JP2009210802A - Reflective mask blank for extreme ultraviolet lithography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflective mask blank for extreme ultraviolet (EUV) lithography in which the mask has low reflectance in a wavelength range of EUV light and pattern inspection light and has an absorbent layer that is easily controlled to a desired film composition and a film thickness. <P>SOLUTION: The reflective mask blank for EUV lithography has a reflection layer 12 reflecting EUV light and an absorbent layer 14 absorbing EUV light formed in this order on a substrate 11 wherein the absorbent layer contains tantalum (Ta) and hafnium (Hf), and the layer has a rate of an Hf content from 20 to 60 at%, a rate of a Ta content from 40 to 80 at% and a rate of an oxygen content of smaller than 25 at%. <P>COPYRIGHT: (C)2009,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, a material mainly composed of Cr or Ta, for example, is used.

In Patent Document 1, a tantalum boron alloy nitride (TaBN), a tantalum boron alloy oxide (TaBO), and a tantalum boron alloy oxynitride (TaBNO) have a high absorption coefficient for EUV light. Since the reflectivity of deep ultraviolet light in the wavelength region (190 nm to 260 nm) of pattern inspection light is low, it is considered preferable as a material for the absorber layer.
Further, Patent Documents 1 and 2 indicate that in order to make the surface of the absorber layer excellent in smoothness, the crystalline state of the absorber layer is preferably amorphous, and a TaBN film and a TaBO film. In order to make the crystal state of the TaBNO film amorphous, it is considered that the B content in these films is preferably 5 to 25 at%.

Japanese Patent Laid-Open No. 2004-6798 JP 2004-6799 A

However, when the absorber layer is a TaBO film or a TaBNO film, if the O content of the film increases, the insulation of the absorber layer increases, and charge-up occurs when drawing an electron beam on the absorber layer. Therefore, it is not preferable.
In manufacturing an EUVL mask, a dry etching method such as plasma etching, ion beam etching, or gas cluster ion beam etching is usually used to form a fine mask pattern having a pattern width of about 120 nm or less.
In manufacturing an EUVL mask, when forming a pattern on the absorber layer, a dry etching process is usually used. As an etching gas, a chlorine-based gas (or a mixed gas containing a chlorine-based gas) or a fluorine gas is used. (Or a mixed gas containing a fluorine-based 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 contains oxygen, the etching rate is lowered and resist damage is increased, which is not preferable.
On the other hand, when the absorber layer is a TaBN film, there is almost no possibility that charge-up occurs during electron beam drawing.

  When the absorber layer is a TaBN film, it is often formed using a magnetron sputtering method or the like, which is a method in which defects are not easily generated. At this time, for example, a TaBN film can be formed by using a Ta target and a B target and simultaneously discharging these targets in a nitrogen atmosphere. A TaBN film can also be formed by using a TaB compound target and discharging the compound target in a nitrogen atmosphere.

However, for example, in the case of a method using a Ta target and a B target, since the B target has a high resistance value and is a light element, the film formation rate is often 1/10 or less compared to the Ta target. . Therefore, as described in Patent Document 1, in order to add the B content (5 at% or more) necessary for making the crystalline state of the film amorphous, the deposition rate of the Ta target is decreased. Although it is necessary, it is not desirable because the production efficiency is significantly reduced.
On the other hand, in the method using the TaB compound target, for example, when a compound target containing 20 at% B and 80 at% Ta is used, the maximum content of B actually added to the film is about 6 at%. It is difficult to control the B content to 5 at% or more. Furthermore, when N is added, the B content of the film becomes 4 at% or less, and the crystalline state of the film cannot be made amorphous.
In order to solve this problem, an increase in the B content in the TaB compound target is expected (for example, B is 50 at%, Ta is 50 at%). As the B content increases, the density of the target decreases, and the workability deteriorates. Further, the resistance value of the TaB target is increased, the discharge becomes unstable, and the deposition rate is decreased. If the discharge becomes unstable, the composition and thickness of the film may vary, and in some cases, the film formation may become impossible.

  In order to solve the above-described problems of the prior art, the present invention is excellent in properties as an EUV mask blank, particularly has low reflectance in the wavelength region of EUV light and pattern inspection light, and has the desired film composition and film thickness. An object of the present invention is to provide an EUV mask blank having an absorber layer that can be easily controlled.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present application have made the absorber layer a film containing Ta and Hf (TaHf film), so that the crystalline state of the film becomes amorphous and excellent in optical characteristics. In addition, by reducing oxygen in the film, an absorber layer having excellent etching characteristics, particularly when using a chlorine-based gas (or a mixed gas containing a chlorine-based gas) as an etching gas, is obtained. I found out that Furthermore, it has been found that when this TaHf film is used as an absorber layer, it can be stably produced without causing a decrease in film formation rate.

The present invention has been made on the basis of the above knowledge, and a reflective type for EUV lithography in which a reflective layer that reflects EUV light and an absorber layer that absorbs EUV light are formed in this order on a substrate. A mask blank,
The absorber layer contains tantalum (Ta) and hafnium (Hf);
A reflective type for EUV lithography, wherein the absorber layer has a Hf content of 20 to 60 at%, a Ta content of 40 to 80 at%, and an oxygen content of less than 25 at%. A mask blank (hereinafter referred to as “EUV mask blank of the present invention”) is provided.

In the EUV mask blank of the present invention, the absorber layer preferably has a nitrogen (N) content of 35 at% or less.
In the EUV mask blank of the present invention, the absorber layer preferably has a total content of B, Si and Ge of 5 at% or less.
In the EUV mask blank of the present invention, the absorber layer may contain 0.1 to 1.0 at% of Zr.
In the EUV mask blank of the present invention, it is preferable that the crystalline state of the absorber layer is amorphous.
In the EUV mask blank of the present invention, the surface roughness (rms) of the absorber layer surface is preferably 0.5 nm or less.
In the EUV mask blank of the present invention, the absorber layer preferably has a thickness of 50 to 200 nm.

In the EUV mask blank of the present invention, a low reflection layer for inspection light used for inspection of a mask pattern may be formed on the absorber layer.
Further, in the EUV mask blank of the present invention, 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 of the light used for the inspection of the pattern formed on the absorber layer is preferably 30% or more. .

When a protective layer is formed between the reflective layer and the absorber layer, the protective layer is preferably formed of any one of Ru, Ru compound, SiO ₂ and CrN.

  When the low reflection layer is formed on the absorber layer, the reflectance of the surface of the low reflection layer with respect to the wavelength of light used for inspection of the pattern formed on the absorber layer is 15% or less. preferable.

In the EUV mask blank of the present invention, the absorber layer is preferably formed by performing a sputtering method using a TaHf compound target.
The absorber layer has an environment in which a gas containing oxygen atoms (for example, O ₂ , H ₂ O, CO ₂ etc.) is not substantially present, specifically, the total partial pressure of the gas containing oxygen atoms is It is preferably formed by performing a sputtering method using a TaHf compound target in an environment of 1.0 × 10 ⁻⁴ Pa or less.
In order to reduce the oxygen content in the absorber layer, a gas containing hydrogen (H ₂ ) may be used as the sputtering gas. When a gas containing hydrogen is used, the hydrogen concentration of the sputtering gas is preferably 3% or less.
Further, the absorber layer has an environment in which a gas containing nitrogen atoms (for example, N ₂ , NO, etc.) is substantially absent, specifically, the total partial pressure of the gas containing nitrogen atoms is 1 × 10 It is preferably formed by performing a sputtering method using a TaHf compound target in an environment of ⁻⁴ Pa or less.
Here, the composition of the TaHf compound target is preferably Ta = 30 to 70 at% and Hf = 70 to 30 at%.
The TaHf compound target may contain 0.1 to 5.0 at% of Zr.

  In the EUV mask blank of the present invention, since the absorber layer contains Hf having a low electrical resistivity, the absorber layer is formed as in the case where the absorber layer has a high electrical resistivity and contains insulating B. The film formation rate does not decrease during film formation, and the discharge does not become unstable during film formation. As a result, there is no possibility of causing problems such as variations in film composition and film thickness when the absorber layer is formed, and further, film formation becomes impossible.

In the EUV mask blank of the present invention, since the absorber layer has an amorphous crystal state, the absorber surface has excellent smoothness. As a result, the edge roughness of the pattern formed on the absorber layer does not increase, and the dimensional accuracy of the pattern does not deteriorate.
Further, the absorber layer has excellent characteristics as an EUV mask blank, such as low light reflectance of EUV light and low light reflectance in the wavelength region of pattern inspection light.
Further, since the absorber layer containing Ta and Hf has a higher etching rate than that of the TaBN film, an effect of reducing resist damage during etching is expected.
In addition, a reduction in resist thickness is expected due to a reduction in resist damage.
Moreover, in the EUV mask blank of the present invention, the oxygen content of the absorber layer is very low, less than 25 at%, so that the absorber layer has an etching characteristic, particularly a chlorine-based gas (or a mixed gas containing a chlorine-based gas) as an etching gas. Is excellent in etching characteristics.

  Furthermore, when the nitrogen content of the absorber layer is 35 at% or less, the crystal state of the absorber layer is likely to be amorphous, the light reflectance in the wavelength region of pattern inspection light can be reduced, the etching rate can be increased, and It is more excellent in that an increase in electrical resistivity can be suppressed.

  In the EUV mask blank of the present invention, by forming a low reflection layer on the absorber layer, the light reflectance in the wavelength region of pattern inspection light can be further reduced, and this is performed after pattern formation on the mask blank. The contrast at the time of pattern inspection is good. Furthermore, since the crystal structure of the low reflection layer is amorphous, the surface of the absorber is excellent in smoothness. As a result, the edge roughness of the pattern formed on the absorber layer does not increase, and the dimensional accuracy of the pattern does not deteriorate.

  In the EUV mask blank of the present invention, when an absorber layer and a low reflection layer are formed by a sputtering method, by using a TaHf compound target having a specific composition, discharge instability and film composition and film thickness variation Can be avoided.

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 inspection light used for inspection of a mask pattern is formed. However, in the EUV mask blank 1 of the present invention, only the substrate 11, the reflective layer 12 and the absorber layer 14 are essential in the configuration shown in FIG. 1, and the protective layer 13 and the low reflective layer 15 are optional components. .
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 forming the Ru film by a magnetron sputtering method, using a Ru target as the target, charged using Ar gas (gas pressure ^{1.0 × 10 -1 Pa~10 × 10 -1} Pa) as the sputtering gas power 30W It is preferable to form a film so as to have a thickness of 2 to 5 nm at a thickness of ˜500 W and a film formation rate of 5 to 50 nm / min.

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 order to achieve the above characteristics, it is preferable that the material is made of a material having a high EUV light absorption coefficient.
The absorber layer 14 of the EUV mask blank 1 of the present invention achieves the above characteristics by containing tantalum (Ta) and hafnium (Hf) in a specific ratio described below.

The Hf content of the absorber layer 14 is 20 to 60 at%. When the Hf content of the absorber layer 14 is less than 20 at%, the crystal state of the absorber layer 14 is unlikely to be amorphous. If the Hf content of the absorber layer 14 is more than 60 at%, the etching characteristics of the absorber layer are deteriorated and it is difficult to satisfy the required etching selectivity.
In the EUV mask blank of the present invention, when the Hf content of the absorber layer 14 is in the above range, the crystalline state of the absorber layer tends to be amorphous, and the surface of the absorber is excellent in smoothness. Further, the absorber layer 14 has excellent characteristics as an EUV mask blank, such as a low light reflectance of EUV light and a low light reflectance in the wavelength region of pattern inspection light.
As for the content rate of Hf of the absorber layer 14, it is more preferable that it is 30-50 at%, and it is further more preferable that it is 30-45 at%.

Patent Document 1 discloses a low-reflection layer composed of an absorber of inspection light used for mask pattern inspection, with an absorber layer formed of an absorber of exposure light in a short wavelength region including the extreme ultraviolet region as a lower layer. In an absorber having a two-layer structure in which H is an upper layer, Hf is mentioned as an example of a metal element contained in the upper layer and the lower layer, but a structure containing Ta and Hf is not described at all. In Patent Document 1, it is described that when the absorber layer is a TaBN film, a TaBO film, and a TaBNO film, the crystal state is amorphous. However, when the structure includes Hf, the crystal state is amorphous. It is not described at all.
In addition, it is widely known that a metal crystal can be made amorphous by mixing elements such as B and Si, and in Patent Document 1, the absorber layer is made amorphous by using it to smooth the surface. Yes. However, it is not known that a film containing two metal elements of Ta and Hf at the same time becomes amorphous. Even in Patent Document 1, Ta and Hf are examples of many metal elements that can be contained in the absorber layer. It is only mentioned as.

According to the present invention, the crystalline state of the absorber layer can be amorphized without using elements known to contribute to amorphization of conventional metal crystals such as B and Si. In addition to B and Si, Ge can be cited as an element known to contribute to the amorphization of metal crystals. These elements contribute to the amorphization of the metal crystal, but unavoidable problems arise when contained in the absorber layer. For example, when B is contained, since the resistance value of the target used for film formation becomes large, the discharge becomes unstable and the film formation speed becomes slow. The unstable discharge causes problems such as variations in the film composition and film thickness, and in some cases, the film formation becomes impossible. In addition, when Si is contained, since the EUV absorption coefficient of Si is small, problems such as a decrease in EUV light absorption characteristics of the absorber layer occur.
Therefore, the absorber layer 14 preferably does not substantially contain these elements, and the total content of these elements is preferably 5 at% or less. The total content of these elements is more preferably 4 at% or less, and further preferably 3 at% or less.

  In the absorber layer 14, the remainder excluding Hf is preferably Ta. Therefore, the Ta content in the absorber layer 14 is preferably 40 to 80 at%. The content of Ta in the absorber layer 14 is more preferably 50 to 70 at%, and further preferably 55 to 70 at%.

The absorber layer 14 may contain elements other than Ta and Hf as necessary. In this case, the element to be included in the absorber layer 14 needs to satisfy suitability as a mask blank such as EUV light absorption characteristics.
However, it is preferable that the absorber layer 14 does not contain oxygen (O). Specifically, the oxygen content in the absorber layer 14 is less than 25 at%. When pattern formation is performed 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.
However, the absorber layer 14 preferably does not contain nitrogen (N). Specifically, when the nitrogen content in the absorber layer 14 is 35 at% or less, the crystal state of the absorber layer 14 is likely to be amorphous, and the light reflectance in the wavelength region of pattern inspection light can be lowered. It is more preferable in that the etching rate can be increased and the increase in electrical resistivity can be suppressed. The nitrogen content in the absorber layer 14 is more preferably 10 at% or less, further preferably 5 at% or less, further preferably 1 at% or less, and 0.5 at% or less. Is more preferable, and 0.05 at% or less is particularly preferable.

  The total content of Ta and Hf is more preferably 45 to 80 at%, and further preferably 45 to 75 at%. Moreover, the composition ratio of Ta and Hf is more preferably 7: 3 to 4: 6, further preferably 6.5: 3.5 to 4.5: 5.5, and 6: 4 to More preferably, it is 5: 5.

  The absorber layer 14 may contain 0.1 to 1.0 at% of Zr from the target used during film formation.

Since the absorber layer 14 has the above-described configuration, the crystalline state thereof is preferably amorphous. In this specification, the phrase “crystalline state is amorphous” includes a microcrystalline structure other than an amorphous structure having no crystal structure. If the absorber layer 14 is a film having an amorphous structure or a film having a microcrystalline structure, the surface of the absorber layer 14 is excellent in smoothness.
In the EUV mask blank 1 of the present invention, the surface roughness (rms) of the surface of the absorber layer 14 is 0.5 nm or less because the absorber layer 14 is an amorphous structure film or a microcrystalline structure film. preferable. Here, the surface roughness of the surface of the absorber layer 14 can be measured using an atomic force microscope (Atomic Force Microscope). If the surface roughness of the surface of the absorber layer 14 is large, the edge roughness of the pattern formed on the absorber layer 14 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 absorber layer 14 is required to be smooth.
If the surface roughness (rms) of the surface of the absorber layer 14 is 0.5 nm or less, the surface of the absorber layer 14 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 absorber layer 14 is more preferably 0.4 nm or less, and further preferably 0.3 nm or less.

  In addition, it can be confirmed by the X-ray diffraction (XRD) method that the crystalline state of the absorber layer 14 is amorphous, that is, an amorphous structure or a microcrystalline structure. If the crystalline state of the absorber layer 14 is an amorphous structure or a microcrystalline structure, a sharp peak is not observed in a diffraction peak obtained by XRD measurement.

Since the absorber layer 14 has the above-described configuration, the etching speed is high in normal dry etching using a chlorine-based gas (or a mixed gas containing a chlorine-based gas) as an etching gas, and etching selection with the protective layer 13 is performed. The ratio is 10 or more. In this specification, the etching selectivity can be calculated using the following equation.
Etching selectivity = (etching rate of absorber layer 14) / (etching rate of protective layer 13)
The etching selection ratio is preferably 10 or more, more preferably 11 or more, and further preferably 12 or more.

  Since the absorber layer 14 has the above-described configuration and has a low electrical resistivity, the problem of charge-up does not occur when drawing an electron beam. The electrical resistivity of the absorber layer 14 is preferably 0.1 Ω · cm or less, more preferably 0.01 Ω · cm or less, and further preferably 0.001 Ω · cm or less.

  The thickness of the absorber layer 14 is preferably 50 to 200 nm.

The absorber layer 14 having the above-described configuration can be formed by performing a sputtering method using a TaHf compound target, for example, a magnetron sputtering method or an ion beam sputtering method.
Here, the environment in which a gas containing oxygen atoms (for example, O ₂ , H ₂ O, CO _2, etc.) is substantially absent, specifically, the total partial pressure of the gas containing oxygen atoms is 1.0. The sputtering method is preferably performed in an environment of × 10 ⁻⁴ Pa or less.
In addition, an environment in which a gas containing nitrogen atoms (for example, N ₂ , NO, etc.) is not substantially present, specifically, an environment in which the total partial pressure of the gas containing nitrogen atoms is 1 × 10 ⁻⁴ Pa or less. It is preferable to carry out the sputtering method.
As an environment for achieving these, for example, the absorber layer 14 is formed by discharging a TaHf compound target in an inert gas atmosphere such as helium (He), argon (Ar), krypton (Kr), or xenon (Xe). It is preferable to form.
In order to reduce the oxygen content in the absorber layer, a gas containing hydrogen (H ₂ ) may be used as the sputtering gas. When a gas containing hydrogen is used, the hydrogen concentration of the sputtering gas is preferably 3% or less.
The TaHf compound target has a composition of Ta = 30 to 70 at% and Hf = 70 to 30 at%, so that an absorber layer having a desired composition can be obtained, and variations in film composition and film thickness are avoided. It is preferable in that it can be performed. The TaHf compound target may contain 0.1 to 5.0 at% of Zr.
Since TaHf compound target containing Hf with low electrical resistivity is used, the film formation is very stable, unlike the case of using TaB compound target containing high electrical resistivity and insulating B. The film composition and film thickness can be easily controlled.

In order to form the absorber layer 14 by the method described above, specifically, the following film forming conditions may be used.
Sputtering gas: Ar gas (gas pressure ^{1.0 × 10 -1 Pa~50 × 10 -1} Pa, preferably ^{1.0 × 10 -1 Pa~40 × 10 -1} Pa, more preferably 1.0 × 10 ^-1 Pa to 30 x 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

  As shown in FIG. 1, in the EUV mask blank 1 of the present invention, a low reflection layer 15 may be formed on the absorber layer 14. When the low reflection layer 15 is formed, the low reflection layer 15 is formed of a film that exhibits low reflection in the 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 this mask pattern inspection, an inspection machine that normally uses light of about 257 nm as inspection light is used. That is, the difference in reflectance of light of about 257 nm, 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, It is inspected by the difference in reflectance. Here, the former is the surface of the reflective layer 12 or the surface of the protective layer 13, and is usually the surface of the protective layer 13. Therefore, if the difference in reflectance between the surface of 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 of the surface of the absorber layer 14 and the reflectance of the surface of the protective layer 13 at the wavelength of the inspection light becomes small, and there is a possibility that sufficient contrast during inspection cannot be obtained. If sufficient contrast at the time of inspection is not obtained, pattern defects cannot be sufficiently determined in mask inspection, and accurate defect inspection cannot be performed.

In the EUV mask blank 1 of the present invention, the low reflection layer 15 for the inspection light is formed on the absorber layer 14 so that the contrast at the time of inspection is good. In other words, the light beam at the wavelength of the inspection light. The reflectivity is extremely low. Specifically, when the surface of the low reflection layer 15 is irradiated with light in the wavelength region of inspection light, the maximum light reflectance of the wavelength of the inspection light is preferably 15% or less, and preferably 10% or less. Is more preferable, and it is further more preferable that it is 5% or less.
If the light reflectance at the wavelength of the inspection light in the low reflection layer 15 is 15% or less, the contrast at the time of the inspection is good. Specifically, the contrast between the reflected light having the wavelength of the inspection light on the surface of the protective layer 13 and the reflected light having the wavelength of the inspection light on the surface of the low reflective layer 15 is 30% 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 at} the wavelength of the inspection light is the reflectance at the surface of the protective layer 13, and R ₁ is the reflectance at the surface of the low reflective layer 15. The above R ₁ and R ₂ are, as shown in FIG. 2, it is measured in a state of forming a pattern on the absorber layer 14 of the EUV mask blank 1 (and the low reflective layer 15) shown in FIG. 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 45% or more, further preferably 60% or more, and particularly preferably 80% or more.

  In the EUV mask blank 1 of the present invention, it is preferable to form the low reflection layer 15 on the absorber layer 14 because the wavelength of the pattern inspection light and the wavelength of the EUV light are different. Therefore, when EUV light (around 13.5 nm) is used as the pattern inspection light, it is considered unnecessary to form the low reflection layer 15 on the absorber layer 14. The wavelength of the inspection light tends to shift to the short wavelength side as the pattern size becomes smaller, and it is conceivable that it will shift to 193 nm and further to 13.5 nm in the future. When the wavelength of the inspection light is 13.5 nm, it is considered unnecessary to form the low reflection layer 15 on the absorber layer 14.

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.

Example 1
In this example, in order to investigate the etching characteristics of the absorber layer, a TaHf film was formed on the Si chip under the following conditions. For comparison, a Ru film was also formed on the Si chip. In either case, magnetron sputtering was used.
Film formation condition of absorber layer 14 (TaHf film) Target: TaHf compound target (composition ratio: Ta55at%, Hf45at%)
Sputtering gas: Ar gas Input power: 400W
Deposition rate: 1.00 nm / sec
Film thickness: 60nm
Vacuum degree before film formation: 4 × 10 ⁻⁶ Pa
Ru film formation conditions Target: Ru Target sputtering gas: Ar gas (gas pressure: 0.3 Pa)
Output: 150W
Deposition rate: 0.25 nm / sec
Film thickness: 2.5nm

  The composition of the absorber layer (TaHf film) formed as described above was measured using an X-ray photoelectron spectrometer (manufactured by PERKIN ELEMER-PHI: No. 5500). The composition ratio (at%) of the absorber layer (TaHf film) is Ta: Hf = 75: 20 (Ta content is 75 at%, Hf content is 20 at%). The O content in the absorber layer is 5 at% or less. Moreover, the content rate of N in an absorber layer is 0.05 at% or less.

The etching characteristics were evaluated by the following method.
On a sample stage (4-inch quartz substrate) of an RF plasma etching apparatus, a Si chip (10 mm × 30 mm) on which a TaHf film or a Ru film was formed by the method described above was installed as a sample. In this state, the TaHf film or the Ru film of the Si chip placed on the sample stage was subjected to plasma RF etching under the following conditions.
Bias RF: 50W
Etching time: 120 sec
Trigger pressure: 3Pa
Etching pressure: 1Pa
Etching gas: Cl ₂ / Ar
Gas flow rate (Cl ₂ / Ar): 20/80 sccm
Distance between electrode substrates: 55 mm

The etching rate was determined for the Ru film and the TaHf film formed under the above conditions, the etching selectivity was determined using the following formula, and the etching characteristics of the absorber layer were evaluated.
Etching selectivity = (TaHf film etching rate) / (Ru film etching rate)
The etching selectivity of the TaHf film is as follows.
Etching rate of TaHf film: 19.8 (nm / min)
Ru film etching rate: 1.48 (nm / min)
Etching selectivity with Ru film: 13.3
The etching selectivity with the protective layer is preferably 10 or more, but the TaHf film has a sufficient etching selectivity.

Comparative Example 1
The comparative example 1 was implemented in the procedure similar to Example 1 except that an absorber layer contains oxygen 25at% (content rate) or more.
The absorber layer was formed under the following conditions.
Film formation condition of absorber layer (TaHf film) Target: TaHf compound target (composition ratio: Ta55at%, Hf45at%)
Sputtering gas: Ar gas Input power: 400W
Deposition rate: 1.55 nm / sec
Film thickness: 60nm
Vacuum degree before film formation: 4 × 10 ⁻⁶ Pa
The oxygen in the film of the absorber layer was adjusted by controlling the gas pressure during film formation.

When the composition ratio (at%) of the obtained TaHf film was measured by the same method as in Example 1, it was Ta: Ha: O = 50: 25: 25. Moreover, the content rate of N in an absorber layer is 0.05 at% or less.
When the etching characteristics of the obtained TaHf were evaluated by the same method as in Example 1,
Etching rate of TaHf film: 2.0 (nm / min)
Etching selectivity with Ru film: 1.38
Met. A TaHf film containing oxygen at 25 at% or more cannot obtain a sufficient etching selectivity.

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 a pattern is formed on the absorber layer 14 (and the low reflective layer 15) of the EUV mask blank 1 shown in FIG.

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 (16)

A reflective mask blank for EUV lithography in which a reflective layer for reflecting EUV light and an absorber layer for absorbing EUV light are formed in this order on a substrate,
The absorber layer contains tantalum (Ta) and hafnium (Hf);
A reflective type for EUV lithography, wherein the absorber layer has a Hf content of 20 to 60 at%, a Ta content of 40 to 80 at%, and an oxygen content of less than 25 at%. Mask blank.   2. The reflective mask blank for EUV lithography according to claim 1, wherein the absorber layer has a nitrogen (N) content of 35 at% or less.   3. The reflective mask blank for EUV lithography according to claim 1, wherein a composition ratio of Ta and Hf in the absorber layer is Ta: Hf = 7: 3 to 4: 6. 4.   The reflective mask blank for EUV lithography according to any one of claims 1 to 3, wherein the absorber layer has a total content of B, Si and Ge of 5 at% or less.   The reflective mask blank for EUV lithography according to any one of claims 1 to 4, wherein the absorber layer contains 0.1 to 1.0 at% of Zr.   6. The reflective mask blank for EUV lithography according to claim 1, wherein the crystalline state of the absorber layer is amorphous.   The reflective mask blank for EUV lithography according to any one of claims 1 to 6, wherein the surface roughness (rms) of the surface of the absorber layer is 0.5 nm or less.   The reflective mask blank for EUV lithography according to any one of claims 1 to 7, wherein the absorber layer has a thickness of 50 to 200 nm.   The reflective mask blank for EUV lithography according to any one of claims 1 to 8, wherein a low reflection layer for inspection light used for inspection of a mask pattern is formed on the absorber layer. 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 of light used for inspection of the pattern formed on the absorber layer is 30% or more. A reflective mask blank for EUV lithography according to claim 9. The reflective mask blank for EUV lithography according to claim 10, wherein the protective layer is formed of any one of Ru, Ru compound, SiO ₂ and CrN.   The EUV according to claim 9, wherein the reflectance of the surface of the low reflection layer with respect to the wavelength of light used for inspection of a pattern formed on the absorber layer is 15% or less. A reflective mask blank for lithography.   The reflective mask blank for EUV lithography according to claim 1, wherein the absorber layer is formed by performing a sputtering method using a TaHf compound target.   14. The reflective mask blank for EUV lithography according to claim 13, wherein the composition of the TaHf compound target is Ta = 30 to 70 at% and Hf = 70 to 30 at%.   The reflective mask blank for EUV lithography according to claim 13 or 14, wherein the TaHf compound target contains 0.1 to 5.0 at% of Zr. The sputtering method using the TaHf compound target is performed in an environment containing a total partial pressure of a gas containing oxygen atoms of 1.0 × 10 ⁻⁴ Pa or less and 3% or less of hydrogen. The reflective mask blank for EUV lithography according to any one of the above.

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