Reflection type photomask blank, and method for manufacturing reflection type photomask

Abstract

SOLUTION: To provide a reflection type photomask blank comprising: a substrate; a multilayer reflection film which reflects exposure light being extreme ultraviolet region light; a protection film; a light absorption film which absorbs exposure light; and a hard mask film, where the protection film is made up of a first layer provided on the substrate side and a second layer provided on a side separate from the substrate, the second layer of the protection film is formed of a material having resistance to dry etching capable of etching the light absorption film, the light absorption film has a phase shift function and is formed of a single layer or a plurality of layers, and each layer constituting the single layer and the plurality of layers is formed of a material having ruthenium (Ru) as a main component.EFFECT: A fine assist pattern can be formed on a light absorption film having a phase shift function without damaging a multilayer reflection film caused by etching (patterning) of a light absorption film, and a reflection type photomask having a pattern of the light absorption film on which the assist pattern is formed and has a phase shift function can be manufactured.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a reflective photomask used in the manufacture of semiconductor devices and the like, and to a reflective photomask blank used as a material for the reflective photomask in the manufacture thereof. [Background technology]

[0002] As semiconductor devices become increasingly miniaturized, particularly with the increasing integration of large-scale integrated circuits, higher pattern resolution is required for projection exposure. To address this issue, phase-shift masks have been developed as a photomask technology to improve the resolution of transferred patterns. The principle of phase shifting is that the phase of light passing through an opening in the phase-shift film of a photomask is adjusted to be approximately 180 degrees inverted relative to the phase of light passing through the portion of the phase-shift film adjacent to the opening. This causes interference between the transmitted light at the boundary between the opening and the adjacent portion, reducing the light intensity. As a result, the resolution and depth of focus of the transferred pattern are improved. Photomasks that use this principle are collectively called phase-shift masks.

[0003] The most common phase shift mask blanks (transmissive phase shift mask blanks) used as materials for manufacturing conventional phase shift masks (transmissive phase shift masks) have a structure in which a phase shift film is laminated on a transparent substrate such as a glass substrate, and a film formed from a chromium (Cr)-containing material is laminated on the phase shift film. Phase shift films typically have a phase difference of 175 to 185 degrees and a transmittance of approximately 6 to 30% relative to the exposure light, and are typically formed from silicon (Si)-containing materials, particularly materials containing molybdenum (Mo) and silicon (Si). The film formed from the chromium (Cr)-containing material is adjusted to a thickness that, when combined with the phase shift film, achieves the desired optical density. The film formed from the chromium (Cr)-containing material is typically used as both a light-shielding film and an etching mask (hard mask) when etching the phase shift film.

[0004] A typical method for manufacturing a phase shift mask by patterning a phase shift film from a phase shift mask blank having a transparent substrate on which a phase shift film made of a silicon (Si)-containing material and a light-shielding film made of a chromium (Cr)-containing material are formed in this order is as follows: First, a resist film is formed on the light-shielding film made of the chromium (Cr)-containing material of the phase shift mask blank, and a pattern is written on the resist film using light or an electron beam and developed to form a resist pattern. Next, using the resist pattern as an etching mask, the light-shielding film made of the chromium (Cr)-containing material is dry-etched with a chlorine-based gas to form a light-shielding film pattern. Furthermore, using the light-shielding film pattern as an etching mask, the phase shift film made of a silicon (Si)-containing material is dry-etched with a fluorine-based gas to form a phase shift film pattern. The resist pattern is then removed, and the light-shielding film pattern is removed by dry-etching with a chlorine-based gas.

[0005] In this case, a light-shielding film is left outside the portion where the phase shift film pattern (circuit pattern) is formed, and the outer peripheral edge of the phase shift mask is formed as a light-shielding portion (light-shielding pattern) with an optical density of 3 or more, combining the phase shift film and the light-shielding film. This is to prevent exposure light from leaking from the outer peripheral edge of the phase shift mask and irradiating the resist film on an adjacent chip on the wafer from the portion outside the circuit pattern when the circuit pattern is transferred to the wafer using a wafer exposure device. A typical method for forming such a light-shielding pattern involves forming a phase shift film pattern, removing the resist pattern, forming a new resist film, and then patterning and developing the resist pattern, leaving the resist film on the outer peripheral edge of the phase shift mask. Using this resist pattern as an etching mask, a film made of a material containing chromium (Cr) is etched, leaving the light-shielding film on the outer peripheral edge of the phase shift mask.

[0006] For phase-shift masks, which require high-precision pattern formation, dry etching using gas plasma is the mainstream. For films made of chromium (Cr)-containing materials, dry etching using chlorine-based gases (chlorine-based dry etching) is used. For films made of silicon (Si)-containing materials or films containing molybdenum (Mo) and silicon (Si), dry etching using fluorine-based gases (fluorine-based dry etching) is used. In particular, for chlorine-based dry etching of films made of chromium (Cr)-containing materials, dry etching using an oxygen-containing chlorine-based gas, such as a mixture of chlorine gas (Cl2 gas) and 10 to 25% by volume of oxygen gas (O2 gas), is known to enhance chemical reactivity and improve the etching rate.

[0007] As circuit patterns become finer, technology is required to form finer circuit patterns on phase shift masks. In particular, assist patterns for line patterns, which support the resolution of the main pattern of a phase shift mask, must be smaller than the main pattern so that they are not transferred to the wafer when the circuit pattern is transferred to the wafer using a wafer exposure tool. For phase shift masks of the generation in which the half pitch of the circuit line and space pattern on the wafer is 10 nm, the line width of the assist patterns for the circuit line pattern on the phase shift mask is required to be approximately 40 nm.

[0008] On the other hand, chemically amplified resists are commonly used as resists. Chemically amplified resists, which can form fine patterns, consist of a base resin, an acid generator, a surfactant, etc., and can be used in many reactions in which the acid generated by exposure acts as a catalyst, making it possible to achieve high sensitivity. The use of chemically amplified resists makes it possible to form fine patterns with line widths of 0.1 μm or less when forming mask patterns such as phase shift film patterns. The resist is applied to the photomask blank by spin coating using a resist coater.

[0009] However, resists are no longer able to keep up with the miniaturization of circuit patterns. The thickness of the resist film used in cutting-edge phase-shift mask blanks is 100 to 150 nm. The reason it is difficult to form finer assist patterns on phase-shift masks is that the resist pattern for forming the assist pattern, which is formed on a light-shielding film made of a material containing chromium (Cr), has a high aspect ratio. During the development process of resist pattern formation, the resist pattern collapses due to impact from the developer or pure water during rinsing.

[0010] One way to reduce the impact of the developer or the pure water during rinsing is to reduce the aspect ratio of the resist pattern. This requires a thinner resist film. However, if the resist film is thinned, it may disappear during dry etching of a light-shielding film made of a chromium (Cr)-containing material. This results in pinhole defects being formed in the light-shielding film made of a chromium (Cr)-containing material. When a phase shift film is dry-etched using the light-shielding film made of a chromium (Cr)-containing material as an etching mask, plasma generated during etching of the phase shift film may reach the phase shift film through the pinholes, resulting in pinhole defects in the phase shift film. This prevents the manufacture of a phase shift mask that functions properly in wafer manufacturing.

[0011] To solve this problem, a hard mask film made of a material containing silicon (Si) but not chromium (Cr) is provided on a light-shielding film made of a material containing chromium (Cr). In this case, the hard mask film made of a material containing silicon (Si) but not chromium (Cr) is a thin film with a thickness of 5 to 15 nm, and the thickness of the resist film formed on the hard mask film can be set to 80 to 110 nm, which is relatively thin.

[0012] When dry etching a light-shielding film made of a material containing chromium (Cr) using a chlorine-based gas containing oxygen, it is necessary to perform over-etching of 100 to 300% of the clear time in addition to the clear time required for the light-shielding film made of a material containing chromium (Cr) to disappear. This is because chlorine-based dry etching containing oxygen is an isotropic etching dominated by chemical components, and the pattern of the light-shielding film made of a material containing chromium (Cr) is insufficiently etched at the boundary with the phase shift film, resulting in a footing shape and preventing the desired pattern width from being stably formed.

[0013] Furthermore, because oxygen-containing chlorine-based dry etching is an isotropic etching process dominated by chemical components, oxygen-containing chlorine-based plasma moves both vertically and horizontally relative to the substrate, causing side etching of the pattern of the light-shielding film made of a material containing chromium (Cr). To make the critical dimension (CD), which is the pattern line width, uniform across the entire surface of the light-shielding film made of a material containing chromium (Cr), it is necessary to obtain the same amount of side etching across the entire surface of the light-shielding film made of a material containing chromium (Cr). To achieve this, long dry etching times are required until the amount of side etching reaches saturation and stabilizes.

[0014] On the other hand, when dry etching a phase shift film made of a silicon (Si)-containing material using a fluorine-based gas, over-etching is performed for up to about 20% of the clear time (e.g., a short over-etching of 1 to 6 seconds) in addition to the clear time required for the silicon (Si)-containing phase shift film to disappear. The transparent substrate in contact with the phase shift film is also slightly etched by dry etching to adjust the phase difference to 175 to 185 degrees with respect to the exposure light. In this case, the phase shift film made of a silicon (Si)-containing material is typically set to an initial phase difference of 175 to 179 degrees, and the transparent substrate is then dug by over-etching to achieve the desired phase difference, i.e., 175 to 185 degrees.

[0015] The reason why fluorine-based dry etching can achieve the desired characteristics with short over-etching times is that fluorine-based dry etching is anisotropic etching dominated by physical components, so the pattern of the phase shift film made of a material containing silicon (Si) does not have a trailing shape at the boundary with the substrate, and the fluorine-based plasma moves perpendicular to the substrate surface, faithfully reproducing the CD of the light-shielding film made of a material containing chromium (Cr) that functions as an etching mask, so long over-etching is not required.

[0016] Because fluorine-based dry etching is anisotropic etching dominated by physical components, the amount of resist loss is generally greater than that in chlorine-based dry etching. Therefore, a resist film for forming a pattern on a hard mask film made of a silicon (Si)-containing material must be thick enough. However, a hard mask film made of a silicon (Si)-containing material functions as an etching mask when a light-shielding film made of a chromium (Cr)-containing material is dry-etched using a chlorine-based gas. Because the hard mask film has sufficient etching resistance to the chlorine-based gas, it is possible to thin the hard mask film made of a silicon (Si)-containing material. A thinner hard mask film made of a silicon (Si)-containing material shortens the fluorine-based dry etching time for the hard mask film, and as a result, the resist film required for forming a pattern on a hard mask film made of a silicon (Si)-containing material can also be thinned.

[0017] For these reasons, by using a hard mask film formed from a material containing silicon (Si), it is possible to thin the resist film used in etching the hard mask film, specifically the resist film initially used in a phase shift mask blank. Furthermore, by thinning the resist film, the aspect ratio of the resist pattern is reduced, which reduces the impact of impact from the developer or pure water during rinsing in the development step of resist pattern formation, allowing for the formation of a good assist pattern and achieving high resolution of the transfer pattern.

[0018] A typical method for manufacturing a phase shift mask by patterning a phase shift film from a phase shift mask blank having a phase shift film made of a silicon (Si)-containing material, a light-shielding film made of a chromium (Cr)-containing material, and a hard mask film made of a silicon (Si)-containing material formed in that order on a transparent substrate is as follows: First, a resist film is formed on the hard mask film, and a pattern is written on the resist film using light or an electron beam and developed to form a resist pattern. Next, using the resist pattern as an etching mask, the hard mask film made of a silicon (Si)-containing material is dry-etched using a fluorine-based gas to form a hard mask film pattern, and then the resist pattern is removed. Next, using the hard mask film pattern as an etching mask, the light-shielding film made of a chromium (Cr)-containing material is dry-etched using a chlorine-based gas to form a light-shielding film pattern. Furthermore, using the pattern of the light-shielding film as an etching mask, a phase shift film formed of a material containing silicon (Si) is dry-etched using a fluorine-based gas to form a pattern of the phase shift film and at the same time remove the pattern of the hard mask film, and then the pattern of the light-shielding film is removed by etching using a chlorine-based gas.

[0019] However, the higher pattern resolution required for projection exposure in recent years has become difficult to achieve even with phase shift masks. Therefore, for the logic 7nm generation and beyond, EUV lithography, which uses extreme ultraviolet light (EUV light) as the exposure light, has begun to be used.

[0020] Extreme ultraviolet light is easily absorbed by all materials, making it impossible to apply transmissive lithography, such as conventional photolithography using ArF excimer laser light. Therefore, lithography using extreme ultraviolet light (EUV (Extreme Ultraviolet) light) as exposure light (EUV lithography) uses a reflective optical system. The wavelength of extreme ultraviolet light used in EUV lithography is 13 to 14 nm, while the wavelength of conventional ArF excimer laser light is 193 nm. Therefore, compared to photolithography using conventional ArF excimer laser light, EUV lithography has a shorter exposure wavelength, making it possible to transfer finer patterns onto a reflective photomask.

[0021] Reflective photomask blanks used in EUV lithography generally have a structure in which a reflective film that reflects extreme ultraviolet light, a protective film to protect the reflective film, and a light-absorbing film that absorbs extreme ultraviolet light are formed in this order on a substrate such as a glass substrate. The reflective film is a multilayer reflective film, which is composed of alternating low-refractive index layers and high-refractive index layers, thereby increasing the reflectivity when extreme ultraviolet light is irradiated onto the surface of the reflective film. Typically, molybdenum (Mo) layers are used as the low-refractive index layers, and silicon (Si) layers are used as the high-refractive index layers. Ruthenium (Ru) films are typically used as the protective films. Meanwhile, materials with a high absorption coefficient for extreme ultraviolet light, specifically materials containing chromium (Cr) or tantalum (Ta) as the main components, are used for the light-absorbing films. In the early generation of EUV lithography, binary reflective photomasks, in which the light-absorbing films do not reflect light, are used.

[0022] A reflective photomask blank is used to produce a reflective photomask, in which a light-absorbing film of the reflective photomask blank is patterned. A reflective photomask blank has a substrate on which a reflective film that reflects extreme ultraviolet region light, a protective film for protecting the reflective film, and a light-absorbing film that absorbs extreme ultraviolet region light are formed in this order. Specifically, the following method is commonly used to produce a reflective photomask by patterning the light-absorbing film. First, a resist film is formed on the light-absorbing film, and a pattern is written on this resist film using light or an electron beam, followed by development to form a resist pattern. Next, the light-absorbing film is patterned using the resist pattern as an etching mask to form a pattern of the light-absorbing film, and then the resist pattern is removed.

[0023] In binary-type reflective photomasks used in EUV lithography, the line and space assist patterns that support the resolution of the main pattern become smaller as the main pattern becomes finer, and the line width of the assist pattern needs to be reduced to about 30 nm, especially about 25 nm. Therefore, compared to transmissive phase-shift mask blanks, binary-type reflective photomask blanks require even thinner resist films. In order to form line and space assist patterns of about 30 nm, especially about 25 nm, in a reflective photomask, the thickness of the resist film needs to be 80 nm or less.

[0024] Furthermore, in EUV lithography, an optical system with an exposure machine numerical aperture (NA) of 0.33 to 0.55 is used to form finer patterns on the wafer. In this case, in reflective photomasks, assist patterns (line and space patterns) that support the resolution of the main pattern become even smaller as the main pattern becomes finer, and the line width of the assist pattern needs to be finer, to 20 nm or less, especially to around 18 nm. Therefore, reflective photomask blanks for reflective photomasks used in exposure machines with a numerical aperture (NA) of 0.55 require even thinner resist films.

[0025] For example, when a pattern (circuit pattern) of a light-absorbing film containing tantalum (Ta) as a main component is formed by fluorine-based dry etching using a resist pattern as an etching mask, the fluorine-based dry etching is anisotropic etching in which physical components are dominant, and the etching rate for the resist pattern is relatively fast. Therefore, if the resist pattern is too thin, the resist pattern will disappear during the dry etching of the light-absorbing film, resulting in the formation of pinhole defects in the light-absorbing film, making it impossible to manufacture a reflective photomask that functions normally in EUV lithography.

[0026] To prevent pinhole defects, the resist film must be thickened. However, the thicker the resist film, the higher the aspect ratio of the resist pattern required to form a finer assist pattern. Therefore, in the development step of resist pattern formation, the resist pattern collapses due to impact from the developer or pure water during rinsing, making it impossible to obtain the desired resolution.

[0027] Furthermore, in EUV lithography, reflective photomasks that utilize the phase shift effect are used to form finer patterns on wafers for the logic 5nm generation and beyond. By using a phase-shift reflective photomask, higher wafer transfer characteristics (NILS (Normalized Image Log Slope): the contrast of light intensity transferred onto the wafer) can be obtained than with a binary reflective photomask, allowing finer patterns to be formed on the wafer.

[0028] In this case, in a reflective phase-shift photomask, the assist patterns of line patterns and space patterns that assist the resolution of the main pattern become even smaller as the main pattern becomes finer. Therefore, compared with a binary-type reflective photomask blank, a reflective phase-shift photomask blank requires a thinner resist film, and an etching mask film (hard mask film) that assists dry etching is required.

[0029] For example, International Publication No. 2015 / 098400 (Patent Document 1) describes a reflective mask blank for EUV lithography, which includes, on a substrate, a multilayer reflective film that reflects EUV light, a Ru-based protective film that protects the multilayer reflective film, an anti-diffusion layer that suppresses interdiffusion due to thermal diffusion between the protective film and a phase shift film (absorber film), a phase shift film (absorber film) that is composed of a laminated structure of multiple materials and absorbs EUV light while reflecting a portion of it to shift the phase, and an etching mask film, which are formed in this order. The reflective mask obtained from this reflective mask blank achieves a phase difference of 170 to 190 degrees between light reflected from the phase shift film (absorber film) in the patterned portion and light reflected from the multilayer reflective film without the phase shift film (absorber film) pattern, thereby achieving high contrast. Furthermore, the formation of the etching mask film allows the resist film to be thinner, which is advantageous for pattern miniaturization.

[0030] Furthermore, International Publication No. 2015 / 098400 (Patent Document 1) describes a method for fabricating a reflective mask from a reflective mask blank for EUV lithography. In this method, a resist film is first formed on the etching mask film of the reflective mask blank, a desired pattern is drawn (exposed) on the resist film, and a predetermined resist film pattern is formed by developing and rinsing. Next, using the resist film pattern as a mask, dry etching is performed with a fluorine-based gas to form an etching mask film pattern. Next, using the resist film pattern and the etching mask film pattern as masks, dry etching is performed on a chromium-based material layer with a mixed gas of Cl and O, and then dry etching is performed on a tantalum-based material layer with Cl gas to form a phase shift film (absorber film) pattern. Finally, the etching mask film pattern is etched away with a fluorine-based gas to obtain a reflective mask. [Prior art documents] [Patent documents]

[0031] [Patent Document 1] International Publication No. 2015 / 098400 Summary of the Invention [Problem to be solved by the invention]

[0032] In International Publication No. 2015 / 098400 (Patent Document 1), a phase shift film (absorber film) is fabricated as a multi-layer structure of a tantalum-based material layer and a chromium-based material layer or a ruthenium-based material layer, or as a multi-layer structure of a tantalum-based material layer, a chromium-based material layer, and a ruthenium-based material layer, to achieve phase shifting functionality. However, the tantalum-based material layer is etched with an oxygen-free chlorine-based gas, while the chromium-based material layer and the ruthenium-based material layer are etched with an oxygen-containing chlorine-based gas. To obtain a pattern in the phase shift film (absorber film), two types of dry etching using different gases are required. In this case, the etching rate differs for each layer, making it difficult to control the amount of side etching. It is also difficult to form a uniform pattern of the multi-material layer structure perpendicular to the substrate. Therefore, a phase shift film (absorber film) with poor perpendicularity cannot achieve sufficient resolution for finer patterns. Furthermore, when the phase shift film has a laminated structure of multiple materials and a pattern of the phase shift film is formed from the phase shift film, a complicated process such as changing the dry etching gas becomes necessary, which leads to a decrease in productivity.

[0033] On the other hand, as a material for the phase shift film (light absorbing film) in a reflective photomask, a material containing ruthenium (Ru) is advantageous in terms of optical properties (light absorption properties, phase shift properties) against extreme ultraviolet light. However, in the case of a phase shift film (light absorbing film) formed from a material containing ruthenium (Ru), if a material containing ruthenium (Ru), which is effective as a material for protecting a multilayer reflective film, is used as a protective film, the protective film will also be etched during etching (patterning) of the phase shift film, and the protective film will not be able to function as a film for protecting the multilayer reflective film.

[0034] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a reflective photomask blank that allows a fine assist pattern to be formed in a light-absorbing film without damaging the multilayer reflective film due to etching (patterning) of the light-absorbing film, and a method for producing a reflective photomask from the reflective photomask blank. [Means for solving the problem]

[0035] The present inventors have conducted extensive research to solve the above-mentioned problems regarding reflective photomask blanks using a light-absorbing film made of a material containing ruthenium (Ru), which is an excellent material for light-absorbing films having a phase shift function. As a result, they have found that the above-mentioned problems can be solved by forming the light-absorbing film having a phase shift function from a single layer containing ruthenium (Ru) as a main component or multiple layers consisting of only layers containing ruthenium (Ru) as a main component, providing a hard mask film on the light-absorbing film, and further forming a protective film from a first layer and a second layer, with the second layer in contact with the light-absorbing film being made of a material that is resistant to dry etching that can etch the light-absorbing film, thereby completing the present invention.

[0036] Therefore, the present invention provides the following reflective photomask blank and method for producing a reflective photomask. 1. A photomask comprising: a substrate; a multilayer reflective film formed on the substrate and reflecting exposure light in the extreme ultraviolet region; a protective film formed on the multilayer reflective film; a light absorbing film formed on and in contact with the protective film and absorbing the exposure light; and a hard mask film formed on and in contact with the light absorbing film; the protective film comprises a first layer provided on the substrate side and a second layer provided on the side away from the substrate, the second layer of the protective film is formed of a material that is resistant to dry etching that can etch the light absorbing film, The light absorbing film has a phase shift function and is formed of a single layer or multiple layers, and each layer constituting the single layer and the multiple layers is formed of a material containing ruthenium (Ru) as a main component. A reflective photomask blank characterized by: 2. The second layer of the protective film is formed of a material that is resistant to chlorine-based dry etching containing oxygen, 2. The reflective photomask blank according to 1, wherein the light absorbing film is formed from a material that can be etched by chlorine-based dry etching that includes oxygen. 3. The second layer of the protective film is formed of a material that is resistant to chlorine-based dry etching containing oxygen and is resistant to chlorine-based dry etching not containing oxygen; the light absorbing film is formed of a material that can be etched by chlorine-based dry etching containing oxygen, has resistance to chlorine-based dry etching not containing oxygen, and has resistance to fluorine-based dry etching; The hard mask film is formed of a material that is resistant to chlorine-based dry etching containing oxygen, can be etched by chlorine-based dry etching not containing oxygen, and can be etched by fluorine-based dry etching. 3. The reflective photomask blank according to 2. 4. The reflective photomask blank according to 3, wherein the first layer of the protective film is formed from a material that is resistant to oxygen-free chlorine-based dry etching. 5. The reflective photomask blank described in 1, characterized in that the material containing ruthenium (Ru) as a main component contains ruthenium (Ru) at a content of 20 atomic % or more and is a material that contains ruthenium (Ru) most abundantly in terms of atomic ratio to the total amount of metal elements and semi-metal elements. 6. The reflective photomask blank according to 1, wherein the light absorbing film has a phase shift function with a reflectance of 8% or more and 28% or less and a phase difference of 180 degrees or more and 240 degrees or less for the exposure light. 7. The reflective photomask blank according to 1, wherein the thickness of the light-absorbing film is 28 nm or more and 50 nm or less. 8. The reflective photomask blank according to 1, wherein the second layer of the protective film is formed from a material containing at least one element selected from tantalum (Ta) and silicon (Si), and oxygen (O). 9. The reflective photomask blank according to 8, wherein the hard mask film is formed from a material containing silicon (Si) and nitrogen (N). 10. The reflective photomask blank according to 9, wherein the first layer of the protective film is formed from a material containing ruthenium (Ru). 11. The reflective photomask blank according to 1, wherein the thickness of the second layer of the protective film is 1 nm or more and 10 nm or less. 12. The reflective photomask blank according to 11, wherein the thickness of the first layer of the protective film is 1 nm or more and 6 nm or less. 13. The reflective photomask blank according to 1, wherein the thickness of the hard mask film is 2 nm or more and 16 nm or less. 14. A method for producing a reflective photomask comprising the substrate, the multilayer reflective film, the protective film, and the light-absorbing film pattern from the reflective photomask blank according to 3 or 9, comprising the steps of: (A) forming a resist film on and in contact with the hard mask film; (B) patterning the resist film to form a resist pattern; (C) patterning the hard mask film by fluorine-based dry etching using the resist pattern as an etching mask to form a hard mask film pattern; (D) removing the resist pattern; (E) patterning the light absorbing film by chlorine-based dry etching containing oxygen using the pattern of the hard mask film as an etching mask to form a pattern of the light absorbing film; (F) removing the pattern of the hard mask film by oxygen-free chlorine-based dry etching; A method for manufacturing a reflective photomask, comprising: 15. The manufacturing method according to 14, wherein the thickness of the resist film is 60 nm or less, and the pattern of the light absorbing film includes a line pattern having a width of 20 nm or less. [Effects of the Invention]

[0037] According to the reflective photomask blank of the present invention, a fine assist pattern can be formed in a light-absorbing film having a phase shift function without damaging the multilayer reflective film due to etching (patterning) of the light-absorbing film, and a reflective photomask having an assist pattern and a pattern of the light-absorbing film having a phase shift function can be manufactured. In particular, the reflective photomask blank of the present invention can form an assist pattern having a line width of 20 nm or less, particularly 18 nm or less, in the light-absorbing film having a phase shift function using a thin resist film, for example, a resist film having a thickness of 60 nm or less. [Brief explanation of the drawings]

[0038] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a first embodiment of a reflective photomask blank of the present invention. [Figure 2] 1 is a cross-sectional view showing an example of a reflective photomask of the present invention. [Figure 3] FIG. 2 is a cross-sectional view showing an example of a second embodiment of the reflective photomask blank of the present invention. [Figure 4] 1(A) to 1(F) are cross-sectional views illustrating the steps of producing a reflective photomask from the reflective photomask blank of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be described in more detail below. The reflective photomask blank of the present invention comprises a substrate, a multilayer reflective film formed on the substrate, a protective film formed on the multilayer reflective film, a light-absorbing film formed on the protective film, and a hard mask film formed on the light-absorbing film. In the reflective photomask blank of the present invention, the protective film comprises a first layer provided on the substrate side and a second layer provided on the side away from the substrate.

[0040] The structures of the reflective photomask blank and reflective photomask of the present invention will be described below with reference to the drawings. In the description of the drawings, the same components are given the same reference numerals and their description may be omitted. Furthermore, the drawings may be enlarged for convenience, and the dimensional ratios of the components may not necessarily be the same as in reality.

[0041] 1 is a cross-sectional view showing an example of a first embodiment of a reflective photomask blank of the present invention. This reflective photomask blank 101 has a substrate 1, a multilayer reflective film 2 formed on and in contact with the substrate 1, a protective film 3 formed on and in contact with the multilayer reflective film 2, a light-absorbing film 4 formed on and in contact with the protective film 3, and a hard mask film 5 formed on and in contact with the light-absorbing film 4. The protective film 3 consists of a first layer 31 formed in contact with the multilayer reflective film 2 and a second layer 32 formed in contact with the light-absorbing film 4. In the reflective photomask blank 101 of the first embodiment, the multilayer reflective film 2, the first layer 31 of the protective film 3, the second layer 32 of the protective film 3, the light-absorbing film 4, and the hard mask film 5 are laminated in this order from the substrate 1 side.

[0042] From the reflective photomask blank of the present invention, it is possible to obtain a reflective photomask comprising, for example, a substrate, a multilayer reflective film formed on the substrate, a protective film formed on the multilayer reflective film, a light absorbing film formed on the protective film, and a pattern of the light absorbing film formed on the protective film (circuit pattern or photomask pattern).

[0043] 2 is a cross-sectional view showing an example of a reflective photomask of the present invention. This reflective photomask 200 has a substrate 1, a multilayer reflective film 2 formed on and in contact with the substrate 1, a protective film 3 formed on and in contact with the multilayer reflective film 2, and a light-absorbing film pattern 4a formed on and in contact with the protective film 3. The protective film 3 consists of a first layer 31 formed on and in contact with the multilayer reflective film 2 and a second layer 32 formed on and in contact with the light-absorbing film pattern 4a. In this reflective photomask 200, the multilayer reflective film 2, the first layer 31 of the protective film 3, the second layer 32 of the protective film 3, and the light-absorbing film pattern 4a are stacked in this order from the substrate 1 side.

[0044] In the present invention, chlorine (Cl)-based dry etching containing oxygen (O) (dry etching using chlorine (Cl)-based gas containing oxygen (O)) includes dry etching using a chlorine-based gas containing oxygen gas (O gas) together with chlorine gas (Cl gas), specifically, dry etching using an etching gas consisting of chlorine gas (Cl gas) and oxygen gas (O gas).

[0045] In the present invention, chlorine (Cl)-based dry etching that does not contain oxygen (O) (dry etching using a chlorine (Cl)-based gas that does not contain oxygen (O)) includes dry etching that uses a chlorine-based gas that contains chlorine gas (Cl gas) but does not contain oxygen gas (O gas), specifically, an etching gas made of chlorine gas (Cl gas).

[0046] In the present invention, fluorine (F)-based dry etching (dry etching using a fluorine (F)-based gas) includes dry etching using a fluorine-based gas such as carbon tetrafluoride gas (CF4 gas) or sulfur hexafluoride gas (SF6 gas), specifically dry etching using an etching gas containing carbon tetrafluoride gas (CF4 gas) or sulfur hexafluoride gas (SF6 gas) and a rare gas such as helium gas (He gas), particularly dry etching using an etching gas consisting of carbon tetrafluoride gas (CF4 gas) or sulfur hexafluoride gas (SF6 gas) and helium gas (He gas).

[0047] In the present invention, a material is considered to be resistant to oxygen-containing chlorine-based dry etching when the etching rate by oxygen-containing chlorine-based dry etching is preferably less than 5 nm / min, more preferably 0.8 nm / min or less, and even more preferably 0.6 nm / min or less, and a material is considered to be etchable by oxygen-containing chlorine-based dry etching when the etching rate by oxygen-containing chlorine-based dry etching is preferably 5 nm / min or more, more preferably 6 nm / min or more.

[0048] In the present invention, a material is considered to be resistant to oxygen-free chlorine-based dry etching when the etching rate by oxygen-free chlorine-based dry etching is preferably less than 4 nm / min, more preferably 0.8 nm / min or less, and even more preferably 0.6 nm / min or less, and a material is considered to be etchable by oxygen-free chlorine-based dry etching when the etching rate by oxygen-free chlorine-based dry etching is preferably 4 nm / min or more, more preferably 5 nm / min or more, and even more preferably 6 nm / min.

[0049] In the present invention, a material is considered to be resistant to fluorine-based dry etching when the etching rate by fluorine-based dry etching is preferably less than 16 nm / min, more preferably 0.8 nm / min or less, and even more preferably 0.6 nm / min or less, and a material is considered to be etchable by fluorine-based dry etching when the etching rate by fluorine-based dry etching is preferably 16 nm / min or more, more preferably 20 nm / min or more.

[0050] [substrate] There are no particular limitations on the type or size of the substrate, and the substrate of the reflective photomask blank and the reflective photomask may or may not be transparent at the exposure wavelength. Examples of substrates that can be used include glass substrates, particularly quartz glass (SiO2) substrates such as synthetic quartz glass substrates, and titania-doped quartz glass (SiO2-TiO2-based glass) substrates. Furthermore, suitable substrates include those designated by the SEMI standard as 6-inch square substrates with a thickness of 0.25 inches, known as 6025 substrates. In SI units, a 6025 substrate is typically expressed as a substrate with a thickness of 152 mm square and a thickness of 6.35 mm.

[0051] [Multilayer reflective film] The multilayer reflective film is a film that reflects exposure light, which is extreme ultraviolet light. The multilayer reflective film is preferably formed in contact with the substrate. Extreme ultraviolet light is called EUV light, and the wavelength of EUV light is 13 to 14 nm, and EUV light usually has a wavelength of about 13.5 nm.

[0052] Specific examples of materials constituting the multilayer reflective film include materials containing molybdenum (Mo) and materials containing silicon (Si). As the multilayer reflective film, a laminated film (Mo / Si laminated film) in which approximately 20 to 60 molybdenum (Mo) layers and silicon (Si) layers are alternately laminated is generally used. Each of the molybdenum (Mo) layer and the silicon (Si) layer may be a single layer or multiple layers (for example, a layer composed of 2 to 4 sublayers).

[0053] The molybdenum (Mo) layer may be a layer of simple molybdenum (Mo) or a layer of a molybdenum (Mo) compound containing molybdenum (Mo) and one or more light elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H). The silicon (Si) layer may be a layer of simple silicon (Si) or a layer of a silicon (Si) compound containing silicon (Si) and one or more light elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H).

[0054] The thickness of the multilayer reflective film is preferably 200 nm or more, more preferably 220 nm or more, and preferably 340 nm or less, more preferably 280 nm or less. The thickness of the molybdenum (Mo) layer is preferably 1 nm or more, more preferably 2 nm or more, and preferably 5 nm or less, more preferably 4 nm or less. The thickness of the silicon (Si) layer is preferably 2 nm or more, more preferably 3 nm or more, and preferably 6 nm or less, more preferably 5 nm or less. The reflectance of the multilayer reflective film for extreme ultraviolet light (specifically, light with a wavelength of 13.5 nm) is preferably 65% ​​or more.

[0055] [Protective film] The protective film is a film for protecting the multilayer reflective film. The protective film of the present invention comprises a first layer provided on the substrate side and a second layer provided on the side away from the substrate. The protective film is preferably formed in contact with the multilayer reflective film. The protective film has the function of preventing oxidation of the multilayer reflective film and the function of protecting the multilayer reflective film during cleaning in processing into a reflective photomask and repair of the reflective photomask. The protective film also has the function of protecting the multilayer reflective film when patterning the light absorbing film by etching. In the present invention, the second layer is mainly responsible for the function of protecting the multilayer reflective film when patterning the light absorbing film by etching. On the other hand, the function of preventing oxidation of the multilayer reflective film and the function of protecting the multilayer reflective film during cleaning in processing into a reflective photomask and repair of the reflective photomask may be performed by both the first layer and the second layer, but this function is not particularly limited, and it is preferable that it is mainly performed by the first layer.

[0056] [First layer of protective film] The first layer of the protective film is preferably made of a material that is resistant to oxygen-free chlorine-based dry etching.

[0057] The first layer of the protective film may be formed from a material that is resistant to oxygen-containing chlorine-based dry etching, or may be formed from a material that can be etched by oxygen-containing chlorine-based dry etching. However, from the standpoint of the function of preventing oxidation of the multilayer reflective film and the function of protecting the multilayer reflective film during cleaning in processing into a reflective photomask and repair of the reflective photomask, it is preferable that the first layer of the protective film be formed from a material that can be etched by oxygen-containing chlorine-based dry etching.

[0058] The first layer of the protective film may be formed from a material that is resistant to fluorine-based dry etching, or may be formed from a material that can be etched by fluorine-based dry etching. However, it is preferable that the first layer of the protective film be formed from a material that can be etched by fluorine-based dry etching in order to prevent oxidation of the multilayer reflective film and to protect the multilayer reflective film during cleaning in processing into a reflective photomask and during repair of the reflective photomask.

[0059] The first layer of the protective film is preferably formed from a material that is resistant to cleaning solutions containing sulfuric acid or alkaline cleaning solutions, such as sulfuric acid hydrogen peroxide (SPM).

[0060] The first layer of the protective film may be a single layer or multiple layers (for example, a layer composed of 2 to 4 sublayers), and each layer constituting the single layer or multiple layers may have a gradient composition.

[0061] The material constituting the first layer of the protective film is preferably a material containing ruthenium (Ru). The material constituting the first layer of the protective film may be ruthenium (Ru) alone, or may be a ruthenium compound doped with one or more additive elements selected from molybdenum (Mo), niobium (Nb), zirconium (Zr), yttrium (Y), boron (B), titanium (Ti), and lanthanum (La) to improve resistance to oxygen-free chlorine-based dry etching and to cleaning solutions containing sulfuric acid and alkali. In particular, the ruthenium compound is preferably composed of ruthenium (Ru) and one or more additive elements selected from molybdenum (Mo), niobium (Nb), zirconium (Zr), yttrium (Y), boron (B), titanium (Ti), and lanthanum (La).

[0062] The thickness of the first layer of the protective film is preferably 6 nm or less, more preferably 4 nm or less, and preferably 1 nm or more, because a thinner first layer of the protective film can more effectively utilize the reflection of exposure light from the multilayer reflective film and improve productivity in exposure using a reflective photomask, and because if the first layer of the protective film is too thin, it may not fully function as a protective film.

[0063] [Second layer of protective film] The second layer of the protective film has the function of protecting the multilayer reflective film (preventing etching of the multilayer reflective film) when the light-absorbing film is patterned by etching, and is formed of a material that is resistant to dry etching that can etch the light-absorbing film. Since the protective film of the reflective photomask blank of the present invention has the second layer, the protective film is not significantly damaged during etching for patterning the light-absorbing film, and long-term overetching is possible during etching for patterning the light-absorbing film.

[0064] The second layer of the protective film is preferably made of a material that is resistant to chlorine-based dry etching that includes oxygen.

[0065] The second layer of the protective film may be formed of a material that is resistant to oxygen-free chlorine-based dry etching, or may be formed of a material that can be etched by oxygen-free chlorine-based dry etching. However, it is preferable that the second layer of the protective film be formed of a material that is resistant to oxygen-free chlorine-based dry etching in order to protect the multilayer reflective film (prevent etching of the multilayer reflective film) when the hard mask film is removed by oxygen-free chlorine-based dry etching.

[0066] The second layer of the protective film may be formed from a material that is resistant to fluorine-based dry etching, or may be formed from a material that can be etched by fluorine-based dry etching. However, it is preferable that the second layer of the protective film be formed from a material that can be etched by fluorine-based dry etching in order to prevent oxidation of the multilayer reflective film and to protect the multilayer reflective film during cleaning in processing into a reflective photomask and during repair of the reflective photomask.

[0067] The second layer of the protective film may be a single layer or multiple layers (for example, a layer composed of 2 to 4 sublayers), and each layer constituting the single layer or multiple layers may have a gradient composition.

[0068] The material constituting the second layer of the protective film is preferably a material containing one or more elements selected from tantalum (Ta) and silicon (Si). The material constituting the second layer of the protective film is preferably a material that does not contain ruthenium (Ru). The material constituting the second layer of the protective film may be a material consisting of one or more elements selected from tantalum (Ta) and silicon (Si), but is preferably a material containing one or more elements selected from tantalum (Ta) and silicon (Si) as well as other elements, such as one or more light elements selected from oxygen (O), nitrogen (N), and carbon (C). Specifically, a material containing one or more elements selected from tantalum (Ta) and silicon (Si) and oxygen (O) is preferred, and a material consisting of one or more elements selected from tantalum (Ta) and silicon (Si) and oxygen (O) (silicon oxide (SiO), tantalum oxide (TaO), tantalum silicon oxide (TaSiO)) is more preferred. In the case of a material containing oxygen (O), the content of oxygen (O) is not particularly limited, but is preferably 20 atomic % or more, and more preferably 30 atomic % or more.

[0069] When the material constituting the second layer of the protective film contains elements other than tantalum (Ta) and silicon (Si), the total content of tantalum (Ta) and silicon (Si) is less than 100 atomic %, but is preferably 80 atomic % or less, more preferably 70 atomic % or less, and even more preferably 60 atomic %. A lower total content of tantalum (Ta) and silicon (Si) improves resistance to chlorine-based dry etching that does not contain oxygen, but may decrease resistance to chlorine-based dry etching that does contain oxygen. Therefore, the total content of tantalum (Ta) and silicon (Si) is preferably 20 atomic % or more, more preferably 30 atomic % or more.

[0070] When the second layer of the protective film is made of tantalum oxide (TaO), the tantalum (Ta) content is preferably 80 atomic % or less, more preferably 70 atomic % or less, and even more preferably 60 atomic % or less, and is preferably 20 atomic % or more, and more preferably 30 atomic % or more. In this case, the oxygen (O) content is the remainder relative to the tantalum (Ta) content.

[0071] When the second layer of the protective film is made of silicon oxide (SiO), the silicon (Si) content is preferably 80 atomic % or less, more preferably 70 atomic % or less, and even more preferably 60 atomic % or less, and is preferably 20 atomic % or more, and more preferably 30 atomic % or more. In this case, the oxygen (O) content is the remainder relative to the silicon (Si) content.

[0072] The thinner the thickness of the second layer of the protective film, the more effectively the reflection of exposure light from the multilayer reflective film can be utilized, improving productivity in exposure using a reflective photomask. However, if the second layer of the protective film is too thin, it may not fully function as a protective film. Therefore, the thickness is preferably 10 nm or less, more preferably 4 nm or less, even more preferably 2 nm or less, and is preferably 1 nm or more, more preferably 1.5 nm or more.

[0073] [Light-absorbing film] The light-absorbing film is a film that absorbs exposure light in the extreme ultraviolet region, and is preferably formed in contact with the protective film (second layer of the protective film).

[0074] The second layer of the protective film is formed of a material that is resistant to dry etching that can etch the light-absorbing film, so that the etching of the light-absorbing film is an etching that the second layer of the protective film is resistant to, and the material of the light-absorbing film is selected so that the second layer of the protective film is resistant to the etching of the light-absorbing film. Therefore, the light-absorbing film is formed of a material that has etching properties different from those of the second layer of the protective film. It is preferable that the light-absorbing film is formed of a material that can be etched by chlorine-based dry etching that contains oxygen.

[0075] The light absorbing film may be formed of a material that is resistant to oxygen-free chlorine-based dry etching, or may be formed of a material that can be etched by oxygen-free chlorine-based dry etching. However, it is preferable that the light absorbing film be formed of a material that is resistant to oxygen-free chlorine-based dry etching so that the hard mask film is not etched when being removed by oxygen-free chlorine-based dry etching.

[0076] The light absorbing film may be formed of a material that is resistant to fluorine-based dry etching, or may be formed of a material that can be etched by fluorine-based dry etching. However, it is preferable that the light absorbing film be formed of a material that is resistant to fluorine-based dry etching so that the hard mask film is not etched when patterned by fluorine-based dry etching.

[0077] In the present invention, the light-absorbing film is formed of a material containing ruthenium (Ru), preferably a material containing ruthenium (Ru) as a main component. The light-absorbing film is formed of a single layer or multiple layers (e.g., 2 to 5 layers), and it is more preferable that each layer constituting the single layer or multiple layers is formed of a material containing ruthenium (Ru) as a main component. By forming the light-absorbing film from a single material, a light-absorbing film pattern having a good cross section can be formed. In this respect, it is preferable that the light-absorbing film is formed of a single layer. When the light-absorbing film is formed of multiple layers, it is preferable that the constituent elements in all layers are the same, and in this case, it is sufficient that the ratio of the constituent elements in each layer is different. Furthermore, each layer constituting the single layer or multiple layers may have a gradient composition.

[0078] A material containing ruthenium (Ru) as a main component is a material that contains ruthenium (Ru) most abundantly in terms of atomic ratio relative to the total amount of metal elements and metalloid elements contained in the material containing ruthenium (Ru) as a main component. The ratio of ruthenium (Ru) to the total amount of metal elements and metalloid elements contained in the material containing ruthenium (Ru) as a main component is preferably 40 atomic % or more, more preferably 50 atomic % or more, and even more preferably 52 atomic % or more. The content of ruthenium (Ru) in the material containing ruthenium (Ru) is preferably 20 atomic % or more, more preferably 50 atomic % or more, and even more preferably 52 atomic % or more.

[0079] A material containing ruthenium (Ru) as a main component may contain one or more elements selected from metal elements and metalloid elements other than ruthenium (Ru), and may contain one or more elements selected from niobium (Nb), molybdenum (Mo), and tantalum (Ta) as the metal elements and metalloid elements other than ruthenium (Ru).Furthermore, a material containing ruthenium (Ru) as a main component may contain, in addition to the metal elements and metalloid elements, one or more light elements selected from oxygen (O), nitrogen (N), and carbon (C).

[0080] Examples of materials containing ruthenium (Ru) as a main component include simple ruthenium (Ru) and ruthenium compounds containing ruthenium (Ru) and one or more selected from niobium (Nb), molybdenum (Mo), tantalum (Ta), oxygen (O), and nitrogen (N). Specific examples include simple ruthenium (Ru), ruthenium oxide (RuO) composed of ruthenium (Ru) and oxygen (O), ruthenium oxynitride (RuON) composed of ruthenium (Ru), oxygen (O), and nitrogen (N), ruthenium tantalum nitride (RuTaN) composed of ruthenium (Ru), tantalum (Ta), and nitrogen (N), and ruthenium molybdenum nitride (RuMoN) composed of ruthenium (Ru), molybdenum (Mo), and nitrogen (N).

[0081] When the material containing ruthenium (Ru) as the main component contains ruthenium (Ru) and oxygen (O), particularly when it is ruthenium oxide (RuO), the ruthenium (Ru) content is preferably 60 atomic % or more, more preferably 65 atomic % or more, and preferably 90 atomic % or less, more preferably 85 atomic % or less. On the other hand, the oxygen (O) content is preferably 10 atomic % or more, more preferably 15 atomic % or more, and preferably 40 atomic % or less, more preferably 35 atomic % or less.

[0082] When a material containing ruthenium (Ru) as a main component contains ruthenium (Ru), oxygen (O), and nitrogen (N), particularly when it is ruthenium oxynitride (RuON), the ruthenium (Ru) content is preferably 80 atomic % or more, more preferably 85 atomic % or more, and preferably 96 atomic % or less, more preferably 90 atomic % or less. The oxygen (O) content is preferably 2 atomic % or more, more preferably 4 atomic % or more, and preferably 10 atomic % or less, more preferably 8% or less. Meanwhile, the nitrogen (N) content is preferably 2 atomic % or more, more preferably 4 atomic % or more, and preferably 10 atomic % or less, more preferably 8% or less.

[0083] When the material containing ruthenium (Ru) as the main component contains ruthenium (Ru), tantalum (Ta), and nitrogen (N), particularly when it is ruthenium tantalum nitride (RuTaN), the ruthenium (Ru) content is preferably 40 atomic % or more, more preferably 50 atomic % or more, and preferably 80 atomic % or less, more preferably 60 atomic % or less. The tantalum (Ta) content is preferably 8 atomic % or more, more preferably 10 atomic % or more, and preferably 30 atomic % or less, more preferably 20 atomic % or less. On the other hand, the nitrogen (N) content is preferably 2 atomic % or more, more preferably 4 atomic % or more, even more preferably 10 atomic % or more, and preferably 50 atomic % or less, more preferably 40 atomic % or less.

[0084] When a material containing ruthenium (Ru) as a main component contains ruthenium (Ru), molybdenum (Mo), and nitrogen (N), particularly when it is ruthenium molybdenum nitride (RuMoN), the ruthenium (Ru) content is preferably 30 atomic % or more, more preferably 40 atomic % or more, and preferably 80 atomic % or less, more preferably 60 atomic % or less. The molybdenum (Mo) content is preferably 5 atomic % or more, more preferably 10 atomic % or more, and preferably 50 atomic % or less, more preferably 40 atomic % or less. On the other hand, the nitrogen (N) content is preferably 10 atomic % or more, more preferably 20 atomic % or more, and preferably 50 atomic % or less, more preferably 30 atomic % or less.

[0085] Suitable materials containing ruthenium (Ru) as a main component include ruthenium niobium (RuNb) made of ruthenium (Ru) and niobium (Nb), ruthenium niobium oxide (RuNbO) made of ruthenium (Ru), niobium (Nb), and oxygen (O), and ruthenium niobium oxynitride (RuNbON) made of ruthenium (Ru), niobium (Nb), oxygen (O), and nitrogen (N).

[0086] Ruthenium oxide (RuO), ruthenium oxynitride (RuON), ruthenium tantalum nitride (RuTaN), ruthenium molybdenum nitride (RuMoN), ruthenium niobium (RuNb), ruthenium niobium oxide (RuNbO), and ruthenium niobium nitride (RuNbON), which are given as specific examples of materials containing ruthenium (Ru) as a main component, are particularly suitable as materials that can be etched with chlorine-based dry etching that contains oxygen, have resistance to chlorine-based dry etching that does not contain oxygen, and have resistance to fluorine-based dry etching.

[0087] In the present invention, the light-absorbing film is a film having a phase shift function, i.e., a phase shift film. The reflective photomask blank and reflective photomask of the present invention can be called a reflective photomask blank having a phase shift function (reflective phase shift photomask blank) and a reflective photomask having a phase shift function (reflective phase shift photomask), respectively. The phase shift function can improve wafer transfer characteristics (NILS: Normalized Image Log-Slope).

[0088] The light-absorbing film of the present invention is formed on the second layer of the protective film, and the second layer of the protective film is formed from a material that is resistant to dry etching that can etch the light-absorbing film. However, the second layer of the protective film is provided between the multilayer reflective film and the light-absorbing film, and unlike a buffer layer that is removed in the process of manufacturing a reflective photomask after patterning the light-absorbing film, it can be left on the reflective photomask. Therefore, it is possible to make the light-absorbing film alone exhibit the predetermined phase shift function (reflectance, phase difference).

[0089] The light-absorbing film having a phase shift function (phase shift film) has a reflectance of preferably 8% or more, more preferably 14% or more, and preferably 28% or less, more preferably 18% or less, for exposure light in the extreme ultraviolet region. This reflectance is a relative reflectance for the multilayer reflective film, and specifically, is the ratio of the reflectance of light reflected from the light-absorbing film formed on the substrate via the multilayer reflective film and the protective film to the reflectance of light reflected from the multilayer reflective film and the protective film formed on the substrate.

[0090] The light-absorbing film having a phase shift function (phase shift film) has a phase difference with respect to exposure light, which is extreme ultraviolet region light, of preferably 180 degrees or more, more preferably 210 degrees or more, and preferably 240 degrees or less, more preferably 220 degrees or less. This phase difference is a relative phase difference with respect to the multilayer reflective film, and specifically, is the difference between the phase of light reflected from the multilayer reflective film and protective film formed on the substrate and the phase of light reflected from the light-absorbing film formed on the substrate via the multilayer reflective film and protective film.

[0091] In the present invention, the thickness of the light-absorbing film is preferably 10 nm or more, more preferably 15 nm or more, even more preferably 20 nm or more, particularly preferably 28 nm or more, and especially preferably 35 nm or more, and is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 60 nm or less, particularly preferably 50 nm or less, and especially preferably 48 nm or less.

[0092] [Hard mask film] The hard mask film functions as an etching mask when the light absorbing film is patterned by dry etching. The hard mask film is preferably formed in contact with the light absorbing film. The hard mask film is formed of a material having etching properties different from those of the light absorbing film. Specifically, the light absorbing film is preferably formed of a material having resistance to chlorine-based dry etching containing oxygen.

[0093] The hard mask film may be formed of a material that is resistant to oxygen-free chlorine-based dry etching, or may be formed of a material that can be etched by oxygen-free chlorine-based dry etching. However, in order to enable the hard mask film to be removed by oxygen-free chlorine-based dry etching, it is preferable that the hard mask film be formed of a material that can be etched by oxygen-free chlorine-based dry etching.

[0094] The hard mask film may be formed of a material that is resistant to etching by fluorine-based dry etching, or may be formed of a material that can be etched by fluorine-based dry etching. However, it is preferable that the hard mask film be formed of a material that can be etched by fluorine-based dry etching so that the hard mask film can be etched when patterning by fluorine-based dry etching.

[0095] In the present invention, the hard mask film may be a single layer or multiple layers (for example, 2 to 5 layers), and each layer constituting the single layer or multiple layers may have a gradient composition.

[0096] The material constituting the hard mask film is preferably a material containing silicon (Si). The material constituting the hard mask film is preferably a material not containing ruthenium (Ru). The material constituting the hard mask film may be a material made of silicon (Si), but is preferably a material containing, together with silicon (Si), one or more light elements selected from the group consisting of oxygen (O), nitrogen (N), and carbon (C).

[0097] When the material constituting the hard mask film contains elements other than silicon (Si), the silicon (Si) content is less than 100 atomic %, but preferably 90 atomic % or less, and more preferably 80 atomic % or less. A low silicon (Si) content increases resistance to oxygen-free chlorine-based dry etching, so the silicon (Si) content is preferably 40 atomic % or more, and more preferably 50 atomic % or more. As the material constituting the hard mask film, a material containing silicon (Si) and nitrogen (N), particularly a material composed of silicon (Si) and nitrogen (N) (silicon nitride (SiN)), is particularly preferred. When the material constituting the hard mask film contains nitrogen (N), the nitrogen (N) content is preferably 10 atomic % or more, and more preferably 20 atomic % or more.

[0098] When the material constituting the hard mask film is silicon nitride (SiN), the silicon (Si) content is preferably 40 atomic % or more, more preferably 50 atomic % or more, and is preferably 90 atomic % or less, more preferably 80 atomic % or less. In this case, the nitrogen (N) content is the remainder relative to the silicon (Si) content.

[0099] When the silicon (Si) content of a hard mask film is low, the etching rate by a fluorine-based gas in fluorine-based dry etching is high, and the resist film used in patterning the hard mask film can be made thinner, but the surface roughness of the hard mask film is reduced, the adhesion between the hard mask film and the resist film is low, and the resolution of the resist pattern is deteriorated.On the other hand, when the silicon (Si) content is high, the etching rate by a fluorine-based gas in fluorine-based dry etching is low, and the resist film cannot be made thinner, but the surface roughness of the hard mask film is increased, the adhesion between the hard mask film and the resist film is high, and the resolution of the resist pattern is improved.

[0100] Therefore, by lowering the silicon (Si) content on the substrate side of the hard mask film and increasing the silicon (Si) content on the side away from the substrate, a film with high adhesion to the resist film and a high etching rate can be obtained. From this perspective, it is also preferable to increase the light element (e.g., nitrogen (N)) content on the substrate side of the hard mask film and decrease the light element (e.g., nitrogen (N)) content on the side away from the substrate.

[0101] The hard mask film is usually patterned using a resist pattern as an etching mask. However, the thinner the hard mask film, the shorter the etching time. If the hard mask film is too thin, it may lose its function as an etching mask in etching the light absorbing film, and the sensitivity of defect inspection of the hard mask film may decrease. Therefore, the thickness of the hard mask film is preferably 16 nm or less, more preferably 10 nm or less, and is preferably 2 nm or more, more preferably 4 nm or more.

[0102] [Conductive film] When a reflective photomask is held on a mask stage of an exposure tool, it is usually fixed by an electrostatic chuck. Therefore, the reflective photomask blank and the reflective photomask of the present invention may be provided with a conductive film (back surface film) on the back surface of the substrate (the surface opposite to the front surface on which the multilayer reflective film etc. is formed) for fixing the reflective photomask by the electrostatic chuck. The conductive film is preferably formed in contact with the substrate.

[0103] The conductive film preferably has a sheet resistance of 100 Ω / □ or less, and there are no particular limitations on the material. Examples of conductive film materials include materials containing tantalum (Ta) or chromium (Cr). Materials containing tantalum (Ta) or chromium (Cr) may also contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. The thickness of the conductive film is not particularly limited as long as it functions as an electrostatic chuck, but is typically about 20 to 300 nm.

[0104] [Resist film] The reflective photomask blank of the present invention may further comprise a resist film. When a reflective photomask is produced from a reflective photomask blank that does not comprise a resist film, a resist film is formed on the reflective photomask blank, usually on the hard mask film. The resist film is preferably formed in contact with the hard mask film.

[0105] 3 is a cross-sectional view showing an example of a second embodiment of the reflective photomask blank of the present invention. This reflective photomask blank 102 has a substrate 1, a multilayer reflective film 2 formed on and in contact with the substrate 1, a protective film 3 formed on and in contact with the multilayer reflective film 2, a light-absorbing film 4 formed on and in contact with the protective film 3, a hard mask film 5 formed on and in contact with the light-absorbing film 4, and a resist film 6 formed on and in contact with the hard mask film 5. The protective film 3 consists of a first layer 31 formed in contact with the multilayer reflective film 2 and a second layer 32 formed in contact with the light-absorbing film 4. In the reflective photomask blank 102 of the second embodiment, the multilayer reflective film 2, the first layer 31 of the protective film 3, the second layer 32 of the protective film 3, the light-absorbing film 4, the hard mask film 5, and the resist film 6 are laminated in this order from the substrate 1 side.

[0106] In the present invention, the resist film may be an electron beam resist that is written by an electron beam or a photoresist that is written by light, but a chemically amplified resist is preferred. The chemically amplified resist may be either a positive or negative type, and may, for example, contain a base resin such as a hydroxystyrene-based resin or a (meth)acrylic acid-based resin, an acid generator, and, if necessary, may contain a crosslinker, a quencher, a surfactant, etc.

[0107] [Method of film formation] The multilayer reflective film, protective film (first and second layers), light absorbing film, hard mask film, and conductive film of the present invention are preferably formed by sputtering, since this method is easy to control and allows for the formation of films with desired properties. The sputtering method may be DC sputtering, RF sputtering, or the like, and is not particularly limited.

[0108] When a laminated film of a molybdenum (Mo) layer and a silicon (Si) layer is formed as a multilayer reflective film, a molybdenum (Mo) target and a silicon (Si) target can be used as sputtering targets.

[0109] When the first layer of the protective film is formed from a material containing ruthenium (Ru), the sputtering target can be a ruthenium (Ru) target and, if necessary, a target appropriately selected from a molybdenum (Mo) target, a niobium (Nb) target, a zirconium (Zr) target, an yttrium (Y) target, a titanium (Ti) target, and a lanthanum (La) target.

[0110] When the second layer of the protective film is formed of a material containing tantalum (Ta), a tantalum (Ta) target can be used as the sputtering target, and when the second layer of the protective film is formed of a material containing silicon (Si), a silicon (Si) target can be used as the sputtering target.

[0111] When the light absorbing film is formed from a material containing ruthenium (Ru), the sputtering target may be a ruthenium (Ru) target and, if necessary, a target appropriately selected from a niobium (Nb) target, a molybdenum (Mo) target, and a tantalum (Ta) target.

[0112] When the hard mask film is formed from a material containing silicon (Si), a silicon (Si) target can be used as the sputtering target.

[0113] When the conductive film is formed from a material containing tantalum (Ta) or chromium (Cr), a tantalum (Ta) target or a chromium (Cr) target can be used as the sputtering target.

[0114] The power input to the sputtering target can be set appropriately depending on the size of the sputtering target, cooling efficiency, ease of control of film formation, etc., and is usually 50 to 3000 W / cm as the power per area of ​​the sputtering surface of the sputtering target. 2Furthermore, a rare gas such as helium gas (He gas), neon gas (Ne gas), or argon gas (Ar gas) is used as the sputtering gas, and when a film (a layer constituting a film, or a sub-layer constituting a layer) is formed using only the element of the target, only a rare gas may be used as the sputtering gas.

[0115] When a film (a layer constituting the film or a sublayer constituting the layer) is formed from a material containing one or more light elements selected from oxygen (O), nitrogen (N), carbon (C), and hydrogen (H), reactive sputtering is preferred. In reactive sputtering, a rare gas such as helium gas (He gas), neon gas (Ne gas), or argon gas (Ar gas) and a reactive gas are used as sputtering gases.

[0116] As the reactive gas, for example, oxygen gas (O2 gas) can be used when forming the film from a material containing oxygen (O); nitrogen gas (N2 gas) can be used when forming the film from a material containing nitrogen (N); nitric oxide gases such as nitric oxide gas (NO gas), nitrogen dioxide gas (NO2 gas), and nitrous oxide gas (NO gas) can be used when forming the film from a material containing oxygen (O) and nitrogen (N); carbon oxide gases such as carbon monoxide gas (CO gas) and carbon dioxide gas (CO2 gas) can be used when forming the film from a material containing carbon (C) and oxygen (O); and methane gas (CH4 gas) can be used when forming the film from a material containing carbon (C) and hydrogen (H).

[0117] Furthermore, when the film is formed from a material containing boron (B), a target doped with boron (B) can be used.

[0118] The pressure during formation of the film (a layer constituting the film, or a sub-layer constituting the layer) may be appropriately set in consideration of film stress, chemical resistance, cleaning resistance, etc., and is preferably 0.01 Pa or more, more preferably 0.03 Pa or more, and preferably 1 Pa or less, more preferably 0.3 Pa or less, to particularly improve chemical resistance. The flow rate of each gas may be appropriately set to obtain the desired composition, and is usually 0.1 to 100 sccm.

[0119] In the manufacturing process of a reflective photomask blank, before forming a resist film, the substrate or the substrate and the film formed on the substrate may be subjected to a heat treatment. The heat treatment method may be infrared heating, resistance heating, or the like, and the treatment conditions are not particularly limited. The heat treatment may be carried out, for example, in an oxygen (O)-containing gas atmosphere. The concentration of the oxygen (O)-containing gas is not particularly limited, and in the case of oxygen gas (O gas), for example, it may be 1 to 100% by volume. The heat treatment temperature is preferably 200°C or higher, more preferably 400°C or higher.

[0120] Furthermore, in the manufacturing process of a reflective photomask blank, a film formed on a substrate, particularly a hard mask film, may be subjected to ozone treatment or plasma treatment before forming a resist film. Either treatment can be performed for the purpose of increasing the oxygen concentration in the surface portion of the film, and in this case, the treatment conditions may be appropriately adjusted to achieve a predetermined oxygen concentration. Note that when a film is formed by sputtering, the oxygen concentration in the surface portion of the film can also be increased by adjusting the ratio of a rare gas to an oxygen-containing gas (oxidizing gas) such as oxygen gas (O gas), carbon monoxide gas (CO gas), or carbon dioxide gas (CO gas) in the sputtering gas.

[0121] Furthermore, in the manufacturing process of a reflective photomask blank, a cleaning treatment may be performed before forming a resist film to remove defects present on the surface of the substrate or the film formed on the substrate. Cleaning can be performed using one or both of ultrapure water and functional water, which is ultrapure water containing ozone gas (O gas), hydrogen gas (H gas), etc. Furthermore, after cleaning with ultrapure water containing a surfactant, further cleaning may be performed using one or both of ultrapure water and functional water. Cleaning can be performed while irradiating with ultrasonic waves as necessary, and UV light irradiation can also be combined.

[0122] The method for forming the resist film (applying the resist) is not particularly limited, and known methods such as spin coating can be applied.

[0123] [Reflective photomask manufacturing] From the reflective photomask blank of the present invention, a reflective photomask comprising a substrate, a multilayer reflective film, a protective film, and a light-absorbing film pattern can be manufactured. Unlike the buffer layer (buffer layer) that is removed in the process of manufacturing the reflective photomask, the protective film of the reflective photomask, particularly the second layer of the protective film, can be left on the reflective photomask, so the step of removing the second layer of the protective film is not essential, and it is preferable not to include the step of removing the second layer of the protective film.

[0124] Ideally, the protective film of a reflective photomask will remain entirely (entirely in the thickness direction) of the protective film formed on the reflective photomask blank. Therefore, the reflective photomask of the present invention is preferably manufactured so that the entire protective film (first and second layers) (entirely in the thickness direction) remains. However, since the exposed protective film is exposed to etching during the manufacturing process of the reflective photomask, particularly during patterning of the light-absorbing film and removal of the pattern of the hard mask film, the reflective photomask of the present invention may be manufactured so that at least a portion of the first layer of the protective film (a portion of the thickness direction), preferably the entire first layer of the protective film (the entire thickness direction) and a portion of the second layer (a portion of the thickness direction) remain.

[0125] In the manufacture of a reflective photomask, if a resist film is not formed on a reflective photomask blank, a resist film is formed on a hard mask film. Then, using a resist pattern obtained by patterning a resist film or a film pattern obtained by patterning a film such as a hard mask film as an etching mask, a reflective photomask can be manufactured by patterning or removing the film by dry etching appropriately selected from oxygen-containing chlorine-based dry etching, oxygen-free chlorine-based dry etching, fluorine-based dry etching, etc., depending on the etching characteristics of the material forming each film. In the manufacture of a reflective photomask, the resist pattern can be removed with sulfuric acid / hydrogen peroxide (SPM).

[0126] Next, an example of a method for producing a reflective photomask from the reflective photomask blank of the first aspect of the present invention will be specifically described with reference to the drawings. Fig. 4 is a cross-sectional view illustrating the process for producing a reflective photomask from the reflective photomask blank of the present invention.

[0127] First, as shown in FIG. 4(A), a resist film 6 is formed on and in contact with the hard mask film 5 of a reflective photomask blank 101 of the first embodiment, or a reflective photomask blank 102 of the second embodiment is prepared (step (A)).

[0128] Next, as shown in FIG. 4(B), the resist film 6 is patterned to form a resist pattern 6a (step (B)).

[0129] Next, as shown in FIG. 4(C), the hard mask film 5 is patterned by fluorine-based dry etching using the resist pattern 6a as an etching mask to form a hard mask film pattern 5a (step (C)).

[0130] Next, as shown in FIG. 4(D), the resist pattern 6a is removed (step (D)).

[0131] Next, as shown in FIG. 4(E), the light absorbing film 4 is patterned by chlorine-based dry etching containing oxygen using the pattern 5a of the hard mask film as an etching mask to form a pattern 4a of the light absorbing film (step (E)).

[0132] Next, as shown in FIG. 4(F), the pattern 5a of the hard mask film is removed by chlorine-based dry etching that does not contain oxygen (step (F)).

[0133] This method for manufacturing a reflective photomask is suitable as a method for manufacturing a reflective photomask from a reflective photomask blank in which the second layer of the protective film is formed from a material that is resistant to chlorine-based dry etching containing oxygen and also resistant to chlorine-based dry etching not containing oxygen, the light-absorbing film is formed from a material that can be etched by chlorine-based dry etching containing oxygen, is resistant to chlorine-based dry etching not containing oxygen, and is resistant to fluorine-based dry etching, and the hard mask film is formed from a material that is resistant to chlorine-based dry etching containing oxygen, is etchable by chlorine-based dry etching not containing oxygen, and is etchable by fluorine-based dry etching.

[0134] Furthermore, this method for manufacturing a reflective photomask is suitable as a method for manufacturing a reflective photomask from a reflective photomask blank in which the second layer of the protective film is formed from a material containing at least one selected from tantalum (Ta) and silicon (Si) and oxygen (O), the light absorbing film is formed from a material mainly containing ruthenium (Ru), and the hard mask film is formed from a material containing silicon (Si) and nitrogen (N).

[0135] In the present invention, the thickness of the resist film (the thickness of the resist film formed on the reflective photomask blank of the first embodiment and the thickness of the resist film formed on the reflective photomask blank of the second embodiment) is preferably 80 nm or less, more preferably 70 nm or less, from the viewpoint of reducing the aspect ratio of the resist pattern for forming a fine assist pattern in the development step of resist pattern formation (from the viewpoint of making it less likely to collapse due to impact with the developer or pure water during rinsing).

[0136] The reflective photomask blank of the present invention can form a good fine pattern with a line width of 25 nm or less (e.g., 16 to 25 nm), particularly 20 nm or less (e.g., 16 to 20 nm), and especially 18 nm or less (e.g., 16 to 18 nm) in a light-absorbing film having a phase shift function by reducing the aspect ratio of the resist pattern with a thin resist film, and can also form a pattern with a highly controlled shape (e.g., cross section of the pattern).In the present invention, the lower limit of the width of a line pattern such as an assist pattern that can be formed in the pattern of the light-absorbing film of a reflective photomask is not particularly limited, but is usually 10 nm or more.

[0137] The thickness of the resist film is preferably 60 nm or less from the viewpoint of favorably forming a line pattern such as an assist pattern having a width of 25 nm or less (25 nm or less), particularly 20 nm or less (20 nm or less), and especially 18 nm or less (18 nm or less). The lower limit of the resist film thickness is sufficient as long as the resist pattern remains at a predetermined thickness after etching, for example, preferably 10 nm or more, more preferably 15 nm or more, and also as long as the resist film can be formed with a stable thickness. The thickness of the resist film is not particularly limited, but is preferably 15 nm or more, more preferably 20 nm or more, and even more preferably 40 nm or more. [Example]

[0138] The present invention will be specifically explained below by showing examples, but the present invention is not limited to the following examples.

[0139] [Examples 1 to 10] A reflective multilayer film, a protective film, a light-absorbing film, and a hard mask film were laminated in this order on a quartz substrate having a size of 152 mm square and a thickness of approximately 6 mm, to produce a reflective photomask blank (reflective photomask blank of the first embodiment) as shown in FIG. 1 .

[0140] First, a molybdenum (Mo) target and a silicon (Si) target were used as the sputtering targets, and argon gas (Ar) was used as the sputtering gas. The power applied to the targets was adjusted, and the flow rate of the sputtering gas was also adjusted. Sputtering with the molybdenum (Mo) target and sputtering with the silicon (Si) target were alternately performed on a quartz substrate to form a multilayer reflective film (with a reflectivity of 65% for light with a wavelength of 13.5 nm) consisting of a laminated film (thickness 280 nm) in which molybdenum (Mo) layers and silicon (Si) layers were alternately stacked. The stacking of molybdenum (Mo) layers and silicon (Si) layers was performed 40 times (40 layers each of molybdenum (Mo) layers and silicon (Si) layers).

[0141] Next, a ruthenium (Ru) target was used as the target, and argon gas (Ar gas) was used as the sputtering gas. The power applied to the target was adjusted, and the flow rate of the sputtering gas was also adjusted. Sputtering was then performed using the ruthenium (Ru) target to form a layer (2 nm thick) made of ruthenium (Ru) alone as the first layer of the protective film on the multilayer reflective film.

[0142] Next, a tantalum (Ta) target or a silicon (Si) target was used as the target, and argon gas (Ar gas) and oxygen gas (O gas) were used as the sputtering gas. The power applied to the target was adjusted, and the flow rate of the sputtering gas was also adjusted to perform sputtering, thereby forming a layer (2 nm thick) made of tantalum oxide (TaO) or silicon oxide (SiO) as the second layer of the protective film on top of the first layer of the protective film.

[0143] Next, a ruthenium (Ru) target was used as the target, and argon (Ar), oxygen (O), and nitrogen (N) gases were used as the sputtering gases. By adjusting the power applied to the target and the flow rate of the sputtering gas, sputtering was performed to form a 40-nm-thick light-absorbing film made of ruthenium oxynitride (RuON) on the second protective film layer. The composition of this light-absorbing film was 87 atomic % ruthenium (Ru), 6 atomic % oxygen (O), and 7 atomic % nitrogen (N). The reflectivity (relative to the multilayer reflective film) of this light-absorbing film for light with a wavelength of 13.5 nm was 15%, and the phase difference (relative to the multilayer reflective film) was 215 degrees.

[0144] Next, a silicon (Si) target was used as the target, and argon gas (Ar gas) and nitrogen gas (N gas) were used as the sputtering gas. The power applied to the target was adjusted, and the flow rate of the sputtering gas was also adjusted to perform sputtering. This formed a hard mask film made of silicon nitride (SiN) on the light-absorbing film, thereby obtaining a reflective photomask blank.

[0145] The composition of the second layer of the protective film and the film thickness and composition of the hard mask film are shown in Table 1. In the examples, the compositions of the multilayer reflective film, the first and second layers of the protective film, the light-absorbing film, and the hard mask film were measured using an X-ray photoelectron spectrometer, and their thicknesses were measured using an X-ray diffractometer.

[0146] [Table 1]

[0147] [Evaluation 1: Fluorine-based dry etching of hard mask film] Using the reflective photomask blank samples of Examples 1 to 10, the time until the hard mask film disappeared (clear time) was measured by fluorine-based dry etching. The clear time was measured by etching the hard mask film under the following conditions (condition 1), and the time until the end point was detected (time until endpoint). Thereafter, etching was continued for a period of time calculated by adding 25% of the clear time to the total etching time, and the etching was completed. The clear time, etching rate, and total etching time are shown in Table 2.

[0148] <Conditions for fluorine-based dry etching of hard mask film (Condition 1)> Equipment: ICP (Inductively Coupled Plasma) method Etching gas: SF6 gas + He gas Gas pressure: 4.0 mTorr (0.53 Pa) ICP power: 400W

[0149] [Table 2]

[0150] In Example 8, it is believed that the etching rate by fluorine-based dry etching was low because the hard mask film had a high silicon (Si) content.

[0151] [Evaluation 2: Oxygen-containing chlorine-based dry etching of light-absorbing film] Using the sample after Evaluation 1, the time until the light-absorbing film disappeared (clear time) was measured by chlorine-based dry etching containing oxygen. The clear time was measured by etching the light-absorbing film under the following conditions (condition 2), and was the time until the end point was detected (time to endpoint). After that, the etching was continued until the total etching time was reached, which was calculated by adding 100% of the clear time. The clear time, etching rate, and total etching time are shown in Table 3. After etching, the thickness of the second layer of the protective film after etching the light-absorbing film was measured, and the reduction in the thickness of the second layer of the protective film was calculated. The results are shown in Table 3.

[0152] <Conditions for chlorine-based dry etching containing oxygen for light-absorbing films (Condition 2)> Equipment: ICP (Inductively Coupled Plasma) method Etching gas: Cl2 gas + O2 gas Gas pressure: 3.0 mTorr (0.40 Pa) ICP power: 350W

[0153] [Table 3]

[0154] In Example 9, the silicon (Si) content of the second layer of the protective film was high, which is thought to have resulted in a high etching rate by chlorine-based dry etching containing oxygen, resulting in a large reduction in the thickness of the second layer of the protective film.

[0155] [Evaluation 3: Oxygen-free chlorine-based dry etching of hard mask film] Using the reflective photomask blank samples of Examples 1 to 10, the time until the hard mask film disappeared (clear time) was measured by oxygen-free chlorine-based dry etching. The clear time was measured by etching the hard mask film under the following conditions (condition 3), and the time until the end point was detected (time to endpoint). The clear time and etching rate are shown in Table 4.

[0156] Next, using the samples after Evaluation 2, the amount of reduction in the second layer of the protective film due to over-etching in oxygen-free chlorine-based dry etching of the hard mask film was evaluated. The total etching time was calculated by adding 100% of the clear time to the clear time. The total etching time is shown in Table 4. The difference between the clear time and the total etching time was calculated as the over-etching time, and oxygen-free chlorine-based dry etching was performed on the second layer of the protective film under Condition 3 below for the over-etching time shown in Table 4. After etching, the thickness of the second layer of the protective film was measured, and the amount of reduction in the thickness of the second layer of the protective film was calculated. The results are shown in Table 4.

[0157] <Conditions for oxygen-free chlorine-based dry etching of hard mask film (Condition 3)> Equipment: ICP (Inductively Coupled Plasma) method Etching gas: Cl2 gas Gas pressure: 3.0 mTorr (0.40 Pa) ICP power: 350W

[0158] [Table 4]

[0159] In Examples 9 and 10, the second layer of the protective film had a high content of tantalum (Ta) or silicon (Si), which is thought to have resulted in a high etching rate by oxygen-free chlorine-based dry etching, resulting in a large reduction in the thickness of the second layer of the protective film.

[0160] [Evaluation 4: Fluorine-based dry etching of resist film] Using the reflective photomask blanks of Examples 1 to 10, the amount of resist film loss due to fluorine-based dry etching was evaluated.

[0161] First, a positive chemically amplified electron beam resist was spin-coated to form a resist film with a thickness of 60 nm.

[0162] Next, an electron beam lithography system was used to irradiate the substrate with a dose of 100 μC / cm 2 A total of 20 isolated line patterns with long sides of 100 μm and short sides of 60 nm were written using a thermal treatment device. Next, a post-exposure bake (PEB) was performed at 115°C for 14 minutes. A development process was then performed using a paddle developer for 40 seconds to form a resist pattern. Next, using the resist pattern as an etching mask, fluorine-based dry etching was performed on the hard mask film under the aforementioned Condition 1 for the total etching time shown in Table 2 to form a hard mask film pattern.

[0163] Next, the thickness of the resist film after etching the hard mask film was measured, and the amount of thickness reduction of the resist film was calculated. The results are shown in Table 5. In the examples, the thickness of the resist pattern was measured using an atomic force microscope (AFM), and the measurement range was a square region of 200 nm × 200 nm.

[0164] If the resist pattern remaining after etching is too thin, the fluorine-based plasma may reach the hard mask film, causing pinhole defects. Therefore, a specific thickness of resist pattern must remain after fluorine-based dry etching of the hard mask film. From the amount of reduction in resist film thickness, the resist film thickness required to leave a 15 nm thick resist pattern after fluorine-based dry etching of the hard mask film was calculated. The resist film thickness required to leave a 15 nm thick resist pattern is shown in Table 5.

[0165] [Table 5]

[0166] [Reflective photomask manufacturing] In order to evaluate the resolution limit of a fine pattern equivalent to the assist pattern of an isolated line pattern, a reflective photomask was manufactured from the reflective photomask blank.

[0167] First, a positive chemically amplified electron beam resist was spin-coated to form a resist film with the thickness shown in Table 6. The thickness of the resist film used here was determined to be 40 nm or more if the thickness required for the resist pattern to remain at a thickness of 15 nm after fluorine-based dry etching of the hard mask film was 40 nm or more. If the thickness required for the resist pattern to remain at a thickness of 15 nm after fluorine-based dry etching of the hard mask film was less than 40 nm, the thickness was determined to be 40 nm, the lower limit at which a resist film with a stable thickness could be formed using the resist material used. The thicknesses of the resist films used are shown in Table 6.

[0168] Next, an electron beam lithography system was used to irradiate the substrate with a dose of 100 μC / cm 2 As a test pattern equivalent to the assist pattern of the line pattern, a total of 200,000 isolated patterns with different short sides (widths), with the long side being 80 nm and the short side varying in 1 nm increments from 10 nm to 60 nm, were written. Next, a heat treatment (PEB: Post Exposure Bake) was performed at 115°C for 14 minutes using a heat treatment device. Next, a development process was performed using a puddle developer for 40 seconds to form a resist pattern.

[0169] Next, using the resist pattern as an etching mask, the hard mask film was subjected to fluorine-based dry etching under the above-mentioned Condition 1 for the total etching time shown in Table 2, thereby forming a pattern of the hard mask film.

[0170] Next, the remaining resist pattern was removed by washing with sulfuric acid / hydrogen peroxide (SPM), which is a mixture of sulfuric acid and hydrogen peroxide (sulfuric acid:hydrogen peroxide=3:1 (volume ratio)).

[0171] Next, using the pattern of the hard mask film as an etching mask, the light absorbing film was subjected to chlorine-based dry etching containing oxygen under the above condition 2 for the total etching time shown in Table 3, thereby forming a pattern of the light absorbing film.

[0172] Next, the pattern of the hard mask film was subjected to oxygen-free chlorine-based dry etching under the above-mentioned Condition 3 for the total etching time shown in Table 4, thereby removing the pattern of the hard mask film and obtaining a reflective photomask.

[0173] Next, the resolution limit of the test pattern of the obtained reflective photomask was evaluated using a mask visual inspection device. All isolated patterns were evaluated for pattern loss, pattern collapse, and pattern shape defects. Isolated patterns in which the visual inspection device detected either pattern loss, pattern collapse, or pattern shape defects were considered defective, and the minimum short side dimension of any isolated pattern in which a defect was not detected was considered the resolution limit. In addition, the thickness of the protective film (thickness of the first and second layers) of the obtained reflective photomask was measured. The results are shown in Table 6.

[0174] [Table 6]

[0175] In Examples 1 to 6, 9, and 10, the clear time of fluorine-based dry etching was short, and fluorine-based dry etching of the hard mask film was possible with a thin resist film. Even in patterns with narrow line widths, the aspect ratio of the resist pattern was low and the resist pattern was less likely to collapse, resulting in a smaller resolution limit.

[0176] On the other hand, in Example 7, the hard mask film was thick, and in Example 8, the silicon (Si) content of the hard mask film was high and the etching rate by fluorine-based dry etching was low. In both cases, therefore, a thicker resist film was required, and the aspect ratio of the resist pattern was high and the resist pattern was prone to collapse, which is thought to have increased the resolution limit.

[0177] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any other configurations that are identical or substantially identical to the technical concept of the present invention and that provide the same or similar effects are included within the technical scope of the present invention. [Explanation of symbols]

[0178] 1 board 2 Multilayer reflective film 3 Protective film 31 1st layer 32 2nd layer 4. Light-absorbing film 4a Light absorbing film pattern 5 Hard mask film 5a Hard mask film pattern 6 Resist 6a Resist pattern 101, 102 Reflective photomask blanks 200 Reflective Photomask

Claims

1. a multilayer reflective film formed on the substrate and reflecting exposure light in the extreme ultraviolet region; a protective film formed on the multilayer reflective film; a light absorbing film formed on the protective film in contact with the protective film and absorbing the exposure light; and a hard mask film formed on the light absorbing film in contact with the light absorbing film; the protective film comprises a first layer provided on the substrate side and a second layer provided on a side away from the substrate, the second layer of the protective film is formed of a material that is resistant to dry etching that can etch the light absorbing film, The light absorbing film has a phase shift function and is formed of a single layer or multiple layers, and each layer constituting the single layer and the multiple layers is formed of a material containing ruthenium (Ru) as a main component. A reflective photomask blank characterized by:

2. the second layer of the protective film is formed of a material that is resistant to chlorine-based dry etching that includes oxygen, 2. The reflective photomask blank according to claim 1, wherein the light absorbing film is formed from a material that can be etched by chlorine-based dry etching that includes oxygen.

3. the second layer of the protective film is formed of a material that is resistant to chlorine-based dry etching containing oxygen and is resistant to chlorine-based dry etching not containing oxygen, the light absorbing film is formed of a material that can be etched by chlorine-based dry etching containing oxygen, has resistance to chlorine-based dry etching not containing oxygen, and has resistance to fluorine-based dry etching; The hard mask film is formed of a material that is resistant to chlorine-based dry etching containing oxygen, can be etched by chlorine-based dry etching not containing oxygen, and can be etched by fluorine-based dry etching.

3. The reflective photomask blank according to claim 2.

4. 4. The reflective photomask blank according to claim 3, wherein the first layer of the protective film is formed from a material that is resistant to oxygen-free chlorine-based dry etching.

5. 2. The reflective photomask blank according to claim 1, wherein the material containing ruthenium (Ru) as a main component contains ruthenium (Ru) at a content of 20 atomic % or more and is a material that contains ruthenium (Ru) in the largest amount in terms of atomic ratio to the total amount of metal elements and semi-metal elements.

6. 2. The reflective photomask blank according to claim 1, wherein the light absorbing film has a phase shift function with a reflectance of 8% or more and 28% or less and a phase difference of 180 degrees or more and 240 degrees or less for the exposure light.

7. 2. The reflective photomask blank according to claim 1, wherein the light-absorbing film has a thickness of 28 nm or more and 50 nm or less.

8. 2. The reflective photomask blank according to claim 1, wherein the second layer of the protective film is formed from a material containing at least one element selected from tantalum (Ta) and silicon (Si), and oxygen (O).

9. 9. The reflective photomask blank according to claim 8, wherein the hard mask film is formed of a material containing silicon (Si) and nitrogen (N).

10. 10. The reflective photomask blank according to claim 9, wherein the first layer of the protective film is formed from a material containing ruthenium (Ru).

11. 2. The reflective photomask blank according to claim 1, wherein the second layer of the protective film has a thickness of 1 nm or more and 10 nm or less.

12. 12. The reflective photomask blank according to claim 11, wherein the first layer of the protective film has a thickness of 1 nm or more and 6 nm or less.

13. 2. The reflective photomask blank according to claim 1, wherein the hard mask film has a thickness of 2 nm or more and 16 nm or less.

14. A method for producing a reflective photomask including the substrate, the multilayer reflective film, the protective film, and the light absorbing film pattern from the reflective photomask blank according to claim 3 or 9, comprising the steps of: (A) forming a resist film on and in contact with the hard mask film; (B) patterning the resist film to form a resist pattern; (C) patterning the hard mask film by fluorine-based dry etching using the resist pattern as an etching mask to form a hard mask film pattern; (D) removing the resist pattern; (E) patterning the light absorbing film by chlorine-based dry etching containing oxygen using the pattern of the hard mask film as an etching mask to form a pattern of the light absorbing film; (F) removing the pattern of the hard mask film by oxygen-free chlorine-based dry etching; A method for manufacturing a reflective photomask, comprising:

15. 15. The manufacturing method according to claim 14, wherein the resist film has a thickness of 60 nm or less, and the pattern of the light absorbing film includes a line pattern having a width of 20 nm or less.

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