Reflective mask blank and manufacturing method thereof

Abstract

SOLUTION: A reflective mask blank includes a substrate, a multilayer reflection film that is formed on one main surface of the substrate and reflects exposure light. The multilayer reflection film has a periodically laminated structure in which repeating units are stacked in multiple layers. The repeating unit includes one high refractive index layer, one low refractive index layer, and one medium refractive index layer that has a refractive index lower than the high refractive index layer and higher than the low refractive index layer. In the repeating unit, the high refractive index layer and the medium refractive index layer are disposed at the substrate side and the side remote from the substrate, respectively, with respect to the low refractive index layer.EFFECT: The reflective mask blank has reduced 3D effect compared to conventional multilayer reflection films. A reflective mask with a high reflectance can be obtained from the reflective mask blank.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

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

[0003] However, due to the continuous miniaturization of device patterns, the formation of further fine patterns has been required, and thus, extreme ultraviolet (hereinafter referred to as "EUV") lithography technology using EUV light having a wavelength shorter than that of ArF excimer laser light has been increasingly used as the exposure light. EUV light is light having a wavelength of about 0.2 to 100 nm, and more specifically, light having a wavelength of around 13.5 nm. Since EUV light has extremely low transparency to substances and cannot use conventional transmissive projection optical systems or masks, reflective optical elements are used. Therefore, reflective masks have been proposed as masks for pattern transfer.

[0004] A general reflective mask has a multilayer reflective film that reflects EUV light formed on a substrate, and an absorber film that absorbs EUV light formed in a pattern on the multilayer reflective film. On the other hand, generally, the state before patterning the absorber film (including the state where a resist film is formed) is called a reflective mask blank, and this is used as the material for the reflective mask. The reflective mask blank has a substrate and a multilayer reflective film formed on the substrate that reflects EUV light, and in many cases, further has a basic structure having an absorber film that absorbs EUV light formed on the multilayer reflective film.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In EUV lithography, the EUV light, which is the exposure light, is incident obliquely on the reflective mask, and the incident angle is mainly 6 degrees with respect to the normal of the main surface of the reflective mask. A part of the obliquely incident exposure light is blocked by the side wall of the absorber pattern, and a so-called 3D effect (three-dimensional effect, shadowing effect) occurs. The 3D effect causes misregistration and dimensional deviation in the transferred pattern, and it is preferable to be small in the miniaturization of the pattern. The thinner the thickness, the smaller the 3D effect, so thinning of the absorber pattern is desired.

[0007] On the one hand, in addition to the thickness of the absorber pattern, the 3D effect also varies depending on the structure of the multilayer reflective film. The reflection of EUV light, which is the exposure light by the multilayer reflective film, is caused by the superposition of reflections generated from the interfaces of each layer inside the multilayer reflective film. In the reflection of the exposure light by the multilayer reflective film, if the contribution of the reflection from a deeper position from the surface of the multilayer reflective film is large, it becomes a factor for increasing the 3D effect. Therefore, it is advantageous for reducing the 3D effect that the multilayer reflective film relatively increases the contribution of the reflection from a position closer to the surface.

[0008] 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. A multilayer reflective film (Mo / Si multilayer reflective film) in which molybdenum (Mo) and silicon (Si) are alternately laminated, for example, 40 cycles, is known to efficiently reflect EUV light and is currently used as the mainstream multilayer reflective film in EUV mask blanks.

[0009] The present invention has been made to solve the above problems, and an object thereof is to provide a reflective mask blank having a multilayer reflective film with a reduced 3D effect and a high reflectance, and a method for manufacturing the same.

Means for Solving the Problems

[0010] Ruthenium (Ru) is a material having a lower refractive index and a larger attenuation coefficient in EUV light with a wavelength of 13.5 nm, which is the exposure light, compared to molybdenum (Mo). Therefore, the low refractive index layer of ruthenium (Ru) has a higher reflection coefficient than the low refractive index layer of molybdenum (Mo) at an ideal interface (an interface without interdiffusion or roughness) with a high refractive index layer using silicon (Si) or the like.

[0011] Therefore, in a multilayer reflective film, a multilayer reflective film (Ru / Si multilayer reflective film) using ruthenium (Ru) as a low refractive index layer exhibits a higher reflectivity than a Mo / Si multilayer reflective film with a smaller number of layers. Also, in a comparison with the same number of layers, the Ru / Si multilayer reflective film has a relatively larger contribution from reflection from a position closer to the surface, and from the viewpoint of reducing the 3D effect, the Ru / Si multilayer reflective film is more advantageous. On the other hand, since ruthenium (Ru) has a larger attenuation coefficient, when the number of layers of the multilayer reflective film increases, the reflectivity of the Ru / Si multilayer reflective film becomes lower than that of the Mo / Si multilayer reflective film.

[0012] As a result of intensive studies to solve the above problems, the inventors of the present invention have found that a multilayer reflective film, which is a basic element of a reflective mask blank and a reflective mask, is composed of a high refractive index layer, a low refractive index layer, and a medium refractive index layer, and in particular, includes an intermediate layer together with the high refractive index layer, the low refractive index layer, and the medium refractive index layer, and by configuring it to have a periodically laminated structure portion in which a plurality of repeating units in which each layer is laminated in a predetermined order are laminated, a multilayer reflective film with a reduced 3D effect and a high reflectivity is obtained, and thus the present invention has been completed.

[0013] Therefore, the present invention provides the following reflective mask blank and a method for manufacturing the reflective mask blank. 1. A reflective mask blank having a substrate and a multilayer reflective film formed on one main surface of the substrate for reflecting exposure light, wherein the multilayer reflective film has a periodically laminated structure portion in which a plurality of repeating units each including one high refractive index layer, one low refractive index layer, and one medium refractive index layer having a refractive index smaller than that of the high refractive index layer and larger than that of the low refractive index layer are laminated, In the repeating unit, the high refractive index layer is disposed on the substrate side and the medium refractive index layer is disposed on the side away from the substrate with respect to the low refractive index layer. A reflective mask blank characterized by this. 2. The high refractive index layer, low refractive index layer, and medium refractive index layer of the repeating unit satisfy the following formulas (1) and (2) at the wavelength of the exposure light k H <k L (1) k M<((k H -k L ) / (n H -n L ))×(n M -n L )+k L (2) (wherein, n H , n L and n M are 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 attenuation coefficients of the high refractive index layer, the low refractive index layer, and the medium refractive index layer, respectively.) The reflective mask blank according to 1, characterized in that all of are satisfied. 3. The reflective mask blank according to 1, characterized in that the high refractive index layer contains silicon (Si), the low refractive index layer contains ruthenium (Ru), and the medium refractive index layer contains one or more selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr). 4. The reflective mask blank according to 1, characterized in that one or more of the interfaces between the high refractive index layer and the low refractive index layer, between the low refractive index layer and the medium refractive index layer, and between the medium refractive index layer and the high refractive index layer of the multilayer reflective film contain an intermediate layer. 5. The reflective mask blank according to 4, characterized in that the intermediate layer is included between the high refractive index layer and the low refractive index layer of the multilayer reflective film. 6. The high refractive index layer of the repeating unit, 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 satisfy the following formulas (1), (2), and (3) at the wavelength of the exposure light k H <k L (1) k M <((k H -k L ) / (n H -n L ))×(n M -n L )+k L (2) k I >((k H -k L ) / (n H -nL )) × (n I - n L ) + k L (3) (wherein, n H , n I , n L and n M are, respectively, 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, and k H , k I , k L and k M represent the attenuation 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.) The reflective mask blank according to 5, characterized by satisfying all of 7. The repeating unit is composed of one each of the high refractive index layer, the intermediate layer, the low refractive index layer, and the medium refractive index layer, and in the repeating unit, from the substrate side, the high refractive index layer, the intermediate layer, the low refractive index layer, and the medium refractive index layer are arranged in this order. The reflective mask blank according to 5, characterized by this. 8. The multilayer reflective film is composed of the periodic laminated structure portion and a high refractive index layer provided on the side farthest from the substrate. The reflective mask blank according to 7, characterized by this. 9. The high refractive index layer contains silicon (Si), the intermediate layer contains 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 one or more selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr). The reflective mask blank according to 7, characterized by this. 10. The high refractive index layer is made of silicon (Si), the intermediate layer is made of one or both of silicon nitride (SiN) and tantalum nitride (TaN), the low refractive index layer is made of ruthenium (Ru), and the medium refractive index layer is made of one or more selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr). The reflective mask blank according to 7, characterized by this. 11. The thickness of the high refractive index layer is 2.5 nm or more and 5.5 nm or less, the thickness of the intermediate layer is 0.2 nm or more and 1 nm or less, the thickness of the low refractive index layer is 0.5 nm or more and 4 nm or less, and the thickness of the medium refractive index layer is 0.5 nm or more and 4 nm or less. The reflective mask blank according to 10, characterized in that. 12. A method for manufacturing the reflective mask blank according to any one of 1 to 11, wherein the multilayer reflective film is formed by sputtering by sequentially discharging three or more targets using a sputtering apparatus capable of simultaneously mounting three or more targets in a chamber. A method for manufacturing a reflective mask blank, characterized by that.

Effects of the Invention

[0014] The reflective mask blank of the present invention has a reduced 3D effect compared to a conventional multilayer reflective film, and a reflective mask having a high reflectivity can be obtained from the reflective mask blank of the present invention.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in more detail. The reflective mask blank of the present invention has a substrate and a multilayer reflective film formed on one main surface (front side surface) of the substrate that reflects exposure light.

[0017] 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 wavelength of the EUV light used in EUV lithography using EUV light as exposure light is 13 to 14 nm, and is usually light having a wavelength of about 13.5 nm.

[0018] The substrate preferably has low thermal expansion characteristics for EUV light exposure, for example, the thermal expansion coefficient is ±2×10 -8 / °C or less, preferably within the range of ±5×10 -9 / °C, and is preferably formed of a material within this range. Examples of such materials include titania-doped quartz glass (SiO 2 -TiO 2 -based glass). Further, it is preferable to use a substrate having a sufficiently flattened surface, and the surface roughness of the main surface of the substrate is preferably 0.5 nm or less, more preferably 0.2 nm or less, in terms of RMS value. Such surface roughness can be obtained by polishing the substrate or the like. The size of the substrate is preferably such that the size of the main surface of the substrate is 152 mm square and the thickness of the substrate is 6.35 mm. A substrate of this size is a substrate called a so-called 6025 substrate (a substrate having a main surface size of 6 inches square and a thickness of 0.25 inches).

[0019] The multilayer reflective film is a film that reflects EUV light, which is exposure light, in a reflective mask. The multilayer reflective film may be provided in contact with one main surface of the substrate, or an underlayer film may be provided between the substrate and the multilayer reflective film. The reflectivity of the multilayer reflective film with respect to EUV light (wavelength: 13.5 nm), which is exposure light, is preferably 60% or more, more preferably 62% or more, and still more preferably 65% or more with respect to the exposure light incident from an angle of 6 degrees with respect to the normal of the main surface of the multilayer reflective film.

[0020] FIG. 1 is a cross-sectional view showing an example of the reflective mask blank of the present invention. This 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.

[0021] The multilayer reflective film of the present invention has a periodic laminated structure portion in which a plurality of repeating units each including one high refractive index layer, one low refractive index layer, and one medium refractive index layer are laminated. The number of cycles (the number of repeating units) of the periodic laminated structure portion is preferably 10 cycles or more, more preferably 20 cycles or more, and is preferably 50 cycles or less, more preferably 40 cycles or less, still more preferably 30 cycles or less.

[0022] The high refractive index layer is a layer formed of a material having a relatively high refractive index with respect to EUV light which is exposure light, and the low refractive index layer is a layer formed of a material having a relatively low refractive index with respect to EUV light which is exposure light. On the other hand, the medium refractive index layer is a layer formed of a material having a refractive index smaller than that of the material constituting the high refractive index layer and larger than that of the material constituting the low refractive index layer. Therefore, 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 respectively n H 、n L and n M If we denote them as such, the refractive indices within the repeating unit are n H >n M >n L

[0023] Also, from the viewpoint of obtaining a high reflectance, the high refractive index layer, the low refractive index layer, and the medium refractive index layer of the repeating unit satisfy the following formulas (1) and (2) at the wavelength of the exposure light k H <k L (1) k M <((k H -k L ) / (n H -n L ))×(n M -n L )+k L (2) (In the formulas, n H 、n L and n M are 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 attenuation coefficients of the high refractive index layer, the low refractive index layer, and the medium refractive index layer, respectively. It is preferable to satisfy all of them.

[0024] In the repeating unit, for the low refractive index layer, it is preferable that the high refractive index layer is disposed on the substrate side, and for the low refractive index layer, it is preferable that the medium refractive index layer is disposed on the side away from the substrate. In particular, when the medium refractive index layer is disposed on the side away from the substrate with respect to the low refractive index layer, a high reflectance can be obtained. Furthermore, when the high refractive index layer is disposed on the substrate side with respect to the low refractive index layer, an even higher reflectance can be obtained. Therefore, it is preferable that the high refractive index layer, the low refractive index layer, and the medium refractive index layer are arranged in this way.

[0025] The multilayer reflective film of the present invention may be composed only of a periodically laminated structure portion in which a plurality of repeating units are laminated. However, as another layer on the side most distant from the substrate of the multilayer reflective film, it is preferable to provide a high refractive index layer. Also, as another layer on the side most distant from the substrate of the multilayer reflective film, a layer (protective layer) for protecting the periodically laminated structure portion can be provided. When providing another layer, the multilayer reflective film can be composed of a periodically laminated structure portion in which a plurality of repeating units are laminated and another layer (such as a high refractive index layer, a protective layer, etc.) provided on the side most distant from the substrate. When no other layer is provided on the side most distant from the substrate of the multilayer reflective film, on the repeating unit on the side most distant from the substrate of the periodically laminated structure portion, when another layer is provided on the side most distant from the substrate of the multilayer reflective film, a protective film or an absorber film described later is provided on the other layer.

[0026] An intermediate layer may be provided between each layer of the high refractive index layer, the low refractive index layer, and the medium refractive index layer of the multilayer reflective film in order to prevent the formation of layers (reaction layer, interdiffusion layer) that can be formed at the interface during the formation of the multilayer reflective film or during 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 (one or more places) between the high refractive index layer and the low refractive index layer, at one or more (one or more places) between the low refractive index layer and the medium refractive index layer, or at one or more (one or more places) between the medium refractive index layer and the high refractive index layer.

[0027] The intermediate layer is preferably included in any one or all of the layers between the high refractive index layer and the low refractive index layer, between the low refractive index layer and the medium refractive index layer, and between the medium refractive index layer and the high refractive index layer. In particular, it is preferable to include the intermediate layer between the high refractive index layer and the low refractive index layer. In this case, between the high refractive index layer and the low refractive index layer, and between the low refractive index layer and the medium refractive index layer are the layers within the same repeating unit, and between the medium refractive index layer and the high refractive index layer are the layers between adjacent repeating units.

[0028] When a low refractive index layer, particularly a low refractive index layer containing ruthenium (Ru), is formed by sputtering in contact with a high refractive index layer, particularly a high refractive index layer containing silicon (Si), due to the energy of sputtered particles such as ruthenium (Ru) atoms and clusters sputtered from the target, a reaction layer containing silicon (Si) and ruthenium (Ru) is likely to be formed at the interface between the high refractive index layer containing silicon (Si) and the low refractive index layer containing ruthenium (Ru). The formation of this reaction layer causes a decrease in the reflectance of the multilayer reflective film. Therefore, it is particularly preferable to include an intermediate layer in one or more (any one or more) and particularly all of the layers between the high refractive index layer and the low refractive index layer. By forming the intermediate layer, the formation of such a reaction layer can be effectively prevented.

[0029] Among the layers between the high refractive index layer and the low refractive index layer, between the low refractive index layer and the medium refractive index layer, and between the medium refractive index layer and the high refractive index layer, it is preferable from the viewpoint of obtaining a high reflectance that the intermediate layer is formed between the high refractive index layer and the low refractive index layer.

[0030] When the multilayer reflective film of the present invention includes an intermediate layer between the high refractive index layer and the low refractive index layer, the high refractive index layer of the repeating unit, the intermediate layer between the high refractive index layer and the low refractive index layer, and the low refractive index layer satisfy the following formula (3) at the wavelength of the exposure light k I >((k H -k L ) / (n H -n L ))×(n I -n L) + k L (3) (wherein n H , n I and n L are 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, respectively, and k H , k I and k L represent the attenuation 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, respectively.) It is preferable to satisfy

[0031] Even when the multilayer reflective film of the present invention includes an intermediate layer, it is preferable that the high refractive index layer, the low refractive index layer, and the intermediate refractive index layer of the repeating unit satisfy all of the above formulas (1) and (2) at the wavelength of the exposure light.

[0032] Specifically, as the configuration of the repeating unit, there is an example composed of three layers: one high refractive index layer, one low refractive index layer, and one intermediate refractive index layer. In this case, in the repeating unit, each layer is arranged in the order of the high refractive index layer, the low refractive index layer, and the intermediate refractive index layer from the substrate side.

[0033] FIG. 2 is a cross-sectional view showing an example of the multilayer reflective film of the present invention. This multilayer reflective film 2 has a periodically laminated structure portion 200 in which a plurality of repeating units 20 each composed of a high refractive index layer 21, a low refractive index layer 23, and an intermediate refractive index layer 24 are laminated in order from the substrate side (the lower side in the figure). On the side of the periodically laminated structure portion 200 away from the substrate (the uppermost part in the figure), a high refractive index layer 21 is formed in contact with the periodically laminated structure portion 200 as the layer farthest from the substrate of the multilayer reflective film 2.

[0034] Also, specifically, as the configuration of the repeating unit, there are examples composed of 4, 5, or 6 layers including one high refractive index layer, one low refractive index layer, one intermediate refractive index layer, and 1, 2, or 3 intermediate layers. As such, it is preferable that the repeating unit is composed of one each of a high refractive index layer, an intermediate layer, a low refractive index layer, and an intermediate refractive index layer, and in the repeating unit, they are arranged in the order of the high refractive index layer, the intermediate layer, the low refractive index layer, and the intermediate refractive index layer from the substrate side.

[0035] Figure 3 is a cross-sectional view showing another example of the multilayer reflective film of the present invention. This multilayer film 2 has a periodic laminated structure portion 200 in which a plurality of repeating units 20 each composed of a high refractive index layer 21, an intermediate layer 22, a low refractive index layer 23, and a medium refractive index layer 24 are laminated in order from the substrate side (lower side in the figure). On the side of the periodic laminated structure portion 200 away from the substrate (uppermost part in the figure), a high refractive index layer 21 is formed in contact with the periodic laminated structure portion 200 as the layer on the side of the multilayer reflective film 2 farthest from the substrate.

[0036] The material constituting the high refractive index layer preferably has a refractive index of 0.98 or more and 1.02 or less as the refractive index with respect to EUV light (wavelength: 13.5 nm) which is the exposure light. Examples of such a material include silicon (Si). The high refractive index layer preferably contains silicon (Si).

[0037] The high refractive index layer may further contain one or more light elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H) as long as the high refractive index layer is within a range where it has a predetermined refractive index. However, when the multilayer reflective film includes an intermediate layer, it is preferable that the high refractive index layer does not contain the light elements contained in the intermediate layer among the light elements. Also, the high refractive index layer preferably does not contain the metals and semimetals contained in the materials constituting the low refractive index layer and the medium refractive index layer. In particular, the high refractive index layer preferably consists of silicon (Si).

[0038] The thickness of the high refractive index layer is preferably 2.5 nm or more, more preferably 3 nm or more, and is preferably 5.5 nm or less, more preferably 5 nm or less.

[0039] The material constituting the low refractive index layer preferably has a refractive index of 0.87 or more and 0.90 or less as the refractive index with respect to EUV light (wavelength: 13.5 nm) which is the exposure light. Examples of such a material include ruthenium (Ru). The low refractive index layer preferably contains ruthenium (Ru).

[0040] The low refractive index layer may contain one or more additive metals selected from molybdenum (Mo) and niobium (Nb) as long as the low refractive index layer has a predetermined refractive index. Further, the low refractive index layer may further contain one or more light elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H) as long as the low refractive index layer has a predetermined refractive index. Also, it is preferable that the low refractive index layer does not contain metals and metalloids contained in the material constituting the high refractive index layer. On the other hand, the low refractive index layer may contain metals and metalloids contained in the material constituting the medium refractive index layer, but it is more preferable that the low refractive index layer does not contain metals and metalloids contained in the material constituting the medium refractive index layer. In particular, it is preferable that the low refractive index layer is made of ruthenium (Ru) or is made of ruthenium (Ru) and an additive metal (for example, RuMo, RuNb, RuMoNb, etc.).

[0041] From the viewpoint of obtaining a high reflectivity, the thickness of the low refractive index layer is preferably 0.5 nm or more, more preferably 1 nm or more, and is preferably 4 nm or less, more preferably 3.5 nm or less.

[0042] The material constituting the medium refractive index layer preferably has a refractive index greater than 0.90, particularly 0.91 or more and less than 0.98, particularly 0.97 or less, as the refractive index with respect to EUV light (wavelength: 13.5 nm) which is the exposure light. Examples of such materials include molybdenum (Mo), niobium (Nb), yttrium (Y), and zirconium (Zr). The medium refractive index layer preferably contains one or more selected from molybdenum (Mo), niobium (Nb), yttrium (Y), and zirconium (Zr), and more preferably contains one or more selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr).

[0043] The intermediate refractive index layer may contain ruthenium (Ru) as an additive metal as long as the intermediate refractive index layer is within a range of a predetermined refractive index. Further, the intermediate refractive index layer may further contain one or more light elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H) as long as the intermediate refractive index layer is within a range of a predetermined refractive index. Also, it is preferable that the intermediate refractive index layer does not contain metals and metalloids contained in the material constituting the high refractive index layer. On the other hand, the intermediate refractive index layer may contain metals and metalloids contained in the material constituting the low refractive index layer, but it is more preferable that the intermediate refractive index layer does not contain metals and metalloids contained in the material constituting the low refractive index layer. In particular, the intermediate refractive index layer is composed of one or more selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr) (Mo, Nb, Zr, MoNb, MoZr, NbZr, MoNbZr), or one or more selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr) and an additive metal (for example, MoRu, NbRu, ZrRu, MoNbRu, MoZrRu, NbZrRu, MoNbZrRu, etc.) is preferable.

[0044] From the viewpoint of obtaining high reflectivity, the thickness of the intermediate refractive index layer is preferably 0.5 nm or more, more preferably 1 nm or more, and is preferably 4 nm or less, more preferably 3.5 nm or less.

[0045] The total thickness of the low refractive index layer and the intermediate refractive index layer is preferably 1 nm or more, more preferably 1.5 nm or more, and is preferably 4.5 nm or less, more preferably 4 nm or less.

[0046] The material constituting the intermediate layer may be any material that can prevent the formation of layers (reaction layers, interdiffusion layers) that can be formed at the interface during the formation of the multilayer reflective film or during heat treatment after the formation of the multilayer reflective film among the high refractive index layer, low refractive index layer, and intermediate refractive index layer of the multilayer reflective film, and it is preferable that the material does not extremely reduce the reflectivity of the multilayer reflective film.

[0047] As the material constituting the intermediate layer, a material containing carbon (C) or one or more 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) is preferable, and this material more preferably further contains one or more light elements selected from nitrogen (N), carbon (C), and boron (B), particularly one or both of nitrogen (N) and carbon (C). Specifically, 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), germanium nitride (GeN), etc. may be mentioned. The intermediate layer preferably contains these materials, particularly preferably contains one or both of silicon nitride (SiN) and tantalum nitride (TaN), and preferably consists of these materials, particularly preferably consists of one or both of silicon nitride (SiN) and tantalum nitride (TaN).

[0048] The intermediate layer between the high refractive index layer and the low refractive index layer is preferably a material that satisfies the above formula (3). In particular, as the material constituting the intermediate layer between a high refractive index layer containing silicon (Si), particularly a high refractive index layer made of silicon (Si), and a low refractive index layer containing ruthenium (Ru), particularly a low refractive index layer made of ruthenium (Ru), a material containing one or more selected from tantalum (Ta), tungsten (W), chromium (Cr), titanium (Ti), hafnium (Hf), aluminum (Al), and germanium (Ge) is preferable, and a material containing one or more selected from tantalum (Ta), tungsten (W), chromium (Cr), titanium (Ti), hafnium (Hf), aluminum (Al), and germanium (Ge) and one or both of nitrogen (N) and carbon (C) is more preferable. Also, a material containing silicon nitride (SiN) is preferable.

[0049] The thickness of the intermediate layer is preferably 1 nm or less, more preferably 0.8 nm or less, and still more preferably 0.5 nm or less. The lower limit of the thickness of the intermediate layer is usually 0.2 nm or more. The presence of the intermediate layer is a factor that reduces the reflectance of the multilayer reflective film. However, due to the presence of the intermediate layer, the formation of reaction layers and interdiffusion layers formed between the high refractive index layer, the low refractive index layer, and the intermediate refractive index layer of the multilayer reflective film is prevented, and relatively high reflectance can be obtained. Therefore, high reflectance can be obtained by appropriately adjusting the thickness of the intermediate layer, the position where the intermediate layer is provided, the number of intermediate layers, and the like.

[0050] As a method for forming a multilayer reflective film, there are a sputtering method in which power is supplied to a target, and the supplied power is used to plasmaize (ionize) an atmospheric gas to perform sputtering, and an ion beam sputtering method in which an ion beam is irradiated onto the target. As the sputtering method, there are 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, the magnetron sputtering method that efficiently performs sputtering using a magnetic field is advantageous in terms of productivity. The power applied to the target may be DC or RF, and for DC, pulse sputtering in which a negative bias applied to the target is inverted for a short time to prevent charge-up of the target is also included.

[0051] The multilayer reflective film can be formed, for example, by a sputtering method using a sputtering apparatus capable of mounting a plurality of, particularly three or more targets. In particular, the reflective mask blank of the present invention preferably forms the multilayer reflective film by sequentially discharging three or more targets using a sputtering apparatus capable of simultaneously mounting three or more targets in a chamber and performing sputtering.

[0052] Specifically, as the target, a metal or semi-metal target for forming a high refractive index layer, an intermediate layer, a low refractive index layer or a medium refractive index layer, for example, a silicon (Si) target for forming a layer containing silicon (Si), a ruthenium (Ru) target for forming a layer containing ruthenium (Ru), a molybdenum (Mo) target for forming a layer containing molybdenum (Mo), a niobium (Nb) target for forming a layer containing niobium (Nb), a zirconium (Zr) target for forming a layer containing zirconium (Zr), a tantalum (Ta) target for forming a layer containing tantalum (Ta), etc. are appropriately selected and used, and as the sputtering gas, it can be formed using a noble gas such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, xenon (Xe) gas.

[0053] In addition, by reactive sputtering using a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas, a carbon-containing gas, or a hydrogen-containing gas together with a noble gas, a layer containing light elements such as oxygen (O), nitrogen (N), carbon (C), and hydrogen (H) can be formed. Specifically, as the reactive gas, oxygen (O 2 ) gas, nitrogen (N 2 ) gas, hydrogen (H 2 ) gas, nitrous oxide (N 2 O) gas, nitric oxide (NO) gas, nitrogen dioxide (NO 2 ) gas and other nitrogen oxide gases, carbon monoxide (CO) gas, carbon dioxide (CO 2 ) gas and other carbon oxide gases, methane (CH 4 ) gas and other hydrocarbon gases can be mentioned. For example, when forming a layer containing silicon nitride (SiN), it can be formed by reactive sputtering using a nitrogen-containing gas such as nitrogen (N 2 ) gas simultaneously with a noble gas.

[0054] Furthermore, when forming a layer containing boron (B), a boron carbide (B 4 C) target, a target of a metal or a metalloid added with boron (B), etc. can be used. Examples of the target of a metal or a metalloid added with boron (B) include a silicon (Si) target added with boron (B) (boronized silicon (SiB) target), a ruthenium (Ru) target added with boron (B) (boronized ruthenium (RuB) target), a molybdenum (Mo) target added with boron (B) (boronized molybdenum (MoB) target), a niobium (Nb) target added with boron (B) (boronized niobium (NbB) target), a zirconium (Zr) target added with boron (B) (boronized zirconium (ZrB) target), a tantalum (Ta) target added with boron (B) (boronized tantalum (TaB) target), etc.

[0055] A reflective mask blank generally has an absorber film together with a substrate and a multilayer reflective film. Further, a protective film is usually provided between the multilayer reflective film and the absorber film. Specifically, such a reflective mask blank includes a substrate, a multilayer reflective film formed on one main surface of the substrate for reflecting exposure light, a protective film formed on the multilayer reflective film, and an absorber film formed on the protective film for absorbing exposure light.

[0056] From a reflective mask blank having an absorber film, an absorber pattern can be formed by patterning the absorber film to obtain a reflective mask. From a reflective mask blank having a multilayer reflective film, a protective film, and an absorber film, a reflective mask having a substrate, a multilayer reflective film formed on one main surface of the substrate for reflecting exposure light, a protective film formed on the multilayer reflective film, and a pattern of the absorber film (absorber pattern) formed on the protective film for absorbing exposure light can be manufactured.

[0057] The reflective mask blank of the present invention may have 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, cleaning in the manufacturing process of the reflective mask, exposure environment during use of the reflective mask, and cleaning treatment in the regeneration process after use (resistance to various dry etching, cleaning in the manufacturing process of the reflective mask, exposure environment during use of the reflective mask, and cleaning treatment in the regeneration process after use). The protective film may be composed of a plurality of layers. The protective film may be formed via another film between the multilayer reflective film, but is usually formed in contact with the multilayer reflective film.

[0058] As the material of the protective film, materials containing ruthenium (Ru), particularly materials composed of ruthenium (Ru), materials containing ruthenium (Ru) and one or more additive metals selected from niobium (Nb), zirconium (Zr), titanium (Ti) and rhodium (Rh), particularly materials composed of ruthenium (Ru) and one or more additive metals selected from niobium (Nb), zirconium (Zr), titanium (Ti) and rhodium (Rh) can be mentioned. The material of the protective film may further contain oxygen (O), nitrogen (N), carbon (C), etc. The film thickness of the protective film is not particularly limited, but is usually about 2 to 5 nm.

[0059] 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 can be used to form a film containing ruthenium (Ru), and a niobium (Nb) target or a niobium (Nb) alloy target can be used to form a film containing niobium (Nb). Specifically, it can be appropriately selected and used from a ruthenium (Ru) target, a niobium (Nb) target, an alloy target of ruthenium (Ru) and niobium (Nb), etc. The protective film can be formed by sputtering using a noble gas such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, 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 together with the noble gas.

[0060] The reflective mask blank of the present invention may have an absorber film that absorbs exposure light (reduces reflectance) on the multilayer reflective film. The absorber film is a film that functions as a pattern-forming film. The absorber film may be formed in contact with the multilayer reflective film, but is preferably formed via another film, and is usually formed via a protective film.

[0061] FIG. 4 is a cross-sectional view showing another example of the reflective mask blank of the present invention. This reflective mask blank 10 includes a substrate 1, 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.

[0062] The material of the absorber film may be any material that absorbs EUV light and enables pattern processing. The material of the absorber film is not particularly limited, and examples thereof include materials containing tantalum (Ta) or chromium (Cr). Further, the material containing Ta or Cr may contain oxygen (O), nitrogen (N), carbon (C), boron (B), or the like. Examples of the material containing Ta include tantalum compounds such as Ta alone, TaO, TaN, TaON, TaC, TaCO, TaCN, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCOB, TaCNB, and TaCONB. Examples of the material containing Cr include chromium compounds such as Cr alone, CrO, CrN, CrON, CrC, CrCO, CrCN, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCOB, CrCNB, and CrCONB. The film thickness of the absorber film is not particularly limited, but is usually about 40 to 80 nm.

[0063] The absorber film can be formed by sputtering, and magnetron sputtering is preferably used for sputtering. Specifically, metal targets such as chromium (Cr) targets and tantalum (Ta) targets, and metal compound targets such as chromium compound targets and tantalum compound targets (targets containing metals such as Cr and Ta and oxygen (O), nitrogen (N), carbon (C), boron (B), etc.) are used. As the sputtering gas, sputtering using noble gases such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas, and also reactive sputtering using reactive gases such as oxygen-containing gas, nitrogen-containing gas, and carbon-containing gas together with the noble gas can be used. Further, when forming a film containing boron (B), a chromium (Cr) target added with boron (B) (chromium boride (CrB) target), a tantalum (Ta) target added with boron (B) (tantalum boride (TaB) target), etc. can be used.

[0064] On the side spaced apart from the substrate on the absorber film, a hard mask film (etching mask film for the absorber film) having etching characteristics different from those of the absorber film may preferably be provided in contact with the absorber film. This hard mask film is a film that functions as an etching mask when dry-etching the absorber film. After forming the absorber pattern, this hard mask film may be left as a reflectivity reduction layer for reducing the reflectivity at the wavelength of light used in inspections such as pattern inspection, as a part of the absorber film, or removed so as not to remain on the reflective mask. Examples of the material for the hard mask film include materials containing chromium (Cr). The hard mask film formed of a material containing Cr is particularly suitable when the absorber film is formed of a material containing Ta and not containing Cr. When forming a layer (reflectivity reduction layer) mainly responsible for the function of reducing the reflectivity at the wavelength of light used in inspections such as pattern inspection on the absorber film, the hard mask film can be formed on the reflectivity reduction layer of the absorber film. The hard mask film can be formed, for example, by magnetron sputtering. The film thickness of the hard mask film is not particularly limited, but is usually about 5 to 20 nm.

[0065] On the other main surface (the back surface), which is the surface on the side opposite to one main surface of the substrate, a conductive film used for electrostatically chucking the reflective mask to the exposure apparatus may preferably be provided in contact with the other main surface.

[0066] The conductive film preferably has a sheet resistance of 100 Ω / sq or less. The material of the conductive film is not particularly limited, and examples thereof include materials containing tantalum (Ta) or chromium (Cr). Further, the material containing tantalum (Ta) or chromium (Cr) may contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Examples of the material containing tantalum (Ta) include tantalum (Ta) compounds such as Ta alone, TaO, TaN, TaON, TaC, TaCO, TaCN, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCOB, TaCNB, TaCONB. Examples of the material containing chromium (Cr) include chromium (Cr) compounds such as Cr alone, CrO, CrN, CrON, CrC, CrCO, CrCN, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCOB, CrCNB, CrCONB.

[0067] The thickness of the conductive film only needs to function as an electrostatic chuck and is not particularly limited, but is usually about 20 to 300 nm. The thickness of the conductive film is preferably formed so that the film stress is balanced with the films or film patterns formed on the main surface on the front side of the substrate, such as the multilayer reflective film, the protective film, and the pattern of the absorber film (absorber pattern), after forming the reflective mask and particularly after forming the pattern of the absorber film (absorber pattern).

[0068] The conductive film may be formed before forming the multilayer reflective film, or may be formed after forming all the films on the multilayer reflective film side of the substrate. Alternatively, after forming some of the films on the multilayer reflective film side of the substrate, the conductive film may be formed, and then the remaining films on the multilayer reflective film side of the substrate may be formed.

[0069] The conductive film can be formed by sputtering, and magnetron sputtering is preferably used for sputtering. Specifically, metal targets such as chromium (Cr) targets and tantalum (Ta) targets, and metal compound targets such as chromium compound targets and tantalum compound targets (targets containing metals such as Cr and Ta and oxygen (O), nitrogen (N), carbon (C), boron (B), etc.) are used. As the sputtering gas, sputtering using noble gases such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas, or reactive sputtering using reactive gases such as oxygen-containing gas, nitrogen-containing gas, and carbon-containing gas together with the noble gas can be used. Further, when forming a film containing boron (B), a chromium (Cr) target added with boron (B) (chromium boride (CrB) target), a tantalum (Ta) target added with boron (B) (tantalum boride (TaB) target), etc. can be used.

[0070] The reflective mask blank may further have a resist film formed on the side farthest from the substrate. The resist film is preferably an electron beam (EB) resist.

Examples

[0071] Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0072] [Examples 1 to 4] As the substrate, a low thermal expansion glass substrate (SiO 2 -TiO 2 -based glass substrate) with a size of 152 mm square and a thickness of 6.35 mm was used. A sputtering apparatus capable of mounting a plurality of targets and discharging the targets one by one or simultaneously was used. The main surfaces of the target and the substrate were opposed to each other, and while the substrate was rotated, a multilayer reflective film was formed by DC magnetron sputtering.

[0073] A silicon (Si) target, a ruthenium (Ru) target, and a molybdenum (Mo) target were installed in the chamber of the sputtering apparatus, and a substrate was placed. First, while flowing argon (Ar) gas (flow rate: 12 SCCM) into the chamber, power was 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 application of power to the silicon (Si) target was stopped.

[0074] Next, while flowing argon gas (flow rate: 15 SCCM) and nitrogen (N 2 ) gas (flow rate: 50 SCCM) into the chamber, power was 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 application of power to the silicon (Si) target was stopped.

[0075] Next, while flowing argon gas (flow rate: 15 SCCM) into the chamber, power was applied to the ruthenium (Ru) target to form a ruthenium (Ru) layer as a low refractive index layer, and then the application of power to the ruthenium (Ru) target was stopped. The thickness of the low refractive index layer was 2 nm in Example 1, 1.5 nm in Example 2, 1 nm in Example 3, and 0.5 nm in Example 4.

[0076] Next, while flowing argon gas (flow rate: 30 SCCM) into the chamber, power was applied to the molybdenum (Mo) target to form a molybdenum (Mo) layer as a medium refractive index layer, and then the application of power to the molybdenum (Mo) target was stopped. The thickness of the medium refractive index layer was 0.5 nm in Example 1, 1 nm in Example 2, 1.5 nm in Example 3, and 2 nm in Example 4.

[0077] The operations of forming these high refractive index layer, intermediate layer, low refractive index layer, and medium refractive index layer were regarded as one cycle, and by repeating this operation, a periodic laminated structure portion was formed. The number of repetitions of the periodic laminated structure portion was 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, which is a high refractive index layer, was formed as the uppermost layer of the multilayer reflective film by the above method to obtain a multilayer reflective film.

[0078] At a wavelength of 13.5 nm of EUV light that is exposure light, the refractive index n of silicon (Si) constituting the high refractive index layer H is 0.999, and the attenuation coefficient k H is 0.0018. The refractive index n of silicon nitride (SiN) constituting the intermediate layer I is 0.973, and the attenuation coefficient k I is 0.0093. The refractive index n of ruthenium (Ru) constituting the low refractive index layer L is 0.886, and the attenuation coefficient k L is 0.017. The refractive index n of molybdenum (Mo) constituting the medium refractive index layer M is 0.923, and the attenuation coefficient k M is 0.0065.

[0079] Therefore, all of the formed multilayer reflective films of Examples 1 to 4 satisfy the following formulas (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) k I >((k H -k L ) / (n H -n L ))×(n I -n L )+k L (3) .

[0080] For the obtained multilayer reflective film, when the reflectance of EUV light with a wavelength of 13.1 to 14 nm was measured at an incident angle of 6 degrees, the reflectance was maximum at 13.5 nm, and the values were 65.0% in Example 1, 66.1% in Example 2, 67.1% in Example 3, and 65.7% in Example 4.

[0081] [Example 5] As the substrate, a low thermal expansion glass substrate (SiO 2 -TiO 2 -based glass substrate) with a size of 152 mm square and a thickness of 6.35 mm was used. A sputtering apparatus capable of mounting a plurality of targets and discharging the targets one by one or simultaneously was used. The main surfaces of the target and the substrate were opposed to each other, and while the substrate was rotated, a multilayer reflective film was formed by DC magnetron sputtering.

[0082] A silicon (Si) target, a ruthenium (Ru) target, and a molybdenum (Mo) target were mounted in the chamber of the sputtering apparatus, and the substrate was placed. First, while flowing argon (Ar) gas (flow rate: 12 SCCM) into the chamber, power was 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 the application of power to the silicon (Si) target was stopped. In this example, an intermediate layer was not formed.

[0083] Next, while flowing argon gas (flow rate: 15 SCCM) into the chamber, power was applied to the ruthenium (Ru) target to form a ruthenium (Ru) layer with a thickness of 1 nm as a low refractive index layer same as in Example 3, and the application of power to the ruthenium (Ru) target was stopped.

[0084] Next, while flowing argon gas (flow rate: 30 SCCM) into the chamber, power was applied to the molybdenum (Mo) target to form a molybdenum (Mo) layer with a thickness of 1.5 nm as a medium refractive index layer same as in Example 3, and the application of power to the molybdenum (Mo) target was stopped.

[0085] The operations of forming these high refractive index layer, low refractive index layer, and medium refractive index layer were regarded as one cycle, and by repeating this operation, a periodically laminated structure portion was formed. The number of repetitions of the periodically laminated structure portion was 30 cycles. After forming the medium refractive index layer of the 30th cycle, finally, as the uppermost layer of the multilayer reflective film, a silicon (Si) layer with a thickness of 4.5 nm which is a high refractive index layer was formed by the above method to obtain a multilayer reflective film.

[0086] At a wavelength of 13.5 nm of EUV light that is exposure light, the refractive index n of silicon (Si) constituting the high refractive index layer H is 0.999, and the attenuation coefficient k H is 0.0018. The refractive index n of ruthenium (Ru) constituting the low refractive index layer L is 0.886, and the attenuation coefficient k L is 0.017. The refractive index n of molybdenum (Mo) constituting the medium refractive index layer M is 0.923, and the attenuation coefficient k M is 0.0065. Therefore, the formed multilayer reflective film of Example 5 satisfies the above formulas (1) and (2).

[0087] Regarding the obtained multilayer reflective film, when the reflectance of EUV light with a wavelength of 13.1 to 14 nm was measured at an incident angle of 6 degrees, the reflectance was maximized at 13.5 nm, and the value was 64.2%.

[0088] [Examples 6 to 8] As a substrate, a low thermal expansion glass substrate (SiO 2 -TiO 2 system glass substrate) with a size of 152 mm square and a thickness of 6.35 mm was used. A sputtering apparatus capable of mounting a plurality of targets and discharging the targets one by one or simultaneously was used. The main surfaces of the target and the substrate were opposed to each other, and while the substrate was rotated, a multilayer reflective film was formed by DC magnetron sputtering.

[0089] A silicon (Si) target, a ruthenium (Ru) target, and a niobium (Nb) target were mounted in the chamber of the sputtering apparatus, and the substrate was installed. First, while flowing argon (Ar) gas (flow rate: 12 SCCM) into the chamber, power was applied to the silicon (Si) target to form a 4-nm-thick silicon (Si) layer as the high refractive index layer, and the application of power to the silicon (Si) target was stopped.

[0090] Next, argon gas (flow rate: 15 SCCM) and nitrogen (N 2While flowing gas (flow rate: 50 SCCM), power was applied to a silicon (Si) target to form a silicon nitride (SiN) layer with a thickness of 0.5 nm as an intermediate layer, and then the application of power to the silicon (Si) target was stopped.

[0091] Next, while flowing argon gas (flow rate: 15 SCCM) into the chamber, power was applied to a ruthenium (Ru) target to form a ruthenium (Ru) layer as a low refractive index layer, and then the application of power to the ruthenium (Ru) target was stopped. The thickness of the low refractive index layer was 2 nm in Example 6, 1.5 nm in Example 7, and 1 nm in Example 8.

[0092] Next, while flowing argon gas (flow rate: 30 SCCM) into the chamber, power was applied to a niobium (Nb) target to form a niobium (Nb) layer as a medium refractive index layer, and then the application of power to the niobium (Nb) target was stopped. The thickness of the medium refractive index layer was 0.5 nm in Example 6, 1 nm in Example 7, and 1.5 nm in Example 8.

[0093] The operations of forming these high refractive index layers, the intermediate layer, the low refractive index layer, and the medium refractive index layer were defined as one cycle, and by repeating this operation, a periodic multilayer structure portion was formed. The number of repetitions of the periodic multilayer structure portion was 30 cycles. After forming the medium refractive index layer in the 30th cycle, finally, as the uppermost layer of the multilayer reflective film, a silicon (Si) layer with a thickness of 4.5 nm, which is a high refractive index layer, was formed by the above method to obtain a multilayer reflective film.

[0094] At a wavelength of 13.5 nm of EUV light, which is the exposure light, the refractive index n H of silicon (Si) constituting the high refractive index layer H is 0.999, and the extinction coefficient k I of silicon nitride (SiN) constituting the intermediate layer I is 0.973, and the extinction coefficient k L of ruthenium (Ru) constituting the low refractive index layer L is 0.886, and the extinction coefficient k Mis 0.934, and the attenuation coefficient k M is 0.0052. Therefore, all of the multilayer reflective films formed in Examples 6 to 8 satisfy the above formulas (1), (2), and (3).

[0095] Regarding the obtained multilayer reflective film, when the reflectance of EUV light with a wavelength of 13.1 to 14 nm was measured at an incident angle of 6 degrees, the reflectance was maximized at 13.5 nm, and the values were 65.3% in Example 6, 66.7% in Example 7, and 65.1% in Example 8.

[0096] [Comparative Example 1] A multilayer reflective film was formed in the same manner as in Example 1, except that a silicon (Si) layer with a thickness of 4.5 nm was formed as the high refractive index layer, a ruthenium (Ru) layer with a thickness of 2.5 nm was formed as the low refractive index layer, and the intermediate layer and the medium refractive index layer were not formed, and a reflective mask blank was obtained.

[0097] Regarding the obtained multilayer reflective film, when the reflectance of EUV light with a wavelength of 13.1 to 14 nm was measured at an incident angle of 6 degrees, the reflectance was maximized at 13.5 nm, and the value was 56.5%.

[0098] From the comparison between Examples 1 to 8 and Comparative Example 1, it was found that a high reflectance can be obtained with a multilayer reflective film having a periodic laminated structure portion in which a plurality of repeating units each including one high refractive index layer, one low refractive index layer, and one medium refractive index layer are laminated.

[0099] [Comparative Examples 2 and 3] A multilayer reflective film was formed in the same manner as in Example 3 in Comparative Example 2 and in the same manner as in Example 7 in Comparative Example 3, except that the order of forming the low refractive index layer and the medium refractive index layer was reversed, and a reflective mask blank was obtained.

[0100] Regarding the obtained multilayer reflective film, when the reflectance of EUV light with a wavelength of 13.1 to 14 nm was measured at an incident angle of 6 degrees, the reflectance was maximized at 13.5 nm, and the values were 59.9% in Comparative Example 2 and 58.7% in Comparative Example 3.

[0101] From the comparison between Example 3 and Comparative Example 2 and the comparison between Example 7 and Comparative Example 3, it was found that in the repeating unit, a high reflectivity can be obtained by a multilayer reflective film having a periodically laminated structure portion arranged in the order of a high refractive index layer, an intermediate layer, a low refractive index layer, and a medium refractive index layer from the substrate side.

[0102] [Example 9] As the substrate, a low thermal expansion glass substrate (SiO 2 -TiO 2 -based glass substrate) with a size of 152 mm square and a thickness of 6.35 mm was used. A sputtering apparatus capable of mounting a plurality of targets and discharging the targets one by one or a plurality of targets simultaneously was used. The main surfaces of the target and the substrate were opposed to each other, and while the substrate was rotated, a multilayer reflective film was formed by DC magnetron sputtering.

[0103] A silicon (Si) target, a ruthenium (Ru) target, and a zirconium (Zr) target were mounted in the chamber of the sputtering apparatus, and the substrate was installed. First, while flowing argon (Ar) gas (flow rate: 12 SCCM) into the chamber, power was applied to the silicon (Si) target to form a silicon (Si) layer with a thickness of 4 nm as the high refractive index layer, and the application of power to the silicon (Si) target was stopped.

[0104] Next, while flowing argon gas (flow rate: 15 SCCM) and nitrogen (N 2 ) gas (flow rate: 50 SCCM) into the chamber, power was applied to the silicon (Si) target to form a silicon nitride (SiN) layer with a thickness of 0.5 nm as the intermediate layer, and the application of power to the silicon (Si) target was stopped.

[0105] Next, while flowing argon gas (flow rate: 15 SCCM) into the chamber, power was applied to the ruthenium (Ru) target to form a ruthenium (Ru) layer with a thickness of 2 nm as the low refractive index layer, and the application of power to the ruthenium (Ru) target was stopped.

[0106] Next, while flowing argon gas (flow rate: 30 SCCM) into the chamber, power was applied to a zirconium (Zr) target to form a zirconium (Zr) layer with a thickness of 0.5 nm as the intermediate refractive index layer, and then the application of power to the zirconium (Zr) target was stopped.

[0107] The operations of forming these high refractive index layers, the intermediate layer, the low refractive index layer, and the intermediate refractive index layer were defined as one cycle, and by repeating this operation, a periodic laminated structure portion was formed. The number of repetitions of the periodic laminated structure portion was set to 30 cycles. After forming the intermediate refractive index layer in the 30th cycle, finally, as the top layer of the multilayer reflective film, a silicon (Si) layer with a thickness of 4.5 nm, which is a high refractive index layer, was formed by the above method to obtain a multilayer reflective film.

[0108] 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 is 0.999, and the extinction coefficient k H is 0.0018. The refractive index n of silicon nitride (SiN) constituting the intermediate layer I is 0.973, and the extinction coefficient k I is 0.0093. The refractive index n of ruthenium (Ru) constituting the low refractive index layer L is 0.886, and the extinction coefficient k L is 0.017. The refractive index n of zirconium (Zr) constituting the intermediate refractive index layer M is 0.959, and the extinction coefficient k M is 0.0038. Therefore, the formed multilayer reflective film satisfies the above formulas (1), (2), and (3).

[0109] Regarding the obtained multilayer reflective film, when the reflectance of EUV light with a wavelength of 13.1 to 14 nm was measured at an incident angle of 6 degrees, the reflectance was maximized at 13.5 nm, and the value was 65.5%.

[0110] [Example 10] As the substrate, a low thermal expansion glass substrate (SiO 2 -TiO 2Using a glass substrate, a sputtering apparatus capable of mounting a plurality of targets and discharging the targets one by one or a plurality of targets simultaneously was used. The main surfaces of the target and the substrate were opposed to each other, and while the substrate was rotated, a multilayer reflective film was formed by DC magnetron sputtering.

[0111] A silicon (Si) target, a ruthenium (Ru) target, a molybdenum (Mo) target, and a tantalum (Ta) target were mounted in the chamber of the sputtering apparatus, and a substrate was installed. First, while flowing argon (Ar) gas (flow rate: 12 SCCM) into the chamber, power was applied to the silicon (Si) target, and a silicon (Si) layer with a thickness of 4 nm was formed as a high refractive index layer, and the application of power to the silicon (Si) target was stopped.

[0112] Next, while flowing argon gas (flow rate: 15 SCCM) and nitrogen (N 2 ) gas (flow rate: 50 SCCM) into the chamber, power was applied to the tantalum (Ta) target, and a tantalum nitride (TaN) layer with a thickness of 0.5 nm was formed as an intermediate layer, and the application of power to the tantalum (Ta) target was stopped.

[0113] Next, while flowing argon gas (flow rate: 15 SCCM) into the chamber, power was applied to the ruthenium (Ru) target, and a ruthenium (Ru) layer with a thickness of 1.5 nm was formed as a low refractive index layer, and the application of power to the ruthenium (Ru) target was stopped.

[0114] Next, while flowing argon gas (flow rate: 30 SCCM) into the chamber, power was applied to the molybdenum (Mo) target, and a molybdenum (Mo) layer with a thickness of 1 nm was formed as a medium refractive index layer, and the application of power to the molybdenum (Mo) target was stopped.

[0115] The operation of forming these high refractive index layers, the intermediate layer, the low refractive index layer, and the medium refractive index layer was defined as one cycle, and by repeating this operation, a periodically laminated structure portion was formed. The number of repetitions of the periodically laminated structure portion was set to 30 cycles. After forming the medium refractive index layer in the 30th cycle, finally, as the uppermost layer of the multilayer reflective film, a 4.5-nm-thick silicon (Si) layer, which is a high refractive index layer, was formed by the above method to obtain a multilayer reflective film.

[0116] 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 is 0.999, and the extinction coefficient k H is 0.0018. The refractive index n of tantalum nitride (TaN) constituting the intermediate layer I is 0.950, and the extinction coefficient k I is 0.029. The refractive index n of ruthenium (Ru) constituting the low refractive index layer L is 0.886, and the extinction coefficient k L is 0.017. The refractive index n of molybdenum (Mo) constituting the medium refractive index layer M is 0.923, and the extinction coefficient k M is 0.0065. Therefore, the formed multilayer reflective film satisfies the above formulas (1), (2), and (3).

[0117] When the reflectance of EUV light with a wavelength of 13.1 to 14 nm was measured for the obtained multilayer reflective film at an incident angle of 6 degrees, the reflectance was maximized at 13.5 nm, and the value was 66.4%.

Explanation of Symbols

[0118] 1 Substrate 10 Reflective mask blank 2 Multilayer reflective film 20 Repeating unit 200 Periodically laminated structure portion 21 High refractive index layer 22 Intermediate layer 23 Low refractive index layer 24 Medium refractive index layer 3 Protective film 4 Absorber film

Claims

1. A reflective mask blank having a substrate and a multilayer reflective film formed on one main surface of the substrate and reflecting exposure light, the multilayer reflective film has a periodic laminate structure in which a plurality of repeating units each including a high refractive index layer, a low refractive index layer, and a medium refractive index layer having a refractive index smaller than that of the high refractive index layer and larger than that of the low refractive index layer are laminated; A reflective mask blank, characterized in that in the repeating unit, the high refractive index layer is arranged on the substrate side relative to the low refractive index layer, and the medium refractive index layer is arranged on a side away from the substrate.

2. The high refractive index layer, the low refractive index layer and the medium refractive index layer of the repeating unit are each represented by the following formulas (1) and (2) at the wavelength of the exposure light: k H <k L (1) k M <((k H -k L ) / (n H -n L ))×(n M -n L )+k L (2) (In the formula, n H , n L and n M are 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.) 2. The reflective mask blank according to claim 1, wherein all of the above is satisfied.

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

4. The reflective mask blank according to claim 1, characterized in that it comprises an intermediate layer at least between the high refractive index layer and the low refractive index layer, between the low refractive index layer and the medium refractive index layer, and between the medium refractive index layer and the high refractive index layer of the multilayer reflective film.

5. 5. The reflective mask blank according to claim 4, further comprising the intermediate layer between a high refractive index layer and a low refractive index layer of the multilayer reflective film.

6. 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 of the repeating unit are each represented by the following formulas (1), (2) and (3) at the wavelength of the exposure light: k H <k L (1) k M <((k H -k L ) / (n H -n L ))×(n M -n L )+k L (2) k I >((k H -k L ) / (n H -n L ))×(n I -n L )+k L (3) (In the formula, n H , n I , n L and n M are 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; 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.

6. The reflective mask blank according to claim 5, wherein all of the above is satisfied.

7. 6. The reflective mask blank according to claim 5, characterized in that the repeating unit comprises one each of the high refractive index layer, the intermediate layer, the low refractive index layer, and the 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 this order from the substrate side.

8. 8. The reflective mask blank according to claim 7, wherein the multilayer reflective film comprises the periodic stacked structure and a high refractive index layer provided on the side furthest from the substrate.

9. 8. The reflective mask blank according to claim 7, wherein the high refractive index layer contains silicon (Si), the intermediate layer contains 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 one or more selected from molybdenum (Mo), niobium (Nb), and zirconium (Zr).

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

11. The reflective mask blank according to claim 10, characterized in that the high refractive index layer has a thickness of 2.5 nm or more and 5.5 nm or less, the intermediate layer has a thickness of 0.2 nm or more and 1 nm or less, the low refractive index layer has a thickness of 0.5 nm or more and 4 nm or less, and the medium refractive index layer has a thickness of 0.5 nm or more and 4 nm or less.

12. 12. A method for producing a reflective mask blank according to any one of claims 1 to 11, characterized in that the multilayer reflective film is formed by sputtering using a sputtering apparatus capable of simultaneously mounting three or more types of targets in a chamber, and sequentially discharging the three or more types of targets.

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