JP2009252788A - Reflective mask blank for euv lithography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflective mask blank for EUV lithography having a low reflection layer which exhibits a low reflectance to the wavelength region of EUV light and the inspection light of a mask pattern, and especially exhibits low reflection characteristics to the full wavelength region (190-260 nm) of the inspection light of a mask pattern. <P>SOLUTION: In a reflective mask blank for EUV lithography where a layer 12 reflecting EUV light, a layer 14 for absorbing EUV light, and a low reflection layer 15 for the inspection light (wavelength 190-260 nm) of a mask pattern are formed on a substrate 11 in this order, the low reflection layer 15 contains hafnium Hf, nitrogen N and oxygen O at content in total of 80 at% or more. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a reflective mask blank (hereinafter referred to as “EUV mask blank”) for EUV (Extreme Ultra Violet) lithography used in semiconductor manufacturing and the like.

  2. Description of the Related Art Conventionally, in the semiconductor industry, a photolithography method using visible light or ultraviolet light has been used as a technique for transferring a fine pattern necessary for forming an integrated circuit having a fine pattern on a Si substrate or the like. However, while miniaturization of semiconductor devices is accelerating, the limits of conventional photolithography methods have been approached. In the case of the photolithography method, the resolution limit of the pattern is about ½ of the exposure wavelength, and it is said that the immersion wavelength is about ¼ of the exposure wavelength, and the immersion of ArF laser (193 nm). Even if the method is used, the limit of about 45 nm is expected. Therefore, EUV lithography, which is an exposure technique using EUV light having a wavelength shorter than that of an ArF laser, is promising as an exposure technique for 45 nm and beyond. In this specification, EUV light refers to light having a wavelength in the soft X-ray region or vacuum ultraviolet region, and specifically refers to light having a wavelength of about 10 to 20 nm, particularly about 13.5 nm ± 0.3 nm.

  Since EUV light is easily absorbed by any material and the refractive index of the material is close to 1 at this wavelength, a conventional refractive optical system such as photolithography using visible light or ultraviolet light may be used. Can not. For this reason, in the EUV light lithography, a reflective optical system, that is, a reflective photomask and a mirror are used.

The mask blank is a layered body before patterning used for manufacturing a photomask.
In the case of an EUV mask blank, a reflective layer that reflects EUV light and an absorber layer that absorbs EUV light are formed in this order on a substrate such as glass. As the reflective layer, a multilayer reflective film is generally used in which a high refractive layer and a low refractive layer are alternately laminated to increase the light reflectivity when EUV light is irradiated onto the layer surface. For the absorber layer, a material having a high absorption coefficient for EUV light, specifically, for example, a material mainly composed of Ta or Cr is used.

  On the absorber layer of the EUV mask blank, a low reflection layer for mask pattern inspection light is usually provided. For the presence or absence of pattern defects after the mask pattern is formed, light in the wavelength region of deep ultraviolet light (190 to 260 nm) is used. In the pattern inspection using the light beam in the above wavelength range, the reflectance difference between the region where the low reflection layer and the absorber layer are removed by the patterning process and the region where the low reflection layer and the absorber layer remain, that is, The presence or absence of pattern defects is inspected by the contrast of reflected light on the surfaces of these regions. In order to improve the inspection sensitivity of the mask pattern, it is necessary to increase the contrast. For this purpose, the low reflection layer has low reflection characteristics with respect to the above wavelength range, that is, with respect to the above wavelength range. The reflectivity is required to be 15% or less.

In Patent Document 1, a low reflective layer made of a tantalum boron alloy oxide (TaBO) or a tantalum boron alloy oxynitride (TaBNO) is formed on an absorber layer made of a tantalum boron alloy nitride (TaBN). This is preferable because the reflectance of the mask pattern with respect to the wavelength range (190 nm to 260 nm) of the inspection light is low.
Patent Document 2 discloses that a metal, silicon (Si), oxygen (O), and nitrogen (N) are formed on the absorber layer in order to adjust the reflectance of the mask pattern with respect to the wavelength range (190 nm to 260 nm) of the inspection light. It is preferable to provide a low reflection layer made of

Japanese Patent Laid-Open No. 2004-6798 JP 2006-228767 A

  In Patent Document 1, when the low reflection layer is a TaBO film or a TaBNO film, a sufficient contrast is obtained with respect to the wavelength 257 nm of the inspection light of the mask pattern currently used. As the pattern is further miniaturized in the future, it is predicted that the inspection light of the mask pattern will be shortened to a wavelength of about 190 to 199 nm. However, in Patent Document 1, for a wavelength range of about 190 to 199 nm, There is no indication as to whether these films exhibit low reflection properties.

  On the other hand, in Patent Document 2, the oxygen concentration, the nitrogen concentration and the film thickness of a material (for example, TaSiON, ZrSiON, etc.) made of metal, silicon (Si), oxygen (O) and nitrogen (N) are adjusted as the low reflection layer. As a result, low reflection characteristics can be obtained with respect to 257 nm, which is the wavelength of the inspection light of the mask pattern currently used, and 193 nm, which is the wavelength of the inspection light of the mask pattern that is expected to be used in the future. It is possible. However, the reflectivity of the surface of the low reflection layer for these wavelengths is not specifically shown. In addition, when the above materials are used for the low reflection layer, the mask pattern is inspected in order to develop low reflection characteristics. It is necessary to adjust the oxygen concentration, the nitrogen concentration, and the film thickness in accordance with the wavelength of light, and it is necessary to strictly control the film composition and the film thickness. Furthermore, changing the film composition and film thickness necessitates new optimization of etching conditions during mask patterning.

  In order to solve the above-described problems of the prior art, the present invention is excellent in characteristics as an EUV mask blank, that is, has a low reflectivity with respect to the wavelength range of the EUV light and the inspection light of the mask pattern. An object of the present invention is to provide an EUV mask blank having a low reflection layer exhibiting low reflection characteristics with respect to the entire wavelength range (190 to 260 nm) of light. In other words, the present invention has a low reflection layer capable of maintaining low reflection characteristics without changing the film composition and film thickness over the entire wavelength range (190 to 260 nm) of the inspection light of the mask pattern. An object is to provide an EUV mask blank.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have made the low reflection layer a film containing Hf, O and N (HfON film), so that the entire wavelength region (190 of the inspection light of the mask pattern) can be obtained. It has been found that the low reflection characteristics can be maintained without changing the film composition and film thickness of the low reflection layer.

The present invention has been made on the basis of the above findings, and on a substrate, a reflective layer that reflects EUV light, an absorber layer that absorbs EUV light, and mask pattern inspection light (wavelength 190 to 260 nm). A reflective mask blank for EUV lithography in which a low-reflection layer is formed in this order,
The low reflective layer contains hafnium (Hf), nitrogen (N) and oxygen (O) in a total content of 80 at% or more, and a reflective mask blank for EUV lithography (hereinafter referred to as “EUV of the present invention”). "Mask blank").

In the EUV mask blank of the present invention, in the low reflection layer, the content of Hf is 10 to 80 at%, the total content of N and O is 20 to 90 at%, and the composition (atom) ratio of N and O Is preferably N: O = 9: 1 to 1: 9.
In the EUV mask blank of the present invention, the low reflective layer preferably has a tantalum (Ta) content of 10 at% or less.
In the EUV mask blank of the present invention, the low reflection layer may contain 0.1 to 1.0 at% of Zr.
In the EUV mask blank of the present invention, the surface roughness (rms) of the surface of the low reflective layer is preferably 0.5 nm or less.
In the EUV mask blank of the present invention, it is preferable that the crystal structure of the low reflective layer is amorphous.
In the EUV mask blank of the present invention, the low reflective layer preferably has a thickness of 3 to 30 nm.

In the EUV mask blank of the present invention, the absorber layer is preferably an absorber layer containing tantalum (Ta) as a main component.
In the EUV mask blank of the present invention, the absorber layer contains tantalum (Ta) as a main component, and contains hafnium (Hf), silicon (Si), zirconium (Zr), germanium (Ge), boron (B), and nitrogen ( It may contain at least one element selected from N).
In the EUV mask blank of the present invention, the absorber layer preferably has an oxygen (O) content of less than 25 at%.
In the EUV mask blank of the present invention, the absorber layer preferably has a thickness of 50 to 200 nm.

Further, in the EUV mask blank of the present invention, a protective layer for protecting the reflective layer is formed between the reflective layer and the absorber layer when forming a pattern on the absorber layer,
The contrast between the reflected light on the surface of the protective layer and the reflected light on the surface of the low reflective layer with respect to the wavelength (190 to 260 nm) of the inspection light of the mask pattern is preferably 60% or more.
In the EUV mask blank of the present invention, when a protective layer is formed between the reflective layer and the absorber layer, the protective layer is formed of any one of Ru, Ru compound, SiO ₂ and CrN. It is preferable.

  In the EUV mask blank of the present invention, the reflectance of the low reflective layer surface with respect to the wavelength (190 to 260 nm) of the inspection light of the mask pattern is preferably 15% or less.

In the EUV mask blank of the present invention, the low reflective layer is preferably formed by performing a sputtering method using an Hf target in an inert gas atmosphere containing nitrogen (N) and oxygen (O).
Here, the Hf target may contain 0.1 to 5.0 at% of Zr.

Further, according to the present invention, a reflective layer that reflects EUV light, an absorber layer that absorbs EUV light, and a low reflective layer for mask pattern inspection light (wavelength 190 to 260 nm) are formed in this order on the substrate. A method of manufacturing a reflective mask blank for EUV lithography,
A reflective mask blank for EUV lithography, wherein the low reflective layer is formed by performing a sputtering method using an Hf target in an inert gas atmosphere containing nitrogen (N) and oxygen (O). A manufacturing method is provided.
Here, the Hf target may contain 0.1 to 5.0 at% of Zr.

  The EUV mask blank of the present invention can be used for inspection of a mask pattern expected to be used in the future in addition to the wavelength of inspection light (257 nm) of the current mask pattern without changing the film composition and film thickness of the low reflection layer. It exhibits low reflection characteristics with respect to the entire wavelength range (190 to 260 nm) of the inspection light of the mask pattern including the light wavelength range (190 to 199 nm), and the reflectance of the surface of the low reflection layer with respect to the wavelength range is 15% or less. is there. Therefore, when the wavelength of the inspection light of the mask pattern shifts from 257 nm to around 190 to 199 nm in the future, it is not necessary to adjust the film composition and film thickness of the low reflection layer, so it is necessary to adjust complicated film forming conditions. Absent. In addition, when the wavelength of the inspection light of the mask pattern shifts from 257 nm to around 190 to 199 nm, it is not necessary to change the film composition and film thickness of the low reflection layer, so that the etching conditions are newly optimized in the patterning process. This has the advantage that conventional etching techniques can be used as they are.

Hereinafter, the EUV mask blank of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing an embodiment of the EUV mask blank of the present invention. In the mask blank 1 shown in FIG. 1, a reflective layer 12 that reflects EUV light and an absorber layer 14 that absorbs EUV light are formed on a substrate 11 in this order. A protective layer 13 is formed between the reflective layer 12 and the absorber layer 14 to protect the reflective layer 12 when forming a pattern on the absorber layer 14. On the absorber layer 14, a low reflection layer 15 for the inspection light of the mask pattern is formed. However, in the EUV mask blank 1 of the present invention, only the substrate 11, the reflective layer 12, the absorber layer 14, and the low reflective layer 15 are essential in the configuration shown in FIG. 1, and the protective layer 13 is an optional component. .
Hereinafter, individual components of the mask blank 1 will be described.

The substrate 11 is required to satisfy the characteristics as a substrate for an EUV mask blank.
Therefore, the substrate 11, the low thermal expansion coefficient (specifically, it is preferable that the thermal expansion coefficient at 20 ° C. is ^{0 ± 0.05 × 10 -7 / ℃} , particularly preferably 0 ± 0.03 × 10 ^{- 7} / ° C.) and excellent in smoothness, flatness, and resistance to a cleaning liquid used for cleaning a mask blank or a photomask after pattern formation. Specifically, the substrate 11 is made of glass having a low thermal expansion coefficient, such as SiO ₂ —TiO ₂ glass, but is not limited thereto, and is not limited to crystallized glass, quartz glass, silicon, A substrate made of metal or the like can also be used.
The substrate 11 preferably has a smooth surface with a surface roughness (rms) of 0.15 nm or less and a flatness of 100 nm or less in order to obtain high reflectivity and transfer accuracy in a photomask after pattern formation. .
The size, thickness, etc. of the substrate 11 are appropriately determined by the design value of the mask. In the examples described later, SiO ₂ —TiO ₂ glass having an outer shape of 6 inches (152 mm) square and a thickness of 0.25 inches (6.3 mm) was used.
It is preferable that the surface of the substrate 11 on the side where the reflective layer 12 is formed has no defects. However, even if it exists, the depth of the concave defect and the height of the convex defect are not more than 2 nm so that the phase defect does not occur due to the concave defect and / or the convex defect. It is preferable that the half width of the defect and the convex defect is 60 nm or less.

  The reflective layer 12 is not particularly limited as long as it has desired characteristics as a reflective layer of an EUV mask blank. Here, the characteristic particularly required for the reflective layer 12 is a high EUV light reflectance. Specifically, when the surface of the reflective layer 12 is irradiated with light in the wavelength region of EUV light at an incident angle of 6 degrees, the maximum value of light reflectance near a wavelength of 13.5 nm is preferably 60% or more, More preferably, it is 65% or more. Even when the protective layer 13 and the low reflective layer 15 are provided on the reflective layer 12, the maximum value of the light reflectance near the wavelength of 13.5 nm is preferably 60% or more, and 65% or more. It is more preferable that

  Since the reflective layer 12 can achieve a high EUV light reflectance, a multilayer reflective film in which a high refractive layer and a low refractive index layer are alternately laminated a plurality of times is usually used as the reflective layer 12. In the multilayer reflective film forming the reflective layer 12, Mo is widely used for the high refractive index layer, and Si is widely used for the low refractive index layer. That is, the Mo / Si multilayer reflective film is the most common. However, the multilayer reflective film is not limited to this, and Ru / Si multilayer reflective film, Mo / Be multilayer reflective film, Mo compound / Si compound multilayer reflective film, Si / Mo / Ru multilayer reflective film, Si / Mo / Ru / A Mo multilayer reflective film and a Si / Ru / Mo / Ru multilayer reflective film can also be used.

  The thickness of each layer constituting the multilayer reflective film constituting the reflective layer 12 and the number of repeating units of the layers can be appropriately selected according to the film material used and the EUV light reflectance required for the reflective layer. Taking the Mo / Si reflective film as an example, in order to obtain the reflective layer 12 having a maximum EUV light reflectance of 60% or more, the multilayer reflective film is composed of a Mo layer having a film thickness of 2.3 ± 0.1 nm, A Si layer having a thickness of 4.5 ± 0.1 nm may be laminated so that the number of repeating units is 30 to 60.

In addition, what is necessary is just to form each layer which comprises the multilayer reflective film which comprises the reflective layer 12 so that it may become desired thickness using well-known film-forming methods, such as a magnetron sputtering method and an ion beam sputtering method. For example, when an Si / Mo multilayer reflective film is formed by ion beam sputtering, an Si target is used as a target, and Ar gas (gas pressure 1.3 × 10 ⁻² Pa to 2.7 × 10 ⁻ is used as a sputtering gas. ² Pa), an Si film is formed to have a thickness of 4.5 nm at an ion acceleration voltage of 300 to 1500 V and a film formation rate of 0.03 to 0.30 nm / sec. using a target, using an Ar gas (gas pressure ^{1.3 × 10 -2 Pa~2.7 × 10 -2} Pa), an ion acceleration voltage 300 to 1,500 V, the deposition rate of 0.03 to 0 It is preferable to form the Mo film so that the thickness is 2.3 nm at 30 nm / sec. With this as one period, the Si / Mo multilayer reflective film is formed by laminating the Si film and the Mo film for 40 to 50 periods.

  In order to prevent the surface of the reflective layer 12 from being oxidized, it is preferable that the uppermost layer of the multilayer reflective film forming the reflective layer 12 is a layer made of a material that is difficult to be oxidized. The layer of material that is not easily oxidized functions as a cap layer of the reflective layer 12. As a specific example of the layer of a material that hardly functions to be oxidized and functions as a cap layer, a Si layer can be exemplified. When the multilayer reflective film forming the reflective layer 12 is an Si / Mo film, the uppermost layer can be made to function as a cap layer by making the uppermost layer an Si layer. In that case, the thickness of the cap layer is preferably 11 ± 2 nm.

The protective layer 13 is provided for the purpose of protecting the reflective layer 12 so that the reflective layer 12 is not damaged by the etching process when the absorber layer 14 is patterned by an etching process, usually a dry etching process. . Therefore, as the material of the protective layer 13, a material that is not easily affected by the etching process of the absorber layer 14, that is, the etching rate is slower than that of the absorber layer 14 and is not easily damaged by the etching process is selected. Examples of the material satisfying this condition include Cr, Al, Ta and nitrides thereof, Ru and Ru compounds (RuB, RuSi, etc.), and SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ and mixtures thereof. Is done. Among these, Ru and Ru compounds (RuB, RuSi, etc.), CrN and SiO ₂ are preferable, and Ru and Ru compounds (RuB, RuSi, etc.) are particularly preferable.
The thickness of the protective layer 13 is preferably 1 to 60 nm.

The protective layer 13 is formed using a known film formation method such as magnetron sputtering or ion beam sputtering. When a Ru film is formed by magnetron sputtering, a Ru target is used as a target, and Ar gas (gas pressure: 1.0 × 10 ⁻² Pa to 10 × 10 ⁻¹ Pa) is used as a sputtering gas. It is preferable to form a film so that the thickness is 2 to 5 nm at ˜1500 V and a film formation rate of 0.02 to 1.0 nm / sec.

The characteristic particularly required for the absorber layer 14 is that the EUV light reflectance is extremely low. Specifically, when the surface of the absorber layer 14 is irradiated with light in the wavelength region of EUV light, the maximum light reflectance near a wavelength of 13.5 nm is preferably 0.5% or less, 0.1% The following is more preferable.
In the EUV mask blank 1 of the present invention, even when the surface of the low reflection layer 15 is irradiated with light in the wavelength region of EUV light, the maximum light reflectance near a wavelength of 13.5 nm may be 0.5% or less. Preferably, it is 0.1% or less.

In order to achieve the above characteristics, the absorber layer 14 is made of a material having a high EUV light absorption coefficient. As a material having a high EUV light absorption coefficient, a material mainly composed of tantalum (Ta) is preferably used. In this specification, a material containing tantalum (Ta) as a main component means a material containing Ta in the material at 40 at% or more, preferably 50 at% or more, more preferably 55 at% or more.
The material mainly composed of Ta used for the absorber layer 14 is selected from hafnium (Hf), silicon (Si), zirconium (Zr), germanium (Ge), boron (B) and nitrogen (N) in addition to Ta. It may contain at least one element. Specific examples of the material containing the above element other than Ta include TaN, TaHf, TaHfN, TaBSi, TaBSiN, TaB, TaBN, TaSi, TaSiN, TaGe, TaGeN, TaZr, TaZrN, and the like.

  However, it is preferable that the absorber layer 14 does not contain oxygen (O). Specifically, the O content in the absorber layer 14 is preferably less than 25 at%. When forming a pattern on the absorber layer 14, a dry etching process is usually used. As an etching gas, a chlorine-based gas (or a mixed gas including a chlorine-based gas) or a fluorine gas (or a mixed gas including a fluorine-based gas) is used. Gas) is usually used. When a film containing Ru or a Ru compound is formed as a protective layer on the reflective layer for the purpose of preventing the reflective layer from being damaged by the etching process, the protective layer is less damaged, so that it is mainly used as an etching gas. Chlorine-based gas is used. However, when the dry etching process is performed using a chlorine-based gas, if the absorber layer 14 contains oxygen, the etching rate is lowered, and resist damage is increased, which is not preferable. The oxygen content in the absorber layer 14 is preferably 15 at% or less, more preferably 10 at% or less, and even more preferably 5 at% or less.

  The thickness of the absorber layer 14 is preferably set so that the total thickness of the absorber layer 14 and the low reflection layer 15 is 50 to 200 nm.

The absorber layer 14 having the above-described configuration can be formed by performing a known film forming method, for example, a magnetron sputtering method or an ion beam sputtering method.
For example, when a TaHf film is formed as the absorber layer 14 by using a magnetron sputtering method, it may be performed under the following conditions.
Sputtering target: TaHf compound target (Ta = 30 to 70 at%, Hf = 70 to 30 at%)
Sputtering gas: an inert gas (gas pressure ^{1.0 × 10 -1 Pa~50 × 10 -1} Pa , such as Ar gas, preferably ^{1.0 × 10 -1 Pa~40 × 10 -1} Pa, more preferably 1.0 × 10 ⁻¹ Pa to 30 × 10 ⁻¹ Pa)
Vacuum degree before film formation: 1 × 10 ⁻⁴ Pa or less, preferably 1 × 10 ⁻⁵ Pa or less, more preferably 10 ⁻⁶ Pa or less Input power: 30 to 1000 W, preferably 50 to 750 W, more preferably 80 to 500W
Deposition rate: 2.0-60 nm / min, preferably 3.5-45 nm / min, more preferably 5-30 nm / min
Moreover, what is necessary is just to implement on the following conditions, when forming a TaN layer as the absorber layer 14 using a magnetron sputtering method.
Sputtering target: Ta target Sputtering gas: N ₂ gas (gas pressure ^{1.0 × 10 -1 Pa~50 × 10 -1} Pa diluted with an inert gas such as Ar gas, preferably 1.0 × 10 ^-1 Pa ~40 × 10 ^-1 Pa, more preferably ^{1.0 × 10 -1 Pa~30 × 10 -1} Pa)
Vacuum degree before film formation: 1 × 10 ⁻⁴ Pa or less, preferably 1 × 10 ⁻⁵ Pa or less, more preferably 10 ⁻⁶ Pa or less Input power: 30 to 1000 W, preferably 50 to 750 W, more preferably 80 to 500W
Deposition rate: 2.0-60 nm / min, preferably 3.5-45 nm / min, more preferably 5-30 nm / min

  The low reflection layer 15 is composed of a film exhibiting low reflection characteristics with respect to the wavelength of inspection light used for inspection of the mask pattern. When producing an EUV mask, after forming a pattern in an absorber layer, it is inspected whether this pattern is formed as designed. In the inspection of the mask pattern, an inspection machine using light of about 257 nm is currently used as inspection light. However, as the pattern width becomes smaller, the wavelength used for the inspection light becomes shorter, and it is predicted that wavelengths of 190 to 199 nm will be used in the future. That is, the difference in reflectance with respect to the inspection light having such a wavelength, specifically, the surface where the absorber layer 14 is removed by pattern formation and the surface of the absorber layer 14 that remains without being removed by pattern formation. And the difference in reflectivity, that is, the contrast of reflected light on these surfaces. Here, the former is the surface of the reflective layer 12. However, when the protective layer 13 is formed on the reflective layer 12, it is the surface of the protective layer 13. Therefore, if the difference in reflectance between the surface of the reflective layer 12 or the protective layer 13 and the surface of the absorber layer 14 with respect to the wavelength of the inspection light is small, the contrast at the time of inspection deteriorates and accurate inspection cannot be performed. .

  The absorber layer 14 having the above-described configuration has extremely low EUV light reflectance, and has excellent characteristics as the absorber layer of the EUV mask blank 1, but when viewed with respect to the wavelength of inspection light, the light reflectance is low. It is not necessarily low enough. As a result, the difference between the reflectance on the surface of the absorber layer 14 and the reflectance on the surface of the protective layer 13 with respect to the wavelength of the inspection light becomes small, and there is a possibility that sufficient contrast at the time of inspection cannot be obtained. If sufficient contrast at the time of inspection is not obtained, pattern defects cannot be sufficiently determined in the inspection of the mask pattern, and accurate defect inspection cannot be performed.

In the EUV mask blank 1 of the present invention, by forming the low reflection layer 15 for the inspection light of the mask pattern on the absorber layer 14, the contrast at the time of inspection becomes good. In the case of the EUV mask blank 1 of the present invention, the contrast of the reflected light is the difference in reflectance between the surface of the reflective layer 12 and the surface of the low reflective layer 15 with respect to the wavelength of the inspection light. However, when the protective layer 13 is formed on the reflective layer 12, this is the difference in reflectance between the surface of the protective layer 13 and the surface of the low reflective layer 15.
In the EUV mask blank 1 of the present invention, by forming the low reflection layer 15 on the absorber layer 14, the light reflectance is extremely low with respect to the entire wavelength range (190 to 260 nm) of the inspection light of the mask pattern. Specifically, when the surface of the low reflection layer 15 is irradiated with light in the wavelength range (190 to 260 nm) of the inspection light of the mask pattern, the reflection is low with respect to the entire wavelength range (190 to 260 nm) of the inspection light. The light reflectance on the surface of the layer 15 is preferably 15% or less, more preferably 10% or less, and further preferably 8% or less.
If the maximum light reflectance on the surface of the low reflection layer 15 is 15% or less with respect to the entire wavelength range (190 to 260 nm) of the inspection light of the mask pattern, the contrast at the time of inspection regardless of the wavelength of the inspection light of the mask pattern Is good. Specifically, with respect to the entire wavelength range (190 to 260 nm) of the inspection light of the mask pattern, the reflected light on the surface of the reflective layer 12 (the surface of the protective layer 13 when the protective layer 13 is formed on the reflective layer 12) The contrast between the reflected light on the surface of the low reflective layer 15 and the reflected light on the surface of the low reflective layer 15 is 60% or more.

In this specification, the contrast can be obtained using the following equation.
Contrast (%) = ((R ₂ −R ₁ ) / (R ₂ + R ₁ )) × 100
Here, R ₂ is the reflectance at the surface of the reflective layer 12 with respect to the wavelength of the inspection light. However, when the protective layer 13 is formed on the reflective layer 12, the reflectance is the surface of the protective layer 13. R ₁ is the reflectance at the surface of the low reflection layer 15 with respect to the wavelength of the inspection light. The above R ₁ and R ₂ are, as shown in FIG. 2, is measured in a state of forming a pattern on the absorber layer 14 and the low reflective layer 15 of the EUV mask blank 1 shown in Figure 1. The R ₂ is a value measured on the surface of the reflective layer 12 or the protective layer 13 exposed to the outside after the absorber layer 14 and the low reflective layer 15 are removed by pattern formation in FIG. 2, and R ₁ is the pattern formation. This is a value measured on the surface of the low reflective layer 15 remaining without being removed by.
In the present invention, the contrast represented by the above formula is more preferably 65% or more, and further preferably 70% or more.

In order to achieve the above characteristics, the low reflective layer 15 is preferably made of a material having a refractive index higher than that of the absorber layer 14 with respect to the wavelength range of the inspection light of the mask pattern, and its crystalline state is preferably amorphous.
In the low reflective layer 15 of the EUV mask blank 1 of the present invention, the above characteristics are achieved by containing hafnium (Hf), oxygen (O), and nitrogen (N) in a total content of 80 at% or more.
The low reflective layer 15 preferably contains these elements in specific ratios described below.

  The low reflective layer 15 preferably has a Hf content of 10 to 80 at%. The total content of N and O is preferably 20 to 90 at%. The composition (atom) ratio of N and O is preferably 9: 1 to 1: 9. If the Hf content is less than 10 at%, the conductivity of the low reflective layer 15 is lowered, and there is a possibility that a charge-up problem may occur when drawing an electron beam on the low reflective layer 15. If the total content of Hf is more than 80 at%, there is a possibility that the light reflectance for the wavelength range of the inspection light of the mask pattern cannot be made sufficiently low. Further, when the N and O content is lower than 20 at%, there is a possibility that the light reflectivity with respect to the wavelength range of the inspection light of the mask pattern cannot be sufficiently lowered. When the content ratio of N and O is higher than 90 at%, the acid resistance of the low reflective layer 15 decreases, the insulation of the low reflective layer 15 increases, and charge-up occurs when drawing an electron beam on the low reflective layer 15. Problems can arise. Most preferably, the content of Hf is 10 to 80 at%, the total content of N and O is 20 to 90 at%, and the composition ratio of N and O is 9: 1 to 1: 9. .

The content of Hf is more preferably 15 to 80 at%, further preferably 20 to 80 at%, and particularly preferably 30 to 70 at%. Further, the content of N and O is more preferably 20 to 85 at%, further preferably 20 to 80 at%, and particularly preferably 30 to 70 at%. The composition ratio of N and O is preferably 8.3: 1.7 to 1.7: 8.3 (that is, the value of oxygen / (nitrogen + oxygen) is 17 to 83%). 5: 1.5 to 1.5: 8.5 is more preferable, and 1: 1 to 1.5: 8.5 is particularly preferable.
Further, in the low reflective layer of the EUV mask blank, the content of Ta is preferably 10 at% or less, particularly preferably 5 at% or less, from the viewpoint of reflectivity with respect to 199 nm and 193 nm. It is preferable to reduce the Ta content because the characteristics of Hf can be sufficiently exhibited.

  The low reflection layer 15 may contain 0.1 to 1.0 at% of Zr from the target used during film formation.

Since the low reflection layer 15 has the above-described configuration, the crystal state thereof is preferably amorphous. Note that in this specification, the phrase “crystalline state is amorphous” includes a microcrystalline structure other than an amorphous structure having no crystal structure.
When the low reflective layer 15 is an amorphous structure film or a microcrystalline structure film, the surface roughness (rms) of the surface of the low reflection layer 15 is preferably 0.5 nm or less. Here, the surface roughness of the surface of the absorber layer 15 can be measured using an atomic force microscope (Atomic Force Microscope). If the surface roughness of the surface of the low reflection layer 15 is large, the edge roughness of the pattern formed on the low reflection layer 15 increases, and the dimensional accuracy of the pattern deteriorates. Since the influence of edge roughness becomes more prominent as the pattern becomes finer, the surface of the low reflection layer 15 is required to be smooth.
If the surface roughness (rms) of the surface of the low reflection layer 15 is 0.5 nm or less, the surface of the low reflection layer 15 is sufficiently smooth, and there is no possibility that the dimensional accuracy of the pattern is deteriorated due to the influence of edge roughness. The surface roughness (rms) of the surface of the low reflective layer 15 is more preferably 0.4 nm or less, and further preferably 0.3 nm or less.

  It can be confirmed by the X-ray diffraction (XRD) method that the crystal state of the low reflection layer 15 is amorphous, that is, an amorphous structure or a microcrystalline structure. If the crystal state of the low reflective layer 15 is an amorphous structure or a microcrystalline structure, a sharp peak is not observed in a diffraction peak obtained by XRD measurement.

  The total film thickness of the absorber layer 14 and the low reflection layer 15 is preferably 50 to 200 nm. Further, if the thickness of the low reflective layer 15 is larger than the thickness of the absorber layer 14, the EUV light absorption characteristics in the absorber layer 14 may be deteriorated. It is preferably smaller than the film thickness of the layer. For this reason, it is preferable that the thickness of the low reflection layer 15 is 3-30 nm, and it is more preferable that it is 5-20 nm.

The low reflection layer 15 having the above-described configuration can be formed by performing a sputtering method using an Hf target, for example, a magnetron sputtering method or an ion beam sputtering method.
The low reflection layer 15 having the above-described configuration is formed by discharging the Hf target in an oxygen (O ₂ ) / nitrogen (N ₂ ) mixed gas atmosphere diluted with an inert gas such as argon (Ar). Alternatively, after a film containing Hf and N is formed by discharging the Hf target in a nitrogen (N ₂ ) atmosphere diluted with an inert gas such as argon (Ar), the film is exposed to, for example, oxygen plasma, or oxygen The low reflection layer 15 containing Hf, O, and N may be obtained by oxidizing the formed film by irradiating an ion beam using the above.
The Hf target may contain 0.1 to 5.0 at% of Zr.

In order to form the low reflection layer 15 on the absorber layer 14 by the method described above, specifically, the following film formation conditions may be used.
Deposition conditions for the low reflective layer 15 (HfON film) <br/> sputtering gas: Ar, O ₂ and a mixed gas of N ₂ (Ar gas concentration 3~80vol%, preferably 5~70vol%, more preferably 10 to 60 vol%, O ₂ gas concentration 3 to 80 vol%, preferably 5 to 70 vol%, more preferably 10 to 60 vol%, N ₂ gas concentration 3 to 80 vol%, preferably 5 to 70 vol%, more preferably 10 to 60 vol% ; gas pressure preferably ^{1.0 × 10 -2 Pa~40 × 10 -1} Pa, more preferably ^{1.0 × 10 -1 Pa~30 × 10 -1} Pa)
Input power: 30 to 1000 W, preferably 50 to 750 W, more preferably 80 to 500 W
Deposition rate: 0.1 to 60 nm / min, preferably 0.5 to 45 nm / min, more preferably 1 to 30 nm / min
When an inert gas other than Ar is used, the concentration of the inert gas is set to the same concentration range as the Ar gas concentration described above.

The EUV mask blank 1 of the present invention may have a functional film known in the field of EUV mask blanks in addition to the reflective layer 12, the protective layer 13, the absorber layer 14, and the low reflective layer 15. As a specific example of such a functional film, for example, as described in JP-A-2003-501823, a high dielectric applied to the back side of the substrate in order to promote electrostatic chucking of the substrate. A functional coating. Here, the back surface of the substrate refers to the surface of the substrate 11 in FIG. 1 opposite to the side on which the reflective layer 12 is formed. For the high dielectric coating applied to the back surface of the substrate for such a purpose, the electrical conductivity and thickness of the constituent material are selected so that the sheet resistance is 100Ω / □ or less. The constituent material of the high dielectric coating can be widely selected from those described in known literature. For example, a high dielectric constant coating described in JP-A-2003-501823, specifically, a coating made of silicon, TiN, molybdenum, chromium, or TaSi can be applied. The thickness of the high dielectric coating can be, for example, 10 to 1000 nm.
The high dielectric coating can be formed using a known film forming method, for example, a sputtering method such as a magnetron sputtering method or an ion beam sputtering method, a CVD method, a vacuum evaporation method, or an electrolytic plating method.

The present invention will be further described below using examples.
Example 1
In this example, the EUV mask blank 1 shown in FIG. 1 was produced.
As the substrate 11 for film formation, a SiO ₂ —TiO ₂ glass substrate (outer dimensions 6 inches (152 mm) square, thickness 6.3 mm) was used. This glass substrate has a thermal expansion coefficient of 0.2 × 10 ⁻⁷ / ° C., a Young's modulus of 67 GPa, a Poisson's ratio of 0.17, and a specific rigidity of 3.07 × 10 ⁷ m ² / s ² . This glass substrate was polished to form a smooth surface with a surface roughness (rms) of 0.15 nm or less and a flatness of 100 nm or less.

A high dielectric coating having a sheet resistance of 100Ω / □ was applied to the back side of the substrate 11 by depositing a Cr film having a thickness of 100 nm using a magnetron sputtering method.
A substrate 11 (outer diameter 6 inches (152 mm) square, thickness 6.3 mm) is fixed to a flat electrostatic chuck having a flat plate shape by using the formed Cr film, and ion beam sputtering is performed on the surface of the substrate 11. The Si / Mo multilayer reflective film (reflective layer 12) having a total film thickness of 272 nm ((4.5 nm + 2.3 nm) × 40) is obtained by repeating 40 cycles of alternately forming the Si film and the Mo film using the method. Formed.
Further, a protective layer 13 was formed by forming a Ru film (film thickness: 2.5 nm) on the Si / Mo multilayer reflective film (reflective layer 12) using an ion beam sputtering method.

The deposition conditions for the Si film, the Mo film, and the Ru film are as follows.
Conditions for forming the Si film Target: Si target (boron doped)
Sputtering gas: Ar gas (gas pressure 0.02 Pa)
Voltage: 700V
Deposition rate: 0.077 nm / sec
Film thickness: 4.5nm
Conditions for forming the Mo film Target: Mo target Sputtering gas: Ar gas (gas pressure 0.02 Pa)
Voltage: 700V
Deposition rate: 0.064 nm / sec
Film thickness: 2.3 nm
Ru film formation conditions Target: Ru Target sputtering gas: Ar gas (gas pressure 0.02 Pa)
Voltage: 500V
Deposition rate: 0.023 nm / sec
Film thickness: 2.5nm

Next, a TaHf film containing Ta and Hf was formed as the absorber layer 14 on the protective layer 13 by using a magnetron sputtering method.
The absorber layer 14 (TaHf film) was formed by the following method. The film composition is measured using an X-ray photoelectron spectrometer (manufactured by PERKIN ELEMER-PHI: No. 5500). The composition of the absorber layer is Ta: Hf = 55: 45. The O content in the absorber layer is 0.05 at% or less.
Film formation condition of absorber layer 14 (TaHf film) Target: TaHf compound target (composition ratio: Ta55at%, Hf45at%)
Sputtering gas: Ar gas (gas pressure: 0.3 Pa)
Input power: 150W
Deposition rate: 17.4 nm / min
Film thickness: 70nm
Vacuum degree before film formation: 4 × 10 ⁻⁶ Pa

Next, a low reflection layer 15 (HfON film) containing Hf, O and N is formed on the absorber layer 14 by using a magnetron sputtering method, so that the reflection layer 12 and the protective layer 13 are formed on the substrate 11. The EUV mask blank 1 in which the absorber layer 14 and the low reflection layer 15 were formed in this order was obtained.
The film forming conditions of the low reflective layer 15 (HfON film) are as follows.
Deposition conditions <br/> target of the low reflective layer 15 (HfON film): Hf target Sputtering gas: mixed gas of Ar and N ₂ and _{O 2 (Ar: 45vol%,} N 2: 23vol%, O 2: 32vol% Gas pressure: 0.3 Pa)
Input power: 150W
Deposition rate: 7.8 nm / min
Film thickness: 10nm

The following evaluations (1) to (4) were performed on the low reflective layer 15 (HfON film) of the EUV mask blank obtained by the above procedure.
(1) Film composition The composition of the low reflection layer 15 (HfON) is measured using an X-ray photoelectron spectrometer (manufactured by PERKIN ELEMER-PHI: number 5500). The composition ratio (at%) of the low reflection layer is Hf: N: O = 50: 15: 35.

(2) Crystal State The crystal state of the absorber layer 15 (HfON film) was confirmed with an X-ray diffractometer (manufactured by RIGAKU). Since no sharp peak was observed in the obtained diffraction peak, it was confirmed that the crystalline state of the low reflective layer 15 (HfON film) was an amorphous structure or a microcrystalline structure.

(3) Surface Roughness The surface roughness of the low reflection layer 15 (HfON film) is measured by a dynamic force mode using an atomic force microscope (SII, SPI-3800). The surface roughness measurement area is 1 μm × 1 μm, and SI-DF40 (manufactured by SII) is used as the cantilever.
The surface roughness (rms) of the low reflection layer is 0.30 nm.

(4) Evaluation of reflection characteristics (contrast evaluation)
In this example, when the protective layer 13 (Ru film) is formed, the reflectance of the mask pattern inspection light (wavelength 257 nm, 199 nm, 193 nm) on the surface of the protective layer 13 is measured by a spectrophotometer (HITACH UV-4100). It measured using. Further, after forming the low reflection layer 15 (HfON film), the reflectance of the inspection light of the mask pattern on the surface of the low reflection layer was measured. As a result, the reflectivities with respect to wavelengths of 257 nm, 199 nm, and 193 nm on the surface of the protective layer 13 were 56.0%, 53.6%, and 55%, respectively. On the other hand, the reflectance with respect to each wavelength on the surface of the low reflective layer 15 (HfON film) was 6.2%, 4.7%, and 5.9%, and all were 15% or less. When the contrast was obtained using these results and the above formula, the contrast at each wavelength was as follows.
Contrast at a wavelength of 257 nm: 79.9%
Contrast at a wavelength of 199 nm: 83.8%
Contrast at a wavelength of 193 nm: 80.6%
The contrast between the surface of the protective layer 13 and the surface of the low reflection layer 15 was 70% or more with respect to all the wavelength ranges of the inspection light of the mask pattern, and a sufficient contrast was obtained. About the obtained EUV mask blank 1, the EUV light (wavelength 13.5nm) is irradiated to the surface of the low reflection layer 15 (HfON film | membrane), and the reflectance of EUV light is measured. As a result, the reflectance of EUV light is 0.4%.

Example 2
In this example, the absorber layer 14 was implemented in the same procedure as in Example 1 except that a TaN film containing tantalum (Ta) and nitrogen (N) was formed using the magnetron sputtering method.
The absorber layer 14 (TaN film) was formed by the following method. The film composition was examined in the same manner as in Example 1. The composition of the absorber layer 14 was Ta: N = 57: 43. The O content in the absorber layer was 0.05 at% or less.
Deposition conditions <br/> target of the absorber layer 14 (TaN film): Ta target Sputtering gas: Ar and _{N 2 (Ar: 86vol%,} N 2: 14vol%, gas pressure: 0.3 Pa)
Input power: 150W
Deposition rate: 17.4 nm / min
Film thickness: 70nm
Vacuum degree before film formation: 4 × 10 ⁻⁶ Pa

Next, a low reflection layer 15 (HfON film) was formed on the absorber layer 14 (TaN) film in the same procedure as in Example 1, and the EUV mask blank 1 was obtained. The obtained EUV mask blank 1 was subjected to reflection characteristic evaluation (contrast evaluation) in the same procedure as in Example 1.
The reflectivities with respect to wavelengths of 257 nm, 199 nm, and 193 nm on the surface of the low reflective layer 15 (HfON film) were 6.4%, 4.2%, and 4.5%, and all were 15% or less. From these results and the reflectance of the surface of the protective layer 13, the contrast was determined using the above-described formula, and the contrast at each wavelength was as follows.
Contrast at a wavelength of 257 nm: 79.4%
Contrast at a wavelength of 199 nm: 85.5%
Contrast at a wavelength of 193 nm: 84.9%
The contrast between the surface of the protective layer 13 and the surface of the low reflection layer 15 was 70% or more with respect to all the wavelength ranges of the inspection light of the mask pattern, and a sufficient contrast was obtained. About the obtained EUV mask blank 1, the EUV light (wavelength 13.5nm) is irradiated to the surface of the low reflection layer 15 (HfON film | membrane), and the reflectance of EUV light is measured. As a result, the reflectance of EUV light is 0.5%.

Comparative Example 1
Comparative Example 1 was performed in the same procedure as in Example 1 except that the low reflective layer was an oxynitride of a tantalum hafnium alloy (TaHfON film). That is, the absorber layer 14 has a TaHf film, and the low reflection layer 15 has a TaHfON structure. The TaHfON film was produced under the following conditions using a TaHf target (Ta: Hf = 55 at%: 45 at%). The composition ratio (at%) of the low reflective layer 15 is measured by the same method as in Example 1. The composition ratio (at%) of the low reflective layer 15 is Ta: Hf: N: O = 35: 15: 15: 35.
The film forming conditions of the low reflective layer 15 (TaHfON film) are as follows.
Film formation conditions for the low reflective layer 15 (TaHfON film) Target: TaHf compound target (composition ratio: Ta55at%, Hf45at%)
Sputtering gas: Ar, N ₂ and O ₂ mixed gas (Ar: 45 vol%, N ₂ : 23 vol%, O ₂ : 32 vol%, gas pressure: 0.3 Pa)
Input power: 150W
Deposition rate: 6.8 nm / min
Film thickness: 10nm

The reflection characteristics of the low-reflection layer 15 (TaHfON film) of the EUV mask blank obtained by the above procedure were evaluated in the same manner as in Example 1. The reflectivity for the wavelengths 257 nm, 199 nm, and 193 nm on the surface of the low reflective layer 15 (HfON film) is 0.61%, 16.8%, and 15.9%, and the reflectivity is 15% at the wavelengths of 199 nm and 193 nm. It was over. When the contrast was obtained using these results and the above formula, the contrast at each wavelength was as follows.
Contrast at a wavelength of 257 nm: 97.8%
Contrast at a wavelength of 199 nm: 52.1%
Contrast at a wavelength of 193 nm: 55.1%
For the wavelength of 257 nm, the contrast between the surface of the protective layer 13 and the surface of the low reflection layer 15 was excellent at 90% or more, but for the wavelengths of 193 and 199 nm, the contrast was 60% or less. A sufficient contrast could not be obtained.

Comparative Example 2
Comparative Example 2 was carried out in the same procedure as Example 2 except that the low reflective layer was tantalum (Ta) oxynitride (TaON film). That is, the absorber layer 14 has a TaN film, and the low reflective layer 15 has a TaON structure. The TaON film was produced under the following conditions using a Ta target. The composition of the low reflection layer is measured by the same method as in Example 1. The composition ratio (at%) of the low reflection layer is TaN: O = 50: 15: 35.
The film forming conditions of the low reflective layer 15 (TaON film) are as follows.
Deposition conditions <br/> target of the low reflective layer 15 (TaON film): Ta target Sputtering gas: Ar and _{N 2 (Ar: 86vol%,} N 2: 14vol%, gas pressure: 0.3 Pa)
Input power: 150W
Deposition rate: 8.6 nm / min
Film thickness: 10nm

The reflection characteristics of the low reflective layer 15 (TaON film) of the EUV mask blank obtained by the above procedure were evaluated in the same manner as in Example 1. The reflectivity for the wavelengths 257 nm, 199 nm, and 193 nm on the surface of the low reflective layer 15 (TaON film) is 9.0%, 22.0%, and 23.0%, and the reflectivity is 15% at the wavelengths of 199 nm and 193 nm. It was over. When the contrast was obtained using these results and the above formula, the contrast at each wavelength was as follows.
Contrast at a wavelength of 257 nm: 72.3%
Contrast at a wavelength of 199 nm: 41.8%
Contrast at a wavelength of 193 nm: 41.0%
For the wavelength 257 nm, the contrast between the surface of the protective layer 13 and the surface of the low reflection layer 15 was 70% or more, which was a sufficient reflection contrast, but for the wavelengths 193 and 199 nm, the reflection contrast was 50% or less. And sufficient contrast could not be obtained.

FIG. 1 is a schematic cross-sectional view showing an embodiment of the EUV mask blank of the present invention. FIG. 2 shows a state where the absorber layer 14 and the low reflection layer 15 of the EUV mask blank 1 shown in FIG. 1 are patterned.

Explanation of symbols

1: EUV mask blank 11: Substrate 12: Reflective layer (multilayer reflective film)
13: Protective layer 14: Absorber layer 15: Low reflective layer

Claims (18)

For EUV lithography, a reflective layer that reflects EUV light, an absorber layer that absorbs EUV light, and a low reflective layer for mask pattern inspection light (wavelength 190 to 260 nm) are formed in this order on a substrate. A reflective mask blank,
The reflective mask blank for EUV lithography, wherein the low reflective layer contains hafnium (Hf), nitrogen (N), and oxygen (O) in a total content of 80 at% or more.   In the low reflection layer, the Hf content is 10 to 80 at%, the total content of N and O is 20 to 90 at%, and the composition (atom) ratio of N and O is N: O = 9: 1. The reflective mask blank for EUV lithography according to claim 1, which is ˜1: 9.   The reflective mask blank for EUV lithography according to claim 1, wherein the low reflective layer has a tantalum (Ta) content of 10 at% or less.   The reflective mask blank for EUV lithography according to any one of claims 1 to 3, wherein the low reflective layer contains 0.1 to 1.0 at% of Zr.   The reflective mask blank for EUV lithography according to any one of claims 1 to 4, wherein the surface roughness (rms) of the surface of the low reflective layer is 0.5 nm or less.   6. The reflective mask blank for EUV lithography according to claim 1, wherein the crystal structure of the surface of the low reflective layer is amorphous.   The reflective mask blank for EUV lithography according to any one of claims 1 to 6, wherein the low reflective layer has a thickness of 3 to 30 nm.   The reflective mask blank for EUV lithography according to any one of claims 1 to 7, wherein the absorber layer contains tantalum (Ta) as a main component.   The absorber layer has at least one selected from tantalum (Ta) as a main component and selected from hafnium (Hf), silicon (Si), zirconium (Zr), germanium (Ge), boron (B), and nitrogen (N). The reflective mask blank for EUV lithography according to any one of claims 1 to 8, characterized by comprising:   The reflective mask blank for EUV lithography according to any one of claims 1 to 9, wherein the absorber layer has an oxygen (O) content of less than 25 at%.   The reflective mask blank for EUV lithography according to any one of claims 1 to 10, wherein the absorber layer has a thickness of 50 to 200 nm. A protective layer is formed between the reflective layer and the absorber layer to protect the reflective layer when forming a pattern on the absorber layer.
The contrast between the reflected light on the surface of the protective layer and the reflected light on the surface of the low reflective layer with respect to the wavelength (190 to 260 nm) of the inspection light of the mask pattern is 60% or more. Item 12. A reflective mask blank for EUV lithography according to any one of Items 1 to 11. The reflective mask blank for EUV lithography according to claim 12, wherein the protective layer is formed of any one of Ru, Ru compound, SiO ₂ and CrN.   The reflective type for EUV lithography according to any one of claims 1 to 13, wherein the reflectance of the surface of the low reflective layer with respect to the wavelength (190 to 260 nm) of the inspection light of the mask pattern is 15% or less. Mask blank.   15. The low reflection layer is formed by performing a sputtering method using an Hf target in an inert gas atmosphere containing nitrogen (N) and oxygen (O). A reflective mask blank for EUV lithography described in 1.   The reflective mask blank for EUV lithography according to claim 15, wherein the Hf target contains 0.1 to 5.0 at% of Zr. A reflective layer for EUV lithography is formed by forming a reflective layer for reflecting EUV light, an absorber layer for absorbing EUV light, and a low reflective layer for mask pattern inspection light (wavelength 190 to 260 nm) in this order on the substrate. A method for manufacturing a mask blank, comprising:
A reflective mask blank for EUV lithography, wherein the low reflective layer is formed by performing a sputtering method using an Hf target in an inert gas atmosphere containing nitrogen (N) and oxygen (O). Production method.   The method for producing a reflective mask blank for EUV lithography according to claim 17, wherein the Hf target contains 0.1 to 5.0 at% of Zr.

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