TW202331406A - Reflection-type mask blank, reflection-type mask, and method for producing reflection-type mask - Google Patents

Abstract

The present invention relates to a reflection-type mask blank comprising a substrate and a multi-layer reflection film capable of reflecting EUV light, an intermediate film, a protection film and an absorbent film provided on the substrate in this order, in which the intermediate film is at least one selected from the group consisting of a silicon nitride film, a silicon oxide film and a silicon oxynitride film, and the thickness of the intermediate film is 7 to 11 nm.

Description

Reflective photomask base, reflective photomask, manufacturing method of reflective photomask

The present invention relates to a reflective photomask, a manufacturing method thereof, and a reflective photomask substrate as an original plate of a reflective photomask. : extreme ultraviolet light) exposure.

In recent years, in order to further miniaturize semiconductor devices, EUV lithography using EUV light with a center wavelength near 13.5 nm as a light source is being studied.

In EUV exposure, reflective optical systems and reflective masks are used according to the characteristics of EUV light. The reflective mask is formed on the substrate with a multilayer reflective film that reflects EUV light, and an absorber film that absorbs EUV light is patterned on the multilayer reflective film. A protective film is also often formed between the multilayer reflective film and the absorber film to protect the multilayer reflective film from the influence of etching when forming a mask pattern (Patent Document 1).

The EUV light incident on the reflective mask from the illumination optical system of the exposure device is reflected in the portion without the absorber film (opening) and absorbed in the portion with the absorber film (non-opening). As a result, the mask pattern is transferred on the wafer in the form of a resist pattern through the reduction projection optical system of the exposure device, and subsequent processing is performed.

On the other hand, the electromagnetic waves emitted from the light source of EUV light may also include ultraviolet light other than EUV light. Light in the ultraviolet wavelength region other than the above-mentioned EUV light is called OOB (Out of Band, out-of-band) light. Resists used to form resist patterns are photosensitive not only to EUV light but also to OOB light above in most cases, and to ultraviolet light with a wavelength of 150 to 300 nm (hereinafter also referred to as "resist photosensitive ultraviolet light"). Light") is especially high in photosensitivity. The reflectance of resist photosensitive ultraviolet light in the non-opening part can be reduced by providing a low reflection film on the above-mentioned absorber film, but in the opening part, the resist photosensitive ultraviolet light can be generated by the multilayer reflective film. reflection of light. FIG. 2 shows the reflectance at a wavelength of 10 to 400 nm of the multilayer reflective film having a Ru protective film cited in Non-Patent Document 1. The multilayer reflective film with Ru protective film has a reflectance of about 65% under EUV light with a wavelength of around 13.5 nm. On the other hand, in addition to EUV light, the reflectance is also relatively high under ultraviolet light with a wavelength of 150 nm or more. [Prior Art Literature] [Patent Document]

Patent Document 1: Japanese Patent Laid-Open No. 2006-332153 [Non-patent literature]

Non-Patent Document 1: S. A. George et al., Proc. SPIE Vol. 7636, 763626 (2010)

[Problem to be solved by the invention]

If the resist photosensitive ultraviolet light is reflected by the multilayer reflective film in the opening as described above, the resist photosensitive ultraviolet light will not form an image on the wafer during projection exposure to EUV light, but can Exposure of the entire resist degrades the shape of the resist pattern. Therefore, development of a reflective photomask in which reflection of resist photosensitive ultraviolet light is suppressed in openings, that is, regions where no absorber film exists, is desired in the industry. In addition, for reflective masks, higher reflectivity of EUV light is required.

Patent Document 1 discloses a reflective photomask substrate in which a thermal diffusion suppressing film is provided between a protective film and a multilayer reflective film. The film thickness of the above-mentioned thermal diffusion suppressing film is preferably 0.5-2.5 nm, and in the reflective photomask formed using the above-mentioned photomask base, the suppression of the reflection of photosensitive ultraviolet light of the resist is not sufficient.

Therefore, the object of the present invention is to provide a reflective photomask substrate, which can suppress the decrease in the reflection of EUV light and achieve the suppression of the reflection of resist photosensitive ultraviolet light when manufacturing a reflective photomask. Moreover, the subject of this invention is also providing the manufacturing method of the reflective type mask which used the said reflective type mask base, and a reflective type mask. [Technical means to solve the problem]

The inventors of the present invention have conducted earnest research on the above-mentioned subject, and found that by providing a film thickness of 7-11 nm between the multilayer reflective film and the protective film, it is selected from a silicon nitride film, a silicon oxide film, and a silicon oxynitride film. The present invention has been accomplished by achieving the above-mentioned object as one of the intermediate films among the group of films.

That is, the inventors found that the above-mentioned problems can be solved by the following configurations. [1] A reflective photomask substrate, which sequentially has a multilayer reflective film that reflects EUV light, an intermediate film, a protective film, and an absorber film on a substrate, and The intermediate film is one selected from the group consisting of a silicon nitride film, a silicon oxide film, and a silicon oxynitride film, The film thickness of the above-mentioned intermediate film is 7-11 nm. [2] The reflective photomask substrate according to [1], which has a hard mask film on the side opposite to the protective film side of the absorber film, and The material constituting the above-mentioned hard mask film is any one of chromium and silicon, or a material containing chromium and one or more elements selected from the group consisting of oxygen, nitrogen, carbon, and hydrogen, or a material containing silicon, Materials with one or more elements selected from the group consisting of oxygen, nitrogen, carbon and hydrogen. [3] The reflective photomask substrate as described in [1], wherein the absorber film is a simple substance of ruthenium metal, or Contains one or more elements selected from the group consisting of ruthenium, tantalum, and tin, and selected from the group consisting of chromium, gold, platinum, rhenium, hafnium, titanium, silicon, niobium, oxygen, nitrogen, boron, and hydrogen One or more of the elements. [4] The reflective photomask substrate according to [1], wherein the protective film contains at least one element selected from the group consisting of ruthenium and rhodium. [5] A reflective photomask having an absorber film pattern formed by patterning the absorber film of the reflective photomask base described in any one of [1] to [4]. [6] A method of manufacturing a reflective photomask, including the step of patterning the absorber film of the reflective photomask base described in any one of [1] to [4]. [Effect of Invention]

According to the present invention, it is possible to provide a reflective photomask substrate, which can suppress the decrease in the reflection of EUV light and achieve the suppression of the reflection of resist photosensitive ultraviolet light when manufacturing a reflective photomask. Moreover, according to this invention, the manufacturing method of the reflective mask using a reflective mask base, and a reflective mask can also be provided.

Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. Indicates the meaning of each description in this specification. In this specification, the numerical range represented by "~" means the range which includes the numerical value described before and after "~" as a lower limit and an upper limit. In this specification, elements such as hydrogen, boron, carbon, nitrogen, oxygen, fluorine, silicon, chlorine, titanium, chromium, niobium, ruthenium, rhodium, tin, hafnium, tantalum, platinum, and gold are sometimes represented by their corresponding element symbols (H, B, C, N, O, F, Si, Cl, Ti, Cr, Nb, Ru, Rh, Sn, Hf, Ta, Pt, Au, etc.)

＜Reflective mask base＞ The reflective photomask base of this embodiment has a multilayer reflective film that reflects EUV light, an intermediate film, a protective film, and an absorber film in sequence on a substrate. Also, the intermediate film is one selected from the group consisting of a silicon nitride film, a silicon oxide film, and a silicon oxynitride film, and the film thickness of the intermediate film is 7 to 11 nm. A reflective photomask base according to this embodiment will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of an aspect of a reflection-type photomask base according to this embodiment. The reflective photomask substrate 10 shown in FIG. 1 has a substrate 11, a multilayer reflective film 12, an intermediate film 13, a protective film 14, and an absorber film 15 in sequence, and on the side opposite to the multilayer reflective film 12 side of the substrate 11, The face has a back conductive film 16 . The reflective photomask substrate 10 shown in FIG. 1 has a backside conductive film 16 , and may also have a backside conductive film 16 . Furthermore, as shown in FIG. 3 , the reflective photomask substrate 10a of this embodiment may also have an aspect in which a substrate 11, a multilayer reflective film 12, an intermediate film 13, a protective film 14, and an absorber film are sequentially provided. 15, and a hard mask film 17, and a back conductive film 16 is provided on the surface of the substrate 11 opposite to the multilayer reflective film 12. Furthermore, the reflective photomask substrate 10 a shown in FIG. 3 has a back conductive film 16 , but may also have a back conductive film 16 .

Here, when a reflective photomask is produced by patterning the absorber film 15 using the above-mentioned reflective photomask base 10, in the region where the protective film 14 is exposed, the resist photosensitive ultraviolet light (wavelength 150 to 300 nm ultraviolet light). The reflected light from the resist photosensitive ultraviolet light of the reflective photomask is considered to be generated on the exposed surface of the protective film 14 and the multilayer reflective film 12 (mainly the interface with the intermediate film 13). In the case where the intermediate film 13 is in the above aspect, since the intermediate film is transparent to the resist photosensitive ultraviolet light, the reflected light of the resist photosensitive ultraviolet light generated above interferes with each other, and the reflection is suppressed. Also, at the same time, when the intermediate film 13 is in the above-mentioned form, the reflectance of the EUV light possessed by the multilayer reflective film 12 can be maintained.

Hereinafter, the configuration of the reflective photomask base of the present embodiment will be described. Furthermore, in the following, when producing a reflective photomask, the fact that the decrease in the reflection of EUV light is suppressed in the area without the absorber film (the area where the protective film is exposed) is also referred to as "excellent reflectance of EUV light". ". In addition, when making a reflective photomask, the fact that the reflection of resist photosensitive ultraviolet light is suppressed in the area without the absorber film (the area where the protective film is exposed) is also called "resist photosensitive ultraviolet light". Excellent low reflectivity of light."

(Substrate) The substrate included in the reflective photomask base of this embodiment preferably has a small coefficient of thermal expansion. The thermal expansion coefficient of the substrate is small, which can suppress the strain of the absorber film pattern due to the heat during EUV light exposure. The thermal expansion coefficient of the substrate is preferably 0±1.0×10 ^-7 /°C at 20°C, more preferably 0±0.3×10 ^-7 /°C. As a material with a small thermal expansion coefficient, SiO ₂ -TiO ₂ glass can be exemplified, but it is not limited thereto. Crystallized glass, quartz glass, metal silicon, and metal β-quartz solid solution can also be used. and other substrates. SiO ₂ -TiO ₂ -based glass is preferably quartz glass containing 90 to 95% by mass of SiO ₂ and 5 to 10% by mass of TiO ₂ . If the content of TiO ₂ is 5-10% by mass, the coefficient of linear expansion near room temperature is almost zero, and there is almost no dimensional change near room temperature. Furthermore, the SiO ₂ -TiO ₂ based glass may also contain trace components other than SiO ₂ and TiO ₂ .

The surface of the substrate on which the multilayer reflective film is laminated (hereinafter also referred to as "the first main surface") preferably has high surface smoothness. The surface smoothness of the first main surface can be evaluated by surface roughness. The surface roughness of the first main surface is preferably 0.15 nm or less in terms of root mean square roughness Rq. In addition, the surface roughness can be measured using an atomic force microscope, and the surface roughness will be described as the root mean square roughness Rq based on JIS B0601:2013.

In terms of improving the pattern transfer accuracy and positional accuracy of the reflective mask obtained using the reflective mask base, it is preferable to perform surface processing on the first main surface so as to have a specific flatness. In a specific region (for example, a region of 132 mm×132 mm) of the first main surface of the substrate, the flatness is preferably 100 nm or less, more preferably 50 nm or less, further preferably 30 nm or less. The flatness can be measured, for example, with an interferometer for planar measurement manufactured by Fuji Film Corporation. The size, thickness, and the like of the substrate can be appropriately determined according to the design value of the photomask, and the like. For example, it can be exemplified: the outer shape is 6 inches (152 mm) square, and the thickness is 0.25 inches (6.3 mm).

Furthermore, the substrate preferably has high rigidity from the viewpoint of preventing deformation of the film (multilayer reflective film, absorber film, etc.) formed on the substrate due to film stress. For example, the Young's modulus of the substrate is preferably 65 GPa or more.

(multilayer reflective film) The multilayer reflective film of the reflective mask base of this embodiment is not particularly limited as long as it has the required characteristics as the reflective layer of the EUV mask base. The multilayer reflective film preferably has higher reflectivity to EUV light, specifically, when EUV light is incident on the surface of the multilayer reflective film at an incident angle of 6°, the reflectivity of EUV light near a wavelength of 13.5 nm is the largest The value is preferably at least 60%, more preferably at least 65%. Also, even when a protective film is laminated on the multilayer reflective film, the maximum value of the reflectance of EUV light near a wavelength of 13.5 nm is preferably 60% or more, more preferably 65% or more.

Regarding the multilayer reflective film, in terms of achieving a higher reflectance of EUV light, it is common to use a high-refractive-index layer that exhibits a higher refractive index for EUV light, and a layer that exhibits a lower refractive index for EUV light. A multi-layer reflective film formed by alternately laminating multiple low-refractive-index layers. The multi-layer reflective film can be laminated with a layered structure in which a high-refractive-index layer and a low-refractive-index layer are sequentially laminated from the substrate side as one cycle, and multiple cycles can be laminated, or a low-refractive-index layer and a high-refractive-index layer can be sequentially laminated. The lamination structure of the layers is assumed to be one cycle and a plurality of cycles are laminated.

As the high refractive index layer, a layer containing Si can be used. As the material containing Si, besides Si simple substance, Si compounds containing one or more kinds selected from the group consisting of B, C, N, and O in Si may be used. By using a high-refractive-index layer containing Si, a reflection-type photomask excellent in reflectance of EUV light can be obtained. As the low refractive index layer, a layer containing a metal selected from the group consisting of Mo, Ru, Rh, and Pt, or an alloy thereof can be used. Si is widely used in the above-mentioned high refractive index layer, and Mo is widely used in the low refractive index layer. That is, Mo/Si multilayer reflective films are 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/Mo multilayer reflective film, Si/Ru/Mo/Ru multilayer reflective film.

The film thickness of each layer constituting the multilayer reflective film and the number of repeating units of the layer can be appropriately selected according to the film material used and the reflectivity of EUV light required for the reflective layer. Taking Mo/Si multilayer reflective film as an example, when making a multilayer reflective film with a maximum reflectance of EUV light of more than 60%, it is only necessary to combine the Mo film with a film thickness of 2.3±0.1 nm and the Mo film with a film thickness of 4.5±0.1 nm. The Si film may be laminated so that the number of repeating units becomes 30 to 60.

In addition, each layer which comprises a multilayer reflective film can be formed into a film so that it may become a desired thickness using well-known film-forming methods, such as a magnetron sputtering method and an ion beam sputtering method. For example, when an ion beam sputtering method is used to produce a multilayer reflective film, ion particles are supplied from an ion source to a target made of a high-refractive-index material and a target made of a low-refractive-index material. When the multilayer reflective film is a Mo/Si multilayer reflective film, an Si layer with a specific film thickness is formed on the substrate by ion beam sputtering, for example, using a Si target first. Thereafter, using a Mo target, a Mo layer having a specific film thickness is formed into a film. The Si layer and the Mo layer were set as one cycle and laminated for 30 to 60 cycles to form a Mo/Si multilayer reflective film.

The layer of the multilayer reflective film that is in contact with the intermediate film is preferably a layer made of a material that is not easily oxidized. A layer comprising a material that is not easily oxidized functions as a capping layer of the multilayer reflective film. As a layer made of a material that is not easily oxidized, a Si layer may, for example, be mentioned. When the multilayer reflective film is a Si/Mo multilayer reflective film, if the layer in contact with the intermediate film is an Si layer, the layer in contact with the intermediate film functions as a capping layer. In this case, the film thickness of the cap layer is preferably 11±2 nm.

(Interlayer) The reflective photomask substrate of this embodiment has an intermediate film selected from the group consisting of a silicon nitride film, a silicon oxide film, and a silicon nitride oxide film, and the film thickness of the intermediate film is 7-11 nm. .

When the intermediate film is a silicon nitride film, the intermediate film means a film containing Si and N, preferably a film composed of Si and N. Examples of the silicon nitride film include: Si ₃ N ₄ film, Si-Si ₃ N ₄ film (mixture film of Si and Si ₃ N ₄ ), and SiN _x film (uniform film of SiN _x composition, x=0.1 ~1.3). The molar ratio of Si ₃ N ₄ to Si in the Si-Si ₃ N ₄ film is preferably from 0.25 to 4.00, more preferably from 0.43 to 1.50. x in the SiN _x film is preferably from 0.1 to 1.0, more preferably from 0.2 to 0.5. Furthermore, the silicon nitride film may contain elements other than Si and N, excluding O.

When the intermediate film is a silicon oxide film, the intermediate film means a film containing Si and O, preferably a film composed of Si and O. The silicon oxide film may, for example, be _SiO2 film, SiO film, Si- _SiO2 film (mixture film of Si and _SiO2 ), Si-SiO film (mixture film of Si and SiO), and SiOx film ( _SiOx film). Uniform film of _x composition, x=0.1～1.9). The molar ratio of SiO ₂ to Si in the Si-SiO ₂ film is preferably from 0.67 to 9.00, more preferably from 1.50 to 4.00. x in the SiO _x film is preferably from 0.4 to 1.6, more preferably from 0.7 to 1.3. Furthermore, the silicon oxide film may contain elements other than Si and O, excluding N.

When the intermediate film is a silicon oxynitride film, the intermediate film means a film containing Si, O, and N, preferably a film composed of Si, O, and N. Examples of silicon oxynitride films include Si ₂ N ₂ O films, Si-Si ₂ N ₂ O films (mixture films of Si and Si ₂ N ₂ O), and SiO _x N _y films (SiO _x N _y compositions Uniform film, x=0.1~1.9, y=0.1~1.3). The molar ratio of Si ₂ N ₂ O to Si in the Si-Si ₂ N ₂ O film is preferably from 0.25 to 4.00, more preferably from 0.43 to 2.33. x in the SiO _x N _y film is preferably from 0.05 to 0.3, more preferably from 0.1 to 0.2. y in the SiO _x N _y film is preferably from 0.1 to 0.6, more preferably from 0.2 to 0.5. Furthermore, the silicon oxynitride film may contain elements other than Si, O, and N.

Also, the film thickness of the intermediate film is 7 to 11 nm. By making the film thickness of the interlayer film 7 to 11 nm, it is possible to suppress the decrease in the reflection of EUV light, and to suppress the reflection of resist photosensitive ultraviolet light. The film thickness of the interlayer is preferably 7.5-10.5 nm, more preferably 8-10 nm. The film thickness of the interlayer film can be determined by making a cross-section of the reflective mask substrate and analyzing it by scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDS).

The interlayer film is preferably transparent to resist photosensitive ultraviolet light from the point of being excellent in low reflectivity of resist photosensitive ultraviolet light. When the interlayer film is transparent to resist UV light, it can interfere with each resist UV light from the multilayer reflective film and protective film, and the resist UV light has excellent low reflectivity . Furthermore, the above-mentioned "transparent to the photosensitive ultraviolet light of the resist" means that the transmittance of the photosensitive ultraviolet light of the resist is 30% or higher, preferably 50% or higher, more preferably 70% or higher. In addition, it is preferable that the interlayer film does not reduce the high reflectance of EUV light exhibited by the multilayer reflective film. In this regard, the intermediate film preferably has a higher transmittance of EUV light. In terms of high EUV light transmittance, the intermediate film is preferably a silicon nitride film or a silicon oxynitride film, more preferably a silicon nitride film.

The crystalline state of the intermediate film may be crystalline or amorphous, preferably amorphous.

The intermediate film can be formed so as to have a desired thickness using known film forming methods such as magnetron sputtering and ion beam sputtering. For example, when forming an intermediate film of a silicon nitride film by ion beam sputtering, ion particles are supplied from an ion source to a Si target, and nitrogen gas is contained in the film forming environment. If the type of gas contained in the above-mentioned film-forming environment is changed, an intermediate film of a silicon oxide film or a silicon oxynitride film can be formed. Also, by changing the amount and ratio of the gases contained in the above-mentioned film forming environment, the ratio of each element contained in the intermediate film can be adjusted.

(protective film) The protective film of the reflective photomask base of this embodiment is provided for the purpose of protecting the multi-layer reflective film and making the multi-layer reflective when the absorber film is patterned by an etching process (usually a dry etching process). The membrane will not be damaged by the etching process.

As a material capable of achieving the above object, a material containing at least one element selected from the group consisting of Ru and Rh is exemplified. That is, the protective film preferably contains at least one element selected from the group consisting of Ru and Rh. More specifically, as the above-mentioned material, for example: Ru metal single substance, Ru alloy containing Ru, and one or more metals selected from the group consisting of Si, Ti, Nb, Rh, Ta, and Zr, including Ru-based materials such as the above-mentioned Ru alloys and nitrogen-containing Ru nitrides; and Rh metal simple substances, Rh alloys containing Rh and one or more metals selected from the group consisting of Si, Ti, Nb, Rh, Ta, and Zr , including Rh-based materials such as the above-mentioned Rh alloy and nitrogen-containing Rh nitride. Moreover, Cr, Al, Ta, the nitride containing these metals and nitrogen, and _Al2O3 etc. _can also be illustrated as a material which can achieve the said object. Among them, the material capable of achieving the above-mentioned purpose is preferably a Ru-based material or an Rh-based material, and more preferably a single Ru metal, an Ru alloy, a single Rh metal, or an Rh alloy. The Ru alloy is preferably a Ru-Si alloy, and the Rh alloy is preferably a Rh-Si alloy.

When the protective film is formed of a Ru alloy, the Ru content in the Ru alloy is preferably 30 at% or more and less than 100 at%. When the protective film is formed of a Rh alloy, the Rh content in the Rh alloy is preferably 30 at% or more and less than 100 at%. When the Ru content or the Rh content is within the above range, the protective film can sufficiently ensure the reflectance of EUV light and function as an etching stopper when etching the absorber film. Furthermore, cleaning resistance can be imparted to the reflective photomask, and deterioration over time of the multilayer reflective film can be prevented.

The thickness of the protective film is not particularly limited as long as it can function as a protective film. In terms of securing the reflectance of EUV light reflected by the multilayer reflective film, the film thickness of the protective film is preferably 1 to 10 nm, more preferably 1.5 to 6 nm, and still more preferably 2 to 5 nm. It is also preferable that the material of the protective film is Ru metal simple substance, Ru alloy, Rh metal simple substance, or Rh alloy, and the film thickness of the protective film is the above-mentioned preferred film thickness. The film thickness of the protective film can be determined by making a cross-section of the reflective mask substrate and analyzing it by scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDS).

The protective film can be formed using a known film-forming method such as magnetron sputtering or ion beam sputtering. When forming a Ru film by a magnetron sputtering method, it is preferable to form a film using a Ru target as a target and Ar gas as a sputtering gas.

(absorbent film) For the absorber film included in the reflective photomask base of this embodiment, when patterning the absorber film, the contrast between the EUV light reflected by the multilayer reflective film and the EUV light from the absorber film is required to be high. The patterned absorber film (absorber film pattern) can absorb EUV light to function as a binary mask, and can also function as a phase-shift mask that reflects EUV light and integrates with the The EUV light of the reflective film interferes to generate contrast.

As an aspect of the absorber film, for example, the absorber film is a form of Ru metal simple substance; or contains one or more elements selected from the group consisting of Ru, Ta, and Sn, and elements selected from the group consisting of Cr, A state of one or more elements in the group consisting of Au, Pt, Re, Hf, Ti, Si, Nb, O, N, B, and H. The above aspect can use the following absorber film pattern as a binary mask or a phase shift mask.

When the absorber film pattern is used as a binary mask, the absorber film must absorb EUV light, and the reflectance of EUV light is low. Specifically, when EUV light is irradiated onto the surface of the absorber film, the maximum value of the reflectance of EUV light near a wavelength of 13.5 nm is preferably 2% or less. The absorber film may contain one or more elements selected from the group consisting of Ta, Ti, Sn, and Cr, and one or more elements selected from the group consisting of O, N, B, Hf, and H. Among them, N or B is preferably included. By including N or B, the crystalline state of the absorber film can be made into an amorphous or microcrystalline structure. The crystalline state of the absorber film is preferably amorphous. Thereby, smoothness and flatness of the absorber film can be improved. Moreover, if the smoothness and flatness of the absorber film become high, the edge roughness of the absorber film pattern becomes small, and the dimensional accuracy of the absorber film pattern can be improved.

When using the absorber film pattern as a phase shift mask, the reflectance of the absorber film for EUV light is preferably 2% or more. In order to fully obtain the phase shift effect, the reflectance of the absorber film is preferably 9 to 15%. If the absorber film is used as a phase shift mask, the contrast of the optical image on the wafer is improved and the exposure margin is increased. As the material for forming the phase shift mask, for example: Ru metal simple substance; Ru alloy containing Ru and one or more metals selected from the group consisting of Cr, Au, Pt, Re, Hf, Ti and Si; Alloys of Ta and Nb; oxides containing Ru alloys or TaNb alloys and oxygen; nitrides containing Ru alloys or TaNb alloys and nitrogen; nitrogen oxides containing Ru alloys or TaNb alloys, oxygen and nitrogen, etc. Here, regarding the material for forming the phase shift mask, a material different from the material for forming the above-mentioned protective film is selected.

The absorber film may be a single-layer film or a multi-layer film including a plurality of layers. When the absorber film is a single-layer film, the number of steps in the manufacture of the photomask substrate can be reduced and the production efficiency can be improved. When the absorber film is a multilayer film, the layer disposed on the side opposite to the protective film side of the absorber film may be an antireflection film when inspecting the absorber film pattern using inspection light (eg, wavelength 193 to 248 nm) .

The absorber film can be formed using a known film-forming method such as magnetron sputtering or ion beam sputtering. For example, when using a magnetron sputtering method to form a Ru oxide film as an absorber film, the absorber film can be formed by sputtering by supplying a gas containing Ar gas and oxygen gas using a Ru target.

(Conductive film on the back) The reflective photomask base of this embodiment may have a back conductive film on the surface (second main surface) of the substrate opposite to the above-mentioned first main surface. By having a backside conductive film, reflective photomask substrates can be handled using electrostatic chucks. The back conductive film preferably has a lower sheet resistance. The sheet resistance of the back conductive film is, for example, preferably 200 Ω/□ or less, more preferably 100 Ω/□ or less. The constituent material of the back conductive film can be widely selected from those described in known documents. For example, a coating with a high dielectric constant described in Japanese Patent Application Laid-Open No. 2003-501823, specifically, a coating containing Si, Mo, Cr, CrON, or TaSi can be applied. Also, the constituent material of the back conductive film may also include Cr and one or more Cr compounds selected from the group consisting of B, N, O, and C, or Ta, and a compound selected from B, N, O, and C. More than one Ta compound in the group formed. The thickness of the back conductive film is preferably 10-1000 nm, more preferably 10-400 nm. In addition, the back conductive film may have a function of adjusting the stress on the second main surface side of the reflection type photomask base. That is, the rear conductive film can be adjusted to a state in which it is in balance with the stress generated by various films formed on the first main surface side, so that the reflective photomask base becomes flat. The back conductive film can be formed using known film-forming methods, such as magnetron sputtering, ion beam sputtering and other sputtering methods, CVD (chemical vapor deposition, chemical vapor deposition) method, vacuum evaporation method, electrolytic plating, etc. Law.

(Other films) The reflective photomask base of this embodiment may have other films. As another film, a hard mask film is mentioned. The hard cover film is preferably arranged on the side opposite to the protective film side of the absorber film. As the hard mask film, it is preferable to use a material having high resistance to dry etching, such as a Cr-based film and a Si-based film. As the material of the hard mask, specifically, any material in chromium (Cr) and silicon (Si); including Cr, and one selected from the group consisting of O, N, C and H A material of the above elements; or a material containing Si, and one or more elements selected from the group consisting of O, N, C, and H, etc. More specifically, CrO, CrN, _SiO2 , SiON, SiN, SiO, Si, SiC, SiCO, SiCN, SiCON, etc. are mentioned. If the hard mask film is formed on the absorber film, dry etching can be performed even if the minimum line width of the absorber film pattern becomes small. Therefore, it is effective for miniaturization of the absorber film pattern.

<Manufacturing method of reflective mask and reflective mask> The reflective photomask is obtained by patterning the absorber film of the reflective photomask base. That is, the reflective photomask base of this embodiment has the absorber film pattern formed by patterning the absorber film of the reflective photomask base of this embodiment.

An example of the manufacturing method of the reflection type photomask is demonstrated with reference to FIG. 4(a) - FIG. 4(b). FIG. 4(a) shows a state where a resist pattern 18 is formed on a reflective photomask substrate having a back conductive film 16, a substrate 11, a multilayer reflective film 12, an intermediate film 13, a protective film 14, and an absorber film 15 in sequence. . The formation method of the resist pattern 18 can use a well-known method, for example, apply a resist on the absorber film 15 of a reflective mask base, perform exposure and development, and form the resist pattern 18. Furthermore, the resist pattern 18 corresponds to the pattern formed on the wafer using a reflective mask. Thereafter, the absorber film 15 is etched and patterned with the resist pattern 18 of FIG. A laminate of the film pattern 15a. Then, as shown in Figure 4(c), a resist pattern 19 corresponding to the frame of the exposure area is formed on the laminate in Figure 4(b), and the resist pattern 19 in Figure 4(c) is used as a photomask for dry etch. Dry etching is performed until reaching the substrate 11 . After dry etching, the resist pattern 19 is removed to obtain a reflective mask as shown in FIG. 4( d ).

About dry etching at the time of forming the absorber film pattern 15a, the dry etching using Cl type gas, and the dry etching using F type gas are mentioned, for example. What is necessary is just to perform the removal of the resist pattern 18 or 19 by a well-known method, and removal using a cleaning solution is mentioned, for example. The cleaning solution may, for example, be sulfuric acid-hydrogen peroxide solution (SPM), sulfuric acid, ammonia water, ammonia-hydrogen peroxide solution (APM), OH radical cleaning water, or ozone water.

The reflective mask obtained by patterning the absorber film of the reflective mask base of this embodiment is suitable as a reflective mask used for EUV light exposure. The reflective mask of this embodiment can suppress the reflection of resist photosensitive ultraviolet light from the opening of the absorber film pattern (the region where the absorber film does not exist), and has a high reflectivity of EUV light, so The resist pattern can be formed on the wafer without deteriorating the shape of the resist pattern provided on the wafer.

As described above, the following configurations are disclosed in this specification. <1> A reflective photomask substrate, which sequentially has a multilayer reflective film that reflects EUV light, an intermediate film, a protective film, and an absorber film on the substrate, and The intermediate film is one selected from the group consisting of a silicon nitride film, a silicon oxide film, and a silicon oxynitride film, The film thickness of the above-mentioned intermediate film is 7-11 nm. <2> The reflective photomask substrate as described in <1>, which has a hard mask film on the side opposite to the protective film side of the absorber film, and The material constituting the above-mentioned hard mask film is any one of chromium and silicon, or a material containing chromium and one or more elements selected from the group consisting of oxygen, nitrogen, carbon, and hydrogen, or a material containing silicon, Materials with one or more elements selected from the group consisting of oxygen, nitrogen, carbon and hydrogen. <3> The reflective photomask substrate as described in <1> or <2>, wherein the absorber film is a simple substance of ruthenium metal, or Contains one or more elements selected from the group consisting of ruthenium, tantalum, and tin, and selected from the group consisting of chromium, gold, platinum, rhenium, hafnium, titanium, silicon, niobium, oxygen, nitrogen, boron, and hydrogen One or more of the elements. <4> The reflective photomask substrate according to any one of <1> to <3>, wherein the protective film contains at least one element selected from the group consisting of ruthenium and rhodium. <5> A reflective photomask having an absorber film pattern formed by patterning the absorber film of the reflective photomask base described in any one of <1> to <4>. <6> A method of manufacturing a reflective photomask, including the step of patterning the absorber film of the reflective photomask base described in any one of <1> to <4>. [Example]

Hereinafter, the present invention will be described in more detail based on examples. About the material, usage-amount, ratio, etc. shown in the following Example, it can change suitably without departing from the range of the summary of this invention. Therefore, the scope of the present invention should not be limitedly interpreted by the Examples shown below.

＜Implementation of Simulation＞ The simulation was carried out under the conditions shown below. Furthermore, the complex refractive index in the EUV light region is quoted from the database (https://henke.lbl.gov/optical_constants) provided by CXRO (The Center for X-Ray Optics, X-ray Optics Center). The complex refractive index in the ultraviolet region is quoted from the database provided by Angstrom Sun Technologies (http://www.angstec.com/database) and the database of Refractive Index. INFO (https://refractiveindex.info/).

(Ru Protective Film) As the multilayer reflective film, a multilayer reflective film in which 3.09 nm Mo layers and 3.95 nm Si layers were alternately laminated for 40 layers was set. The setting is a system in which an intermediate film is provided on a multilayer reflective film, and a protective film is further provided on the intermediate film. A system having a multilayer reflective film, an intermediate film, and a protective film corresponds to an opening portion (a region where no absorber film exists) of an absorber film pattern in a reflective photomask. In addition, the end of the multilayer reflective film, that is, the layer in contact with the intermediate film of the multilayer reflective film was set as the Mo layer. When the material of the protective film is set as Ru metal and the film thickness of the protective film is set to 2.4 nm, the intermediate film is set as Si film, Si ₃ N ₄ film, and Si-Si ₃ N ₄ film (Si and Si 3 N ₄ In the case of a mixture film of N ₄ , where the molar ratio of Si ₃ N ₄ to Si is 1.00), the dependence of the reflectance of ultraviolet light with a wavelength of 180 nm on the film thickness of the intermediate film at this time is shown in Fig. 5 middle. Example 1 is the case where the intermediate film is a Si film, Example 2 is the case where the intermediate film is a Si ₃ N ₄ film, Example 3 is the case where the intermediate film is a Si-Si ₃ N ₄ film, Example 1 is a comparative example, Example 2 and Example 3 is an embodiment. Also, the reflectance dependence of EUV light with a wavelength of 13.5 nm on the film thickness of the interlayer is shown in FIG. 6 . In addition, ultraviolet light with a wavelength of 180 nm is included in resist photosensitive ultraviolet light.

According to Fig. 5, when the film thickness of the intermediate film is set to 7-11 nm, and the intermediate film is Si ₃ N ₄ film and Si-Si ₃ N ₄ film, the reflection of ultraviolet light with a wavelength of 180 nm is obtained inhibition. Also, it can be seen that when the intermediate film is a Si ₃ N ₄ film, the reflection of ultraviolet light with a wavelength of 180 nm is further suppressed. On the other hand, when the interlayer film is a Si film, reflection of ultraviolet light with a wavelength of 180 nm cannot be suppressed. It can be seen from FIG. 6 that regardless of the type of the interlayer film, the reflectance of EUV light attains the maximum value in the region (preferably 8-10 nm region) where the film thickness of the interlayer film is 7-11 nm. It can be seen that when the intermediate film is Si-Si ₃ N ₄ film, the reflectance of EUV light is higher. Therefore, according to FIGS. 5 and 6 , it can be said that the reflective mask substrate of this embodiment suppresses the decrease in the reflection of EUV light and achieves the suppression of the reflection of resist photosensitive ultraviolet light when manufacturing a reflective mask.

(Rh Protective Film) In the above system in the case of the Ru protective film, the material of the protective film was Rh metal simple substance and the film thickness of the protective film was 2.5 nm, and the same simulation as above was performed. When the interlayer film is made of Si film, Si ₃ N ₄ film, and Si-Si ₃ N ₄ film, the dependence of the reflectance of ultraviolet light with a wavelength of 180 nm on the film thickness of the interlayer film at this time is shown in Figure 7. The case where the interlayer is a Si film is example 4, the case where the interlayer is a Si ₃ N ₄ film is example 5, the case where the interlayer is a Si-Si ₃ N ₄ film is example 6, example 4 is a comparative example, example 5 and Example 6 is an embodiment. Also, the reflectance dependence of EUV light with a wavelength of 13.5 nm on the film thickness of the interlayer is shown in FIG. 8 .

According to Fig. 7, when the film thickness of the intermediate film is set to 7-11 nm, and the intermediate film is Si ₃ N ₄ film and Si-Si ₃ N ₄ film, the reflection of ultraviolet light with a wavelength of 180 nm is obtained inhibition. Also, it can be seen that when the intermediate film is a Si ₃ N ₄ film, the reflection of ultraviolet light with a wavelength of 180 nm is further suppressed. On the other hand, when the interlayer film is a Si film, reflection of ultraviolet light with a wavelength of 180 nm cannot be suppressed. It can be seen from FIG. 8 that regardless of the type of the interlayer film, the reflectance of EUV light has a maximum value in the region (preferably 8-10 nm region) where the film thickness of the interlayer film is 7-11 nm. Also, it can be seen that the reflectance of EUV light is higher when the intermediate film is a Si—Si ₃ N ₄ film. Therefore, according to FIGS. 7 and 8 , it can be said that the reflective photomask substrate of this embodiment suppresses the decrease in the reflection of EUV light and achieves the suppression of the reflection of resist photosensitive ultraviolet light when manufacturing a reflective photomask.

As above, various embodiments have been described with reference to the drawings, but it is clear for those skilled in the art that changes and corrections can be added without departing from the spirit and scope of the present invention. In addition, this application is based on the Japanese patent application (Japanese Patent Application No. 2022-003847) for which it applied on January 13, 2022, The content is taken in this application as a reference.

10: Reflective mask substrate 10a: Reflective mask substrate 11: Substrate 12:Multilayer reflective film 13: Intermediate film 14: Protective film 15: Absorber film 15a: Absorber film pattern 16: Conductive film on the back 17: hard mask 18: Resist pattern 19: Resist pattern

FIG. 1 is a schematic diagram showing an example of an aspect of a reflection type photomask base according to this embodiment. FIG. 2 is a graph of the reflectivity of the multilayer reflective film cited in Non-Patent Document 1 at a wavelength of 10-400 nm. FIG. 3 is a schematic diagram showing an example of an aspect of a reflective photomask base according to this embodiment. 4(a) to 4(d) are schematic diagrams showing an example of the manufacturing steps of a reflective mask using the reflective mask base of this embodiment. Fig. 5 is a graph obtained by simulating the reflectance of a laminate having a Ru protective film, an intermediate film and a multilayer reflective film to 180 nm ultraviolet rays. 6 is a graph obtained by simulating the reflectivity of a laminate having a Ru protective film, an intermediate film and a multilayer reflective film to EUV light. Fig. 7 is a graph obtained by simulating the reflectance of a laminate having a Rh protective film, an intermediate film and a multilayer reflective film to 180 nm ultraviolet rays. Fig. 8 is a graph obtained by simulating the reflectance of a laminate having a Rh protective film, an intermediate film and a multilayer reflective film to EUV light.

10: Reflective mask substrate

11: Substrate

12:Multilayer reflective film

13: Intermediate film

14: Protective film

15: Absorber film

16: Conductive film on the back

Claims (6)

A reflective photomask substrate, which sequentially has a multilayer reflective film for reflecting EUV light, an intermediate film, a protective film, and an absorber film on the substrate, and The intermediate film is one selected from the group consisting of a silicon nitride film, a silicon oxide film, and a silicon oxynitride film, The film thickness of the above-mentioned intermediate film is 7-11 nm. The reflective photomask substrate according to claim 1, which has a hard mask film on the side opposite to the protective film side of the above-mentioned absorber film, and The material constituting the above-mentioned hard mask film is any one of chromium and silicon, or a material containing chromium and one or more elements selected from the group consisting of oxygen, nitrogen, carbon, and hydrogen, or a material containing silicon, Materials with one or more elements selected from the group consisting of oxygen, nitrogen, carbon and hydrogen. The reflective photomask substrate as claimed in item 1, wherein the above-mentioned absorber film is a simple substance of ruthenium metal, or Contains one or more elements selected from the group consisting of ruthenium, tantalum, and tin, and selected from the group consisting of chromium, gold, platinum, rhenium, hafnium, titanium, silicon, niobium, oxygen, nitrogen, boron, and hydrogen One or more of the elements. The reflective photomask substrate according to claim 1, wherein the protective film contains at least one element selected from the group consisting of ruthenium and rhodium. A reflective photomask having an absorber film pattern formed by patterning the absorber film of the reflective photomask substrate according to any one of claims 1 to 4. A method for manufacturing a reflective photomask, comprising the step of patterning the absorber film of the reflective photomask substrate according to any one of claims 1 to 4.