JP2009260183A - Method of manufacturing reflective mask blank for euv lithography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a mask blank for EUV lithography (EUVL), in which in-plane nonuniformity of a peak reflectivity in an EUV wavelength range on a multilayer reflective film surface is corrected. <P>SOLUTION: The method of manufacturing a reflective mask blank for EUV lithography (EUVL) includes: a step of forming a multilayer reflective film, which is composed of alternately laminated high-refractive-index layers and low-refractive-index layers and reflects EUV light, on a substrate; a step of determining a peak reflectivity distribution in an EUV wavelength range on the multilayer reflective film surface; a step of locally heating at least a portion of a region having a higher peak reflectivity in the EUV wavelength range than a region having the lowest peak reflectivity in the EUV wavelength range on the basis of the obtained peak reflectivity distribution in the EUV wavelength range on the multilayer reflective film surface, thereby correcting peak reflectivity nonuniformity in the EUV wavelength range on the multilayer reflective film surface so that the requested value related to in-plane uniformity of the peak reflectivity in the EUV wavelength range on the multilayer reflective film surface is within ±0.25%; and a step of forming an absorbing film that absorbs EUV light on the multilayer reflective film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a reflective mask blank for EUV lithography.

  Conventionally, in lithography technology, an exposure apparatus for manufacturing an integrated circuit by transferring a fine circuit pattern onto a wafer has been widely used. As integrated circuits become highly integrated, faster, and more functional, miniaturization of integrated circuits advances, and the exposure apparatus is required to image a high-resolution circuit pattern on the wafer surface with a deep focal depth. The wavelength of the exposure light source is being shortened. As an exposure light source, an ArF excimer laser (wavelength 193 nm) has started to be used further from the conventional g-line (wavelength 436 nm), i-line (wavelength 365 nm), and KrF excimer laser (wavelength 248 nm). In order to support next-generation integrated circuits with circuit line widths of 45 nm or less, an immersion light source in which the space between the bottom lens and the wafer as an exposure light source is filled with water having a high refractive index instead of the conventional inert gas. The use of lithography (ArF excimer laser as the light source) is considered promising, but this is also expected to cover only the line width up to 45 nm generation or 32 nm generation.

  In such technical trends, lithography technology using extreme ultraviolet (EUV for short) light as an exposure light source for the next generation is considered to be applicable over a plurality of generations of 45 nm and beyond, and is attracting attention. . EUV light refers to light in the wavelength band of the soft X-ray region or the vacuum ultraviolet region, specifically, light having a wavelength of about 0.2 to 100 nm. At present, the use of light having a wavelength of about 13.5 nm is being studied as a lithography light source. The exposure principle of this EUV lithography (hereinafter abbreviated as “EUVL”) is the same as that of conventional lithography in that the mask pattern is transferred using a projection optical system, but light is transmitted in the EUV light energy region. Since there is no material to be used, the refractive optical system cannot be used, and a reflective optical system is used.

The mask blank is a laminated body before patterning used for photomask manufacturing. A schematic cross-sectional view of a general EUV mask blank is shown in FIG. As shown in FIG. 1, in the case of the EUV mask blank 1, a structure in which a reflection film 12 that reflects EUV light and an absorption film 14 that absorbs EUV light are formed in this order on a substrate 11 such as a glass substrate. have. As the reflective film 12, by alternately laminating a high refractive index film and a low refractive index film, the peak reflectivity in the EUV wavelength range when the film surface is irradiated with light in the wavelength range of EUV light can be increased. A multilayer reflective film is usually used. For the absorption film, a material having a high absorption coefficient for EUV light, specifically, a material mainly composed of Cr or Ta, for example, is used.
The EUVL mask blank may have only a reflection film and an absorption film, but usually has a film other than these. For example, a protective film for preventing oxidation of the reflective film surface may be formed on the reflective film. In addition, in order to prevent the reflective film 12 from being damaged during the etching process, a buffer film 13 serving as an etching stopper may be provided on the reflective film 12. Here, in the case where the protective film can serve as a buffer film, a single film may be provided as a protective film that also serves as the buffer film. (For example, refer to Patent Document 1.)
In addition, in order to increase the contrast at the time of inspection of the mask pattern, that is, the difference in reflectance between the reflective film (a protective film when a protective film is formed on the reflective film) and the absorption film, the inspection of the mask pattern In some cases, an antireflection film 15 having a low reflectance with respect to the inspection light used for the film is formed on the absorber film 14.

International Publication Number 03/85709 Pamphlet

In the EUVL mask blank, there is a problem that an in-plane distribution occurs in the peak reflectance in the EUV wavelength region on the surface of the multilayer reflective film. When the reflectance spectrum in the EUV wavelength region on the surface of the multilayer reflective film is measured, the reflectance value differs depending on the wavelength to be measured, and has a maximum value. This maximum value is referred to as a peak reflectance in the EUV wavelength region in this specification. When an in-plane distribution occurs in the peak reflectance of the EUV wavelength region on the surface of the multilayer reflective film (that is, the peak reflectance varies depending on the location of the multilayer reflective film), an EUVL mask created from the EUVL mask blank is used. When EUVL is used, an in-plane distribution of the EUV exposure amount applied to the resist on the wafer is generated, causing variation in pattern dimensions in the exposure field, which is a problem.
Here, strictly speaking, the reflectance in the EUV wavelength region on the surface of the multilayer reflective film is not the ratio of the intensity of the light reflected only on the outermost surface of the multilayer reflective film to the incident light intensity, but the highest relative to the incident light intensity. It is the ratio of the cumulative intensity of light reflected from each interface between the high refractive index film and the low refractive index film laminated on the surface and below. For the sake of convenience, the expression “reflectance at the film surface” will be used hereinafter. This expression means the intensity ratio of the reflected light from the outermost surface to the incident light, and in addition from the outermost surface and the lower layer to the incident light. May mean the intensity ratio of the accumulated reflected light.

There are various causes for the in-plane distribution of the peak reflectance in the EUV wavelength region on the surface of the multilayer reflective film. For example, (1) there is an in-plane distribution in the substrate surface roughness, and (2) in-plane with respect to the film thickness of each layer constituting the multilayer reflective film used as the reflective film, that is, the high refractive index film and the low refractive index film. (3) a diffusion layer is formed at the interface of each film constituting the multilayer reflection film used as the reflection film, that is, the interface between the high refractive index film and the low refractive index film, and the thickness of the diffusion layer is For example, there is an in-plane distribution, and (4) a diffusion layer is generated at the interface between the multilayer reflective film and the protective film, and the in-plane distribution exists in the thickness of the diffusion layer. Here, the diffusion layer is a layer that is formed when the constituent materials of the layers that are in contact with each other at the interface diffuse into the opposite layers, and the constituent materials of the layers that are in contact with each other react to form a compound. Point to. For example, when the multilayer reflective film is a Mo / Si multilayer reflective film in which Mo films and Si films are alternately laminated, Mo constituting the Mo film and Si forming the Si film are the Mo film / Si film. It is a layer generated by reacting at the interface to form a compound (MoSi _x ).

  In order to solve the above-described problems of the prior art, the present invention provides a method for manufacturing a mask blank for EUVL which is excellent in in-plane uniformity of peak reflectance in the EUV wavelength region on the surface of a multilayer reflective film. Objective.

In order to achieve the above object, according to the present invention, a multilayer reflective film that reflects EUV light is formed on a substrate by alternately laminating high refractive index layers and low refractive index layers, and EUV on the surface of the multilayer reflective film is formed. Peak reflectance distribution in the wavelength range is obtained, and based on the obtained peak reflectance distribution in the EUV wavelength range on the surface of the multilayer reflective film, the peak reflectance in the EUV wavelength range is lower than the region where the peak reflectance in the EUV wavelength range is the lowest. By locally heating at least a part of the part having a high rate, the required value regarding the in-plane uniformity of the peak reflectance in the EUV wavelength region on the surface of the multilayer reflective film is within ± 0.25%. A reflective mask bra for EUV lithography (EUVL), wherein a peak reflectance distribution in the EUV wavelength region on the surface of the multilayer reflective film is corrected, and an absorption film that absorbs EUV light is formed on the multilayer reflective film. To provide a method of manufacturing a click.
Here, locally heating at least a part of the region where the peak reflectance in the EUV wavelength region is higher than the region where the peak reflectance in the EUV wavelength region is the lowest is that of the region where the peak reflectance in the EUV wavelength region is high. It may be achieved by heating the entire surface of the multilayer reflective film such that the temperature is relatively higher than the temperature of other parts of the surface of the multilayer reflective film.

In the present invention, on the substrate, a high refractive index layer and a low refractive index layer are alternately laminated to form a multilayer reflective film that reflects EUV light, and a protective film is formed on the multilayer reflective film. The peak reflectance distribution in the EUV wavelength region on the surface of the protective film is obtained, and based on the obtained peak reflectance distribution in the EUV wavelength region on the surface of the protective film, the peak reflectance in the EUV wavelength region is lower than the lowest part. By locally heating at least a part of a part having a high peak reflectance in the EUV wavelength region, the required value regarding the in-plane uniformity of the peak reflectance in the EUV wavelength region on the surface of the protective film is within ± 0.25%. A reflective mask blank for EUVL, comprising correcting the peak reflectance distribution in the EUV wavelength region on the surface of the protective film and forming an absorption film that absorbs EUV light on the protective film. Provide a method.
Here, locally heating at least a part of the region where the peak reflectance in the EUV wavelength region is higher than the region where the peak reflectance in the EUV wavelength region is the lowest is that of the region where the peak reflectance in the EUV wavelength region is high. It may be achieved by heating the entire surface of the protective film so that the temperature is relatively higher than the temperature of other parts of the surface of the protective film.
Hereinafter, the method described in this paragraph and the previous paragraph is referred to as “mask blank manufacturing method of the present invention” in the present specification. )

  In the mask blank manufacturing method of the present invention, an antireflection film for inspection light used for inspection of a mask pattern may be further formed on the absorption film.

  In the mask blank manufacturing method of the present invention, the local heating is preferably performed at a heating temperature of 180 ° C. or less, and more preferably performed at a heating temperature of 180 ° C. or less and a heating time of 1 to 10 minutes.

  In the mask blank manufacturing method of the present invention, it is preferable to use light or electron beam irradiation for the local heating.

  In the mask blank manufacturing method of the present invention, it is preferable to use a minute heat generating member for the local heating.

  Moreover, in the mask blank manufacturing method of this invention, it is preferable to use spraying the gas heated previously for the said local heating.

  According to the mask blank manufacturing method of the present invention, the in-plane distribution of the peak reflectance in the EUV wavelength region on the surface of the multilayer reflective film can be eliminated. As a result, when EUVL is performed using the EUVL mask produced from the obtained EUVL mask blank, in-plane distribution does not occur in the EUV exposure amount irradiated to the resist formed on the wafer, There is no variation in pattern dimensions within the exposure field. Therefore, an EUVL mask with high pattern dimensional accuracy can be realized.

Hereinafter, the manufacturing method of the mask blank of this invention is demonstrated.
The manufacturing method of the mask blank of this invention is shown in order below.
(1) Prepare a substrate.
(2) A multilayer reflective film that reflects EUV light is formed on the substrate.
(3) The peak reflectance in the EUV wavelength region on the surface of the multilayer reflective film is corrected so as to satisfy a predetermined peak reflectance distribution.
(4) An absorption film is formed on the multilayer reflective film.
Here, in order to stably maintain the characteristics required for the multilayer reflective film over a long period of time, the step (5) of forming a protective film on the multilayer reflective film is replaced with the step (2) and the step (3). ) May be added. In this case, in the step (3), the peak reflectance in the EUV wavelength region on the surface of the protective film is corrected so as to satisfy a predetermined peak reflectance distribution.
In addition, the step (6) of forming a buffer film serving as an etching stopper on the multilayer reflective film or the protective film when the absorption film is partially etched to form a pattern, You may add between 3) and said process (4).
In order to enable inspection of the mask pattern, a step (7) of forming an antireflection film on the absorption film may be added after the step (4).
In addition, a cleaning process may be added between each process in order to remove particles adhering to the film surface in each process and contaminants adsorbed on the film surface.
The details of each step will be described below in order.

[substrate]
The substrate is required to satisfy the characteristics of the EUVL mask blank as a substrate. Therefore, the substrate preferably has a low coefficient of thermal expansion (0 ± 1.0 × 10 ⁻⁷ / ° C., more preferably 0 ± 0.3 × 10 ⁻⁷ / ° C., more preferably at the temperature during exposure. 0 ± 0.2 × 10 ⁻⁷ / ° C., more preferably 0 ± 0.1 × 10 ⁻⁷ / ° C., particularly preferably 0 ± 0.05 × 10 ⁻⁷ / ° C.), smoothness and flatness Those having excellent properties and resistance to a cleaning liquid used for cleaning a mask blank or a photomask after pattern formation are preferred. As the substrate, specifically, glass having a low thermal expansion coefficient, for example, SiO ₂ —TiO ₂ glass or the like is used. However, the substrate is not limited thereto, and crystallized glass, quartz glass, silicon or metal on which β quartz solid solution is precipitated is used. A substrate such as can also be used. A film such as a stress correction film may be formed on the substrate.
It is preferable that the substrate has a smooth surface of 0.15 nm rms or less and a flatness of 100 nm or less because high reflectivity and high transfer accuracy can be obtained in the EUVL mask after manufacture.
The size, thickness, and the like of the substrate are appropriately determined depending on the design value of the manufactured EUVL mask. For example, an example is a substrate having an outer shape of 6 inches (152.4 mm) square and a thickness of 0.25 inches (6.3 mm).
It is preferable that no defects exist on the surface (film formation surface) of the substrate on which the multilayer reflective film is formed. However, even if it exists, the depth of the concave defect and the height of the convex defect are not more than 2 nm so that the phase defect does not occur due to the concave defect and / or the convex defect. It is preferable that the half width (FWHM (full width of half maximum)) of the defect and the convex defect is 60 nm or less.

[Multilayer reflective film]
As the reflective film of the EUVL mask blank, since a high reflectance can be achieved in the EUV wavelength region, a multilayer reflective film in which a high refractive index film and a low refractive index film are alternately laminated a plurality of times is used.
The multilayer reflective film is not particularly limited as long as it has desired characteristics as a reflective film of a mask blank for EUVL. Here, the characteristic particularly required for the multilayer reflective film is that the peak reflectance in the EUV wavelength region is high. Specifically, the peak reflectivity in the EUV wavelength region is preferably 60% or more, and 65% or more when the multilayer reflective film surface is irradiated with light in the EUV light wavelength region at an incident angle of 6 to 8 degrees. It is more preferable that

  In the multilayer reflective film, Si (refractive index at a wavelength of 13.5 nm = 0.999) is widely used for the high refractive index film, and Mo (same refractive index = 0.924) is widely used for the low refractive index film. The That is, the Mo / Si multilayer reflective film is the most common. However, the multilayer reflective film is not limited to this, and Ru / Si multilayer reflective film, Mo / Be multilayer reflective film, Rh / Si multilayer reflective film, Pt / Si 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, and the like can also be used.

  The thickness of each layer constituting the multilayer reflective film and the number of repeating units of the layers can be appropriately selected according to the film material to be used and the peak reflectance in the EUV wavelength region required for the multilayer reflective film. Taking a Mo / Si multilayer reflective film as an example, in order to obtain a multilayer reflective film having a peak reflectivity in the EUV wavelength region of 60% or more, a Si layer having a thickness of 4.5 ± 0.1 nm, and a thickness of 2. What is necessary is just to laminate | stack Mo layer of 3 +/- 0.1nm in this order so that a repeating unit number may be set to 30-60.

In addition, what is necessary is just to form each layer which comprises a multilayer reflective film so that it may become a desired film thickness using well-known film-forming methods, such as a magnetron sputtering method and an ion beam sputtering method. For example, when forming a Mo / Si multilayer reflective film using ion beam sputtering, a Si target is used as a target, and Ar gas (gas pressure 1.3 × 10 ⁻² Pa to 2.7 × 10 6) is used as a sputtering gas. ^-2 Pa), an Si film is formed to have a film thickness of 4.5 nm at an ion acceleration voltage of 300 to 1500 V and a film formation rate of 0.03 to 0.30 nm / sec. using Mo target, using an Ar gas (gas pressure ^{1.3 × 10 -2 Pa~2.7 × 10 -2} Pa), an ion acceleration voltage 300 to 1,500 V, the deposition rate 0.03 It is preferable to form the Mo film so that the film thickness is 2.3 nm at 0.30 nm / sec. With this as one period, the Mo / Si multilayer reflective film is formed by laminating the Si film and the Mo film for 40 to 50 periods.

[Protective film]
In order to prevent the surface of the multilayer reflective film and its vicinity from being naturally oxidized during storage or oxidized during cleaning, a protective film can be provided on the multilayer reflective film. As the protective film, Si, Ru, Rh, C, SiC, a mixture of these elements, or those obtained by adding nitrogen or boron to these elements can be used. The use of Ru as the protective film is particularly preferable because it can also function as a buffer film described later. When Si is used as the protective film, when the multilayer reflective film is made of Mo / Si, the uppermost layer can be made to function as the protective film by making the uppermost layer an Si film. In this case, the thickness of the uppermost Si film that also serves as a protective film is preferably 5 to 15 nm, which is thicker than the usual 4.5 nm. Further, after forming a Si film as a protective film, a Ru film serving as both a protective film and a buffer film may be formed on the Si film.
The film such as the multilayer reflective film or the protective film does not necessarily have to be one layer, and may be two or more layers.
When a protective film is provided on the multilayer reflective film, the peak reflectance in the EUV wavelength region of the protective film needs to satisfy the above range.

[Correction of peak reflectance]
Next, the in-plane distribution of the peak reflectivity in the EUV wavelength region on the surface of the multilayer reflective film formed on the substrate is obtained. When a protective film is provided on the multilayer reflective film, the in-plane distribution of peak reflectance in the EUV wavelength region on the surface of the protective film is obtained.
Since the peak reflectance is the maximum value of the reflectance in the EUV wavelength region as defined in [Problems to be Solved by the Invention], a diagram showing the wavelength dependence of the reflectance in the EUV wavelength region, so-called reflectance spectrum Can be determined by measuring. The reflectance spectrum is sequentially measured at a plurality of different points on the multilayer reflective film (or protective film) by any one of the methods described below, and the maximum value distribution of the reflectance spectrum at the plurality of measurement points, that is, the peak reflectance Can be obtained.
As a method for measuring the reflectance spectrum, the first method is to divide a ray in the EUV wavelength region, and then to form a multilayer reflective film (a protective film when a protective film is provided on the multilayer reflective film. These are collectively referred to as a multilayer reflective / protective film), and the intensity of the reflected light is directly measured by a photodiode, a charged coupled device (CCD) or the like. Second, after splitting the light in the EUV wavelength region, the multilayer reflection / protection film is irradiated at an incident angle of 6 to 8 degrees, and the reflected light in the EUV wavelength region is irradiated with light in other wavelength regions using a scintillator or the like. An indirect method in which the intensity is converted into a visible light or ultraviolet light (for example, the intensity is measured with a photomultiplier tube). Third, after splitting the light in the EUV wavelength region, the reflected light when the multilayer reflective / protective film is irradiated at an incident angle of 6 to 8 degrees is split, and the intensity of each reflected light split into each wavelength is multi-valued. It can be obtained by a method such as measurement using a channel photodiode array or a multi-channel CCD array. In these methods, a reflectance spectrum can be obtained by actually measuring using a so-called spectrophotometer.
Specific examples of the spectrophotometer include an EUV reflectometer manufactured by US EUV technology, which employs the first method, and an EUV-mask blank reflectometer (MBR) manufactured by AIXUV, which employs the third method. Can do. As a light source that emits light in the EUV wavelength range, capillary discharge in the presence of light emitted from plasma generated by irradiating a target such as xenon gas or tin with YAG laser light, or xenon gas or tin. For example, light emitted from plasma generated by discharging by pinch discharge or the like can be used.
In these methods, the spectrophotometer is used to measure the distribution of the reflectance spectrum on the surface of the multilayer reflection / protection film, and the peak reflectance distribution on the surface of the multilayer reflection / protection film is obtained using the result. be able to.

As a specific example, a method for measuring a reflectance spectrum using an EUV-mask blank reflectometer (MBR) manufactured by AIXUV, Germany will be described below.
The EUV light emitted from the plasma generated by the discharge by the xenon gas pinch discharge is passed through the slit, the multilayer reflection / protection film and the reference mirror (reflectance (= R _ref (λ)) in the EUV wavelength region are known, The surface of the mirror having a multilayer reflective film formed on the substrate is irradiated at an incident angle of 6 to 8 degrees. After the reflected light from the multilayer reflection / protection film and the reference mirror is dispersed with a grating mirror, it is projected onto a multi-channel CCD (Charged Coupled Device) array, and from the multilayer reflection / protection film and the reference mirror at each wavelength. The reflected light intensity (I (λ), I _ref (λ)) is measured, and the reflectance spectrum R (λ) of the multilayer reflective / protective film is obtained by Equation (1).
R (λ) = R _ref (λ) × I (λ) / I _ref (λ) Equation (1)
An example of the reflectance spectrum obtained by the above series of procedures is shown in FIG. In FIG. 2, the vertical axis represents reflectivity (%), and the horizontal axis represents wavelength (nm). 2 shows a multilayer reflection in which 50 layers of Si films (film thickness: 4.5 nm) and Mo films (film thickness: 2.3 nm) are alternately stacked in this order on a substrate (made of SiO ₂ —TiO ₂ glass). After forming the film, a Si film (film thickness: 4.5 nm) is formed as a protective film on the multilayer reflective film, and a Ru film (film thickness: 2. nm) serving as a protective film and a buffer film is formed on the Si film. 5 nm is a reflectance spectrum in the EUV wavelength region (12.5 to 14.5 nm) when EUV light is irradiated at an incident angle of 6 degrees on the surface of the protective film of the multilayer reflective film and the substrate with the protective film. As shown in FIG. 2, the reflectance spectrum depends on the wavelength and has a maximum value. This maximum value is the peak reflectance.

  Next, based on the peak reflectance distribution in the EUV wavelength region on the surface of the obtained multilayer reflective / protective film, the EUV wavelength is lower than the region having the lowest peak reflectance in the EUV wavelength region (hereinafter referred to as the minimum reflectance region). By locally heating a portion having a high peak reflectance in the region (hereinafter referred to as a high reflectance portion), the peak reflectance distribution in the EUV wavelength region on the multilayer reflective / protective film surface is corrected.

The inventors of the present application have found that when the multilayer reflective film or the protective film is heated, the peak reflectance in the EUV wavelength region on the surface of these films decreases.
Specifically, when the multilayer reflective film is heated, a high refractive material and a low refractive material forming the multilayer reflective film diffuse and react with each other to form a diffusion layer, and the peak reflectance and EUV wavelength in the EUV wavelength region are formed. The central wavelength of the reflected light in the region changes. The central wavelength of the reflected light in the EUV wavelength region is a wavelength corresponding to the half width of the peak reflectance (FWHM (full width of half maximum)) in the reflectance spectrum in the EUV wavelength region as λ ₁ and λ ₂ . Then, the wavelength becomes the median value of these wavelengths ((λ ₁ + λ ₂ ) / 2).
When the protective film is heated, the material that forms the surface layer of the multilayer reflective film and the material that forms the protective film diffuse and react with each other to form a diffusion layer and / or multilayer reflective that is under the protective film The high refractive material and low refractive material forming the film diffuse and react with each other to form a diffusion layer, and the peak reflectance in the EUV wavelength region and the center wavelength of reflected light in the EUV wavelength region change.

3 and 4, 40 layers of Si films (film thickness 4.5 nm) and Mo films (film thickness 2.3 nm) are alternately laminated in this order on a substrate (made of SiO ₂ —TiO ₂ glass). After forming the multilayer reflective film, an Si film (film thickness: 4.5 nm) is formed as a protective film on the multilayer reflective film, and an Ru film (film thickness) serving as a protective film and a buffer film is formed on the Si film. 2.5 nm) shows the heating temperature dependence of the amount of decrease in central wavelength and the amount of decrease in peak reflectance when a multilayer reflective film and a substrate with a protective film are heated for 10 minutes using a hot plate in an air atmosphere. . In FIG. 3, the vertical axis represents the central wavelength decrease (Decrease in CWL) (nm), and the horizontal axis represents 1000 / T (bake temperature) (1 / K). In FIG. 4, the vertical axis represents the peak reflectivity reduction amount (Decrease in Peak% R), and the horizontal axis represents 1000 / T (bake temperature) (1 / K).
First, in the dependence of the central wavelength reduction amount on the heating temperature shown in FIG. 3, since the multilayer reflective film is a kind of Bragg reflection mirror, the central wavelength reduction amount is almost linearly dependent on the thickness of the diffusion layer to be generated. The temperature dependence follows the Arrhenius equation which is the temperature dependence of the general reaction rate. In addition, since the thickness of the diffusion layer increases in proportion to the reaction time (= heating time), the heating temperature and the heating time dependency of the central wavelength reduction amount follows the following formula (2a). In the case of the example shown in FIG. 3, the expression (2a) is expressed by the expression (2b).
Center wavelength drop ∝ Diffusion layer thickness
加熱 Heating time × exp (a + b / heating temperature (K))
(Where a and b are constants) Equation (2a)
Center wavelength decrease amount (nm) = 4120 × heating time (min)
Xexp (-6380 / heating temperature (K))
Formula (2b)
On the other hand, the peak reflectivity decrease amount is not as simple as the center wavelength decrease amount because the dependency on the thickness of the diffusion layer to be generated is relatively complicated, but as clearly shown in FIG. As a result, according to the Arrhenius equation, the heating temperature and heating time dependency of the peak reflectance reduction amount follows the following equation (3a). In the case of the example shown in FIG. 4, the formula (3a) is expressed by the formula (3b).
Peak reflectivity drop ∝ Diffusion layer thickness
加熱 Heating time × exp (a + b / heating temperature (K))
(Where a and b are constants) Equation (3a)
Peak reflectance decrease (%) = 9130 × heating time (min)
Xexp (-4370 / heating temperature (K))
Formula (3b)
Table 1 shows the temperature dependence of the amount of change (decrease amount) in peak reflectance and center wavelength due to heating obtained from FIGS. 3 and 4.

  As apparent from FIG. 4 and Table 1, by heating the multilayer reflective film or protective film, the peak reflectance in the EUV wavelength region on the surface of these films can be lowered. At this time, not only the peak reflectivity in the EUV wavelength region is reduced, but the center wavelength is shifted to the short wavelength side, but the change in the center wavelength is slight compared to the decrease in the peak reflectivity, causing a problem. There is no. For example, when heated at 110 ° C. for 10 minutes, the amount of decrease in peak reflectivity is about 1%, which varies greatly compared to the required value of in-plane distribution of peak reflectivity (± 0.25%). The amount of decrease is 0.002 nm, which is a little smaller than the in-plane distribution required value (± 0.03 nm) of the center wavelength on the multilayer reflective / protective film surface of the EUVL mask blank. The required value related to the in-plane uniformity of the center wavelength is an allowable value of the difference between the largest center wavelength and the smallest center wavelength when the center wavelength is measured over the entire surface of the multilayer reflective / protective film. Since the wavelength during exposure is constant, the in-plane distribution of the center wavelength is preferably as uniform as possible. The required value for the in-plane uniformity of the center wavelength is preferably within ± 0.03 nm, and more preferably within ± 0.01 nm.

As described above, by heating the multilayer reflection / protection film, the peak reflectivity in the EUV wavelength region on these film surfaces can be reduced, so by devising the heating method, the multilayer reflection / protection film surface It is possible to adjust the overall peak reflectance so that the in-plane distribution is as small as possible.
On the other hand, the required value for the in-plane uniformity of the peak reflectivity in the EUV wavelength region on the multilayer reflective / protective film surface of the EUVL mask blank is ± 0.25%, preferably ± 0.125%. The required value for the in-plane uniformity of the peak reflectivity is the allowable value for the difference between the maximum peak reflectivity and the minimum peak reflectivity when the peak reflectivity is measured at multiple points throughout the multilayer reflective / protective film. It is. Since the light amount distribution during exposure is preferably as small as possible, the in-plane distribution of peak reflectance is preferably as uniform as possible, and it is required to satisfy the above required value. The results shown in Table 1 are the results when the entire surface of the protective film of the multilayer reflective film and the substrate with the protective film is heated. From this result, the peak reflectance in the EUV wavelength region on the surface of the multilayer reflective / protective film is described above. When there is an in-plane distribution that exceeds the required value, the high reflectance part is locally heated to lower the peak reflectance in the EUV wavelength region of the part, thereby improving the in-plane distribution of the peak reflectance. Thus, it is considered that the above required value can be satisfied.

Here, as one mode of the method of locally heating the high reflectance part, there is a method of selectively heating the high reflectance part without heating the lowest reflectance part.
However, in the present invention, when saying "locally heating a high reflectance part", as long as the temperature of the high reflectance part is relatively higher than the temperature of other parts, the high reflectance part (i.e., Heating other parts) is also included. In this case, the entire surface of the multilayer reflective / protective film may be heated as long as the temperature of the high reflectance part is relatively higher than the temperature of the other part. Therefore, a method of heating the entire surface of the multilayer reflective / protective film by changing the heating condition of each part in accordance with the in-plane distribution of peak reflectance in the EUV wavelength region (hereinafter referred to as heating method A) is a high reflectance part. It is another one aspect | mode of the method of heating locally.

The heating method used for local heating is not particularly limited. In the case of the former method described in the previous paragraph, only the portion of the multilayer reflective / protective film surface where the peak reflectance in the EUV wavelength region is desired to be reduced is selectively locally heated. The method is not particularly limited as long as it can be performed. On the other hand, in the case of the heating method A described in the previous paragraph, as long as the heating method of each part is changed according to the in-plane distribution of the peak reflectance in the EUV wavelength region, the entire multilayer reflection / protective film surface can be heated. There is no particular limitation.
The multilayer reflection film and the protective film are usually formed by magnetron sputtering or ion beam sputtering. The spatial wavelength (horizontal axis) of the film thickness distribution indicates how often the film thickness distribution fluctuates. If the graph is created by plotting the film thickness on the vertical axis and the film thickness on the vertical axis, the film thickness takes extreme values at several positions (twice the interval between the adjacent maximum and minimum values is the film thickness distribution space wavelength). Is at least 10 mm or more, usually 30 mm or more. For example, it continuously changes from the center to the outer periphery.
Therefore, in the case of the former method described in the previous paragraph, the size of the region to be locally heated is preferably 10 mm × 10 mm or less, or 30 mm × 30 mm or less.
In the case of Method A described in the previous paragraph, the entire multilayer reflection / protection film surface may be heated by changing the heating conditions of each part so that the center temperature is the highest and the temperature decreases toward the outer periphery.
FIG. 5 shows a multilayer reflective film in which 40 layers of Si films (film thickness 4.5 nm) and Mo films (film thickness 2.3 nm) are alternately laminated in this order on a substrate (made of SiO ₂ —TiO ₂ glass). After film formation, a Si film (film thickness: 4.5 nm) is formed as a protective film on the multilayer reflective film, and a Ru film (film thickness: 2.5 nm) serving as a protective film and a buffer film is formed on the Si film. 2 shows an example of the result of measuring the peak reflectance distribution in the EUV wavelength region on the surface of the protective film for the multilayer reflective film and the substrate with the protective film formed by forming a film. FIG. 5 shows the results of measuring the peak reflectance at 49 points in the central 132 nm □ region of the protective film.

As an example of a suitable heating method used for local heating, a portion of the multilayer reflective / protective film surface where the peak reflectance in the EUV wavelength region is to be lowered is locally irradiated with a high-energy light beam using a laser or lamp as a light source, Direct heating method that performs local heating by locally irradiating an electron beam, or spraying a preheated gas to the part where the peak reflectance in the EUV wavelength region of the multilayer reflective / protective film surface is to be lowered, and multilayer reflective / Examples include an indirect heating method in which local heating is performed using heat conduction to the protective film. When irradiating a light beam using a laser or a lamp as a light source, it is necessary to select a light beam in a wavelength region that has absorption in the material constituting the multilayer reflection / protection film, but an F ₂ laser (wavelength of about 157 nm), ArF excimer laser (About 193 nm), KrF excimer laser (about 248 nm), YAG laser quadruple harmonic (about 266 nm), XeCl excimer laser (about 308 nm), Ar laser (about 488 nm), YAG laser (about 1064 nm) And a laser light source such as a CO ₂ laser (10.6 um), a lamp light source such as a xenon arc lamp (about 300 to about 1000 nm) and a halogen lamp (about 600 to about 6000 nm). In the case of a method of blowing a preheated gas, an inert gas such as helium gas, argon gas or nitrogen gas, air or hydrogen gas, or a mixed gas thereof can be used. Gas is preferred.

  As another example of a suitable heating method used for local heating, a minute heating member by resistance heating or induction heating is brought close to a part where the peak reflectance in the EUV wavelength region of the multilayer reflection / protection film surface is to be lowered, and radiation is performed. Or the method of heating locally by the heat conduction through gas is mentioned. Specifically, a heating member by resistance heating using a filament such as tungsten or carbon, and a heating member by induction heating using a magnetic material such as carbon, iron, or stainless steel can be exemplified. In addition, an atomic force microscope (AFM) having a heatable probe, a scanning tunneling microscope (STM), or a stylus-type step meter can be mentioned. As a commercial product, local thermal analysis of nano-TA manufactured by Anasys Instruments of the United States. There are systems.

  The heating method described above can also be preferably applied to the heating method A described above.

  Conditions for local heating, that is, heating temperature and heating time, are the configuration of the multilayer reflective / protective film, that is, the constituent material of the multilayer reflective film, the number of repeated layers and the thickness of each layer, or the constituent material and thickness of the protective film And the degree of peak reflectance in the EUV wavelength region to be improved, that is, the amount to be reduced may be selected as appropriate. However, when the multilayer reflective / protective film is locally heated, not only the peak reflectivity in the EUV wavelength region on the surface of these films is lowered, but also the center wavelength shifts to the short wavelength side. Therefore, care must be taken not to exceed the required value (± 0.03 nm) for the in-plane uniformity of the central wavelength. From the results shown in Table 1 and the examples described later, when the target is a multilayer reflective film in which a Ru film is formed as a protective film on a Mo / Si multilayer reflective film and the substrate with the protective film is heated for 10 minutes The heating temperature is preferably 180 ° C. or lower, more preferably 170 ° C. or lower, and further preferably 150 ° C. or lower. The heating temperature is preferably 110 ° C. or higher, and more preferably 130 ° C. or higher.

In order to suppress the shift amount of the center wavelength to less than the required value for in-plane uniformity while exhibiting the effect of improving the peak reflectance, the heating temperature is preferably 180 ° C. or less, and 170 ° C. or less. Is more preferable, and it is more preferable that it is 150 degrees C or less. Moreover, it is preferable that heating temperature is 110 degreeC or more, and it is more preferable that it is 130 degreeC or more.
In the case of the heating method A described above, it is preferable that the heating temperature of the portion of the multilayer reflective / protective film surface where the temperature is highest satisfies the above range.
Although the heating time depends on the heating temperature, it is preferably 1 to 10 minutes when the heating temperature is 180 ° C. or lower.
In addition, the environment which implements local heating is not specifically limited, You may implement in air | atmosphere and may implement in inert gas like a noble gas or nitrogen gas. However, in order to prevent an increase in surface roughness due to surface oxidation, it is preferable to carry out in an inert gas such as a rare gas or nitrogen gas.

  After carrying out local heating, the peak reflectance distribution in the EUV wavelength region on the multilayer reflection / protection film surface is measured again, and after confirming that the peak reflectance distribution has been improved, it is absorbed on the multilayer reflection / protection film. It is preferable to form a film. When the peak reflectance distribution in the EUV wavelength region on the multilayer reflective / protective film surface is insufficiently improved, the high reflectance portion is selectively heated locally based on the newly obtained peak reflectance distribution. The peak reflectance distribution in the EUV wavelength region on the surface of the multilayer reflective / protective film may be further modified.

[Absorbing film]
The characteristic particularly required for the absorption film is that the reflectance in the EUV wavelength region is somewhat low. Specifically, it is preferable that the reflectance in the EUV wavelength region is 5% or less when light in the EUV light wavelength region is irradiated onto the absorption film surface at an incident angle of 6 to 8 degrees.
The absorption film is made of a material having a high absorption coefficient for EUV light. Specifically, the film contains Cr or Ta, for example, a film containing a nitride of Cr or Ta, or a film containing Ta and Hf. (TaBN film or TaHf film).
The film thickness of the absorption film may be appropriately adjusted so as to ensure the intensity ratio of the reflected light from the absorption film and the reflected light from the multilayer reflection / protection film, and is preferably 10 to 100 nm.

The absorbing film is not particularly limited as long as the above characteristics are satisfied. Among them, a film containing Ta, preferably a TaHf film or a TaN film, is preferable because the crystalline state of the film becomes amorphous and the surface of the absorbing film is excellent in smoothness. . If the surface roughness of the absorbing film is large, the edge roughness of the pattern formed on the absorbing film is increased and the dimensional accuracy of the pattern is deteriorated. In addition, scattered light (commonly called flare) is generated and pattern contrast in EUV lithography is lowered. Let Since this problem becomes more prominent as the pattern becomes finer, the surface of the absorption film is required to be smooth.
If the absorption film is a film containing Ta (for example, TaHf film, TaN film, etc.), the film has an amorphous structure or a microcrystalline structure. Therefore, the surface roughness of the absorption film surface is 0.5 nm rms or less and the absorption film surface is Since it is sufficiently smooth, not only is there no possibility that the dimensional accuracy of the pattern deteriorates due to the influence of edge roughness, but also flare can be suppressed to a level where there is no problem. The surface roughness of the absorption film surface is more preferably 0.4 nm rms or less, and further preferably 0.3 nm rms or less.

Note that in this specification, the phrase “crystalline state is amorphous” includes a microcrystalline structure other than an amorphous structure having no crystal structure. If the absorption film is an amorphous structure or a microcrystalline structure, the surface of the absorption film is excellent in smoothness.
Note that it can be confirmed by an X-ray diffraction (XRD) method that the crystalline state of the absorption film is amorphous, that is, an amorphous structure or a microcrystalline structure. If the crystalline state of the absorption film is an amorphous structure or a microcrystalline structure, a sharp peak is not seen in a diffraction peak obtained by XRD measurement.

When the absorption film is a TaHf film, it is preferable to contain Ta and Hf at a specific ratio described below.
It is preferable that the content of Hf in the absorption film is 20 to 60 at% because the crystalline state of the absorption film tends to be amorphous and the surface of the absorption film is excellent in smoothness. In addition, it has excellent characteristics as a mask blank for EUVL, such that the reflectance in the EUV wavelength region and the reflectance in the wavelength region of pattern inspection light can be relatively lowered with a thinner film thickness.
The Hf content of the absorption film is more preferably 30 to 50 at%, and further preferably 30 to 45 at%.

  In the absorption film, the remainder excluding Hf is preferably Ta. Accordingly, the Ta content in the absorption film is preferably 40 to 80 at%. The content of Ta in the absorption film is more preferably 50 to 70 at%, and further preferably 55 to 70 at%.

  In the absorption film, the composition ratio of Ta and Hf is more preferably 7: 3 to 4: 6, further preferably 6.5: 3.5 to 4.5: 5.5, and 6: More preferably, it is 4-5: 5.

The TaHf film can be formed by performing a sputtering method using a TaHf compound target in an inert gas atmosphere, for example, a magnetron sputtering method or an ion beam sputtering method.
When the TaHf compound target has a composition of Ta = 30 to 70 at% and Hf = 70 to 30 at%, an absorption film having a desired composition can be obtained, and variations in film composition and film thickness can be avoided. This is preferable.

In order to form the TaHf film by the above-described method, specifically, it may be carried out under the following film formation conditions.
Sputtering gas: Ar gas (gas pressure ^{1.0 × 10 -1 Pa~50 × 10 -1} Pa, preferably ^{1.0 × 10 -1 Pa~40 × 10 -1} Pa, more preferably 1.0 × 10 ^-1 Pa to 30 x 10 ^-1 Pa)
Input power: 30 to 1000 W, preferably 50 to 750 W, more preferably 80 to 500 W
Deposition rate: 2.0-60 nm / min, preferably 3.5-45 nm / min, more preferably 5-30 nm / min

When the absorption film is a TaN layer, it is preferable to contain Ta and N at a specific ratio described below.
The N content of the TaN film is preferably 10 at% or more and less than 50 at%. In the present invention, when the TaN film contains Ta and N at a specific ratio, the crystalline state becomes amorphous.

[Buffer membrane]
In the mask blank manufacturing method of the present invention, when a pattern is formed on the absorption film of the EUVL mask blank by an etching process, usually a dry etching process, the multilayer reflective film is prevented from being damaged. A buffer film that plays a role may be provided between the protective film and the absorption film. Therefore, as the material of the buffer film, a material that is not easily affected by the absorption film etching process, that is, the etching rate is slower than that of the absorption film and is not easily damaged by the etching process is selected. Examples of the material satisfying this condition include Cr, Al, Ru, Ta, and nitrides thereof, and SiO ₂ , Si ₃ N ₄ , Al ₂ O _3, and mixtures thereof. Among these, Ru, CrN, and SiO ₂ are preferable, CrN and Ru are more preferable, and Ru is particularly preferable because it combines the functions of a protective film and a buffer film.
The thickness of the buffer film is preferably 1 to 60 nm.

The buffer film is formed using a known film formation method such as a magnetron sputtering method or an ion beam sputtering method. When forming the Ru film by a magnetron sputtering method, using a Ru target as the target, charged using Ar gas (gas pressure ^{1.0 × 10 -1 Pa~10 × 10 -1} Pa) as the sputtering gas power 30W It is preferable to form the film so that the film thickness is 2 to 5 nm at ˜500 W and the film formation speed is 5 to 50 nm / min.

[Antireflection film]
In the mask blank manufacturing method of the present invention, an antireflection film having a low reflectance with respect to inspection light used for inspection of the mask pattern may be provided on the absorption film.
After manufacturing the EUVL mask, it is inspected whether the mask pattern is formed as designed. In the inspection of the mask pattern, it is expected that an inspection machine that uses ultraviolet light having a normal wavelength of 257 nm as inspection light and in the future using ultraviolet light having a wavelength of 190 to 200 nm will be used. In other words, the difference in reflectance at the wavelength of the inspection light, specifically, the surface of the multilayer reflective film exposed by removing the absorber film by etching (protection is provided when a protective film is formed under the absorbing film). Using the difference in reflectance between the film surface and the buffer film surface (if a buffer film is formed under the absorption film) and the absorber film surface left unintentionally left unetched Inspected. Therefore, if the difference in reflectance at the wavelength of the inspection light between the multilayer reflective film surface (or the protective film surface or buffer film surface) and the absorber film surface is small, the contrast at the time of inspection deteriorates and accurate inspection cannot be performed. It will be.

The absorption film containing Ta has a relatively low reflectivity in the EUV wavelength range and has excellent characteristics as an absorption film of the EUV mask blank, but the reflectivity in the wavelength range of inspection light is not necessarily low enough. I can not say. As a result, the reflectance of the absorption film surface in the wavelength range of the inspection light and the surface of the multilayer reflection film (if a protective film is formed under the absorption film, the buffer film is formed under the protective film surface and the absorption film). In this case, the difference from the reflectance of the buffer film surface) becomes small, and there is a possibility that sufficient contrast at the time of inspection cannot be obtained.
Therefore, it is preferable to form an antireflection film on the absorption film containing Ta. If an antireflection film is formed, the reflectance of the antireflection film surface in the wavelength range of the inspection light becomes extremely low, and the contrast at the time of inspection becomes good. Specifically, when a light beam in the wavelength region of the inspection light is irradiated at an incident angle of about 10 degrees, the surface of the multilayer reflective film (if a protective film is formed under the absorption film, the surface of the protective film, under the absorption film) The reflectance at the wavelength of the inspection light on the surface of the buffer film in the case where a buffer film is formed is about 60 to 70%, although it depends on the material, the wavelength of the inspection light of the antireflection film The reflectance of the region is preferably 20% or less, and more preferably 10% or less. In this case, the contrast at the time of the inspection becomes good. Specifically, the surface of the multilayer reflective film (if the protective film is formed on the multilayer reflective film, the surface of the protective film, and the buffer film is formed below the absorption film) In this case, the contrast between the reflected light of the inspection light wavelength on the buffer film surface) and the reflected light of the inspection light wavelength on the antireflection film surface is 30% or more.

In this specification, the contrast can be obtained using the following equation.
Contrast (%) = ((R ₂ −R ₁ ) / (R ₂ + R ₁ )) × 100
Here, R ₂ in the wavelength region of the inspection light is the surface of the multilayer reflective film (the surface of the protective film when a protective film is formed under the absorbing film, and the buffer when the buffer film is formed under the absorbing film) R ₁ is the reflectance at the antireflection film surface. R ₁ is a state in which an absorption film and an antireflection film are formed in this order on the surface of the multilayer reflection film formed on the substrate, and R ₂ is a multilayer reflection film (in some cases, a protective film). In the state where the film and the buffer film are formed, the reflectance is measured. Alternatively, R ₁ and R ₂ may be measured in a state where the absorption film and the antireflection film of the EUV mask blank are patterned.
In the present invention, the contrast represented by the above formula is more preferably 45% or more, further preferably 60% or more, and particularly preferably 80% or more.

  When the antireflection film is formed on the absorption film, the total film thickness of the absorption film and the antireflection film is preferably 20 to 100 nm. However, if the film thickness of the antireflection film is larger than the film thickness of the absorption film, the EUV light absorption characteristics of the absorption film may be lowered, and the etching rate of the antireflection film is generally slower than the etching rate of the absorption film, Since the etching of the antireflection film becomes rate-limiting in the patterning step, the film thickness of the antireflection film is preferably smaller than that of the absorption film and as thin as possible. For this reason, it is preferable that the film thickness of an antireflection film is 1-30 nm, and it is more preferable that it is 2-10 nm.

  In order to achieve the above characteristics, the antireflection film is preferably made of a material having a higher refractive index in the wavelength region of inspection light than a film containing Ta, and its crystal state is preferably amorphous.

  The antireflection film formed on the absorbing film containing Ta is preferably an oxide film, an oxynitride film, or a nitride film. Specifically, when a TaHf film is used as the absorption film, it is preferable to use a TaHfO film as the antireflection film, and it is preferable to contain Ta, Hf and O in a specific ratio described below.

  The TaHfO film preferably has a total content of Ta and Hf of 30 to 80 at% and a composition ratio of Ta and Hf of 8: 2 to 4: 6. When the total content of Ta and Hf is less than 30 at%, the conductivity of the TaHfO film is lowered, and there is a possibility that a charge-up problem occurs when drawing an electron beam. When the total content of Ta and Hf is more than 80 at%, the peak reflectance in the wavelength region of the pattern inspection light cannot be sufficiently lowered. Further, when Hf is lower than the above composition ratio, the crystalline state is unlikely to be amorphous. When Hf is higher than the above composition ratio, the etching characteristics may be deteriorated and the required etching selectivity may not be satisfied.

  The O content in the TaHfO film is preferably 20 to 70 at%. If the O content is lower than 20 at%, the peak reflectance in the wavelength region of the pattern inspection light may not be sufficiently lowered. When the content of O is higher than 70 at%, the acid resistance is lowered, the low anti-insulation property is increased, and there is a possibility that problems such as charge-up occur when drawing an electron beam.

  The total content of Ta and Hf in the TaHfO film is more preferably 35 to 80 at%, and further preferably 35 to 75 at%. The composition ratio of Ta and Hf is more preferably Ta: Hf = 7: 3 to 4: 6, further preferably 6.5: 3.5 to 4.5: 5.5, More preferably, it is 6: 4-5: 5. The content of O is more preferably 20 to 65 at%, and further preferably 25 to 65 at%.

The TaHfO film may contain elements other than Ta, Hf, and O as necessary. In this case, the element to be included in the TaHfO film needs to satisfy suitability as a mask blank, such as EUV light absorption characteristics.
An example of an element that can be included in the TaHfO film is N. In this case, it is considered that the surface smoothness is improved when the TaHfO film contains N.
When the TaHfO film contains N (that is, a TaHfON film), the total content of Ta and Hf is 30 to 80 at%, and the composition ratio of Ta and Hf is Ta: Hf = 8: 2 to 4: 6, the total content of N and O is 20 to 70 at%, and the composition ratio of N and O is preferably 9: 1 to 1: 9. When the total content of Ta and Hf is less than 30 at%, the conductivity is lowered, and there is a possibility that a charge-up problem occurs when drawing an electron beam. When the total content of Ta and Hf is more than 80 at%, the peak reflectance in the wavelength region of the pattern inspection light cannot be sufficiently lowered. When Hf is lower than the above composition ratio, the crystalline state may not be amorphous. When Hf is higher than the above composition ratio, the etching characteristics may be deteriorated and the required etching selectivity may not be satisfied. Moreover, when the content rates of N and O are lower than 20 at%, there is a possibility that the peak reflectance in the wavelength region of the pattern inspection light cannot be made sufficiently low. When the content ratio of N and O is higher than 70 at%, the acid resistance is lowered, the insulation property is increased, and there is a possibility that problems such as charge-up occur when drawing an electron beam.

  In the TaHfON film, the total content of Ta and Hf is more preferably 35 to 80 at%, and further preferably 35 to 75 at%. The composition ratio of Ta and Hf is more preferably Ta: Hf = 7: 3 to 4: 6, further preferably 6.5: 3.5 to 4.5: 5.5, More preferably, it is 6: 4-5: 5. The total content of N and O is more preferably 20 to 65 at%, and further preferably 25 to 65 at%.

Since the TaHfON film has the above-described configuration, its crystal state is amorphous and its surface is excellent in smoothness. Specifically, the surface roughness (rms) is 0.5 nm or less.
As described above, the surface of the absorption film is required to be smooth in order to prevent deterioration of the dimensional accuracy of the pattern due to the influence of edge roughness. The TaHfON film formed as an antireflection film on the absorption film is required to have a smooth surface.
If the surface roughness (rms) of the TaHfON film surface is 0.5 nm or less, the surface is sufficiently smooth, and there is no possibility that the dimensional accuracy of the pattern deteriorates or the scattered light increases due to the influence of edge roughness. The surface roughness (rms) of the TaHfON layer surface is more preferably 0.4 nm or less, and further preferably 0.3 nm or less.

  Note that whether the TaHfON film is in an amorphous state, that is, an amorphous structure or a microcrystalline structure can be confirmed by an X-ray diffraction (XRD) method. If the crystal state of the TaHfON film is an amorphous structure or a microcrystalline structure, a sharp peak is not observed in a diffraction peak obtained by XRD measurement.

The TaHfO film and the TaHfON film can be formed by performing a sputtering method using a TaHf compound target, for example, a magnetron sputtering method or an ion beam sputtering method.
In the case of a TaHfO film, the film is formed by discharging a TaHf compound target in an oxygen (O ₂ ) atmosphere diluted with, for example, argon. Alternatively, after a TaHf compound target is discharged in an inert gas atmosphere to form a film containing Ta and Hf, the film is formed by exposure to oxygen plasma or irradiation with an ion beam using oxygen, for example. The TaHfO film may be formed by oxidizing the formed film.
On the other hand, a TaHfON film is formed by discharging a TaHf compound target in an oxygen (O ₂ ) / nitrogen (N ₂ ) mixed gas atmosphere diluted with argon. Alternatively, after a TaHf compound target is discharged in a nitrogen (N ₂ ) atmosphere diluted with argon to form a film containing Ta, Hf and N, the film is exposed to, for example, oxygen plasma, or ions using oxygen A TaHfON film may be formed by oxidizing the formed film by irradiation with a beam.
The TaHf compound target has a composition of Ta = 30 to 70 at% and Hf = 70 to 30 at%, so that a TaHfO film and a TaHfON film having a desired composition can be obtained, and variations in film composition and film thickness can be obtained. Is preferable in that it can be avoided. The TaHf compound target may contain 0.1 to 5.0 at% of Zr.

In order to form the TaHfO film and the TaHfON film by the above-described method, specifically, the following film-forming conditions may be used.
If <br/> sputtering gas to deposit a TaHfO film: mixed gas of Ar and O ₂ (O ₂ gas concentration 3~80vol%, preferably 5~60vol%, more preferably 10~40vol%; gas pressure 1. ^{0 × 10 -1 Pa~50 × 10 -1} Pa, preferably ^{1.0 × 10 -1 Pa~40 × 10 -1} Pa, more preferably ^{1.0 × 10 -1 Pa~30 × 10 -1} Pa )
Input power: 30 to 1000 W, preferably 50 to 750 W, more preferably 80 to 500 W
Deposition rate: 2.0-60 nm / min, preferably 3.5-45 nm / min, more preferably 5-30 nm / min
If <br/> sputtering gas to deposit a TaHfON film: Ar, O ₂ and a mixed gas of N ₂ (O ₂ gas concentration 5~40vol%, N ₂ gas concentration 5~40vol%, preferably O ₂ gas concentration: 6 ~35vol%, N ₂ gas concentration 6~35vol%, more preferably O ₂ gas concentration 10 to 30 vol%, N ₂ gas concentration 10 to 30 vol%; gas pressure 1.0 × 10 ^-1 Pa~50 × 10 ^-1 Pa, preferably ^{1.0 × 10 -1 Pa~40 × 10 -1} Pa, more preferably ^{1.0 × 10 -1 Pa~30 × 10 -1} Pa)
Input power: 30 to 1000 W, preferably 50 to 750 W, more preferably 80 to 500 W
Deposition rate: 2.0-60 nm / min, preferably 3.5-45 nm / min, more preferably 5-30 nm / min

In the EUV mask blank manufacturing method of the present invention, in addition to the multilayer reflective film, protective film, buffer film, absorption film, and antireflection film, a functional film known in the field of EUV mask blanks may be provided on the EUVL mask blank. . As a specific example of such a functional film, for example, as described in JP-A-2003-501823, in order to promote electrostatic chucking of the substrate, the back side of the substrate (with respect to the film formation surface) And a high dielectric coating applied. For the high dielectric coating applied to the back surface of the substrate for such a purpose, the electrical conductivity and thickness of the constituent material are selected so that the sheet resistance is 100Ω / □ or less. The constituent material of the high dielectric coating can be widely selected from those described in known literature. For example, a high dielectric constant coating described in JP-A-2003-501823, specifically, a coating made of silicon, titanium nitride, molybdenum, chromium, or tantalum silicide can be applied. The thickness of the high dielectric coating can be, for example, 10 to 1000 nm.
The high dielectric coating can be formed using a known film formation method, for example, a sputtering method such as a magnetron sputtering method or an ion beam sputtering method, a CVD method, a vacuum evaporation method, or an electrolytic plating method.

  An EUVL mask can be obtained by forming a desired pattern on the absorption film of the EUVL mask blank obtained by the above procedure using a photolithography process.

<Preparation of reflection mirror substrate and peak reflectance measurement>
On a synthetic quartz glass substrate (made of SiO ₂ —TiO ₂ glass, size 152.4 × 152.4 × 6.3 mm), using an ion beam sputtering apparatus (Veco NexusLDD), a Si film (film thickness: 4. 5 nm) and Mo film (film thickness 2.3 nm) are alternately stacked in this order to form a multilayer reflective film, and then a Si film (4.5 nm thickness) as a protective film on the multilayer reflective film. A reflective mirror substrate (multilayer reflective film) having a peak reflectivity in the vicinity of a wavelength of 13.5 nm is formed on the Si film by forming a Ru film (2.5 nm thickness) that also serves as a protective film and a buffer film. And a substrate with a protective film). On the obtained reflection mirror substrate, more specifically, the reflectance at a wavelength of 13 to 14 nm on a lattice point with a pitch of 22 mm within the center 132 mm □ of the Ru film of the reflection mirror substrate is measured with an EUV reflectometer (MBR manufactured by AIXUV). And measure the peak reflectance distribution in the same wavelength region. The result is shown in FIG. The legend in the figure indicates the peak reflectance, and the unit is%. The average peak reflectance is 63.7%, the peak reflectance distribution is 1.2%, and the peak reflectance at the center is high and the peak reflectance at the outer periphery is low.

<Example 1>
In the embodiment, the halogen lamp heater (glass tube outer diameter 11 mm) is installed on the reflecting mirror substrate, the surface temperature at the mark x in FIG. 5 is the highest at about 100 ° C., and the surface temperature at the outer peripheral portion is about 20 ° C. Then, heat treatment is performed for 10 minutes so as to have the temperature distribution shown in FIG. The legend in FIG. 6 indicates temperature, and the unit is ° C.
The peak reflectance distribution of the reflective mirror substrate after the heat treatment is measured by the same method as described above. The result is shown in FIG. The legend in the figure indicates the peak reflectance, and the unit is%. The reflection mirror substrate after the heat treatment has an average peak reflectance of 63.6% and a peak reflectance distribution of 0.8%, and the peak reflectance distribution is about 33 with almost no loss of the average peak reflectance. % Improvement.

<Comparative Example 1>
The same reflective mirror substrate as in Example 1 is prepared. The same reflective mirror substrate as that of the example is formed so as to have the temperature distribution shown in FIG. 8 so that the surface temperature at the mark x in FIG. 5 is the highest at about 185 ° C. and the surface temperature at the outer periphery is about 20 ° C. Heat treatment is performed for 10 minutes using a halogen lamp heater. The legend in FIG. 8 indicates temperature, and the unit is ° C.
The peak reflectance distribution of the reflective mirror substrate after the heat treatment is measured by the same method as described above. The result is shown in FIG. The legend in the figure indicates the peak reflectance, and the unit is%. The reflective mirror substrate after the heat treatment has an average peak reflectance of 62.7% and a peak reflectance distribution of 6.3%, which not only deteriorates the peak reflectance distribution but also impairs the average peak reflectance. It is.

FIG. 1 is a schematic cross-sectional view of a general EUV mask blank. FIG. 2 is a reflectance spectrum in the EUV wavelength region when EUV light is irradiated on the protective film surface of a substrate with a multilayer reflective film (Mo / Si multilayer reflective film) and a protective film (Si film, Ru film). FIG. 3 shows the heating temperature of the decrease in central wavelength when a substrate with a multilayer reflective film (Mo / Si multilayer reflective film) and a protective film (Si film, Ru film) is heated for 10 minutes using a hot plate in an air atmosphere. It is the graph which showed the dependence. FIG. 4 shows the heating of the decrease in peak reflectance when a substrate with a multilayer reflective film (Mo / Si multilayer reflective film) and a protective film (Si film, Ru film) is heated for 10 minutes using a hot plate in an air atmosphere. It is the graph which showed temperature dependence. FIG. 5 is a diagram showing a peak reflectance distribution before the heat treatment of the reflecting mirror substrate of Example 1. FIG. FIG. 6 is a diagram showing the temperature distribution during the heat treatment of the reflecting mirror substrate of Example 1. FIG. FIG. 7 is a diagram showing the peak reflectance distribution after the heat treatment of the reflecting mirror substrate of Example 1. FIG. 8 is a view showing the temperature distribution during the heat treatment of the reflecting mirror substrate of Comparative Example 1. FIG. 9 is a diagram showing the peak reflectance distribution after the heat treatment of the reflecting mirror substrate of Comparative Example 1.

Explanation of symbols

1: EUV mask blank 11: Substrate 12: Reflective film (multilayer reflective film)
13: Buffer film 14: Absorption film 15: Antireflection film

Claims (13)

  On the substrate, a high-refractive index layer and a low-refractive index layer are alternately laminated to form a multilayer reflective film that reflects EUV light, and the peak reflectance distribution in the EUV wavelength region on the surface of the multilayer reflective film is obtained and obtained. Further, based on the peak reflectance distribution in the EUV wavelength region on the surface of the multilayer reflective film, at least a part of the region having the highest peak reflectance in the EUV wavelength region is locally heated than the region having the lowest peak reflectance in the EUV wavelength region. Thus, the peak reflection in the EUV wavelength region on the surface of the multilayer reflective film is such that the required value regarding the in-plane uniformity of the peak reflectivity in the EUV wavelength region on the surface of the multilayer reflective film is within ± 0.25%. A method of manufacturing a reflective mask blank for EUV lithography (EUVL), comprising correcting a rate distribution and forming an absorption film that absorbs EUV light on the multilayer reflective film.   On the substrate, a high-refractive index layer and a low-refractive index layer are alternately laminated to form a multilayer reflective film that reflects EUV light, a protective film is formed on the multilayer reflective film, and the surface of the protective film is The peak reflectivity distribution in the EUV wavelength range is obtained, and the peak reflectivity in the EUV wavelength range is lower than the region where the peak reflectivity in the EUV wavelength range is the lowest based on the obtained peak reflectivity distribution in the EUV wavelength range on the surface of the protective film. By locally heating at least a part of the part having a high rate, the required value for the in-plane uniformity of the peak reflectance in the EUV wavelength region on the surface of the protective film is within ± 0.25%. A method of manufacturing a reflective mask blank for EUVL, comprising correcting a peak reflectance distribution in an EUV wavelength region on a film surface and forming an absorption film that absorbs EUV light on the protective film.   The local heating of at least a part of the region where the peak reflectance in the EUV wavelength region is higher than the region where the peak reflectance in the EUV wavelength region is the lowest is the temperature of the region where the peak reflectance in the EUV wavelength region is high. 2. The reflective mask for EUVL according to claim 1, wherein the reflective mask for EUVL according to claim 1 is achieved by heating the entire surface of the multilayer reflective film so as to be relatively higher than the temperature of other portions of the surface of the multilayer reflective film. Blank manufacturing method.   The local heating of at least a part of the region where the peak reflectance in the EUV wavelength region is higher than the region where the peak reflectance in the EUV wavelength region is the lowest is the temperature of the region where the peak reflectance in the EUV wavelength region is high. 3. The reflective mask blank for EUVL according to claim 2, wherein the reflective mask blank for EUVL according to claim 2 is achieved by heating the entire surface of the protective film so as to be relatively higher than the temperature of other parts of the surface of the protective film. Production method.   The method for manufacturing a reflective mask blank for EUVL according to any one of claims 1 to 4, wherein an antireflection film for inspection light used for inspection of a mask pattern is further formed on the absorber film.   The said local heating is implemented at the heating temperature of 180 degrees C or less, The manufacturing method of the reflective mask blank for EUVL in any one of Claims 1-5 characterized by the above-mentioned.   The method for producing a reflective mask blank for EUVL according to claim 6, wherein the local heating is performed in a heating time of 1 to 10 minutes.   The method for producing a reflective mask blank for EUVL according to any one of claims 1 to 7, wherein irradiation with light or an electron beam is used for the local heating.   The method for producing a reflective mask blank for EUVL according to claim 1, wherein a minute heating member is used for the local heating.   The method for manufacturing a reflective mask blank for EUVL according to any one of claims 1 to 7, wherein the local heating is performed by locally blowing a preheated gas.   Peak reflectance distribution in the EUV wavelength region on the surface of the multilayer reflective film so that the required value regarding the in-plane uniformity of the central wavelength of the reflected light in the EUV wavelength region on the surface of the multilayer reflective film is within ± 0.03 nm. The manufacturing method of the reflective mask blank for EUVL in any one of 1, 3, 5-10 which correct | amends.   The peak reflectance distribution in the EUV wavelength region on the surface of the protective film is corrected so that the required value regarding the in-plane uniformity of the central wavelength of the reflected light in the EUV wavelength region on the surface of the protective film is within ± 0.03 nm. The manufacturing method of the reflective mask blank for EUVL in any one of 2, 4-10.   The manufacturing method of the reflective mask for EUVL formed by further patterning the reflective mask blank for EUVL in any one of Claims 1-12.