Reflective mask blank, reflective mask, and producing method of semiconductor device

Abstract

To provide a reflective mask blank capable of performing a mask inspection with high accuracy, while satisfying a phase shift function and optical characteristics required for a reflective phase shift mask.SOLUTION: A reflective mask blank that has a multilayer reflective film, a first thin film, and a second thin film in this order on a main surface of a substrate, where the relative reflectivity R2 of the second thin film with respect to the reflectivity of the multilayer reflective film at light with a wavelength of 13.5 nm is 3% or more, and when k1 is the extinction coefficient of the first thin film at the wavelength of 13.5 nm and d1 [nm] is the thickness of the first thin film, the relationship of (formula 1) is satisfied. (Formula 1): 21.5×k12×d12-52.5×k1×d1+32.1>R2.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a reflective mask blank, which is an original for producing an exposure mask used in the manufacture of a semiconductor device, a reflective mask, a method for manufacturing a reflective mask, and a method for manufacturing a semiconductor device. [Background technology]

[0002] Exposure equipment for semiconductor device manufacturing has been evolving while gradually shortening the wavelength of the light source. In order to realize finer pattern transfer, EUV lithography using extreme ultraviolet (EUV: Extreme Ultra Violet, hereinafter sometimes referred to as EUV light) with a wavelength of about 13.5 nm has been developed. In EUV lithography, a reflective mask is used because there are few materials transparent to EUV light. Representative reflective masks include a reflective binary mask and a reflective phase shift mask (reflective halftone phase shift mask). A reflective binary mask has a relatively thick absorber pattern that sufficiently absorbs EUV light. A reflective phase shift mask has a relatively thin absorber pattern (phase shift pattern) that attenuates EUV light by optical absorption and generates reflected light with a phase inverted at a desired angle with respect to the reflected light from the multilayer reflective film. A reflective phase shift mask can obtain a high transfer optical image contrast by the phase shift effect, so that the resolution can be further improved. Furthermore, since the thickness of the absorber pattern (phase shift pattern) of the reflective phase shift mask is thin, a fine phase shift pattern can be formed with high accuracy.

[0003] Such reflective masks for EUV lithography and techniques relating to mask blanks for producing the same are described in Patent Documents 1 and 2.

[0004] Patent Document 1 discloses a reflective mask blank having a multilayer reflective film, an absorber film, and an etching mask film in this order on a substrate, with the intention that the reflectance of the absorber film for EUV light is 2% or less, in which the absorber film has a buffer layer and an absorbing layer provided on the buffer layer, the buffer layer is made of a material containing tantalum (Ta) or silicon (Si), and the film thickness of the buffer film is 0.5 nm or more and 25 nm or less, the absorbing layer is made of a material containing chromium (Cr) and has a larger extinction coefficient than the buffer film for EUV light, and the etching mask film is made of a material containing tantalum (Ta) or silicon (Si), and the film thickness of the etching mask film is 0.5 nm or more and 14 nm or less.

[0005] Patent Document 2 discloses a reflective mask blank having, on a substrate, a multilayer reflective film, a protective film, and a phase shift film that shifts the phase of EUV light, in that order, in which the phase shift film has a first layer and a second layer, the first layer being made of a material containing at least one element of tantalum (Ta) and chromium (Cr), and the second layer being made of a material containing a metal including ruthenium (Ru) and at least one element of chromium (Cr), nickel (Ni), cobalt (Co), vanadium (V), niobium (Nb), molybdenum (Mo), tungsten (W), and rhenium (Re). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2020 / 175354 [Patent Document 2] International Publication No. 2019 / 225737 Summary of the Invention [Problem to be solved by the invention]

[0007] The finer the pattern and the higher the precision of the pattern dimensions and pattern position, the better the electrical characteristics and performance of the semiconductor device will be, and the greater the degree of integration and the smaller the chip size will be. For this reason, EUV lithography is required to have a pattern transfer performance with higher precision and finer dimensions than ever before. Currently, there is a demand for ultra-fine and highly accurate pattern formation compatible with the hp16nm (half pitch 16nm) generation. In response to these demands, there is a demand for reflective phase shift masks that use EUV light as exposure light and also utilize the phase shift effect.

[0008] When manufacturing a reflective mask having an ultrafine and highly accurate pattern using a reflective mask blank, a pattern is formed on the absorber film by dry etching. However, it is difficult to form all patterns on the absorber film with high accuracy, and it is becoming difficult to avoid the occurrence of so-called black defects, in which the absorber film in the region that should be removed by etching is not completely removed after patterning the absorber film. Such black defects in the absorber pattern can often be corrected by defect correction technology. In recent years, a defect correction (EB defect correction) is often used in which a non-excited etching gas (fluorine-based gas, etc.) is supplied to the periphery of the black defect while a charged particle such as an electron beam is irradiated on the black defect to volatilize and remove the black defect. However, depending on the constituent elements of the absorber film, when the black defect is corrected by this EB defect correction, the correction rate difference between the absorber film and the protective film may not be sufficiently secured. Meanwhile, in recent years, various materials have been considered as materials for forming the absorber film. Depending on the material of the absorber film, sufficient etching selectivity may not be ensured between the absorber film and the protective film during dry etching for patterning the absorber film.

[0009] For these reasons, a buffer film having sufficient etching selectivity for both the protective film and the absorber film may be provided between the protective film and the absorber film. In the process of manufacturing a reflective mask from a reflective mask blank having this buffer film, after the process of forming a transfer pattern on the absorber film by dry etching and before the process of forming a transfer pattern on the buffer film by dry etching, a mask inspection (defect inspection) is performed, which is an inspection including the presence or absence of black defects in the absorber pattern. In this mask inspection, the region on the substrate where the absorber film exists is detected from the contrast between the reflected light from the region where the absorber film exists with respect to the inspection light and the reflected light from the region where the absorber film is removed and the buffer film is exposed. For this reason, in order to perform a highly accurate defect inspection, it is necessary to ensure a sufficient contrast between the reflected light of the absorber film and the reflected light of the buffer film with respect to the inspection light. In addition, a mask blank for a reflective mask has optical constraints since the transfer pattern is formed of a laminated structure of an absorber film, a buffer film, and an absorber film. In particular, in the case of a reflective phase shift mask, it is necessary to exhibit the desired phase shift function in the entire transfer pattern of the laminated structure of the buffer film and the absorber film. Under these circumstances, there is a demand for providing a reflective mask blank that satisfies the optical characteristics required for a reflective mask against EUV light and that allows mask inspection to be performed with high accuracy.

[0010] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a reflective mask blank that satisfies the optical characteristics required for a reflective mask and allows mask inspection to be performed with high accuracy.

[0011] Another object of the present invention is to provide a reflective mask produced by using the above-mentioned reflective mask blank and a method for producing the same, as well as to provide a method for producing a semiconductor device by using the reflective mask. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention has the following configuration.

[0013] (Configuration 1) A reflective mask blank comprising a multilayer reflective film, a first thin film, and a second thin film in this order on a main surface of a substrate, a relative reflectance R2 of the second thin film to the reflectance of the multilayer reflective film for light having a wavelength of 13.5 nm is 3% or more; A reflective mask blank characterized by satisfying the relationship of (Equation 1), where k1 is the extinction coefficient of the first thin film for light with a wavelength of 13.5 nm, and d1 [nm] is the thickness of the first thin film. (Formula 1) 21.5×k1 2 ×d1 2 -52.5×k1×d1+32.1>R2

[0014] (Configuration 2) 2. The reflective mask blank according to claim 1, wherein the relative reflectance R2 is 32% or less.

[0015] (Configuration 3) 3. The reflective mask blank according to structure 1 or 2, wherein the first thin film has an extinction coefficient k1 of 0.05 or less.

[0016] (Configuration 4) 4. The reflective mask blank according to any one of configurations 1 to 3, wherein the first thin film has a thickness d1 of 1 nm or more and 30 nm or less.

[0017] (Configuration 5) 5. The reflective mask blank according to any one of configurations 1 to 4, wherein the first thin film contains a metal element and at least one of oxygen and nitrogen.

[0018] (Configuration 6) 6. The reflective mask blank according to any one of configurations 1 to 5, wherein the second thin film contains a metal element.

[0019] (Configuration 7) 7. The reflective mask blank according to any one of configurations 1 to 6, further comprising a protective film between the multilayer reflective film and the first thin film.

[0020] (Configuration 8) 8. The reflective mask blank according to claim 7, wherein the protective film contains ruthenium.

[0021] (Configuration 9) A reflective mask, comprising the reflective mask blank according to any one of Structures 1 to 8, and a transfer pattern formed on the first thin film and the second thin film.

[0022] (Configuration 10) A method for producing a reflective mask using a reflective mask blank according to any one of configurations 1 to 8, comprising the steps of: forming a transfer pattern on the second thin film; a step of inspecting the second thin film on which the transfer pattern is formed, using inspection light including light having a wavelength of 13.5 nm, to inspect the transfer pattern for defects; a step of repairing defects present in the transferred pattern of the second thin film detected by the defect inspection by irradiating the charged particles while supplying a substance containing fluorine; forming a transfer pattern on the first thin film after the defect is repaired; 2. A method for manufacturing a reflective mask comprising the steps of:

[0023] (Configuration 11) 10. A method for manufacturing a semiconductor device, comprising the step of exposing and transferring a transfer pattern onto a resist film on a semiconductor substrate using the reflective mask according to configuration 9.

[0024] (Configuration 12) 11. A method for manufacturing a semiconductor device, comprising the step of exposing and transferring a transfer pattern onto a resist film on a semiconductor substrate by using a reflective mask manufactured by the method for manufacturing a reflective mask according to configuration 10. Effect of the Invention

[0025] According to the present invention, it is possible to provide a reflective mask blank that satisfies the optical characteristics required for a reflective mask and allows highly accurate mask defect inspection.

[0026] Furthermore, according to the present invention, it is possible to provide a reflective mask manufactured using the above-mentioned reflective mask blank and a method for manufacturing the same, as well as to provide a method for manufacturing a semiconductor device using the reflective mask. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic cross-sectional view of a main portion for explaining an example of a schematic configuration of a reflective mask blank according to an embodiment of the present invention. [Diagram 2] 1A to 1C are process diagrams showing, in schematic cross-sectional views of essential parts, steps for producing a reflective mask from a reflective mask blank. [Diagram 3] 13 is a graph showing the relationship between the thickness of the buffer film, the relative reflectance of the absorber film, and the contrast for light with a wavelength of 13.5 nm when the buffer film is made of a TaBO material. [Figure 4] 13 is a graph showing the relationship between the thickness of the buffer film, the relative reflectance of the absorber film, and the contrast for light with a wavelength of 13.5 nm when the buffer film is made of a CrN material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, the embodiments of the present invention will be described, but first, the background to the invention will be described. The present inventors have conducted extensive research into means for correcting pattern defects while satisfying the optical characteristics required for a reflective mask. Here, detailed research has been conducted on a reflective phase shift mask, which has greater restrictions on optical characteristics than a reflective binary mask. First, the inventors have focused on the fact that in order to exert a desired phase shift function, the relative reflectance of an absorber film (hereinafter simply referred to as an "absorber film") having a phase shift function with respect to a multilayer reflective film in EUV exposure light is required to be 3% or more.

[0029] Meanwhile, in recent years, inspection devices that use EUV light for inspection as inspection light have been put to practical use. This inspection device performs inspection using light of the same wavelength (13.5 nm) as the EUV light (hereinafter, sometimes referred to as EUV exposure light) used in EUV lithography exposure devices, and is therefore preferable in that it can grasp defects that may become problematic during exposure compared to inspection devices that use other wavelengths. However, when repairing defects in an absorber pattern (phase shift pattern) while leaving a buffer film, absorption and attenuation occur in the buffer film.

[0030] As a result of studying this point, the present inventors found that a contrast of more than 40% between the absorber film and the buffer film is necessary for performing mask inspection well, even in the presence of the buffer film. Here, the contrast is a value calculated by the following formula. In addition, in this specification, the "relative reflectance" refers to the relative reflectance when the reflectance [%] of the multilayer reflective film is set to 100. ((relative reflectance of buffer film [%] - relative reflectance of absorber film [%]) / (relative reflectance of buffer film [%] + relative reflectance of absorber film [%])) × 100

[0031] We investigated the conditions for obtaining the desired contrast and found that the main factors were the relative reflectance of the absorber film, the thickness of the buffer film, and the extinction coefficient k. Based on this knowledge, the inventors performed simulations to determine the conditions for obtaining a desired contrast by varying the thickness and extinction coefficient k of the buffer film and the relative reflectance of the absorber film for light with a wavelength of 13.5 nm. Examples are shown in Figures 3 and 4.

[0032] Figure 3 is a graph showing the relationship between the thickness of the buffer film, the relative reflectance of the absorber film, and the contrast for light with a wavelength of 13.5 nm when the buffer film is made of TaBO. In Figure 3, the extinction coefficient k1 is set to 0.022, the refractive index n1 is set to 0.955, the buffer film thickness is changed from 0 to 30 nm, and the relative reflectance of the absorber film is changed from 0 to 40%, to perform a simulation of the contrast.

[0033] Figure 4 is a graph showing the relationship between the thickness of the buffer film, the relative reflectance of the absorber material, and the contrast when the buffer film is made of CrN. In Figure 4, the extinction coefficient k1 is set to 0.039, the refractive index n1 is set to 0.928, the thickness of the buffer film is changed from 0 to 30 nm, and the relative reflectance of the absorber film is changed from 0 to 40%, to perform a simulation of the contrast.

[0034] 3 and 4, regions a, b, . . . j indicate contrast regions of 0-10, 10-20, . As a result of carrying out various such simulations and repeated investigations, the present inventors have found that a desired contrast exceeding 40% can be obtained within a range that satisfies the following formula: (Formula 1) 21.5×k1 2 ×d1 2 -52.5×k1×d1+32.1>R2

[0035] Here, k1 is the extinction coefficient of the buffer film, d1 is the thickness of the buffer film, and R2 is the relative reflectance of the absorber film. Curve A1 in FIG. 3 and curve A2 in FIG. 4 correspond to the equal sign part of formula 1. That is, in FIG. 3, if it is in the region below curve A1, the desired contrast exceeding 40% can be obtained. Also, in FIG. 4, if it is in the region below curve A2, the desired contrast exceeding 40% can be obtained. Note that even in the case of a reflective binary mask, if the condition of the above formula 1 is satisfied, the desired contrast exceeding 40% can be obtained. The present invention has been made as a result of the above-mentioned intensive research. Note that, in the present embodiment, the buffer film is the first thin film and the absorber film is the second thin film, but the present invention is not limited to this.

[0036] 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. Note that in the drawings, the same or corresponding parts are given the same reference numerals, and the description thereof may be simplified or omitted.

[0037] <Configuration of the Reflective Mask Blank 100 and Its Manufacturing Method> FIG. 1 is a schematic cross-sectional view of a main part for explaining the configuration of a reflective mask blank 100 of this embodiment. As shown in FIG. 1, the reflective mask blank 100 has a substrate 1, a multilayer reflective film 2, a protective film 3, a buffer film (first thin film) 4, and an absorber film (second thin film) 5, which are laminated in this order. The multilayer reflective film 2 is formed on the first main surface (front surface) side and reflects EUV light, which is exposure light, with high reflectance. The protective film 3 is provided to protect the multilayer reflective film 2, and is made of a material that is resistant to an etchant and a cleaning solution used when patterning the buffer film 4 described later. The buffer film 4 and the absorber film 5 absorb EUV light and have a phase shift function. In addition, a conductive film (not shown) for electrostatic chuck is formed on the second main surface (rear surface) side of the substrate 1. An etching mask film may be provided on the absorber film 5.

[0038] In this specification, "having a multilayer reflective film 2 on the main surface of the substrate 1" means that the multilayer reflective film 2 is disposed in contact with the surface of the substrate 1, and also includes the case where another film is disposed between the substrate 1 and the multilayer reflective film 2. The same applies to other films. For example, "having a film B on a film A" means that the films A and B are disposed so as to be in direct contact with each other, and also includes the case where another film is disposed between the films A and B. In addition, in this specification, for example, "having a film A in contact with the surface of film B" means that the films A and B are disposed so as to be in direct contact with each other, without another film being disposed between the films A and B.

[0039] Hereinafter, this embodiment will be described for each layer.

[0040] <<Substrate 1>> In order to prevent distortion of the absorber pattern (transfer pattern) 5a (see FIG. 2) due to heat during exposure to EUV light, the substrate 1 is preferably one having a low thermal expansion coefficient within the range of 0±5 ppb / ° C. Examples of materials having a low thermal expansion coefficient within this range include SiO2-TiO2 glass and multi-component glass ceramics.

[0041] The first main surface of the substrate 1 on which the transfer pattern (corresponding to the buffer pattern 4a and absorber pattern 5a described later) 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, 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 a 132 mm×132 mm area of ​​the main surface (first main surface) on which the transfer pattern of the substrate 1 is formed. In addition, the second main surface on the opposite side to the side on which the transfer pattern is formed is a surface that is electrostatically chucked when set in an exposure device, and 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 a 132 mm×132 mm area. The flatness of the second main surface side of the reflective mask blank 100 in an area of ​​142 mm×142 mm is preferably 1 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.3 μm or less.

[0042] In addition, the surface smoothness of the substrate 1 is also an extremely important item. The surface roughness of the first main surface of the substrate 1 is preferably 0.1 nm or less in terms of root mean square roughness (RMS). The surface smoothness can be measured by an atomic force microscope.

[0043] Furthermore, the substrate 1 preferably has high rigidity in order to suppress deformation due to film stress of 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.

[0044] <<Multilayer reflective film 2>> The multilayer reflective film 2 imparts a function of reflecting EUV light to the reflective mask 200, and is a multilayer film in which layers containing elements with different refractive indices as main components are periodically laminated.

[0045] Generally, a multilayer film in which a thin film (high refractive index layer) of a light element or its compound, 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, are alternately stacked for about 40 to 60 periods, is used as the multilayer reflective film 2. The multilayer film may be stacked multiple times, with a high refractive index layer / low refractive index layer stacked in this order from the substrate 1 side as one period. The multilayer film may also be stacked multiple times, with a low refractive index layer / high refractive index layer stacked in this order from the substrate 1 side as one period. Note that the top layer of the multilayer reflective film 2, that is, the surface layer of the multilayer reflective film 2 on the opposite side to the substrate 1, is preferably a high refractive index layer. In the above-mentioned multilayer film, when a high refractive index layer / low refractive index layer stacked in this order from the substrate 1 is stacked multiple times, with a high refractive index layer / low refractive index layer stacked in this order as one period, the top layer is a low refractive index layer. In this case, if the low refractive index layer constitutes the top surface of the multilayer reflective film 2, it is easily oxidized, and the reflectance of the reflective mask 200 decreases. For this reason, it is preferable to further form a high refractive index layer on the uppermost low refractive index layer to form the multilayer reflective film 2. On the other hand, in the above-mentioned multilayer film, when a laminate structure of low refractive index layer / high refractive index layer in which a low refractive index layer and a high refractive index layer are laminated in this order from the substrate 1 side is one period, the uppermost layer is the high refractive index layer and may be left as it is.

[0046] In this embodiment, a layer containing silicon (Si) is used as the high refractive index layer. In addition to simple Si, a Si compound containing boron (B), carbon (C), nitrogen (N), and oxygen (O) in addition to Si can be used as the material containing Si. By using a layer containing Si as the high refractive index layer, a reflective mask 200 for EUV lithography with excellent reflectance of EUV light can be obtained. In this embodiment, a glass substrate is preferably used as the substrate 1. Si also has excellent adhesion to the glass substrate. In addition, a simple metal selected from molybdenum (Mo), ruthenium (Ru), rhodium (Rh), and platinum (Pt), or an alloy thereof is used as the low refractive index layer. For example, as the multilayer reflective film 2 for EUV light with a wavelength of 13 nm to 14 nm, a Mo / Si periodic laminate film in which Mo films and Si films are alternately laminated for about 40 to 60 periods is preferably used. In addition, the high refractive index layer, which is the uppermost layer of the multilayer reflective film 2, may be formed of silicon (Si).

[0047] The reflectance of the multilayer reflective film 2 alone is usually 65% ​​or more, with the upper limit usually being 73%. The thickness and period of each constituent layer of the multilayer reflective film 2 may be appropriately selected according to the exposure wavelength, and are selected so as to satisfy the law of Bragg reflection. The multilayer reflective film 2 has a plurality of high refractive index layers and a plurality of low refractive index layers, but the thicknesses of the high refractive index layers and the low refractive index layers do not have to be the same. 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 layer (high refractive index layer) can be in the range of 3 nm to 10 nm.

[0048] The method of forming the multilayer reflective film 2 is known in the art. For example, the multilayer reflective film 2 can be formed by depositing each layer by ion beam sputtering. In the case of the Mo / Si periodic laminated film described above, a Si film with a thickness of about 4 nm is first deposited on the substrate 1 using a Si target by ion beam sputtering, for example. Then, a Mo film with a thickness of about 3 nm is deposited using a Mo target. This Si film / Mo film is regarded as one period, and 40 to 60 periods are laminated to form the multilayer reflective film 2 (the top layer is a Si layer). For example, when the multilayer reflective film 2 is formed with 60 periods, the number of steps increases compared to 40 periods, but the reflectance for EUV light can be increased. In addition, when forming the multilayer reflective film 2, it is preferable to form the multilayer reflective film 2 by supplying krypton (Kr) ion particles from an ion source and performing ion beam sputtering.

[0049] <<Protective film 3>> The reflective mask blank 100 of this embodiment preferably includes a protective film 3 between the multilayer reflective film 2 and the buffer film 4 .

[0050] In order to protect the multilayer reflective film 2 from dry etching and cleaning in the manufacturing process of the reflective mask 200 described below, a protective film 3 can be formed on the multilayer reflective film 2 or in contact with the surface of the multilayer reflective film 2. The protective film 3 is made of a material that is resistant to an etchant and a cleaning solution used in patterning the buffer film 4. By forming the protective film 3 on the multilayer reflective film 2, damage to the surface of the multilayer reflective film 2 can be suppressed when manufacturing a reflective mask 200 (EUV mask) using a substrate 1 having the multilayer reflective film 2 and the protective film 3. Therefore, the reflectance characteristic of the multilayer reflective film 2 for EUV light becomes good.

[0051] The protective film 3 preferably contains ruthenium. The material of the protective film 3 may be Ru metal alone, or may be a Ru alloy containing at least one metal selected from titanium (Ti), niobium (Nb), molybdenum (Mo), zirconium (Zr), yttrium (Y), boron (B), lanthanum (La), cobalt (Co), and rhenium (Re), and may contain nitrogen. Such a protective film 3 is particularly effective when the buffer film 4 is patterned by dry etching with a chlorine-based gas (Cl-based gas). The protective film 3 is preferably formed of a material that provides an etching selectivity ratio (etching rate of buffer film 4 / etching rate of protective film 3) of 1.5 or more, preferably 3 or more, of the buffer film 4 to the protective film 3 in dry etching using a chlorine-based gas. Here, FIG. 1 shows the case where the protective film 3 is one layer, but it may also be a laminated structure of three or more layers. For example, the protective film 3 may have the bottom and top layers made of a material containing Ru, with a metal other than Ru or an alloy interposed between the bottom and top layers. On the other hand, the protective film 3 may be made of a material selected from silicon-based materials such as silicon (Si), a material containing silicon (Si) and oxygen (O), a material containing silicon (Si) and nitrogen (N), or a material containing silicon (Si), oxygen (O) and nitrogen (N).

[0052] In EUV lithography, since there are few substances transparent to the exposure light, it is technically not easy to make an EUV pellicle that prevents foreign matter from adhering to the mask pattern surface. For this reason, pellicle-less operation that does not use a pellicle has become mainstream. Also, in EUV lithography, exposure contamination occurs, such as the deposition of a carbon film on the mask or the growth of an oxide film due to EUV exposure. Therefore, when the reflective mask 200 for EUV exposure is used in the manufacture of semiconductor devices, it is necessary to frequently clean the mask to remove foreign matter and contamination on the mask. For this reason, the reflective mask 200 for EUV exposure is required to have a mask cleaning resistance that is orders of magnitude higher than that of a transmission mask for optical lithography. The reflective mask 200 has a protective film 3, which can increase the cleaning resistance against cleaning liquid.

[0053] The thickness of the protective film 3 is not particularly limited as long as it can function to protect the multilayer reflective film 2. From the viewpoint of the reflectance of EUV light, the thickness of the protective film 3 is preferably 1.0 nm or more and 8.0 nm or less, more preferably 1.5 nm or more and 6.0 nm or less.

[0054] The method for forming the protective film 3 can be any known film formation method without any particular limitations, and specific examples include sputtering and ion beam sputtering.

[0055] <<Buffer film (first thin film) and absorber film (second thin film)>> In the reflective mask blank 100 of this embodiment, a buffer film (first thin film) 4 and an absorber film (second thin film) 5 are formed on the multilayer reflective film 2 or on the protective film 3 formed on the multilayer reflective film 2. In the state of the reflective mask 200, the buffer film 4 has a buffer pattern 4a formed therein, and the absorber film 5 has an absorber pattern 5a formed therein, and the buffer pattern 4a and the absorber pattern 5a constitute a transfer pattern. The relative reflectance R2 of the absorber film 5 to the reflectance of the multilayer reflective film 2 for light with a wavelength of 13.5 nm (EUV exposure light or EUV light for inspection) is 3% or more. When the extinction coefficient of the buffer film 4 for light with a wavelength of 13.5 nm is k1 and the thickness of the buffer film 4 is d1 [nm], the relationship of (Formula 1) is satisfied. (Formula 1) 21.5×k1 2 ×d1 2 -52.5×k1×d1+32.1>R2

[0056] In the reflective mask 200 of this embodiment, which will be described later, the buffer film 4 and the absorber film 5 (buffer pattern 4a and absorber pattern 5a) absorb the EUV light and reduce the light while reflecting a part of the light at a level that does not adversely affect the pattern transfer. On the other hand, in the opening (the portion without the buffer film 4 and the absorber film 5), the EUV light is reflected from the multilayer reflective film 2 (from the multilayer reflective film 2 via the protective film 3 if the protective film 3 is present). The reflected light from the portion where the buffer film 4 and the absorber film 5 are formed forms a desired phase difference with the reflected light from the opening. The buffer film 4 and the absorber film 5 are formed so that the phase difference between the reflected light from the buffer film 4 and the absorber film 5 and the reflected light from the multilayer reflective film 2 is 130 degrees to 230 degrees. The light with the inverted phase difference of about 180 degrees or about 220 degrees interferes with each other at the pattern edge portion, thereby improving the image contrast of the projected optical image. With the improvement in image contrast, the resolution increases and various latitudes relating to exposure, such as exposure dose latitude and focus latitude, are expanded. Each film will be described below.

[0057] <<Buffer film (first thin film)>> In the reflective mask blank 100 of this embodiment, a buffer film (first thin film) 4 is formed on the multilayer reflective film 2 or on a protective film 3 formed on the multilayer reflective film 2. The buffer film 4 preferably contains a metal element. This metal element may be a metal element in the broad sense, and may be selected from among alkali metals, alkaline earth metals, transition metals, and semimetals. The buffer film 4 has etching selectivity with the multilayer reflective film 2 (etching selectivity with the protective film 3, if the protective film 3 is formed), and may be selected from the metal elements in the broad sense described above, so long as it satisfies the relationship of the above-mentioned (Formula 1). Moreover, the buffer film (first thin film) 4 preferably contains a metal element and at least one of oxygen and nitrogen. By containing oxygen or nitrogen, the extinction coefficient can be reduced, and the degree of freedom in design can be increased. Furthermore, by containing oxygen or nitrogen in advance, the expansion and deformation of the pattern formed in the buffer film 4 due to oxidation can be suppressed.

[0058] The thickness d1 of the buffer film 4 is preferably 1 nm or more, and more preferably 3 nm or more. This is because damage to the multilayer reflective film 2 or the protective film 3 can be suppressed when performing defect repair on the absorber pattern 5a. On the other hand, the thickness d1 of the buffer film 4 is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 15 nm or less. The upper limit of the relative reflectance of the absorber pattern 5a required to make the above contrast greater than 40% increases, and the design freedom of the absorber film 5 increases. This is also because damage to the absorber pattern 5a and the progression of side etching can be suppressed.

[0059] The material of the buffer film 4 is not particularly limited as described above, but tantalum-based materials and chromium-based materials can be preferably used. As the tantalum-based material, in addition to tantalum metal, it is preferable to apply a material in which tantalum (Ta) contains one or more elements selected from nitrogen (N), oxygen (O), boron (B) and carbon (C). In particular, it is preferable to apply a material containing tantalum (Ta) and at least one element selected from oxygen (O) and boron (B). Furthermore, when the buffer film 4 is formed of a material containing chromium, it is preferable to apply a material in which chromium (Cr) contains one or more elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B) and fluorine (F) in addition to chromium metal. In particular, a material containing a nitride of chromium (Cr) is preferable.

[0060] The refractive index n1 of the buffer film 4 is preferably 0.975 or less, and more preferably 0.955 or less, and preferably 0.890 or more, and more preferably 0.910 or more. and the extinction coefficient k1 is preferably in the range of 0.016 to 0.039. The extinction coefficient k1 of the buffer film 4 is preferably 0.05 or less, more preferably 0.04 or less, and even more preferably 0.03 or less. From the results of optical simulations, it is presumed that the light intensity of the reflected light from the multilayer reflective film 2 is stronger than that of the reflected light from the buffer film 4 for light with a wavelength of 13.5 nm, and that the reflected light from the buffer film 4 decreases as the extinction coefficient k1 of the buffer film 4 increases. It is presumed that the extinction coefficient k1 in the above range can suppress the decrease in the reflected light from the buffer film 4, and is therefore preferable. <<Absorber film (second thin film) 5>> In the reflective mask blank 100 of this embodiment, the absorber film 5 is formed on the buffer film 4. As described above, the relative reflectance R2 of the absorber film 5 with respect to the reflectance of the multilayer reflective film 2 for light with a wavelength of 13.5 nm (EUV exposure light or EUV light for inspection) is 3% or more. This relative reflectance R2 is calculated including not only the reflected light reflected by the absorber film 5 (strictly speaking, both the light reflected by the surface of the absorber film 5 and the light reflected by the interface between the absorber film 5 and the buffer film 4) but also the reflected light reflected by the buffer film 4 (light reflected by the interface between the buffer film 4 and the protective film 3). That is, this relative reflectance R2 can also be defined as the surface reflectance in the laminated structure of the buffer film 4 and the absorber film 5. Moreover, the relative reflectance R2 is preferably 32% or less in order to ensure sufficient contrast in mask inspection for light with a wavelength of 13.5 nm, and to ensure sufficient contrast in the pattern image during exposure transfer.

[0061] Although it depends on the pattern and exposure conditions, in order to obtain a phase shift effect, the absolute reflectance of the transfer pattern (buffer pattern 4a and absorber pattern 5a) to EUV light is preferably 4% to 27%, and more preferably 10% to 17%.

[0062] The absorber film 5 of this embodiment preferably contains a metal element. Although not particularly limited, for example, the absorber film 5 may be formed of a material containing ruthenium (Ru) and chromium (Cr). It is more preferable that the absorber film 5 uses a material containing ruthenium (Ru) and chromium (Cr) and at least one element selected from nitrogen (N), oxygen (O), boron (B) and carbon (C).

[0063] On the other hand, the absorber film 5 may be made of a material containing tantalum (Ta) and at least one element selected from tellurium (Te), antimony (Sb), platinum (Pt), iodine (I), bismuth (Bi), iridium (Ir), osmium (Os), tungsten (W), rhenium (Re), tin (Sn), indium (In), polonium (Po), iron (Fe), gold (Au), mercury (Hg), gallium (Ga), and aluminum (Al). Furthermore, the absorber film 5 may be made of a material containing tantalum (Ta) and iridium (Ir). It is more preferable that the absorber film 5 be made of a material containing ruthenium (Ru) and chromium (Cr) and at least one element selected from nitrogen (N), oxygen (O), boron (B), and carbon (C).

[0064] The phase difference and reflectance of the absorber film 5 can be adjusted by changing the refractive index n2, the extinction coefficient k2, and the film thickness. The film thickness of the absorber film 5 is preferably 60 nm or less, more preferably 50 nm or less, and even more preferably 45 nm or less. The film thickness of the absorber film 5 is preferably 20 nm or more. In addition, when the protective film 3 is provided, the phase difference and reflectance of the absorber film 5 can also be adjusted in consideration of the refractive index n, the extinction coefficient k, and the film thickness of the protective film 3. The refractive index n2 of the absorber film 5 for light having a wavelength of 13.5 nm is preferably 0.870 or more, more preferably 0.885 or more. The refractive index n2 of the absorber film 5 is preferably 0.955 or less, more preferably 0.940 or less. The extinction coefficient k2 of the absorber film 5 for light having a wavelength of 13.5 nm is preferably 0.01 or more, more preferably 0.02 or more. The extinction coefficient k2 of the absorber film 5 is preferably 0.05 or less, more preferably 0.04 or less.

[0065] The absorber film 5 of the above-mentioned predetermined material can be formed by known methods such as sputtering methods such as DC sputtering and RF sputtering, and reactive sputtering using oxygen gas. The target may contain one type of metal, and when the absorber film 5 is composed of two or more types of metals, an alloy target containing two or more types of metals (for example, Ru and Cr) can be used. When the absorber film 5 is composed of two or more types of metals, the thin film constituting the absorber film 5 can be formed by co-sputtering using a Ru target and a Cr target. The phase shift film 4 may be a multi-layer film including two or more layers.

[0066] <<Etching mask film>> An etching mask film can be formed on the absorber film 5 or in contact with the surface of the absorber film 5. The material of the etching mask film is one that has a high etching selectivity of the phase shift film 4 to the etching mask film. Here, the "etching selectivity of B to A" refers to the ratio of the etching rate of A, which is a layer that does not need to be etched (a layer that serves as a mask), to B, which is a layer that needs to be etched. Specifically, it is specified by the formula "etching selectivity of B to A=etching rate of B / etching rate of A". In addition, "high selectivity" refers to a high selectivity value as defined above with respect to a comparison target. The etching selectivity of the absorber film 5 to the etching mask film is preferably 1.5 or more, more preferably 3 or more.

[0067] The absorber film 5 made of a Ru-based material in this embodiment can be etched by dry etching using a chlorine-based gas containing oxygen or oxygen gas. As a material having a high etching selectivity of the Ru-based absorber film 5 to the etching mask film, silicon (Si) or a silicon compound material can be used.

[0068] Silicon compounds that can be used for the etching mask film include materials containing silicon (Si) and at least one element selected from nitrogen (N), oxygen (O), carbon (C) and hydrogen (H), as well as metal silicon (metal silicide) or metal silicon compound (metal silicide compound) containing metal in silicon or silicon compound. Metal silicon compounds include materials containing metal and Si and at least one element selected from N, O, C and H.

[0069] The thickness of the etching mask film is desirably 2 nm or more from the viewpoint of obtaining the function as an etching mask for accurately forming a transfer pattern in the absorber film 5. Moreover, the thickness of the etching mask film is desirably 15 nm or less from the viewpoint of reducing the thickness of the resist film.

[0070] <<Conductive film>> A conductive film (not shown) for an electrostatic chuck is generally formed on the second main surface (rear surface) of the substrate 1 (opposite the surface on which the multilayer reflective film 2 is formed). The electrical characteristics (sheet resistance) required for the conductive film for an electrostatic chuck are usually 100 Ω / □ (Ω / Square) or less. The conductive film can be formed, for example, by magnetron sputtering or ion beam sputtering using targets of metals and alloys such as chromium (Cr) and tantalum (Ta).

[0071] The chromium (Cr)-containing material of the conductive film is preferably a Cr compound that contains Cr and further contains at least one selected from boron (B), nitrogen (N), oxygen (O), and carbon (C).

[0072] As the material containing tantalum (Ta) for the conductive film, it is preferable to use Ta, an alloy containing Ta, or a Ta compound containing at least one of boron, nitrogen, oxygen, and carbon in any of these.

[0073] The thickness of the conductive film is not particularly limited as long as it satisfies the function for electrostatic chuck. The thickness of the conductive film is usually 10 nm to 200 nm. This conductive film also serves to adjust the stress on the second main surface side of the mask blank 100. That is, the conductive film 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.

[0074] <Reflection mask 200 and its manufacturing method> The reflective mask 200 of this embodiment has a transfer pattern (buffer pattern 4a and absorber pattern 5a) formed on the buffer film 4 and absorber film 5 of the reflective mask blank 100. The buffer film 4 and absorber film 5 (buffer pattern 4a and absorber pattern 5a) on which the transfer pattern is formed are the same as the buffer film 4 and absorber film 5 of the reflective mask blank 100 of this embodiment described above. The transfer pattern (buffer pattern 4a and absorber pattern 5a) can be formed by patterning the buffer film 4 and absorber film 5 of the reflective mask blank 100 of this embodiment described above. The patterning of the phase shift film 4 can be performed by a predetermined dry etching gas. The buffer pattern 4a and absorber pattern 5a of the reflective mask 200 can absorb EUV light and reflect a part of the EUV light with a predetermined phase difference from the opening (a portion where the buffer pattern 4a and absorber pattern 5a are not formed). The predetermined dry etching gas can be a mixed gas of a chlorine-based gas and an oxygen gas, oxygen gas, a fluorine-based gas, or the like. In order to pattern the buffer pattern 4a and the absorber pattern 5a, an etching mask film can be provided on the buffer pattern 4a and the absorber pattern 5a as necessary. In this case, the buffer pattern 4a and the absorber pattern 5a can be formed by dry etching the buffer film 4 and the absorber film 5 using the etching mask pattern as a mask.

[0075] A method for manufacturing a reflective mask 200 using the reflective mask blank 100 of this embodiment will be described.

[0076] A reflective mask blank 100 is prepared, and a resist film is formed on the absorber film 5 on the first main surface thereof (not necessary if the reflective mask blank 100 is provided with a resist film). A desired transfer pattern is written (exposed) on this resist film, which is then developed and rinsed to form a predetermined resist pattern 6a (resist film having a transfer pattern) (see FIG. 2(a)).

[0077] Next, the absorber film 5 is etched using the resist pattern 6a as a mask to form an absorber pattern 5a (absorber film 5 having a transfer pattern). Since the buffer film 4 has sufficient etching selectivity for this etching, the buffer film 4 remains over the entire surface. After the absorber pattern 5a is formed, the remaining resist pattern 6a is removed (if an etching mask film is formed, the etching mask film is etched using the resist pattern 6a as a mask to form an etching mask pattern, the absorber pattern 5a is formed using this etching mask pattern as a mask, and the etching mask pattern is removed). At this time, defective parts 5b may remain in the absorber pattern 5a (see FIG. 2(b)). A mask inspection (defect inspection) is performed on the absorber pattern 5a using light with a wavelength of 13.5 nm (EUV light for inspection) to detect the defective parts 5b. As described above, the reflective mask blank 100 in this embodiment has a relative reflectance R2 of 3% or more with respect to the reflectance of the multilayer reflective film 2 for light with a wavelength of 13.5 nm (EUV exposure light or EUV light for inspection), and satisfies the relationship of (Formula 1) when the extinction coefficient of the buffer film 4 for light with a wavelength of 13.5 nm is k1 and the thickness of the buffer film 4 is d1 [nm]. (Formula 1) 21.5×k1 2 ×d1 2 -52.5×k1×d1+32.1>R2 As a result, a suitable contrast of more than 40% can be ensured between the absorber film 5 and the buffer film 4, making it possible to accurately detect defective portions 5b (including defective portions in which the absorber film 5 has been partially scraped off as shown in the figure) that may cause problems in forming a transfer pattern.

[0078] Then, a non-excited fluorine-based gas (a substance containing fluorine) is supplied to the detected defective portion 5b while an electron beam (charged particles) is irradiated to the portion, thereby removing the defective portion 5b (see FIG. 2(c)). Then, the buffer film 4 is etched using the absorber pattern 5a as a mask to form a buffer pattern 4a (buffer film 4 having a transfer pattern). Finally, wet cleaning is performed using an acidic or alkaline aqueous solution to manufacture the reflective mask 200 of this embodiment (see FIG. 2(d)).

[0079] As described above, the manufacturing method of the reflective mask 200 of this embodiment is a manufacturing method of the reflective mask 200 using the reflective mask blank 100, and is characterized by comprising the steps of: forming an absorber pattern 5a constituting a transfer pattern in the absorber film 5, which is the second thin film; inspecting the absorber pattern 5a for defects using inspection light including light with a wavelength of 13.5 nm; repairing defective portions 5b present in the absorber pattern 5a detected by the defect inspection by irradiating charged particles while supplying a substance containing fluorine; and, after the defect repair, forming a buffer pattern 4a constituting a transfer pattern in the buffer film, which is the first thin film.

[0080] <Method of manufacturing semiconductor devices> This embodiment is a method for manufacturing a semiconductor device, which includes a step of exposing and transferring a transfer pattern to a resist film on a semiconductor substrate using the above-mentioned reflective mask 200 or a reflective mask 200 manufactured by the above-mentioned manufacturing method for the reflective mask 200. A semiconductor device can be manufactured by setting the reflective mask 200 of this embodiment in an exposure apparatus having an exposure light source of EUV light and transferring the transfer pattern to a resist film formed on a transfer substrate. Therefore, a semiconductor device having a fine and highly accurate transfer pattern can be manufactured. EXAMPLES

[0081] Hereinafter, examples will be described with reference to the drawings. The present embodiment is not limited to these examples. In the examples, the same components are designated by the same reference numerals, and the description will be simplified or omitted.

[0082] [Example 1] As a first embodiment, a method for manufacturing a reflective mask blank 100 will be described.

[0083] A SiO2-TiO2-based glass substrate, which is a low-thermal expansion glass substrate having a size of 6025 (approximately 152 mm × 152 mm × 6.35 mm) with both the first and second main surfaces polished, was prepared as substrate 1. In order to obtain a flat and smooth main surface, polishing was performed using a rough polishing process, a precision polishing process, a localized polishing process, and a touch polishing process.

[0084] Next, a conductive film made of CrN film was formed under the following conditions by magnetron sputtering (reactive sputtering) on ​​the second main surface (rear surface) of the SiO2-TiO2-based glass substrate 1. The conductive film was formed to a thickness of 20 nm using a Cr target in a mixed gas atmosphere of argon (Ar) gas and nitrogen (N2) gas.

[0085] Next, a multilayer reflective film 2 was formed on the main surface (first main surface) of the substrate 1 opposite to the side on which the conductive film was formed. The multilayer reflective film 2 formed on the substrate 1 was a periodic laminated 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 laminating 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 with a thickness of 4.2 nm, and then a Mo film was formed with a thickness of 2.8 nm. This constitutes one period, and 40 periods were laminated in the same manner, and finally a Si film was formed with a thickness of 4.0 nm to form the multilayer reflective film 2.

[0086] Subsequently, a protective film 3 made of a Ru film was formed on the surface of the multilayer reflective film 2 by sputtering using a Ru target in an Ar gas atmosphere to a thickness of 3.5 nm.

[0087] Next, a thin film (TaBO film) made of tantalum (Ta), oxygen (O) and boron (B) was formed by DC magnetron sputtering (reactive sputtering) as the buffer film 4 in Example 1. The buffer film 4 was formed to a thickness of 6 nm in an atmosphere of a mixed gas of argon (Ar) gas and oxygen (O2) gas using a mixed target of tantalum (Ta) and boron (B).

[0088] The buffer film 4 (TaBO film) of Example 1 formed as described above had the following refractive index n1, extinction coefficient (imaginary part of refractive index) k1, and relative reflectance R1 at a wavelength of 13.5 nm, respectively. TaBO film: n1 = 0.955, k1 = 0.022, R1 = 80.1%

[0089] Next, a DC magnetron sputtering method (reactive sputtering method) was used to form a thin film (RuCrN film) made of ruthenium (Ru), chromium (Cr) and nitrogen (N) as the absorber film 5. The absorber film 5 was formed to a thickness of 40.0 nm using a Ru target and a Cr target in a mixed gas atmosphere of krypton (Kr) gas and nitrogen (N2) gas.

[0090] The absorber film 5 (RuCrN film) of Example 1 formed as described above had the following refractive index n2, extinction coefficient (imaginary part of refractive index) k2, and relative reflectance R2 at a wavelength of 13.5 nm, respectively. RuCrN film: n2=0.900, k2=0.021, R2=19.9%

[0091] By the above procedure, the reflective mask blank 100 of Example 1 was manufactured.

[0092] When an investigation was conducted on whether the buffer film 4 and the absorber film 5 in the reflective mask blank 100 of Example 1 satisfied the relationship in Formula 1, it was found that the left side of Formula 1 (21.5×k1 2 ×d1 2The value of (-52.5×k1×d1+32.1) was 25.6, and the value of the right side (R2) was 19.9, which satisfied the relationship of Formula 1. The contrast between the absorber film 5 and the buffer film 4 in Example 1 was 60.2%, which was a good value exceeding 40%.

[0093] Next, the reflective mask 200 of Example 1 was manufactured using the reflective mask blank 100 according to the steps shown in FIG. 2(b), a mask inspection (defect inspection) was performed on the absorber pattern 5a in Example 1 using light with a wavelength of 13.5 nm (EUV light for inspection), and a defective portion 5b that may be a problem in forming a transfer pattern could be detected with high accuracy. As a result, the defective portion 5b was removed by irradiating the detected defective portion 5b with an electron beam while supplying a fluorine-based gas to the defective portion 5b, and a reflective mask 200 having a good absorber pattern 5a could be manufactured.

[0094] 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. The exposed resist film was then developed to form a resist pattern on the semiconductor substrate on which the film to be processed was formed. This resist pattern was transferred to the film to be processed by etching, and various processes such as the formation of an insulating film and a conductive film, the introduction of a dopant, and annealing were performed to manufacture a semiconductor device having desired characteristics.

[0095] [Example 2] In Example 2, a reflective mask blank 100 was produced with the same structure and method as in Example 1, except for the buffer film 4 and the absorber film 5. After forming a multilayer reflective film 2 and a protective film 3 on a substrate 1 in the same manner as in Example 1, a thin film (CrN film) made of chromium (Cr) and nitrogen (N) was formed by DC magnetron sputtering (reactive sputtering) as a buffer film 4 in Example 2. The buffer film 4 was formed to a thickness of 6 nm using a chromium (Cr) target in an atmosphere of a mixed gas of argon (Ar) gas and nitrogen (N2) gas.

[0096] The refractive index n1, extinction coefficient (imaginary part of refractive index) k1, and relative reflectance R1 at a wavelength of 13.5 nm of the buffer film 4 (CrN film) of Example 2 formed as described above were as follows. CrN film: n1=0.928, k1=0.039, R1=67.4%

[0097] Next, a DC magnetron sputtering method (reactive sputtering method) was used to form a thin film (IrTaO film) made of iridium (Ir), tantalum (Ta) and oxygen (O) as the absorber film 5. The absorber film 5 was formed by reactive sputtering using an Ir target and a Ta target in a mixed gas atmosphere of krypton (Kr) gas and oxygen (O2) gas to a film thickness of 40.0 nm.

[0098] The absorber film 5 (IrTaO film) of Example 2 formed as described above had the following refractive index n2, extinction coefficient (imaginary part of refractive index) k2, and relative reflectance R2 at a wavelength of 13.5 nm, respectively. IrTaO film: n2=0.927, k2=0.033, R2=5.2%

[0099] Through the above procedure, the reflective mask blank 100 of Example 2 was manufactured.

[0100] When an investigation was conducted on whether the buffer film 4 and the absorber film 5 in the reflective mask blank 100 of Example 2 satisfied the relationship in Formula 1, it was found that the left side of Formula 1 (21.5×k1 2 ×d1 2The value of (-52.5×k1×d1+32.1) was 21.0, and the value of the right side (R2) was 5.2, which satisfied the relationship of Formula 1. The contrast between the absorber film 5 and the buffer film 4 in Example 2 was 85.7%, which was a good value exceeding 40%.

[0101] Next, a reflective mask 200 of Example 2 was manufactured using the reflective mask blank 100 according to the steps shown in FIG. 2(b), a mask inspection (defect inspection) was performed on the absorber pattern 5a in Example 2 using light with a wavelength of 13.5 nm (EUV light for inspection), and a defective portion 5b that may be a problem in forming a transfer pattern could be detected with high accuracy. As a result, the defective portion 5b was removed by irradiating the detected defective portion 5b with an electron beam while supplying a fluorine-based gas to the defective portion 5b, and a reflective mask 200 having a good absorber pattern 5a could be manufactured.

[0102] The reflective mask 200 produced in Example 2 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. The exposed resist film was then developed to form a resist pattern on the semiconductor substrate on which the film to be processed was formed. This resist pattern was transferred to the film to be processed by etching, and various processes such as the formation of an insulating film and a conductive film, the introduction of a dopant, and annealing were performed to manufacture a semiconductor device having desired characteristics.

[0103] [Comparative Example 1] In Comparative Example 1, a reflective mask blank was produced with the same structure and method as in Example 1, except for the buffer film and absorber film. After forming a multilayer reflective film and a protective film on a substrate in the same manner as in Example 1, a thin film (TaBO film) made of tantalum (Ta), oxygen (O) and boron (B) was formed by DC magnetron sputtering (reactive sputtering) as a buffer film in Comparative Example 1. The buffer film was formed to a thickness of 10 nm in an atmosphere of a mixed gas of argon (Ar) gas and oxygen (O2) gas using a mixed target of tantalum (Ta) and boron (B).

[0104] The buffer film (TaBO film) of Comparative Example 1 formed as described above had the following refractive index n1, extinction coefficient (imaginary part of refractive index) k1, and relative reflectance R1 at a wavelength of 13.5 nm, respectively. TaBO film: n1 = 0.955, k1 = 0.022, R1 = 60.8%

[0105] Next, a thin film (RuN film) consisting of ruthenium (Ru) and nitrogen (N) was formed as an absorber film by DC magnetron sputtering (reactive sputtering). The absorber film was formed to a thickness of 40.0 nm using a Ru target in a mixed gas atmosphere of krypton (Kr) gas and nitrogen (N2) gas.

[0106] The refractive index n2, extinction coefficient (imaginary part of refractive index) k2, and relative reflectance R2 at a wavelength of 13.5 nm of the absorber film (RuN film) of Comparative Example 1 formed as described above were as follows. RuN film: n2=0.890, k2=0.016, R2=27.4%

[0107] Through the above procedures, a reflective mask blank of Comparative Example 1 was manufactured.

[0108] When the buffer film and absorber film in the reflective mask blank of Comparative Example 1 were examined to see whether they satisfied the relationship in Equation 1, it was found that the left side of Equation 1 (21.5×k1 2 ×d1 2The value of (-52.5×k1×d1+32.1) was 21.7, and the value of the right side (R2) was 27.4, which did not satisfy the relationship of Formula 1. The contrast between the absorber film and the buffer film in Comparative Example 1 was 37.9%, which was below 40%.

[0109] Next, the reflective mask 200 of Comparative Example 1 was manufactured using the above reflective mask blank according to the steps shown in FIG. 2(b), a mask inspection (defect inspection) was performed on the absorber pattern in Comparative Example 1 using light with a wavelength of 13.5 nm (EUV light for inspection), but defective parts that could be problematic in forming a transfer pattern could not be detected with high accuracy. All defective parts to be repaired could not be detected, and defective parts remained in the absorber pattern and the buffer pattern, making it impossible to manufacture a reflective mask with a good absorber pattern.

[0110] The reflective mask prepared in Comparative Example 1 was set in an EUV scanner, and EUV exposure was performed on a wafer having a workpiece film and a resist film formed on a semiconductor substrate. The exposed resist film was then developed to form a resist pattern on the semiconductor substrate having the workpiece film formed thereon. When the resist pattern was transferred to the workpiece film by etching, the remaining defective parts were transferred. Therefore, unlike the cases of Examples 1 and 2, when the reflective mask produced in Comparative Example 1 was used, a semiconductor device having desired characteristics could not be manufactured. [Explanation of symbols]

[0111] 1 Board 2 Multilayer reflective film 3 Protective film 4 Buffer film (first thin film) 4a Buffer pattern (transfer pattern) 5. Absorber film with phase shift function (second thin film) 5a Absorber pattern (transfer pattern) 5b Defective part 6a Resist pattern 100 Reflective mask blank 200 Reflective mask

Claims

1. A reflective mask blank comprising a multilayer reflective film, a first thin film, and a second thin film in this order on a main surface of a substrate, Relative reflectance R of the second thin film to the reflectance of the multilayer reflective film at a wavelength of 13.5 nm ２ is 3% or more, The extinction coefficient of the first thin film for light with a wavelength of 13.5 nm is k １ , the thickness of the first thin film is d １ A reflective mask blank, characterized in that, when expressed as a distance (nm), the following relationship (Equation 1) is satisfied: (Formula 1) 21.5×k １ ２ ×d １ ２ -52.5×k １ ×d １ +32.1>R ２

2. The relative reflectance R ２ 2. The reflective mask blank according to claim 1, wherein the reflection ratio is 32% or less.

3. The extinction coefficient k of the first thin film １ 3. The reflective mask blank according to claim 1, wherein:

4. The thickness d of the first thin film １ 4. The reflective mask blank according to claim 1, wherein the thickness of the first insulating film is 1 nm or more and 30 nm or less.

5. 5. The reflective mask blank according to claim 1, wherein the first thin film contains a metal element and at least one of oxygen and nitrogen.

6. 6. The reflective mask blank according to claim 1, wherein the second thin film contains a metal element.

7. 7. The reflective mask blank according to claim 1, further comprising a protective film between the multilayer reflective film and the first thin film.

8. 8. The reflective mask blank according to claim 7, wherein the protective film contains ruthenium.

9. 9. A reflective mask, comprising the reflective mask blank according to claim 1, wherein a transfer pattern is formed on the first thin film and the second thin film.

10. A method for producing a reflective mask using a reflective mask blank according to any one of claims 1 to 8, comprising the steps of: forming a transfer pattern on the second thin film; a step of inspecting the second thin film on which the transfer pattern is formed, using inspection light including light having a wavelength of 13.5 nm, to inspect the transfer pattern for defects; a step of repairing defects present in the transferred pattern of the second thin film detected by the defect inspection by irradiating the charged particles while supplying a substance containing fluorine; forming a transfer pattern on the first thin film after the defect is repaired; 2. A method for manufacturing a reflective mask comprising the steps of:

11. 10. A method for manufacturing a semiconductor device, comprising the step of exposing and transferring a transfer pattern onto a resist film on a semiconductor substrate using the reflective mask according to claim 9.

12. 11. A method for manufacturing a semiconductor device, comprising the step of exposing and transferring a transfer pattern onto a resist film on a semiconductor substrate by using a reflective mask manufactured by the method for manufacturing a reflective mask according to claim 10.

Images