficient, when increasing the number of layers in the multi-layer reflective film, the Ru / Si multi-layer reflective film forms a lower reflectivity compared to the Mo / Si multi-layer reflective film.

[0013] The inventors conducted intensive research to solve the above problems. As a result, the inventors found a multi-layer reflective film that is a basic component in a reflective mask blank and a reflective mask. The multi-layer reflective film includes a high refractive index layer, a low refractive index layer, and a medium refractive index layer, and particularly further includes an intermediate layer together with the high refractive index layer, the low refractive index layer, and the medium refractive index layer. The inventors also found a multi-layer reflective film having a periodic stacked structure with multiple stacked repeating units in which each layer is stacked in a specific order. Additionally, the inventors found that the multi-layer reflective film has a reduced 3D effect and a high reflectivity.

[0014] In one aspect, the present invention provides a reflective mask blank including a substrate and a multi-layer reflective film formed on one main surface of the substrate and reflecting exposure light, wherein

[0015] the multi-layer reflective film has a periodic stacked structure with multiple stacked repeating units therein,

[0016] each repeating unit includes one high refractive index layer, one low refractive index layer, and one medium refractive index layer. The medium refractive index layer has a refractive index lower than that of the high refractive index layer and higher than that of the low refractive index layer, and

[0017] in the repeating unit, the high refractive index layer and the medium refractive index layer are respectively disposed on the substrate side and the side away from the substrate with respect to the low refractive index layer.

[0018] Preferably, with respect to the wavelength of the exposure light, the high refractive index layer, the low refractive index layer, and the medium refractive index layer in the repeating unit satisfy all of the following expressions (1) and (2):

[0019] k H <k L (1), and

[0020] k M <((k H -k L ) / (n H -n L ))×(n M -n L) + k L (2),

[0021] where n H , n L and n M represent the refractive indices of the high refractive index layer, the low refractive index layer, and the medium refractive index layer, respectively, and k H , k L and k M represent the extinction coefficients of the high refractive index layer, the low refractive index layer, and the medium refractive index layer, respectively.

[0022] Preferably, the high refractive index layer contains silicon (Si), the low refractive index layer contains ruthenium (Ru), and the medium refractive index layer contains at least one selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr).

[0023] Preferably, the multilayer reflective film includes an intermediate layer at one or more positions selected from the following: a position between the high refractive index layer and the low refractive index layer, a position between the low refractive index layer and the medium refractive index layer, and a position between the medium refractive index layer and the high refractive index layer.

[0024] Preferably, the multilayer reflective film includes an intermediate layer between the high refractive index layer and the low refractive index layer.

[0025] Preferably, with respect to the wavelength of the exposure light, the high refractive index layer, the intermediate layer between the high refractive index layer and the low refractive index layer, the low refractive index layer, and the medium refractive index layer in the repeating unit satisfy all of the following expressions (1), (2), and (3):

[0026] k H < k L (1),

[0027] k M < ((k H - k L ) / (n H - n L )) × (n M - n L ) + k L (2), and

[0028] k I > ((k H - k L ) / (n H - n L )) × (n I - n L ) + k L (3),

[0029] where n H , n I , nL and n M represent the refractive indices of the high refractive index layer, the intermediate layer between the high refractive index layer and the low refractive index layer, the low refractive index layer, and the medium refractive index layer, respectively, and k H , k I , k L and k M represent the extinction coefficients of the high refractive index layer, the intermediate layer between the high refractive index layer and the low refractive index layer, the low refractive index layer, and the medium refractive index layer, respectively.

[0030] Preferably, the repeating unit is composed of one high refractive index layer, one intermediate layer, one low refractive index layer, and one medium refractive index layer each, and in the repeating unit, the high refractive index layer, the intermediate layer, the low refractive index layer, and the medium refractive index layer are arranged in sequence from the substrate side.

[0031] Preferably, the multilayer reflective film is composed of a periodic stacked structure and an additional high refractive index layer provided on the side farthest from the substrate.

[0032] Preferably, the high refractive index layer contains silicon (Si), the intermediate layer contains any one or both of silicon nitride (SiN) and tantalum nitride (TaN), the low refractive index layer contains ruthenium (Ru), and the medium refractive index layer contains at least one selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr).

[0033] Preferably, the high refractive index layer is composed of silicon (Si), the intermediate layer is composed of any one or both of silicon nitride (SiN) and tantalum nitride (TaN), the low refractive index layer is composed of ruthenium (Ru), and the medium refractive index layer is composed of at least one selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr).

[0034] Preferably, the high refractive index layer has a thickness of not less than 2.5 nm and not more than 5.5 nm, the intermediate layer has a thickness of not less than 0.2 nm and not more than 1 nm, the low refractive index layer has a thickness of not less than 0.5 nm and not more than 4 nm, and the medium refractive index layer has a thickness of not less than 0.5 nm and not more than 4 nm.

[0035] In another aspect, the present invention provides a method for manufacturing a reflective mask blank, the method including the step of forming a multilayer reflective film by using a sputtering device capable of simultaneously installing three or more types of targets in its chamber and sequentially discharging three or more types of targets for sputtering.

[0036] Advantages of the Present Invention

[0037] The reflective mask blank of the present invention has a multilayer reflective film, which has a reduced 3D effect compared with a conventional multilayer reflective film. Starting from the reflective mask blank of the present invention, a reflective mask with a high reflectivity can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a cross-sectional view showing an example of a reflective mask blank of the present invention.

[0039] Figure 2 is a cross-sectional view showing an example of a multilayer reflective film of the present invention.

[0040] Figure 3 is a cross-sectional view showing another example of a multilayer reflective film of the present invention.

[0041] Figure 4 is a cross-sectional view showing another example of a reflective mask blank of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0042] The reflective mask blank of the present invention includes a substrate and a multilayer reflective film formed on one main surface (front surface) of the substrate and reflecting exposure light.

[0043] The reflective mask blank of the present invention is suitable as a material (EUV mask blank) for a reflective mask (EUV mask) used in EUV lithography using EUV light as exposure light. The EUV light used as exposure light in EUV lithography has a wavelength of 13 to 14 nm, typically about 13.5 nm.

[0044] For exposure using EUV light, the substrate preferably has low thermal expansion properties. For example, the substrate is preferably made of a material having a thermal expansion coefficient of within ±2×10 -8 / °C, preferably within ±5×10 -9 / °C. As the material, for example, titanium dioxide-doped quartz glass (SiO 2 -TiO 2 -based glass) is exemplified. In addition, a substrate having a sufficiently flat surface is preferably used. The main surface of the substrate has a surface roughness preferably not greater than 0.5 nm, more preferably not greater than 0.2 nm, expressed in terms of RMS value. Such a surface roughness can be obtained by polishing the substrate or the like. The substrate preferably has a main surface with a size of 152 mm square and a thickness of 6.35 mm. A substrate having this size is a so-called 6025 substrate, whose main surface has a size of 6 inches square and a thickness of 0.25 inches.

[0045] The multilayer reflective film is a film that reflects EUV light as exposure light in a reflective mask. The multilayer reflective film can be formed in contact with one main surface of the substrate, and an underlayer film can be formed between the substrate and the multilayer reflective film. The multilayer reflective film has a reflectivity of preferably not less than 60%, more preferably not less than 62%, and even more preferably not less than 65% for EUV light (wavelength: 13.5 nm) as exposure light with an incident angle of 6 degrees with respect to the normal of the main surface of the multilayer reflective film.

[0046] Figure 1 It is a cross-sectional view showing an example of a reflective mask blank of the present invention. The reflective mask blank 10 includes a substrate 1, and a multilayer reflective film 2 formed in contact with the substrate 1 on the substrate 1.

[0047] The multilayer reflective film of the present invention has a periodic stacked structure in which repeating units are stacked multiple times. The repeating unit includes one high refractive index layer, one low refractive index layer, and one medium refractive index layer each. The periodic stacked structure preferably has a number of cycles (number of repeating units) of not less than 10 cycles, more preferably not less than 20 cycles, and not more than 50 cycles, more preferably not more than 40 cycles, and even more preferably not more than 30 cycles.

[0048] The high refractive index layer is a layer made of a material having a relatively high refractive index with respect to EUV light as the exposure light, and the low refractive index layer is a layer made of a material having a relatively low refractive index with respect to EUV light as the exposure light. On the other hand, the medium refractive index layer is a layer made of a material having a refractive index lower than that of the high refractive index layer and higher than that of the low refractive index layer. Therefore, when the refractive indices of the high refractive index layer, the low refractive index layer, and the medium refractive index layer (the refractive index of the material constituting the high refractive index layer, the refractive index of the material constituting the low refractive index layer, and the refractive index of the material constituting the medium refractive index layer) are n H 、n L and n M respectively, the refractive indices in the repeating unit satisfy the expression: n H >n M >n L .

[0049] In addition, from the viewpoint of obtaining a high reflectance, the high refractive index layer, the low refractive index layer, and the medium refractive index layer in the repeating unit preferably satisfy all of the following expressions (1) and (2) with respect to the wavelength of the exposure light:

[0050] k H <k L (1), and

[0051] k M <((k H -k L ) / (n H -n L ))×(n M -n L )+k L (2),

[0052] where, n H 、n L and n Mrepresent the refractive indices of the high refractive index layer, the low refractive index layer, and the medium refractive index layer, respectively, and k H , k L , and k M represent the extinction coefficients of the high refractive index layer, the low refractive index layer, and the medium refractive index layer, respectively.

[0053] Regarding the arrangement of the high refractive index layer, the low refractive index layer, and the medium refractive index layer in the repeating unit, preferably, the high refractive index layer is disposed on the substrate side with respect to the low refractive index layer, and preferably, the medium refractive index layer is disposed on the side away from the substrate with respect to the low refractive index layer. In particular, a high reflectance can be obtained by the arrangement of disposing the medium refractive index layer on the side away from the substrate with respect to the low refractive index layer, and furthermore, a higher reflectance can be obtained by the arrangement of disposing the high refractive index layer on the substrate side with respect to the low refractive index layer. Therefore, it is preferred to arrange the high refractive index layer, the low refractive index layer, and the medium refractive index layer in this way.

[0054] The multilayer reflective film of the present invention may be composed of a periodic laminated structure in which the repeating unit is stacked multiple times, and preferably, a high refractive index layer is formed in the multilayer reflective film as another layer disposed on the side farthest from the substrate. Additionally, a layer (protective layer) for protecting the periodic laminated structure may be formed in the multilayer reflective film as another layer disposed on the side farthest from the substrate. In the case of forming the other layer, the multilayer reflective film may be composed of a periodic laminated structure in which the repeating unit is stacked multiple times and other layers (high refractive index layer, protective layer, etc.) formed on the side farthest from the substrate. In the multilayer reflective film, in the case where no other layer is formed, a protective film or an absorber layer described below is formed on the repeating unit on the side farthest from the substrate, or in the case where other layers are formed on the side farthest from the substrate in the multilayer reflective film, a protective film or an absorber layer described below is formed on the other layer.

[0055] In the multilayer reflective film, an intermediate layer may be formed at a position between the layers of the high refractive index layer, the low refractive index layer, and the medium refractive index layer to prevent the formation of layers (reaction layer, interdiffusion layer) that may be formed at the interface portion of the layers during the formation of the multilayer reflective film or due to heat treatment after the formation of the multilayer reflective film. The multilayer reflective film of the present invention preferably includes an intermediate layer at one or more positions between the high refractive index layer and the low refractive index layer, at one or more positions between the low refractive index layer and the medium refractive index layer, or at one or more positions between the medium refractive index layer and the high refractive index layer.

[0056] Preferably, an intermediate layer is included at any one or two or more positions selected from all positions between the high refractive index layer and the low refractive index layer, all positions between the low refractive index layer and the middle refractive index layer, and all positions between the middle refractive index layer and the high refractive index layer. In particular, preferably, an intermediate layer is included at the position between the high refractive index layer and the low refractive index layer. In this case, the position between the high refractive index layer and the low refractive index layer and the position between the low refractive index layer and the middle refractive index layer are located in the same repeating unit, and the position between the middle refractive index layer and the high refractive index layer is located between adjacent repeating units.

[0057] In the case where the low refractive index layer, particularly a ruthenium (Ru)-containing low refractive index layer, is formed in contact with the high refractive index layer, particularly a silicon (Si)-containing high refractive index layer, by sputtering, at the interface portion between the silicon (Si)-containing high refractive index layer and the ruthenium (Ru)-containing low refractive index layer, a reaction layer containing silicon (Si) and ruthenium (Ru) tends to be formed by utilizing the energy of sputtered particles such as ruthenium (Ru) atoms and clusters from the target. The formation of the reaction layer causes a reduction in the reflectance of the multilayer reflective film. Therefore, it is more preferable that an intermediate layer is included at one or more positions, particularly all positions, between the high refractive index layer and the low refractive index layer, and the formation of the intermediate layer effectively prevents the formation of the reaction layer.

[0058] Among the positions between the high refractive index layer and the low refractive index layer, the position between the low refractive index layer and the middle refractive index layer, and the position between the middle refractive index layer and the high refractive index layer, from the viewpoint of obtaining a high reflectance, it is preferable to form an intermediate layer at the position between the high refractive index layer and the low refractive index layer.

[0059] In the case where the multilayer reflective film of the present invention includes an intermediate layer at the position between the high refractive index layer and the low refractive index layer, with respect to the wavelength of the exposure light, the high refractive index layer, the intermediate layer between the high refractive index layer and the low refractive index layer, and the low refractive index layer in the repeating unit preferably satisfy the following expression (3):

[0060] k I >((k H -k L ) / (n H -n L ))×(n I -n L )+k L (3),

[0061] wherein, n H 、n I and n L respectively represent the refractive indices of the high refractive index layer, the intermediate layer between the high refractive index layer and the low refractive index layer, and the low refractive index layer, and k H 、k I and kL respectively represent the extinction coefficients of the high refractive index layer, the intermediate layer between the high refractive index layer and the low refractive index layer, and the low refractive index layer.

[0062] In addition, when the multilayer reflective film of the present invention includes an intermediate layer, with respect to the wavelength of the exposure light, the high refractive index layer, the low refractive index layer, and the intermediate refractive index layer in the repeating unit preferably satisfy all of the above expressions (1) and (2).

[0063] Examples of the repeating unit include a repeating unit composed of three layers of one high refractive index layer, one low refractive index layer, and one intermediate refractive index layer. In this case, in the repeating unit, starting from the substrate side, the layers are arranged in the order of the high refractive index layer, the low refractive index layer, and the intermediate refractive index layer.

[0064] Figure 2 is a cross-sectional view showing an example of the multilayer reflective film of the present invention. This multilayer reflective film 2 includes a periodic stacked structure 200 in which the repeating unit 20 is composed of multiple stacks of a high refractive index layer 21, a low refractive index layer 23, and an intermediate refractive index layer 24 starting from the substrate side (the bottom side in the figure). On the side of the periodic stacked structure 200 far from the substrate (the uppermost part in the figure), the high refractive index layer 21, which is the layer of the multilayer reflective film 2 farthest from the substrate, is formed in contact with the periodic stacked structure 200.

[0065] In addition, examples of the repeating unit include a repeating unit composed of four, five, or six layers of one high refractive index layer, one low refractive index layer, one intermediate refractive index layer, and one, two, or three intermediate layers. Therefore, the repeating unit preferably consists of one high refractive index layer, one intermediate layer, one low refractive index layer, and one intermediate refractive index layer each, and in the repeating unit, the layers are preferably arranged in the order of the high refractive index layer, the intermediate layer, the low refractive index layer, and the intermediate refractive index layer starting from the substrate side.

[0066] Figure 3 is a cross-sectional view illustrating another example of the multilayer reflective film of the present invention. This multilayer reflective film 2 includes a periodic stacked structure 200 in which the repeating unit 20 is composed of multiple stacks of a high refractive index layer 21, an intermediate layer 22, a low refractive index layer 23, and an intermediate refractive index layer 24 starting from the substrate side (the bottom side in the figure). On the side of the periodic stacked structure 200 far from the substrate (the uppermost part in the figure), the high refractive index layer 21, which is the layer of the multilayer reflective film 2 farthest from the substrate, is formed in contact with the periodic stacked structure 200.

[0067] The material constituting the high refractive index layer preferably has a refractive index less than 0.98 and not greater than 1.02 for EUV light (wavelength: 13.5 nm) as the exposure light. Examples of this material include silicon (Si). The high refractive index layer preferably contains silicon (Si).

[0068] The high refractive index layer may additionally contain at least one light element selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H), provided that the high refractive index layer has a refractive index within a specified range. Further, in the case where the multilayer reflective film includes an intermediate layer, among the light elements, the high refractive index layer preferably does not contain the light elements contained in the intermediate layer. Additionally, the high refractive index layer preferably does not contain the metals and metalloids contained in the material constituting the low refractive index layer and the material constituting the medium refractive index layer. In particular, the high refractive index layer is preferably composed of silicon (Si).

[0069] The high refractive index layer has a thickness that is preferably not less than 2.5 nm, more preferably not less than 3 nm and preferably not more than 5.5 nm, more preferably not more than 5 nm.

[0070] The material constituting the low refractive index layer has a refractive index of not less than 0.87 and not more than 0.90 for EUV light (wavelength: 13.5 nm) as the exposure light. Examples of such materials include ruthenium (Ru). The low refractive index layer preferably contains ruthenium (Ru).

[0071] The low refractive index layer may additionally contain at least one additive metal selected from molybdenum (Mo) and niobium (Nb), provided that the low refractive index layer has a refractive index within a specified range. The low refractive index layer may additionally contain at least one light element selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H), provided that the low refractive index layer has a refractive index within a specified range. Additionally, the low refractive index layer preferably does not contain the metals and metalloids contained in the material constituting the high refractive index layer. On the other hand, the low refractive index layer may contain the metals or metalloids contained in the material constituting the medium refractive index layer. However, the low refractive index layer preferably does not contain the metals and metalloids contained in the material constituting the medium refractive index layer. In particular, the low refractive index layer is preferably composed of ruthenium (Ru), or preferably composed of ruthenium (Ru) and an additive metal (such as RuMo, RuNb, or RuMoNb).

[0072] From the viewpoint of obtaining a high reflectance, the low refractive index layer has a thickness that is preferably not less than 0.5 nm, more preferably not less than 1 nm and preferably not more than 4 nm, more preferably not more than 3.5 nm.

[0073] The material constituting the medium refractive index layer preferably has a refractive index greater than 0.90, particularly not less than 0.91 and less than 0.98, particularly not more than 0.97 for EUV light (wavelength: 13.5 nm) as the exposure light. Examples of such materials include molybdenum (Mo), niobium (Nb), yttrium (Y), and zirconium (Zr). The medium refractive index layer preferably contains at least one selected from molybdenum (Mo), niobium (Nb), yttrium (Y), and zirconium (Zr), more preferably at least one selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr).

[0074] The intermediate refractive index layer may additionally contain ruthenium (Ru) as an additive metal, as long as the intermediate refractive index layer has a refractive index within a specified range. The intermediate refractive index layer may additionally contain at least one light element selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H), as long as the intermediate refractive index layer has a refractive index within a specified range. Additionally, the intermediate refractive index layer preferably does not contain the metals and metalloids contained in the material constituting the high refractive index layer. On the other hand, the intermediate refractive index layer may contain the metals and metalloids contained in the material constituting the low refractive index layer. However, the intermediate refractive index layer preferably does not contain the metals and metalloids contained in the material constituting the low refractive index layer. In particular, the intermediate refractive index layer is preferably composed of at least one selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr) (Mo, Nb, Zr, MoNb, MoZr, NbZr, MoNbZr), or preferably composed of at least one selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr) and an additive metal (e.g., MoRu, NbRu, ZrRu, MoNbRu, MoZrRu, NbZrRu, MoNbZrRu).

[0075] From the viewpoint of obtaining a high reflectance, the intermediate refractive index layer has a thickness preferably not less than 0.5 nm, more preferably not less than 1 nm and preferably not more than 4 nm, more preferably not more than 3.5 nm.

[0076] The low refractive index layer and the intermediate refractive index layer have a total thickness preferably not less than 1 nm, more preferably not less than 1.5 nm and preferably not more than 4.5 nm, more preferably not more than 4 nm.

[0077] The material constituting the intermediate layer can be any material that can prevent the formation of layers (reaction layer, interdiffusion layer) that may form at the interface portions between the high refractive index layer, the low refractive index layer, and the intermediate refractive index layer of the multilayer reflective film during the formation of the multilayer reflective film or due to heat treatment after the formation of the multilayer reflective film. The material is preferably not a material that excessively reduces the reflectance of the multilayer reflective film.

[0078] The material constituting the intermediate layer is preferably carbon (C), or a material containing at least one selected from silicon (Si), molybdenum (Mo), niobium (Nb), zirconium (Zr), tantalum (Ta), tungsten (W), chromium (Cr), titanium (Ti), hafnium (Hf), aluminum (Al), and germanium (Ge). This material more preferably contains at least one light element selected from nitrogen (N), carbon (C), and boron (B), particularly either or both of nitrogen (N) and carbon (C). In particular, examples of this material include silicon carbide (SiC), silicon nitride (SiN), molybdenum carbide (MoC), molybdenum nitride (MoN), niobium carbide (NbC), niobium nitride (NbN), zirconium carbide (ZrC), zirconium nitride (ZrN), tantalum carbide (TaC), tantalum nitride (TaN), tungsten carbide (WC), tungsten nitride (WN), chromium carbide (CrC), chromium nitride (CrN), titanium carbide (TiC), titanium nitride (TiN), hafnium carbide (HfC), hafnium nitride (HfN), aluminum carbide (AlC), aluminum nitride (AlN), germanium carbide (GeC), and germanium nitride (GeN). The intermediate layer preferably contains this material, particularly either or both of silicon nitride (SiN) and tantalum nitride (TaN). The intermediate layer is more preferably composed of this material, particularly either or both of silicon nitride (SiN) and tantalum nitride (TaN).

[0079] The intermediate layer between the high refractive index layer and the low refractive index layer is preferably composed of a material that satisfies the above expression (3). In particular, the material constituting the intermediate layer between a high refractive index layer containing silicon (Si), particularly composed of silicon (Si), and a low refractive index layer containing ruthenium (Ru), particularly composed of ruthenium (Ru), is preferably a material containing at least one selected from tantalum (Ta), tungsten (W), chromium (Cr), titanium (Ti), hafnium (Hf), aluminum (Al), and germanium (Ge), more preferably a material containing at least one selected from tantalum (Ta), tungsten (W), chromium (Cr), titanium (Ti), hafnium (Hf), aluminum (Al), and germanium (Ge), and either or both of nitrogen (N) and carbon (C). In addition, a material containing silicon nitride (SiN) is also preferred.

[0080] The intermediate layer preferably has a thickness of not more than 1 nm, more preferably not more than 0.8 nm, and even more preferably not more than 0.5 nm. The intermediate layer generally has a lower limit of thickness of not less than 0.2 nm. The presence of the intermediate layer results in a reduction in the reflectivity of the multilayer reflective film. However, the presence of the intermediate layer prevents the formation of a reaction layer or an interdiffusion layer between the high refractive index layer, the low refractive index layer, and the intermediate refractive index layer of the multilayer reflective film, so a relatively high reflectivity can be obtained. Therefore, by appropriately adjusting the thickness of the intermediate layer, the position where the intermediate layer is located, and the number of intermediate layers, a high reflectivity can be obtained.

[0081] Examples of methods for forming a multilayer reflective film include a sputtering method in which power is supplied to a target for sputtering and plasma of atmospheric gas (ionizing the atmospheric gas) is formed by the supplied power, and an ion beam sputtering method in which a target is irradiated with an ion beam. Sputtering methods include a DC sputtering method in which a DC voltage is applied to the target and an RF sputtering method in which a high-frequency voltage is applied to the target. In particular, a magnetron sputtering method that efficiently performs sputtering using a magnetic field has advantages in terms of productivity. Power can be applied to the target through a DC system or an RF system. The DC system also includes pulsed sputtering, in which the negative bias voltage applied to the target is reversed in a short time to prevent target charging.

[0082] The multilayer reflective film can be formed, for example, by a sputtering method using a sputtering apparatus to which a plurality of targets, particularly three or more targets, are mounted. In particular, for the reflective mask blank of the present invention, it is preferable to form the multilayer reflective film by using a sputtering apparatus capable of simultaneously mounting three or more types of target materials in a chamber and sequentially discharging the three or more types of targets for sputtering.

[0083] In particular, targets appropriately selected from metal targets and metalloid targets for forming a high refractive index layer, an intermediate layer, a low refractive index layer, and a medium refractive index layer can be used as targets to form the multilayer reflective film, such as a silicon (Si) target for forming a silicon (Si)-containing layer, a ruthenium (Ru) target for forming a ruthenium (Ru)-containing layer, a molybdenum (Mo) target for forming a molybdenum (Mo)-containing layer, a niobium (Nb) target for forming a niobium (Nb)-containing layer, a zirconium (Zr) target for forming a zirconium (Zr)-containing layer, a tantalum (Ta) target for forming a tantalum (Ta)-containing layer, and other targets, and rare gases such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas are used as sputtering gases.

[0084] In addition, by reactive sputtering using a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas, a carbon-containing gas, a hydrogen-containing gas and a rare gas, a layer containing light elements such as oxygen (O), nitrogen (N), carbon (C), and hydrogen (H) can be formed. Examples of reactive gases include oxygen (O 2 ) gas, nitrogen (N 2 ) gas, hydrogen (H 2 ) gas, nitrogen oxide gases such as nitrous oxide (N 2 O) gas, nitric oxide (NO) gas, and nitrogen dioxide (NO 2 ) gas, carbon oxide gases such as carbon monoxide (CO) gas and carbon dioxide (CO 2 ) gas, and hydrocarbon gases such as methane (CH 4 ) gas. For example, when forming a layer containing silicon nitride (SiN), a nitrogen-containing gas such as nitrogen (N 2) and reactive sputtering with noble gases to form the layer.

[0085] In addition, when forming a layer containing boron (B), a boron carbide (B 4 C) target or a metal or metalloid target doped with boron (B) can be used. Examples of the metal or metalloid target doped with boron (B) include a silicon (Si) target doped with boron (B) (a silicon boride (SiB) target), a ruthenium (Ru) target doped with boron (B) (a ruthenium boride (RuB) target), a molybdenum (Mo) target doped with boron (B) (a molybdenum boride (MoB) target), a niobium (Nb) target doped with boron (B) (a niobium boride (NbB) target), a zirconium (Zr) target doped with boron (B) (a zirconium boride (ZrB) target), and a tantalum (Ta) target doped with boron (B) (a tantalum boride (TaB) target).

[0086] A reflective mask blank generally includes an absorber film, a substrate, and a multilayer reflective film. A protective film is usually formed between the multilayer reflective film and the absorber film. As such a reflective mask blank, a particular example of such a reflective mask blank is provided, which includes a 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, and an absorber film formed on the protective film and absorbing exposure light.

[0087] A reflective mask can be manufactured from a reflective mask blank including an absorber film by patterning the absorber film to form an absorber pattern. A reflective mask can be manufactured from a reflective mask blank including a multilayer reflective film, a protective film, and an absorber film, the reflective mask including a 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, and a pattern (absorber pattern) of an absorber film formed on the protective film and absorbing exposure light.

[0088] The reflective mask blank of the present invention may include a protective film on the multilayer reflective film. The protective film is required to have a function of protecting the multilayer reflective film from various dry etching and cleaning processes during the manufacturing process of the reflective mask, the exposure environment during the use of the reflective mask, or the cleaning process during the recycling process after use (resistance to various dry etching and cleaning processes during the manufacturing process of the reflective mask, the exposure environment during the use of the reflective mask, or the cleaning process during the recycling process after use). The protective film may be composed of multiple layers. The protective film may be formed on the multilayer reflective film with other films intervening therebetween, but is usually formed in contact with the multilayer reflective film.

[0089] Examples of the material of the protective film include materials containing ruthenium (Ru), particularly materials composed of ruthenium (Ru), materials containing ruthenium (Ru) and at least one additive metal selected from niobium (Nb), zirconium (Zr), titanium (Ti), and rhodium (Rh), particularly materials composed of ruthenium (Ru) and at least one additive metal selected from niobium (Nb), zirconium (Zr), titanium (Ti), and rhodium (Rh). The material of the protective film may additionally contain oxygen (O), nitrogen (N), carbon (C), etc. The protective film generally has a thickness of about 2 to 5 nm, although there is no particular limitation thereto.

[0090] The protective film can be formed, for example, by a sputtering method. As the target, a ruthenium (Ru) target or a ruthenium (Ru) alloy target for forming a film containing ruthenium (Ru), or a niobium (Nb) target or a niobium (Nb) alloy target for forming a film containing niobium (Nb) can be used. In particular, a target appropriately selected from a ruthenium (Ru) target, a niobium (Nb) target, an alloy target of ruthenium (Ru) and niobium (Nb), etc. can be used. The protective film can be formed by sputtering using a noble gas such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas as the sputtering gas, or by reactive sputtering using a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas, a carbon-containing gas and a noble gas.

[0091] The reflective mask blank of the present invention may include an absorber film that absorbs exposure light (reduces the reflectance) on the multilayer reflective film. The absorber film is a film that serves as a film for forming a pattern. The absorber film can be formed in contact with the multilayer reflective film, although it is preferably formed with another film therebetween, and generally a protective film is formed therebetween with the multilayer reflective film.

[0092] Figure 4 is a cross-sectional view showing another example of the reflective mask blank of the present invention. The reflective mask 10 includes a substrate 1, and a multilayer reflective film 2 formed in contact with the substrate 1 on the substrate 1, a protective film 3 formed in contact with the multilayer reflective film 2, and an absorber film 4 formed in contact with the protective film 3.

[0093] The material of the absorber film can be a material that absorbs EUV light and can be processed into a pattern. As the material of the absorber film, for example, a material containing tantalum (Ta) or chromium (Cr) is exemplified, but there is no particular limitation thereto. The material containing Ta or Cr may contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Examples of the material containing Ta include elemental Ta, tantalum compounds such as TaO, TaN, TaON, TaC, TaCO, TaCN, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCOB, TaCNB, and TaCONB. Examples of the material containing Cr include elemental Cr, and chromium compounds such as CrO, CrN, CrON, CrC, CrCO, CrCN, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCOB, CrCNB, and CrCONB. The absorber film generally has a thickness of about 40 to 80 nm, but there is no particular limitation thereto.

[0094] The absorber film can be formed by sputtering, and the sputtering is preferably magnetron sputtering. In particular, a metal target such as a chromium (Cr) target and a tantalum (Ta) target, etc., or a metal compound target such as a chromium compound target and a tantalum compound target (a target containing metals such as Cr and Ta and oxygen (O), nitrogen (N), carbon (C), and / or boron (B)), and a rare gas such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, xenon (Xe) gas is used as a sputtering gas for sputtering, or the absorber film is formed by reactive sputtering using a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas, and a carbon-containing gas in reaction with a rare gas. In addition, when forming a film containing boron (B), a chromium (Cr) target added with boron (B) (chromium boride (CrB) target) or a tantalum (Ta) target added with boron (B) (tantalum boride (TaB) target) can be used.

[0095] On the side of the absorber film away from the substrate, preferably in contact with the absorber film, a hard mask film (etch mask film for the absorber film) having etching properties different from those of the absorber film can be formed. This hard mask film is a film that serves as an etch mask during dry etching of the absorber film. After forming the absorber pattern, the hard mask film can be left, for example, as part of the absorber film to serve as a reflectivity reducing layer for reducing the reflectivity at the wavelength of light used for inspection such as pattern inspection, or the hard mask film can be removed so that it does not remain on the reflective mask. Examples of materials for the hard mask film include materials containing chromium (Cr). When the absorber film is made of a material containing Ta and not containing Cr, a hard mask film made of a material containing Cr is particularly suitable. When forming a layer (reflectivity reducing layer) mainly responsible for reducing the reflectivity at the wavelength of light used for inspection such as pattern inspection on the absorber film, the hard mask film can be formed on the reflectivity reducing layer on the absorber film. The hard mask film can be formed, for example, by a magnetron sputtering method. The hard mask film generally has a thickness of about 5 to 20 nm, although there is no particular limitation thereto.

[0096] On the other main surface (back surface), which is the surface opposite to one main surface of the substrate, of the reflective mask blank, preferably, a conductive film for electrostatically adsorbing the reflective mask to the exposure apparatus can be formed in contact with the other main surface.

[0097] The conductive film preferably has a sheet resistance of not more than 100 Ω / square. Examples of materials for the conductive film include, for example, materials containing tantalum (Ta) or chromium (Cr), although there is no particular limitation thereto. Materials containing tantalum (Ta) or chromium (Cr) can contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Examples of materials containing tantalum (Ta) include elemental Ta and tantalum (Ta) compounds such as TaO, TaN, TaON, TaC, TaCO, TaCN, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCOB, TaCNB, and TaCONB. Examples of materials containing chromium (Cr) include elemental Cr and chromium (Cr) compounds such as CrO, CrN, CrON, CrC, CrCO, CrCN, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCOB, CrCNB, and CrCONB.

[0098] The conductive film has a thickness of generally about 20 to 300 nm. However, there is no particular limitation thereto as long as the thickness is sufficient to function as electrostatic adsorption. It is preferable to form a conductive film having a certain thickness at which, after processing into a reflective mask and particularly after forming a pattern (absorber pattern) of the absorber film, a film stress balance is achieved among the pattern of the absorber film (absorber film pattern), the pattern of the film formed on the front main surface side such as a multilayer reflective film and a protective film, and the (one or more layers of) said film, and the conductive film.

[0099] The conductive film may be formed before forming the multilayer reflective film or after forming all the films on the substrate on the multilayer reflective film side. The conductive film may be formed after forming a part of the films on the substrate on the multilayer reflective film side, and then, the remaining part of the films on the multilayer reflective film side may be formed on the substrate.

[0100] The conductive film may be formed by sputtering, and preferably magnetron sputtering. In particular, a metal target such as a chromium (Cr) target and a tantalum (Ta) target, or a metal compound target such as a chromium compound target and a tantalum compound target (a target containing metals such as Cr and Ta, and oxygen (O), nitrogen (N), carbon (C) and / or boron (B)) may be used, and sputtering may be performed using a noble gas such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas and xenon (Xe) gas as a sputtering gas, or the conductive film may be formed by reactive sputtering using a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas and a carbon-containing gas in combination with a noble gas. Further, when forming a film containing boron (B), a chromium (Cr) target added with boron (B) (chromium boride (CrB) target) or a tantalum (Ta) target added with boron (B) (tantalum boride (TaB) target) may be used.

[0101] The reflective mask blank may further include a resist film formed on the side farthest from the substrate. The resist film is preferably an electron beam (EB) resist.

[0102] Embodiment

[0103] Embodiments of the present invention are given below by way of illustration and not limitation.

[0104] Embodiments 1 to 4

[0105] A low-thermal-expansion glass substrate (SiO 2 -TiO 2 series glass substrate) having a size of 152 mm square and a thickness of 6.35 mm is used as the substrate. Using a sputtering apparatus capable of mounting a plurality of targets and capable of discharging one or a plurality of targets simultaneously, a multilayer reflective film is formed by DC magnetron sputtering while rotating the substrate with the targets arranged facing the main surface of the substrate.

[0106] A silicon (Si) target, a ruthenium (Ru) target, and a molybdenum (Mo) target are installed in the chamber of a sputtering apparatus, and a substrate is placed in the chamber. First, while supplying argon (Ar) gas (flow rate: 12 SCCM) into the chamber, power is applied to the silicon (Si) target to form a silicon (Si) layer with a thickness of 4 nm as a high refractive index layer, and then the power supply to the silicon (Si) target is terminated.

[0107] Next, while supplying argon (Ar) gas (flow rate: 15 SCCM) and nitrogen (N 2 ) gas (flow rate: 50 SCCM) into the chamber, power is applied to the silicon (Si) target to form a silicon nitride (SiN) layer with a thickness of 0.5 nm as an intermediate layer, and then the power supply to the silicon (Si) target is terminated.

[0108] Next, while supplying argon (Ar) gas (flow rate: 15 SCCM) into the chamber, power is applied to the ruthenium (Ru) target to form a ruthenium (Ru) layer as a low refractive index layer, and then the power supply to the ruthenium (Ru) target is terminated. The thickness of the low refractive index layer is 2 nm in Example 1, 1.5 nm in Example 2, 1 nm in Example 3, and 0.5 nm in Example 4.

[0109] Next, while supplying argon (Ar) gas (flow rate: 30 SCCM) into the chamber, power is applied to the molybdenum (Mo) target to form a molybdenum (Mo) layer as a medium refractive index layer, and then the power supply to the molybdenum (Mo) target is terminated. The thickness of the medium refractive index layer is 0.5 nm in Example 1, 1 nm in Example 2, 1.5 nm in Example 3, and 2 nm in Example 4.

[0110] The processes for forming the high refractive index layer, the intermediate layer, the low refractive index layer, and the medium refractive index layer, which constitute one cycle, are repeated to form a periodic laminated structure. The repetition count is 30 cycles. After forming the medium refractive index layer in the 30th cycle, finally, a silicon (Si) high refractive index layer with a thickness of 4.5 nm, which is the uppermost layer of the multilayer reflective film, is formed in the above-described manner to obtain the multilayer reflective film.

[0111] At a wavelength of 13.5 nm of EUV light, which is the exposure light, the refractive index n H and the extinction coefficient k H of silicon (Si) that constitutes the high refractive index layer are 0.999 and 0.0018 respectively, and the refractive index n I and the extinction coefficient k I of silicon nitride (SiN) that constitutes the intermediate layer are 0.973 and 0.0093 respectively, and the refractive index n L and the extinction coefficient k LThey are 0.886 and 0.017 respectively, and the refractive index n of molybdenum (Mo) that constitutes the middle refractive index layer M and the extinction coefficient k M are 0.923 and 0.0065 respectively.

[0112] Therefore, each of the multilayer reflective films formed in Examples 1 to 4 satisfies the following expressions (1), (2), and (3):

[0113] k H <k L (1),

[0114] k M <((k H -k L ) / (n H -n L ))×(n M -n L )+k L (2), and

[0115] k I >((k H -k L ) / (n H -n L ))×(n I -n L )+k L (3).

[0116] The reflectance of each of the multilayer reflective films measured at an incident angle of 6 degrees for EUV light having a wavelength of 13.1 to 14 nm. Each reflectance is maximum at 13.5 nm, with the value in Example 1 being 65.0%, the value in Example 2 being 66.1%, the value in Example 3 being 67.1%, and the value in Example 4 being 65.7%.

[0117] Embodiment 5

[0118] A low-thermal-expansion glass substrate (SiO 2 -TiO 2 -based glass substrate) having a size of 152 mm square and a thickness of 6.35 mm is used as the substrate. Using a sputtering device capable of mounting multiple targets and capable of discharging one by one or multiple targets simultaneously, while rotating the substrate, the targets are arranged facing the main surface of the substrate, thereby forming a multilayer reflective film.

[0119] A silicon (Si) target, a ruthenium (Ru) target, and a molybdenum (Mo) target are installed in the chamber of a sputtering apparatus, and a substrate is placed in the chamber. First, while supplying argon (Ar) gas (flow rate: 12 SCCM) into the chamber, power is applied to the silicon (Si) target to form a silicon (Si) layer with a thickness of 4.5 nm as a high refractive index layer, and then the power supply to the silicon (Si) target is terminated. In this embodiment, no intermediate layer is formed.

[0120] Next, while supplying argon (Ar) gas (flow rate: 15 SCCM) into the chamber, power is applied to the ruthenium (Ru) target to form a ruthenium (Ru) layer as a low refractive index layer with a thickness of 1 nm, the same as in Example 3, and then the power supply to the ruthenium (Ru) target is terminated.

[0121] Next, while supplying argon (Ar) gas (flow rate: 30 SCCM) into the chamber, power is applied to the molybdenum (Mo) target to form a molybdenum (Mo) layer as a medium refractive index layer with a thickness of 1.5 nm, the same as in Example 3, and then the power supply to the molybdenum (Mo) target is terminated.

[0122] The processes of forming the high refractive index layer, the low refractive index layer, and the medium refractive index layer, which constitute one cycle, are repeated to form a periodic laminated structure. The repetition count is 30 cycles. After forming the medium refractive index layer in the 30th cycle, finally, a silicon (Si) layer high refractive index layer with a thickness of 4.5 nm, which is the uppermost layer of the multi-layer reflective film, is formed in the above manner to obtain the multi-layer reflective film.

[0123] At a wavelength of 13.5 nm of EUV light, which is the exposure light, the refractive index n H and the extinction coefficient k H of silicon (Si) that constitutes the high refractive index layer are 0.999 and 0.0018 respectively, the refractive index n L and the extinction coefficient k L of ruthenium (Ru) that constitutes the low refractive index layer are 0.886 and 0.017 respectively, and the refractive index n M and the extinction coefficient k M of molybdenum (Mo) that constitutes the medium refractive index layer are 0.923 and 0.0065 respectively. Therefore, the multi-layer reflective film formed in Example 5 satisfies the above expressions (1) and (2).

[0124] The reflectivity of the multi-layer reflective film obtained by measuring at an incident angle of 6 degrees with respect to EUV light having a wavelength in the range of 13.1 to 14 nm is measured. The reflectivity is maximum at 13.5 nm, and the value is 64.2%.

[0125] Embodiments 6 to 8

[0126] A low-thermal-expansion glass substrate with a size of 152 mm square and a thickness of 6.35 mm (SiO 2 -TiO 2 -based glass substrate) is used as the substrate. Using a sputtering device capable of mounting multiple targets and capable of discharging one or multiple targets simultaneously, through DC magnetron sputtering, while rotating the substrate, the targets are arranged facing the main surface of the substrate to form a multilayer reflective film.

[0127] A silicon (Si) target, a ruthenium (Ru) target, and a niobium (Nb) target are mounted in the chamber of the sputtering device, and the substrate is placed in the chamber. First, while supplying argon (Ar) gas (flow rate: 12 SCCM) into the chamber and applying power to the silicon (Si) target, a silicon (Si) layer with a thickness of 4 nm is formed as the high refractive index layer, and then the power supply to the silicon (Si) target is terminated.

[0128] Next, while supplying argon (Ar) gas (flow rate: 15 SCCM) and nitrogen (N 2 ) gas (flow rate: 50 SCCM) into the chamber and applying power to the silicon (Si) target, a silicon nitride (SiN) layer with a thickness of 0.5 nm is formed as the intermediate layer, and then the power supply to the silicon (Si) target is terminated.

[0129] Next, while supplying argon (Ar) gas (flow rate: 15 SCCM) into the chamber and applying power to the ruthenium (Ru) target, a ruthenium (Ru) layer is formed as the low refractive index layer, and then the power supply to the ruthenium (Ru) target is terminated. The thickness of the low refractive index layer is 2 nm in Example 6, 1.5 nm in Example 7, and 1 nm in Example 8.

[0130] Next, while supplying argon (Ar) gas (flow rate: 30 SCCM) into the chamber and applying power to the niobium (Nb) target, a niobium (Nb) layer is formed as the medium refractive index layer, and then the power supply to the niobium (Nb) target is terminated. The thickness of the medium refractive index layer is 0.5 nm in Example 6, 1 nm in Example 7, and 1.5 nm in Example 8.

[0131] The processes for forming the high refractive index layer, the intermediate layer, the low refractive index layer, and the medium refractive index layer, which constitute one cycle, are repeated to form a periodic laminated structure. The repetition count is 30 cycles. After forming the medium refractive index layer in the 30th cycle, finally, a silicon (Si) high refractive index layer with a thickness of 4.5 nm, which is the uppermost layer of the multilayer reflective film, is formed in the above manner to obtain the multilayer reflective film.

[0132] At a wavelength of 13.5 nm of EUV light, which is the exposure light, the refractive index n of silicon (Si) constituting the high refractive index layer H and the extinction coefficient kH are 0.999 and 0.0018 respectively, which are the refractive index n of silicon nitride (SiN) forming the intermediate layer I and the extinction coefficient k I are 0.973 and 0.0093 respectively, which are the refractive index n of ruthenium (Ru) forming the low refractive index layer L and the extinction coefficient k L are 0.886 and 0.017 respectively, which are the refractive index n of niobium (Nb) forming the medium refractive index layer M and the extinction coefficient k M are 0.934 and 0.0052 respectively. Therefore, the multilayer reflective films formed in Examples 6 to 8 satisfy the above expressions (1), (2), and (3).

[0133] The reflectance of each of the multilayer reflective films measured at an incident angle of 6 degrees for EUV light having a wavelength of 13.1 to 14 nm. Each reflectance is maximum at 13.5 nm, with the value in Example 6 being 65.3%, the value in Example 7 being 66.7%, and the value in Example 8 being 65.1%.

[0134] Comparative Example 1

[0135] Except for forming a silicon (Si) layer with a thickness of 4.5 nm as the high refractive index layer and a ruthenium (Ru) layer with a thickness of 2.5 nm as the low refractive index layer and not forming the intermediate layer and the medium refractive index layer, a reflective mask blank is obtained by forming a multilayer reflective film in the same manner as in Example 1.

[0136] The reflectance of the multilayer reflective film measured at an incident angle of 6 degrees for EUV light having a wavelength of 13.1 to 14 nm. The reflectance is maximum at 13.5 nm, and the value is 56.5%.

[0137] By comparing Examples 1 to 8 with Comparative Example 1, it was confirmed that: a high reflectance can be obtained by a multilayer reflective film having a periodic laminated structure in which a repeating unit including one each of a high refractive index layer, a low refractive index layer, and a medium refractive index layer is stacked multiple times.

[0138] Comparative Examples 2 and 3

[0139] In Comparative Examples 2 and 3, except for swapping the formation order of the low refractive index layer and the medium refractive index layer, reflective mask blanks were obtained by forming multilayer reflective films in the same manner as in Examples 3 and 7 respectively.

[0140] The reflectance of each of the multilayer reflective films measured at an incident angle of 6 degrees for EUV light having a wavelength of 13.1 to 14 nm. Each reflectance is maximum at 13.5 nm, with the value in Comparative Example 2 being 59.9% and the value in Comparative Example 3 being 58.7%.

[0141] By comparing Example 3 with Comparative Example 2 or by comparing Example 7 with Comparative Example 3, it was confirmed that a high reflectance can be obtained with a multilayer reflective film having a periodic laminated structure in which a high refractive index layer, an intermediate layer, a low refractive index layer, and a medium refractive index layer are sequentially arranged from the substrate side with repeating units therein.

[0142] Embodiment 9

[0143] A low thermal expansion glass substrate (SiO 2 -TiO 2 -based glass substrate) having a size of 152 mm square and a thickness of 6.35 mm was used as the substrate. Using a sputtering device capable of mounting multiple targets and capable of discharging one by one or multiple targets simultaneously, by DC magnetron sputtering, while rotating the substrate, the targets were arranged facing the main surface of the substrate to form a multilayer reflective film.

[0144] A silicon (Si) target, a ruthenium (Ru) target, and a zirconium (Zr) target were installed in the chamber of the sputtering device, and the substrate was placed in the chamber. First, a silicon (Si) layer having a thickness of 4 nm was formed as the high refractive index layer by applying power to the silicon (Si) target while supplying argon (Ar) gas (flow rate: 12 SCCM) into the chamber, and then the power supply to the silicon (Si) target was terminated.

[0145] Next, a silicon nitride (SiN) layer having a thickness of 0.5 nm was formed as the intermediate layer by applying power to the silicon (Si) target while supplying argon (Ar) gas (flow rate: 15 SCCM) and nitrogen (N 2 ) gas (flow rate: 50 SCCM) into the chamber, and then the power supply to the silicon (Si) target was terminated.

[0146] Next, a ruthenium (Ru) layer having a thickness of 2 nm was formed as the low refractive index layer by applying power to the ruthenium (Ru) target while supplying argon (Ar) gas (flow rate: 15 SCCM) into the chamber, and then the power supply to the ruthenium (Ru) target was terminated.

[0147] Next, a zirconium (Zr) layer having a thickness of 0.5 nm was formed as the medium refractive index layer by applying power to the zirconium (Zr) target while supplying argon (Ar) gas (flow rate: 30 SCCM) into the chamber, and then the power supply to the zirconium (Zr) target was terminated.

[0148] The process of forming a high refractive index layer, an intermediate layer, a low refractive index layer, and a medium refractive index layer by repeating as a cycle is repeated to form a periodic laminated structure. The repetition count is 30 cycles. After forming the medium refractive index layer in the 30th cycle, finally, a silicon (Si) layer with a thickness of 4.5 nm as the uppermost layer of the multilayer reflective film is formed in the above-described manner to obtain a multilayer reflective film.

[0149] At a wavelength of 13.5 nm of EUV light as the exposure light, the refractive index n of silicon (Si) constituting the high refractive index layer H and the extinction coefficient k H are 0.999 and 0.0018 respectively. The refractive index n of silicon nitride (SiN) constituting the intermediate layer I and the extinction coefficient k I are 0.973 and 0.0093 respectively. The refractive index n of ruthenium (Ru) constituting the low refractive index layer L and the extinction coefficient k L are 0.886 and 0.017 respectively. The refractive index n of zirconium (Zr) constituting the medium refractive index layer M and the extinction coefficient k M are 0.959 and 0.0038 respectively. Therefore, the formed multilayer reflective film satisfies the above expressions (1), (2), and (3).

[0150] The reflectance of the multilayer reflective film measured at an incident angle of 6 degrees for EUV light having a wavelength of 13.1 to 14 nm. The reflectance is maximum at 13.5 nm, and the value is 65.5%.

[0151] Embodiment 10

[0152] A low thermal expansion glass substrate (SiO 2 -TiO 2 series glass substrate) having a size of 152 mm square and a thickness of 6.35 mm is used as the substrate. Using a sputtering device capable of mounting multiple targets and capable of discharging one by one or multiple targets simultaneously, by DC magnetron sputtering, while rotating the substrate, the targets are arranged facing the main surface of the substrate to form a multilayer reflective film.

[0153] A silicon (Si) target, a ruthenium (Ru) target, a molybdenum (Mo) target, and a tantalum (Ta) target are installed in the chamber of the sputtering device, and the substrate is placed in the chamber. First, while supplying argon (Ar) gas (flow rate: 12 SCCM) into the chamber and applying power to the silicon (Si) target, a silicon (Si) layer with a thickness of 4 nm is formed as the high refractive index layer, and then the power application to the silicon (Si) target is terminated.

[0154] Next, while supplying argon (Ar) gas (flow rate: 15 SCCM) and nitrogen (N2 )While supplying a gas (flow rate: 50 SCCM) into the chamber, an electric power is applied to a tantalum (Ta) target to form a tantalum nitride (TaN) layer with a thickness of 0.5 nm as an intermediate layer, and then the application of the electric power to the tantalum (Ta) target is terminated.

[0155] Next, while supplying an argon (Ar) gas (flow rate: 15 SCCM) into the chamber, an electric power is applied to a ruthenium (Ru) target to form a ruthenium (Ru) layer with a thickness of 1.5 nm as a low refractive index layer, and then the application of the electric power to the ruthenium (Ru) target is terminated.

[0156] Next, while supplying an argon (Ar) gas (flow rate: 30 SCCM) into the chamber, an electric power is applied to a molybdenum (Mo) target to form a molybdenum (Mo) layer with a thickness of 1 nm as a medium refractive index layer, and then the application of the electric power to the molybdenum (Mo) target is terminated.

[0157] The processes for forming a high refractive index layer, an intermediate layer, a low refractive index layer, and a medium refractive index layer, which are configured as one cycle, are repeated to form a periodic laminated structure. The repetition count is 30 cycles. After forming the medium refractive index layer in the 30th cycle, finally, a high refractive index layer of a silicon (Si) layer with a thickness of 4.5 nm, which is the uppermost layer of the multilayer reflective film, is formed in the above-described manner to obtain a multilayer reflective film.

[0158] At a wavelength of 13.5 nm of EUV light, which is the exposure light, the refractive index n H and the extinction coefficient k H of silicon (Si) that constitutes the high refractive index layer are 0.999 and 0.0018, respectively, and the refractive index n I and the extinction coefficient k I of tantalum nitride (TaN) that constitutes the intermediate layer are 0.950 and 0.029, respectively, and the refractive index n L and the extinction coefficient k L of ruthenium (Ru) that constitutes the low refractive index layer are 0.886 and 0.017, respectively, and the refractive index n M and the extinction coefficient k M of molybdenum (Mo) that constitutes the medium refractive index layer are 0.923 and 0.0065, respectively. Therefore, the formed multilayer reflective film satisfies the above-described expressions (1), (2), and (3).

[0159] The reflectance of the multilayer reflective film measured at an incident angle of 6 degrees for EUV light having a wavelength of 13.1 to 14 nm. The reflectance is maximum at 13.5 nm, and the value is 66.4%.

Claims

1. A reflective mask blank comprising a substrate, a multilayer reflective film formed on one main surface of the substrate and reflecting exposure light, wherein The multilayer reflective film has a periodic stacked structure in which repeating units are stacked multiple times, The repeating unit includes one each of a high refractive index layer, a low refractive index layer and a medium refractive index layer, the medium refractive index layer having a refractive index lower than that of the high refractive index layer and higher than that of the low refractive index layer, and In the repeating unit, the high refractive index layer and the medium refractive index layer are disposed on a substrate side and a side away from the substrate, respectively, with respect to the low refractive index layer.

2. The reflective mask blank according to claim 1, wherein: With respect to the wavelength of exposure light, the high refractive index layer, the low refractive index layer and the medium refractive index layer in the repeating unit satisfy all of the following expressions (1) and (2): k H <k L (1), and k M <((k H -k L ) / (n H -n L ))×(n M -n L )+k L (2), Among them, n H 、n L and n M represent the refractive indices of the high refractive index layer, the low refractive index layer and the medium refractive index layer, respectively, and k H , k L and k M Represent the extinction coefficients of the high refractive index layer, low refractive index layer and medium refractive index layer respectively.

3. The reflective mask blank according to claim 1, wherein: The high refractive index layer includes silicon (Si), the low refractive index layer includes ruthenium (Ru), and the medium refractive index layer includes at least one selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr).

4. The reflective mask blank according to claim 1, wherein: The multilayer reflective film includes an intermediate layer at one or more positions selected from the following: a position between a high refractive index layer and a low refractive index layer, a position between a low refractive index layer and a medium refractive index layer, and a position between a medium refractive index layer and a high refractive index layer.

5. The reflective mask blank according to claim 4, wherein: The multilayer reflective film includes an intermediate layer between a high refractive index layer and a low refractive index layer.

6. The reflective mask blank according to claim 5, wherein: With respect to the wavelength of exposure light, the high refractive index layer, the intermediate layer between the high refractive index layer and the low refractive index layer, the low refractive index layer and the medium refractive index layer in the repeating unit satisfy all of the following expressions (1), (2) and (3): k H <k L (1), k M <((k H -k L ) / (n H -n L ))×(n M -n L )+k L (2), and k I >((k H -k L ) / (n H -n L ))×(n I -n L )+k L (3), Among them, n H 、n I 、n L and n M represent the refractive index of the high refractive index layer, the intermediate layer between the high refractive index layer and the low refractive index layer, the low refractive index layer and the medium refractive index layer, respectively. H , k I , k L and k M They represent the extinction coefficients of the high refractive index layer, the intermediate layer between the high refractive index layer and the low refractive index layer, the low refractive index layer, and the medium refractive index layer, respectively.

7. The reflective mask blank according to claim 5, wherein: The repeating unit consists of one each of a high refractive index layer, an intermediate layer, a low refractive index layer and a medium refractive index layer, and in the repeating unit, the high refractive index layer, the intermediate layer, the low refractive index layer and the medium refractive index layer are arranged in order from the substrate side.

8. The reflective mask blank according to claim 7, wherein: The multilayer reflective film consists of a periodically stacked structure and an additional high refractive index layer disposed on a side farthest from a substrate.

9. The reflective mask blank according to claim 7, wherein: The high refractive index layer contains silicon (Si), the intermediate layer contains either or both of silicon nitride (SiN) and tantalum nitride (TaN), the low refractive index layer contains ruthenium (Ru), and the medium refractive index layer contains at least one selected from molybdenum (Mo), niobium (Nb) and zirconium (Zr).

10. The reflective mask blank according to claim 7, wherein: The high refractive index layer is composed of silicon (Si), the intermediate layer is composed of either or both of silicon nitride (SiN) and tantalum nitride (TaN), the low refractive index layer is composed of ruthenium (Ru), and the medium refractive index layer is composed of at least one selected from molybdenum (Mo), niobium (Nb) and zirconium (Zr).

11. The reflective mask blank according to claim 10, wherein: The high refractive index layer has a thickness of not less than 2.5 nm and not more than 5.5 nm, the intermediate layer has a thickness of not less than 0.2 nm and not more than 1 nm, the low refractive index layer has a thickness of not less than 0.5 nm and not more than 4 nm, and the medium refractive index layer has a thickness of not less than 0.5 nm and not more than 4 nm.

12. A method for manufacturing a reflective mask blank according to any one of claims 1 to 11, comprising the step of forming a multilayer reflective film by using a sputtering device capable of simultaneously mounting three or more types of targets in its chamber, and sequentially discharging the three or more types of targets for sputtering.

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