WO2012114980A1

WO2012114980A1 - Reflective mask blank for euv lithography

Info

Publication number: WO2012114980A1
Application number: PCT/JP2012/053712
Authority: WO
Inventors: 和幸林; 和伸前重; 俊之宇野
Original assignee: 旭硝子株式会社
Priority date: 2011-02-24
Filing date: 2012-02-16
Publication date: 2012-08-30
Also published as: JPWO2012114980A1; TWI582530B; TW201243492A

Abstract

The present invention provides an EUV mask blank in which the thickness of the absorbing layer is optimized, whereby the thickness of the absorption layer can be reduced in comparison with conventional thickness in a range that does not affect pattern characteristics. A reflective mask blank for EUV lithography in which a reflective layer for reflecting EUV light and a absorbing layer for absorbing EUV light are formed in the stated order, the reflective mask blank for EUV lithography characterized in that the thickness of the absorbing layer is set so as to be within a range of ±2.0% of minimum thickness and so that the average beam reflectivity is 4.0% or less in a wavelength region of 13.3 to 13.7 nm.

Description

Reflective mask blank for EUV lithography

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

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 ArF laser (wavelength: 193 nm) is used. Even if the immersion method is used, the wavelength is expected to be about 45 nm. Therefore, EUV lithography, which is an exposure technique using EUV light having a wavelength shorter than that of an ArF laser, is promising as a next-generation exposure technique using a wavelength shorter than 45 nm. In this specification, EUV light refers to light having a wavelength in the soft X-ray region or the 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.

EUV light is easily absorbed by any substance, and the refractive index of the substance is close to 1 at this wavelength, so that a conventional refractive optical system such as photolithography using visible light or ultraviolet light cannot be used. 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. The EUV mask blank has a structure in which a reflective layer that reflects EUV light and an absorption layer that absorbs EUV light are formed in this order on a glass substrate or the like. As the reflective layer, a multilayer reflective film is generally used in which the high-refractive index layer and the low-refractive index layer are alternately laminated to increase the light reflectivity when EUV light is irradiated on the surface of the layer. For the absorption layer, a material having a high absorption coefficient for EUV light, specifically, a material mainly composed of Ta, for example, is used.
In addition, a low reflection layer for the pattern inspection wavelength (190 to 260 nm) may be formed on the absorption layer of the EUV mask blank. In this case, a material having low reflection characteristics with respect to the pattern inspection wavelength, specifically, a material mainly composed of Ta and O is used for the low reflection layer.

The basic characteristic required for the absorption layer and low reflection layer of an EUV mask blank is how to absorb EUV light. In general, it is understood that sufficient pattern transfer characteristics can be obtained if the light reflectance of the surface of the absorbing layer or the surface of the low reflective layer is 0.5% or less for a specific EUV wavelength (13.5 nm). ing. In order to satisfy the above basic characteristics, the absorption layer needs to be thicker than 80 nm. Even in the case where the low reflection layer is formed on the absorption layer, the absorption layer and the low reflection layer require a total film thickness greater than 80 nm.
On the other hand, in the EUV mask, in order to reduce the “bevel effect” shown below, the film thickness of the absorption layer (when the low reflection layer is formed on the absorption layer, the total film thickness of the absorption layer and the low reflection layer). ) Is desired to be thinner. Here, the “tilt effect” means that in EUV exposure, incident light is incident on the mask pattern at an angle of 6 °, so that the shadow of the pattern affects the reflection intensity distribution and the line width on the transfer wafer. The problem is that the accuracy deteriorates. As a method of solving the problem due to the oblique effect, there is a method of setting the film thickness of the absorption film so that the EUV reflectance of the absorption film serving as a low reflection portion of the exposure light is in the vicinity of the minimum value (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-268255

In Patent Document 1, the minimum value of the EUV reflectance is obtained by optimizing the film thickness of the absorption film, particularly the film thickness of the uppermost layer of the absorption film composed of two or more thin films. This is a technique for reducing the change in the EUV reflectivity with respect to the change in thickness. The film thickness of the absorption film, that is, the film thickness of the absorption layer of the EUV mask blank (a low reflection layer is formed on the absorption layer) In this case, the total film thickness of the absorption layer and the low reflection layer is not reduced.

On the other hand, in recent years, with regard to pattern transfer characteristics, not the light reflectance at a specific wavelength (13.5 nm) but the average light reflectance at a specific wavelength range (13.3 to 13.7 nm) is more effective for pattern characteristics. It has been found to have an impact. If the average light reflectance in the above wavelength range is 4.0% or less, it is predicted that there is no problem in pattern characteristics.

In order to solve the above-mentioned problems of the prior art, the present invention optimizes the film thickness of the absorption layer and compares the film thickness of the absorption layer with the conventional film thickness within a range that does not affect the pattern characteristics. Thus, an object of the present invention is to provide an EUV mask blank that can be made thin.
In addition, the present invention optimizes the total film thickness of the absorption layer and the low reflection layer, and compares the total film thickness of the absorption layer and the low reflection layer with the conventional film thickness within a range that does not affect the pattern characteristics. Thus, an object of the present invention is to provide an EUV mask blank that can be made thin.

As a result of intensive studies to solve the above problems, the present inventors have determined that the thickness of the absorption layer of the EUV mask blank is ±± the thickness at which the average light reflectance in a specific EUV wavelength range is a minimum value. It has been found that by setting to be within the range of 2.0%, the thickness can be made thinner than the thickness of the conventional absorption layer within a range that does not affect the pattern characteristics.
Further, the total film thickness of the absorption layer and the low reflection layer of the EUV mask blank is within a range of ± 2.0% with respect to the total film thickness at which the average light reflectance in a specific EUV wavelength range is a minimum value. It has been found that the thickness can be made thinner than the total thickness of the conventional absorption layer and the low reflection layer within a range that does not affect the pattern characteristics.

The present invention has been made based on the above findings, and the present invention relates to a reflective mask for EUV lithography in which a reflective layer that reflects EUV light and an absorption layer that absorbs EUV light are formed in this order. Blank,
The film thickness of the absorbing layer is within the range of ± 2.0% with respect to the film thickness at which the average light reflectance in the wavelength region of 13.3 to 13.7 nm is 4.0% or less and the minimum value. A reflective mask blank for EUV lithography (a reflective mask blank for EUV lithography according to the first embodiment) is provided.

Also, the present invention provides a reflective layer for reflecting EUV light, an absorbing layer for absorbing EUV light, and a low reflective layer for mask pattern inspection light (wavelength 190 to 260 nm) in this order. A reflective mask blank,
The total film thickness of the absorption layer and the low reflection layer is ± 3% with respect to the total film thickness at which the average light reflectance in the wavelength region of 13.3 to 13.7 nm is 4.0% or less and a minimum value. Provided is a reflective mask blank for EUV lithography (second type reflective mask blank for EUV lithography), which is set to fall within a range of 2.0%.
The term “to” indicating the above numerical range is used in the sense that the numerical values described before and after it are used as the lower limit value and the upper limit value, and unless otherwise specified, “to” is the same in the following specification. Used with meaning.

The reflective mask blank for EUV lithography of the first and second embodiments described above is hereinafter referred to as “the EUV mask blank of the present invention”.

In the EUV mask blank of the present invention, the absorption layer preferably contains tantalum (Ta) and nitrogen (N) as main components. In the EUV mask blank of the present invention, it is preferable that the film thickness of the absorption layer is 46 nm or more and 80 nm or less.

In the EUV mask blank of the present invention in which a low reflection layer is formed, the low reflection layer preferably contains tantalum (Ta) and oxygen (O) as main components. Moreover, in the EUV mask blank of the present invention in which the low reflection layer is formed, the total film thickness of the absorption layer and the low reflection layer is preferably 46 nm or more and 80 nm or less.

In the EUV mask blank of the present invention, a protective layer for protecting the reflective layer may be formed between the reflective layer and the absorbent layer when forming a pattern on the absorbent layer. In this case, the protective layer is preferably formed of any one of Ru, Ru compound, SiO ₂ and Cr compound.

In the EUV mask blank of the present invention, the absorption layer and the low reflection layer can be thinned without affecting the pattern characteristics. By reducing the thickness of the absorption layer and the low reflection layer, it is expected to suppress the oblique effect and to improve the pattern accuracy. Furthermore, the thickness of the resist at the time of pattern formation can be reduced by reducing the thickness of the absorption layer and the low reflection layer, and an improvement in pattern resolution is expected.

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 absorption layer 14 (and the low reflection layer 15) of the EUV mask blank 1 shown in FIG. FIG. 3 is a graph showing the relationship between the total film thickness of the absorption layer and the low reflection layer in the EUV mask blank of the example and the average light reflectance in the wavelength region of 13.3 to 13.7 nm. FIG. 4 is a partially enlarged view of the total film thickness in the range of 43 to 51 nm in FIG. FIG. 5 is a partially enlarged view of the total film thickness in the range of 50 to 58 nm in FIG. FIG. 6 is a partially enlarged view of the total film thickness in the range of 57 to 65 nm in FIG. FIG. 7 is a partially enlarged view of the total film thickness in the range of 65 to 73 nm in FIG. FIG. 8 is a partially enlarged view of the total film thickness of 72 to 80 nm in FIG. FIG. 9 is a partially enlarged view of the total film thickness in the range of 80 to 88 nm in FIG.

The present invention will be described below 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 absorbing layer 14 that absorbs EUV light are formed on a substrate 11 in this order. A protective layer 13 for protecting the reflective layer 12 is formed between the reflective layer 12 and the absorbent layer 14 when a pattern is formed on the absorbent layer 14. On the absorption 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 and the absorbing 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, it is a low thermal expansion coefficient is required, specifically, the thermal expansion coefficient of preferably 0 ± 0.05 × 10 ^-7 / ℃ at 20 ℃, 0 ± 0.03 × 10 - ⁷ / ° C is more preferable. The substrate preferably has excellent 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 to this. Crystallized glass, quartz glass, silicon or the like on which β quartz solid solution is precipitated is used. A substrate such as metal can be used.
Since the substrate 11 has a smooth surface with a surface roughness (rms) of 0.15 nm or less and a flatness of 100 nm or less, high reflectivity and transfer accuracy can be obtained in a photomask after pattern formation. Is preferred.
The size and thickness of the substrate 11 are appropriately determined according to 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. The full width at half maximum of the size of the defect and the convex defect is preferably 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 the light reflectance in the wavelength region of 13.3 to 13.7 nm is 60% or more. Is preferable, and 65% or more is more preferable. Further, even when the protective layer 13 is provided on the reflective layer 12, the maximum value of the light reflectance in the wavelength region of 13.3 to 13.7 nm is preferably 60% or more, more preferably 65% or more. preferable.

Since the reflective layer 12 can achieve high EUV light reflectance, a multilayer reflective film in which a high refractive index 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, Si is widely used for the high refractive index layer, and Mo 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, a Si / Ru / Mo / Ru multilayer reflective film, or the like can also be used.

The film thickness of each layer constituting the multilayer reflective film constituting the reflective layer 12 and the number of repeating units of the layer 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 light reflectance of 60% or more in the wavelength range of 13.3 to 13.7 nm, the multilayer reflective film has a film thickness of 2.3. A Mo layer with a thickness of ± 0.1 nm and a Si layer with a thickness of 4.5 ± 0.1 nm may be laminated so that the number of 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 a Mo / Si 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 ⁻ 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, Ar gas (gas pressure 1.3 × 10 ⁻² Pa to 2.7 × 10 ⁻² Pa) as a sputtering gas, ion acceleration voltage 300 to 1500 V, film formation rate 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 cycle, the Mo / Si multilayer reflective film is formed by laminating 30 to 60 cycles of the Si film and the Mo film.

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

A protective layer 13 may be formed between the reflective layer 12 and the absorption layer 14. 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 absorption layer 14 is patterned by an etching process, usually a dry etching process. Therefore, the material of the protective layer 13 is selected from a material that is not easily affected by the etching process of the absorbing layer 14, that is, the etching rate is slower than that of the absorbing layer 14 and is not easily damaged by the etching process. 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. The protective layer 13 is preferably at least one selected from the group consisting of Ru, Ru compounds, SiO ₂ and Cr compounds. 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, Ar gas (gas pressure: 1.0 × 10 ⁻² Pa to 10 × 10 ⁻¹ Pa) is used as a sputtering gas, and an input voltage is 30 V. It is preferable to form the film so that the thickness is 2 to 5 nm at a film forming speed of 0.02 to 1.0 nm / sec.

The characteristic particularly required for the absorption layer 14 is that the EUV light reflectance is extremely low. Specifically, when the surface of the absorption layer 14 is irradiated with light in the wavelength region of EUV light, the average light reflectance in the wavelength region of 13.3 to 13.7 nm is 4.0% or less, and 3.8 % Or less is preferable, and 3.5% or less is more preferable.
When the low reflection layer 15 for the inspection light of the mask pattern is formed on the absorption layer 14 as in the EUV mask blank 1 of the present invention, the surface of the low reflection layer 15 is irradiated with light in the wavelength region of EUV light. In this case, the average light reflectance in the wavelength range of 13.3 to 13.7 nm is 4.0% or less, preferably 3.8% or less, and more preferably 3.5% or less.

In order to achieve the above characteristics, the absorption 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) and nitrogen (N) has an average light reflectance of 4.0% or less in a wavelength range of 13.3 to 13.7 nm. In addition to being easy to form a layer, the crystalline state of the absorption layer is likely to be amorphous, and the surface is small and the surface is excellent in smoothness. In this specification, when a material mainly composed of Ta and N is used, Ta and N in the material are 40 atomic% or more (hereinafter referred to as atomic%) in total content, preferably 50 at. %, More preferably 55 at% or more, and TaN is exemplified.
The materials mainly composed of Ta and N used for the absorption layer 14 include, in addition to Ta and N, hafnium (Hf), silicon (Si), zirconium (Zr), germanium (Ge), boron (B), and hydrogen (H). It may contain at least one element selected from Specific examples of the material containing the above elements in addition to Ta and N include TaNH, TaHfN, TaBSiN, TaBSiNH, TaBN, TaBNH, TaSiN, TaGeN, TaZrN, and the like.

The absorption layer 14 having the above-described configuration, that is, an absorption layer made of a material mainly composed of Ta and N can be formed by a known film formation method, for example, a magnetron sputtering method or an ion beam sputtering method.
For example, when a TaNH film is formed as the absorption layer 14 using a magnetron sputtering method, a Ta target is used as a target, and a mixed gas of Ar, N ₂ and H ₂ (H ₂ gas concentration 1 to 50 vol%) as a sputtering gas. N ₂ gas concentration 1 to 80 vol%, Ar gas concentration 5 to 95 vol%, gas pressure 1.0 × 10 ⁻¹ Pa to 50 × 10 ⁻¹ Pa), input power 30 to 3000 W, film formation rate It is preferable to form a TaNH film so as to have a film thickness described later at 0.5 to 60 nm / min.
In addition, when using inert gas other than Ar, it is preferable that the density | concentration of the inert gas sets it as the same concentration range as above-mentioned Ar gas concentration. Further, when a plurality of types of inert gases are used, it is preferable that the total concentration of the inert gases is in the same concentration range as the Ar gas concentration described above.

The low reflection layer 15 is composed of a film that exhibits low reflection in inspection light used for inspection of a mask pattern. When producing an EUV mask, after forming a pattern in the absorption 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 190 to 260 nm as inspection light is used. That is, the difference in reflectance of light of about 190 to 260 nm, specifically, the surface exposed by removing the absorption layer 14 by pattern formation, the surface of the absorption layer 14 remaining 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 reflective layer 12 or the protective layer 13 and the surface of the absorption 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 absorption layer 14 having the above-described configuration, that is, an absorption layer composed of a material mainly composed of Ta and N, has extremely low EUV light reflectance, and has excellent characteristics as an absorption layer of the EUV mask blank 1. However, when looking at the wavelength of the inspection light, the light reflectance is not necessarily low enough. As a result, the difference between the reflectance of the surface of the absorption layer 14 at the wavelength of the inspection light and the reflectance of the surface of the reflective layer 12 or the surface of the protective layer 13 becomes small, and there is a possibility that sufficient contrast during inspection cannot be obtained. is there. 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, by forming the low reflection layer 15 for the inspection light on the absorption layer 14, the light reflectance at the wavelength of the inspection light becomes extremely low, and the contrast at the time of inspection becomes good.
In this specification, the contrast at the time of inspection can be obtained using the following equation.
Contrast at the time of inspection (%) = ((R ₂ −R ₁ ) / (R ₂ + R ₁ )) × 100
Here, R _{2 at} the wavelength of the inspection light is a reflectance on the surface of the reflective layer 12 or the protective layer 13, and R ₁ is a reflectance on the surface of the low reflective layer 15. Note that R ₁ and R ₂ are as shown in FIG. 2 when the low reflection layer 15 for the mask pattern inspection light is formed on the absorption layer 14 as in the EUV mask blank 1 shown in FIG. The measurement is performed in a state where a pattern is formed on the absorption layer 14 and the low reflection layer 15 of the EUV mask blank 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 absorption layer 14 and the low reflection layer 15 are removed by pattern formation in FIG. 2, and R ₁ is obtained by pattern formation. This is a value measured on the surface of the low reflective layer 15 remaining without being removed. In addition, when the low reflection layer is not formed on an absorption layer, it measures in the state which formed the pattern in the absorption layer.
When the EUV mask blank of the present invention has a low reflection layer, the contrast at the time of inspection represented by the above formula is preferably 30% or more, more preferably 45% or more, still more preferably 60% or more, and more than 80%. Particularly preferred.
In order for the contrast at the time of inspection to satisfy the above, the maximum light reflectance of the wavelength of the inspection light when the surface of the low reflection layer 15 is irradiated with the light of the wavelength of the inspection light is preferably 15% or less. % Or less is more preferable, and 5% or less is more preferable.

The low reflection layer 15 is made of a material whose refractive index at the wavelength of the inspection light is lower than that of the absorption layer 14 in order to achieve the above characteristics. As a material whose refractive index at the wavelength of the inspection light is lower than that of the absorption layer 14, a material mainly composed of tantalum (Ta) and oxygen (O) is used, and the maximum light reflectance at the wavelength of the inspection light is 15%. In addition to being easy to form the following low reflection layer, the low reflection layer is likely to be amorphous and the surface is small in surface roughness and excellent in smoothness. In this specification, when a material mainly composed of Ta and O is used, a material containing Ta and O in the material in a total content of 40 at% or more, preferably 50 at% or more, more preferably 55 at% or more. Meaning TaO.
The material mainly composed of Ta and O used for the low reflection layer 15 may contain at least one element selected from Hf, Si, Zr, Ge, B, N and H in addition to Ta and O. Specific examples of the material containing the above elements in addition to Ta and O include TaON, TaONH, TaHfO, TaHfON, TaBSiO, TaBSiON, and the like.

The low reflective layer 15 having the above-described configuration, that is, the low reflective layer made of a material mainly composed of Ta and O can be formed by a known film formation method, for example, a magnetron sputtering method or an ion beam sputtering method.
For example, when a TaONH film is formed as the low reflection layer 15 using a magnetron sputtering method, a Ta target is used as a target, and a mixed gas of Ar, O ₂ , N _2, and H ₂ (H ₂ gas) as a sputtering gas. (Concentration 1 to 50 vol%, O ₂ gas concentration 1 to 80 vol%, N ₂ gas concentration 1 to 80 vol%, Ar gas concentration 5 to 95 vol%, gas pressure 1.0 × 10 ⁻¹ Pa to 50 × 10 ⁻¹ Pa) It is preferable to form a TaONH film with a power of 30 to 3000 W and a film formation rate of 0.01 to 60 nm / min.
In addition, when using inert gas other than Ar, it is preferable that the density | concentration of the inert gas sets it as the same concentration range as above-mentioned Ar gas concentration.

As described above, in the EUV mask blank of the present invention, the average light reflectance in the wavelength region of 13.3 to 13.7 nm in the absorption layer is 4.0% or less. When a low reflection layer is formed on the absorption layer, the average light reflectance in the wavelength range of 13.3 to 13.7 nm in the low reflection layer is 4.0% or less.
As shown in FIG. 3 of the example described later, when the low reflection layer is formed on the absorption layer, the average light reflectance in the wavelength range of 13.3 to 13.7 nm in the low reflection layer is as follows. And is dependent on the total film thickness of the low-reflection layer, and periodically increases and decreases (ie, increases and decreases between the maximum and minimum values) and decreases as the total film thickness increases. Go.
Therefore, in the case of an EUV mask blank having a low reflection layer formed on the absorption layer, the average light reflectance in the wavelength range of 13.3 to 13.7 nm in the low reflection layer is 4.0% or less. It is necessary to set the total film thickness of the absorption layer and the low reflection layer.
The same applies to the average light reflectance in the wavelength region of 13.3 to 13.7 nm in the absorption layer in which the low reflection layer is not formed on the absorption layer, and is dependent on the thickness of the absorption layer and is periodic. While increasing and decreasing repeatedly (that is, repeating increasing and decreasing between the maximum value and the minimum value), it decreases as the total film thickness increases.
Therefore, in the case of an EUV mask blank in which a low reflection layer is not formed on the absorption layer, the average light reflectance in the wavelength range of 13.3 to 13.7 nm in the absorption layer is 4.0% or less. It is necessary to set the film thickness of the absorption layer.

In the EUV mask blank of the present invention, the absorption is further performed so that the average light reflectance in the wavelength range of 13.3 to 13.7 nm is within a range of ± 2.0% with respect to the minimum film thickness. The film thickness of the layer or the total film thickness of the absorption layer and the low reflection layer is set.
In the case of an EUV mask blank in which a low reflection layer is not formed on the absorption layer, ± 2 with respect to the film thickness at which the average light reflectance in the wavelength region of 13.3 to 13.7 nm in the absorption layer is a minimum value. The film thickness of the absorption layer is set so as to be in the range of 0.0%.
Here, “within the range of ± 2.0% with respect to the film thickness at which the average light reflectance becomes a minimum value”, in other words, the film thickness at which the average light reflectance becomes a minimum value is 100. 0.0% corresponds to a film thickness range of 98.0% to 102.0%.
In the case of an EUV mask blank in which a low reflection layer is formed on the absorption layer, the average film reflectivity in the wavelength range of 13.3 to 13.7 nm in the low reflection layer is ±± The total film thickness of the absorption layer and the low reflection layer is set so as to be within the range of 2.0%.

As described above, in order to obtain a sufficient pattern transfer characteristic, the light reflectance of a specific EUV wavelength on the surface of the absorption layer (the surface of the low reflection layer when a low reflection layer is formed on the absorption layer), Specifically, it was conventionally considered that the light reflectance at a wavelength of 13.5 nm needs to be 0.5% or less. In order to satisfy this, the film thickness of the absorption layer (when the low reflection layer is formed on the absorption layer, the total film thickness of the absorption layer and the low reflection layer) needs to be thicker than 80 nm. There was a problem.
On the other hand, if the film thickness of the absorption layer or the total film thickness of the absorption layer and the low reflection layer is set so that the light reflectance at the wavelength of 13.5 nm is near the minimum value, sufficient pattern transfer characteristics can be obtained. It is the idea in Patent Document 1 that it is obtained.
Patent Document 1 is expected to reduce the thickness of the absorption layer, or the absorption layer and the low reflection layer based on such a concept, but as described in paragraph [0022] of Patent Document 1. , The width of the OD (Optical Density) near the maximum value is narrow, the OD value is likely to change due to the change of the film thickness, and strict accuracy is required for controlling the film thickness. Here, since the OD value and the light reflectance are directly related to each other, the width near the minimum value of the light reflectance at the wavelength of 13.5 nm is narrow, and it is shown that the light reflectance changes with the change of the film thickness. I can say that. Therefore, in Patent Document 1, since strict precision is required for controlling the film thickness, it is difficult to reduce the thickness of the absorption layer or the absorption layer and the low reflection layer.

On the other hand, in the EUV mask blank of the present invention, the average light reflectance in the wavelength region of 13.3 to 13.7 nm is within a range of ± 2.0% with respect to the film thickness at which the minimum value is obtained. The film thickness of the absorption layer or the total film thickness of the absorption layer and the low reflection layer is set.
As shown in FIGS. 3 to 9, particularly FIGS. 4 to 9, in the examples described later, in the case of the average light reflectance in the wavelength region of 13.3 to 13.7 nm, the total film thickness of the absorbing layer and the low reflecting layer is The change of the average light reflectivity with respect to the change, particularly the change of the average light reflectivity near the minimum value is gradual. With respect to this point, in FIGS. 4 to 9 of the examples described later, the range of the total film thickness that is ± 2.0% with respect to the total film thickness at which the average light reflectance becomes the minimum value is shown in gray tone. . As shown in the table of Examples to be described later, the change in the average light reflectance in the range is as small as 0.3% at the maximum. Such a very small change in the average light reflectance is considered not to affect the pattern characteristics.
The same applies to the case of an EUV mask blank in which a low reflection layer is not formed on the absorption layer, and the average light reflectance in the wavelength range of 13.3 to 13.7 nm with respect to the thickness of the absorption layer, particularly in the vicinity of the minimum value. If the change of the average light reflectivity is gradual and the film thickness of the absorption layer is ± 2.0% with respect to the film thickness at which the average light reflectivity is a minimum value, the average light reflection in the range is within the range. The change in rate is very small and it is considered that the pattern characteristics are not affected.

As shown in FIG. 3 of the example described later, the average light reflectance in the wavelength region of 13.3 to 13.7 nm takes a plurality of different minimum values depending on the total film thickness of the absorption layer and the low reflection layer. As long as the average light reflectance at the minimum value is 4.0% or less, the total film thickness of the absorption layer and the low reflection layer may be set for any minimum value. This is the same for the EUV mask blank in which the low reflection layer is not formed on the absorption layer.
However, in order to reduce the thickness of the absorption layer and the low reflection layer, the thickness of the absorption layer or the total thickness of the absorption layer and the low reflection layer is 80 nm or less, more preferably 75 nm or less, more preferably 70 nm or less. Therefore, it is preferable to select the thickness of the absorbing layer at which the average light reflectance in the wavelength range of 13.3 to 13.7 nm is a minimum value, or the total thickness of the absorbing layer and the low reflecting layer. In addition, the lower limit of the film thickness of the absorption layer is preferably 46 nm or more from the viewpoint of obtaining a functional surface as the absorption layer and an average light reflectance of 4.0% or less. The lower limit of the total film thickness is preferably 46 nm or more from the viewpoint of obtaining a functional surface as an absorption layer and an average light reflectance of 4.0% or less.

In the case of an EUV mask blank in which a low reflection layer is formed on the absorption layer, if the film thickness of the low reflection layer is larger than the film thickness of the absorption layer, the EUV light absorption characteristics in the absorption layer may be reduced. The film thickness of the low reflection layer is preferably thinner than the film thickness of the absorption layer. For this reason, the film thickness of the low reflection layer is preferably 1 to 20 nm, more preferably 1 to 15 nm, and even more preferably 1 to 10 nm.

The EUV mask blank of the present invention may have a functional film known in the field of EUV mask blanks in addition to the reflective layer, the absorbing layer, and the protective layer and the low reflective layer formed as necessary. As a specific example of such a functional film, for example, as described in Japanese Patent Application Publication No. 2003-501823, a high dielectric material 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.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.
In this example, regarding the case where a TaNH film is formed as the absorption layer 14 of the EUV mask blank 1 shown in FIG. 1 and a TaONH film is formed as the low reflection layer 15, the film thickness dependence of the EUV light reflectance, more specifically, The dependence of the average light reflectance in the wavelength range of 13.3 to 13.7 nm on the total film thickness of the absorption layer 14 and the low reflection layer 15 was calculated. Here, the low reflection layer 15 has a maximum light reflectance of 10% or less for the wavelength (190 to 260 nm) of the pattern inspection light, so that the film thickness is fixed at 7 nm and only the film thickness of the absorption layer 14 is changed. It was. The composition ratio (atomic ratio) of the absorbing layer is Ta: N: H = 55: 39: 6, and the composition ratio (atomic ratio) of the low reflective layer is Ta: O: N: H = 22: 65. : 5: 8.
The average light reflectance in the wavelength region of 13.3 to 13.7 nm is calculated by calculating the integral value of the light reflectance in the wavelength region of 13.3 to 13.7 nm and the number of data used when calculating the integral value. The value was divided.

In FIG. 3, the horizontal axis represents the total film thickness (nm) of the absorption layer (TaNH film) and the low reflection layer (TaONH film), and the vertical axis represents the average light reflectance (%) in the wavelength range of 13.3 to 13.7 nm. The film thickness dependence of the average light reflectance is shown. As shown in FIG. 3, the average light reflectance in the wavelength range of 13.3 to 13.7 nm is dependent on the total film thickness of the absorption layer and the low reflection layer, and is periodically increased and decreased (that is, , While increasing and decreasing between the maximum and minimum values), it decreases as the total film thickness increases.
4 to 9 are partial enlarged views showing the vicinity of the minimum value of the average light reflectance in FIG. 4 to 9 are partial enlarged views in which the total thickness of the absorption layer and the low reflection layer is in the range of 43 to 51 nm, 50 to 58 nm, 57 to 65 nm, 65 to 73 nm, 72 to 80 nm, and 80 to 88 nm, respectively. There are minimum values near 47 nm, 54 nm, 62 nm, 69 nm, 76 nm, and 83 nm, respectively. Further, the average light reflectance near the minimum value in each total film thickness range is 4.0% or less, which satisfies the required characteristics of the EUV mask blank. Among these minimum values, those having a total film thickness of about 83 nm are approximately the same as the total film thickness of the absorption layer and the low reflection layer in the conventional EUV mask blank. Must not. The film thickness that can be substantially reduced is preferably 76 nm, 69 nm, 62 nm, 54 nm, and 47 nm.

In FIGS. 4 to 9, the range of the total film thickness that is ± 2.0% with respect to the total film thickness at which the average light reflectance is a minimum value is shown in gray tone. 4 to 9, the film thickness at which the average light reflectance becomes a minimum value, the film thickness at which the average light reflectance becomes ± 2.0% with respect to the film thickness at which the average light reflectance becomes a minimum value, and the film thicknesses thereof. The average light reflectance was estimated. The results are shown in the table below.
Table 1 shows that the total film thickness of the absorbing layer and the low reflection layer is 43 to 51 nm, Table 2 shows that the total film thickness is 50 to 58 nm, and Table 3 shows that the total film thickness is 57 to 65 nm. Table 4 shows the case where the same total film thickness is 65 to 73 nm, Table 5 shows the case where the same total film thickness is 72 to 80 nm, and Table 6 shows the case where the same total film thickness is 80 to 88 nm. The value of was shown.

As is apparent from the above table, in any total film thickness at which the average light reflectance becomes a minimum value, the average light reflectance is 4 within the range of ± 2.0 with respect to the total film thickness. Since the difference from the average light reflectance that is a minimum value is 0.0% or less and is extremely small at 0.3% at the maximum, the pattern characteristics are not deteriorated. In particular, if the total film thickness of the absorption layer and the low reflection layer is set to 80 nm or less and the average light reflectance is set to a minimum value, the absorption layer can be made thin without deteriorating the pattern characteristics. Become.

According to the present invention, the absorption layer and the low reflection layer of the EUV mask blank are thinned, so that it is expected to suppress the oblique effect and thereby improve the pattern accuracy, which is useful as a reflective photomask for EUV optical lithography. is there.
The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2011-038428 filed on February 24, 2011 are incorporated herein by reference. .

1: EUV mask blank 11: Substrate 12: Reflective layer (multilayer reflective film)
13: Protection layer 14: Absorption layer 15: Low reflection layer

Claims

A reflective mask blank for EUV lithography in which a reflective layer for reflecting EUV light and an absorption layer for absorbing EUV light are formed in this order,
The film thickness of the absorbing layer is within the range of ± 2.0% with respect to the film thickness at which the average light reflectance in the wavelength region of 13.3 to 13.7 nm is 4.0% or less and the minimum value. A reflective mask blank for EUV lithography, which is set to be
A reflective mask blank for EUV lithography in which a reflective layer for reflecting EUV light, an absorption layer for absorbing EUV light, and a low reflective layer for mask pattern inspection light (wavelength 190 to 260 nm) are formed in this order. And
The total film thickness of the absorption layer and the low reflection layer is ± 3% with respect to the total film thickness at which the average light reflectance in the wavelength region of 13.3 to 13.7 nm is 4.0% or less and a minimum value. A reflective mask blank for EUV lithography, which is set to be within a range of 2.0%.
3. The reflective mask blank for EUV lithography according to claim 1, wherein the absorption layer contains tantalum (Ta) and nitrogen (N) as main components.
The reflective mask blank for EUV lithography according to claim 2 or 3, wherein the low reflective layer contains tantalum (Ta) and oxygen (O) as main components.
The reflective mask blank for EUV lithography according to any one of claims 1 to 3, wherein the absorption layer has a thickness of 46 nm or more and 80 nm or less.
The reflective mask blank for EUV lithography according to any one of claims 2 to 4, wherein a total film thickness of the absorption layer and the low reflection layer is 46 nm or more and 80 nm or less.
A protective layer is formed between the reflective layer and the absorbing layer to protect the reflective layer when forming a pattern on the absorbing layer.
The reflective mask blank for EUV lithography according to any one of claims 1 to 6, wherein the protective layer is formed of at least one selected from the group consisting of Ru, Ru compounds, SiO 2 and Cr compounds.