Reflective mask blank, reflective mask, and method for manufacturing a semiconductor device

Abstract

Provided is a reflective mask blank which makes it possible to form a transfer pattern having a fine pattern shape on a transfer target substrate, and which can be used for the manufacture of a reflective mask having a transfer pattern that enables high-throughput EUV exposure.　The reflective mask blank comprises a substrate, a multi-layer reflective film provided on the substrate, and an absorber film provided on the multi-layer reflective film, the reflective mask blank being characterized in that the absorber film contains iridium (Ir) and an additive element, the additive element comprises at least one element selected from boron (B), silicon (Si), phosphorus (P), titanium (Ti), germanium (Ge), arsenic (As), selenium (Se), niobium (Nb), molybdenum (Mo), ruthenium (Ru) and tantalum (Ta), and the content of the iridium (Ir) in the absorber film is more than 50 at.%.

Description

Technical Field

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

Background Art

[0002] The types of light sources of exposure apparatuses in semiconductor device manufacturing are g-line with a wavelength of 436 nm, i-line with a wavelength of 365 nm, KrF laser with a wavelength of 248 nm, and ArF laser with a wavelength of 193 nm, and the wavelength is gradually becoming shorter. In order to achieve more fine pattern transfer, EUV lithography using extreme ultraviolet light (EUV: Extreme Ultra Violet) with 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. The reflective mask has a multilayer reflective film for reflecting exposure light on a low thermal expansion substrate. The basic structure of the reflective mask is a structure in which a desired transfer pattern is formed on a protective film for protecting the multilayer reflective film. Further, as typical reflective masks, there are a binary type reflective mask and a phase shift type reflective mask (halftone phase shift type reflective mask). The transfer pattern of the binary type reflective mask is composed of a relatively thick absorber pattern that sufficiently absorbs EUV light. The transfer pattern of the phase shift type reflective mask is composed of a relatively thin absorber pattern that attenuates EUV light by light absorption and generates reflected light whose phase is almost inverted (phase inversion of about 180°) with respect to the reflected light from the multilayer reflective film. The phase shift type reflective mask (halftone phase shift type reflective mask) has an effect of improving resolution because a high transfer optical image contrast can be obtained by the phase shift effect, similar to a transmissive optical phase shift mask. Further, since the film thickness of the absorber pattern (phase shift pattern) of the phase shift type reflective mask is thin, a fine phase shift pattern can be formed with high accuracy.

[0003] In EUV lithography, a projection optical system consisting of multiple mirrors is used due to the relationship between light transmittance. EUV light is incident on the reflective mask at an oblique angle, so that these multiple mirrors do not obstruct the projected light (exposure light). Currently, the prevailing incident angle is 6° relative to the plane perpendicular to the reflective mask substrate. With improvements in the numerical aperture (NA) of the projection optical system, research is underway to move towards a more oblique incident angle of around 8°.

[0004] EUV lithography has an inherent problem called the shadowing effect because the exposure light is incident at an oblique angle. The shadowing effect is a phenomenon in which the dimensions and position of the transferred pattern change when the exposure light is incident at an oblique angle on an absorber pattern with a three-dimensional structure, creating a shadow. The three-dimensional structure of the absorber pattern acts as a wall, creating a shadow on the shaded side, which changes the dimensions and position of the transferred pattern. For example, if the orientation of the placed absorber pattern is parallel to the direction of the obliquely incident light, and if it is perpendicular to it, a difference will occur in the dimensions and position of the transferred pattern, reducing the transfer accuracy.

[0005] Such reflective masks for EUV lithography and technologies related to mask blanks for fabricating them are disclosed in Patent Documents 1 and 2. Patent Document 1 also describes providing a reflective mask that has a small shadowing effect, allows for phase-shift exposure, and has sufficient light-shielding frame performance. Conventionally, by using a phase-shift reflective mask as a reflective mask for EUV lithography, the film thickness of the phase-shift pattern can be made relatively thinner than in the case of a binary reflective mask. By making the film thickness of the phase-shift pattern relatively thin, it is possible to suppress the decrease in transfer accuracy due to the shadowing effect.

[0006] Patent Document 3 describes a mask for EUV lithography. Specifically, the mask described in Patent Document 3 comprises a substrate, a multilayer coating applied to the substrate, and a mask structure having an absorbent material applied to the multilayer coating. Patent Document 3 states that the mask structure has a maximum thickness of less than 100 nm.

[0007] Patent Document 4 describes a method for manufacturing an extreme ultraviolet (EUV) mask blank. Specifically, the method described in Patent Document 4 includes providing a substrate, forming a laminate of multiple reflective layers on the substrate, forming a capping layer on the laminate of multiple reflective layers, and forming an absorption layer on the capping layer. Patent Document 4 also describes that the absorption layer comprises an alloy of at least two different absorption materials.

[0008] Patent Document 5 describes a reflective mask blank comprising a substrate, a multilayer reflective film formed on the substrate that reflects exposure light, an absorber film formed on the multilayer reflective film that absorbs exposure light, and a buffer layer. Furthermore, Patent Document 5 describes that the buffer layer is disposed between the multilayer reflective film and the absorber film, and that its etching characteristics differ from those of the absorber film. Patent Document 5 also describes that the absorber film is made of a material mainly composed of tantalum (Ta), and further containing at least one element selected from tellurium (Te), antimony (Sb), platinum (Pt), iodine (I), bismuth (Bi), iridium (Ir), osmium (Os), tungsten (W), rhenium (Re), tin (Sn), indium (In), polonium (Po), iron (Fe), gold (Au), mercury (Hg), gallium (Ga), and aluminum (Al).

[0009] In addition, Patent Document 6 describes a reflective mask for lithography that is used to project the pattern onto an exposure target by reflecting soft X-rays or vacuum ultraviolet rays from a light source on which a pattern as an original plate is formed. The reflective mask for lithography of Patent Document 6 is configured such that the pattern is composed of an absorber pattern provided on a reflective portion that reflects the soft X-rays or vacuum ultraviolet rays. When the wavelength of the soft X-rays or vacuum ultraviolet rays is λ and the optical constants of the substance forming the absorber pattern are represented as 1 - δ - ik (δ and k are real numbers, and i is an imaginary unit), 0.29 < k / |δ| < 1.12 holds, and the thickness d of the absorber pattern satisfies 3λ / (16|δ|) < d < 5λ / (16|δ|).

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Disclosure of the Invention

[0011] In EUV lithography, a resist transfer pattern is transferred onto a resist layer formed on a substrate to be transferred (semiconductor substrate) using a transfer pattern formed on a reflective mask. A predetermined fine circuit is formed in a semiconductor device using the resist transfer pattern.

[0012] To improve the electrical characteristics and other performance of semiconductor devices, increase integration density, and reduce chip size, it is necessary to make transfer patterns finer, that is, to reduce the dimensions of the transfer patterns and improve the positional accuracy of the transfer patterns. Therefore, EUV lithography is required to have transfer performance that can transfer transfer patterns of a higher precision and finer dimensions than before. Currently, there is a demand for ultra-fine, high-precision transfer pattern formation compatible with the hp16nm (half pitch 16nm) generation. In response to these demands, the transfer patterns formed on reflective masks are also required to be further miniaturized. Furthermore, in order to reduce the shadowing effect during EUV exposure, the thin films constituting the transfer patterns on reflective masks are required to be even thinner. Specifically, the film thickness of the absorber film (phase shift film) of the reflective mask is required to be 50nm or less.

[0013] Furthermore, along with the miniaturization of the transfer patterns mentioned above, the pattern shapes of the transfer patterns are also becoming more diverse. Therefore, reflective masks require absorbent membranes that can form transfer patterns that can accommodate these diverse pattern shapes.

[0014] Furthermore, in order to manufacture semiconductor devices at low cost, it is necessary to be able to perform EUV lithography (EUV exposure) with high throughput.

[0015] As disclosed in Patent Documents 1 and 2, Ta has conventionally been used as a material for forming absorber films (phase-shift films) in reflective mask blanks. However, the refractive index (n) of Ta at EUV light (for example, wavelength 13.5 nm) is approximately 0.943. When utilizing the phase-shift effect of a Ta thin film, the thinning of the absorber film (phase-shift film) formed solely of Ta is limited to 60 nm. To achieve thinner films, for example, a metallic material with a high extinction coefficient (k) (high absorption effect) can be used as the absorber film in a binary-type reflective mask blank. For example, Patent Documents 3 and 4 describe platinum (Pt) and iridium (Ir) as metallic materials with a large extinction coefficient (k) at a wavelength of 13.5 nm.

[0016] Furthermore, if the absorber film has a phase shift effect, it is preferable to use a metallic material with a low refractive index (n) as the absorber film. By using a metallic material with a low refractive index (n), high transfer optical image contrast can be obtained due to the phase shift effect during exposure in EUV lithography.

[0017] Therefore, the present invention aims to provide a reflective mask blank for manufacturing a reflective mask having a transfer pattern that can form a fine pattern shape on a transfer substrate and that can perform EUV exposure at high throughput. Specifically, the aim is to provide a reflective mask blank having an absorber film with a small refractive index (n), a high extinction coefficient (k), and good processing characteristics.

[0018] Furthermore, the present invention aims to provide a reflective mask having a transfer pattern that can form a transfer pattern of a fine pattern shape on a transfer substrate and that can perform EUV exposure at high throughput. The present invention also aims to provide a method for manufacturing a semiconductor device that can form diverse fine pattern shapes on a transfer substrate at high throughput.

[0019] To solve the above problems, an embodiment of the present invention has the following configuration.

[0020] (Configuration 1) Configuration 1 of the present embodiment is a reflective mask blank including a substrate, a multilayer reflective film on the substrate, and an absorber film on the multilayer reflective film, where the absorber film contains iridium (Ir) and an additive element, the additive element is at least one selected from boron (B), silicon (Si), phosphorus (P), titanium (Ti), germanium (Ge), arsenic (As), selenium (Se), niobium (Nb), molybdenum (Mo), ruthenium (Ru), and tantalum (Ta), and the content of iridium (Ir) in the absorber film is more than 50 atomic %, which is a reflective mask blank characterized thereby.

[0021] (Configuration 2) Configuration 2 of the present embodiment is a reflective mask blank of Configuration 1, characterized in that the additive element contains tantalum (Ta).

[0022] (Configuration 3) Configuration 3 of the present embodiment is a reflective mask blank of Configuration 1 or 2, characterized in that the additive element contains tantalum (Ta), and the content of tantalum (Ta) in the absorber film is 2 to 30 atomic %.

[0023] (Configuration 4) Configuration 4 of the present embodiment is a reflective mask blank according to any one of Configurations 1 to 3, characterized in that the absorber film further contains oxygen (O), and the content of oxygen (O) is 5 atomic % or more.

[0024] (Configuration 5) Configuration 5 of the present embodiment is that the absorber film includes a buffer layer and an absorber layer provided on the buffer layer, the buffer layer contains chromium (Cr), The absorption layer is a reflective mask blank of any of configurations 1 to 4, characterized in that it contains iridium (Ir) and the additive element.

[0025] (Composition 6) Configuration 6 of this embodiment is a reflective mask blank of configuration 5, characterized in that the thickness of the absorber film is 50 nm or less, and the thickness of the buffer layer is 10 nm or less.

[0026] (Composition 7) Configuration 7 of this embodiment is a reflective mask characterized in that the absorbent film in any of the reflective mask blanks of configurations 1 to 6 has a patterned absorbent pattern.

[0027] (Composition 8) Configuration 8 of this embodiment is a method for manufacturing a reflective mask, characterized by patterning the absorbent film of any of the reflective mask blanks of configurations 1 to 6 to form an absorbent pattern.

[0028] (Composition 9) Configuration 9 of this embodiment is a method for manufacturing a semiconductor device, characterized by having the step of setting the reflective mask of configuration 7 in an exposure apparatus having an exposure light source that emits EUV light, and transferring a transfer pattern to a resist film formed on a substrate to be transferred.

[0029] According to embodiments of the present invention, a reflective mask blank can be provided for manufacturing a reflective mask having a transfer pattern that can form a transfer pattern with a fine pattern shape on a transfer substrate and that can be subjected to EUV exposure at high throughput. Specifically, according to embodiments of the present invention, a reflective mask blank can be provided having an absorber film with a low refractive index (n), a high extinction coefficient (k), and good processing characteristics.

[0030] Furthermore, according to embodiments of the present invention, it is possible to provide a reflective mask having a transfer pattern that can form a transfer pattern with a fine pattern shape on a substrate to be transferred, and that can perform EUV exposure at high throughput. Furthermore, according to embodiments of the present invention, it is possible to provide a method for manufacturing a semiconductor device that can form diverse fine pattern shapes on a substrate to be transferred at high throughput. [Brief explanation of the drawing]

[0031] [Figure 1] This is a schematic cross-sectional view of the main part illustrating the general configuration of the reflective mask blank of the present invention. [Figure 2] This is a schematic cross-sectional view of a key part illustrating the general configuration of another embodiment of the reflective mask blank of the present invention. [Figure 3A-D] Figures 3A to 3D are process diagrams showing the process of manufacturing a reflective mask from a reflective mask blank, with schematic cross-sectional views of the main parts. [Figure 4] This figure shows the values ​​of the normalized evaluation function obtained by simulation #1a, where the reflective mask has a vertical L / S (line and space) pattern of hp16nm and a RuNb film is used as the protective film (Cap film), and the distribution of the values ​​of the normalized evaluation function with respect to the refractive index (n) and extinction coefficient (k) of the absorber film. [Figure 5] This figure combines the distributions of the normalized evaluation function values ​​obtained from simulations, showing the distribution when all normalized evaluation function values ​​obtained from simulations #1a to #3a and #1b to #3b are 1.015 or greater (white) and when they are not (black). [Modes for carrying out the invention]

[0032] The embodiments of the present invention will be described in detail below with reference to the drawings. The following embodiments are merely examples of how the present invention can be implemented, and do not limit the present invention to their scope. In the drawings, identical or corresponding parts are denoted by the same reference numerals, and their descriptions may be simplified or omitted.

[0033] <Structure of reflective mask blank 100 and method for manufacturing the same> Figure 1 is a schematic cross-sectional view of the main parts illustrating the configuration of a reflective mask blank 100 according to an embodiment of the present invention. As shown in Figure 1, the reflective mask blank 100 of this embodiment comprises a substrate 1, a multilayer reflective film 2 on the substrate 1, and an absorber film 4 on the multilayer reflective film 2. In this specification, the surface of the substrate 1 on which the multilayer reflective film 2 is formed may be referred to as the first main surface (front surface). The absorber film 4 of the reflective mask blank 100 of this embodiment contains iridium (Ir) and a predetermined additive element. The reflective mask blank 100 of this embodiment may have a protective film 3 between the multilayer reflective film 2 and the absorber film 4. Furthermore, a back surface conductive film 5 for an electrostatic chuck may be formed on the second main surface (back surface) side of the substrate 1.

[0034] By using the reflective mask blank 100 of this embodiment, it is possible to form a transfer pattern with a fine pattern shape on the substrate to be transferred, and to manufacture a reflective mask 200 having a transfer pattern that enables high throughput EUV exposure. Specifically, it is possible to obtain a reflective mask blank 100 having an absorber film with a low refractive index (n), a high extinction coefficient (k), and good processing characteristics.

[0035] The reflective mask blank 100 includes a configuration in which the back surface conductive film 5 is not formed. Furthermore, the reflective mask blank 100 also includes a configuration of a mask blank with a resist film, in which a resist film 11 is formed on the etching mask film.

[0036] In this specification, for example, the phrase "multilayer reflective film 2 on substrate 1" means not only that the multilayer reflective film 2 is placed in contact with the surface of substrate 1, but also that there is another film between substrate 1 and the multilayer reflective film 2. The same applies to other films. Furthermore, in this specification, for example, "film A is placed in contact with film B" means that film A and film B are placed in direct contact with each other without any other film in between.

[0037] The following provides a detailed explanation of each component of the reflective mask blank 100.

[0038] <<Circuit Board 1>> To prevent distortion of the absorber pattern 4a due to heat during exposure with EUV light, the substrate 1 is preferably made of a material with a low thermal expansion coefficient in the range of 0 ± 5 ppb / °C. Examples of materials with a low thermal expansion coefficient in this range include SiO2-TiO2 glass and multi-component glass ceramics.

[0039] The first main surface of the substrate 1 on the side where the transfer pattern (corresponding to the absorber pattern 4a obtained by patterning the absorber film 4 described later) is formed is surface-processed to have high flatness, at least from the viewpoint of obtaining pattern transfer accuracy and positional accuracy. In the case of EUV exposure, the flatness of the 132 mm × 132 mm area of ​​the main surface of the substrate 1 on the side 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. The second main surface on the side opposite to the side where the absorber film 4 is formed is the surface that is electrostatically chucked when set in the exposure apparatus, and the flatness of the 142 mm × 142 mm area is preferably 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.03 μm or less.

[0040] Furthermore, the surface smoothness of the substrate 1 is also an extremely important factor. The surface roughness of the first main surface of the substrate 1 on which the transfer pattern (absorber pattern 4a) is formed is preferably 0.1 nm or less in terms of root mean square roughness (RMS). Surface smoothness can be measured using an atomic force microscope.

[0041] Furthermore, the substrate 1 is preferably made of high rigidity in order to prevent deformation due to film stress of the film (such as the multilayer reflective film 2) formed thereon. In particular, it is preferable that it has a high Young's modulus of 65 GPa or more.

[0042] <<Multilayer reflective film 2>> The multilayer reflective film 2 provides the reflective mask 200 with the function of reflecting EUV light. The multilayer reflective film 2 has a multilayer structure in which each layer, mainly composed of elements with different refractive indices, is periodically stacked.

[0043] Generally, a multilayer film is used as the multilayer reflective film 2, in which thin films of light elements or compounds thereof, which are high refractive index materials (high refractive index layers), and thin films of heavy elements or compounds thereof, which are low refractive index materials, are alternately stacked for about 40 to 60 periods. The multilayer film may be stacked in multiple periods, with a high refractive index layer / low refractive index layer stacking structure, where the high refractive index layer and the low refractive index layer are stacked in this order from the substrate 1 side, as one period. Alternatively, the multilayer film may be stacked in multiple periods, with a low refractive index layer / high refractive index layer stacking structure, where the low refractive index layer and the high refractive index layer are stacked in this order from the substrate 1 side, as one period. It is preferable that 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, be a high refractive index layer. In the above-described multilayer film, when multiple periods are stacked with a high refractive index layer / low refractive index layer stacking structure, where the high refractive index layer and the low refractive index layer are stacked in this order from the substrate 1, as one period, 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 will be easily oxidized, causing a decrease in the reflectivity of the reflective mask 200. Therefore, it is preferable to further form a high refractive index layer on top of the uppermost low refractive index layer to form the multilayer reflective film 2. On the other hand, in the above-described multilayer film, if a low refractive index layer and a high refractive index layer are stacked in this order from the substrate 1 side, and multiple periods of stacking are performed with this low refractive index layer / high refractive index layer stacking as one period, the uppermost layer will be the high refractive index layer, so it can be left as is.

[0044] In this embodiment, a layer containing silicon (Si) is used as the high refractive index layer. The Si-containing material may be Si alone, or a Si compound containing boron (B), carbon (C), nitrogen (N), and oxygen (O). By using the Si-containing layer as the high refractive index layer, a reflective mask 200 for EUV lithography with excellent EUV light reflectivity can be obtained. In this embodiment, a glass substrate is preferably used as the substrate 1. Si also exhibits excellent adhesion to the glass substrate. Furthermore, as the low refractive index layer, a metal element selected from molybdenum (Mo), ruthenium (Ru), rhodium (Rh), and platinum (Pt), or an alloy thereof, can be used. For example, as the multilayer reflective film 2 for EUV light with a wavelength of 13 nm to 14 nm, a Mo / Si periodic multilayer film is preferably used, in which Mo films and Si films are alternately stacked for approximately 40 to 60 periods. Alternatively, the uppermost high-refractive-index layer of the multilayer reflective film 2 may be formed of silicon (Si), and a silicon oxide layer containing silicon and oxygen may be formed between the uppermost layer (Si) and the Ru-based protective film 3. This can improve the mask's resistance to washing.

[0045] The reflectivity of such a multilayer reflective film 2 on its own is typically 65% ​​or higher, with an upper limit of typically 73%. The film thickness and period of each constituent layer of the multilayer reflective film 2 can be appropriately selected according to the exposure wavelength, and are chosen to satisfy Bragg's law of reflection. Multiple high-refractive-index layers and multiple low-refractive-index layers exist in the multilayer reflective film 2. The film thicknesses of the high-refractive-index layers and the low-refractive-index layers do not have to be the same. In addition, the film thickness of the outermost Si layer of the multilayer reflective film 2 can be adjusted within a range that does not reduce the reflectivity. The film thickness of the outermost Si (high-refractive-index layer) can be from 3 nm to 10 nm.

[0046] 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 using an ion beam sputtering method. In the case of the Mo / Si periodic multilayer film described above, for example, a Si film with a thickness of about 4 nm is first deposited on the substrate 1 using a Si target by an ion beam sputtering method. Then, a Mo film with a thickness of about 3 nm is deposited using a Mo target. The Si and Mo films deposited in this way constitute one period, and the multilayer reflective film 2 is formed by stacking 40 to 60 periods (the outermost layer is the Si layer). Furthermore, 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 during the deposition of the multilayer reflective film 2. The multilayer reflective film 2 is preferably about 40 periods in terms of improving reflectivity by increasing the number of stacking periods and reducing throughput by increasing the number of processes. However, the number of stacking periods of the multilayer reflective film 2 is not limited to 40 periods; for example, it may be 60 periods. While a 60-cycle design requires more processes than a 40-cycle design, it allows for a higher reflectivity to EUV light.

[0047] <<Protective film 3>> In this embodiment, it is preferable that the reflective mask blank 100 has a protective film 3 between the multilayer reflective film 2 and the absorber film 4. By forming the protective film 3 on the multilayer reflective film 2, damage to the surface of the multilayer reflective film 2 when manufacturing a reflective mask 200 (EUV mask) using the reflective mask blank 100 can be suppressed. Therefore, the presence of the protective film 3 results in good reflectivity characteristics for EUV light.

[0048] The protective film 3 is formed on the multilayer reflective film 2 to protect it from dry etching and cleaning during the manufacturing process of the reflective mask 200, which will be described later. It also serves to protect the multilayer reflective film 2 during black defect correction of the absorber pattern 4a using an electron beam (EB). The protective film 3 is made of a material that is resistant to etchants and cleaning solutions. Figure 1 shows the case where the protective film 3 is a single layer, but it can also be a laminated structure of three or more layers. For example, the bottom layer and the top layer can be made of the material containing Ru, and a protective film 3 can be made with a metal other than Ru or an alloy interposed between the bottom layer and the top layer. For example, the protective film 3 can also be made of a material mainly composed of ruthenium. Specifically, the material of the protective film 3 can be pure Ru metal. Furthermore, the material of the protective film 3 can be a Ru alloy containing Ru and at least one metal selected from titanium (Ti), niobium (Nb), Rh (rhodium), molybdenum (Mo), zirconium (Zr), yttrium (Y), boron (B), lanthanum (La), cobalt (Co), and rhenium (Re). In addition, the elemental Ru or Ru alloy may further contain nitrogen. Such a protective film 3 is particularly effective when patterning the absorber film 4 (or the buffer layer 42 described later) by dry etching using a fluorine-based gas (F-based gas) or an oxygen-free chlorine-based gas (Cl-based gas) as the etching gas. It is preferable that the protective film 3 is formed from a material such that the etching selectivity ratio of the absorber film 4 to the protective film 3 (etching rate of the absorber film 4 / etching rate of the protective film 3) in dry etching using these etching gases is 1.5 or higher, preferably 3 or higher.

[0049] As fluorine-based gases, gases such as CF4, CHF3, C2F6, C3F6, C4F6, C4F8, CH2F2, CH3F, C3F8, SF6, and / or F2 can be used. As chlorine-based gases, gases such as Cl2, SiCl4, CHCl3, CCl4, and / or BCl3 can be used. In addition, a mixed gas containing a fluorine-based gas and / or a chlorine-based gas and O2 in a predetermined ratio can be used. These etching gases may further contain inert gases such as He and / or Ar as needed.

[0050] When the material of the protective film 3 is a Ru alloy, the Ru content of the Ru alloy is 50 atomic% or more and less than 100 atomic%, preferably 80 atomic% or more and less than 100 atomic%, and more preferably 95 atomic% or more and less than 100 atomic%. In particular, when the Ru content of the Ru alloy is 95 atomic% or more and less than 100 atomic%, it is possible to ensure sufficient reflectivity of EUV light while suppressing the diffusion of elements (silicon) constituting the multilayer reflective film 2 into the protective film 3. Furthermore, in the case of this protective film 3, it is possible to combine the functions of the protective film 3, such as resistance to mask washing, etching stopper function when the absorber film 4 is etched, and prevention of aging of the multilayer reflective film 2.

[0051] The material of protective film 3 can be a material containing silicon (Si). Materials containing silicon (Si) include, for example, silicon (Si), silicon oxide (SiO, SiO2, and Si3O2, etc.). x O y (x and y are integers greater than or equal to 1), silicon nitride (SiN and Si3N4, etc.) x N y (x and y are integers greater than or equal to 1), and silicon oxide nitride (Si such as SiON). x O y N zThe protective film 3 comprises at least one material selected from (x, y, and z are integers of 1 or more). Such a protective film 3 is particularly effective when a buffer layer 42, described later, is provided as a lower layer of the absorber film 4, and the buffer layer is patterned by dry etching with a chlorine-based gas (Cl-based gas) containing oxygen gas. The protective film 3 is preferably formed of a material such that the etching selectivity ratio of the absorber film 4 to the protective film 3 (etching rate of the absorber film 4 / etching rate of the protective film 3) in dry etching using a chlorine-based gas containing oxygen gas is 1.5 or higher, preferably 3 or higher.

[0052] In the reflective mask blank 100 of this embodiment, it is preferable that the protective film 3 is made of a material containing ruthenium (Ru) or silicon (Si). or By forming the protective film 3 from a Ru alloy, damage to the surface of the multilayer reflective film 2 can be effectively suppressed. Furthermore, by forming the protective film 3 from a silicon (Si)-containing material, the degree of freedom in selecting the material for the absorber film 4 can be greatly increased.

[0053] In EUV lithography, since there are few materials that are transparent to exposure light, the EUV pellicle, which prevents foreign matter from adhering to the mask pattern surface, is not technically easy to manufacture. For this reason, pellicle-less operation is the mainstream. In addition, exposure contamination occurs in EUV lithography, such as the deposition of carbon films or the growth of oxide films on the mask due to EUV exposure. Therefore, when using the EUV reflective mask 200 in the manufacturing of semiconductor devices, it is necessary to frequently clean the mask to remove foreign matter and contamination. For this reason, the EUV reflective mask 200 requires a level of mask cleaning resistance that is orders of magnitude higher than that of transmissive masks used for photolithography. By using a Ru-based protective film 3 containing Ti, the mask can meet the requirements for mask cleaning resistance by exhibiting particularly high cleaning resistance to cleaning solutions such as sulfuric acid, sulfuric acid hydrogen peroxide (SPM), ammonia, ammonia hydrogen peroxide (APM), OH radical cleaning water, or ozone water with a concentration of 10 ppm or less.

[0054] The thickness of the protective film 3, which is composed of ruthenium (Ru) or an alloy thereof, or silicon (Si), is not particularly limited as long as it can perform its function as a protective film 3. From the viewpoint of EUV light reflectance, the thickness of the protective film 3 is preferably 1.0 nm to 8.0 nm, more preferably 1.5 nm to 6.0 nm.

[0055] The method for forming the protective film 3 can be any known film formation method without any particular limitations. Specific examples include sputtering and ion beam sputtering.

[0056] <<Absorbing membrane 4>> In the reflective mask blank 100 of this embodiment, an absorber film 4 that absorbs EUV light is formed on the multilayer reflective film 2 or protective film 3. The absorber film 4 has the function of absorbing EUV light. The absorber film 4 may be an absorber film 4 intended for absorbing EUV light, or it may be an absorber film 4 that has a phase shift function that also takes into account the phase difference of EUV light.

[0057] First, the absorber film 4 used in the reflective mask blank 100 of the first embodiment will be described. The absorber film 4 of the reflective mask blank 100 of this embodiment (first embodiment) contains iridium (Ir) and additive elements. First, the reason why the absorber film 4 of this embodiment contains iridium (Ir) will be explained.

[0058] To achieve high integration and low cost in semiconductor devices, it is necessary to form transfer patterns with fine pattern shapes on the substrate at high throughput during the EUV exposure process. To transfer fine pattern shapes, it is necessary to suppress shadowing effects. Therefore, the film thickness of the absorber pattern 4a needs to be thinner than conventional methods. Furthermore, to form transfer patterns at high throughput, the contrast during the EUV exposure process needs to be increased.

[0059] To meet the above requirements, it is necessary to appropriately select the material for the absorber film 4. An "evaluation function" is used as a guideline for selecting the material for the absorber film 4. The "evaluation function" is the product of the normalized image logarithmic gradient (NILS) and the light intensity threshold for exposure of a given resist. Alternatively, a "normalized evaluation function," which is a normalized version of the "evaluation function," can be used as a guideline for selecting the material for the absorber film 4.

[0060] The normalized image logarithmic gradient (NILS) is defined as shown in Equation 1 below. In Equation 1, W (unit: nm) represents the pattern size and I represents the light intensity. threshold This indicates that the derivative is a predetermined derivative value at a location corresponding to the edge of the pattern of pattern size W (i.e., where the light intensity is the threshold described later). In this specification, the normalized image logarithmic gradient is sometimes simply referred to as "NILS".

[0061] (Formula 1)

number

[0062] In this specification, "Normalized Image Logarithmic Gradient (NILS)" refers to the magnitude of the slope when the horizontal axis is the position and the vertical axis is the logarithm of the light intensity of the exposure light. In other words, the higher the NILS, the higher the contrast. In EUV lithography, a predetermined transfer pattern is transferred to the resist layer on the substrate to be transferred. The resist layer is photosensitive in accordance with the dose of exposure light (light intensity multiplied by time). Therefore, when the resist is developed after exposure, the higher the contrast (NILS), the greater the slope of the shape of the pattern edge portion of the transfer pattern. When the slope of the shape of the pattern edge portion is large (steep), the dependence of the position of the pattern edge on the dose of exposure light becomes small. Therefore, even if there is a change in the dose, the change in the shape of the transfer pattern becomes small. For these reasons, a high Normalized Image Logarithmic Gradient (NILS) is preferable in order to obtain a fine and highly accurate transfer pattern. Furthermore, it can be said that the higher the Normalized Image Logarithmic Gradient (NILS), the easier it is to form a transfer pattern with a fine pattern shape on the substrate to be transferred. The transfer pattern formed on the substrate to be transferred is sometimes called a resist transfer pattern.

[0063] In this specification, the "threshold" of the light intensity for exposure of a given resist refers to the light intensity at which the resist is exposed to light at a predetermined hp during EUV exposure to form a resist transfer pattern of a predetermined half-pitch (sometimes simply referred to as "hp") line-and-space pattern (sometimes simply referred to as "L / S"). For example, in a graph (aerial image) with light intensity on the vertical axis and L / S hp on the horizontal axis, the "threshold" refers to the light intensity at which the resist is exposed to light at a predetermined hp. Specifically, for example, when a negative-type photosensitive material is used as the resist, the threshold means the light intensity at which the negative-type photosensitive material becomes completely insoluble after exposure at a predetermined light intensity and subsequent development. The higher the threshold, the less exposure light is required during EUV exposure, thus increasing the throughput of the EUV exposure process. Therefore, to increase the throughput of the EUV exposure process, a high threshold is preferable.

[0064] In this specification, the "evaluation function" is the product of the normalized image logarithmic gradient (NILS) and the light intensity threshold for exposure of a given resist. The larger the value of the evaluation function of the reflective mask 200 having an absorber pattern 4a of a given material, the more reliably it is possible to form a transfer pattern (resist transfer pattern) with a fine pattern shape on the substrate to be transferred, and to perform EUV exposure at a high throughput.

[0065] In this specification, "normalized evaluation function" means the ratio of the evaluation function values ​​of the comparison film, which is normalized by setting the value of the evaluation function of the reflective mask 200, which uses a pattern (reference film pattern) of a film (referred to here as the "reference film") having a refractive index (n) of 0.95 and an extinction coefficient (k) of 0.03 for EUV light at a wavelength of 13.5 nm as the absorber pattern 4a, to 1.

[0066] The values ​​of the "evaluation function" and the "normalized evaluation function" can be obtained through simulation. Therefore, the values ​​of the normalized evaluation function were determined by simulation when the refractive index (n) and extinction coefficient (k) of the absorber film 4 (absorber pattern 4a) of the reflective mask 200 were varied, for exposure with light of a wavelength of 13.5 nm. The reflective mask 200 used for the simulation had a structure in which a multilayer reflective film 2 made of Mo and Si (40 periodic stackings of pairs of 4.2 nm Si film and 2.8 nm Mo film) and a protective film 3 of RuNb film (n=0.9016, k=0.0131, film thickness 3.5 nm) were formed on a substrate 1 (SiO2-TiO2 glass substrate), and the absorber pattern 4a was placed on top of the protective film 3. The film thickness of the absorber pattern 4a was optimized to obtain the highest evaluation function value.

[0067] Figure 4 shows the values ​​of the normalized evaluation function obtained from a simulation (Simulation #1a) for the reflective mask 200 (protective film 3 is a RuNb film) described above, where the absorber pattern 4a is a vertical L / S (line and space) pattern with an hp of 16 nm. Figure 4 is a diagram showing the distribution of the values ​​of the normalized evaluation function when a predetermined incident light is irradiated onto absorber patterns 4a with different refractive indices (n) and extinction coefficients (k) in the reflective mask 200 of Simulation #1a. In the simulation shown in Figure 4, numerous simulations were performed assuming absorber films 4 with many combinations of refractive indices (n) and extinction coefficients (k) within the range shown in Figure 4. The values ​​of the normalized evaluation function are shown in grayscale in Figure 4.

[0068] Simulations similar to those in Simulation #1a, whose results are shown in Figure 4, were performed for the case where the absorber pattern 4a is a horizontal L / S pattern (horizontal L / S, hp=16nm) (Simulation #2a) and the case where it is a contact hole pattern (Contact Hole, diameter 24nm) (Simulation #3a). In addition, the material of the protective film 3 in Simulation #1a was changed to a RuRh film (n=0.8898, k=0.0155, film thickness 3.5nm), and simulations #1b, #2b, and #3b were performed in the same manner as simulations #1a, #2a, and #3a.

[0069] Figure 5 shows the distribution of normalized evaluation function values ​​obtained by combining all simulations #1a to #3a and #1b to #3b. Figure 5 shows the distribution binarized into two cases: one where the normalized evaluation function value is 1.015 or greater in all simulations (white), and another where it is not (black).

[0070] From the simulation results above, it can be seen that in the distribution of refractive index (n) and extinction coefficient (k) of absorber pattern 4a (absorber film 4), the region where the values ​​of the normalized evaluation function are all 1.015 or greater corresponds to the region shown in white in Figure 5. The individual materials belonging to the region where the values ​​of the normalized evaluation function are all 1.015 or greater include Ag, Co, Pt, Au, Fe, Pd, Ir, W, Cr, Rh, and Ru. Therefore, if absorber film 4 is formed using these materials, it is possible to more reliably form a transfer pattern with a finer pattern shape on the transfer substrate and to perform EUV exposure at a high throughput, compared to absorber film 4 made from conventional materials such as TaBN and TaN films.

[0071] The inventors focused on the fact that iridium (Ir) falls within the region where the values ​​of the normalized evaluation function are all 1.015 or greater. However, iridium (Ir) has a slow etching rate and poor processability. Therefore, when an absorber film 4 consisting only of Ir is used, there is a problem in that it is not easy to form an absorber pattern 4a. The inventors have found that the processability problem of Ir can be solved by using a material containing Ir and a predetermined additive element as the material for the absorber film 4 of the reflective mask blank 100. Therefore, by using a reflective mask blank 100 having the predetermined absorber film 4 of this embodiment (absorber film 4 containing Ir and a predetermined additive element), it is possible to form a transfer pattern with a fine pattern shape on the transfer substrate and to manufacture a reflective mask 200 having a transfer pattern that allows for high-throughput EUV exposure.

[0072] In the reflective mask blank 100 of this embodiment, the iridium (Ir) content in the absorber film 4 is more than 50 atomic percent, preferably 60 atomic percent or more, and more preferably 70 atomic percent or more. The refractive index of iridium (Ir) for EUV light at a wavelength of 13.5 nm is 0.905, and the extinction coefficient is 0.044. That is, the extinction coefficient of iridium (Ir) is higher than that of tantalum (Ta), etc., and the refractive index of iridium (Ir) is lower than that of tantalum (Ta), etc. Therefore, by having a relatively high iridium (Ir) content in the absorber film 4, a reflective mask 200 having an absorber pattern 4a with high contrast and a thin film thickness can be obtained. As a result, the shadowing effect during exposure can be reduced.

[0073] When an absorber film 4 consisting solely of iridium (Ir) is used, it is not easy to form an absorber pattern 4a by etching. Therefore, the iridium (Ir) content (upper limit) in the absorber film 4 is preferably 90 atomic percent or less, and more preferably 80 atomic percent or less.

[0074] The absorber film 4 of this embodiment contains an additive element. The additive element is at least one selected from boron (B), silicon (Si), phosphorus (P), titanium (Ti), germanium (Ge), arsenic (As), selenium (Se), niobium (Nb), molybdenum (Mo), ruthenium (Ru), and tantalum (Ta). By including these elements as additives in the absorber film 4, the etching rate of the absorber film 4 with respect to a suitable etching gas (e.g., a fluorine-based etching gas) can be improved, thereby improving the processability of the absorber film 4.

[0075] The additive element included in the absorber film 4 is preferably at least one selected from tantalum (Ta), molybdenum (Mo), niobium (Nb), and boron (B). By using these elements as the additive element in the absorber film 4, the etching rate of the absorber film 4 with respect to fluorine-based etching gases can be further improved.

[0076] In the reflective mask blank 100 of this embodiment, it is even more preferable that the additive element contained in the absorber membrane 4 includes tantalum (Ta).

[0077] Since iridium (Ir) is a material with compressive stress, it is preferable to select tantalum (Ta), which has tensile stress, as the additive element. Therefore, by including tantalum (Ta) in the absorber film 4, an absorber film 4 with balanced stress can be obtained. Furthermore, tantalum (Ta) has been widely used in recent years as the material for the absorber film 4 of the reflective mask blank 100 and is highly reliable. In addition, the absorber film 4 containing iridium (Ir) and tantalum (Ta) can be easily etched using a fluorine-based etching gas, resulting in good processability. Therefore, by including tantalum (Ta) in the absorber film 4, a reflective mask blank 100 with high reliability and good processability can be obtained.

[0078] In the reflective mask blank 100 of this embodiment, when the additive element contains tantalum (Ta), the tantalum (Ta) content in the absorber film 4 is preferably 2 atomic percent or more, and more preferably 10 atomic percent or more. Furthermore, the tantalum (Ta) content is preferably 30 atomic percent or less, and more preferably 20 atomic percent or less. By having a tantalum (Ta) content of 2 to 30 atomic percent in the absorber film 4, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0079] When the additive element in the absorber film 4 includes boron (B), the B content in the absorber film 4 is preferably 2 atomic percent or more, and more preferably 5 atomic percent or more. Furthermore, the B content is preferably 25 atomic percent or less, and more preferably 20 atomic percent or less. By having the B content in the absorber film 4 within the above range, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0080] When silicon (Si) is included as an additive element in the absorber film 4, the Si content in the absorber film 4 is preferably 2 atomic percent or more, and more preferably 5 atomic percent or more. Furthermore, the Si content is preferably 25 atomic percent or less, and more preferably 20 atomic percent or less. By having the Si content in the absorber film 4 within the above range, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0081] When the additive element in the absorber film 4 includes phosphorus (P), the P content in the absorber film 4 is preferably 2 atomic percent or more, and more preferably 5 atomic percent or more. Furthermore, the P content is preferably 20 atomic percent or less, and more preferably 10 atomic percent or less. By having the P content in the absorber film 4 within the above range, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0082] When the additive element in the absorber film 4 includes titanium (Ti), the Ti content in the absorber film 4 is preferably 2 atomic percent or more, and more preferably 10 atomic percent or more. Furthermore, the Ti content is preferably 30 atomic percent or less, and more preferably 20 atomic percent or less. By having the Ti content in the absorber film 4 within the above range, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0083] When the additive element in the absorber membrane 4 includes germanium (Ge), the Ge content in the absorber membrane 4 is preferably 2 atomic percent or more, and more preferably 5 atomic percent or more. Furthermore, the Ge content is preferably 30 atomic percent or less, and more preferably 20 atomic percent or less. Content As long as the above range is maintained, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0084] When the additive element in the absorber film 4 includes arsenic (As), the As content in the absorber film 4 is preferably 2 atomic percent or more, and more preferably 5 atomic percent or more. Furthermore, the As content is preferably 30 atomic percent or less, and more preferably 20 atomic percent or less. By having the As content in the absorber film 4 within the above range, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0085] When the absorber film 4 contains selenium (Se) as an additive element, the Se content in the absorber film 4 is preferably 2 atomic percent or more, and more preferably 5 atomic percent or more. Furthermore, the Se content is preferably 30 atomic percent or less, and more preferably 20 atomic percent or less. By having the Se content in the absorber film 4 within the above range, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0086] When the absorber film 4 contains niobium (Nb) as an additive element, the Nb content in the absorber film 4 is preferably 2 atomic percent or more, and more preferably 5 atomic percent or more. Furthermore, the Nb content is preferably 30 atomic percent or less, and more preferably 25 atomic percent or less. By having the Nb content in the absorber film 4 within the above range, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0087] When the absorber film 4 contains molybdenum (Mo) as an additive element, the Mo content in the absorber film 4 is preferably 2 atomic percent or more, and more preferably 5 atomic percent or more. Furthermore, the Mo content is preferably 49 atomic percent or less, and more preferably 45 atomic percent or less. By having the Mo content in the absorber film 4 within the above range, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0088] When the absorber film 4 contains ruthenium (Ru) as an additive element, the Ru content in the absorber film 4 is preferably 2 atomic percent or more, and more preferably 5 atomic percent or more. Furthermore, the Ru content is preferably 49 atomic percent or less, and more preferably 45 atomic percent or less. By having the Ru content in the absorber film 4 within the above range, an absorber film 4 with an excellent balance of optical properties, processing properties, and stress can be obtained.

[0089] Furthermore, in the reflective mask blank 100 of this embodiment, the additive element contained in the absorber film 4 is tantalum (Ta), and the content ratio of Ir to Ta (Ir:Ta) is preferably 4:1 to 22:1, and more preferably 6:1 to 15:1. By setting the content ratio of Ir to Ta within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processing properties, and stress.

[0090] When the absorber film 4 contains boron (B) as an additive element, the ratio of Ir to B (Ir:B) is preferably 3:1 to 20:1, and more preferably 4:1 to 9:1. By setting the ratio of Ir to B within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processing properties, and stress.

[0091] When the additive elements in the absorber film 4 include silicon (Si), the ratio of Ir to Si (Ir:Si) is preferably 3:1 to 20:1, and more preferably 4:1 to 9:1. By setting the ratio of Ir to Si within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processing properties, and stress characteristics.

[0092] When the absorber film 4 contains phosphorus (P) as an additive element, the ratio of Ir to P (Ir:P) is preferably 4:1 to 30:1, and more preferably 9:1 to 20:1. By setting the ratio of Ir to P within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processing properties, and stress characteristics.

[0093] When the absorber film 4 contains titanium (Ti) as an additive element, the Ir:Ti content ratio is preferably 2.2:1 to 30:1, and more preferably 4:1 to 24:1. By setting the Ir:Ti content ratio within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processing properties, and stress characteristics.

[0094] When the absorber film 4 contains germanium (Ge) as an additive element, the ratio of Ir to Ge (Ir:Ge) is preferably 2.2:1 to 30:1, and more preferably 4:1 to 24:1. By setting the ratio of Ir to Ge within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processing properties, and stress characteristics.

[0095] When the absorber film 4 contains arsenic (As) as an additive element, the ratio of Ir to As (Ir:As) is preferably 2.2:1 to 30:1, and more preferably 4:1 to 24:1. By setting the ratio of Ir to As within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processing properties, and stress characteristics.

[0096] When the absorber film 4 contains selenium (Se) as an additive element, the ratio of Ir to Se (Ir:Se) is preferably 2.2:1 to 30:1, and more preferably 4:1 to 24:1. By setting the ratio of Ir to Se within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processing properties, and stress characteristics.

[0097] When the absorber film 4 contains niobium (Nb) as an additive element, the ratio of Ir to Nb (Ir:Nb) is preferably 2.2:1 to 30:1, and more preferably 4:1 to 24:1. By setting the ratio of Ir to Nb within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processing properties, and stress characteristics.

[0098] When the absorber film 4 contains molybdenum (Mo) as an additive element, the ratio of Ir to Mo (Ir:Mo) is preferably 1.2:1 to 9:1, and more preferably 1.5:1 to 4:1. By setting the ratio of Ir to Mo within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processing properties, and stress characteristics.

[0099] When the absorber film 4 contains ruthenium (Ru) as an additive element, the ratio of Ir to Ru (Ir:Ru) is preferably 1.2:1 to 9:1, and more preferably 1.5:1 to 4:1. By setting the ratio of Ir to Ru within a predetermined range, it is possible to reliably obtain an absorber film 4 with an excellent balance of optical properties, processability, and stress characteristics.

[0100] In the reflective mask blank 100 of this embodiment, the absorber film 4 preferably further contains at least one selected from oxygen (O), nitrogen (N), and carbon (C). Furthermore, the content of oxygen (O), nitrogen (N), and / or carbon (C) is preferably 5 atomic percent or more, and more preferably 10 atomic percent or more. By further containing predetermined amounts of oxygen (O), nitrogen (N), and / or carbon (C) in the absorber film 4, the processability of the absorber film 4 by etching can be improved compared to an absorber film 4 made of Ir alone.

[0101] Furthermore, if the oxygen (O), nitrogen (N), and / or carbon (C) content in the absorbent membrane 4 is too high, the extinction coefficient (k) of the absorbent membrane 4 may decrease. Therefore, the oxygen (O), nitrogen (N), and / or carbon (C) content in the absorbent membrane 4 is preferably 60 atomic% or less, more preferably 50 atomic% or less, and even more preferably 25 atomic% or less.

[0102] The absorbent membrane 4 of the reflective mask blank 100 in this embodiment more preferably contains oxygen (O). Furthermore, the oxygen (O) content of the absorbent membrane 4 is preferably 5 atomic percent or more, and more preferably 10 atomic percent or more. The upper limit of the oxygen (O) content in the absorbent membrane 4 is preferably 60 atomic percent or less, more preferably 50 atomic percent or less, and even more preferably 25 atomic percent or less.

[0103] An IrTaO film containing oxygen (O) (absorber film 4) can be easily etched using a fluorine-based etching gas (for example, a mixture of CF4 gas and oxygen gas). The flow rate ratio of the fluorine-based gas can be, for example, CF4:O2 = 90:10. Therefore, by including a predetermined amount of oxygen (O) in the absorber film 4, the processability of the absorber film 4 by etching can be further improved. In addition, by including a predetermined amount of oxygen (O) in the absorber film 4, the film stress of the absorber film 4 can be adjusted, thereby improving its optical properties.

[0104] Furthermore, it is preferable that the refractive index of the absorber membrane 4 material is in the range of 0.86 to 0.95, and the extinction coefficient of the absorber membrane 4 material is in the range of 0.015 to 0.065. It is preferable to adjust the composition ratio of Ir and the added element so that the refractive index and extinction coefficient of the absorber membrane 4 fall within the above ranges.

[0105] As shown in Figure 2, the absorber film 4 of the reflective mask blank 100 in this embodiment may include a buffer layer 42 containing chromium (Cr) and an absorber layer 44 provided on the buffer layer 42. In this case, the material of the absorber film 4 described above can be used as the material of the absorber layer 44. That is, the absorber layer 44 may include iridium (Ir) and additive elements.

[0106] The buffer layer 42 can be placed when the etching selectivity ratio between the material of the absorption layer 44 (absorber film 4) and the material of the multilayer reflective film 2 or protective film 3 is not high. By placing the buffer layer 42, the formation of the absorber pattern 4a is facilitated, making it possible to thin the absorber pattern 4a. Furthermore, the material of the absorber film 4 (material containing iridium (Ir) and additive elements) described above can be used as the material of the absorption layer 44. In this case, it is preferable that the material of the buffer layer 42 is a material that has an etching selectivity ratio of 1.5 or higher with respect to the material of the absorption layer 44. By providing the buffer layer 42, it is possible to broaden the range of materials that can be selected for the absorption layer 44 and the protective film 3 without reducing the effects of the present invention.

[0107] When etching an iridium (Ir)-containing absorption layer 44 (e.g., an IrTaO film), a fluorine-based etching gas (e.g., a mixed gas of CF4 gas and O2 gas) can be used. On the other hand, etching with a fluorine-based etching gas containing oxygen may damage the protective film 3 (e.g., a Ru-based protective film). The absorber film 4 has a buffer layer 42 positioned between the absorption layer 44 and the protective film 3, and the buffer layer 42 contains chromium (Cr), thereby avoiding damage to the protective film 3 when etching the absorption layer 44.

[0108] Furthermore, the material of the buffer layer 42 may be a material containing chromium (Cr) and one or more elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H). Specifically, the material of the buffer layer 42 may include CrN, CrO, CrC, CrON, CrOC, CrCN, or CrOCN. The chromium-containing buffer layer 42 can be etched using a chlorine-based gas (for example, a mixed gas of Cl2 gas and O2 gas).

[0109] The thickness of the buffer layer 42 is preferably 1 / 3 or less of the total thickness of the absorber film 4 (absorption layer 44 and buffer layer 42). The thickness of the buffer layer 42 is preferably 10 nm or less, and more preferably 5 nm or less. The lower limit of the thickness of the buffer layer 42 can be 2 nm or more, preferably 3 nm or more. In order to make the thickness of the absorber film 4 as thin as possible and reduce the shadowing effect, it is preferable that the thickness of the buffer layer 42 be as close to the minimum thickness necessary to minimize the influence on the optical properties of the absorption layer 44 and to achieve the effect of the buffer layer 42.

[0110] Next, we will describe the absorbent membrane 4 used in the reflective mask blank 100 of the second embodiment.

[0111] The reflective mask blank 100 of the second embodiment comprises a substrate 1, a multilayer reflective film 2 on the substrate 1, and an absorber film 4 on the multilayer reflective film 2. The absorber film 4 includes an uppermost layer and other lower layers. The thickness of the uppermost layer is 0.5 nm or more and less than 5 nm. The uppermost layer may contain iridium (Ir) alone, or iridium (Ir) and the aforementioned additive elements. The additive elements are at least one selected from boron (B), silicon (Si), phosphorus (P), titanium (Ti), germanium (Ge), arsenic (As), selenium (Se), niobium (Nb), molybdenum (Mo), ruthenium (Ru), and tantalum (Ta). The material of the absorber film 4 of the first embodiment (a material containing iridium (Ir) and additive elements) can be used as the material for the uppermost layer.

[0112] The layer beneath the absorber film 4 in the second embodiment is not particularly limited, as long as it is a material that has the function of absorbing EUV light and is etching selective with respect to the protective film 3. Preferably, such materials include at least one metal selected from palladium (Pd), silver (Ag), platinum (Pt), gold (Au), tungsten (W), chromium (Cr), cobalt (Co), manganese (Mn), tin (Sn), tantalum (Ta), vanadium (V), nickel (Ni), hafnium (Hf), iron (Fe), copper (Cu), tellurium (Te), zinc (Zn), magnesium (Mg), germanium (Ge), aluminum (Al), rhodium (Rh), ruthenium (Ru), molybdenum (Mo), niobium (Nb), titanium (Ti), zirconium (Zr), yttrium (Y), and silicon (Si), an alloy containing two or more metals, or a compound thereof.

[0113] Furthermore, the lower layer of the absorber film 4 in the second embodiment may preferably be at least one metal selected from Ag, Co, Pt, Au, Fe, Pd, W, Cr, Rh, and Ru, an alloy containing two or more metals, or a compound thereof, which belong to the region in which the normalized evaluation function value described above is 1.015 or higher. The lower layer of the absorber film 4 preferably contains more than 50 atomic percent of the above metal or alloy, and more preferably contains 60 atomic percent or more.

[0114] The above-mentioned compound may contain oxygen (O), nitrogen (N), carbon (C), and / or boron (B) in addition to the above-mentioned metal or alloy.

[0115] In the first and second embodiments, in the case of an absorber film 4 intended for absorbing EUV light, the film thickness is set such that the reflectance of EUV light to the absorber film 4 is 2% or less, preferably 1% or less.

[0116] Furthermore, the thickness of the absorber film 4 in the reflective mask blank 100 of the first and second embodiments is preferably 50 nm or less, and more preferably 45 nm or less. By having a thickness of 50 nm or less for the absorber film 4 of the reflective mask blank 100, the shadowing effect during EUV exposure can be reduced. In addition, for sufficient absorption of EUV light, the lower limit of the thickness of the absorber film 4 can be 35 nm or more, preferably 40 nm or more.

[0117] The absorber film 4 of the first and second embodiments can be formed by sputtering (coarse sputtering) using an Ir target and a target of a single additive element. Alternatively, the absorber film 4 can be formed by sputtering using an alloy target consisting of Ir and an additive element.

[0118] <<Etching Mask Film>> The reflective mask blank 100 of this embodiment may include an etching mask film. The thickness of the etching mask film is 0.5 nm or more and 14 nm or less.

[0119] By having an appropriate etching mask film, it is possible to obtain a reflective mask blank 100 that can further reduce the shadowing effect of the reflective mask 200 and form a fine and highly accurate absorber pattern 4a.

[0120] As shown in Figure 1, the etching mask film is formed on the absorber film 4. As the material for the etching mask film, a material with a high etching selectivity ratio of the absorber film 4 to the etching mask film is used. Here, "etching selectivity ratio of B to A" refers to the ratio of the etching rates of layer A, which is the layer that should not be etched (the mask layer), and layer B, which is the layer that should be etched. Specifically, it is determined by the formula "etching selectivity ratio of B to A = etching rate of B / etching rate of A". Also, "high selectivity ratio" means that the value of the selectivity ratio as defined above is large compared to the comparison target. The etching selectivity ratio of the absorber layer 44 to the etching mask film is preferably 1.5 or higher, and more preferably 3 or higher.

[0121] In this embodiment, the reflective mask blank 100 preferably has an etching mask film material that contains chromium (Cr) and one or more elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H). Materials Specifically, examples include CrN, CrO, CrC, CrON, CrOC, CrCN, or CrOCN.

[0122] From the viewpoint of obtaining the function of an etching mask that accurately forms a transfer pattern on the absorber film 4, the thickness of the etching mask film is preferably 0.5 nm or more, more preferably 1 nm or more, more preferably 2 nm or more, and even more preferably 3 nm or more. Furthermore, from the viewpoint of reducing the thickness of the resist film 11, the thickness of the etching mask film is preferably 14 nm or less, more preferably 12 nm or less, and more preferably 10 nm or less.

[0123] If the absorber film 4 consists of two layers, a buffer layer 42 and an absorber layer 44, the etching mask film and the buffer layer 42 may be made of the same material. Alternatively, the etching mask film and the buffer layer 42 may be made of materials with different composition ratios, even if they contain the same metal. If the etching mask film and the buffer layer 42 contain chromium, the chromium content of the etching mask film may be greater than that of the buffer layer 42, and the thickness of the etching mask film may be greater than that of the buffer layer 42. If the etching mask film and the buffer layer 42 contain hydrogen, the hydrogen content of the etching mask film may be greater than that of the buffer layer 42.

[0124] <<Resist film 11>> The reflective mask blank 100 of this embodiment may have a resist film 11 on top of the etching mask film. The reflective mask blank 100 of this embodiment also includes a form having a resist film 11. In the reflective mask blank 100 of this embodiment, the resist film 11 can be thinned by selecting an absorber film 4 and etching gas of an appropriate material and / or appropriate thickness.

[0125] For example, a chemically-amplified resist (CAR) can be used as the material for the resist film 11. By patterning the resist film 11 and etching the absorber film 4 (buffer layer 42 and absorber layer 44), a reflective mask 200 having a predetermined transfer pattern can be manufactured.

[0126] <<Back surface conductive film 5>> Generally, a back-side conductive film 5 for electrostatic chucks is formed on the second main surface (back side) of the substrate 1 (the surface opposite to the surface on which the multilayer reflective film 2 is formed). The required electrical properties (sheet resistance) of the back-side conductive film 5 for electrostatic chucks are usually 100 Ω / □ (Ω / Square) or less. For forming the back-side conductive film 5, for example, magnetron sputtering and ion beam sputtering can be used. The target for sputtering can be selected from metal targets such as chromium (Cr) and tantalum (Ta), as well as targets of their alloys.

[0127] The chromium (Cr)-containing material of the back surface conductive film 5 is preferably a Cr compound containing at least one selected from boron, nitrogen, oxygen, and carbon. Examples of Cr compounds include CrN, CrON, CrCN, CrCON, CrBN, CrBON, CrBCN, and CrBOCN.

[0128] As the tantalum (Ta)-containing material for the back surface conductive film 5, 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. Examples of Ta compounds include TaB, TaN, TaO, TaON, TaCON, TaBN, TaBO, TaBON, TaBCON, TaHf, TaHfO, TaHfN, TaHfON, TaHfCON, TaSi, TaSiO, TaSiN, TaSiON, and TaSiCON.

[0129] For materials containing tantalum (Ta) or chromium (Cr), it is preferable that the nitrogen (N) present on the surface layer is low. Specifically, the nitrogen content on the surface layer of the back conductive film 5 of a material containing tantalum (Ta) or chromium (Cr) is preferably less than 5 atomic percent, and it is more preferable that the surface layer is substantially nitrogen-free. This is because a lower nitrogen content on the surface layer of the back conductive film 5 of a material containing tantalum (Ta) or chromium (Cr) results in higher wear resistance.

[0130] The back surface conductive film 5 is preferably made of a material containing tantalum and boron. By making the back surface conductive film 5 of a material containing tantalum and boron, a back surface conductive film 5 with abrasion resistance and chemical resistance can be obtained. When the back surface conductive film 5 contains tantalum (Ta) and boron (B), the B content is preferably 5 to 30 atomic percent. The ratio of Ta to B (Ta:B) in the sputtering target used to deposit the back surface conductive film 5 is preferably 95:5 to 70:30.

[0131] The thickness of the back conductive film 5 is not particularly limited as long as it satisfies the function for use as an electrostatic chuck. The thickness of the back conductive film 5 is usually 10 nm to 200 nm. reflective type It also serves to adjust the stress on the second main surface side of the mask blank 100. In other words, the back surface conductive film 5 is adjusted to balance the stress from the various films formed on the first main surface side, so that a flat reflective mask blank 100 can be obtained.

[0132] <Reflective mask 200 and method for manufacturing the same> This embodiment is a reflective mask 200 having an absorber pattern 4a formed by patterning the absorber film 4 of the reflective mask blank 100 described above. By using the reflective mask 200 of this embodiment, it is possible to form a transfer pattern with a fine pattern shape on the transfer substrate and to perform EUV exposure with high throughput.

[0133] The absorber pattern 4a of the reflective mask 200 absorbs EUV light, and the aperture of the absorber pattern 4a reflects the EUV light. Therefore, by irradiating the reflective mask 200 with EUV light using a predetermined optical system, a predetermined fine transfer pattern can be transferred to the object to be transferred.

[0134] A reflective mask 200 can be manufactured by patterning the absorbent film 4 of the reflective mask blank 100 of this embodiment. Here, only an overview of the manufacturing method of the reflective mask 200 will be described, and a detailed explanation will be given later in the examples with reference to the drawings.

[0135] Prepare a reflective mask blank 100. Form a resist film 11 on the absorber film 4 of the first main surface of the reflective mask blank 100 (this step is unnecessary if the reflective mask blank 100 already has a resist film 11). Draw (expose) a desired pattern onto this resist film 11, and then develop and rinse to form a predetermined resist pattern 11a.

[0136] In the case of a reflective mask blank 100, the absorber pattern 4a is formed by etching the absorber film 4 using the resist pattern 11a as a mask. The resist pattern 11a is removed by a wet treatment such as oxygen ashing or hot sulfuric acid. Finally, wet cleaning is performed using an acidic or alkaline aqueous solution.

[0137] By following the above steps, the reflective mask 200 of this embodiment can be manufactured.

[0138] <Manufacturing method for semiconductor devices> The semiconductor device manufacturing method of this embodiment includes the step of setting the reflective mask 200 of this embodiment in an exposure apparatus having an exposure light source that emits EUV light, and transferring a transfer pattern to a resist layer formed on a substrate to be transferred. The semiconductor device manufacturing method of this embodiment makes it possible to form a transfer pattern with a fine pattern shape on the substrate to be transferred, and allows EUV exposure to be performed with high throughput.

[0139] According to the semiconductor device manufacturing method of this embodiment, by using the reflective mask 200 of this embodiment, it is possible to form a transfer pattern with a fine pattern shape on the substrate to be transferred. Furthermore, by using the reflective mask 200 of this embodiment, EUV exposure can be performed with high throughput.

[0140] By performing EUV exposure using the reflective mask 200 of this embodiment, a desired pattern can be formed on a semiconductor substrate with high dimensional accuracy and high throughput. In addition to this lithography process, a semiconductor device with a desired electronic circuit can be manufactured by going through various processes such as etching the workpiece, forming insulating films and conductive films, introducing dopants, and annealing.

[0141] More specifically, an EUV exposure system consists of a laser plasma light source that generates EUV light, an illumination optical system, a mask stage system, a reduction projection optical system, a wafer stage system, and vacuum equipment. The light source is equipped with a debris trap function, a cut filter to cut out long-wavelength light other than the exposure light, and equipment for differential vacuum pumping. The illumination optical system and the reduction projection optical system are composed of reflective mirrors. The EUV exposure reflective mask 200 is electrostatically attracted to the mask stage by a back-side conductive film 5 formed on its second main surface (back surface).

[0142] Light from an EUV light source is irradiated onto the reflective mask 200 via an illumination optical system at an angle of 6° to 8° relative to the vertical plane of the reflective mask 200. The reflected light from the reflective mask 200 in response to this incident light is reflected in the opposite direction to the incident light and at the same angle as the incident light (specular reflection). The reflected light is guided to a reflective projection optical system, which usually has a reduction ratio of 1 / 4, and exposure is performed on the resist layer on the wafer (semiconductor substrate) placed on the wafer stage. During this time, at least the area through which the EUV light passes is evacuated. Furthermore, for this exposure, scan exposure is the mainstream method, in which the mask stage and wafer stage are scanned in synchronization at a speed corresponding to the reduction ratio of the reduction projection optical system, and exposure is performed through a slit. Then, by developing the exposed resist on the resist layer, a resist transfer pattern can be formed on the semiconductor substrate. Then, by using this resist transfer pattern as a mask and performing etching, for example, a predetermined wiring pattern can be formed on the semiconductor substrate. Semiconductor devices are manufactured through processes such as exposure, processing of the workpiece, formation of insulating films and conductive films, dopant introduction, annealing, and other necessary steps. [Examples]

[0143] The following describes the embodiments with reference to the drawings. In the embodiments, the same reference numerals are used for similar components, and their descriptions are simplified or omitted.

[0144] (Experiments 1-7) In Experiments 1-7, thin films corresponding to absorber film 4 (referred to as "experimental absorber films") were manufactured. The suitability of the experimental absorber films for use in Experiments 1-7 was evaluated by assessing their composition, film thickness, optical properties (refractive index (n) and extinction coefficient (k)), film stress, and etching properties. The experimental absorber films in Experiments 5 and 6 are absorber films 4 used in the reflective mask blanks 100 of Examples 1 and 2.

[0145] Table 1 shows the materials and compositions of the absorber membranes used in Experiments 1-7. Note that the absorber membrane in Experiment 7 is a thin film made solely of Ir and is used for comparison with Experiments 1-6.

[0146] For experiments 1-7, a multilayer reflective substrate was first manufactured, comprising a substrate 1, a multilayer reflective film 2, and a protective film 3. A back-side conductive film 5 was formed on the back surface of substrate 1. An experimental absorber film was then formed so as to be positioned in contact with the protective film 3 of this multilayer reflective substrate. Therefore, the structure of the experimental absorber film after formation is similar to that of the reflective mask blank 100 shown in Figure 1.

[0147] First, I will explain the multilayer reflective substrates used for experiments 1-7.

[0148] A SiO2-TiO2 glass substrate, a low thermal expansion glass substrate of size 6025 (approximately 152 mm x 152 mm x 6.35 mm), with both the first and second main surfaces polished, was prepared and designated as substrate 1. Polishing was performed using a rough polishing process, a precision polishing process, a local polishing process, and a touch polishing process to obtain a flat and smooth main surface.

[0149] Next, a back surface conductive film 5 made of a CrN film was formed on the second main surface (back surface) of the SiO2-TiO2 glass substrate 1 by magnetron sputtering (reactive sputtering) under the following conditions. Formation conditions for the conductive film 5 on the back surface: Cr target, mixed gas atmosphere of Ar and N2 (Ar: 90%, N: 10%), film thickness 20 nm.

[0150] Next, a multilayer reflective film 2 was formed on the main surface (first main surface) of the substrate 1 opposite to the side where the back surface conductive film 5 was formed. To make the multilayer reflective film 2 formed on the substrate 1 suitable for EUV light with a wavelength of 13.5 nm, a periodic multilayer reflective film 2 made of Mo and Si was formed. The multilayer reflective film 2 was formed by alternately stacking Mo layers and Si layers on the substrate 1 using an ion beam sputtering method in an Ar gas atmosphere with a Mo target and a Si target. First, a Si film was deposited with a thickness of 4.2 nm, followed by a Mo film with a thickness of 2.8 nm. This constituted one period, and 40 periods were stacked in the same manner, and finally a Si film with a thickness of 4.0 nm was deposited to form the multilayer reflective film 2.

[0151] Subsequently, in an Ar gas atmosphere, a protective film 3 made of RuNb was deposited to a thickness of 3.5 nm using ion beam sputtering with a RuNb target.

[0152] As described above, the multilayer reflective substrates used in Experiments 1-7 were manufactured.

[0153] Next, a buffer layer 42 made of CrON was formed on the protective film 3. Specifically, the buffer layer 42 made of a CrON film was first formed by DC magnetron sputtering. The CrON film was deposited with a thickness of 6 nm by reactive sputtering using a Cr target in a mixed gas atmosphere of Ar gas, O2 gas, and N2 gas.

[0154] Subsequently, experimental absorber films were formed using the materials shown in Table 1. Specifically, the experimental absorber films were deposited using DC magnetron sputtering with the targets and sputtering gases shown in Table 2. In the case of experiments 5 and 6, which included oxygen (O), the experimental absorber films were deposited by reactive sputtering using a sputtering gas containing O2 gas.

[0155] The experimental absorber film prepared as described above was subjected to the following measurements. The measurement results are shown in Table 1.

[0156] The elemental composition (atomic %) of the absorber films used in Experiments 1-7 was measured by X-ray photoelectron spectroscopy (XPS). In the following explanation, the elemental composition (atomic %) of the thin film may be referred to as "composition" or "composition ratio."

[0157] The film thickness of the experimental absorber membranes used in Experiments 1-7 was measured by XRR (X-ray reflectivity).

[0158] The refractive index (n) and extinction coefficient (k) of the experimental absorber films used in Experiments 1-7 at a wavelength of 13.5 nm were measured using an EUV reflectometer.

[0159] The membrane stress in Experiments 1-7 was evaluated by measuring the flatness of the experimental absorber membrane before and after deposition using a flatness measuring device (Tropel UltraFlat200) and comparing the two. Specifically, the membrane stress was evaluated by taking the difference between the flatness of the experimental absorber membrane before deposition and the flatness after deposition. The measurement results of the difference in flatness are shown in Table 1.

[0160] The etching rates for Experiments 1-7 were evaluated as follows. First, the etching rates of the absorber films used in Experiments 1-7 were measured when etched with a fluorine-based etching gas (a mixture of CF4 gas and oxygen (O2) gas, with a flow rate ratio of CF4:O2 = 90:10). Next, the etching rates were evaluated by determining the ratio of etching rates (relative etching rates) to the etching rate of Experiment 7 (material: Ir), which was set to 1. Table 1 shows the relative etching rates. Note that the absorber film used in Experiment 7 is a thin film made only of Ir and is an absorber film used for comparison with Experiments 1-6.

[0161] As is clear from Table 1, the extinction coefficient (k) at a wavelength of 13.5 nm was greater than 0.03 for the experimental absorber films in Experiments 1-6. The extinction coefficient (k) at a wavelength of 13.5 nm for the TaBN film used as absorber film 4 in Comparative Example 1, described later, was 0.03. TaBN film is currently one of the materials commonly used as absorber film 4 for reflective mask blanks 100. Therefore, it can be said that by using the experimental absorber films with the compositions of Experiments 1-6 as absorber film 4, an absorber film 4 with a high extinction coefficient (k) can be obtained. The experimental absorber film in Experiment 7 also has a high extinction coefficient (k), similar to Experiments 1-6.

[0162] As is clear from Table 1, the refractive index (n) at a wavelength of 13.5 nm of the experimental absorber films in Experiments 1-6 was less than 0.95. The TaBN film used as absorber film 4 in Comparative Example 1, described later, has a refractive index (n) of 0.95 at a wavelength of 13.5 nm. Therefore, it can be said that by using the experimental absorber films with the compositions of Experiments 1-6 as absorber film 4, an absorber film 4 with a low refractive index (n) can be obtained. The experimental absorber film in Experiment 7 also has a low refractive index (n), similar to Experiments 1-6.

[0163] As is clear from Table 1, the difference in flatness of the experimental absorber films used in Experiments 1-6 was less than 300 nm. In contrast, the difference in flatness of the experimental absorber film used in Experiment 7 (material: Ir) was 811 nm. Therefore, it can be said that by using the experimental absorber films used in Experiments 1-6 as absorber film 4, it is possible to obtain an absorber film 4 that can adjust the film stress and suppress the deformation of the reflective mask blank 100.

[0164] As is clear from Table 1, when the etching rate of the experimental absorber film (material: Ir) in Experiment 7 is set to 1, the relative etching rates of the experimental absorber films in Experiments 1-6 were 1.3-1.8. Therefore, it can be said that by using the experimental absorber films from Experiments 1-6 as absorber film 4, an absorber film 4 with a fast etching rate and good processability can be obtained.

[0165] Based on these results, it can be concluded that by using the experimental absorber films from Experiments 1 to 6 as the absorber film 4 of the reflective mask blank 100, it is possible to form a transfer pattern with a fine pattern shape on the transfer substrate and to manufacture a reflective mask 200 having a transfer pattern that allows for high-throughput EUV exposure.

[0166] (Example 1) As Example 1, a thin film with the same composition and thickness as the experimental absorbent film used in Experiment 5 was formed as absorbent film 4 to manufacture a reflective mask 200.

[0167] As shown in Figure 2, the reflective mask blank 100 of Example 1 has a back surface conductive film 5, a substrate 1, a multilayer reflective film 2, a protective film 3, and an absorber film 4 (buffer layer 42 and absorber layer 44). Note that a structure in which a resist film 11 is formed on the absorber film 4, as shown in Figure 3A, is also the reflective mask blank 100 of this embodiment. Figures 3A to 3D are schematic cross-sectional views of key parts illustrating the process of manufacturing a reflective mask 200 from the reflective mask blank 100.

[0168] First, we will describe the reflective mask blank 100 of Example 1.

[0169] A SiO2-TiO2 glass substrate was prepared in the same manner as in Experiments 1-7 and designated as Substrate 1. Polishing was performed in the same manner as in Experiments 1-7, consisting of a rough polishing process, a precision polishing process, a localized polishing process, and a touch polishing process.

[0170] Next, similar to experiments 1-7, a back surface conductive film 5 made of a CrN film was formed on the second main surface (back surface) of the SiO2-TiO2 glass substrate 1 by magnetron sputtering (reactive sputtering) under the following conditions. Formation conditions for the conductive film 5 on the back surface: Cr target, mixed gas atmosphere of Ar and N2 (Ar: 90%, N: 10%), film thickness 20 nm.

[0171] Next, similar to experiments 1-7, Si layers (4.2 nm) and Mo layers (2.8 nm) were alternately stacked 40 times on the main surface (first main surface) of the substrate 1 opposite to the side where the back surface conductive film 5 was formed, and finally a Si film with a thickness of 4.0 nm was deposited to form a multilayer reflective film 2.

[0172] Subsequently, a protective film 3 made of RuNb was deposited to a thickness of 3.5 nm, similar to experiments 1-7.

[0173] Next, a buffer layer 42 made of CrON was formed on the protective film 3. Specifically, the CrON film was deposited to a thickness of 6 nm by reactive sputtering using a Cr target in a mixed gas atmosphere of Ar gas, O2 gas, and N2 gas. Subsequently, an absorption layer 44 made of IrTaO film (composition ratio Ir:Ta:O = 52:4:44, film thickness 40 nm) was formed by DC magnetron sputtering, similar to Experiment 5. Therefore, the reflective mask blank 100 of Example 1 includes an absorber film 4 consisting of a buffer layer 42 made of CrON film and an absorption layer 44 made of IrTaO film.

[0174] As described above, the reflective mask blank 100 of Example 1 was manufactured.

[0175] The absorption layer 44 of the reflective mask blank 100 in Example 1 is the same thin film as the experimental absorber film in Experiment 5. Therefore, by using the reflective mask blank 100 in Example 1, it is possible to form a transfer pattern with a fine pattern shape on the transfer substrate and to manufacture a reflective mask 200 having a transfer pattern that allows for high-throughput EUV exposure.

[0176] Next, the reflective mask 200 of Example 1 was manufactured using the reflective mask blank 100 of Example 1.

[0177] A resist film 11 was formed to a thickness of 80 nm on the absorber film 4 of the reflective mask blank 100 (Figure 3A). Chemically amplified resist (CAR) was used to form the resist film 11. A desired pattern was drawn (exposed) on this resist film 11, and then developed and rinsed to form a predetermined resist pattern 11a (Figure 3B). Next, using the resist pattern 11a as a mask, dry etching of the absorber layer 44 (IrTaO film) was performed using a mixed gas of CF4 gas and O2 gas (CF4+O2 gas). Subsequently, dry etching of the CrON film (buffer layer 42) was performed using a mixed gas of Cl2 gas and O2 gas (Cl2+O2 gas) to form an absorber pattern 4a (Figure 3C).

[0178] Subsequently, the resist pattern 11a was removed by oxygen ashing (Figure 3D). Finally, wet washing with pure water (DIW) was performed to produce the reflective mask 200 of Example 1.

[0179] Furthermore, if necessary, a mask defect inspection can be performed after wet cleaning, and mask defects can be corrected as appropriate.

[0180] The reflective mask 200 of Example 1 was set in an EUV scanner, and EUV exposure was performed on a wafer on which the film to be processed and the resist layer were formed on the semiconductor substrate. Then, by developing the exposed resist of the resist layer, a resist transfer pattern was formed on the semiconductor substrate on which the film to be processed was formed.

[0181] It was confirmed that by forming a resist transfer pattern on the substrate to be transferred using the reflective mask 200 of Example 1, it is possible to form a transfer pattern with a fine pattern shape and to perform EUV exposure at a high throughput.

[0182] By transferring this resist transfer pattern to the workpiece by etching, and then going through various processes such as forming insulating films and conductive films, introducing dopants, and annealing, we were able to manufacture a semiconductor device with the desired properties.

[0183] (Example 2) As Example 2, the procedure was the same as in Example 1, but a thin film with the same composition and thickness as the experimental absorber film used in Experiment 6 was formed as the absorption layer 44 to produce a reflective mask blank 100 and a reflective mask 200. That is, the reflective mask blank 100 and reflective mask 200 of Example 2 are the same as in Example 1, except that the absorption layer 44 (IrTaO film, thickness 40 nm) has a composition ratio of Ir:Ta:O = 70:11:19. Therefore, the reflective mask blank 100 of Example 2 includes an absorber film 4 consisting of a buffer layer 42 of a CrON film and an absorption layer 44 of an IrTaO film.

[0184] The absorption layer 44 of the reflective mask blank 100 in Example 2 is the same thin film as the experimental absorber film in Experiment 6. Therefore, by using the reflective mask blank 100 of Example 2, it is possible to form a transfer pattern with a fine pattern shape on the transfer substrate and to manufacture a reflective mask 200 having a transfer pattern that allows for high-throughput EUV exposure.

[0185] Furthermore, it was confirmed that by forming a resist transfer pattern on the substrate to be transferred using the reflective mask 200 of Example 2, it is possible to form a transfer pattern with a fine pattern shape and to perform EUV exposure at a high throughput.

[0186] (Comparative Example 1) As Comparative Example 1, a reflective mask blank 100 and a reflective mask 200 were manufactured, which were basically the same as in Example 1, but with a TaBN film with a thickness of 55 nm formed as the absorber film 4. That is, the reflective mask blank 100 and reflective mask 200 of Comparative Example 1 are the same as in Example 1, except that the absorber film 4 is a TaBN film (Ta:B:N = 75:12:13 (composition ratio)), the film thickness is 55 nm, and there is no buffer layer 42. The reason for setting the film thickness of the TaBN film to 55 nm is that the extinction coefficient (k) of the TaBN film is lower than the extinction coefficient (k) of the absorber film 4 (IrTaO film) used in Examples 1 and 2.

[0187] In addition, when dry etching the absorber film 4 (TaBN film) to manufacture the reflective mask 200 of Comparative Example 1, the absorber pattern 4a was formed by dry etching the TaBN film using a mixed gas of CF4 gas and He gas (CF4+He gas) (Figure 3C).

[0188] The absorber film 4 of the reflective mask blank 100 in Comparative Example 1 is a TaBN film. The extinction coefficient (k) of this TaBN film at a wavelength of 13.5 nm was 0.03, and the refractive index (n) was 0.95. Therefore, the extinction coefficient (k) of the absorber film 4 in Comparative Example 1 is lower than that of the absorber film 4 in Examples 1 and 2. Also, the refractive index (n) of the absorber film 4 in Comparative Example 1 is higher than that of the absorber film 4 in Examples 1 and 2. Furthermore, as shown in Figure 5, it is clear that the value of the normalized evaluation function when a thin film containing Ta is used as the absorber film 4 is higher than the value of the normalized evaluation function when a thin film containing Ir is used as the absorber film 4. Therefore, when using the reflective mask blank 100 in Comparative Example 1, it was not easy to form a transfer pattern with a fine pattern shape on the transfer substrate compared to Examples 1 and 2, and it could not be said that EUV exposure could be performed at a high throughput.

[0189] Furthermore, by forming a resist transfer pattern on the substrate using the reflective mask 200 of Comparative Example 1, it was possible to form a transfer pattern with a relatively fine pattern shape. However, because the thickness of the absorber film 4 in Comparative Example 1 was thicker than that of the absorber film 4 in Examples 1 and 2, a decrease in transfer accuracy, presumably due to the shadowing effect, was observed.

[0190] [Table 1]

[0191] [Table 2] [Explanation of symbols]

[0192] 1 circuit board 2 Multilayer reflective film 3 Protective film 4 Absorbent membrane 4a Absorber pattern 5. Conductive film on the back surface 42 Buffer Layers 44 Absorption layer 11. Resist film 11a Resist Pattern 100 Reflective Mask Blanks 200 Reflective Masks

Claims

1. A reflective mask blank comprising a substrate, a multilayer reflective film on the substrate, and an absorbent film on the multilayer reflective film, The absorber membrane contains iridium (Ir) and an additive element. The aforementioned additive element is tantalum (Ta), The iridium (Ir) content in the absorber membrane is more than 50 atomic percent. The content of the additive element in the absorbent membrane is 2 to 20 atomic percent. The reflective mask blank is characterized in that the absorbent membrane further contains oxygen (O).

2. The reflective mask blank according to Claim 1, characterized in that the content ratio of Ir to the additive element in the absorber membrane is 4:1 to 22:

1.

3. The reflective mask blank according to claim 1 or 2, characterized in that the oxygen (O) content is 5 atomic percent or more.

4. The reflective mask blank according to any one of claims 1 to 3, characterized in that the oxygen (O) content is 60 atomic percent or less.

5. A reflective mask blank according to any one of claims 1 to 4, characterized in that the refractive index of the absorber film is in the range of 0.86 to 0.95, and the extinction coefficient of the absorber film is in the range of 0.015 to 0.

065.

6. The absorbent membrane includes a buffer layer and an absorbent layer provided on the buffer layer. The buffer layer contains chromium (Cr), The reflective mask blank according to any one of claims 1 to 5, characterized in that the absorption layer comprises iridium (Ir) and the additive element.

7. The thickness of the absorber film is 50 nm or less. The reflective mask blank according to claim 6, characterized in that the thickness of the buffer layer is 10 nm or less.

8. The absorbent membrane includes an uppermost layer and other lower layers. The uppermost layer comprises iridium (Ir) and the additive element, The reflective mask blank according to any one of claims 1 to 5, characterized in that the lower layer comprises at least one metal selected from silver (Ag), cobalt (Co), platinum (Pt), gold (Au), iron (Fe), palladium (Pd), tungsten (W), chromium (Cr), rhodium (Rh), and ruthenium (Ru), an alloy containing two or more metals, or a compound thereof.

9. An etching mask film is provided on the absorber film, The reflective mask blank according to any one of claims 1 to 8, characterized in that the etching mask film comprises chromium (Cr) and at least one selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H).

10. A reflective mask characterized in that the absorbent film in the reflective mask blank according to any one of claims 1 to 9 has a patterned absorbent pattern.

11. A method for manufacturing a semiconductor device, characterized by comprising the steps of setting a reflective mask according to claim 10 in an exposure apparatus having an exposure light source that emits EUV light, and transferring a transfer pattern to a resist film formed on a substrate to be transferred.

Images