Manufacturing method of mask blank, reflective mask, and semiconductor device

Abstract

To provide a mask blank comprising a thin film having a sufficiently fast etching rate.SOLUTION: A mask blank comprises a multilayer reflective film and a pattern-forming thin film in this order on the main surface of a substrate. The thin film contains tantalum, molybdenum, and nitrogen, and the ratio of the nitrogen content [atom%] to the total content [atom%] of the tantalum and molybdenum in the thin film is at least 0.15.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a mask blank for an exposure mask used in the manufacture of semiconductor devices and the like, a reflective mask which is a reflective exposure mask using this mask blank, and a method for manufacturing a semiconductor device using this reflective mask.

Background Art

[0002] As a manufacturing technology for manufacturing semiconductor devices, EUV lithography using extreme ultraviolet light (EUV: Extreme Ultra Violet) having a wavelength near 13.5 nm has been developed. In EUV lithography, since there are few materials transparent to EUV light, a reflective mask is used. For the reflective mask, EUV light, which is exposure light, is incident obliquely. For this reason, a unique problem called the shadowing effect occurs. The shadowing effect is a phenomenon in which a shadow is formed when exposure light (EUV light) is incident obliquely on an absorber pattern having a three-dimensional structure, and the dimensions and positions of the pattern to be transferred change. In order to suppress this shadowing effect, it is necessary to thin the absorber film constituting the absorber pattern in the mask blank that is the original plate of the reflective mask.

[0003] As one of the methods for thinning the absorber film, there is a method of using a low refractive index material to form the absorber film and using the reflective mask as a reflective phase shift mask (reflective half-tone phase shift mask). As that technology, Patent Documents 1 and 2 below exemplify using an alloy such as TaMo as the material constituting the half-tone film.

[0004] Also, as a technology related to a reflective mask, Patent Document 3 below describes a mask blank in which an absorber film has an absorber layer composed of an absorber for EUV light as a lower layer and a low-reflection layer composed of an absorber for inspection light used for inspecting a mask pattern as an upper layer. It is described that the absorber of the exposure light in the lower layer in the absorber layer can be composed of chromium, manganese, cobalt, copper, zinc, gallium, germanium, molybdenum, palladium, silver, cadmium, tin, antimony, tellurium, iodine, hafnium, tantalum, tungsten, titanium, gold, an alloy containing these elements, and at least one substance selected from these elements or an alloy containing these elements and a substance containing nitrogen and / or oxygen.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] Here, the absorber pattern of the reflective mask is obtained by patterning the absorber film by etching. Therefore, if the etching rate of the absorber film is high, an improvement in the productivity of the reflective mask and an improvement in the etching selectivity with respect to the etching mask and the underlying layer can be expected. However, alloys such as TaMo described above have a slow etching rate and an insufficient etching selectivity with respect to the etching mask and the underlying layer.

[0007] Therefore, an object of the present invention is to provide a mask blank provided with a thin film having a sufficiently high etching rate, a reflective mask formed using this mask blank, and a method for manufacturing a semiconductor device using this reflective mask.

Means for Solving the Problem

[0008] In order to solve the above problems, the present invention has the following configurations.

[0009] (Configuration 1) A mask blank comprising a multilayer reflective film and a thin film for pattern formation on the main surface of a substrate in this order, wherein the thin film contains tantalum, molybdenum, and nitrogen, and the ratio of the nitrogen content [atomic%] to the total content of tantalum and molybdenum [atomic%] in the thin film is 0.15 or more Mask blank.

[0010] (Configuration 2) The ratio of the nitrogen content [atomic%] to the total content of tantalum and molybdenum [atomic%] in the thin film is 1.0 or less The mask blank according to Configuration 1.

[0011] (Configuration 3) The ratio of the molybdenum content [atomic%] to the total content of tantalum and molybdenum [atomic%] in the thin film is 0.5 or less The mask blank according to Configuration 1 or 2.

[0012] (Configuration 4) The total content of tantalum, molybdenum, and nitrogen in the thin film is 90 atomic% or more The mask blank according to any one of Configurations 1 to 3.

[0013] (Configuration 5) The refractive index n of the thin film at the wavelength of extreme ultraviolet light is 0.955 or less The mask blank according to any one of Configurations 1 to 4.

[0014] (Configuration 6) The attenuation coefficient k of the thin film at the wavelength of extreme ultraviolet light is 0.02 or more The mask blank according to any one of Configurations 1 to 5.

[0015] (Configuration 7) A reflective mask including, in this order, a multilayer reflective film and a thin film having a transfer pattern formed on a main surface of a substrate, wherein the thin film contains tantalum, molybdenum, and nitrogen, and a ratio of a nitrogen content [atomic%] to a total content of tantalum and molybdenum [atomic%] in the thin film is 0.15 or more. Reflective mask.

[0016] (Configuration 8) and a ratio of a nitrogen content [atomic%] to a total content of tantalum and molybdenum [atomic%] in the thin film is 1.0 or less. The reflective mask according to Configuration 7.

[0017] (Configuration 9) and a ratio of a molybdenum content [atomic%] to a total content of tantalum and molybdenum [atomic%] in the thin film is 0.5 or less. The reflective mask according to Configuration 7 or 8.

[0018] (Configuration 10) and a total content of tantalum, molybdenum, and nitrogen in the thin film is 90 atomic% or more. The reflective mask according to any one of Configurations 7 to 9.

[0019] (Configuration 11) and a refractive index n of the thin film at a wavelength of EUV is 0.955 or less. The reflective mask according to any one of Configurations 7 to 10.

[0020] (Configuration 12) and an attenuation coefficient k of the thin film at a wavelength of extreme ultraviolet light is 0.02 or more as follows The reflective mask according to any one of Configurations 7 to 11.

[0021] (Configuration 13) Using the reflective mask according to any one of items 7 to 12, the method includes a step of exposing and transferring a transfer pattern to a resist film on a semiconductor substrate. A method for manufacturing a semiconductor device.

Advantages of the Invention

[0022] According to the present invention, it is possible to provide a mask blank having a thin film with a sufficiently high etching rate, a reflective mask formed using this mask blank, and a method for manufacturing a semiconductor device using this reflective mask.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0024] ≪Mask Blank and Reflective Mask≫ FIG. 1 is a cross-sectional view showing the configuration of a mask blank 100 according to an embodiment of the present invention. The mask blank 100 shown in this figure is a master for a reflective mask for EUV lithography using extreme ultraviolet light (EUV: Extreme Ultra Violet, hereinafter referred to as EUV light) as exposure light. FIG. 2 is a cross-sectional view showing the configuration of a reflective mask 200 according to an embodiment of the present invention, which is manufactured by processing the mask blank 100 shown in FIG. 1. Hereinafter, the configurations of the mask blank 100 and the reflective mask 200 according to the embodiment will be described with reference to FIGS. 1 and 2.

[0025] The mask blank 100 shown in FIG. 1 includes a substrate 1, a multilayer reflective film 2, a protective film 3, and a thin film 4 that are sequentially laminated from the substrate 1 side on one main surface 1a of the substrate 1. The thin film 4 is a film on which a transfer pattern is formed by processing. The mask blank 100 may be configured to be provided with an etching mask film 5 on the thin film 4 as necessary. The mask blank 100 has a conductive film 10 on the other main surface (hereinafter referred to as the back surface 1b) of the substrate 1.

[0026] The reflective mask 200 shown in FIG. 2 is obtained by patterning the thin film 4 in the mask blank 100 shown in FIG. 1 as a transfer pattern 4a. Hereinafter, the details of each part constituting the mask blank 100 and the reflective mask 200 will be described based on FIGS. 1 and 2.

[0027] <Substrate 1> In order to prevent distortion of the transfer pattern 4a due to heat generation during exposure with EUV light (EUV exposure) using the reflective mask 200, a substrate 1 having a low coefficient of thermal expansion within the range of 0 ± 5 ppb / °C is preferably used. As a material having a low coefficient of thermal expansion in this range, for example, SiO2-TiO2-based glass, multi-component glass ceramics, etc. can be used. The transfer pattern 4a is a pattern formed by processing the thin film 4 as described above.

[0028] The main surface 1a of the substrate 1 is surface-treated to have a high flatness from the viewpoint of obtaining pattern transfer accuracy and position accuracy in EUV exposure using the reflective mask 200. In the case of EUV exposure, in the region of 132 mm × 132 mm on the main surface 1a of the substrate 1, the flatness is preferably 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.03 μm or less.

[0029] Also, the back surface 1b of the substrate 1 is a surface that is electrostatically chucked when the reflective mask 200 is set in the exposure apparatus. In the region of 132 mm × 132 mm, the flatness is preferably 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.03 μm or less. Note that for the back surface 1b of the mask blank 100, in the region of 142 mm × 142 mm, the flatness is preferably 1 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.3 μm or less.

[0030] Also, the surface smoothness height of the substrate 1 is also an extremely important item. The surface roughness of the main surface 1a of the substrate 1 is preferably 0.1 nm or less in terms of the root mean square roughness [Sq] calculated within a square region with a side length of 1 μm. Note that the surface smoothness can be measured with an atomic force microscope.

[0031] Furthermore, the substrate 1 preferably has high rigidity in order to suppress deformation due to the film stress of the films formed on the main surface 1a and the back surface 1b. In particular, the substrate 1 preferably has a high Young's modulus of 65 GPa or more.

[0032] <Multilayer reflective film 2> The multilayer reflective film 2 is formed on the main surface 1a and reflects EUV light, which is the exposure light, with a high reflectivity. This multilayer reflective film 2 imparts a function of reflecting EUV light in the reflective mask 200 formed using this mask blank 100, and is a multilayer film in which layers mainly composed of elements with different refractive indices are periodically laminated.

[0033] Generally, a multilayer film in which a thin film of a light element or its compound (high refractive index layer), which is a high refractive index material, and a thin film of a heavy element or its compound (low refractive index layer), which is a low refractive index material, are alternately laminated about 40 to 60 cycles is used as the multilayer reflective film 2. The multilayer film may be laminated with a plurality of cycles with a lamination structure of a high refractive index layer / low refractive index layer in which the high refractive index layer and the low refractive index layer are laminated in this order from the substrate 1 side as one cycle. Further, the multilayer film may be laminated with a plurality of cycles with a lamination structure of a low refractive index layer / high refractive index layer in which the low refractive index layer and the high refractive index layer are laminated in this order from the substrate 1 side as one cycle. Note that the outermost layer of the multilayer reflective film 2, that is, the surface layer on the side opposite to the substrate 1 of the multilayer reflective film 2 is preferably a high refractive index layer. In the above-described multilayer film, when a plurality of cycles are laminated with a lamination structure of a high refractive index layer / low refractive index layer in which the high refractive index layer and the low refractive index layer are laminated in this order from the substrate 1 as one cycle, the uppermost layer is a low refractive index layer. In this case, if the low refractive index layer constitutes the outermost surface of the multilayer reflective film 2, it is easily oxidized, and the reflectance of the reflective mask 200 decreases. Therefore, it is preferable to further form a high refractive index layer on the low refractive index layer of the uppermost layer to form the multilayer reflective film 2. On the other hand, in the above-described multilayer film, when a plurality of cycles are laminated with a lamination structure of a low refractive index layer / high refractive index layer in which the low refractive index layer and the high refractive index layer are laminated in this order from the substrate 1 side as one cycle, since the uppermost layer is a high refractive index layer, it may be left as it is.

[0034] In this embodiment, as the high refractive index layer, a layer containing silicon (Si) is adopted. As the material containing Si, in addition to Si alone, Si compounds containing boron (B), carbon (C), nitrogen (N), and oxygen (O) can be used for Si. By using the layer containing Si as the high refractive index layer, a reflective mask 200 for EUV lithography excellent in the reflectivity of EUV light can be obtained. Also, in this embodiment, a glass substrate is preferably used as the substrate 1. Si is also excellent in adhesion to the glass substrate. Further, as the low refractive index layer, a single metal selected from molybdenum (Mo), ruthenium (Ru), rhodium (Rh), and platinum (Pt), or an alloy thereof is used. For example, as the multilayer reflective film 2 for EUV light with a wavelength of 13 nm to 14 nm, a Mo / Si periodically laminated film in which a Mo film and a Si film are alternately laminated about 40 to 60 cycles is preferably used. Note that the high refractive index layer, which is the outermost layer of the multilayer reflective film 2, may be formed of silicon (Si).

[0035] The reflectivity of the multilayer reflective film 2 alone is usually 65% or more, and the upper limit is usually 73%. Note that the film 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 to satisfy the Bragg reflection law. In the multilayer reflective film 2, there are a plurality of high refractive index layers and low refractive index layers, respectively, but the film thicknesses of the high refractive index layers and the low refractive index layers do not have to be the same. Also, the film thickness of the Si layer on the outermost surface of the multilayer reflective film 2 can be adjusted within a range that does not reduce the reflectivity. The film thickness of the Si layer (high refractive index layer) on the outermost surface can be in the range of 3 nm to 10 nm.

[0036] The method for forming the multilayer reflective film 2 is known in the art. For example, it can be formed by depositing each layer of the multilayer reflective film 2 by the ion beam sputtering method. In the case of the Mo / Si periodic multilayer film described above, for example, by the ion beam sputtering method, first, a Si film with a thickness of about 4.2 nm is deposited on the substrate 1 using a Si target. Then, a Mo film with a thickness of about 2.8 nm is deposited using a Mo target. Taking this Si film / Mo film as one cycle, 40 to 60 cycles are stacked to form the multilayer reflective film 2 (the outermost layer is a Si layer). Note that, for example, when the multilayer reflective film 2 has 60 cycles, although the number of processes increases compared to 40 cycles, the reflectivity for EUV light can be increased. Also, 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.

[0037] <Protective film 3> The protective film 3 is a film provided to protect the multilayer reflective film 2 from etching and cleaning when manufacturing the reflective mask 200 for EUV lithography by processing this mask blank 100. This protective film 3 is provided on the multilayer reflective film 2, in contact with the multilayer reflective film 2 or via another film. Also, the protective film 3 also serves to protect the multilayer reflective film 2 when correcting the black defects of the transfer pattern 4a using an electron beam (EB) in the reflective mask 200.

[0038] Here, in FIGS. 1 and 2, the case where the protective film 3 is a single layer is shown, but the protective film 3 can also have a laminated structure of two or more layers. The protective film 3 is formed of a material having resistance to the etchant and cleaning liquid used when patterning the thin 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 the reflective mask 200 using the substrate 1 having the multilayer reflective film 2 and the protective film 3. Therefore, the reflectivity characteristics of the multilayer reflective film 2 for EUV light become good.

[0039] Hereinafter, the case where the protective film 3 is a single layer will be described as an example. When the protective film 3 includes a plurality of layers, in the relationship with the thin film 4, the properties of the material of the uppermost layer (the layer in contact with the thin film 4) of the protective film 3 become important.

[0040] In the mask blank 100 of the present embodiment, as the material of the protective film 3, a material resistant to the etching gas used for dry etching for patterning the thin film 4 formed on the protective film 3 can be selected.

[0041] The protective film 3 preferably contains ruthenium (Ru). The material of the protective film 3 may be a single Ru metal, or a Ru alloy containing at least one metal selected from titanium (Ti), niobium (Nb), molybdenum (Mo), zirconium (Zr), yttrium (Y), rhodium (Rh), boron (B), lanthanum (La), cobalt (Co), and rhenium (Re), and may contain nitrogen. On the other hand, as the protective film 3, 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), and a material containing silicon (Si), oxygen (O), and nitrogen (N) can also be used.

[0042] In EUV lithography, there are few substances that are transparent to EUV light, which is the exposure light. Therefore, it is technically difficult to dispose of a dust-proof mask (EUV pellicle) for preventing foreign matter adhesion on the formation surface side of the transfer pattern 4a in the reflective mask 200. For this reason, pellicle-free operation without using a dust-proof mask has become mainstream. Also, in EUV lithography, exposure contamination such as carbon film deposition or oxide film growth occurs on the reflective mask 200 due to EUV exposure. Therefore, when the reflective mask 200 is used in the manufacture of semiconductor devices, it is necessary to perform cleaning frequently to remove foreign matter and contamination on the mask. For this reason, the reflective mask 200 is required to have mask cleaning resistance far beyond that of a transmissive mask for ordinary lithography. By having the protective film 3 on the reflective mask 200, the cleaning resistance to cleaning liquid can be increased.

[0043] The film thickness of the protective film 3 is not particularly limited as long as it can fulfill the function of protecting the multilayer reflective film 2. From the viewpoint of the reflectivity of EUV light, the film 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.

[0044] As a method for forming the protective film 3, the same methods as known film formation methods can be adopted without particular limitation. Specific examples include various sputtering methods, such as DC sputtering method, RF sputtering method, and ion beam sputtering method, and atomic layer deposition (ALD) method, etc.

[0045] <Thin film 4 and transfer pattern 4a> The thin film 4 is a film used as an absorber film that absorbs EUV light, and becomes a film for forming the transfer pattern 4a of the reflective mask 200 configured using this mask blank 100. The transfer pattern 4a is formed by patterning this thin film 4. In the present embodiment, this thin film 4 is a TaMoN thin film containing tantalum (Ta), molybdenum (Mo), and nitrogen (N).

[0046] - Nitrogen content ratio [N] / [Ta + Mo] - In this thin film 4, the ratio of the nitrogen (N) content [atomic%] to the total content [atomic%] of tantalum (Ta) and molybdenum (Mo) (nitrogen content ratio [N] / [Ta + Mo]) is 0.15 or more.

[0047] Here, FIG. 3 is a graph showing the nitrogen content ratio [N] / [Ta + Mo] and the etching rate ratio in the TaMoN thin film. The etching rate ratio is the value when the etching rate of a tantalum (Ta)-molybdenum (Mo) alloy (Ta:Mo = 7:3) that does not contain nitrogen (N) is set to 1. The tantalum (Ta)-molybdenum (Mo) alloy is an alloy having a refractive index suitable for a thin film for a phase shift mask.

[0048] Also, the etching is dry etching using chlorine gas (Cl2) as the etching gas and dry etching using carbon tetrafluoride (CF4) as the etching gas, which are widely used in the production of the reflective mask 200. The detailed composition of the thin film shown in FIG. 3 will be shown in the following examples.

[0049] As shown in the graph of FIG. 3, for a TaMoN thin film with a nitrogen content ratio [N] / [Ta + Mo] of 0.15 or more, the etching rate ratio in dry etching using chlorine gas (Cl2) as the etching gas is 1.5 or more. Also, this etching rate ratio increases as the nitrogen content ratio [N] / [Ta + Mo] increases. From this, it can be seen that by setting the nitrogen content ratio [N] / [Ta + Mo] ≧ 0.15, the etching rate of the thin film 4 in dry etching using chlorine gas (Cl2) as the etching gas becomes 1.5 times or more the etching rate of the tantalum (Ta)-molybdenum (Mo) alloy.

[0050] Furthermore, as shown in the graph of FIG. 3, for TaMoN thin films with a nitrogen content ratio [N] / [Ta+Mo] of 0.3 or more, the etching rate ratio in dry etching using chlorine gas (Cl2) as the etching gas is 2 or more. On the other hand, in the case of a thin film composed of tantalum (Ta) and nitrogen (N) (TaN thin film), as the nitrogen content ratio [N] / [Ta] increases, the etching rate ratio in dry etching using chlorine gas (Cl2) as the etching gas tends to decrease. That is, the relationship between the nitrogen content ratio and the etching rate ratio in dry etching using chlorine gas (Cl2) as the etching gas is significantly different between the case of adding nitrogen (N) to a tantalum (Ta)-based material without molybdenum (Mo) and the case of adding nitrogen (N) to a material containing tantalum (Ta) and molybdenum (Mo). Note that the upper limit value of the nitrogen content ratio [N] / [Ta+Mo] is set to [N] / [Ta+Mo] ≦ 1.0 from the viewpoint of suppressing the surface roughness of the thin film 4.

[0051] - Molybdenum content ratio [Mo] / [Ta+Mo] - Also, in this thin film 4, the ratio of the content [atomic%] of molybdenum (Mo) to the total content [atomic%] of tantalum (Ta) and molybdenum (Mo) (molybdenum content ratio [Mo] / [Ta+Mo]) is preferably 0.5 or less.

[0052] FIG. 4 is a graph showing the relationship between the molybdenum content ratio [Mo] / [Ta+Mo] and the refractive index and extinction coefficient in a TaMoN thin film. The refractive index [n] and extinction coefficient [k] are the refractive index [n] and extinction coefficient [k] for the EUV wavelength. The detailed composition of the thin film shown in FIG. 4 will be shown in the later examples.

[0053] As shown in the graph of FIG. 4, it can be seen that for TaMoN thin films with a molybdenum content ratio [Mo] / [Ta+Mo] of 0.5 or less, the attenuation coefficient [k] with respect to the wavelength of EUV light is maintained at 0.02 or more. On the other hand, as shown in the graph of FIG. 4, it can be seen that by incorporating molybdenum into thin film 4, the refractive index [n] with respect to the wavelength of EUV light is maintained at 0.955 or less. Furthermore, it can be seen that by setting [Mo] / [Ta+Mo] of the TaMoN film to 0.15 or more, the refractive index [n] with respect to the wavelength of EUV light can be set to 0.95 or less.

[0054] TaMoN thin films having such an attenuation coefficient [k] and refractive index [n] can have a film thickness set in a thinner range. Therefore, when the reflective mask 200 is a phase shift mask, the transfer pattern 4a, which is a phase shift pattern, can be thinned, and the occurrence of the shadowing effect of the reflective mask 200 can be suppressed.

[0055] -Overall Composition- Note that the above-mentioned thin film 4 preferably has a total content of tantalum (Ta), molybdenum (Mo), and nitrogen (N) of 90 atomic% or more, more preferably 95 atomic% or more, and even more preferably 100 atomic%. When this thin film 4 contains materials other than tantalum (Ta), molybdenum (Mo), and nitrogen (N), the other materials that may be contained in the thin film 4 are, for example, boron (B), carbon (C), oxygen (O), and hydrogen (H).

[0056] As described in the following examples, it was found that the thin film 4 having the above composition has a small surface roughness and film stress, and sufficient washing resistance and contrast with respect to ultraviolet light and visible light.

[0057] For example, when the thin film 4 has a film thickness of about 50 nm, the surface roughness [Sq] (root mean square roughness) is less than 0.3 [nm]. This root mean square roughness [Sq] is a value measured by an atomic force microscope (AFM) with a square region of 1 [μm] on each side as the measurement region for the thin film formed on the test substrate. The root mean square roughness [Sq] is a parameter for evaluating the surface roughness defined in ISO 25178, and is a parameter obtained by extending the root mean square roughness [Rq] in the line direction representing the two-dimensional surface properties, which were defined by ISO 4287 and JIS B0601 until now, to three dimensions (surface). Thus, the thin film 4 with a small surface roughness has an amorphous crystallinity, and the edge roughness when a pattern is formed on the thin film 4 by etching can be reduced.

[0058] Furthermore, the film stress of the thin film 4 is such that the amount of deformation of the test substrate caused by forming the thin film 4 is 150 [nm] or less. The amount of deformation of the test substrate is expressed as the difference between the maximum height and the minimum height in the inner region of a square with a side length of 142 [mm] with the center of the test substrate of the differential shape calculated from the difference shape between the surface shape of the thin film 4 and the surface shape of the test substrate before forming the thin film 4 as the reference. The test substrate is made of the same SiO2-TiO2-based glass as the substrate 1 of the mask blank 100, and has a size of 6025 (about 152 mm × 152 mm × 6.35 mm) with both main surfaces polished. Thus, the transfer pattern 4a of the reflective mask 200 obtained by patterning the thin film 4 with low film stress is a pattern with good formation position accuracy.

[0059] As a method for forming the thin film 4, the same known film forming methods can be adopted without particular limitation. Specific examples include various sputtering methods, such as DC sputtering method, RF sputtering method, and ion beam sputtering method, as well as atomic layer deposition (ALD) method and the like. For example, when the thin film 4 is formed by the DC sputtering method, it is formed by a sputtering method using a mixed target of tantalum (Ta) and molybdenum (Mo) and using nitrogen gas (N2) as the sputtering gas. At this time, by adjusting the ratio of tantalum (Ta) and molybdenum (Mo) in the target, the flow rate of the sputtering gas, the sputtering gas pressure, etc., a thin film 4 satisfying the above-described composition range can be obtained. In addition, a so-called co-sputtering in which a tantalum (Ta) target and a molybdenum (Mo) target are installed in the film formation chamber and a voltage is applied to both targets simultaneously may be used to form the thin film 4.

[0060] Here, when the thin film 4 is used as a phase shift film, the film thickness of the thin film 4 is adjusted so as to have the following reflectance. That is, when the transfer pattern 4a of the reflective mask 200 is a phase shift pattern, this thin film 4 is configured as a phase shift film. Such a thin film 4 absorbs EUV light and reflects a part of the EUV light at a level that does not adversely affect pattern transfer. Further, in the formation portion of the transfer pattern 4a in the reflective mask 200, the protective film 3 is exposed in the opening where the thin film 4 is removed. Therefore, the EUV light irradiated to the reflective mask 200 is reflected by the surface of the thin film 4 and the multilayer reflective film 2 through the protective film 3 exposed from the thin film 4.

[0061] When the transfer pattern 4a is a phase shift pattern, the thin film 4 is set in terms of material and film thickness such that the reflected EUV light on the surface of the thin film 4 and the reflected EUV light in the opening where the thin film 4 is removed have a desired phase difference. This phase difference is about 130 degrees to 230 degrees, and the image contrast of the projection optical image is improved by the interference of the reflected lights with inverted phase differences near 180 degrees or near 220 degrees at the pattern edge portion. With the improvement of the image contrast, the resolution increases, and various margins related to exposure such as the exposure margin and the focus margin are expanded.

[0062] In order to obtain such a phase shift effect, although it depends on the pattern and exposure conditions, the relative reflectance of the thin film 4 with respect to EUV light on the surface of the thin film 4 is preferably 2% to 40%, more preferably 6% to 35%, still more preferably 15% to 35%, and particularly preferably 15% to 25%. Here, the relative reflectance of the transfer pattern 4a is the reflectance of the EUV light reflected from the thin film 4 when the EUV light reflected from the portion without the thin film 4 is set as a reflectance of 100%.

[0063] Although it depends on the pattern and exposure conditions, in order to obtain the phase shift effect, the absolute reflectance of the thin film 4 (or the transfer pattern 4a serving as the phase shift pattern) with respect to EUV light is preferably 1% to 30%, more preferably 2% to 25%, and the film thickness is set so as to obtain such an absolute reflectance.

[0064] The film thickness of the thin film 4 is preferably less than 100 nm, and preferably 90 nm or less. Also, the film thickness of the thin film 4 is preferably 15 nm or more, and more preferably 20 nm or more. Note that the thin film 4 as described above can also be used as an absorber film for a binary mask by adjusting the film thickness. Further, one or more other thin films may be formed above or below the thin film 4, and a phase shift film or an absorber film for a binary mask may be configured with a laminated structure of the thin film 4 and one or more other thin films. In this case, the ratio of the thin film 4 to the total film thickness of the phase shift film or the absorber film is preferably 0.5 or more.

[0065] <Etching mask film 5> The etching mask film 5 is a layer provided on or in contact with the surface of the thin film 4 in the mask blank 100, and is a film that becomes a mask pattern when patterning the thin film 4. This etching mask film 5 may be removed at the stage when the reflective mask 200 is completed.

[0066] As the material of such an etching mask film 5, a material is used such that the etching selectivity of the thin film 4 with respect to the etching mask film 5 becomes sufficiently high. The etching selectivity of the thin film 4 with respect to the etching mask film 5 is preferably 1.5 or more, and more preferably 3 or more.

[0067] The thin film 4 in this embodiment is a TaMoN thin film containing tantalum (Ta)-molybdenum (Mo)-nitrogen (N), with a nitrogen content ratio [N] / [Ta+Mo] of 0.15 or more, and is a film with a high etching rate for dry etching using chlorine gas (Cl2) as the etching gas. Therefore, as the material for the etching mask film 5, it is preferable to use a material with a low etching rate for dry etching using chlorine gas (Cl2) as the etching gas. Examples of such materials include materials containing chromium (Cr). Specific examples of materials containing chromium (Cr) include, for example, materials containing one or more elements selected from nitrogen, oxygen, carbon, and boron in chromium. For example, CrN, CrON, CrCN, CrCON, CrBN, CrBON, CrBCN, and CrBOCN can be mentioned. The etching mask film 5 formed of a material containing chromium can be patterned by dry etching with a mixed gas of chlorine gas (Cl2) and oxygen gas (O2). The damage to the thin film 4 during dry etching when removing the etching mask film 5 can be reduced. For these materials, metals other than chromium may be contained within the range where the effects of the present invention can be obtained. Such a method for forming the etching mask film 5 can be formed using a chromium (Cr) target by, for example, magnetron sputtering or ion beam sputtering.

[0068] In addition, when the pattern of the etching mask film 5 remains at the stage when the reflective mask 200 is completed and constitutes part of the phase shift pattern or part of the absorber pattern, the etching mask film 5 may be formed of a material containing silicon and oxygen or a material containing tantalum and oxygen.

[0069] The film thickness of the etching mask film 5 is desirably 2 nm or more from the viewpoint of obtaining the function as an etching mask for accurately forming a transfer pattern on the thin film 4. Further, the film thickness of the etching mask film 5 is preferably 15 nm or less, more preferably 10 nm or less, from the viewpoint of reducing the film thickness of the resist film formed on the upper part of the etching mask film 5 when manufacturing the reflective mask 200 by processing the mask blank 100.

[0070] <Conductive film 10> The conductive film 10 is a film for attaching the reflective mask 200 to the exposure apparatus by the electrostatic chuck method. The electrical characteristics (sheet resistance) required for such a conductive film 10 for electrostatic chuck are usually 100 Ω / □ (Ω / Square) or less. The conductive film 10 can be formed, for example, by a magnetron sputtering method or an ion beam sputtering method using targets of metals and alloys such as chromium (Cr) and tantalum (Ta).

[0071] The material containing chromium (Cr) of the conductive film 10 is preferably a Cr compound containing Cr and further containing at least one selected from boron (B), nitrogen (N), oxygen (O), and carbon (C).

[0072] As the material containing tantalum (Ta) of the conductive film 10, it is preferable to use Ta (tantalum), 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 10 is not particularly limited as long as the function as an electrostatic chuck is satisfied. The thickness of the conductive film 10 is usually 10 nm to 200 nm. Further, this conductive film 10 also serves to adjust the stress on the back surface 1b side of the mask blank 100. That is, the conductive film 10 is adjusted so as to balance the stress from various films formed on the main surface 1a side to obtain a flat mask blank 100 and reflective mask 200.

[0074] <Method for manufacturing a reflective mask> FIG. 5 is a manufacturing process diagram showing the method for manufacturing a reflective mask of the present invention, and shows the procedure for manufacturing the reflective mask 200 shown in FIG. 2 using the mask blank 100 shown in FIG. 1. Hereinafter, the method for manufacturing a reflective mask will be described with reference to FIG. 5.

[0075] First, as shown in FIG. 5(1), a mask blank 100 is prepared. This mask blank 100 is the mask blank 100 described with reference to FIG. 1, and for example, an etching mask film 5 is formed on the thin film 4. However, if the mask blank 100 does not have the etching mask film 5, the etching mask film 5 is formed on the thin film 4. Thereafter, a resist film 20 is formed on the etching mask film 5 by, for example, spin coating. Note that the mask blank 100 may be provided with the resist film 20, and in this case, the procedure for forming the resist film 20 is unnecessary.

[0076] Next, as shown in FIG. 5(2), the resist film 20 is patterned by performing a lithography process on the resist film 20 to form a resist pattern 20a. In this lithography process, for example, exposure by electron beam drawing, development processing, and rinsing processing are performed.

[0077] Next, as shown in FIG. 5(3), the etching mask film 5 is etched using the resist pattern 20a as a mask to form an etching mask pattern 5a. Thereafter, the resist pattern 20a is removed by ashing or a resist stripper or the like.

[0078] Next, as shown in FIG. 5(4), using this etching mask pattern 5a as a mask, the thin film 4 is etched to form a transfer pattern 4a. At this time, the thin film 4 is a TaMoN thin film with a nitrogen content ratio [N] / [Ta + Mo] of 0.15 or more. Therefore, dry etching is performed using chlorine gas (Cl2) as the etching gas. In this etching, the protective film 3 made of a material containing ruthenium (Ru) or silicon oxide (SiO2) serves as an etching stopper, preventing the multilayer reflection film 2 from being damaged by etching.

[0079] After the above, by removing the etching mask pattern 5a, the reflection mask 200 shown in FIG. 2 is obtained. Note that for the removal of the etching mask pattern 5a, wet cleaning is performed using an acidic or alkaline aqueous solution. Also in this wet cleaning, the protective film 3 prevents damage to the multilayer reflection film 2.

[0080] In the above method for manufacturing the reflection mask 200, since the transfer pattern 4a is formed by etching the thin film 4 with a high etching rate, productivity can be improved. Also, the thin film 4 is patterned by etching with a high etching selectivity with respect to the etching mask pattern 5a and the protective film 3. For this reason, it is possible to improve the shape accuracy and miniaturize by thinning the etching mask pattern 5a. Furthermore, it is also possible to prevent surface roughness of the protective film 3.

[0081] ≪Method for manufacturing semiconductor device≫ The method for manufacturing a semiconductor device according to the present invention is characterized in that, using the reflection mask 200 described above, the transfer pattern 4a of the reflection mask 200 is exposed and transferred onto a resist film on a substrate. The method for manufacturing such a semiconductor device is performed as follows.

[0082] First, prepare a substrate on which a semiconductor device is to be formed. This substrate may be, for example, a semiconductor substrate, a substrate having a semiconductor thin film, or a substrate on which a fine processing film is formed on top of these. A resist film is formed on the prepared substrate, and pattern exposure is performed on this resist film using the reflective mask 200 of the present invention, and the transfer pattern 4a formed on the reflective mask 200 is exposed and transferred onto the resist film. At this time, EUV light is used as the exposure light.

[0083] After the above, the resist film on which the transfer pattern 4a has been exposed and transferred is developed to form a resist pattern, and using this resist pattern as a mask, etching is performed on the surface layer of the substrate or a process of introducing impurities is carried out. After the process is completed, the resist pattern is removed.

[0084] By performing the above-described processes and further performing necessary processing, a semiconductor device is completed.

[0085] In the manufacture of a semiconductor device as described above, by performing pattern exposure using EUV light as the exposure light with a reflective mask 200 having a transfer pattern 4a with good shape accuracy, a resist pattern with an accuracy sufficient to fully meet the initial design specifications can be formed on the substrate. Further, when this reflective mask 200 is a reflective phase shift mask, the occurrence of the shadowing effect can be suppressed, and a resist pattern with good shape accuracy and position accuracy can be formed. From the above, when the pattern of this resist film is used as a mask to dry-etch the underlying film to form a circuit pattern, a high-precision circuit pattern without wiring short circuits or disconnections due to insufficient accuracy can be formed.

Example

[0086] Next, an example to which the present invention is applied will be described. FIG. 6 is a diagram showing the composition of the thin film and the physical properties of the thin film in the example. Hereinafter, Example Nos. 1-13 will be described with reference to FIGS. 1 and 6 above.

[0087] <Example No. 1-12> The mask blank 100 of Example No. 1-12 was fabricated as follows. First, a SiO2-TiO2-based glass substrate, which is a low thermal expansion glass substrate with a size of 6025 (about 152 mm × 152 mm × 6.35 mm) and whose both main surfaces are polished, was prepared as substrate 1. Polishing consisting of a rough polishing process, a precision polishing process, a local processing process, and a touch polishing process was performed so that both main surfaces of substrate 1 are flat and smooth.

[0088] Next, one main surface of substrate 1 was defined as the back surface 1b, and a conductive film 10 made of a CrN film was formed on the back surface 1b side by magnetron sputtering (reactive sputtering). The conductive film 10 was formed to have a film thickness of 20 nm using a Cr target in a mixed gas atmosphere of argon (Ar) gas and nitrogen (N2) gas.

[0089] Next, the side opposite to the back surface 1b side where the conductive film 10 was formed was defined as the main surface 1a of substrate 1, and a multilayer reflective film 2 was formed on this main surface 1a. The multilayer reflective film 2 formed on substrate 1 was a periodic multilayer reflective film made of molybdenum (Mo) and silicon (Si) in order to be a 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 substrate 1 by an ion beam sputtering method in a krypton (Kr) gas atmosphere using a Mo target and a Si target. First, a Si film was formed to have a film thickness of 4.2 nm, and then a Mo film was formed to have a film thickness of 2.8 nm. This was defined as one cycle, and in the same manner, 40 cycles were laminated. Finally, a Si film was formed to have a film thickness of 4.0 nm to form the multilayer reflective film 2.

[0090] Subsequently, in an Ar gas atmosphere, a protective film 3 made of a RuRh film was formed on the surface of the multilayer reflective film 2 to have a film thickness of 2.6 nm by an RF sputtering method using a RuRh target (Ru:Rh = 8:2 atomic% ratio).

[0091] Next, as the thin film 4, a TaMoN film was formed. At this time, in a PVD apparatus using a tantalum (Ta) target and a molybdenum (Mo) target, a thin film 4 was formed to a film thickness of 50 nm by reactive sputtering (co-sputtering) using nitrogen gas (N2) as the sputtering gas. Also, in the formation of each thin film 4 of Example No. 1-12, by adjusting the ratio of tantalum (Ta) and molybdenum (Mo) in the target, the flow rate of nitrogen gas (N2), and the gas pressure, thin films 4 with the compositions shown in FIG. 6 were obtained. The composition of each thin film 4 is a value obtained by elemental analysis by RBS (Rutherford Backscattering Spectrometry).

[0092] <Example No. 13> In the manufacturing procedure of the mask blank 100 of Example No. 1-12, only the formation of a thin film of a tantalum (Ta)-molybdenum (Mo) alloy as the thin film 4 was different. At this time, a thin film of a tantalum (Ta)-molybdenum (Mo) alloy with a film thickness of 50 nm was formed by co-sputtering using a tantalum (Ta) target and a molybdenum (Mo) target in an argon gas atmosphere. The composition of the thin film of the tantalum (Ta)-molybdenum (Mo) alloy is a value obtained by elemental analysis by RBS.

[0093] ≪Evaluation of Thin Films in Each Mask Blank≫ The thin films of the mask blanks prepared in Example No. 1-13 were directly formed on a substrate, and the physical properties of each formed thin film were evaluated. As the substrate, the same substrate as that used in the preparation of the mask blank was used.

[0094] <Etching Rate> For each of the thin films of Examples No. 1 - 13, the etching rate of each thin film was measured. The etching rate was measured as the etching rate of the thin film in a state where the thin film 4 was exposed to a chlorine gas (Cl2) atmosphere used as an etchant for the thin film 4 when processing a mask blank to create a reflective mask. The results are as shown in FIG. 3 as the etching rate ratio when the etching rate of the tantalum (Ta)-molybdenum (Mo) alloy thin film of Example No. 13 was taken as 1.

[0095] As described above with reference to FIG. 3, the TaMoN thin films of Examples No. 3 - 12 (see FIG. 6) with a nitrogen content ratio [N] / [Ta + Mo] of 0.15 or more have an etching rate ratio of 1.5 or more in dry etching using chlorine gas (Cl2) as the etching gas, and it can be seen that it is 1.5 times or more the etching rate of the TaMo alloy.

[0096] <Refractive Index and Extinction Coefficient> For each of the thin films of Examples No. 1 - 12, the refractive index [n] and extinction coefficient [k] were calculated. Also, as a reference example, a TaBN film (a thin film with an atomic% ratio of Ta:B:N = 70:15:15, that is, a thin film with [Mo] / [Ta + Mo] = 0) was formed on a substrate by sputtering, and the refractive index [n] and extinction coefficient [k] were calculated. The results are as shown in FIG. 4 as the relationship between the molybdenum content ratio [Mo] / [Ta + Mo] and the refractive index and extinction coefficient in each of the thin films of Examples No. 1 - 12 and the reference example.

[0097] As shown in FIG. 4, it can be seen that for the TaMoN films of Examples No. 1-12 (see FIG. 6) with a molybdenum content ratio [Mo] / [Ta+Mo] of 0.5 or less, the attenuation coefficient [k] with respect to the wavelength of EUV light is maintained at 0.02 or more. Also, for the TaMoN films of Examples No. 1-12 other than the TaBN film of the reference example ([Mo] / [Ta+Mo]=0 thin film), the refractive index [n] with respect to the wavelength of EUV light is maintained at 0.955 or less. Such TaMoN thin films can have a film thickness set in a thinner range, and when the reflective mask 200 is a phase shift mask, the transfer pattern 4a, which is the phase shift pattern, can be thinned, so that the occurrence of the shadowing effect of the reflective mask 200 can be suppressed.

[0098] <Surface roughness> The surface roughness of each thin film of Example No. 1-13 was measured, and the results are shown in accordance with FIG. 6. The surface roughness [Sq] (root mean square roughness) is the value measured by AFM with a square region with a side length of 1 [μm] as the measurement region as described above. As shown in FIG. 6, it was confirmed that for the TaMoN thin films of Examples No. 3-12 with a nitrogen content ratio [N] / [Ta+Mo]≧0.15, the surface roughness [Sq] (root mean square roughness) was suppressed to less than 0.3 [nm].

[0099] <Crystallinity> The crystallinity of each thin film of Example No. 1-13 was evaluated by XRD (X-ray diffraction), and the results are shown in accordance with FIG. 6. As shown in FIG. 6, it was confirmed that the TaMoN thin films of Examples No. 3-12 with a nitrogen content ratio [N] / [Ta+Mo]≧0.15 were amorphous.

[0100] <Film stress> The film stress of each thin film of Examples No. 1 - No. 13 was measured, and the results are shown in accordance with Figure 6. The film stress was expressed as the difference between the maximum height and the minimum height (substrate warping amount) in the inner region of a square with a side of 142 [mm] with the center of the substrate of the differential shape calculated from the difference in the surface shape of the thin film and the surface shape of the substrate before forming the thin film. The measurement of each surface shape was performed using a surface shape measuring device UltraFLAT200M (manufactured by Corning TROPEL).

[0101] As shown in Figure 6, it was confirmed that the TaMoN thin films of Examples No. 3 - 12 with a nitrogen content ratio [N] / [Ta + Mo] ≥ 0.15 had a film stress (substrate warping amount) suppressed to 150 [nm] or less.

[0102] <SPM film removal rate> The SPM film removal rate of each thin film of Examples No. 1 - 3, 7 - 11, 13 was measured for two cleanings as the cleaning resistance, and the results are shown in accordance with Figure 6. In this case, the film removal amount (SPM film removal amount) of the thin film after exposing the thin film to the SPM cleaning solution for a predetermined time and cleaning was measured, and the SPM film removal rate for each of the two cleanings was calculated.

[0103] As shown in Figure 6, the SPM film removal rate of the TaMoN thin films of Examples No. 3 - 12 with a nitrogen content ratio [N] / [Ta + Mo] ≥ 0.15 was slower than the SPM film removal rate in the first cleaning of the TaMo alloy thin film of Example No. 13 for both the first and second cleanings. Thereby, it was confirmed that the TaMoN thin film with a nitrogen content ratio [N] / [Ta + Mo] ≥ 0.15 had sufficient SPM resistance.

[0104] <Contrast> For each of the thin films of Examples Nos. 2, 7 - 11, and 13, the contrast with respect to ultraviolet light having a wavelength of 193 nm and visible light having a wavelength of 405 nm was evaluated. Here, the contrast between the multilayer reflective film 2 provided with the protective film 3 and each thin film was measured. As a result, it was confirmed that the contrast of the TaMoN thin films of Examples Nos. 7 - 11 with a nitrogen content ratio [N] / [Ta + Mo] ≧ 0.15 was higher than the contrast of the TaMo alloy thin film of Example No. 13, and accurate inspection using ultraviolet light and visible light as inspection light was possible.

Explanation of Signs

[0105] 1…Substrate 1a…Main surface 2…Multilayer reflective film 3…Protective film 4…Thin film 4a…Transfer pattern 100 Mask blank 200 Reflective mask

Claims

1. A mask blank comprising a multilayer reflective film and a thin film for pattern formation on a main surface of a substrate in this order, wherein the thin film contains tantalum, molybdenum, and nitrogen, and a ratio of a nitrogen content [atomic%] to a total content of tantalum and molybdenum [atomic%] in the thin film is 0.15 or more. Mask blank.

2. The ratio of the nitrogen content [atomic%] to the total content of tantalum and molybdenum [atomic%] in the thin film is 1.0 or less. The mask blank according to claim 1.

3. The ratio of the molybdenum content [atomic%] to the total content of tantalum and molybdenum [atomic%] in the thin film is 0.5 or less. The mask blank according to claim 1 or 2.

4. The total content of tantalum, molybdenum, and nitrogen in the thin film is 90 atomic% or more. The mask blank according to any one of claims 1 to 3.

5. The refractive index n of the thin film at the wavelength of extreme ultraviolet light is 0.955 or less. The mask blank according to any one of claims 1 to 4.

6. The attenuation coefficient k of the thin film at the wavelength of extreme ultraviolet light is 0.02 or more. The mask blank according to any one of claims 1 to 5.

7. A reflective mask comprising a multilayer reflective film and a thin film on which a transfer pattern is formed on a main surface of a substrate in this order, wherein the thin film contains tantalum, molybdenum, and nitrogen, and a ratio of a nitrogen content [atomic%] to a total content of tantalum and molybdenum [atomic%] in the thin film is 0.15 or more. Reflective mask.

8. The ratio of the nitrogen content [atomic%] to the total content of tantalum and molybdenum [atomic%] in the thin film is 1.0 or less. The reflective mask according to claim 7.

9. The ratio of the molybdenum content [atomic%] to the total content of tantalum and molybdenum [atomic%] in the thin film is 0.5 or less. The reflective mask according to claim 7 or 8.

10. The total content of tantalum, molybdenum, and nitrogen in the thin film is 90 atomic% or more. The reflective mask according to any one of claims 7 to 9.

11. The refractive index n of the thin film at the wavelength of extreme ultraviolet light is 0.955 or less. The reflective mask according to any one of claims 7 to 10.

12. The attenuation coefficient k of the thin film at the wavelength of extreme ultraviolet light is 0.02 or more. The reflective mask according to any one of claims 7 to 11.

13. A method for manufacturing a semiconductor device, comprising a step of exposing and transferring a transfer pattern onto a resist film on a semiconductor substrate using the reflective mask according to any one of claims 7 to 12. ​

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