Mask blank, reflective mask, and method for manufacturing semiconductor device

Abstract

The objective of this invention is to provide a mask substrate capable of producing a reflective mask with excellent transfer characteristics when exposed to EUV light. A mask substrate comprises multiple layers of reflective films and pattern-forming thin films sequentially disposed on the main surface of a substrate. The thin films are composed of a metallic material, such that the refractive index of the thin film relative to light with wavelength λL = 13.2 nm is nL, the refractive index of the thin film relative to light with wavelength λM = 13.5 nm is nM, and the refractive index of the thin film relative to light with wavelength λH = 13.8 nm is nH. When the coefficient P = [(1-nH) / λH-(1-nL) / λL)] / [(1-nM) / λM], the absolute value of the coefficient P becomes 0.09 or less.

Description

[Technical Field]

[0001] This invention relates to a mask substrate for a master of an exposure mask used in the manufacture of semiconductor devices, a reflective mask, and a method for manufacturing semiconductor devices. [Previous Technology]

[0002] Exposure equipment used in semiconductor device manufacturing is constantly evolving while gradually shortening the wavelength of the light source. To achieve finer pattern transfer, EUV lithography, which uses extreme ultraviolet (EUV) light with a wavelength of approximately 13.5 nm, has been developed. In EUV lithography, since there is less material that is transparent to EUV light, reflective masks are used. Representative reflective masks include reflective binary masks and reflective phase-shift masks (reflective halftone phase-shift masks).

[0003] The above-mentioned reflective mask for EUV lithography and the related technologies for making the mask substrate thereon have been described in Patent Documents 1 and 2.

[0004] Patent Document 1 discloses an extreme ultraviolet (EUV) exposure mask comprising a high-reflectivity portion formed by a multilayer film on a substrate and a low-reflectivity portion formed by a single-layer film on a portion of the multilayer film. In this mask, the reflected light from the low-reflectivity portion has a reflectivity of 5-15% relative to the reflected light from the high-reflectivity portion, and has a phase difference of 175-185 degrees relative to the reflected light from the high-reflectivity portion. The refractive index (1-δ) and extinction coefficient β of the single-layer film constituting the low-reflectivity portion relative to the exposure wavelength are located in a plane coordinate system with the refractive index (1-δ) and extinction coefficient β as coordinate axes, within the region connecting the coordinates (1-δ, β) of a specific point.

[0005] Patent Document 2 discloses a reflective shielding substrate, which has multiple layers of reflective film, protective film, and phase-shifting film that causes phase shift of EUV light on a substrate. The reflective shielding substrate is characterized in that the phase-shifting film is made of an alloy of two or more metals, so that the reflectivity of the phase-shifting film surface is greater than 3% but less than 20%, and has a specific phase difference of 170 degrees to 190 degrees. Group A is defined as the group of metal elements with a refractive index n and extinction coefficient k satisfying k > α*n + β, and group B is defined as the group of metal elements with a refractive index n and extinction coefficient k satisfying k < α*n + β. The alloy system selects one or more metal elements from groups A and B respectively, and adjusts the composition ratio so that when the film thickness of the phase-shifting film changes by ±0.5% relative to a set film thickness, the change in phase difference is within the range of ±2 degrees, and the change in reflectivity is within the range of ±0.2%. (Where α: proportionality constant, β: constant.)

[0006] Patent Document 1: Japanese Patent Application Publication No. 2006-228766; Patent Document 2: Japanese Patent Application Publication No. 2018-146945 [Summary of the Invention]

[0007] If the pattern becomes finer and the accuracy of the pattern size or position is improved, the electrical characteristics and performance of the semiconductor device will be enhanced, and the density can be increased while the wafer size can be reduced. Therefore, EUV lithography has been required to have significantly improved high-precision and fine-size pattern transfer performance compared to the past. Currently, it is required to be able to form ultra-fine and high-precision patterns corresponding to the hp16nm (half-pitch 16nm) generation. In response to these requirements, it has been required to use a reflective mask that uses EUV light as the exposure light and further utilizes a phase-shifting effect.

[0008] A reflective mask employing the aforementioned phase-shifting effect has been designed to have multiple reflective films disposed on the main surface of the substrate at the center wavelength (i.e., 13.5 nm) of EUV light, and to allow the pattern-forming thin film (e.g., an absorber film) disposed on the multiple reflective films to have a phase-shifting effect. Reflective masks have been required to further enhance their exposure transfer characteristics. In particular, in the case of reflective masks (which are thin films having a transfer pattern (e.g., an absorber pattern) that utilizes a phase-shifting effect), it has been required to further enhance the optical properties of the thin film.

[0009] Therefore, the object of the present invention is to provide a mask substrate that can produce a reflective mask with excellent transfer characteristics when exposed to EUV exposure.

[0010] Furthermore, the object of the present invention is to provide a reflective mask that can achieve excellent transfer characteristics when exposure transfer is performed using an EUV exposure apparatus, and to provide a method for manufacturing a semiconductor device using the reflective mask.

[0011] To solve the above-mentioned problems, the present invention has the following structure.

[0012] (Composition 1) A masking substrate, wherein multiple layers of reflective film and pattern forming film are sequentially disposed on the main surface of a substrate; the film is made of a metal-containing material; the refractive index of the film relative to light with wavelength λL=13.2nm is nL; the refractive index of the film relative to light with wavelength λM=13.5nm is nM; the refractive index of the film relative to light with wavelength λH=13.8nm is nH; when the coefficient P=[(1-nH) / λH-(1-nL) / λL)] / [(1-nM) / λM]; the absolute value of the coefficient P will be 0.09 or less.

[0013] (Construction 2) The shielding substrate as in Construction 1, wherein the refractive index nM of the thin film relative to light with wavelength λM is 0.96 or less.

[0014] (Construction 3) As in Construction 1 or 2, wherein the thickness of the thin film is less than 100 nm.

[0015] (Construction 4) Any of the shielding substrates in Construction 1 to 3, wherein a protective film is provided between the multilayer reflective film and the thin film.

[0016] (Construction 5) As in any of the shielding substrates 1 to 4, wherein the thin film, relative to light of wavelength λM, causes a phase difference of 130 to 230 degrees between the reflected light from the thin film and the reflected light from the multilayer reflective film.

[0017] (Structure 6) A reflective shield, wherein multiple reflective films and thin films with transfer patterns are sequentially disposed on the main surface of a substrate; the thin films are made of a metallic material; the refractive index of the thin film relative to light with wavelength λL=13.2nm is nL; the refractive index of the thin film relative to light with wavelength λM=13.5nm is nM; the refractive index of the thin film relative to light with wavelength λH=13.8nm is nH; when the coefficient P=[(1-nH) / λH-(1-nL) / λL)] / [(1-nM) / λM]; the absolute value of the coefficient P will be 0.09 or less.

[0018] (Structure 7) The reflective shield as in Structure 6, wherein the refractive index nM of the thin film relative to light with wavelength λM is 0.96 or less.

[0019] (Construction 8) A reflective mask as in Construction 6 or 7, wherein the thickness of the thin film is less than 100 nm.

[0020] (Construction 9) As in any of the reflective shields in Construction 6 to 8, a protective film is provided between the multilayer reflective film and the thin film.

[0021] (Configuration 10) As in any of configurations 6 to 9, the thin film, relative to light of wavelength λM, causes a phase difference of 130 to 230 degrees between the reflected light from the thin film and the reflected light from the multilayer reflective film.

[0022] (Construction 11) A method for manufacturing a semiconductor device, comprising a step of using any of the reflective masks as described in Constructions 6 to 10 to expose and transfer a transfer pattern onto a resist film on a semiconductor substrate.

[0023] According to the present invention, a mask substrate is provided that can produce a reflective mask that can achieve excellent transfer characteristics when exposed and transferred using an EUV exposure device.

[0024] Furthermore, according to the present invention, a reflective mask that can be manufactured to achieve excellent transfer characteristics when exposed to EUV exposure equipment is provided, and a method for manufacturing the reflective mask thereon is also provided, and a method for manufacturing a semiconductor device using the reflective mask is also provided.

Implementation Method

[0026] Hereinafter, embodiments of the present invention will be described, starting with the process by which the present invention was completed. The inventors of this case have painstakingly examined a method that can achieve excellent transfer characteristics when performing exposure transfer using an EUV exposure apparatus. The inventors of this case believe that if the wavelength band other than the center wavelength of EUV light is also considered in the selection of the material of the absorber film constituting the pattern forming film, the optical characteristics of the absorber pattern of the reflective mask can be improved. In this regard, FIG3 will be used for explanation. FIG3 is a graph showing the relationship between reflectivity and wavelength on the multilayer reflective film in the reflective mask substrate of the embodiment of the present invention when EUV light is used as the exposure light. As can be seen from the same figure, in the EUV exposure apparatus, the EUV light incident on the multilayer reflective film not only has a center wavelength (i.e., 13.5 nm), but also has a certain degree of amplitude in the wavelength band near it. As shown in the figure, although the multilayer reflective film has a high reflectivity of over 70% at the center wavelength (i.e., 13.5 nm), it also has a non-negligible reflectivity in the surrounding wavelength bands. For example, it has a reflectivity of over 10% in the wavelength band of 13.0 nm to 14.0 nm, and over 30% in the wavelength band of 13.2 nm to 13.8 nm.

[0027] The refractive index n of the film material will change depending on the wavelength of the exposed light. On the other hand, in a reflective mask, the phase difference φ between the EUV light reflected from the multilayer reflective film and the EUV light reflected from the absorber film can be calculated by the following formula (1), which uses the wavelength λ of the light, the refractive index n at that wavelength λ, and the film thickness d (since it is a reflective type, the light path difference will become 2d). The phase difference φ with respect to vacuum (n=1): 2π(1-n)×2d / λ=4π(1-n)d / λ… Formula (1) It is speculated that if the phase difference φ is closer to the same value at each wavelength of EUV light with wavelength bands (the smaller the variation Δφ of the phase difference φ at each wavelength of EUV light with wavelength bands), the phase shift effect will be higher.

[0028] In the above equation (1), the film thickness d is limited from the perspective of optical properties. Therefore, we focus on the part of 4π(1-n) / λ in the above equation (1) other than the film thickness d. After painstaking research, the following conclusions were reached: If the refractive indices of the thin film relative to wavelengths λL=13.2nm, λM=13.5nm, and λH=13.8nm are taken as nL, nM, and nH, respectively, and if the film satisfies the condition |P|≦0.09 when the coefficients AL=4π×(1-nL) / λL, AM=4π×(1-nM) / λM, AH=4π×(1-nH) / λH, and the coefficient P=(AH-AL) / AM, then when using an EUV exposure device for exposure transfer, the variation Δφ (=φH-φL; hereinafter, it may also be simply referred to as "phase difference Δφ") of the phase difference φL~φH in the EUV light wavelength band λL=13.2nm~λH=13.8nm can be suppressed to below 20 degrees, thereby achieving excellent transfer characteristics. Here, the coefficient P can be expanded as follows. The coefficient P = (AH - AL) / AM = [(1 - nH) / λH - (1 - nL) / λL)] / [(1 - nM) / λM]

[0029] This invention is the result of the aforementioned painstaking research. Furthermore, the method for deriving the coefficient P described above is not limited to the scope of this invention (coefficients AL, AM, and AH are not essential elements of this invention). This embodiment is designed so that the phase difference φM at the center wavelength λM of EUV light is approximately 1.2π (approximately 216 degrees). This is because, due to double diffraction caused by reflective optical systems, or the influence of absorber patterns and multilayer films, the effective reflective surface is located closer to the substrate side than the interface between the absorber film and the multilayer reflective film. However, this invention is not limited to this and can also be applied to, for example, patterned thin films designed to have a phase difference φM of π (180 degrees) at the center wavelength λM of EUV light. If the phase difference φM is made to be π (180 degrees), then in the wavelength band of EUV light (λL~λH), by making the absolute value of the coefficient P less than 0.09, the magnitude of the phase difference Δφ (=φH-φL) can be suppressed to less than 17 degrees.

[0030] Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. Furthermore, the following embodiments are merely embellishments of the present invention and are not intended to limit the scope of the invention. Additionally, in the drawings, the same or equivalent parts may be given the same reference numerals, and their descriptions may be simplified or omitted.

[0031] <Structure and Manufacturing Method of Reflective Mask Substrate 100> Figure 1 is a schematic cross-sectional view of the main parts of the structure of the reflective mask substrate 100 of this embodiment. As shown in Figure 1, the reflective mask substrate 100 has a structure in which a substrate 1, a multilayer reflective film 2, a protective film 3, and an absorber film 4 are sequentially laminated. The multilayer reflective film 2 is formed on the first main surface (outer surface) side and reflects exposure light, i.e., EUV light, with high reflectivity. The protective film 3 is provided to protect the multilayer reflective film 2 and is formed of a material that is resistant to the etchant and cleaning solution used when patterning the absorber film 4 (described later). The absorber film 4 not only absorbs EUV light but also has a phase-shifting function. Furthermore, a conductive film for electrostatic clamping (not shown in the figure) is formed on the second main surface (inner surface) side of the substrate 1. In addition, an etch mask film may also be formed on the absorber film 4.

[0032] In this specification, "having a multilayer reflective film 2 on the main surface of substrate 1" refers not only to the case where the multilayer reflective film 2 is disposed in contact with the surface of substrate 1, but also to the case where there are other films between substrate 1 and multilayer reflective film 2. The same applies to other films. For example, "having film B on film A" refers not only to the case where film A and film B are disposed in direct contact, but also to the case where there are other films between film A and film B. Furthermore, in this specification, for example, "film A is disposed in contact with the surface of film B" means that no other film is provided between film A and film B, and film A and film B are disposed in direct contact.

[0033] The following describes this implementation for each layer.

[0034] <<Substrate 1>> In order to prevent the absorber pattern (transfer pattern) 4a (see Figure 2) from deforming due to the heat during EUV light exposure, it is preferable to use a material with a low coefficient of thermal expansion in the range of 0±5 ppb / ℃. Materials with this low coefficient of thermal expansion can be used, such as SiO2-TiO2 glass or multi-component glass ceramics.

[0035] The first main surface of the substrate 1 on the side where the transfer pattern (the absorber pattern 4a described later corresponds to this) is processed to have high flatness from the viewpoint of obtaining at least pattern transfer accuracy and positional accuracy. During EUV exposure, the flatness of the main surface (first main surface) on the side of the substrate 1 where the transfer pattern is formed 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. Furthermore, the second main surface, which is the opposite side to the side where the transfer pattern is formed, is the surface that will be electrostatically clamped when mounted on the exposure apparatus; its flatness in a 132 mm × 132 mm area is preferably 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.03 μm or less. Furthermore, the flatness of the second main surface side of the reflective mask substrate 100 in the 142mm×142mm region is preferably less than 1μm, more preferably less than 0.5μm, and especially preferably less than 0.3μm.

[0036] Furthermore, the surface smoothness of substrate 1 is also an extremely important factor. The surface roughness of the first main surface of substrate 1, in terms of root mean square roughness (RMS), is preferably below 0.1 nm. In addition, surface smoothness can be measured using an atomic force microscope.

[0037] Furthermore, in order to suppress the deformation of the substrate 1 caused by the film stress of the film (multilayer reflective film 2, etc.) formed thereon, it is preferable to have high rigidity. In particular, the substrate 1 is preferably high Young's coefficient of 65 GPa or higher.

[0038] <<Multilayer reflective film 2>> The multilayer reflective film 2 is a film that enables EUV light to be reflected in the reflective shield 200, and is a multilayer film with layers of elements with different refractive indices as the main components, which are periodically stacked.

[0039] Generally, the multilayer reflective film 2 is constructed by alternating layers of thin films (high refractive index layers) of light elements or their compounds that are high refractive index materials and thin films (low refractive index layers) of heavy elements or their compounds that are low refractive index materials, with approximately 40 to 60 cycles of such layers. The multilayer film can be constructed by sequentially depositing high refractive index layers and low refractive index layers on the substrate 1 side, with one cycle and multiple cycles thereof. Alternatively, the multilayer film can be constructed by sequentially depositing low refractive index layers and high refractive index layers on the substrate 1 side, with one cycle and multiple cycles thereof. Furthermore, the outermost layer of the multilayer reflective film 2, i.e., the surface layer of the multilayer reflective film 2 opposite to the substrate 1, is preferably a high refractive index layer. In the aforementioned multilayer film, if a high-refractive-index layer / low-refractive-index layer is sequentially deposited from substrate 1 as one cycle and multiple cycles are performed, then the uppermost layer will become a low-refractive-index layer. In this case, if the low-refractive-index layer forms the outermost surface of the multilayer reflective film 2, it will be easily oxidized, resulting in a reduction in the reflectivity of the reflective shield 200. Therefore, it is preferable to 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 aforementioned multilayer film, if a low-refractive-index layer / high-refractive-index layer is sequentially deposited from substrate 1 as one cycle and multiple cycles are performed, since the uppermost layer will become a high-refractive-index layer, this can be maintained.

[0040] In this embodiment, a silicon (Si) layer is used as the high refractive index layer. Besides Si monomers, Si compounds containing boron (B), carbon (C), nitrogen (N), and oxygen (O) can be used as the Si-containing material. By using a Si-containing layer as the high refractive index layer, an EUV lithography reflective mask 200 with excellent EUV light reflectivity can be obtained. Furthermore, in this embodiment, a glass substrate is preferably used as the substrate 1. Si also exhibits excellent adhesion to the glass substrate. A metal monomer selected from molybdenum (Mo), ruthenium (Ru), rhodium (Rh), and platinum (Pt), or an alloy thereof, is used as the low refractive index layer. As the multilayer reflective film 2 for EUV light with wavelengths of, for example, 13 nm to 14 nm, a Mo / Si periodic laminate film with approximately 40 to 60 alternating periods of Mo and Si films is preferably used. Alternatively, silicon (Si) can be used to form the uppermost high refractive index layer of the multilayer reflective film 2.

[0041] The reflectivity of the multilayer reflective film 2 is typically 65% ​​or higher, with an upper limit of 73%. Furthermore, the thickness and period of each constituent layer of the multilayer reflective film 2 can be appropriately selected according to the exposure wavelength, ensuring that the Bragg reflection law is satisfied. Although the multilayer reflective film 2 contains multiple high-refractive-index layers and low-refractive-index layers, the thicknesses of the high-refractive-index layers and the low-refractive-index layers can also differ. Moreover, the thickness of the outermost Si layer of the multilayer reflective film 2 can be adjusted within a range that does not reduce reflectivity. The thickness of the outermost Si layer (high-refractive-index layer) can be in the range of 3 nm to 10 nm.

[0042] The method for forming the multilayer reflective film 2 is known in the art. For example, it can be formed by forming each layer of the multilayer reflective film 2 by ion beam sputtering. In the case of the above-mentioned Mo / Si periodic laminated film, for example, by ion beam sputtering, a Si film with a thickness of about 4 nm is first formed on the substrate 1 using a Si target. Then, a Mo film with a thickness of about 3 nm is formed using a Mo target. Using this Si film / Mo film as 1 cycle, the multilayer reflective film 2 (the outermost layer is the Si layer) is formed by laminating for 40 to 60 cycles. In addition, for example, if the multilayer reflective film 2 is formed with 60 cycles, although the number of processes will increase compared to 40 cycles, the reflectivity relative to EUV light can be improved. Furthermore, during the formation of the multilayer reflective film 2, it is preferable to supply krypton (Kr) ion particles from an ion source and perform ion beam sputtering to form the multilayer reflective film 2.

[0043] <<Protective film 3>> In this embodiment, the reflective shielding substrate 100 preferably has a protective film 3 between the multilayer reflective film 2 and the absorber film 4.

[0044] In order to protect the multilayer reflective film 2 from the dry etching and cleaning processes in the manufacturing process of the reflective mask 200 described later, a protective film 3 may be formed on or adjacent to the surface of the multilayer reflective film 2. The protective film 3 is formed of a material that is resistant to the etchant and cleaning solution used when patterning the absorber film 4. By forming the protective film 3 on the multilayer reflective film 2, damage to the surface of the multilayer reflective film 2 can be suppressed when manufacturing the reflective mask 200 (EUV mask) using the substrate 1 having the multilayer reflective film 2 and the protective film 3. As a result, the reflectivity characteristics of the multilayer reflective film 2 relative to EUV light become good.

[0045] When the absorber film 4 adhering to the surface of the protective film 3 is a thin film made of a material containing ruthenium (Ru) (Ru-based material), the material of the protective film 3 can be selected from silicon (Si), materials containing silicon (Si) and oxygen (O), materials containing silicon (Si) and nitrogen (N), and materials containing silicon (Si), oxygen (O), and nitrogen (N), etc., which are silicon-based materials. On the other hand, when the absorber film 4 adhering to the surface of the protective film 3 is a thin film made of tantalum-based or chromium-based material, the protective film 3 preferably contains ruthenium. The material of the protective film 3 can be a Ru metal monomer, or a Ru alloy in which Ru contains 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 the presence of nitrogen is also acceptable.

[0046] In EUV lithography, since there are relatively few transparent materials relative to the exposed light, it is technically difficult to prevent foreign matter from adhering to the mask pattern surface using an EUV protective film. Therefore, the use of a film-free mask without a protective film has become the mainstream. Furthermore, in EUV lithography, carbon film deposition or so-called oxide film growth, or exposure contamination, can occur on the reflective mask due to EUV exposure. Therefore, when using the reflective mask 200 for EUV exposure in the semiconductor device manufacturing stage, it must be cleaned each time to remove foreign matter or contamination from the mask. Therefore, the reflective mask 200 for EUV exposure is required to have a mask cleaning tolerance that is several orders of magnitude higher than that of the transparent mask used in photolithography. By having a protective film 3 in the reflective mask 200, the cleaning tolerance to cleaning solutions can be improved.

[0047] The thickness of the protective film 3 is not particularly limited as long as it can achieve the function of protecting the multilayer reflective film 2. From the viewpoint of EUV light reflectivity, the thickness of the protective film 3 is preferably 1.0 nm to 8.0 nm, and more preferably 1.5 nm to 6.0 nm.

[0048] The method for forming the protective film 3 is not particularly limited, and can be the same as a known film forming method. Specific examples include sputtering and ion beam sputtering.

[0049] <<Absorber Film>> In this embodiment, the reflective mask substrate 100 has an absorber film (pattern forming film) 4 formed on the multilayer reflective film 2 or on the protective film 3 formed on the multilayer reflective film 2. In the reflective mask 200 state, the absorber film 4 has an absorber pattern 4a formed, which constitutes a transfer pattern. Under EUV exposure light (center wavelength (i.e., 13.5 nm)), the relative reflectance R of the absorber film 4 relative to the reflectance of the multilayer reflective film 2 is preferably 1% or more, more preferably 2% or more. Furthermore, this relative reflectance R is preferably 40% or less. This is to ensure sufficient contrast during mask inspection relative to EUV exposure light, and to ensure sufficient contrast during the pattern image during exposure transfer.

[0050] In the reflective mask 200 described later in this embodiment, the portion where the absorber film 4 (absorber pattern 4a) is provided reflects some light to a degree that absorbs EUV light, weakens the light, and does not adversely affect the pattern transfer. On the other hand, at the opening (the portion without the absorber film 4), EUV light is reflected from the multilayer reflective film 2 (or, if there is a protective film 3, from the multilayer reflective film 2 through the protective film 3). The reflected light from the portion where the absorber film 4 is formed forms a desired phase difference with the reflected light from the opening. The absorber film 4 is formed such that, relative to the wavelength λM (=13.5nm), the phase difference between the reflected light from the absorber film 4 and the reflected light from the multilayer reflective film 2 is 130 to 230 degrees. Light with a phase difference reversal of about 180 degrees or 220 degrees interferes with each other at the edge of the pattern, thereby improving the image contrast of the projected optical image. Resolution increases with image contrast, which in turn expands exposure margins and focus margins, among other exposure-related margins.

[0051] The absorber membrane 4 is composed of a material containing a metallic element. This metallic element can be a broad category of metallic elements, selected from alkali metals, alkaline earth metals, transition metals, or metalloids. The absorber membrane 4 can be selected from the aforementioned broad category of metallic elements as long as it exhibits etching selectivity with the multilayer reflective film 2 (or etching selectivity with the protective film 3 if one is formed). For example, chromium (Cr), vanadium (V), palladium (Pd), titanium (Ti), iridium (Ir), rhodium (Rh), tantalum (Ta), niobium (Nb), molybdenum (Mo), ruthenium (Ru), tin (Sn), platinum (Pt), and other metallic elements contained in the absorber membrane 4 can be used. Furthermore, the absorber membrane 4 can contain at least one of oxygen, nitrogen, carbon, and boron, without departing from the effects of the present invention.

[0052] The refractive index of the absorber film 4 relative to light with wavelength λL = 13.2 nm is nL, the refractive index relative to light with wavelength λM = 13.5 nm is nM, and the refractive index relative to light with wavelength λH = 13.8 nm is nH. When the coefficient P = [(1-nH) / λH-(1-nL) / λL)] / [(1-nM) / λM], the absolute value of the coefficient P will be 0.09 or less. Therefore, when performing exposure transfer using an EUV exposure device, the phase difference Δφ (=φH-φL) in the EUV light wavelength band λL~λH can be suppressed to less than 20 degrees. Furthermore, if the absolute value of the coefficient P of the absorber film 4 in the EUV light wavelength band λL = 13.2 nm~λH = 13.8 nm is 0.085 or less, the phase difference Δφ can be suppressed to within 18 degrees, which is preferable. Then, if the absolute value of the coefficient P of the absorber film 4 in the EUV light wavelength band λL=13.2nm~λH=13.8nm becomes less than 0.07, the phase difference Δφ can be suppressed to within 15 degrees, which is even better. Furthermore, if the absolute value of the coefficient P of the absorber film 4 in the EUV light wavelength band λL=13.2nm~λH=13.8nm becomes less than 0.045, the phase difference Δφ can be suppressed to within 10 degrees, which is even better. The absorber film 4 has a refractive index of nL relative to light with wavelength λL = 13.0 nm, a refractive index of nM relative to light with wavelength λM = 13.5 nm, and a refractive index of nH relative to light with wavelength λH = 14.0 nm. When the coefficient P = [(1-nH) / λH-(1-nL) / λL)] / [(1-nM) / λM], the absolute value of the coefficient P will be 0.15 or less. Therefore, when performing exposure transfer using an EUV exposure device, the phase difference Δφ (=φH-φL) in the EUV light wavelength band λL~λH can be suppressed to less than 35 degrees. Furthermore, if the absolute value of the coefficient P of the absorber film 4 in the EUV light wavelength band λL = 13.0 nm~λH = 14.0 nm is less than 0.14, the phase difference Δφ can be suppressed to within 30 degrees, which is preferable. Then, if the absolute value of the coefficient P of the absorber film 4 is less than 0.11 in the EUV light wavelength band λL=13.0nm~λH=14.0nm, the phase difference Δφ can be suppressed to within 25 degrees, which is even better. Furthermore, if the absolute value of the coefficient P of the absorber film 4 is less than 0.09 in the EUV light wavelength band λL=13.0nm~λH=14.0nm, the phase difference Δφ can be suppressed to within 20 degrees, which is even better.

[0053] As for the material of the absorber membrane 4, there are no particular limitations as described above, but tantalum-based materials or chromium-based materials are preferred. As for tantalum-based materials, in addition to tantalum metal, materials in which tantalum (Ta) contains one or more elements selected from nitrogen (N), oxygen (O), boron (B), and carbon (C) are preferred. Among these, materials containing at least one element selected from tantalum (Ta), oxygen (O), and boron (B) are particularly preferred. Furthermore, when the absorber membrane 4 is formed using a chromium-containing material, in addition to chromium metal, materials in which chromium (Cr) contains one or more elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and fluorine (F) are preferred. Materials containing chromium (Cr) nitrides are especially preferred.

[0054] Furthermore, the refractive index nM of the absorber film 4 relative to light with wavelength λM (=13.5nm) is preferably 0.960 or less, more preferably 0.955 or less. Also, the refractive index nM of the absorber film 4 is preferably 0.850 or more, more preferably 0.870 or more. The extinction coefficient kM of the absorber film 4 relative to light with wavelength λM is preferably 0.10 or less, more preferably 0.08 or less, and even more preferably 0.05 or less. Based on the results of optical simulations, it is speculated that the intensity of the light reflected from the multilayer reflective film 2 is stronger than the light reflected from the absorber film 4 relative to light with wavelength 13.5nm, and the reflected light from the absorber film 4 decreases as the extinction coefficient kM of the absorber film 4 increases. It is speculated that this is because by making the extinction coefficient kM within the above range, the decrease in reflected light from the absorber film 4 can be suppressed, which is therefore preferable.

[0055] Although it varies depending on the pattern or exposure conditions, in order to obtain the phase-shifting effect, the absolute reflectance of the transfer pattern (absorber pattern 4a) relative to EUV light (center wavelength (i.e. 13.5nm)) is preferably 1% to 30%, and more preferably 2% to 25%.

[0056] The phase difference and reflectivity of the absorber film 4 can be adjusted by changing the refractive index nL, nM, nH, extinction coefficient kL, kM, kH, and film thickness d in the EUV exposure light. The film thickness of the absorber film 4 is preferably less than 100 nm, more preferably less than 98 nm, and even more preferably less than 90 nm. The film thickness of the absorber film 4 is preferably 30 nm or more. Furthermore, when a protective film 3 is present, the phase difference and reflectivity of the absorber film 4 can also be adjusted by considering the refractive index n, extinction coefficient k, and film thickness of the protective film 3.

[0057] The absorber film 4 of the aforementioned specific material can be formed by known methods such as DC sputtering, RF sputtering, and reactive sputtering using oxygen. The target material may contain one metal. When the absorber film 4 is composed of two or more metals, an alloy target containing two or more metals (e.g., Ru and Cr) can be used. Furthermore, when the absorber film 4 is composed of two or more metals, the thin film constituting the absorber film 4 can be formed by co-sputtering, for example, using a Ru target and a Cr target. In addition, the absorber film 4 may also be a multilayer film containing two or more layers. In this case, it is preferable that all layers of the absorber film 4 satisfy the condition that the absolute value of the coefficient P is 0.09 or less.

[0058] <<Etching Mask Film>> An etching mask film (not shown in the figure) may be formed on or adjacent to the surface of the absorber film 4. The material used for the etching mask film is one that provides a higher etch selectivity ratio to the absorber film 4 relative to the etching mask film. Here, "etch selectivity ratio of B relative to A" refers to the ratio of the etching rate of the layer that does not require etching (the mask layer) (i.e., A) to the etching rate of the layer that requires etching (i.e., B). Specifically, it is defined by the formula "etch selectivity ratio of B relative to A = etching rate of B / etching rate of A". Furthermore, "higher selectivity" means that the selectivity ratio defined above is a larger value relative to the comparison object. The etch selectivity ratio of the absorber film 4 relative to the etching mask film is preferably 1.5 or higher, and more preferably 3 or higher.

[0059] From the viewpoint that the thickness of the etching mask film is preferably 2 nm or more to achieve the function of an etching mask by accurately forming a transfer pattern on the absorber film 4. Furthermore, from the viewpoint that the thickness of the etching mask film is to make the resist film thinner, it is preferably 15 nm or less.

[0060] <<Conductive Film>> A conductive film for electrostatic clamping (not shown in the figure) is generally formed on the second main surface (inner surface) side of substrate 1 (opposite to the surface where the multilayer reflective film 2 is formed). The required electrical characteristics (sheet resistance) of the conductive film for electrostatic clamping are typically 100Ω / □ (Ω / Square) or less. The conductive film can be formed by, for example, magnetron sputtering or ion beam sputtering, using a target material of metals and alloys such as chromium (Cr) and tantalum (Ta).

[0061] The chromium (Cr) material of the conductive film is preferably Cr-containing and further contains a Cr compound selected from at least one of boron (B), nitrogen (N), oxygen (O) and carbon (C).

[0062] As a tantalum (Ta)-containing material for conductive films, it is preferable to use Ta (tantalum), alloys containing Ta, or Ta compounds containing at least one of boron, nitrogen, oxygen and carbon in any of these.

[0063] The thickness of the conductive film is not particularly limited as long as it satisfies the function of being used as an electrostatic clamp. The thickness of the conductive film is typically 10 nm to 200 nm. Furthermore, the conductive film also serves as a stress adjustment function on the second main surface side of the mask substrate 100. That is, the conductive film is adjusted to balance the stress from the various films formed on the first main surface side, thereby obtaining a flat reflective mask substrate 100.

[0064] <Reflective Mask 200 and its Manufacturing Method> The reflective mask 200 of this embodiment has a transfer pattern (absorber pattern 4a) formed on the absorber film 4 of the reflective mask substrate 100. The absorber film 4 (absorber pattern 4a) with the transfer pattern is the same as the absorber film 4 of the reflective mask substrate 100 of this embodiment. The transfer pattern (absorber pattern 4a) can be formed by patterning the absorber film 4 of the reflective mask substrate 100 of this embodiment. The patterning of the absorber film 4 can be performed by a specific dry etching gas. The absorber pattern 4a of the reflective mask 200 can absorb EUV light and cause a portion of the EUV light to be reflected at the opening (the portion where the absorber pattern 4a is not formed) with a specific phase difference. The specific dry etching gas can be a mixture of chlorine-based gases and oxygen, oxygen, or fluorine-based gases, etc. To pattern the absorber pattern 4a, an etch mask film can be provided on the absorber pattern 4a as needed. In this case, the etch mask pattern can be used as a mask to dry etch the absorber film 4a to form the absorber pattern 4a.

[0065] A method for manufacturing a reflective mask 200 using the reflective mask substrate 100 of this embodiment will be described.

[0066] Prepare a reflective mask substrate 100 and form a resist film on the absorber film 4 on its first main surface (this is not necessary if the reflective mask substrate 100 already has a resist film). Draw (expose) the desired transfer pattern on the resist film, and further develop and wash to form a specific resist pattern (a resist film with a transfer pattern).

[0067] Next, the absorber film 4 is etched using the resist pattern as a mask to form an absorber pattern 4a (an absorber film 4 with a transfer pattern). After forming the absorber pattern 4a, the remaining resist pattern is removed (when an etch mask film is formed, the etch mask film is etched using the resist pattern as a mask to form an etch mask pattern, and the absorber pattern 4a is formed using this etch mask pattern to remove the etch mask pattern). Finally, a wet cleaning is performed using an acidic or alkaline aqueous solution to manufacture the reflective mask 200 of this embodiment.

[0068] <Method for Manufacturing a Semiconductor Device> This embodiment is a method for manufacturing a semiconductor device, which includes a step of exposing and transferring a transfer pattern onto a resist film on a semiconductor substrate using the aforementioned reflective mask 200 or a reflective mask 200 manufactured by the aforementioned method for manufacturing a reflective mask 200. By mounting the reflective mask 200 of this embodiment onto an exposure apparatus with an exposure light source having EUV light, and transferring the transfer pattern onto the resist film formed on the substrate to be transferred, a semiconductor device can be manufactured. Thus, a semiconductor device with a fine and high-precision transfer pattern can be manufactured.

[0069] [Examples and Comparative Examples] Examples 1-16 and Comparative Examples 1 and 2 Hereinafter, Examples 1-16 and Comparative Examples 1 and 2 will be described with reference to the drawings. This embodiment is not limited to these examples. Furthermore, in the examples, the same reference numerals are used to simplify or omit the description of the same constituent elements.

[0070] As Examples 1 to 16 and Comparative Examples 1 and 2, the manufacturing method of the reflective mask substrate 100 will be described.

[0071] A low thermal expansion glass substrate (i.e., a SiO2-TiO2 glass substrate) with dimensions of 6025 (approximately 152mm × 152mm × 6.35mm) with the first and second main surfaces already ground is prepared as substrate 1. A grinding process consisting of rough grinding, precision grinding, localized grinding, and contact grinding is performed to make it a flat and smooth main surface.

[0072] Next, a conductive film consisting of a CrN film is formed on the second main surface (inner surface) of the SiO2-TiO2 glass substrate 1 by magnetron sputtering (reactive sputtering) under the following conditions. The conductive film is formed using a Cr target in a mixed gas atmosphere of argon (Ar) and nitrogen (N2) to achieve a film thickness of 20 nm.

[0073] Next, a multilayer reflective film 2 is formed on the main surface (first main surface) of the substrate 1, which is opposite to the side where the conductive film is formed. In order to make the multilayer reflective film 2 formed on the substrate 1 suitable for EUV light with a wavelength of 13.5 nm, it is made into a periodically laminated reflective film composed of molybdenum (Mo) and silicon (Si). The multilayer reflective film 2 is formed by using Mo and Si targets and by interleaving Mo and Si layers on the substrate 1 in a krypton atmosphere using ion beam sputtering. First, a Si film is formed with a thickness of 4.2 nm, then a Mo film is formed with a thickness of 2.8 nm. This is repeated for 40 cycles, and finally, a Si film is formed with a thickness of 4.0 nm to form the multilayer reflective film 2.

[0074] Next, in an Ar gas atmosphere, a protective film 3 with a thickness of 3.5 nm is formed on the surface of the multilayer reflective film 2 by sputtering. In addition, in the above Examples 1 to 16 and Comparative Examples 1 and 2, the material of the protective film 3 is appropriately selected to have etching resistance relative to the dry etching gas used when patterning the absorber film 4.

[0075] Next, in an Ar gas atmosphere, an absorber film 4 is formed on the surface of the protective film 3 by sputtering. In Examples 1-16 and Comparative Examples 1 and 2 above, the constituent elements of the absorber film 4 are shown in Tables 1-1 and 1-2 below, and sputtering targets suitable for each constituent element are appropriately selected. Furthermore, in Examples 1-16 and Comparative Examples 1 and 2 above, the absorber film 4 is designed such that the phase difference φM at the center wavelength λM of EUV light is 1.2π (216 degrees). Afterwards, specific cleaning processes are performed to manufacture the reflective shielding substrate 100 in Examples 1-16 and Comparative Examples 1 and 2.

[0076] Next, for the reflective mask substrate 100 in Examples 1 to 16 and Comparative Examples 1 and 2, as described in the method for manufacturing the reflective mask 200 above, the absorber film 4 is etched by forming a resist pattern and using the resist pattern as a mask to form an absorber pattern 4a (an absorber film 4 with a transfer pattern), and wet cleaning is performed using an acidic or alkaline aqueous solution to manufacture the reflective mask 200 in Examples 1 to 16 and Comparative Examples 1 and 2.

[0077] The constituent elements of the absorber film 4 in the reflective shield substrate 100 and reflective shield 200 in Examples 1-16 and Comparative Examples 1 and 2; the refractive index nM and extinction coefficient kM at the center wavelength λM (=13.5nm) of EUV light; and the coefficient AL = 4π×(1-nL) / at wavelengths λL=13.2nm, λM=13.5nm, and λH=13.8nm. λL, AM = 4π × (1 - nM) / λM, AH = 4π × (1 - nH) / λH; film thickness d; coefficient P = (AH - AL) / AM (= [(1 - nH) / λH - (1 - nL) / λL)] / [(1 - nM) / λM]) in the EUV light wavelength band λL = 13.2 nm ~ λH = 13.8 nm; and phase difference Δφ are shown in Tables 1-1 and 1-2.

[0078] [Table 1-1]

[0079] [Table 1-2]

[0080] As shown in Tables 1-1 and 1-2, the absorber films 4 shown in Examples 1 to 16 all have a film thickness of less than 100 nm. In the EUV light wavelength band λL=13.2 nm to λH=13.8 nm, the absolute value of the coefficient P is 0.09 or less, which can suppress the phase difference Δφ to within 20 degrees. Furthermore, in the EUV light wavelength band λL=13.2 nm to λH=13.8 nm, the absorber films 4 shown in Examples 1 to 11 and 16 have an absolute value of the coefficient P of 0.085 or less, which can suppress the phase difference Δφ to within 18 degrees. Then, in the EUV light wavelength band λL=13.2 nm to λH=13.8 nm, the absorber films 4 shown in Examples 1 to 6 and 16 have an absolute value of the coefficient P of 0.07 or less, which can suppress the phase difference Δφ to within 15 degrees. In addition, the absorber film 4 shown in Examples 1 to 3 has an absolute value of coefficient P of less than 0.045 in the wavelength band of EUV light λL=13.2nm~λH=13.8nm, which can suppress the phase difference Δφ to within 10 degrees.

[0081] On the other hand, in Comparative Example 1, in the EUV light wavelength band λL=13.2nm~λH=13.8nm, the phase difference Δφ of the absorber film 4 exceeds 22.49 and 20 degrees, respectively, and has a phase difference Δφ that cannot be ignored. Furthermore, in Comparative Example 2, the film thickness of the absorber film 4 is 183.31nm, significantly exceeding 100nm.

[0082] Furthermore, Tables 1-1 and 1-2 also show the coefficients AL=4π×(1-nL) / λL, AH=4π×(1-nH) / λH, coefficient P=(AH-AL) / AM, and phase difference Δφ in the EUV light wavelength band λL=13.0nm~λH=14.0nm. As shown in Tables 1-1 and 1-2, the absolute value of the coefficient P of the absorber film 4 shown in Examples 1-16 in the EUV light wavelength band λL=13.0nm~λH=14.0nm will be less than 0.15, and the phase difference Δφ can be suppressed to within 35 degrees. Then, the absolute value of the coefficient P of the absorber film 4 shown in Examples 1-12 and 16 in the EUV light wavelength band λL=13.0nm~λH=14.0nm will be less than 0.14, and the phase difference Δφ can be suppressed to within 30 degrees. Further, the absolute value of the coefficient P of the absorber film 4 shown in Examples 1-6 and 16 in the EUV light wavelength band λL=13.0nm~λH=14.0nm will be less than 0.11, and the phase difference Δφ can be suppressed to within 25 degrees. Further, the absolute value of the coefficient P of the absorber film 4 shown in Examples 1-5 and 16 in the EUV light wavelength band λL=13.0nm~λH=14.0nm will be less than 0.09, and the phase difference Δφ can be suppressed to within 20 degrees.

[0083] Furthermore, the constituent elements of the absorber film 4 in the reflective shield substrate 100 and reflective shield 200 in Examples 1-16 and Comparative Examples 1 and 2; the coefficients EL=4π×(1-kL) / λL, EM=4π×(1-kM) / λM, EH=4π×(1-kH) / λH at wavelengths λL=13.2nm, λM=13.5nm, and λH=13.8nm; and in The coefficient F = (EH-EL) / EM (=[(1-kH) / λH-(1-kL) / λL)] / [(1-kM) / λM]) in the wavelength band of EUV light λL=13.2nm~λH=13.8nm is shown in Tables 2-1 and 2-2 (kL, kM, and kH are the extinction coefficients at wavelengths λL=13.2nm, λM=13.5nm, and λH=13.8nm, respectively). Furthermore, Tables 2-1 and 2-2 also show the coefficients EL=4π×(1-kL) / λL, EM=4π×(1-kM) / λM, EH=4π×(1-kH) / λH in the wavelength band of EUV light λL=13.0nm~λH=14.0nm, and the coefficient F=(EH-EL) / EM(=[(1-kH) / λH-(1-kL) / λL)] / [(1-kM) / λM] in the wavelength band of EUV light λL=13.0nm~λH=14.0nm.

[0084] [Table 2-1]

[0085] [Table 2-2]

[0086] Regarding the extinction coefficient k, no significant differences were observed in Examples 1-16 and Comparative Examples 1 and 2.

[0087] The reflective mask 200 obtained by Examples 1 to 16 is installed in an EUV scanner to perform EUV exposure on a wafer on which a processing film and a resist film are formed on a semiconductor substrate, and the exposed resist film is developed so that the processing film forms a resist pattern on the semiconductor substrate.

[0088] The reflective mask 200 obtained by Examples 1 to 16 has an absorber pattern 4a with a phase difference φM of 1.2π at the center wavelength λM of EUV light and an absolute value of coefficient P of 0.09 or less in the EUV light wavelength band λL=13.2nm~λH=13.8nm. Therefore, when using EUV light as the exposure light, the phase difference Δφ can be suppressed to within 20 degrees in the EUV light wavelength band λL=13.2nm~λH=13.8nm, and the required fine pattern can be formed with high precision, thereby enabling the manufacture of a semiconductor device with a fine and high-precision transfer pattern.

[0089] Furthermore, the resist pattern can be transferred onto the processed film by etching, and a semiconductor device with the desired characteristics can be manufactured with high yield by various processes such as forming an insulating film and a conductive film, introducing dopants, or annealing.

[0090] The reflective mask 200 of Comparative Example 1 has an absorber pattern 4a in which the absolute value of the coefficient P is greater than 0.09 in the EUV light wavelength band λL=13.2nm~λH=13.8nm. As a result, when EUV light is used as the exposure light, it is impossible to suppress the phase difference Δφ within 22.49 degrees and 20 degrees in the EUV light wavelength band λL=13.2nm~λH=13.8nm, and the phase shift effect cannot be sufficiently obtained. Therefore, it is impossible to form the required fine pattern with good precision, and it is impossible to manufacture a semiconductor device with a fine and high-precision transfer pattern.

[0091] Furthermore, it is impossible to transfer the resist pattern onto the processed film by etching, and it is impossible to manufacture a semiconductor device with the desired characteristics with high yield by various processes such as forming an insulating film, a conductive film, introducing dopants, or annealing.

[0092] The reflective mask 200 of Comparative Example 2 is composed of SiO2 to form the absorber film 4, and does not contain any metal elements. As a result, the thickness of the absorber film 4 will greatly exceed 184.31 nm and 100 nm, and good transfer characteristics cannot be obtained, so it is impossible to manufacture a semiconductor device with fine and high-precision transfer patterns.

[0093] Furthermore, it is impossible to transfer the resist pattern onto the processed film by etching, and it is impossible to manufacture a semiconductor device with the desired characteristics with high yield by various processes such as forming an insulating film, a conductive film, introducing dopants, or annealing. [Simplified Explanation of the Diagram]

[0025] FIG1 is a schematic cross-sectional view of the main parts of a general configuration example of a reflective mask substrate according to an embodiment of the present invention. FIG2 is a schematic cross-sectional view of the main parts of a general configuration example from a reflective mask substrate to a reflective mask. FIG3 is a graph showing the relationship between reflectivity and wavelength on a multilayer reflective film in a reflective mask substrate according to an embodiment of the present invention when EUV light is used as the exposure light.

Claims

1. A masking substrate, wherein multiple layers of reflective films and pattern-forming thin films are sequentially disposed on the main surface of a substrate; the thin films are composed of a metallic material; the refractive index of the thin film relative to light with wavelength λL = 13.2 nm is nL; the refractive index of the thin film relative to light with wavelength λM = 13.5 nm is nM; the refractive index of the thin film relative to light with wavelength λH = 13.8 nm is nH; when the coefficient P = [(1-nH) / λH-(1-nL) / λL)] / [(1-nM) / λM]; the absolute value of the coefficient P is 0.09 or less.

2. The shielding substrate as claimed in claim 1, wherein the refractive index nM of the thin film relative to light with wavelength λM is 0.96 or less.

3. The masking substrate as described in claim 1, wherein the thickness of the thin film is less than 100 nm.

4. The shielding substrate of any one of claims 1 to 3 has a protective film between the multilayer reflective film and the thin film.

5. The masking substrate of any one of claims 1 to 3, wherein the thin film, relative to light of wavelength λM, causes a phase difference of 130 to 230 degrees between reflected light from the thin film and reflected light from the multilayer reflective film.

6. A reflective shield comprising, sequentially disposed on the main surface of a substrate, a multilayer reflective film and a thin film having a transfer pattern formed thereon; the thin film being composed of a metallic material; the refractive index of the thin film relative to light with wavelength λL = 13.2 nm being nL; the refractive index of the thin film relative to light with wavelength λM = 13.5 nm being nM; the refractive index of the thin film relative to light with wavelength λH = 13.8 nm being nH; when the coefficient P = [(1-nH) / λH-(1-nL) / λL)] / [(1-nM) / λM]; the absolute value of the coefficient P will be less than 0.

09.

7. The reflective shield as claimed in claim 6, wherein the refractive index nM of the thin film relative to light with wavelength λM is 0.96 or less.

8. As in claim 6, a reflective mask, wherein the thickness of the film is less than 100 nm.

9. A reflective shield as described in any of claims 6 to 8, wherein a protective film is provided between the multilayer reflective film and the thin film.

10. A reflective mask as claimed in any of claims 6 to 8, wherein the thin film, relative to light of wavelength λM, causes a phase difference of 130 to 230 degrees between reflected light from the thin film and reflected light from the multilayer reflective film.

11. A method for manufacturing a semiconductor device, comprising a step of using a reflective mask, such as any one of claims 6 to 10, to expose and transfer a transfer pattern onto a resist film on a semiconductor substrate.

Images