JP7459399B1 - Reflective mask blank, reflective mask and method for manufacturing the same, and method for manufacturing semiconductor devices - Google Patents

Abstract

The present invention aims to provide a reflective mask blank which prevents electrostatic breakdown while suppressing CD change during dry etching. The reflective mask blank 100 includes a multilayer reflective film 2, an absorber film 4, and an etching mask film 6 in this order, the absorber film 4 includes a buffer layer 42 and an absorber layer 44, the etching mask film 6 includes an element X and oxygen, and when an oxygen concentration ratio is defined as the oxygen content in the etching mask film 6 divided by the total content of the element X and oxygen, the oxygen concentration ratio on the absorber layer side of the etching mask film 6 is higher than the oxygen concentration ratio at the center of the thickness of the etching mask film 6, and the element X includes at least one selected from tantalum and silicon.

Description

The present invention relates to a reflective mask blank that is an original for manufacturing an exposure mask used in manufacturing semiconductor devices, a reflective mask, a method for manufacturing the same, and a method for manufacturing a semiconductor device.

The types of light sources used in exposure equipment used in semiconductor device manufacturing have evolved as the wavelengths have gradually become shorter, including G-line with a wavelength of 436 nm, I-line with a wavelength of 365 nm, KrF laser with a wavelength of 248 nm, and ArF laser with a wavelength of 193 nm. In order to realize fine pattern transfer, EUV lithography using extreme ultraviolet (EUV) having a wavelength of around 13.5 nm has been developed. In EUV lithography, a reflective mask is used because there are few materials that are transparent to EUV light. This reflective mask has a basic mask structure in which a multilayer reflective film that reflects exposure light is formed on a low thermal expansion substrate, and a desired transfer pattern is formed on a protective film to protect the multilayer reflective film. It has a structure. In addition, based on the configuration of the transfer pattern, typical examples include a binary reflective mask consisting of a relatively thick absorber pattern that sufficiently absorbs EUV light, and a binary reflective mask that attenuates EUV light by light absorption and that is made of a multilayer reflective film. There is a phase shift type reflection mask (halftone phase shift type reflection mask) which is made of a relatively thin absorber pattern that generates reflected light whose phase is almost inverted (approximately 180° phase inversion) with respect to the reflected light. This phase shift type reflective mask (halftone phase shift type reflective mask) has the effect of improving resolution because it can obtain high transferred optical image contrast due to the phase shift effect, similar to the transmission type optical phase shift mask. Furthermore, since the absorber pattern (phase shift pattern) of the phase shift reflective mask is thin, a fine phase shift pattern can be formed with high precision.

A reflective mask blank, which is an original plate for manufacturing a reflective mask, typically includes a multilayer reflective film on a substrate to reflect exposure light, and defects etched using dry etching or electron beam (EB). It has a protective film for protecting the multilayer reflective film from modification, an absorber film for forming an absorber pattern, and an etching mask film that serves as a mask for pattern etching the absorber film. . Additionally, if the etching selectivity between the absorber film that absorbs/attenuates EUV light and the protective film is not high enough, dry etching during pattern formation may damage the underlying multilayer reflective film. Most products have a buffer layer that protects them from damage.

By the way, in EUV lithography, a projection optical system consisting of a large number of reflecting mirrors is used due to light transmittance. In such a projection optical system, EUV light is obliquely incident on a reflective mask so that the plurality of reflecting mirrors do not block the projection light (exposure light). With the improvement of the numerical aperture (NA) of projection optical systems, studies are underway to increase the angle of incidence of exposure light to a larger angle of oblique incidence (for example, 6 degrees or more). However, in a projection optical system in which exposure light is obliquely incident on a mask surface, there is a problem of a shadowing effect that reduces the accuracy of the dimensions and position of a pattern to be transferred.

The shadowing effect is mainly caused by the three-dimensional structure of the absorber pattern. Therefore, by making the absorber film as thin as possible, the shadowing effect can be reduced. However, if the absorber film is made thinner, it will not be able to absorb the exposure light sufficiently, and undesirable reflected light from the absorber pattern may adversely affect the transfer accuracy, so there is a limit to how thin the absorber film can be made.

Against this background, for example, Patent Document 1 discloses that an absorber film has a buffer layer and an absorption layer provided on the buffer layer, and the buffer layer is made of tantalum (Ta) or silicon (Si). ), and the absorption layer is made of a material containing chromium (Cr), which has a relatively large extinction coefficient for EUV light (for example, wavelength 13.5 nm). It has been confirmed that with this configuration, an absorber pattern with an EUV light reflectance of 2% or less can be realized even if the thickness of the absorber film is made thinner than before.

Furthermore, in Patent Document 1, in order to be able to remove the etching mask film at the same time when patterning the buffer layer, the etching mask film is made of a material containing the same kind of tantalum (Ta) or silicon (Si) as the buffer layer. This is disclosed.

For example, when patterning an etching mask film containing tantalum (Ta), a fluorine (F)-based gas is used. However, when fluorine (F)-based gas is used for dry etching of the etching mask film, the etching rate of the resist film is relatively high, making it difficult to pattern the etching mask film finely and with high precision using only the resist film. . In connection with this, for example, Patent Document 2 discloses that a hard mask layer as an etching mask film is provided on an absorbing layer containing chromium (Cr), and this hard mask layer is made of tantalum (Ta) for patterning the absorbing layer. )-based hard mask layer and a chromium (Cr)-based second hard mask layer for patterning the first hard mask layer.

International Publication No. 2020/175354 US Patent Application Publication No. 2021/0405519

Generally, the etching mask film is preferably made of oxide in order to suppress CD (critical dimension) changes during a dry etching process using an etching gas containing oxygen. On the other hand, if the oxygen concentration contained in a tantalum-based etching mask film is high, for example, the electrical resistivity will increase, resulting in excessive charging during the manufacturing process of reflective mask blanks and reflective masks. , a problem arose in that the frequency of fatal defects caused by electrostatic damage increased.

The present invention has been made in view of the above-mentioned problems, and by reducing the oxygen concentration ratio at the center of the thickness of the etching mask film than the oxygen concentration ratio at least at the bottom of the etching mask film, it is possible to reduce the oxygen concentration ratio in the dry etching process. A reflective mask blank that prevents electrostatic damage while suppressing CD changes, a reflective mask manufactured from the reflective mask blank, a method for manufacturing the reflective mask, and a semiconductor using the reflective mask The purpose is to provide a method for manufacturing the device.

In order to solve the above problems, the present invention has the following configuration.

(Configuration 1)
Structure 1 of the present invention is a reflective mask blank comprising a multilayer reflective film, an absorber film, and an etching mask film in this order,
The absorber film includes a buffer layer and an absorbent layer having etching resistance with respect to the buffer layer,
The etching mask film has etching resistance with respect to the absorption layer and contains element X and oxygen (O),
Here, if the oxygen concentration ratio is defined as the oxygen (O) content (atomic %) divided by the total content (atomic %) of element X and oxygen (O) in the etching mask film, then the etching mask an oxygen concentration ratio on the absorption layer side of the film is higher than an oxygen concentration ratio at the center of the thickness of the etching mask film;
The reflective mask blank is a reflective mask blank in which the element X includes at least one selected from tantalum (Ta) and silicon (Si).

(Configuration 2)
A second aspect of the present invention is the reflective mask blank according to the first aspect, wherein the oxygen concentration ratio on the surface side of the etching mask film opposite to the absorption layer is higher than the oxygen concentration ratio at the center of the thickness of the etching mask film.

(Configuration 3)
A third aspect of the present invention is the reflective mask blank according to the first or second aspect, wherein the etching mask film has a thickness of 6 nm to 30 nm.

(Configuration 4)
Structure 4 of the present invention is the reflective mask blank according to any one of Structures 1 to 3, in which the ratio of the thickness of the etching mask film to the thickness of the buffer layer is 0.1 to 15.

(Configuration 5)
A fifth aspect of the present invention is the reflective mask blank according to any one of the first to fourth aspects, further comprising a second etching mask film on the first etching mask film, the second etching mask film containing chromium (Cr).

(Configuration 6)
A sixth aspect of the present invention is the reflective mask blank according to any one of the first to fifth aspects, wherein the buffer layer contains at least one selected from the group consisting of tantalum (Ta) and silicon (Si).

(Configuration 7)
Structure 7 of the present invention is the reflective mask blank according to any one of Structures 1 to 6, in which the absorption layer contains at least one selected from chromium (Cr) and ruthenium (Ru).

(Configuration 8)
Structure 8 of the present invention is the reflective mask blank according to any one of Structures 1 to 7, which includes a protective film between the multilayer reflective film and the absorber film.

(Configuration 9)
A ninth aspect of the present invention is a reflective mask having an absorber pattern formed by patterning the absorber film in the reflective mask blank of any one of the first to eighth aspects.

(Configuration 10)
Configuration 10 of the present invention is a method for producing a reflective mask from the reflective mask blank of any of configurations 1 to 8, comprising the steps of dry-etching the etching mask film to form an etching mask film pattern, and patterning the absorber film using the etching mask film pattern as a mask.

(Configuration 11)
Arrangement 11 of the present invention is a method for manufacturing a semiconductor device, comprising a step of setting the reflective mask described in Arrangement 9 in an exposure apparatus and transferring a transfer pattern to a resist film formed on a transfer target substrate. .

According to the present invention, since the oxygen concentration ratio at the center of the thickness of the etching mask film is lower than the oxygen concentration ratio at least at the bottom of the etching mask film, it is possible to suppress CD changes during the dry etching process and still perform static etching. It is possible to provide a reflective mask blank and a method for manufacturing a reflective mask that can prevent fatal defects caused by electric breakdown. Further, according to the present invention, since the etching mask film has a predetermined oxygen concentration ratio, the etching rate of the etching mask film can be adjusted in accordance with the pattern etching of the absorber film. Therefore, it is possible to provide a reflective mask blank and a method for manufacturing a reflective mask that does not damage the surface of the absorber film or the protective film that protects the multilayer reflective film during the dry etching process. Further, according to the present invention, it is possible to provide a reflective mask having a fine and highly accurate absorber pattern in which CD change during the etching process is suppressed. Further, according to the present invention, by using the reflective mask, it is possible to manufacture a semiconductor device in which a fine and highly accurate transfer pattern is formed.

1 is a schematic cross-sectional view for explaining a general configuration of a reflective mask blank according to one embodiment of the present invention. FIG. FIG. 2 is a schematic cross-sectional view for explaining an example of a layer structure of a reflective mask blank. FIG. 2 is a schematic cross-sectional view for explaining another example of a layer structure of a reflective mask blank. 1A to 1C are schematic cross-sectional views for explaining a process for producing a reflective mask from a reflective mask blank. It is a further cross-sectional schematic diagram for explaining the process of producing a reflective mask from a reflective mask blank. It is a further cross-sectional schematic diagram for explaining the process of producing a reflective mask from a reflective mask blank. It is a further cross-sectional schematic diagram for explaining the process of producing a reflective mask from a reflective mask blank. It is a further cross-sectional schematic diagram for explaining the process of producing a reflective mask from a reflective mask blank. 10 is a further schematic cross-sectional view illustrating a process for producing a reflective mask from a reflective mask blank. FIG. 10 is a further schematic cross-sectional view illustrating a process for producing a reflective mask from a reflective mask blank. FIG.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the following embodiment is one form for embodying the present invention, and does not limit the scope of the present invention. In addition, in the drawings, the same or corresponding parts are given the same reference numerals, and the description thereof may be simplified or omitted.

In this specification, "on" a substrate or a film includes not only the case where it is in contact with the upper surface of the substrate or film, but also the case where it is not in contact with the upper surface of the substrate or film. In other words, "on" a substrate or a film includes the case where a new film is formed above the substrate or film, or the case where another film is interposed between the substrate or film. In addition, "on" does not necessarily mean the upper side in the vertical direction, but merely indicates the relative positional relationship in the thickness direction of the substrate or film.

<Structure of reflective mask blank>
FIG. 1 is a schematic cross-sectional view for explaining the configuration of a reflective mask blank 100 according to an embodiment of the present invention. As shown in the figure, the reflective mask blank 100 includes a substrate 1, a multilayer reflective film 2 formed on the first main surface (front surface) side that reflects EUV light that is exposure light, and the multilayer reflective film 2. 2, an absorber film 4 that absorbs EUV light, and an etching mask film 6, which are stacked in this order. In the reflective mask blank 100 of this embodiment, the absorber film 4 includes a buffer layer 42 and an absorbing layer 44 provided on the buffer layer 42 . Further, on the second main surface (back surface) side of the substrate 1, a back conductive film 5 for an electrostatic chuck is formed.

The reflective mask blank 100 may include a configuration in which no rear surface conductive film 5 is formed. The reflective mask blank 100 may also include a configuration of a mask blank with a resist film in which a resist film 11 is formed on an etching mask film 6.

The configuration of each layer of the reflective mask blank 100 according to one embodiment of the present invention will be specifically described below.

<<Substrate>>
The substrate 1 preferably has a low coefficient of thermal expansion within the range of 0±5 ppb/° C. in order to prevent distortion of a transferred pattern (absorber pattern to be described later) due to heat during exposure to EUV light. As a material having a low coefficient of thermal expansion in this range, for example, SiO ₂ -TiO ₂ glass, multi-component glass ceramics, etc. can be used.

The first main surface of the substrate 1 on which the transfer pattern is formed is surface-processed to have a high flatness in terms of obtaining at least pattern transfer accuracy and positional accuracy. In the case of EUV exposure, in a 132 mm x 132 mm area of the main surface of the substrate 1 on which the transfer pattern is formed, the flatness is preferably 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.03 μm or less. In addition, the second main surface on the opposite side to the side on which the absorber film 4 is formed is a surface that is electrostatically chucked when set in an exposure device, and in a 142 mm x 142 mm area, the flatness is preferably 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.03 μm or less.

Further, the surface roughness (surface smoothness) of the first main surface of the substrate 1 on which the transferred pattern is formed is preferably 0.1 nm or less in terms of root mean square roughness (Rq). Note that the surface roughness can be measured using an atomic force microscope.

Furthermore, the substrate 1 preferably has high rigidity in order to prevent deformation due to film stress of the films (such as the multilayer reflective film 2) formed thereon. In particular, the substrate 1 preferably has a high Young's modulus of 65 GPa or more.

<<Multilayer reflective film>>
The multilayer reflective film 2 has a multilayer structure in which a plurality of layers mainly composed of elements having different refractive indexes are stacked periodically. Generally, the multilayer reflective film 2 includes a thin film of a light element or its compound (high refractive index layer), which is a high refractive index material, and a thin film (low refractive index layer) of a heavy element or its compound, which is a low refractive index material. It consists of a multilayer film in which layers are alternately stacked for about 40 to 60 cycles. In order to form the multilayer reflective film 2, a high refractive index layer and a low refractive index layer may be laminated in plural periods in this order from the substrate 1 side. In this case, one (high refractive index layer/low refractive index layer) laminated structure constitutes one period.

Note that the uppermost layer of the multilayer reflective film 2, that is, the surface layer of the multilayer reflective film 2 on the side opposite to the substrate 1, is preferably a high refractive index layer. When a high refractive index layer and a low refractive index layer are laminated in this order from the substrate 1 side, the uppermost layer becomes the low refractive index layer. However, when the low refractive index layer is on the surface of the multilayer reflective film 2, the low refractive index layer is easily oxidized and the reflectance of the surface of the multilayer reflective film decreases. Preferably, a high refractive index layer is formed thereon. On the other hand, when a low refractive index layer and a high refractive index layer are laminated in this order from the substrate 1 side, the uppermost layer becomes the high refractive index layer. In that case, the uppermost high refractive index layer becomes the surface of the multilayer reflective film 2.

The high refractive index layer included in the multilayer reflective film 2 is, for example, a layer made of a material containing silicon (Si). The high refractive index layer may contain simple Si or a Si compound. The Si compound may be a Si compound containing silicon (Si) and boron (B), carbon (C), nitrogen (N), oxygen (O) and hydrogen (H). By using a layer containing Si as the high refractive index layer, a reflective mask 200 for EUV lithography having excellent reflectance for EUV light can be obtained.

The low refractive index layer included in the multilayer reflective film 2 is a layer made of a material containing a transition metal. The transition metal contained in the low refractive index layer is, for example, a metal element selected from molybdenum (Mo), ruthenium (Ru), rhodium (Rh), and platinum (Pt), or an alloy thereof.

For example, as the multilayer reflective film 2 for EUV light with a wavelength of 13 to 14 nm, a Mo/Si multilayer film in which Mo films and Si films are alternately laminated in about 40 to 60 periods can be preferably used.

The reflectance of such a multilayer reflective film 2 alone is, for example, 65% or more. The upper limit of the reflectance of the multilayer reflective film 2 is, for example, 73%. Note that the thickness and period of the layers included in the multilayer reflective film 2 can be selected so as to satisfy Bragg's law. Note that the thickness and period of each constituent layer of the multilayer reflective film 2 may be appropriately selected depending on the exposure wavelength, and are selected so as to satisfy the Bragg reflection law. Although there are a plurality of high refractive index layers and a plurality of low refractive index layers in the multilayer reflective film 2, the thicknesses of the high refractive index layers and the low refractive index layers do not have to be the same. Furthermore, the thickness of the outermost Si layer of the multilayer reflective film 2 can be adjusted within a range that does not reduce the reflectance. The thickness of the outermost Si (high refractive index layer) can be 3 nm to 10 nm.

The multilayer reflective film 2 can be formed by ion beam sputtering. For example, when the multilayer reflective film 2 is a Mo/Si multilayer film, a Mo film having a thickness of about 3 nm is formed on the substrate 1 by ion beam sputtering using a Mo target. Next, a Si film having a thickness of about 4 nm is formed using a Si target. By repeating such an operation, a multilayer reflective film 2 having 40 to 60 periods of Mo/Si films stacked can be formed. At this time, the surface layer of the multilayer reflective film 2 on the side opposite to the substrate 1 is a layer containing Si (Si film). The thickness of one period of Mo/Si film is 7 nm. In addition, when forming the multilayer reflective film 2, krypton (Kr) ion particles may be supplied from an ion source to perform ion beam sputtering to form the multilayer reflective film 2.

<<Protective film>>
It is preferable that the reflective mask blank 100 has a protective film 3 between the multilayer reflective film 2 and the absorber film 4. By forming the protective film 3 on the multilayer reflective film 2, damage to the surface of the multilayer reflective film 2 is suppressed when manufacturing the reflective mask 200 (EUV mask) using the reflective mask blank 100. As a result, the reflectance characteristics for EUV light are improved.

The protective film 3 is formed on the multilayer reflective film 2 in order to protect the multilayer reflective film 2 from dry etching and cleaning in the manufacturing process of the reflective mask 200, which will be described later. It also protects the multilayer reflective film 2 when black defects in the absorber pattern 4a are repaired using an electron beam (EB). The protective film 3 is formed of a material that is resistant to etchants, cleaning solutions, and the like.

Here, although FIG. 1 shows the case where the protective film 3 is a single layer, it can also have a laminated structure of two or more layers.

For example, the protective film 3 can be made of a material containing Ru as a main component. That is, the material of the protective film 3 can be Ru metal alone, Rh metal alone, Ru alloys containing at least one metal selected from titanium (Ti), niobium (Nb), rhodium (Rh), molybdenum (Mo), zirconium (Zr), yttrium (Y), boron (B), lanthanum (La), cobalt (Co), and rhenium (Re), and materials containing nitrogen (N) in any of the above.

Such a protective film 3 is particularly effective when the buffer layer 42 of the absorber film 4 is patterned by dry etching using an oxygen-free fluorine-based gas (F-based gas) or chlorine-based gas (Cl-based gas). The protective film 3 is preferably formed of a material that provides an etching selectivity ratio of the buffer layer 42 to the protective film 3 (etching rate of the buffer layer 42/etching rate of the protective film 3) of 1.5 or more, preferably 3 or more, in dry etching using a fluorine-based gas or a chlorine-based gas.

The thickness of the protective film 3 is not particularly limited as long as it can fulfill its function as the protective film 3. From the viewpoint of reflectance of EUV light, the thickness of the protective film 3 is preferably 1.0 nm to 8.0 nm, more preferably 1.5 nm to 6.0 nm.

Examples of methods for forming the protective film 3 include ion beam sputtering, magnetron sputtering, reactive sputtering, vapor deposition (CVD), and vacuum evaporation. The protective film 3 may be continuously formed by ion beam sputtering after the multilayer reflective film 2 is formed.

<<Absorber membrane>>
An absorber film 4 for absorbing or attenuating EUV light is formed on the multilayer reflective film 2 or the protective film 3 described above. For example, in the reflective mask blank 100 for producing a binary reflective mask, the thickness of the absorber film 4 is preferably as thin as possible in order to obtain a fine and highly accurate absorber pattern (transfer pattern). Therefore, the material for the absorber film 4 is preferably one that has a high absorption rate (low reflectance) for EUV light. Also, in the reflective mask blank 100 for producing a phase-shift reflective mask, the absorber film 4 is formed of a material with high absorption rate in order to invert the phase of EUV reflected light with a relatively thin absorber pattern. It is preferable that

Furthermore, in the reflective mask blank 100 according to this embodiment, the absorber film 4 includes a buffer layer 42 and an absorber layer 44 provided on the buffer layer 42 (on the opposite side to the substrate 1).

Of the absorber film 4 of this embodiment, the material of the absorbing layer 44 has a function of absorbing EUV light and can be processed by etching etc. (preferably chlorine (Cl) gas and/or fluorine (F)). ) and can be etched by dry etching using a system gas), and can be made of a material that has a high etching selectivity with respect to the protective film 3 and the etching mask film 6 to be described later. Palladium (Pd), silver (Ag), platinum (Pt), gold (Au), iridium (Ir), tungsten (W), chromium (Cr), cobalt (Co), and manganese have such functions. (Mn), tin (Sn), tantalum (Ta), vanadium (V), nickel (Ni), hafnium (Hf), iron (Fe), copper (Cu), tellurium (Te), zinc (Zn), magnesium (Mg), germanium (Ge), aluminum (Al), rhodium (Rh), ruthenium (Ru), molybdenum (Mo), niobium (Nb), titanium (Ti), zirconium (Zr), yttrium (Y) and silicon At least one metal selected from (Si), an alloy containing two or more metals, or a compound thereof can be preferably used. The compound may include oxygen (O), nitrogen (N), carbon (C) and/or boron (B) in the metal or alloy.
The material of the absorption layer 44 preferably contains, for example, chromium (Cr) and/or ruthenium (Ru). When a thin film containing Cr or Ru is placed in contact with the surface of the protective film 3 containing Ru as a main component, a problem arises in that the etching selectivity between the absorption layer 44 and the protective film 3 is not high. Therefore, in the reflective mask blank 100 according to the present embodiment, a buffer layer 42 made of a material containing at least one selected from tantalum (Ta) and silicon (Si) is provided between the absorption layer 44 and the protective film 3. It is located.

In one embodiment, the material of buffer layer 42 includes tantalum (Ta). Further, the material of the buffer layer 42 preferably contains tantalum (Ta) and one or more elements selected from oxygen (O), nitrogen (N), and boron (B). Specific examples of the material of the buffer layer 42 containing tantalum (Ta) include Ta, TaN, TaO, TaON, TaB, TaBN, TaBO, TaBON, and the like.
Furthermore, as the material of the buffer layer 42 containing tantalum (Ta), palladium (Pd), silver (Ag), platinum (Pt), gold (Au), iridium (Ir), tungsten (W), and chromium (Cr) are also used. , cobalt (Co), manganese (Mn), tin (Sn), vanadium (V), nickel (Ni), hafnium (Hf), iron (Fe), copper (Cu), tellurium (Te), zinc (Zn) , magnesium (Mg), germanium (Ge), aluminum (Al), rhodium (Rh), ruthenium (Ru), molybdenum (Mo), niobium (Nb), titanium (Ti), zirconium (Zr), yttrium (Y) and silicon (Si), and may contain at least one metal selected from silicon (Si).

When the material of the buffer layer 42 is a material containing Ta and at least one element selected from N and B, the Ta content in the buffer layer 42 is 50 atomic % or more, and 70 atomic % or more. be able to. The Ta content in the buffer layer 42 is 95 atomic % or less, and can be 65 atomic % or less. The total content of N and B in the buffer layer 42 is 50 atomic % or less, and can be 30 atomic % or less. The total content of N and B in the buffer layer 42 can be 5 atomic % or more. The content of N is preferably lower than the content of B. This is because the lower the N content, the faster the etching rate with chlorine gas and the easier it is to remove the buffer layer 42.

Further, when the buffer layer 42 is made of a material containing Ta and O, the Ta content in the buffer layer 42 is 50 atomic % or more, and can be 70 atomic % or more. The Ta content in the buffer layer 42 is 95 atomic % or less, and can be 65 atomic % or less. The O content in the buffer layer 42 is 70 atomic % or less, and can be 60 atomic % or less. From the viewpoint of ease of etching, the O content in the buffer layer 42 is 10 atomic % or more, and can be 20 atomic % or more.

In other embodiments, buffer layer 42 may be formed of a material including silicon (Si). Further, the material of the buffer layer 42 preferably contains silicon (Si) and at least one element selected from oxygen (O), nitrogen (N), carbon (C), and hydrogen (H).

Specific examples of the material containing silicon (Si) include SiO, SiN, SiON, SiC, SiCO, SiCN, SiCON, MoSi, MoSiO, MoSiN, and MoSiON. It is preferable to use SiO, SiN, or SiON as the material containing Si. Note that the material can contain a metalloid or metal other than Si within a range where the effects of the present invention can be obtained. Moreover, molybdenum silicide can be used as the metal Si compound.

The thickness of the buffer layer 42 may be approximately the same as or thinner than the etching mask film 6 described later, as long as the protection film 3 is not damaged during etching of the absorber film 4. Specifically, the thickness of the buffer layer 42 is preferably 2 nm to 50 nm, and can be 4 nm to 30 nm.

As described above, the buffer layer 42 is formed of a material containing at least one selected from tantalum (Ta) and silicon (Si), for example, a fluorine-based gas or a chlorine-based gas that does not contain oxygen. Can be etched. Further, the buffer layer 42 made of such a material can have sufficient etching resistance against the protective film 3 whose main component is Ru.

Next, the absorbing layer 44 disposed on and in contact with the buffer layer 42 can be made of a material containing at least one selected from chromium (Cr) and ruthenium (Ru), as described in detail below. This allows the absorbing layer 44 to have etching resistance against the buffer layer 42, and can satisfy the optical characteristics required of an absorber film (phase shift film) even if the film thickness is made thinner than before.

Here, when layer A has "etching resistance" to layer B, it means that when layer B is etched using layer A as a mask, the etching speed of layer B is sufficiently faster than the etching speed of layer A. say. More specifically, when the etching selectivity ratio of the B layer to the A layer is 1.5 or more, preferably 3 or more, as defined by the formula: B layer etching rate/A layer etching rate, It can be said that the A layer has "etching resistance" with respect to the B layer.

In one embodiment, the material of the absorption layer 44 includes chromium (Cr) alone, or chromium (Cr) and at least one element selected from nitrogen (N), oxygen (O), and carbon (C). It is a Cr compound. Examples of the Cr compound include CrN, CrC, CrON, CrCO, CrCN, CrCON, CrBN, CrBC, CrBON, CrBCN, and CrBOCN. In order to increase the extinction coefficient of the absorption layer 44, it can be made of a material that does not contain oxygen. In this case, it is also possible to increase the etching selectivity with respect to chlorine gas. Examples of oxygen-free Cr compounds include CrN, CrC, CrCN, CrBN, CrBC, and CrBCN. The Cr content of the Cr compound is preferably 50 atom % or more and less than 100 atom %, more preferably 80 atom % or more and less than 100 atom %. In addition, in this specification, "does not contain oxygen" or "does not substantially contain oxygen" refers to a compound in which the oxygen content is 10 atomic % or less, preferably 5 atomic % or less. .

In another embodiment, the absorption layer 44 is formed of a material containing ruthenium (Ru) alone or a Ru compound containing ruthenium (Ru) and at least one element selected from nitrogen (N) and oxygen (O). may be done. Examples of the Ru compound include RuN, RuON, and RuO.

Further, the material of the absorption layer 44 may be a RuCr-based compound containing ruthenium (Ru) and chromium (Cr). Ru-based compounds tend to have a crystallized structure, which adversely affects processing performance. That is, crystallized metal crystal particles tend to have large sidewall roughness when forming an absorber pattern, and therefore the absorber film 4 is preferably amorphous. By adding chromium (Cr) to ruthenium (Ru) as the material for the absorption layer 44, it is possible to make the crystal structure amorphous and improve processing characteristics. Further, by containing at least one element selected from nitrogen (N) and oxygen (O) in addition to ruthenium (Ru) and chromium (Cr), the crystal structure can be made more amorphous. Examples of the RuCr-based compound include RuCrN, RuCrON, and RuCrO. The composition range (atomic ratio) of Ru and Cr can be set to Ru:Cr=40:1 to 1:20, and can be set to 40:1 to 3:7.
Further, the material of the absorption layer 44 may be an RuTa-based compound or a RuPt-based compound containing ruthenium (Ru), tantalum (Ta), or platinum (Pt). The RuTa-based compound or RuPt-based compound may further contain at least one element selected from nitrogen (N), oxygen (O), and boron (B). Examples of the RuTa-based compound include RuTaN, RuTaON, RuTaO, RuTaB, RuTaBN, RuTaBO, and RuTaBNO. Examples of the RuPt-based compound include RuPtN, RuPtON, RuPtO, RuPtB, RuPtBN, RuPtBO, and RuPtBNO. The Ru content of the RuTa-based compound is preferably 30 atom % or more and less than 100 atom %, more preferably 40 atom % or more and less than 100 atom %. The Ru content of the RuPt-based compound is preferably 30 atom % or more and less than 100 atom %, more preferably 40 atom % or more and less than 100 atom %.

The absorption layer 44 containing at least one element selected from chromium (Cr) and ruthenium (Ru) can be etched with a mixed gas of chlorine-based gas and oxygen gas. Alternatively, the absorption layer 44 may be etched using a mixed gas of fluorine-based gas and oxygen gas.

The thickness of the absorption layer 44 is preferably 10 nm to 70 nm, more preferably 20 nm to 60 nm. Further, the total thickness of the absorber film 4 including the buffer layer 42 and the absorption layer 44 is preferably 15 nm to 75 nm, more preferably 25 nm to 65 nm.

Also, an oxide layer may be formed on the surface of the absorber film 4 (absorption layer 44). By forming an oxide layer on the surface of the absorber film 4 (absorption layer 44), the cleaning resistance of the absorber pattern 4a of the obtained reflective mask 200 can be improved. The thickness of the oxide layer is preferably 1.0 nm or more, more preferably 1.5 nm or more. Also, the thickness of the oxide layer is preferably 5 nm or less, more preferably 3 nm or less. If the thickness of the oxide layer is less than 1.0 nm, it is too thin to be effective, and if it exceeds 5 nm, it has a large effect on the surface reflectance for the mask inspection light, making it difficult to control to obtain a predetermined surface reflectance.

The method for forming the oxide layer includes hot water treatment, ozone water treatment, heat treatment in an oxygen-containing gas, and oxygen-containing treatment on the mask blank after the absorber film 4 (absorption layer 44) has been formed. For example, ultraviolet irradiation treatment, O ₂ plasma treatment, etc. may be carried out in a gas that is heated. Further, when the surface of the absorber film 4 (absorbent layer 44) is exposed to the atmosphere after forming the absorber film 4 (absorbent layer 44), an oxidized layer due to natural oxidation may be formed on the surface layer. In particular, in some cases, an oxide layer with a thickness of 1 to 2 nm is formed.

<<Etching mask film>>
In the reflective mask blank 100 of this embodiment, an etching mask film 6 that serves as a mask (also referred to as a "hard mask") for patterning the absorber film 4 is formed. The etching mask film 6 is disposed in contact with the upper surface of the above-mentioned absorption layer 44, and has an etching mask film 61 that is resistant to etching with respect to the absorption layer 44. In addition, the reflective mask blank 100 has an etching mask film 61 disposed in contact with the absorption layer 44 as a first etching mask film, and a second etching mask film having etching resistance with respect to the first etching mask film 61. An etching mask film 62 may be provided.

For example, as in Layer Structure Example 1 shown in FIG. 2, the first etching mask film 61 is made of a compositionally graded film containing a predetermined element X and oxygen (O). Further, the first etching mask film 61 includes layers 64 and 65 containing a predetermined element X and oxygen (O), and layers 64 and 65 containing substantially oxygen (O ) may include a part of the layer 66 that does not contain the layer 66.

In both of the above-described layer structure examples 1 and 2, the predetermined element X contained in the first etching mask film 61 is at least one element selected from tantalum (Ta) and silicon (Si). including. The material of the first etching mask film 61 preferably contains the above-described element X and at least one element selected from oxygen (O), nitrogen (N), and boron (B). Specific examples include TaO, TaON, TaBO, TaBON, SiO, SiON, SiBO, and SiBON.

When the material of the first etching mask film 61 is a material containing Ta and O, the Ta content in the first etching mask film 61 is 50 atomic % or more, and can be 70 atomic % or more. can. The Ta content in the first etching mask film 61 is 95 atomic % or less, and can be 65 atomic % or less. The O content in the first etching mask film 61 is 70 atomic % or less, and can be 60 atomic % or less. The O content in the first etching mask film 61 is 2 atomic % or more, and can be 6 atomic % or more.

When the material of the first etching mask film 61 contains Si and O, the Si content in the first etching mask film 61 is 25 atomic % or more and can be 40 atomic % or more. The Si content in the first etching mask film 61 is 80 atomic % or less and can be 60 atomic % or less. The O content in the first etching mask film 61 is 70 atomic % or less and can be 60 atomic % or less. The O content in the first etching mask film 61 is 10 atomic % or more and can be 20 atomic % or more.

As described above, the material of the etching mask film 61 preferably contains a predetermined element X and oxygen (O) with a predetermined concentration ratio profile in the film thickness direction. When the etching mask film 61 has a predetermined oxygen concentration ratio, damage to the protective film 3 (or the multilayer reflective film 2 when the protective film 3 is not present) or the absorbing layer 44 can be prevented in the process of dry etching the buffer layer 42, as will be described later.

The first etching mask film 61 contains at least one element selected from tantalum (Ta) and silicon (Si), so that it can be etched and removed with a fluorine-based gas. Examples of fluorine-based gases include CF ₄ , CHF ₃ , C ₂ F ₆ , C ₃ F ₆ , C ₄ F ₆ , C ₄ F ₈ , CH ₂ F ₂ , CH ₃ F, C ₃ F ₈ , SF ₆ , and _F2 etc. can be used. Moreover, these etching gases can further contain an inert gas such as He and/or Ar, if necessary.

ここで、上記の定義式（１）において、変数Ｘは、エッチングマスク膜６１を構成する金属元素の合計含有量（原子％）、変数Ｏは酸素の含有量（原子％）を示す。 In this specification, the oxygen concentration ratio in the etching mask film 61 relative to the total content of at least one element X described above is defined by the following equation (1).

Here, in the above defining formula (1), the variable X indicates the total content (atomic %) of the metal elements constituting the etching mask film 61, and the variable O indicates the content (atomic %) of oxygen.

The content of each component constituting the etching mask film 6 can be measured by energy dispersive X-ray analysis (EDX) using a scanning transmission electron microscope (STEM).

In the reflective mask blank 100 according to the preferred embodiment of the present invention, the oxygen concentration ratio on the absorption layer 44 side of the first etching mask film 61 is higher than the oxygen concentration ratio at the center of the film thickness of the etching mask film 61. . Further, it is preferable that the oxygen concentration ratio on the side of the first etching mask film 61 opposite to the absorption layer 44 is higher than the oxygen concentration ratio at the center of the thickness of the etching mask film. By setting the oxygen concentration ratio at the surface layer and the bottom of the first etching mask film 61 to a predetermined level or higher, and by setting the oxygen concentration ratio at the center of the film thickness of the first etching mask film 61 to a predetermined level or less, the CD change during the dry etching process is reduced. This makes it easier to prevent electrostatic damage while suppressing damage caused by electrostatic discharge.

In addition, the oxygen concentration ratio on the side of the first etching mask film 61 facing the absorption layer 44 can be made equal to or higher than the oxygen concentration ratio on the opposite side of the etching mask film 61 facing the absorption layer 44. When the first etching mask film 61 is made of a material containing Ta, the selectivity between the first etching mask film 61 and the absorption layer 44 can be increased in etching with a fluorine-based gas.

Further, the oxygen concentration ratio on the side of the first etching mask film 61 opposite to the absorption layer 44 can be made higher than the oxygen concentration ratio on the side of the absorption layer 44 of the etching mask film 61. In this case, the oxidation expansion that occurs when the second etching mask film 62 is etched with a chlorine-based gas containing oxygen gas can be further suppressed, and the CD change due to the thickening of the first etching mask film 61 can be suppressed. It becomes possible to suppress this.

These characteristics are the oxygen concentration ratio at the interface position x1 between the first etching mask film 61 and the absorption layer 44, the interface position x2 between the first etching mask film 61 and the second etching mask film 62, or the etching mask. It can be defined by the magnitude relationship between the oxygen concentration ratio at the surface position x2 of the film 61 and the oxygen concentration ratio at the center position x3 of the first etching mask film 61 in the film thickness direction.

In other words, if we express these in a comparative expression,
O/(X+O) ratio at film thickness center x3 < O/(X+O) ratio at interface x1;
O/(X+O) ratio at film thickness center x3 < O/(X+O) ratio at interface (surface) x2;
It is preferable that
Furthermore, in order to increase the selectivity between the first etching mask film 61 and the absorption layer 44, the O/(X+O) ratio at the interface (surface) x2 ≦ the O/(X+O) ratio at the interface x1. It can be done. In addition, in order to suppress CD changes caused by the thickening of the first etching mask film 61, the O/(X+O) ratio at interface x1 < the O/(X+O) ratio at interface (surface) x2. It can be done.

In a preferred embodiment of the reflective mask blank 100, the oxygen concentration ratio (O/(X+O) ratio) at the film thickness center position x3 of the first etching mask film 61 is 70% or less, and is 50%.
It can be as follows.

Further, the oxygen concentration ratio (O/(X+O) ratio) at the interface position x1 between the first etching mask film 61 and the absorption layer 44 is 5% or more, and can be 10% or more. Further, the above (O/(X+O) ratio) is 90% or less, and can be 80% or less.

Further, the oxygen concentration ratio (O/(X+O) ratio) at the interface position x1 with the absorption layer 44 with respect to the oxygen concentration ratio (O/(X+O) ratio) at the center position x3 of the first etching mask film 61 ) is 5% or more, and can be 10% or more. Further, the difference in the above (O/(X+O) ratio) is 85% or less, and can be 75% or less.

Further, the oxygen concentration ratio (O/(X+O) ratio) at the interface position x2 between the first etching mask film 61 and the second etching mask film 62 or at the surface position x2 of the first etching mask film 61
is 1% or more, and can be 5% or more. Also, the above (O/(X+O) ratio) is 8
It is 5% or less, and can be 75% or less.

In addition, the oxygen concentration ratio (O/(X+O) ratio) at the interface position x2 between the first etching mask film 61 and the second etching mask film 62 or at the surface position x2 of the first etching mask film 61 relative to the oxygen concentration ratio (O/(X+O) ratio) at the center position x3 of the first etching mask film 61 is
The difference in the (O/(X+O) ratio) is equal to or greater than 1% and can be equal to or greater than 5%. The difference in the (O/(X+O) ratio) is equal to or less than 80% and can be equal to or less than 70%.

According to the reflective mask blank 100 of this embodiment, the dry etching process is reduced by reducing the oxygen concentration ratio (O/(X+O) ratio) at the center position x3 of the first etching mask film 61 to a predetermined value or less. It is possible to prevent the occurrence of fatal defects caused by electrostatic discharge damage while suppressing CD changes. Furthermore, by specifying the oxygen concentration ratio of the etching mask film 61, the etching rate of the etching mask film 61 can be adjusted in accordance with the progress of pattern etching of the buffer layer 42. Damage to the protective film 3 or the absorption layer 44 during the process can be suppressed.

The magnitude relationship of the above-mentioned oxygen concentration ratio (O/(X+O) ratio) can be evaluated by X-ray photoelectron spectroscopy (XPS) in addition to EDX. Moreover, it is also possible to evaluate by combining the results of these analyses with a transmission electron microscope (TEM). Moreover, by fitting the data measured by these methods using a known approximation function, it is possible to determine the interface positions x1 and x2 between the above-mentioned layers and the center position x3 of the etching mask film 61.
In this specification, the oxygen concentration ratio (O/(X+O) ratio) of the etching mask film 61
The magnitude relationship is shown in numerical values obtained by EDX, and the contents of the elements constituting each film are shown in numerical values obtained by XPS.

Usually, near the interface between the first etching mask film 61 and the absorption layer 44, the components (elements) of each layer interdiffuse. Here, in order to determine the interface position x1 between the first etching mask film 61 and the absorption layer 44, an inflection point x1 where the total content of metal elements contained in the absorption layer 44 inflects in the film thickness direction x is determined. We adopted a method that determines the position x1 of the interface. Specifically, the interface position x1 between the first etching mask film 61 and the absorption layer 44 can be measured as follows.

First, the total content (atomic %) of metal elements contained in the absorption layer 44 is measured in the film thickness direction x extending from the first etching mask film 61 to the absorption layer 44 . Here, the total content of metal elements is the Cr content when the absorption layer 44 is made of, for example, CrN, and is the RuCr content when the absorption layer 44 is made of, for example, RuCrN. Next, a function y_abs(x) is obtained by curve fitting the measured total content data.

This curve fitting can employ a known approximation method using an S-shaped function. The S-shaped approximation function is generally used to approximate an S-shaped profile. As the S-shaped approximation function, an odd function selected from a polynomial function of degree 3 or higher, a sigmoid function, an error function, an exponential function, a sine function, etc. can be used.

In order to determine the interface position x1 between the first etching mask film 61 and the absorption layer 44, the range in the film thickness direction x for curve fitting the content of the metal element contained in the absorption layer 44 (x1a to x1b) can be determined as follows.

The starting point (x=x1a) of the fitting range in the first etching mask film 61 is near the interface position x1 with the absorption layer 44, and the total content of the element X constituting the first etching mask film 61 is It can be set at the position where the amount (atomic %) becomes the maximum value. Here, the total content of element X is Ta content when the etching mask film 61 is made of TaBO, for example, and Si content when the etching mask film 61 is made of SiO, For example, in the case of TaSiO, it is the TaSi content.

The end point (x=x1b) of the fitting range in the absorption layer 44 is near the interface position x1 with the first etching mask film 61, and the total content (atomic %) of the metal elements constituting the absorption layer 44 is ) can be set at the position where it has the maximum value.

The inflection point x1 of the total content of metal elements constituting the absorption layer 44 can be found as a solution to the following second derivative equation (2), where the second derivative of y_abs(x) becomes zero. can.

In addition, if there are two or more solutions (inflection points) that satisfy equation (2) obtained by approximating using a high-order S-shaped function, the measured data of metal content can be approximated by a cubic function. However, the inflection point closest to the solution of the second-order derivative equation obtained by second-order differentiation of the third-order approximation function can be estimated as the true interface position x1.

The inflection point x1 of the metal element content approximate profile obtained as described above indicates the position (depth in the film thickness direction) at which the component dominance of the first etching mask film 61 switches to the component dominance of the absorption layer 44. It means. Therefore, the calculated position x1 of the inflection point can be regarded as the interface position x1 between the first etching mask film 61 and the absorption layer 44.

When the etching mask film 6 has the second etching mask film 62, the interface position x2 between the second etching mask film 62 and the first etching mask film 61 is also determined by applying the curve fitting method described above. The determination can be made based on the position of the inflection point where the dominant component switches. That is, in order to determine the interface position x2 between the second etching mask film 62 and the first etching mask film 61, fitting is performed to approximate the total content of metal elements constituting the second etching mask film 62. The position of the inflection point x2, which is obtained by calculating the curve function y_em2(x) and solving the second-order derivative equation where the second-order differential value of y_em2(x) is zero, can be regarded as the interface position x2. .

The thickness of the first etching mask film 61 described above is 6 nm to 30 nm, and can be 8 nm to 20 nm. Further, the ratio of the thickness of the first etching mask film 61 to the thickness of the buffer layer 42 described above is from 0.1 to 15, and can be from 0.3 to 10.

The first etching mask film 61 containing Ta and O can be formed by sputtering using a Ta target in an oxygen gas (O ₂ ) and rare gas atmosphere. Further, the first etching mask film 61 containing Si and O can be formed by sputtering using a Si target in an oxygen gas (O ₂ ) and rare gas atmosphere. At this time, by controlling the supply amount of oxygen gas (O ₂ ) or by changing the supplied oxygen gas to another gas, etching having a predetermined gradient composition of the oxygen concentration ratio profile described above can be achieved. A mask film 61 can be formed (for example, layer configuration example 1 shown in FIG. 2). Further, by forming the etching mask film 61 into a two-layer structure or a three-layer structure, a structure having the above-mentioned oxygen concentration ratio profile can be obtained. For example, as a three-layer structure of layers 64, 65, and 66, layers 64 and 65 containing oxygen and a layer 66 substantially free of oxygen may be formed (for example, the layers shown in FIG. 3). Configuration example 2).

In addition, by adjusting the oxygen concentration in the surface layer of the absorption layer 44 in contact with the first etching mask film 61, it is possible to adjust the oxygen concentration ratio at the interface position x1 between the first etching mask film 61 and the absorption layer 44. By adjusting the oxygen concentration in the bottom part of the second etching mask film 62 in contact with the first etching mask film 61, it is possible to adjust the oxygen concentration ratio at the interface position x2 between the first etching mask film 61 and the second etching mask film 62.

In the reflective mask blank 100 according to this embodiment, the second etching mask film 62 may be formed on the first etching mask film 61, as described above. In that case, the material of the second etching mask film 62 is preferably chromium (Cr) or a Cr compound. Examples of Cr compounds include materials containing chromium (Cr) and at least one element selected from nitrogen (N), oxygen (O), carbon (C), and hydrogen (H). Specifically, the second etching mask film 62 preferably contains CrN, CrO, CrC, CrON, CrOC, CrCN, or CrOCN.

The Cr content in the second etching mask film 62 is 30 atomic % or more and can be 40 atomic % or more. The Cr content in the first etching mask film 61 is 95 atomic % or less and can be 90 atomic % or less.

The thickness of the second etching mask film 62 is 3 nm to 20 nm, and can be 5 nm to 15 nm.

The second etching mask film 62 can be formed by sputtering using a Cr-based target. Since the second etching mask film 62 contains chromium, it can be etched and removed with a mixed gas of a chlorine-based gas and an oxygen gas.

<<Resist film>>
The reflective mask blank 100 of this embodiment can have a resist film 11 on the etching mask film 6. That is, the reflective mask blank 100 of this embodiment also includes a form having the resist film 11. In the reflective mask blank 100 of this embodiment, the resist film 11 can be made thinner by selecting an appropriate material and/or appropriate thickness of the absorber film 4 (buffer layer 42 and absorption layer 44) and etching gas. is also possible.

For example, a chemically amplified resist (CAR) can be used as the material of the resist film 11. The resist film 11 is patterned and the absorber film 4 (the buffer layer 42 and the absorption layer 44) is etched, thereby manufacturing a reflective mask 200 having a predetermined transfer pattern.

<<Back conductive film>>
Generally, a back conductive film 5 for an electrostatic chuck is formed on the second main surface (back surface) side of the substrate 1 (the side opposite to the surface on which the multilayer reflective film 2 is formed). The electrical properties (sheet resistance) required of the back conductive film 5 for electrostatic chucks are usually 100Ω/square or less. The back conductive film 5 can be formed by, for example, magnetron sputtering or ion beam sputtering using a target of metal or alloy such as chromium (Cr) or tantalum (Ta).

The material containing chromium (Cr) of the back conductive film 5 is a Cr compound containing at least one element selected from boron (B), nitrogen (N), oxygen (O), and carbon (C) in Cr. It is preferable that there be. Examples of the Cr compound include CrN, CrON, CrCN, CrCON, CrBN, CrBON, CrBCN, and CrBOCN.

The material containing tantalum (Ta) for the back conductive film 5 is Ta (tantalum), an alloy containing Ta, or any of these containing boron (B), nitrogen (N), oxygen (O), and carbon ( It is preferable to use a Ta compound containing at least one of C). For example, TA compounds include, for example, TAB, TAN, TAO, TAON, TACON, TABO, TABO, TABON, TABON, TABON, TAHFON, TAHFON, TAHFON, TAHFON, TAHFCON, TAHFCON, T some To mention TASION, TASICON, etc. can.

As a material containing tantalum (Ta) or chromium (Cr), it is preferable that nitrogen (N) present in the surface layer is small. Specifically, the nitrogen content in the surface layer of the back conductive film 5 made of a material containing tantalum (Ta) or chromium (Cr) is preferably less than 5 atomic %, and the surface layer does not substantially contain nitrogen. It is more preferable. This is because, in the back conductive film 5 made of a material containing tantalum (Ta) or chromium (Cr), the lower the nitrogen content in the surface layer, the higher the wear resistance.

The rear surface conductive film 5 is preferably made of a material containing tantalum (Ta) and boron (B). When the rear surface conductive film 5 is made of a material containing Ta and B, a conductive film 23 having wear resistance and chemical resistance can be obtained. When the rear surface conductive film 5 contains Ta and B, the B content is preferably 5 to 30 atomic %. The ratio of Ta and B (Ta:B) in the sputtering target used to deposit the rear surface conductive film 5 is preferably 95:5 to 70:30.

The thickness of the back surface conductive film 5 is not particularly limited as long as it satisfies the function for electrostatic chuck, but is usually 10 nm to 200 nm. The back surface conductive film 5 also functions to adjust the stress on the second main surface side of the mask blank 100, and is adjusted to obtain a flat reflective mask blank 100 by balancing with the stress from various films formed on the first main surface side.

<Reflective mask 200 and its manufacturing method>
An outline of a method for manufacturing a reflective mask 200 using the reflective mask blank 100 of this embodiment will be described below.

First, a reflective mask blank 100 is prepared, and a resist film 11 is formed on the etching mask film 6 formed on the absorber film 4 on the first main surface thereof (FIG. 4A). A chemically amplified resist (CAR) can be used to form the resist film 11.

A desired pattern is drawn (exposed) on this resist film 11, and further developed and rinsed to form a predetermined resist pattern 11a (FIG. 4B).

Next, using the resist pattern 11a as a mask, dry etching of the second etching mask film 62 is performed using a mixed gas of chlorine-based gas and oxygen gas, thereby forming a mask pattern 62a (FIG. 4C). .

After the resist pattern 11a is removed by oxygen ashing, the first etching mask film 61 is dry-etched using the mask pattern 62a as a mask and a fluorine-based gas to form a mask pattern 61a (FIG. 4D).

Next, the absorbing layer 44 is dry-etched using a mixed gas of a chlorine-based gas and an oxygen gas with the mask pattern 61a as a mask, thereby forming an absorbing layer pattern 44a (FIG. 4E). In this dry-etching process using a mixed gas of a chlorine-based gas and an oxygen gas, the mask pattern 62a of the second etching mask film 62 is removed.

Thereafter, the buffer layer 42 is patterned by dry etching using a fluorine-based gas, with the absorption layer pattern 44a as a mask. In the same process, the mask pattern 61a of the first etching mask film 61 is removed by a fluorine-based gas (FIG. 4F).

After removing the mask pattern 61a of the first etching mask film 61, if the buffer layer 42 in the absorber pattern 4a is not completely etched, the remaining part can be completely removed using a chlorine-based gas (Figure 4G).

Finally, wet cleaning is performed using pure water or an acidic or alkaline aqueous solution to manufacture the reflective mask 200 of this embodiment. After the wet cleaning, a mask defect inspection can be performed as necessary, and mask defect correction can be performed appropriately.

The reflective mask 200 thus manufactured has an absorber pattern 4a formed by patterning the absorber film 4 in the reflective mask blank 100. The absorber pattern 4a of the reflective mask 200 absorbs EUV light and can reflect the EUV light at the openings of the absorber pattern 4a, so that a predetermined fine transfer pattern can be transferred onto an object to be transferred by irradiating the reflective mask 200 with EUV light using a predetermined optical system.

According to the reflective mask 200 and the method for manufacturing the same of the present embodiment, by specifying the oxygen concentration ratio of the etching mask film 61 in the reflective mask blank 100, the etching mask film is adjusted in accordance with the progress of pattern etching of the buffer layer 42. The etching rate of 61 can be adjusted. Thereby, it is possible to suppress damage to the protective film 3 or the absorption layer 44 during the dry etching process of the buffer layer 42 while suppressing the CD change. Therefore, it is possible to provide a reflective mask 200 having an absorber pattern 4a in which a fine transfer pattern is formed with high precision.

<Method for manufacturing semiconductor devices>
In the method for manufacturing a semiconductor device of this embodiment, the reflective mask 200 of this embodiment is set in an exposure apparatus having an exposure light source that emits EUV light, and a transfer pattern is formed on a resist film formed on a transfer target substrate. It has a step of transferring.

By performing EUV exposure using the reflective mask 200 of this embodiment, a desired transfer pattern based on the absorber pattern 4a on the reflective mask 200 is formed on the semiconductor substrate, resulting in a decrease in transfer dimensional accuracy due to shadowing effect. can be formed by suppressing the Moreover, since the absorber pattern 4a is a fine and highly accurate pattern with little sidewall roughness, a desired pattern can be formed on the semiconductor substrate with high dimensional accuracy. In addition to this lithography process, a semiconductor device with a desired electronic circuit can be manufactured by going through various processes such as etching the film to be processed, forming an insulating film and a conductive film, introducing dopants, and annealing. can.

To explain in more detail, the EUV exposure apparatus includes a laser plasma light source that generates EUV light, an illumination optical system, a mask stage system, a reduction projection optical system, a wafer stage system, vacuum equipment, and the like. The light source is equipped with a debris trap function, a cut filter that cuts long wavelength light other than exposure light, and equipment for vacuum differential pumping. The illumination optical system and the reduction projection optical system are composed of reflective mirrors. The reflective mask 200 for EUV exposure is electrostatically attracted by the conductive film formed on its second main surface and placed on the mask stage.

The light from the EUV light source is irradiated onto the reflective mask 200 at an angle of 6° to 8° with respect to the vertical plane of the reflective mask 200 via the illumination optical system. The reflected light from the reflective mask 200 with respect to this incident light is reflected (regularly reflected) in the opposite direction to the incident direction and at the same angle as the incident angle, and is introduced into a reflective projection optical system that usually has a reduction ratio of 1/4. Then, the resist on the wafer (semiconductor substrate) placed on the wafer stage is exposed. During this time, at least the area through which the EUV light passes is evacuated. Furthermore, in this exposure, scan exposure is the mainstream in which the mask stage and the wafer stage are scanned synchronized at a speed corresponding to the reduction ratio of the reduction projection optical system, and the exposure is performed through a slit. Then, by developing this exposed resist film, a resist pattern can be formed on the semiconductor substrate. In the present invention, a mask is used which has a highly accurate absorber pattern 4a that is a thin film with a small shadowing effect and has little side wall roughness. Therefore, the resist pattern formed on the semiconductor substrate has a desired high dimensional accuracy. By performing etching or the like using this resist pattern as a mask, a predetermined wiring pattern can be formed on the semiconductor substrate, for example. A semiconductor device is manufactured through other necessary steps such as an exposure step, a process for processing a processed film, a step for forming an insulating film or a conductive film, a step for introducing a dopant, or an annealing step.

According to the method for manufacturing a semiconductor device of the present embodiment, the reflective mask 200 in which the absorber film 4 has a high absorptivity for EUV light while having a thin film thickness and in which a fine and highly accurate absorber pattern 4a is formed can be used for manufacturing a semiconductor device. Therefore, a semiconductor device having a fine and highly accurate transfer pattern can be manufactured.

[Example 1]
As shown in FIG. 1, the reflective mask blank 100 of Example 1 includes a back conductive film 5, a substrate 1, a multilayer reflective film 2, a protective film 3, an absorber film 4, and an etching mask film 6. has. The absorber film 4 consists of a buffer layer 42 and an absorbent layer 44.

First, the reflective mask blank 100 of Example 1 will be explained. In the following description, the elemental composition of the formed thin film was measured by X-ray photoelectron spectroscopy (XPS). In addition, the oxygen concentration ratio (O/(X+O) ratio) was measured by energy dispersive X-ray analysis (EDX) using a scanning transmission electron microscope (STEM), and was determined by performing the fitting described above. .

A SiO ₂ -TiO ₂ glass substrate, which is a low thermal expansion glass substrate of 6025 size (approximately 152 mm x 152 mm x 6.35 mm) with both the first and second main surfaces polished, is prepared. did. Polishing consisting of a rough polishing process, a precision polishing process, a local polishing process, and a touch polishing process was performed to obtain a flat and smooth main surface.
A back conductive film 5 made of a CrN film was formed on the second main surface (back surface) of the SiO ₂ --TiO ₂ glass substrate 1 by magnetron sputtering (reactive sputtering) under the following conditions. The back conductive film 5 was formed to a thickness of 20 nm using a Cr target in a mixed gas atmosphere of argon (Ar) gas and nitrogen (N ₂ ) gas.

Next, a multilayer reflective film 2 was formed on the main surface (first main surface) of the substrate 1 on the side opposite to the side on which the back conductive film 5 was formed. The multilayer reflective film 2 formed on the substrate 1 was a periodic multilayer reflective film made of molybdenum (Mo) and silicon (Si) in order to make the multilayer reflective film 2 suitable for EUV light with a wavelength of 13.5 nm. The multilayer reflective film 2 was formed by alternately stacking Mo layers and Si layers on the substrate 1 by ion beam sputtering in a krypton (Kr) gas atmosphere using a Mo target and a Si target. First, a Si film was formed to a thickness of 4.2 nm, and then a Mo film was formed to a thickness of 2.8 nm. This was regarded as one cycle, and 40 cycles were laminated in the same manner. Finally, a Si film was formed to a thickness of 4.0 nm to form a multilayer reflective film 2.

Subsequently, a protective film 3 made of a RuNb film was formed to a thickness of 3.5 nm by DC magnetron sputtering using a RuNb target (Ru:Nb=80 at%:20 at%) in an Ar gas atmosphere.

Next, an absorbent film 4 consisting of a buffer layer 42 and an absorbent layer 44 was formed on the protective film 3. Table 1 shows the materials and film thicknesses of the buffer layer 42, absorption layer 44, and etching mask film 6 of Example 1.
Specifically, first, a buffer layer 42 made of a TaBN film was formed by DC magnetron sputtering. The TaBN film was formed to a film thickness of 10 nm as shown in Table 1 by reactive sputtering in a mixed gas atmosphere of Ar gas and N ₂ gas using a TaB mixed sintered target. The element ratio of the TaBN film was 88 atomic % of Ta, 5 atomic % of B, and 7 atomic % of N.

Next, an absorption layer 44 made of a CrN film was formed by magnetron sputtering. The CrN film was formed to a thickness of 36 nm by reactive sputtering using a Cr target in a mixed gas atmosphere of Ar gas and _N2 gas, as shown in Table 1. The element ratio of the CrN film was 88 atomic % for Cr and 12 atomic % for N.
Next, a first etching mask film 61 made of a TaBO film was formed on the absorbing layer 44 by DC magnetron sputtering. The TaBO film was formed to a thickness of 16 nm by reactive sputtering in a mixed gas atmosphere of Ar gas and _O2 gas using a TaB mixed sintered target, as shown in Table 1. At this time, by changing the supply amount of _O2 gas in the mixed gas atmosphere, a composition gradient film with different oxygen concentration ratios in the film thickness direction shown in Table 2 was obtained.

Next, a second etching mask film 62 made of a CrOCN film was formed on the first etching mask film 61. The CrOCN film was formed to a thickness of 6 nm by a reactive sputtering method using a Cr target in an atmosphere of Ar gas, CO ₂ gas, and N ₂ gas. The element ratios of the CrOCN film were 38 atomic % Cr, 39 atomic % O, 11 atomic % C, and 12 atomic % N.

In the manner described above, the reflective mask blank 100 of Example 1 was manufactured.

Next, using the reflective mask blank 100 of Example 1, a reflective mask 200 of Example 1 was manufactured.
A resist film 11 with a thickness of 50 nm was formed on the second etching mask film 62 of the reflective mask blank 100 (FIG. 4A). A chemically amplified resist (CAR) was used to form the resist film 11. A desired pattern was drawn (exposed) on this resist film 11, and further developed and rinsed to form a predetermined resist pattern 11a (FIG. 4B). Next, using the resist pattern 11a as a mask, a CrOCN film (second etching mask film 62) was formed using a mixed gas of Cl ₂ gas and O ₂ gas, thereby forming a mask pattern 62a (FIG. 4C). . Next, after removing the resist pattern 11a by oxygen ashing, using the mask pattern 62a as a mask, dry etching of the TaBO film (first etching mask film 61) is performed using a mixed gas of CF ₄ gas and He gas. In this way, a mask pattern 61a was formed (FIG. 4D). Using the mask pattern 61a as a mask, the CrN film (absorption layer 44) was dry-etched using a mixed gas of Cl ₂ gas and O ₂ gas, thereby forming an absorption layer pattern 44a (FIG. 4E). At this time, the CrOCN film was also peeled off at the same time.

Thereafter, the buffer layer 42 was patterned by dry etching using CF ₄ gas and He gas using the absorption layer pattern 44a as a mask. At this time, the mask pattern 61a made of the TaBO film was also removed at the same time (FIG. 4F). The remainder of the buffer layer 42 was removed with _Cl2 gas (Fig. 4G). Finally, wet cleaning using pure water (DIW) was performed to produce the reflective mask 200 of Example 1.

In the reflective mask blank 100 used for manufacturing the reflective mask 200 of Example 1, the first etching mask film 61 has an O/(X+O) ratio at the film thickness center x3, as shown in Table 2. The O/(X+O) ratio at interface x1 and the O/(X+O) ratio at film thickness center x3<O/(X+O) ratio at interface x2 were satisfied. Therefore, it was possible to prevent the first etching mask film 61 from being excessively charged and prevent the occurrence of fatal defects caused by electrostatic damage. Moreover, it was possible to suppress the CD change of the first etching mask film 61, and the absorber pattern 4a was able to have a CD of the design value ±6 nm or less.

Further, the reflective mask 200 produced in Example 1 was set in an EUV scanner, and EUV exposure was performed on a wafer on which a film to be processed and a resist film were formed on a semiconductor substrate. Then, by developing this exposed resist film, a resist pattern was formed on the semiconductor substrate on which the film to be processed was formed. By transferring this resist pattern onto the film to be processed by etching, and going through various steps such as forming an insulating film and a conductive film, introducing dopants, and annealing, it is possible to manufacture semiconductor devices with desired characteristics. did it.

[Example 2]
In Example 2, a reflective mask blank 100 and a reflective mask 200 were manufactured using the same structure and method as Example 1 except for the first etching mask film 61. Manufactured semiconductor devices.

A first etching mask film 61 consisting of a laminated film in which a TaBO film, a TaBN film, and a TaBO film were laminated in this order was formed on the absorption layer 44 by a DC magnetron sputtering method. The TaBO film was formed by reactive sputtering in a mixed gas atmosphere of Ar gas and O ₂ gas using a TaB mixed sintered target. The TaBN film was formed by reactive sputtering in a mixed gas atmosphere of Ar gas and N ₂ gas using a TaB mixed sintered target. As a result, a laminated film having the oxygen concentration ratio shown in Table 2 was obtained.

In the reflective mask blank 100 used to manufacture the reflective mask 200 of Example 2, the first etching mask film 61 has an O/(X+O) ratio at the film thickness center x3, as shown in Table 2. The O/(X+O) ratio at interface x1 and the O/(X+O) ratio at film thickness center x3<O/(X+O) ratio at interface x2 were satisfied. Therefore, it was possible to prevent the first etching mask film 61 from being excessively charged and prevent the occurrence of fatal defects caused by electrostatic damage. Moreover, it was possible to suppress the CD change of the first etching mask film 61, and the absorber pattern 4a was able to have a CD of the design value ±6 nm or less.

[Example 3]
In Example 3, a reflective mask blank 100 and a reflective mask 200 were manufactured using the same structure and method as Example 1 except for the first etching mask film 61. Manufactured semiconductor devices.

A first etching mask film 61 made of a SiO film was formed on the absorption layer 44 by RF magnetron sputtering. The SiO film was formed with a film thickness of 20 nm as shown in Table 1 by reactive sputtering using a Si target in a mixed gas atmosphere of Ar gas and O ₂ gas. At this time, by changing the supply amount of O ₂ gas in the mixed gas atmosphere, compositionally graded films having different oxygen concentration ratios in the film thickness direction as shown in Table 2 were obtained.

In the reflective mask blank 100 used to manufacture the reflective mask 200 of Example 3, the first etching mask film 61 has an O/(X+O) ratio at the film thickness center x3, as shown in Table 2. The O/(X+O) ratio at interface x1 and the O/(X+O) ratio at film thickness center x3<O/(X+O) ratio at interface x2 were satisfied. Therefore, it was possible to prevent the first etching mask film 61 from being excessively charged and prevent the occurrence of fatal defects caused by electrostatic damage. Moreover, it was possible to suppress the CD change of the first etching mask film 61, and the absorber pattern 4a was able to have a CD of the design value ±6 nm or less.

[Comparative example 1]
In Comparative Example 1, a reflective mask blank 100 and a reflective mask 200 were manufactured using the same structure and method as Example 1 except for the first etching mask film 61, and the reflective mask blank 100 and the reflective mask 200 were manufactured using the same method as Example 1. Manufactured semiconductor devices.

In the reflective mask blank 100 used for manufacturing the reflective mask 200 of Comparative Example 1, the O/(X+O) ratio at the film thickness center x3, interface x1, and interface x2 of the first etching mask film 61 is as follows: 6
It was uniform at 5%. Therefore, the first etching mask film 61 was excessively charged exceeding its electrostatic breakdown voltage, resulting in a fatal defect that made the reflective mask defective. Furthermore, it was not possible to suppress the CD change of the first etching mask film 61, and the CD of the absorber pattern 4a exceeded the design value of ±6 nm.

1 Substrate 2 Multilayer reflective film 3 Protective film 4 Absorber film 4a Absorber pattern 5 Back conductive film 6 Etching mask film 11 Resist film 42 Buffer layer 44 Absorbing layer 61 First etching mask film 62 Second etching mask film 100 Reflection Type mask blank 200 Reflective type mask

Claims (10)

A reflective mask blank comprising a multilayer reflective film, an absorber film, and an etching mask film in this order,
the absorber film includes a buffer layer and an absorber layer having etching resistance to the buffer layer;
the etching mask film has etching resistance to the absorption layer and contains an element X and oxygen (O);
Here, when the oxygen concentration ratio is defined as the content (atomic %) of oxygen (O) in the etching mask film divided by the total content (atomic %) of element X and oxygen (O), the oxygen concentration ratio on the absorption layer side of the etching mask film is higher than the oxygen concentration ratio at the thickness center of the etching mask film,
an oxygen concentration ratio on a surface side of the etching mask film opposite to the absorption layer is higher than an oxygen concentration ratio at a thickness center of the etching mask film,
The reflective mask blank, wherein the element X comprises at least one selected from tantalum (Ta) and silicon (Si). A reflective mask blank comprising a multilayer reflective film, an absorber film, and an etching mask film in this order,
The absorber film includes a buffer layer and an absorbent layer having etching resistance with respect to the buffer layer,
The etching mask film has etching resistance with respect to the absorption layer and contains element X and oxygen (O),
Here, if the oxygen concentration ratio is defined as the oxygen (O) content (atomic %) divided by the total content (atomic %) of element X and oxygen (O) in the etching mask film, then the etching mask an oxygen concentration ratio on the absorption layer side of the film is higher than an oxygen concentration ratio at the center of the thickness of the etching mask film;
The element X contains at least one selected from tantalum (Ta) and silicon (Si),
A reflective mask blank comprising a second etching mask film on the first etching mask film, the second etching mask film containing chromium (Cr). The reflective mask blank according to claim 1 or 2, wherein the etching mask film has a thickness of 6 nm to 30 nm. 3. The reflective mask blank according to claim 1, wherein the ratio of the thickness of the etching mask film to the thickness of the buffer layer is 0.1 to 15. The reflective mask blank according to claim 1 or 2, wherein the buffer layer contains at least one selected from tantalum (Ta) and silicon (Si). The reflective mask blank according to claim 1 or 2, wherein the absorbing layer contains at least one selected from chromium (Cr) and ruthenium (Ru). The reflective mask blank according to claim 1 or 2, further comprising a protective film between the multilayer reflective film and the absorber film. A reflective mask having an absorber pattern in which the absorber film in the reflective mask blank according to claim 1 or 2 is patterned. 3. A method for manufacturing a reflective mask from a reflective mask blank according to claim 1 or 2, comprising: forming an etching mask film pattern by dry etching the etching mask film; and masking the etching mask film pattern. and patterning the absorber film. A method for manufacturing a semiconductor device, comprising the step of setting the reflective mask according to claim 8 in an exposure device and transferring a transfer pattern to a resist film formed on a transfer target substrate.