Reflection type photomask blank, and production method of reflection type photomask

Abstract

SOLUTION: A reflection type photomask blank includes: a substrate; a multilayered reflection film for reflecting exposure light being extreme ultraviolet region light; a protective film for protecting the multilayered reflection film; a light absorption film for absorbing the exposure light; and a hard mask formed so as to contact the light absorption film, where the light absorption film is a multilayer including an oxide layer of a light absorption film containing oxygen and the light absorption film, the hard mask is a multilayer including a first layer and a second layer, and the second layer is a multilayer including an upper hard mask layer 2A of a second layer containing oxygen, and an under hard mask layer 2B.EFFECT: High resolution is obtained in a transfer pattern of a reflection type photomask since a thickness of a resist film can be thinned, and an assist pattern having a line width of about 20 nm is favorably formed by lowering an aspect ratio of a resist pattern.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This 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, which is used in its manufacture. [Background technology]

[0002] With the miniaturization of semiconductor devices, and especially with the high integration of large-scale integrated circuits, high pattern resolution is required for projection lithography. Therefore, phase-shift masks have been developed as a method to improve the resolution of the transfer pattern in photomasks. The principle of the phase-shift method is to adjust the phase of transmitted light passing through the aperture of the phase-shift film of the photomask so that the phase of the transmitted light passing through the portion of the phase-shift film adjacent to the aperture is reversed by approximately 180 degrees. As a result, the transmitted light interferes at the boundary between the aperture and the adjacent portion, reducing the light intensity, and consequently improving the resolution and depth of focus of the transfer pattern. Photomasks that use this principle are generally called phase-shift masks.

[0003] The most common type of phase-shift mask blank used in the manufacture of phase-shift masks is one in which a phase-shift film is laminated on a transparent substrate such as a glass substrate, and a film made of a chromium (Cr)-containing material is laminated on top of the phase-shift film. The phase-shift film usually has a phase difference of 175 to 185 degrees with respect to exposure light and a transmittance of about 6 to 30%, and is mainly made of a silicon (Si)-containing film, especially a material containing molybdenum (Mo) and silicon (Si). In addition, the film made of the chromium-containing material is adjusted to a thickness that achieves the desired optical density when combined with the phase-shift film, and the film made of the chromium-containing material is generally used as a light-shielding film and as a hard mask layer when etching the phase-shift film.

[0004] A common method for manufacturing a phase-shift mask is to pattern a phase-shift film from a phase-shift mask blank, which has a phase-shift film made of silicon-containing material and a light-shielding film made of chromium-containing material formed in that order on a transparent substrate. Specifically, the following method is generally used: First, a resist film is formed on the light-shielding film made of chromium-containing material of the phase-shift mask blank. A pattern is drawn on this resist film using light or an electron beam, and then developed to form a resist pattern. Next, using the resist pattern as an etching mask, the light-shielding film made of chromium-containing material is etched using a chlorine-based gas to form a pattern for the light-shielding film. Furthermore, using the pattern for the light-shielding film as an etching mask, the phase-shift film made of silicon-containing material is etched using a fluorine-based gas to form a pattern for the phase-shift film. After that, the resist pattern is removed, and the pattern for the light-shielding film is removed by etching with a chlorine-based gas.

[0005] In this case, a light-shielding film is left outside the area where the phase-shift film pattern (circuit pattern) is formed, so that the outer edge of the phase-shift mask becomes a light-shielding area (light-shielding pattern) with a combined optical density of 3 or more from the phase-shift film and the light-shielding film. This is to prevent exposure light from leaking from the outer edge of the phase-shift mask when transferring the circuit pattern to the wafer using a wafer exposure apparatus, and from irradiating the resist film on adjacent chips on the wafer from the area located outside the circuit pattern. A common method for forming such a light-shielding pattern is to form a phase-shift film pattern, remove the resist pattern, then form a new resist film, and create a resist pattern with the resist film remaining on the outer edge of the phase-shift mask by pattern drawing and development. This resist pattern is then used as an etching mask to etch a film formed from a chromium-containing material, leaving the light-shielding film on the outer edge of the phase-shift mask.

[0006] For phase-shift masks, where high-precision pattern formation is required, dry etching using gas plasma is the mainstream method. Dry etching of films formed from chromium-containing materials is performed using chlorine-based dry etching (chlorine-based dry etching), while dry etching of films containing silicon or films containing molybdenum and silicon is performed using fluorine-based dry etching (fluorine-based dry etching). In particular, for dry etching of films formed from chromium-containing materials, it is known that the etching gas is improved by mixing chlorine gas (Cl2 gas) with 10 to 25 volume percent of oxygen gas (O2 gas), thereby increasing chemical reactivity and improving the etching rate.

[0007] As circuit patterns become smaller, techniques for forming finer circuit patterns on phase shift masks are also required. In particular, the assist patterns of line patterns that support the resolution of the main pattern of the phase shift mask need to be formed 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 apparatus. In the generation of phase shift masks where the half-pitch of the line and space pattern of the circuit on the wafer is 10 nm, the line width of the assist patterns of the line patterns of the circuit on the phase shift mask needs to be about 40 nm.

[0008] Chemically amplified resists, which can form fine patterns, consist of a base resin, an acid generator, a surfactant, etc. Because many reactions in which the acid generated by exposure acts as a catalyst can be applied, high sensitivity is possible. Using chemically amplified resists makes it possible to form mask patterns, such as fine phase-shift film patterns with line widths of 0.1 μm or less. The resist is applied onto the photomask blank by spin coating using a resist coating machine.

[0009] The thickness of the resist film used for advanced phase-shift mask blanks is 100-150 nm. The reason why it is difficult to form finer assist patterns on the phase-shift mask is that the aspect ratio of the resist pattern formed on a light-shielding film made of chromium-containing material is high, causing it to collapse during the development process of resist pattern formation due to impact from the developer or from the pure water during the rinsing process.

[0010] Therefore, to minimize the effects of impact from the developer or pure water, it was considered to lower the aspect ratio of the resist pattern. In that case, the resist film would have to be made thinner. However, if the resist film is made thinner, and the resist film disappears during dry etching of the light-shielding film made of chromium-containing material, pinhole defects will be formed in the light-shielding film made of chromium-containing material. When dry etching a phase-shift film using the light-shielding film made of chromium-containing material as an etching mask, the plasma during etching of the phase-shift film reaches the phase-shift film through the pinholes, forming pinhole defects in the phase-shift film as well, making it impossible to manufacture a normal phase-shift mask.

[0011] To solve this problem, a hard mask layer made of silicon-containing material but without chromium was added on top of a light-shielding film made of chromium-containing material. In this case, the hard mask layer made of silicon-containing material but without chromium is a thin film with a thickness of 5 to 15 nm, and the thickness of the resist layer formed on the hard mask layer became thin, at 80 to 110 nm.

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

[0013] Furthermore, because it is an isotropic etching process dominated by chemical components, the oxygen-containing chlorine-based plasma moves perpendicularly and horizontally to the substrate, causing side etching on the pattern of the light-shielding film formed from chromium-containing material. In order to make the pattern line width, or critical dimension (CD), uniform across the entire mask, it is necessary to obtain an equivalent amount of side etching across the entire mask. To achieve this, a long period of dry etching is required until the amount of side etching stabilizes due to saturation.

[0014] On the other hand, when dry etching a phase-shift film formed from a silicon-containing material using a fluorine-based gas, in addition to the clear time required for the silicon-containing material to disappear, over-etching of up to 20% of the clear time (for example, a short over-etching of 1 to 6 seconds) is performed. Through dry etching, the transparent substrate in contact with the phase-shift film is also slightly etched, adjusting the phase difference to 175 to 185 degrees relative to the exposure light. In this case, the phase-shift film formed from the silicon-containing material is initially set to a phase difference of 175 to 179 degrees, and the desired phase difference, i.e., 175 to 185 degrees, is achieved by over-etching and etching into the transparent substrate.

[0015] In fluorine-based dry etching, over-etching can be done in a short time because fluorine-based dry etching is an anisotropic etching process dominated by physical components. The pattern of the phase-shift film formed from silicon-containing material does not develop a trailing shape at the boundary with the substrate. Furthermore, the fluorine-based plasma moves perpendicular to the substrate surface, and the CD of the light-shielding film formed from chromium-containing material, which functions as an etching mask, is faithfully reproduced, thus eliminating the need for prolonged over-etching.

[0016] Fluorine-based dry etching is an anisotropic etching process dominated by physical components, resulting in generally greater resist loss than chlorine-based dry etching, which involves oxygen. Therefore, a considerable thickness is required for the resist film used to form the pattern of a hard mask layer made from silicon-containing material. However, a hard mask layer made from silicon-containing material acts as an etching mask when dry etching a light-shielding film made from chromium-containing material using chlorine-based gas. Because it has sufficient etching resistance to chlorine-based gas, it is possible to make the hard mask layer made from silicon-containing material thinner. A thinner hard mask layer made from silicon-containing material shortens the fluorine-based dry etching time for the hard mask layer, and as a result, the resist film required to form the pattern of the hard mask layer made from silicon-containing material can also be made thinner. For these reasons, using a hard mask layer made from silicon-containing material makes it possible to thin the resist film used for etching the hard mask layer, i.e., the resist film initially used in the phase-shift mask blank. Furthermore, by thinning the resist film, the aspect ratio of the resist pattern is reduced. This reduces the impact of physical shocks when applying the developer during the resist pattern formation development process, or when applying pure water during the rinsing process. As a result, a good assist pattern can be formed, and high resolution of the transferred pattern can be achieved.

[0017] A common method for manufacturing a phase-shift mask is to pattern a phase-shift film from a phase-shift mask blank, which consists of a phase-shift film made of a silicon-containing material, a light-shielding film made of a chromium-containing material, and a hard mask layer made of a silicon-containing material, all formed in this order on a transparent substrate. Specifically, the following method is generally used: First, a resist film is formed on the hard mask layer, a pattern is drawn on this resist film using light or an electron beam, and then developed to form a resist pattern. Next, using the resist pattern as an etching mask, the hard mask layer made of a silicon-containing material is dry-etched using a fluorine-based gas to form a pattern on the hard mask layer, and then the resist pattern is removed. Next, using the hard mask layer pattern as an etching mask, the light-shielding film made of a chromium-containing material is dry-etched using a chlorine-based gas to form a pattern on the light-shielding film. Furthermore, using the pattern on the light-shielding film as an etching mask, the phase-shift film made of a silicon-containing material is dry-etched using a fluorine-based gas to form a phase-shift film pattern and simultaneously remove the pattern on the hard mask layer, and then the pattern on the light-shielding film is etched and removed using a chlorine-based gas.

[0018] Furthermore, the increasingly demanded higher pattern resolution in projection lithography is no longer achievable even with phase-shift masks. Therefore, EUV lithography, which uses extreme ultraviolet light for exposure, has come into use.

[0019] Extreme ultraviolet (EUV) light is readily absorbed by all materials, making it impossible to use transmission lithography like conventional photolithography using ArF excimer laser light. Therefore, EUV lithography employs a reflective optical system. The wavelength of extreme ultraviolet light used in EUV lithography is 13-14 nm, while the wavelength of conventional ArF excimer laser light is 193 nm. Compared to conventional photolithography using ArF excimer laser light, EUV lithography has a shorter exposure wavelength, making it possible to transfer finer patterns on the photomask.

[0020] Photomasks 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. As the reflective film, a multilayer reflective film is used in which the reflectivity when extreme ultraviolet light is irradiated onto the surface of the reflective film is increased by alternately stacking low refractive index layers and high refractive index layers. Typically, a molybdenum (Mo) layer is used as the low refractive index layer of the multilayer reflective film, and a silicon (Si) layer is used as the high refractive index layer. A ruthenium (Ru) film is usually used as the protective film. On the other hand, the light-absorbing film uses a material with a high absorption coefficient for EUV light, specifically, a material containing chromium (Cr) or tantalum (Ta) as the main component.

[0021] A common method for manufacturing a reflective photomask is to pattern a light-absorbing film from a reflective photomask blank, which has 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 formed on a substrate in that order. Specifically, the following method is common: First, a resist film is formed on the light-absorbing film, a pattern is drawn on this resist film using light or an electron beam, and then developed to form a resist pattern. Next, a pattern is formed on the light-absorbing film, and then the resist pattern is removed.

[0022] In reflective photomasks required for EUV lithography, the assist patterns—line patterns and space patterns—that support the resolution of the main pattern become smaller as the main pattern is miniaturized. The line width of the assist patterns needs to be reduced to about 30 nm, and especially to about 25 nm. Therefore, compared to phase-shift mask blanks, reflective photomask blanks require even thinner resist films.

[0023] In a reflective photomask, in order to form assist patterns for line patterns and space patterns at about 30 nm, particularly about 25 nm, it is necessary to make the thickness of the resist film 80 nm or less.

[0024] Furthermore, in EUV lithography, in order to manufacture finer patterns on a wafer, an optical system that changes the numerical aperture NA of the exposure machine from 0.33 to 0.55 is used.

[0025] At this time, in a reflective photomask, assist patterns for line patterns and space patterns that assist the resolution of the main pattern become smaller as the main pattern is miniaturized, and the line width of the assist pattern needs to be reduced to about 25 nm, particularly about 20 nm. Therefore, in a reflective photomask blank used in an exposure machine with an aperture ratio of 0.55, further thinning of the resist film is required. In addition to thinning the resist film, it is necessary to reduce the deterioration of resolution due to the disappearance of minute line patterns during the dry etching process.

[0026] For example, when forming a pattern (circuit pattern) of a light absorption film by fluorine-based dry etching using a resist pattern as an etching mask from a light absorption film containing tantalum as a main component, fluorine-based dry etching is anisotropic etching in which physical components are dominant, and since the etching rate with respect to the resist pattern is relatively high, if the resist pattern is too thin, the resist pattern will disappear during dry etching of the light absorption film, and pinhole defects will be formed in the light absorption film, making it impossible to manufacture a normal reflective photomask.

[0027] In order to prevent this pinhole defect, it is necessary to thicken the resist film. However, the thicker the resist film, the higher the aspect ratio of the resist pattern for forming finer assist patterns, so in the development process of forming the resist pattern, it will fall down due to the impact of the developer or the impact of pure water during the rinse process, and the desired resolution cannot be obtained.

[0028] For example, International Publication No. 2012 / 105508 (Patent Document 1) describes a reflective mask blank for EUV lithography in which a layer that reflects EUV light, an absorption layer that absorbs EUV light, and a hard mask layer are formed in this order on a substrate. In this case, the absorption layer is a layer containing at least one of tantalum (Ta) and palladium (Pd) as a main component, and the hard mask layer contains chromium (Cr), nitrogen (N) or oxygen (O), and hydrogen (H), and the total content ratio of Cr and N or Cr and O is 85 to 99.9 at%, and the content ratio of H is 0.1 to 15 at%. By making it such a layer, the surface roughness of the hard mask layer is small, the etching selectivity under the etching conditions of the absorption layer is sufficiently high, and the crystal state becomes amorphous, and the surface roughness can be made sufficiently small. As a result, the line edge roughness of the pattern of the hard mask layer, and further the pattern of the absorption layer formed using the pattern of the hard mask layer does not increase, and it is described that a high-resolution pattern can be obtained.

[0029] Also, International Publication No. 2012 / 105508 (Patent Document 1) describes the procedure for pattern formation on a reflective mask blank for EUV lithography as follows. First, a resist film is formed on the hard mask layer of the EUV mask blank, and pattern formation is performed on the resist film using an electron beam lithography machine. Next, etching by a chlorine-based gas process is performed using the pattern-formed resist film as a mask to form a pattern on the hard mask layer. Next, etching by a fluorine-based gas process is performed using the pattern-formed hard mask layer as a mask to form a pattern on the absorption layer. Next, etching by a chlorine-based gas process is performed to remove the hard mask layer.

Prior Art Documents

Patent Documents

[0030]

Patent Document 1

Summary of the Invention

[0031] In the method described in International Publication No. 2012 / 105508 (Patent Document 1), for example, a CrNH film or a CrOH film is used as the hard mask layer, and a tantalum-containing film is used as the absorption layer, and the absorption layer is patterned by fluorine-based dry etching. In this case, films formed from chromium-containing materials (CrNH films and CrOH films) have high resistance to fluorine-based dry etching, resulting in a slow etching rate, while films mainly containing tantalum have low resistance to fluorine-based dry etching, resulting in a fast etching rate, thus allowing the hard mask layer to be made thinner. On the other hand, films containing tantalum are patterned by chlorine-based dry etching, but if the hard mask layer is made thinner, the amount of resist film reduction during dry etching is also reduced, so the resist film formed on the hard mask layer can be made thinner. As a result, the aspect ratio of the resist pattern is reduced, and the effects of impact from the developer during the development process of resist pattern formation, or from the pure water during the rinsing process, are reduced, so a good assist pattern can be formed by the hard mask layer.

[0032] However, as mentioned above, when dry etching a hard mask layer formed from a chromium-containing material using a chlorine-based gas containing oxygen, it is necessary to perform over-etching by 100-300% of the clear time in addition to the clear time required for the chromium-containing material to disappear. In this case, the thickness of the resist film cannot be reduced to 80 nm or less. Furthermore, films formed from materials containing chromium are generally resistant to chlorine-based dry etching and fluorine-based dry etching, which do not contain oxygen, and can be removed by chlorine-based dry etching containing oxygen. Therefore, when a hard mask layer formed from a chromium-containing material is stripped off by dry etching using a chlorine-based gas containing oxygen after patterning a light-absorbing film, the protective film protecting the multilayer reflective film is exposed to oxygen and chlorine plasma. Ruthenium-based materials commonly used for protective films have low resistance to chlorine-based dry etching containing oxygen, and there is a possibility that they will disappear during the stripping of the hard mask layer formed from the chromium-containing material, narrowing the process window of the dry etching process using chlorine-based gas containing oxygen. In addition, if the thickness of the protective film is reduced by chlorine-based dry etching containing oxygen, there is a risk that the reflective multilayer film will be exposed due to the reduction of the protective film in the subsequent cleaning process (sulfuric acid cleaning), and the reflective multilayer film will be damaged, resulting in a decrease in reflectivity performance.

[0033] Furthermore, when a hard mask layer formed from a chromium-containing material is patterned by dry etching using an oxygen-containing chlorine-based gas, side etching is more likely to occur, causing minute line patterns to disappear and ultimately degrading the resolution of the line patterns.

[0034] The present invention has been made to solve the aforementioned problems, and its first objective is to provide a reflective photomask blank that can produce a good assist pattern with a line width of about 25 nm, particularly about 20 nm, when manufacturing a reflective photomask blank comprising a multilayer reflective film that reflects exposure light, which is extreme ultraviolet light, on a substrate, a protective film for protecting the multilayer reflective film, and a light-absorbing film that absorbs exposure light, and more specifically, a reflective photomask blank that can produce a good assist pattern with a line width of about 25 nm, particularly about 20 nm, even with a thin resist film, for example, a resist film with a thickness of 60 nm or less, and that can minimize the reduction in the thickness of the protective film after all dry etching processes are completed. Furthermore, the present invention has a second objective to provide a method for manufacturing such a reflective photomask blank from such a reflective photomask blank. [Means for solving the problem]

[0035] As mentioned above, with conventional reflective photomask blanks, there was a problem in that with resist films less than 60 nm thick, the resist film would not remain after dry etching, making it impossible to form fine assist patterns well.

[0036] Therefore, the present inventors conducted extensive research to solve the above problem and have found that a reflective photomask blank comprising a multilayer reflective film that reflects exposure light, which is light in the extreme ultraviolet region, a protective film for protecting the multilayer reflective film, and a light-absorbing film that absorbs exposure light, has a first layer and a second layer that are in contact with the light-absorbing film and function as a hard mask when forming a pattern on the light-absorbing film by dry etching. The light-absorbing film is a multilayer comprising an oxide film layer containing oxygen and an absorption layer containing only a small amount of oxygen. The oxygen film layer of the light-absorbing film is formed of a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching. The absorption layer of the light-absorbing film is formed of a material that is resistant to chlorine-based dry etching containing oxygen and can be removed by chlorine-based dry etching and fluorine-based dry etching that does not contain oxygen. The present invention was discovered that the aforementioned problems can be solved by ensuring that the total etching clear time when the first layer and the upper hard mask layer 2A of the second layer are fluorine-based dry etched is shorter than the total etching clear time when half the thickness of the oxide layer and the absorption layer of the light-absorbing film are etched under the same fluorine-based dry etching conditions.

[0037] Accordingly, the present invention provides the following reflective photomask blanks and methods for manufacturing reflective photomasks. [Concept 1] circuit board and A multilayer reflective film formed on the substrate that reflects exposure light, which is light in the extreme ultraviolet region, A protective film formed on the multilayer reflective film for protecting the multilayer reflective film, A light-absorbing film formed on the protective film and absorbing the exposure light, A hard mask film provided on the light absorption film, Equipped with, The light-absorbing film is composed of a multilayer including an absorption layer and an oxygen-containing oxide layer provided on the side away from the substrate. The oxide layer of the light-absorbing film is formed of a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching. The absorption layer of the light-absorbing film is formed of a material that is resistant to chlorine-based dry etching containing oxygen and can be removed by oxygen-free chlorine-based dry etching and fluorine-based dry etching. The hard mask film consists of a multilayer film comprising a second layer, or a second layer and a first layer formed on the side of the second layer that is separated from the substrate. If the first layer is included, the first layer is formed of a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching. The second layer is composed of a multilayer including an upper hard mask layer 2A and a lower hard mask layer 2B containing oxygen, which are provided on the side away from the substrate. The upper hard mask layer 2A of the second layer is formed of a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching. The lower hard mask layer 2B of the second layer is made of a material that is resistant to oxygen-containing chlorine-based dry etching and can be removed by oxygen-free chlorine-based dry etching and fluorine-based dry etching. If the first layer is not included, the etching clear time when the upper hard mask layer 2A of the second layer is dry-etched with a fluorine-based system under one condition is shorter than the etching clear time when half the thickness of the absorption layer of the light-absorbing film is dry-etched with a fluorine-based system under one condition. If the first layer is included, the sum of the etching clear time when the first layer is dry-etched with a fluorine-based system under one condition and the etching clear time when the upper hard mask layer 2A of the second layer is dry-etched with a fluorine-based system under one condition may be shorter than the sum of the etching clear time when the oxide layer of the light-absorbing film is dry-etched with a fluorine-based system under one condition and the etching clear time when half the thickness of the absorption layer of the light-absorbing film is dry-etched with a fluorine-based system under one condition. [Concept 2] In a reflective photomask blank according to Concept 1, The hard mask film includes the first layer, When the absorption layer of the light-absorbing film and the first layer are dry-etched with a fluorine-based system under the conditions described above, the ratio of the etching rate of the first layer to the etching rate of the absorption layer of the light-absorbing film may be 0.4 or more and 2.0 or less. [Concept 3] In a reflective photomask blank according to Concept 1 or 2, When the absorption layer of the light-absorbing film and the lower hard mask layer 2B of the second layer are dry-etched with a fluorine-based etchant under the conditions described above, the ratio of the etching rate of the lower hard mask layer 2B of the second layer to the etching rate of the absorption layer of the light-absorbing film may be 0.7 or more and 1.3 or less. [Concept 4] In a reflective photomask blank according to any one of concepts 1 to 3, When the absorption layer of the light-absorbing film and the lower hard mask layer 2B of the second layer are dry-etched with an oxygen-free chlorine-based system under the conditions described above, the ratio of the etching rate of the lower hard mask layer 2B of the second layer to the etching rate of the absorption layer of the light-absorbing film may be 0.7 or more and 1.3 or less. [Concept 5] In a reflective photomask blank according to any one of concepts 1 to 4, The hard mask film includes the first layer, The first layer may be formed from a material that contains silicon but does not contain chromium. [Concept 6] In a reflective photomask blank according to any one of concepts 1 to 5, The upper hard mask layer 2A and the lower hard mask layer 2B of the second layer may be made of a material containing tantalum. [Concept 7] In a reflective photomask blank according to any one of concepts 1 to 6, The hard mask film includes the first layer, The thickness of the first layer may be 2 nm or more and 12 nm or less. [Concept 8] In a reflective photomask blank according to any one of concepts 1 to 7, The combined thickness of the upper hard mask layer 2A and the lower hard mask layer 2B of the second layer may be 8 nm or more and 30 nm or less. [Concept 9] In a reflective photomask blank according to any one of concepts 1 to 8, The hard mask film includes the first layer, The difference between the thickness of the first layer and the sum of the thickness of the oxide layer of the light-absorbing film and the thickness of the absorption layer of the light-absorbing film may be 30 nm or more. [Concept 10] In a reflective photomask blank according to any one of concepts 1 to 9, The oxide layer and the absorption layer of the light-absorbing film may be formed from a material containing tantalum. [Concept 11] A method for manufacturing a reflective photomask having an oxide layer pattern of the light-absorbing film and an absorption layer pattern of the light-absorbing film from a reflective photomask blank described in any one of Concepts 1 to 10, (A) A step of forming a resist film in contact with the side of the first layer that is separated from the substrate, (B) A step of patterning the resist film to form a resist pattern, (C) Using the resist pattern as an etching mask, the upper hard mask layer 2A of the first and second layers is simultaneously patterned by dry etching using a fluorine-based gas to simultaneously form the first layer pattern and the upper hard mask layer pattern of the second layer. (D) A step of removing the resist pattern, (E) Using the first layer pattern and the upper hard mask layer pattern of the second layer as etching masks, the lower hard mask layer 2B of the second layer is patterned by dry etching using an oxygen-free chlorine-based gas to form the lower hard mask layer pattern of the second layer. (F) Using the first layer pattern, the upper hard mask layer pattern of the second layer, and the lower hard mask layer pattern of the second layer as etching masks, a portion of the oxide layer and the absorption layer of the light-absorbing film is patterned by dry etching using a fluorine-based gas to form a portion of the oxide layer pattern and the absorption layer pattern of the light-absorbing film, while simultaneously removing a portion of the first layer pattern, the upper hard mask layer pattern of the second layer, and the lower hard mask layer pattern of the second layer. (G) The process may include the step of using a portion of the lower hard mask layer pattern of the second layer as an etching mask, patterning the absorption layer of the light absorption film by dry etching using an oxygen-free chlorine-based gas, and simultaneously removing a portion of the lower hard mask layer pattern of the second layer. [Concept 12] In the method for manufacturing a reflective photomask according to Concept 11, The thickness of the resist film may be 70 nm or less. [Concept 13] In a method for manufacturing a reflective photomask according to concept 11 or 12, The pattern of the light-absorbing film may include line patterns with a width of 20 nm or less. [Effects of the Invention]

[0038] According to the present invention, fine assist patterns can be formed effectively.

[0039] According to one aspect of the present invention, the thickness of the resist film can be reduced, the aspect ratio of the resist pattern can be lowered, and assist patterns with a line width of about 25 nm, particularly about 20 nm, can be formed well. Generally, when using a hard mask layer made of chromium-containing material, it is necessary to perform oxygen-containing chlorine-based dry etching. Oxygen-containing chlorine-based dry etching has a large isotropic etching component dominated by chemical components, which causes side etching on the sidewalls of the chromium pattern, leading to pattern breakage and pattern disappearance during etching. On the other hand, in the present invention, as an example, oxygen-free chlorine-based dry etching can be used for the lower hard mask layer 2B of the second layer. As a result, the isotropic etching component is smaller than that of oxygen-containing chlorine-based dry etching, and side etching does not occur on the side walls of the lower hard mask layer 2B of the second layer, thus preventing pattern loss during etching. Therefore, high resolution can be obtained in the transfer pattern of a reflective photomask manufactured from a reflective photomask blank. Here, the lower hard mask layer 2B of the second layer is made of a chromium-free material. Furthermore, when manufacturing a reflective photomask from a reflective photomask blank, it becomes possible to perform oxygen-free chlorine-based dry etching while simultaneously patterning the absorption layer of the light-absorbing film and removing the lower hard mask layer pattern of the second layer, thereby reducing damage to the protective film. As a result, a reflective photomask with a wide process window and high cleaning resistance can be obtained. [Brief explanation of the drawing]

[0040] [Figure 1] This is a cross-sectional view showing an example of a first embodiment of the reflective photomask blank of the present invention. [Figure 2] This is a cross-sectional view showing an example of a second embodiment of the reflective photomask blank of the present invention. [Figure 3] This is a cross-sectional view showing an example of a reflective photomask of the present invention. [Figure 4A]This is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank in the first form of the present invention. [Figure 4B] Figure 4A is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank in the first embodiment of the present invention. [Figure 4C] Figure 4B is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank in the first embodiment of the present invention. [Figure 4D] Figure 4C is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank in the first embodiment of the present invention. [Figure 4E] Figure 4D is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank in the first embodiment of the present invention. [Figure 4F] Figure 4E is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank in the first embodiment of the present invention. [Figure 4G] Figure 4F is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank in the first embodiment of the present invention. [Figure 5] This is a cross-sectional view showing an example of a third embodiment of the reflective photomask blank of the present invention. [Figure 6A] This is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank according to a third aspect of the present invention. [Figure 6B] Figure 6A is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank according to a third embodiment of the present invention. [Figure 6C] Figure 6B is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank according to a third embodiment of the present invention. [Figure 6D] Figure 6C is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank according to a third embodiment of the present invention. [Figure 6E] Figure 6D follows a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank according to a third embodiment of the present invention. [Figure 6F] Figure 6E is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank according to a third embodiment of the present invention. [Figure 6G] Figure 6F is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank according to a third embodiment of the present invention. [Modes for carrying out the invention]

[0041] The present invention will be described in more detail below. The reflective photomask blank of the present invention may include a substrate, a multilayer reflective film formed on the substrate that reflects exposure light which is in the extreme ultraviolet region, a protective film formed on the multilayer reflective film to protect the multilayer reflective film, a light-absorbing film formed on the protective film that absorbs exposure light which is in the extreme ultraviolet region, and a first layer, an upper hard mask layer 2A of the second layer and a lower hard mask layer 2B of the second layer formed in contact with the light-absorbing film and functioning as a hard mask when patterning the light-absorbing film by dry etching. The hard mask may be a multilayer film (laminated film) consisting of a first layer and a second layer provided on the side furthest from the substrate. The second layer may have an upper hard mask layer 2A containing oxygen on its surface. The light-absorbing film may also have an oxide film containing oxygen on its surface. A reflective photomask blank according to another aspect of the present invention may have an upper hard mask layer 2A and a lower hard mask layer 2B of the second layer, instead of including the above-mentioned first layer which is formed in contact with the light-absorbing film on the light-absorbing film and functions as a hard mask when patterning the light-absorbing film by dry etching, and the second layer may have an upper hard mask layer 2A and a lower hard mask layer 2B of the second layer. The second hard mask layer may be a multilayer film (laminated film). The second layer may have an oxygen-containing upper hard mask layer 2A on its surface. The light-absorbing film may also have an oxygen-containing oxide film on its surface.

[0042] The reflective photomask blank of the present invention may further comprise a resist film.

[0043] From a reflective photomask blank, for example, a reflective photomask can be obtained comprising a substrate, a multilayer reflective film formed on the substrate that reflects exposure light in the extreme ultraviolet region, a protective film formed on the multilayer reflective film to protect the multilayer reflective film, and a pattern (circuit pattern or photomask pattern) of a light-absorbing film formed on the protective film that absorbs exposure light in the extreme ultraviolet region.

[0044] The structure 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, identical components may be given the same reference numerals and their description may be omitted. Also, for convenience, the drawings may be shown in an enlarged form, and the dimensional ratios of each component may not necessarily be the same as in reality.

[0045] Figure 1 is a cross-sectional view showing an example of a first embodiment of the reflective photomask blank of the present invention. This reflective photomask blank 100 includes a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1 that reflects exposure light, which is light in the extreme ultraviolet region, a protective film 3 formed on the multilayer reflective film 2 in contact with the multilayer reflective film 2 to protect the multilayer reflective film 2, a light-absorbing film 4 formed on the protective film 3 in contact with the protective film 3 that absorbs exposure light, and a first layer 51, an upper hard mask layer 2A (hereinafter also referred to as "upper hard mask layer 52"), and a lower hard mask layer 2B (hereinafter also referred to as "lower hard mask layer 53") formed on the light-absorbing film 4 in contact with the light-absorbing film 4 that function as hard masks when patterning the light-absorbing film 4 by dry etching. The light-absorbing film 4 may have an oxide film layer 41 of the light-absorbing film provided on the side away from the substrate, and an absorption layer 42 of the light-absorbing film for absorbing light. To rephrase the above embodiment, the reflective photomask blank 100 has the following layers stacked in this order from the substrate 1 side: multilayer reflective film 2, protective film 3, light absorption layer 42 of the light absorption film, oxide film layer 41 of the light absorption film, lower hard mask layer 53 of the second layer, upper hard mask layer 52 of the second layer, and first layer 51.

[0046] Figure 2 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 100 includes a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1 that reflects exposure light, which is light in the extreme ultraviolet region, a protective film 3 formed on the multilayer reflective film 2 in contact with the multilayer reflective film 2 to protect the multilayer reflective film 2, a light-absorbing film 4 formed on the protective film 3 in contact with the protective film 3 that absorbs exposure light, and a first layer 51, an upper hard mask layer 52 of the second layer, and a lower hard mask layer 53 of the second layer, formed on the light-absorbing film 4 in contact with the light-absorbing film 4, which function as hard masks when patterning the light-absorbing film 4 by dry etching. Furthermore, a resist film 6 is provided on the first layer 51. The light-absorbing film 4 consists of an oxide film layer 41 of the light-absorbing film provided on the side away from the substrate and an absorption layer 42 of the light-absorbing film for absorbing light. To rephrase the above embodiment, the reflective photomask blank 100 has the following layers stacked in this order from the substrate 1 side: a multilayer reflective film 2, a protective film 3, an absorption layer 42 of the light-absorbing film, an oxide film layer 41 of the light-absorbing film, a lower hard mask layer 53 of the second layer, an upper hard mask layer 52 of the second layer, the first layer 51, and a resist film 6.

[0047] Figure 3 is a cross-sectional view showing an example of a reflective photomask 200 of the present invention. This reflective photomask has a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1 that reflects exposure light, which is light in the extreme ultraviolet region, a protective film 3 formed on the multilayer reflective film 2 in contact with the multilayer reflective film 2 to protect the multilayer reflective film, and a light-absorbing film pattern (circuit pattern or photomask pattern) 4a formed on the protective film 3 in contact with the protective film 3 that absorbs exposure light. The light-absorbing film pattern 4a is composed of an oxide film layer pattern 41a of the light-absorbing film and an absorption layer pattern 42a of the light-absorbing film. In other words, in this reflective photomask 200, the multilayer reflective film 2, the protective film 3, and the light-absorbing film pattern 4a are stacked in this order from the substrate 1 side. The light-absorbing film pattern 4a is composed of an oxide film layer pattern 41a of the light-absorbing film and an absorption layer pattern 42a of the light-absorbing film.

[0048] Figure 5 is a cross-sectional view showing an example of a third embodiment of the reflective photomask blank of the present invention. This reflective photomask blank 100 comprises a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1 and reflecting exposure light which is extreme ultraviolet light, a protective film 3 formed on the multilayer reflective film 2 in contact with the multilayer reflective film 2 to protect the multilayer reflective film 2, a light-absorbing film 4 formed on the protective film 3 in contact with the protective film 3 and absorbing exposure light, and an upper hard mask layer 52 and a lower hard mask layer 53 of the second layer formed on the light-absorbing film 4 in contact with the light-absorbing film 4 and functioning as a hard mask when patterning the light-absorbing film 4 by dry etching. In this case, the light-absorbing film 4 is composed of an oxide film layer 41 of the light-absorbing film provided on the side away from the substrate and an absorption layer 42 of the light-absorbing film for absorbing light. In other words, the reflective photomask blank 100 has the following layers stacked in this order from the substrate 1 side: a multilayer reflective film 2, a protective film 3, an absorption layer 42 of the light-absorbing film, an oxide film layer 41 of the light-absorbing film, a lower hard mask layer 53 of the second layer, an upper hard mask layer 52 of the second layer, and a resist film 6.

[0049] [substrate] There are no particular restrictions on the type or size of the substrate, and the substrates of the reflective photomask blank and reflective photomask may be transparent or opaque at the exposure wavelength. For example, glass substrates such as quartz substrates can be used. Alternatively, a substrate called a 6025 substrate, which is 6 inches square and 0.25 inches thick as specified in the SEMI standard, is preferred. When using the SI unit system, a 6025 substrate is usually expressed as a substrate of 152 mm square and 6.35 mm thick. Furthermore, when the reflective mask is held on the mask stage of the exposure apparatus, it is fixed by an electrostatic chuck. Therefore, a back surface film may be formed on the back surface of the substrate (the surface opposite to the surface on which the multilayer reflective film is formed) to facilitate the fixing of the substrate by the electrostatic chuck.

[0050] [Multilayer reflective film] A multilayer reflective film is a film that reflects exposure light, which is in the extreme ultraviolet region. Preferably, the multilayer reflective film is formed in contact with the substrate. This extreme ultraviolet region light is called EUV light, and the wavelength of EUV light is 13-14 nm, typically around 13.5 nm. The material constituting the multilayer reflective film is preferably resistant to dry etching using chlorine-based gases (e.g., Cl2 gas only, or a mixed gas of Cl2 and O2 gas) and removable by dry etching using fluorine-based gases (e.g., CF4 gas or SF6 gas). Specific examples of materials constituting the multilayer reflective film include molybdenum (Mo) and silicon (Si). Generally, a multilayer film (Si / Mo multilayer film) is used, in which approximately 20-60 layers of molybdenum (Mo) and silicon (Si) layers are alternately stacked. The thickness of the multilayer reflective film is preferably 200 nm or more, particularly 220 nm or more, and preferably 340 nm or less, particularly 280 nm or less. The thickness of the molybdenum (Mo) layer is preferably 1 nm or more, particularly 2 nm or more, and preferably 5 nm or less, particularly 4 nm or less. The thickness of the silicon (Si) layer is preferably 2 nm or more, particularly 3 nm or more, and preferably 6 nm or less, particularly 5 nm or less.

[0051] [Protective film] The protective film is a film for protecting the multilayer reflective film. The protective film is preferably formed in contact with the multilayer reflective film. The protective film is provided to protect the multilayer reflective film during processes such as cleaning during processing of a reflective photomask or modification of a reflective photomask. Furthermore, the protective film preferably has the function of protecting the multilayer reflective film when patterning the light-absorbing film by etching and preventing oxidation of the multilayer reflective film. The material constituting the protective film is preferably a material with different etching properties from the light-absorbing film. Specifically, it is preferably a material that is resistant to chlorine-based dry etching and is resistant to cleaning containing sulfuric acid and cleaning containing alkali. Specifically, a material containing ruthenium (Ru) can be used as a material constituting the protective film. The protective film may be a ruthenium compound containing one or more elements selected from Mo, Nb, Zr, Y, B, Ti, and La, in order to be resistant to chlorine-based dry etching, chlorine-based dry etching containing oxygen, cleaning containing sulfuric acid, and cleaning containing alkali. The protective film may be a single layer, a multilayer (for example, a film composed of 2 to 4 layers), or a film with a graded composition. The thickness of the protective film is preferably 1 nm or more, and preferably 20 nm or less.

[0052] [Absorption layer of light-absorbing film] The light-absorbing film is composed of an oxide layer and an absorption layer, and the absorption layer is a film that absorbs exposure light, which is in the extreme ultraviolet region. The absorption layer of the light-absorbing film is preferably formed in contact with a protective film. The absorption layer of the light-absorbing film is preferably made of a material that is resistant to chlorine-based dry etching containing oxygen and can be removed by chlorine-based dry etching and fluorine-based dry etching that do not contain oxygen. The absorption layer of the light-absorbing film is preferably made of a material containing tantalum (Ta). Specifically, as a material containing tantalum, examples of materials for the absorption layer of the light-absorbing film include elemental tantalum (Ta), and tantalum compounds containing tantalum (Ta) and one or more elements selected from nitrogen (N), boron (B), etc. Examples of such materials include a material made of tantalum (Ta), a material made of tantalum and nitrogen (TaN), a material made of tantalum and boron (TaB), and a material made of tantalum, nitrogen, and boron (TaNB). Furthermore, the tantalum compound may contain trace amounts of oxygen (O). The light-absorbing film may be a single layer film, a multilayer film (for example, a film composed of 2 to 4 layers), or a film with a gradient composition. The thickness of the absorption layer of the light-absorbing film is preferably 30 nm or more, particularly 40 nm or more, especially 50 nm or more, and preferably 100 nm or less, particularly 80 nm or less, and especially 74 nm or less.

[0053] [Oxidation layer of light-absorbing film] The oxide layer of a light-absorbing film is a film that reduces light reflectance. Preferably, the oxide layer of the light-absorbing film is formed in contact with the absorption layer of the light-absorbing film. The oxide layer of the light-absorbing film is preferably formed from a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching. The oxide layer of the light-absorbing film is preferably formed from a material containing tantalum (Ta) and oxygen (O). The material containing tantalum and oxygen may be a tantalum compound containing a material selected from nitrogen (N), boron (B), etc. Examples of such materials include a material composed of tantalum and oxygen (TaO), a material composed of tantalum, oxygen and nitrogen (TaON), a material composed of tantalum, oxygen and boron (TaOB), and a material composed of tantalum, oxygen, nitrogen and boron (TaONB). The film may be a single layer or a multilayer film (for example, a film composed of 2 to 4 layers), and may also be a film with a graded composition. The thickness of the oxide layer of the light-absorbing film is preferably 1 nm or more, particularly 2 nm or more, and preferably 10 nm or less, and especially 5 nm or less, in order to reduce the light reflectance.

[0054] For the absorption layer of a light-absorbing film to be removable by oxygen-free chlorine-based dry etching, the oxygen content is preferably 5% or less, and particularly preferably 3% or less. For the oxide layer of the light-absorbing film to be resistant to oxygen-free chlorine-based dry etching, the oxygen content is preferably 15% or more, and particularly preferably 18% or more.

[0055] The oxide layer 41 of the light-absorbing film functions as an etching mask (hard mask) for the absorption layer 42 of the light-absorbing film in oxygen-free chlorine-based dry etching (see Figure 6G). When the absorption layer 42 of the light-absorbing film is subjected to oxygen-free chlorine-based dry etching under a single condition (predetermined identical conditions), it is preferable that the ratio of the etching rate (nm / sec) of the absorption layer 42 of the light-absorbing film to the etching rate (nm / sec) of the oxide layer 41 of the light-absorbing film is 45 or higher, particularly 70 or higher. By achieving such an etching rate (nm / sec) ratio, when forming the absorption layer pattern of the light-absorbing film using oxygen-free chlorine-based dry etching with the lower hard mask layer pattern of the second layer and the oxide layer pattern of the light-absorbing film as hard masks (see Figure 6G), after the lower hard mask layer pattern of the second layer disappears, the slower etching rate of the oxide layer pattern of the light-absorbing film allows for longer over-etching of the absorption layer pattern of the light-absorbing film, thereby improving the stability of the CD. Furthermore, this increases the process window, allowing for the use of more dry etching conditions.

[0056] [Hard Mask] The hard mask of the present invention is composed of multiple layers, including a first layer provided on the side furthest from the substrate and a second layer provided on a side other than the side furthest from the substrate. The hard mask is not limited to being composed of two layers, but may be composed of three or more layers, for example, three, four, or five layers. The three, four, or five layers can be made of a film made of a material with strong cleaning resistance or a film made of a material with high adhesion to the resist. The second layer is preferably provided on the side closest to the substrate.

[0057] The first layer of the hard mask is made of a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching. Due to these dry etching properties, the first layer functions as an etching mask in etching the second layer, the oxide layer of the light-absorbing film, and the absorption layer of the light-absorbing film. A material containing silicon (Si) but not chromium (Cr) is preferred for the first layer.

[0058] On the other hand, the second layer of the hard mask consists of an upper hard mask layer 2A and a lower hard mask layer 2B. The upper hard mask layer 2A of the second layer is made of a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching. The lower hard mask layer 2B of the second layer is made of a material that is resistant to oxygen-containing chlorine-based dry etching and can be removed by oxygen-free chlorine-based dry etching and fluorine-based dry etching. Furthermore, the upper hard mask layer 2A of the second layer functions as an etching mask in oxygen-free chlorine-based dry etching of the absorption layer of the light absorption film. Preferably, the upper hard mask layer 2A of the second layer is made of a material containing tantalum (Ta) and oxygen (O). The material containing tantalum and oxygen may be a tantalum compound containing a material selected from nitrogen (N), boron (B), etc. Examples of such materials include those composed of tantalum and oxygen (TaO), tantalum, oxygen, and nitrogen (TaON), tantalum, oxygen, and boron (TaOB), and tantalum, oxygen, nitrogen, and boron (TaONB). These materials may be single-layer films or multilayer films (for example, films composed of 2 to 4 layers), and may also have a gradient composition. The upper hard mask layer 2A of the second layer is preferably formed of a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching. The lower hard mask layer 2B of the second layer is preferably formed in contact with the upper hard mask layer 2A of the second layer. The lower hard mask layer 2B of the second layer is preferably formed from a material containing tantalum (Ta). Specific examples of materials containing tantalum include elemental tantalum (Ta), and tantalum compounds containing tantalum (Ta) and one or more elements selected from nitrogen (N), boron (B), etc. Examples of such materials include materials consisting of tantalum (Ta), materials consisting of tantalum and nitrogen (TaN), materials consisting of tantalum and boron (TaB), and materials consisting of tantalum, nitrogen, and boron (TaNB). The material may be a single layer film or a multilayer film (for example, a film composed of 2 to 4 layers), and may also be a film with a graded composition. The lower hard mask layer 2B of the second layer is preferably formed of a material that is resistant to oxygen-containing chlorine-based dry etching and can be removed by oxygen-free chlorine-based dry etching and fluorine-based dry etching.

[0059] [First layer] The first layer is the layer that comes into contact with the resist film. The first layer is also a film that functions as an etching mask (hard mask) in oxygen-free chlorine-based dry etching, with the lower hard mask layer 2B of the second layer acting as the etching mask. The first layer is preferably formed from a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching.

[0060] The material of the first layer may contain one or more elements selected from oxygen (O), nitrogen (N), and carbon (C) in addition to silicon, and a material consisting of silicon and one or more elements selected from oxygen, nitrogen, and carbon is particularly preferred. When the material of the first layer contains elements other than silicon, the silicon content is less than 100 atomic%, but preferably 80 atomic% or less, and particularly preferably 60 atomic% or less. A lower silicon content results in a higher etching rate (etching speed) in fluorine-based dry etching of the first layer. On the other hand, the lower limit of the silicon content is usually 20 atomic% or more, and preferably 30 atomic% or more.

[0061] The material of the first layer preferably contains nitrogen, and silicon nitride (SiN), which consists of silicon and nitrogen, is particularly preferred. When the material of the first layer contains nitrogen, the silicon content is preferably 20 atomic% or more, particularly 30 atoms or more, and also preferably 80 atomic% or less, particularly 60 atoms or less. On the other hand, the nitrogen content is preferably 80 atomic% or less, particularly 55 atomic% or less. There is no particular lower limit to the nitrogen content, but it is preferably 20 atomic% or more, particularly 30 atomic% or more.

[0062] The material of the first layer preferably contains oxygen, and silicon oxide (SiO), which consists of silicon and oxygen, is particularly preferred. When the material of the first layer contains oxygen, the silicon content is preferably 20 atomic% or more, particularly 30 atomic% or more, and also preferably 80 atomic% or less, particularly 60 atomic% or less. On the other hand, the oxygen content is preferably 20 atomic% or more, particularly 25 atomic% or more, and also preferably 80 atomic% or less, particularly 68 atomic% or less.

[0063] The material of the first layer preferably contains nitrogen along with oxygen, and silicon nitride oxide (SiON), which consists of silicon, oxygen, and nitrogen, is particularly preferred. The silicon content is preferably 20 atomic% or more, particularly 30 atomic% or more, and also preferably less than 80 atomic%, particularly 60 atomic% or less. On the other hand, the oxygen content is preferably greater than 0 atomic% and less than 80 atomic%, particularly 68 atomic% or less. On the other hand, the nitrogen content is preferably greater than 0 atomic% and less than 80 atomic%, particularly 55 atomic% or less.

[0064] The first layer is patterned by fluorine-based dry etching, using a resist pattern formed in contact with the first layer as an etching mask. Since the etching time is shorter the thinner the layer, the thickness of the first layer is preferably 12 nm or less, and particularly preferably 10 nm or less. On the other hand, if it is too thin, the function of the first layer as an etching mask in etching the lower hard mask layer 2B of the second layer is lost, and the sensitivity of defect inspection of the first layer decreases. Therefore, the thickness of the first layer is preferably 2 nm or more, and particularly preferably 4 nm or more.

[0065] Materials containing silicon but not chromium are resistant to oxygen-free chlorine-based dry etching of the lower hard mask layer 2B of the second layer, and the first layer pattern functions as an etching mask in oxygen-free chlorine-based dry etching of the lower hard mask layer 2B of the second layer. Furthermore, since the first layer can be etched with fluorine-based dry etching, which does not require prolonged over-etching, the thickness of the resist film used for etching the first layer can be reduced. In particular, materials containing both silicon and oxygen but not chromium, preferably materials containing each element in the aforementioned proportions, and more preferably materials with a relatively high oxygen content, have high adhesion to the resist film and, compared to materials containing chromium, are less soluble in a mixture of sulfuric acid and hydrogen peroxide or ammonia-added water, and can stably maintain the optical properties necessary for defect inspection and the like. Furthermore, materials containing oxygen along with silicon but no chromium, preferably materials containing each element in the aforementioned proportions, and more preferably materials with a relatively high oxygen content, have a chemically stable surface compared to materials containing tantalum, and improve the stability of the CD when creating a resist pattern. For these reasons, by making the side of the etching mask film furthest from the substrate the first layer, even fine line patterns such as assist patterns are less likely to collapse due to the impact of the developer during the resist pattern formation development process or the impact of pure water during the rinsing process, allowing for the formation of a good resist pattern and consistently achieving high resolution.

[0066] Furthermore, since the material of the first layer, the material of the upper hard mask layer 2A of the second layer, and the material of the lower hard mask layer 2B of the second layer are materials that can be removed by fluorine-based dry etching, the first layer pattern, the upper hard mask layer pattern of the second layer, and the lower hard mask layer pattern of the second layer can be removed simultaneously with the formation of the absorption layer pattern of the light-absorbing film during fluorine-based dry etching when forming the oxide layer pattern and the absorption layer pattern of the light-absorbing film. In particular, when forming the oxide layer pattern and the absorption layer pattern of a light-absorbing film using fluorine-based dry etching, in order to remove the entire first layer pattern, the entire upper hard mask layer pattern of the second layer, and a portion of the lower hard mask layer pattern of the second layer in the thickness direction simultaneously with the formation of the oxide layer pattern and the absorption layer pattern of the light-absorbing film, it is beneficial that the total etching clear time when the upper hard mask layer 2A of the first and second layers is dry-etched using fluorine-based dry etching under the same conditions is shorter than the total etching clear time when the oxide layer and the absorption layer of the light-absorbing film are 1 / 2 of the thickness (under the same conditions as the fluorine-based dry etching of the upper hard mask layer 2A of the first and second layers).

[0067] Furthermore, when the first layer is not included, in fluorine-based dry etching for forming the oxide layer pattern and the absorption layer pattern of the light-absorbing film, in order to remove the entire upper hard mask layer pattern of the second layer at the same time as forming the oxide layer pattern and the absorption layer pattern of the light-absorbing film, it is beneficial that the etching clear time when the upper hard mask layer 2A of the second layer is dry-etched with fluorine-based etching under the same conditions is shorter than the etching clear time of 1 / 2 the thickness of the oxide layer and the absorption layer of the light-absorbing film (under the same conditions as the fluorine-based dry etching of the upper hard mask layer 2A of the second layer).

[0068] Furthermore, when the absorption layer of the light-absorbing film and the first layer are dry-etched with a fluorine-based system under the same conditions, the ratio of the etching rate (nm / sec) of the first layer to the etching rate (nm / sec) of the absorption layer of the light-absorbing film is preferably 0.4 or higher, particularly 0.7 or higher, and also preferably 2.0 or lower, particularly 1.2 or lower. Moreover, the difference between the thickness of the first layer and the sum of the thickness of the oxide layer of the light-absorbing film and the thickness of the absorption layer of the light-absorbing film is preferably 30 nm or higher, particularly 40 nm or higher, and especially 44 nm or higher.

[0069] Furthermore, when the absorption layer of the light-absorbing film and the lower hard mask layer 2B of the second layer are dry-etched with a fluorine-based system under the same conditions, the ratio of the etching rate (nm / sec) of the lower hard mask layer 2B of the second layer to the etching rate (nm / sec) of the absorption layer of the light-absorbing film is preferably 0.7 or higher, particularly 0.8 or higher, and also preferably 1.3 or lower, particularly 1.2 or lower.

[0070] Furthermore, when the absorption layer of the light-absorbing film and the lower hard mask layer 2B of the second layer are subjected to oxygen-free chlorine-based dry etching under the same conditions, the ratio of the etching rate of the lower hard mask layer 2B of the second layer to the etching rate (nm / second) of the absorption layer of the light-absorbing film is preferably 0.7 or higher, particularly 0.8 or higher, and also preferably 1.3 or lower, particularly 1.2 or lower.

[0071] [Second layer] The second layer consists of an upper hard mask layer 2A and a lower hard mask layer 2B. The upper hard mask layer 2A is a layer that functions to stabilize the surface layer of the second layer, which is made of a chemically active tantalum-containing material, and the lower hard mask layer 2B functions as an etching mask (hard mask) in oxygen-free chlorine-based dry etching of the light-absorbing film.

[0072] The thickness of the second layer (the sum of the thickness of the upper hard mask layer 2A and the lower hard mask layer 2B of the second layer) is preferably 8 nm or more, particularly 10 nm or more, because if it is too thin, it will lose its function as an etching mask in etching the light absorption film and the sensitivity of defect inspection of the second layer will decrease. Furthermore, to shorten the etching clear time, it is preferably 30 nm or less, particularly 20 nm or less. Materials containing tantalum can be removed by oxygen-free chlorine-based dry etching. Compared to oxygen-containing chlorine-based dry etching, oxygen-free chlorine-based dry etching is less likely to cause side etching on the side walls of the pattern, and the pattern shape becomes perpendicular to the substrate. When large side etching occurs in a line pattern, the dimensions near the center of the pattern relative to the vertical direction become smaller relative to the top and bottom of the pattern relative to the vertical direction due to side etching from both sides, making the pattern more prone to bending during dry etching, and consequently degrading the resolution. Furthermore, materials containing tantalum can be removed by fluorine-based dry etching. The upper hard mask layer 2A of the second layer, which is formed of oxygen-containing tantalum, is removed simultaneously when etching the oxide layer and a portion of the absorption layer of the light-absorbing film by fluorine-based dry etching. In addition, a portion of the lower hard mask layer 2B of the second layer, which contains tantalum, is removed simultaneously when etching a portion of the absorption layer of the light-absorbing film by fluorine-based dry etching. Subsequently, the absorption layer of the remaining light-absorbing film is subjected to oxygen-free chlorine-based dry etching to form the absorption layer pattern of the light-absorbing film, and at the same time, a portion of the lower hard mask layer 2B of the second layer that remained as described above is removed. Since the oxide layer of the light-absorbing film has an oxide layer containing oxygen, it is resistant to oxygen-free chlorine etching and functions as an etching prevention film when removing a portion of the lower hard mask layer 2B of the second layer. Also, since oxygen-free chlorine etching is performed when forming the absorption layer pattern of the light-absorbing film, the protective film, which is resistant to oxygen-free chlorine etching, does not experience a reduction in film thickness. Oxygen-containing chlorine-based dry etching is highly reactive with ruthenium and has a faster etching rate compared to oxygen-free chlorine-based dry etching. Therefore, if the protective film is etched for a long time with oxygen-containing chlorine-based dry etching, the protective film will be completely removed and lose its function. For these reasons, by providing the etching mask film with the first layer, an upper hard mask layer 2A of the second layer, and a lower hard mask layer 2B of the second layer, high resolution can be obtained while maintaining the thickness of the protective film. Furthermore, in order to obtain the above effects, it is preferable that the upper hard mask layer 2A of the second layer is tantalum oxynitride containing tantalum, oxygen, and nitrogen, and the lower hard mask layer 2B of the second layer is tantalum nitride containing tantalum and nitrogen. For the lower hard mask layer 2B of the second layer to be removable by oxygen-free chlorine-based dry etching, the oxygen content is preferably 5% or less, and particularly preferably 3% or less. In order for the upper hard mask layer 2A of the second layer to be resistant to oxygen-free chlorine-based dry etching, the oxygen content is preferably 15% or more, and particularly preferably 18% or more. Furthermore, the upper hard mask layer 2A of the second layer functions as an etching mask (hard mask) for the lower hard mask layer 2B of the second layer in oxygen-free chlorine-based dry etching. When the lower hard mask layer 2B of the second layer is subjected to oxygen-free chlorine-based dry etching under the same conditions, it is preferable that the ratio of the etching rate (nm / sec) of the lower hard mask layer 2B of the second layer to the etching rate (nm / sec) of the upper hard mask layer 2A of the second layer is 45 or higher, and particularly 70 or higher. By using this etching rate (nm / second) ratio, as shown in Figure 6E, when forming the lower hard mask layer pattern of the second layer using oxygen-free chlorine-based dry etching with the upper hard mask layer pattern of the second layer as the hard mask, the slower etching rate of the upper hard mask layer pattern of the second layer allows for longer over-etching of the lower hard mask layer pattern of the second layer, thereby improving the stability of the CD. Furthermore, this increases the process window, allowing for the use of a wider range of dry etching conditions.

[0073] Furthermore, since the lower hard mask layer 2B of the second layer is made of a material that can be removed by oxygen-free dry etching, it can be removed simultaneously when removing the absorption layer of the light absorption film by oxygen-free dry etching.

[0074] [Resist film] The resist film may be an electron beam resist drawn with an electron beam or a photoresist drawn with light, but a chemically amplified resist is preferred. The chemically amplified resist may be positive or negative, and examples include a base resin such as a hydroxystyrene resin or a (meth)acrylic acid resin, an acid generator, and optionally a crosslinking agent, quencher, surfactant, etc.

[0075] As described above, the thickness of the resist film formed on the first layer of the present invention can be thin. The thickness of the resist film is preferably 80 nm or less from the viewpoint of making the resist pattern for forming a fine assist pattern in the developing process of resist pattern formation less likely to collapse due to impact from the developer or impact from pure water during the rinsing process. Furthermore, from the viewpoint of forming line patterns such as assist patterns with a width of about 25 nm, and especially about 20 nm, it is preferably 70 nm or less, and particularly preferably 60 nm or less. The lower limit of the resist film thickness is the thickness that functions as an etching mask in etching the first layer, and is not particularly limited as long as the resist pattern remains on the entire pattern of the first layer after etching, but is preferably 15 nm or more, and particularly preferably 20 nm or more.

[0076] The formation of the multilayer reflective film, protective film, light-absorbing film, and the upper hard mask layer 2A of the first and second layers and the lower hard mask layer 2B of the second layer of the present invention is not particularly limited, but formation by sputtering is preferred because it offers good controllability and makes it easy to form films with predetermined characteristics. The sputtering method can be DC sputtering, RF sputtering, etc., and is not particularly limited.

[0077] When forming a multilayer reflective film consisting of a molybdenum layer and a silicon layer, a molybdenum target and a silicon target can be used as the sputtering target. When forming a protective film made of a ruthenium-containing material, a ruthenium target can be used as the sputtering target. When forming a light-absorbing film made of a tantalum-containing material, a tantalum target can be used as the sputtering target. When forming a first layer made of a silicon-containing, chromium-free material, a silicon target can be used as the sputtering target.

[0078] The power supplied to the sputtering target should be set appropriately depending on the size of the sputtering target, cooling efficiency, and ease of controlling film formation. Typically, the power per unit area of ​​the sputtering surface of the sputtering target is 50 to 3000 W / cm². 2 This is how it should be done. Also, noble gases such as helium gas (He gas), neon gas (Ne gas), and argon gas (Ar gas) are used as sputtering gases, and each film and the layers contained within the film are formed. If only the target element is to be formed, only noble gases should be used as the sputtering gas.

[0079] When forming individual films and layers contained within them using materials containing oxygen, nitrogen, or carbon, reactive sputtering is preferred. For reactive sputtering, noble gases such as helium (He), neon (Ne), and argon (Ar) are used as sputtering gases, along with reactive gases. For example, when forming a film with an oxygen-containing material, oxygen (O2) gas is used as the reactive gas; when forming a film with a nitrogen-containing material, nitrogen (N2) gas is used as the reactive gas. When forming a film with a material containing both nitrogen and oxygen, the reactive gas can be appropriately selected from oxygen (O2), nitrogen (N2), and nitrogen oxide gases such as nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O). When forming with carbon-containing materials, carbon-containing gases such as methane (CH4), carbon monoxide (CO), and carbon dioxide (CO2) can be used as reactive gases. When forming with materials containing oxygen, nitrogen, and carbon, for example, oxygen (O2), nitrogen (N2), and carbon dioxide (CO2) can be used simultaneously as reactive gases.

[0080] The pressure during the formation of each membrane and the layers contained within it should be set appropriately, taking into consideration membrane stress, chemical resistance, and wash resistance. Typically, a pressure of 0.01 Pa or higher, particularly 0.03 Pa or higher, and 1 Pa or lower, particularly 0.3 Pa or lower, improves chemical resistance. The flow rate of each gas should be set appropriately to achieve the desired composition, and is typically between 0.1 and 100 sccm.

[0081] In the manufacturing process of a reflective photomask blank, the substrate or the substrate and the film formed on the substrate may be heat-treated before forming the resist film. The heat treatment method can include infrared heating, resistance heating, etc., and there are no particular restrictions on the treatment conditions. The heat treatment can be carried out, for example, in an oxygen-containing gas atmosphere. There are no particular restrictions on the concentration of the oxygen-containing gas; for example, in the case of oxygen gas (O2 gas), it can be 1 to 100 volume percent. The heat treatment temperature is preferably 200°C or higher, and particularly preferably 400°C or higher.

[0082] Furthermore, in the manufacturing process of reflective photomask blanks, the film formed on the substrate, particularly the first layer, may be subjected to ozone treatment or plasma treatment before the resist film is formed, and there are no particular restrictions on the treatment conditions. Any of these treatments can be performed with the aim of increasing the oxygen concentration on the surface of the film, and in that case, the treatment conditions should be adjusted as appropriate to achieve a predetermined oxygen concentration. When forming the film by sputtering, it is also possible to increase the oxygen concentration on the surface of the film by adjusting the ratio of the noble gas in the sputtering gas to oxygen-containing gases (oxidizing gases) such as oxygen gas (O2 gas), carbon monoxide gas (CO gas), and carbon dioxide gas (CO2 gas). Furthermore, the first layer may be a single layer film, a multilayer film (for example, a film composed of 2 to 4 layers), or a film with a gradient composition. If the first layer has a low silicon content and a high nitrogen content, or a high nitrogen and oxygen content, the etching rate with the fluorine-based gas will be faster, making it possible to make the resist film thinner. However, the surface roughness of the film surface will be smaller, resulting in poor adhesion between the first layer and the resist film, and a deterioration in the resolution of the resist pattern. On the other hand, if the silicon content is high and the nitrogen content, or a low nitrogen and oxygen content, is small, the etching rate with the fluorine-based gas will be slower, making it impossible to make the resist film thinner. However, the surface roughness of the film surface will be larger, resulting in good adhesion between the first layer and the resist film, and an improvement in the resolution of the resist pattern. Therefore, it is preferable that the composition of the first layer, on the side separated from the substrate, has a high silicon content and a low nitrogen content, or a low nitrogen and oxygen content, and that as it moves toward the substrate, the silicon content decreases and the nitrogen content, or a high nitrogen and oxygen content, or a high nitrogen and oxygen content, results in a film with good adhesion to the resist film and a fast etching rate.

[0083] Furthermore, in the manufacturing process of reflective photomask blanks, a cleaning treatment may be performed to remove defects present on the surface of the substrate or the film formed on the substrate before forming the resist film. The cleaning can be performed using either or both ultrapure water and functional water, which is ultrapure water containing ozone gas, hydrogen gas, etc. Alternatively, after cleaning with ultrapure water containing a surfactant, further cleaning may be performed using either or both ultrapure water and functional water. The cleaning can be performed while irradiating with ultrasound as needed, and UV light irradiation may also be combined with the cleaning.

[0084] The method for forming the resist film (coating the resist) is not particularly limited, and known methods can be applied.

[0085] Next, a method for manufacturing a reflective photomask from a reflective photomask blank according to the first embodiment of the present invention will be described with reference to the drawings. When manufacturing a reflective photomask from a reflective photomask blank according to the present invention, a resist pattern is formed from a resist film, and the resist pattern is used as an etching mask. Depending on the material forming the film or layer beneath it, dry etching using a fluorine-based gas (fluorine-based dry etching) or dry etching using a chlorine-based gas (chlorine-based dry etching) is applied to form the pattern, and the pattern is removed as appropriate. Furthermore, in the manufacture of a reflective photomask, the resist film and resist pattern can be removed with sulfuric acid peroxide.

[0086] Figure 4 is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank according to the present invention. First, as shown in Figure 4A, a resist film 6 is formed in contact with the side of the reflective photomask blank 100 of the first embodiment that is separated from the substrate 1 (i.e., in contact with the first layer 51) (step (A)).

[0087] Next, as shown in Figure 4B, the resist film 6 is patterned to form a resist film pattern 6a (step (B)).

[0088] Next, as shown in Figure 4C, the resist pattern 6a is used as an etching mask, and the upper hard mask layer 2A of the first layer 51 and the second layer is patterned simultaneously by dry etching using a fluorine-based gas to form the first layer pattern 51a and the upper hard mask layer pattern 52a of the second layer. (Process (C)).

[0089] Next, the resist pattern 6a is removed as shown in Figure 4D (step (D)).

[0090] Next, as shown in Figure 4E, the lower hard mask layer 2B of the second layer is patterned by dry etching using an oxygen-free chlorine-based gas, with the first layer pattern 51a and the upper hard mask layer pattern 52a of the second layer as etching masks, thereby forming the lower hard mask layer pattern 53a of the second layer (step (E)).

[0091] Next, as shown in Figure 4F, the first layer pattern 51a, the upper hard mask layer pattern 52a of the second layer, and the lower hard mask layer pattern 53a of the second layer are used as hard masks to pattern a portion of the oxide layer 41 and the absorption layer 42 of the light-absorbing film by fluorine-based dry etching, thereby forming the oxide layer pattern 41a and the absorption layer pattern 42a of the light-absorbing film. Here, the absorption layer 42 of the light-absorbing film is not completely etched, and a portion remains (step (F)). Furthermore, when patterning a portion of the oxide layer 41 and the absorption layer 42 of the light-absorbing film by fluorine-based dry etching, a portion of the first layer pattern 51a, the upper hard mask layer pattern 52a of the second layer, and the lower hard mask layer pattern 53a of the second layer are removed simultaneously. After dry etching, a portion of the lower hard mask layer pattern 53a remains on the light-absorbing film pattern 41a.

[0092] Next, as shown in Figure 4G, the lower hard mask layer pattern 53a of the second layer and the oxide layer pattern 41a of the light-absorbing film are used as etching masks to remove the absorption layer pattern 42a of the light-absorbing film that remained in Figure 4F by dry etching using an oxygen-free chlorine-based gas (step (G)). At this time, the remaining lower hard mask layer pattern 53a of the second layer is simultaneously removed by oxygen-free chlorine-based dry etching. (The oxide film pattern 41a of the light-absorbing film is resistant to oxygen-free chlorine-based dry etching and therefore functions as an etching prevention film.) After oxygen-free chlorine-based dry etching, only the absorption layer pattern 42a of the light-absorbing film and the oxide layer pattern 41a of the light-absorbing film remain on the protective film 3.

[0093] When manufacturing a reflective photomask from a reflective photomask blank according to a second aspect of the present invention, since a resist film has already been formed, step (A) can be omitted, and steps (B) through (G) can be carried out.

[0094] By this method, a thin resist film is formed on a reflective photomask blank, for example, with a thickness of 60 nm or less, or a light-absorbing film is patterned on a reflective photomask blank on which a thin resist film of, for example, 60 nm or less thickness has been formed, to obtain a reflective photomask in which a light-absorbing film pattern is formed that includes good line patterns such as assist patterns, even if the line width is 25 nm or less (25 nm or less), and especially 20 nm or less (20 nm or less). Furthermore, as shown in the process in Figure 4G, the protective film 3 is exposed to dry etching using an oxygen-free chlorine-based gas, resulting in no damage and no reduction in film thickness. In this invention, the lower limit of the width of line patterns such as assist patterns formed on the light-absorbing film pattern of the reflective photomask is usually 10 nm or more.

[0095] Figure 5 is a cross-sectional view illustrating the process of manufacturing a reflective photomask from a reflective photomask blank of the third embodiment of the present invention. First, as shown in Figure 6A, a resist film 6 is formed in contact with the side of the reflective photomask blank 100 of the third embodiment that is separated from the substrate 1 (i.e., in contact with the upper hard mask layer 2A of the second layer) (step (A)).

[0096] Next, as shown in Figure 6B, the resist film 6 is patterned to form a resist film pattern 6a (step (B)).

[0097] Next, as shown in Figure 6C, the upper hard mask layer 2A of the second layer is patterned by dry etching using a fluorine-based gas, with the resist pattern 6a as the etching mask, to form the upper hard mask layer pattern 52a of the second layer. (Process (C)).

[0098] Next, the resist pattern 6a is removed as shown in Figure 6D (step (D)).

[0099] Next, as shown in Figure 6E, the lower hard mask layer 2B of the second layer is patterned by dry etching using an oxygen-free chlorine-based gas, with the upper hard mask layer pattern 52a of the second layer as an etching mask, thereby forming the lower hard mask layer pattern 53a of the second layer (step (E)).

[0100] Next, as shown in Figure 6F, the upper hard mask layer pattern 52a and the lower hard mask layer pattern 53a of the second layer are used as hard masks to pattern a portion of the oxide layer 41 and the absorption layer 42 of the light-absorbing film by fluorine-based dry etching, thereby forming the oxide layer pattern 41a and the absorption layer pattern 42a of the light-absorbing film. Here, the absorption layer 42 of the light-absorbing film is not completely etched, and a portion remains (step (F)). Furthermore, when patterning a portion of the oxide layer 41 and the absorption layer 42 of the light-absorbing film by fluorine-based dry etching, a portion of the upper hard mask layer pattern 52a and the lower hard mask layer pattern 53a of the second layer are removed simultaneously. After dry etching, a portion of the lower hard mask layer pattern 53a remains on the light-absorbing film pattern 41a.

[0101] Next, as shown in Figure 6G, the lower hard mask layer pattern 53a of the second layer and the oxide layer pattern 41a of the light-absorbing film are used as etching masks to remove the absorption layer pattern 42a of the light-absorbing film that remained in Figure 6F by dry etching using an oxygen-free chlorine-based gas (step (G)). At this time, the remaining lower hard mask layer pattern 53a of the second layer is simultaneously removed by oxygen-free chlorine-based dry etching. (The oxide film pattern 41a of the light-absorbing film is resistant to oxygen-free chlorine-based dry etching and therefore functions as an etching prevention film.) After oxygen-free chlorine-based dry etching, only the absorption layer pattern 42a of the light-absorbing film and the oxide layer pattern 41a of the light-absorbing film remain on the protective film 3.

[0102] When manufacturing a reflective photomask from a reflective photomask blank according to the fourth aspect of the present invention, in which a resist film has already been formed, step (A) can be omitted, and steps (B) to (G) can be carried out.

[0103] By this method, a thin resist film is formed on a reflective photomask blank that does not contain a first layer, for example, with a thickness of 60 nm or less. Alternatively, a light-absorbing film can be patterned on a reflective photomask blank on which a thin resist film of, for example, 60 nm or less thickness has been formed. This allows for the formation of a reflective photomask with a light-absorbing film pattern that includes line patterns such as good assist patterns, even if the line width is 25 nm or less (25 nm or less), and especially 20 nm or less (20 nm or less). Furthermore, as shown in the process in Figure 6G, the protective film 3 is exposed to dry etching using an oxygen-free chlorine-based gas, resulting in no damage and no reduction in film thickness. In this invention, the lower limit of the width of line patterns, such as assist patterns, formed on the light absorption film pattern of a reflective photomask is usually 10 nm or more. [Examples]

[0104] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0105] [Example 1] A reflective photomask blank (a reflective photomask blank of the first embodiment) was manufactured by sequentially laminating a multilayer reflective film, a protective film, a light-absorbing film, and a hard mask consisting of a first and second layer onto a quartz substrate measuring 152 mm square and approximately 6 mm thick, as shown in Figure 1.

[0106] First, using a molybdenum target and a silicon target as targets, and argon gas as the sputtering gas, the power applied to the targets and the flow rate of the sputtering gas were adjusted, and sputtering with the molybdenum target and sputtering with the silicon target were performed alternately to form a multilayer reflective film 2 on a quartz substrate 1. This film consisted of alternating layers of molybdenum (Mo) and silicon (Si) layers with a reflectivity of 65% for light at a wavelength of 13.5 nm. A total of 40 layers of the molybdenum (Mo) / silicon layer combination were formed.

[0107] Next, using ruthenium as the target and argon gas as the sputtering gas, sputtering was performed by adjusting the power applied to the target and the flow rate of the sputtering gas, thereby forming a ruthenium (Ru) film (thickness 5 nm) on the multilayer reflective film as a protective film 3 made of a ruthenium-containing material.

[0108] Next, a tantalum target was used as the target, and argon and nitrogen gases were used as the sputtering gases. By adjusting the power applied to the target and the flow rate of the sputtering gases, sputtering was performed to form a tantalum nitride (TaN) film (65 nm thick) on the protective film as the absorption layer 42 of a light absorption film formed from a tantalum-containing material.

[0109] Next, a tantalum target was used as the target, and argon and oxygen gases were used as the sputtering gases. By adjusting the power applied to the target and the flow rate of the sputtering gases, sputtering was performed to form a tantalum oxide (TaO) film (3 nm thick) on the absorption layer 42 of the light-absorbing film, as the oxide layer 41 of the light-absorbing film, which is made of a material containing tantalum.

[0110] Next, a tantalum target was used as the target, and argon and nitrogen gases were used as the sputtering gases. By adjusting the power applied to the target and the flow rate of the sputtering gases, sputtering was performed to form a tantalum nitride (TaN) film (10 nm thick) on the oxide layer of the light absorption film as a lower hard mask layer 53 of the second layer, which is made of a tantalum-containing material.

[0111] Next, a tantalum target was used as the target, and argon and oxygen gases were used as the sputtering gases. By adjusting the power applied to the target and the flow rate of the sputtering gases, sputtering was performed to form a tantalum oxynitride (TaON) film (3 nm thick) on the lower hard mask layer 53 of the second layer, as the upper hard mask layer 52 of the second layer, which was made of a material containing tantalum.

[0112] Furthermore, using a silicon target as the target and argon and nitrogen gases as the sputtering gases, sputtering was performed by adjusting the power applied to the target and the flow rate of the sputtering gases to form a silicon nitride (SiN) layer (thickness 10 nm) as the first layer 51, which is made of a silicon-containing, chromium-free material, on top of the two layers, thereby obtaining a reflective photomask blank. The composition and film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1. The composition was measured using an X-ray photoelectron spectroscopy analyzer, and the thickness was measured using an X-ray diffractometer (the same applies below).

[0113] [Example 2] A reflective photomask blank was obtained in the same manner as in Example 1, except that the formation of the first layer 51 was modified as follows and the film thickness of the lower hard mask layer 53 of the second layer was changed. For the first layer 51, a silicon target was used as the target, and argon gas and oxygen gas were used as the sputtering gas. By adjusting the power applied to the target and the flow rate of the sputtering gas, sputtering was performed to form a silicon oxide (SiO) layer on the second layer as the first layer 51, which is made of a silicon-containing, chromium-free material. The composition and film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0114] [Example 3] A reflective photomask blank was obtained in the same manner as in Example 1, except that the formation of the first layer 51 was modified as follows. For the first layer 51, a silicon target was used as the target, and argon, nitrogen, and oxygen gases were used as the sputtering gases. By adjusting the power applied to the target and the flow rate of the sputtering gases, sputtering was performed to form a silicon nitride oxide (SiON) layer on the second layer as the first layer 51, which is made of a silicon-containing, chromium-free material. The composition and film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0115] [Example 4] A reflective photomask blank was obtained in the same manner as in Example 3, except that the ratio of silicon, oxygen, and nitrogen in the first layer 51 was changed. The composition and film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0116] [Example 5] A reflective photomask blank was obtained in the same manner as in Example 2, except that the ratio of silicon, oxygen, and nitrogen in the first layer 51 was changed and the film thickness of the lower hard mask layer 53 of the second layer was changed. The composition and film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0117] [Example 6] A reflective photomask blank was obtained in the same manner as in Example 5, except that the film thickness of the upper hard mask layer 52 and the film thickness of the lower hard mask layer 53 of the second layer were changed. The composition and film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0118] [Example 7] A reflective photomask blank was obtained in the same manner as in Example 5, except that the film thickness of the upper hard mask layer 52 and the film thickness of the lower hard mask layer 53 of the second layer were changed. The composition and film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0119] [Example 8] A reflective photomask blank was obtained in the same manner as in Example 5, except that the film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, and the film thickness of the lower hard mask layer 53 of the second layer were changed. The composition and film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0120] [Example 9] A reflective photomask blank was obtained in the same manner as in Example 5, except that the film thickness of the first layer 51 and the film thickness of the upper hard mask layer 52 of the second layer were changed. The composition and film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0121] [Example 10] A reflective photomask blank was obtained in the same manner as in Example 5, except that the material of the lower hard mask layer 53 of the second layer and the film thickness of the lower hard mask layer 53 of the second layer were changed. The composition and film thickness of the first layer 51, the film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0122] [Example 11] A reflective photomask blank was obtained in the same manner as in Example 10, except that the hard mask of the first layer 51 was absent. The film thickness of the upper hard mask layer 52 of the second layer, the film thickness of the lower hard mask layer 53 of the second layer, the material of the lower hard mask layer 53 of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0123] [Comparative Example 1] A reflective photomask blank was obtained in the same manner as in Example 5, except that a hard mask layer (corresponding to the upper hard mask layer 52 and the lower hard mask layer 53 of the second layer) consisting only of layers made of a material containing chromium but not silicon was formed on the oxide layer 41 of the light-absorbing film. The composition and film thickness of the first layer 51, the film thickness of the hard mask layer of the second layer, the material of the hard mask layer of the second layer, the film thickness of the oxide layer 41 of the light-absorbing film, and the film thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0124] [Comparative Example 2] A reflective photomask blank was obtained in the same manner as in Comparative Example 1, except for the thickness of the hard mask layer. The composition and thickness of the first layer 51, the thickness of the second hard mask layer, the material of the second hard mask layer, the thickness of the oxide layer 41 of the light-absorbing film, and the thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0125] [Comparative Example 3] A reflective photomask blank was obtained in the same manner as in Comparative Example 1, except that a hard mask layer (corresponding to a hard mask layer consisting only of the second layer) made of a material containing chromium but not silicon was formed on the oxide layer 41 of the light-absorbing film. The material of the hard mask layer, the thickness of the oxide layer 41 of the light-absorbing film, and the thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0126] [Comparative Example 4] A reflective photomask blank was obtained in the same manner as in Comparative Example 2, except that a hard mask layer (corresponding to a hard mask layer consisting only of the second layer) made of a material containing chromium but not silicon was formed on the oxide layer 41 of the light-absorbing film. The material of the hard mask layer, the thickness of the oxide layer 41 of the light-absorbing film, and the thickness of the absorption layer 42 of the light-absorbing film are shown in Table 1.

[0127] [Table 1]

[0128] [Clear time for fluorine-based dry etching of layer 1, part 51] Using the reflective photomask blanks obtained in Examples 1-10 and Comparative Examples 1-2, the time until the first layer 51 disappeared (clear time) was measured by fluorine-based dry etching. The clear time for fluorine-based dry etching was defined as the time until the endpoint was detected when dry etching was performed on the first layer 51 under the following conditions (Condition 1). The results are shown in Table 2.

[0129] <Conditions for fluorine-based dry etching of the first layer 51 (Condition 1)> Equipment: ICP (Inductively Coupled Plasma) system Gas: SF6 gas + He gas Gas pressure: 4.0 mTorr (0.53 Pa) ICP power: 400W

[0130] [Clear time of fluorine-based dry etching of upper hard mask layer 52 and lower hard mask layer 53] For the reflective photomask blanks obtained in Examples 1 to 11, the clear time of fluorine-based dry etching of the first layer 51 was measured. Then, the time until the upper hard mask layer 52 of the second layer was removed by fluorine-based dry etching, and the time until the lower hard mask layer 53 of the second layer disappeared (clear time) was measured. The clear time of fluorine-based dry etching was defined as the time until the endpoint was detected (time to endpoint) when dry etching was performed on the upper hard mask layer 52 and the lower hard mask layer 53 of the second layer under the same conditions as Condition 1 (Condition 2) described below. The results are shown in Table 2.

[0131] <Conditions for fluorine-based dry etching of the upper hard mask layer 52 and the lower hard mask layer 53 (Condition 2)> Equipment: ICP (Inductively Coupled Plasma) system Gas: SF6 gas + He gas Gas pressure: 4.0 mTorr (0.53 Pa) ICP power: 400W

[0132] <Conditions for oxygen-free chlorine-based dry etching of the lower hard mask layer 53 of the second layer (Condition 3)> For the reflective photomask blanks obtained in Examples 1 to 11, the clear time of fluorine-based dry etching of the first layer 51 was measured. Then, the time until the upper hard mask layer 52 of the second layer was removed by fluorine-based dry etching, and the time until the lower hard mask layer 53 of the second layer disappeared (clear time) was measured. For oxygen-free chlorine-based dry etching, the clear time was measured by performing dry etching on the lower hard mask layer 53 of the second layer under the following conditions (Condition 3), and the time until the endpoint was detected (time to endpoint). The results are shown in Table 2.

[0133] <Conditions for oxygen-free chlorine-based dry etching of the lower hard mask layer 53 of the second layer (Condition 3)> Equipment: ICP (Inductively Coupled Plasma) system Gas: Cl2 gas Gas pressure: 3.0 mTorr (0.40 Pa) ICP power: 350W

[0134] [Clear time of fluorine-based dry etching of the absorption layer 42 of the light-absorbing film] For the reflective photomask blanks obtained in Examples 1-11 and Comparative Examples 1-4, after measuring the clear time of fluorine-based dry etching of the first layer 51 and after measuring the clear time of fluorine-based dry etching of the lower hard mask layer 53 of the second layer, the oxide layer 41 of the light-absorbing film was removed, and the time until the absorption layer 42 of the light-absorbing film disappeared (clear time) was measured. The clear time for fluorine-based dry etching was defined as the time until the endpoint was detected (time to endpoint) when dry etching was performed on the absorption layer 42 of the light-absorbing film under the same conditions as Condition 1 above (Condition 4). The results are shown in Table 2.

[0135] <Conditions for fluorine-based dry etching of the oxide layer 41 and the absorption layer 42 of the light-absorbing film (Condition 4)> Equipment: ICP (Inductively Coupled Plasma) system Gas: SF6 gas + He gas Gas pressure: 4.0 mTorr (0.53 Pa) ICP power: 400W

[0136] [Clear time of oxygen-free chlorine-based dry etching of the absorption layer 42 of the light-absorbing film] For the reflective photomask blanks obtained in Examples 1-11 and Comparative Examples 1-4, after measuring the clear time of fluorine-based dry etching of the first layer 51 and after measuring the clear time of fluorine-based dry etching of the lower hard mask layer 53 of the second layer, the oxide layer 41 of the light-absorbing film was removed under the above condition 3, and the time (clear time) until the absorption layer 42 of the light-absorbing film disappeared was measured. The clear time for oxygen-free chlorine-based dry etching was defined as the time to endpoint detection when dry etching was performed on the absorption layer 42 of the light absorption film under the same conditions as condition 3 above (condition 5). The results are shown in Table 2.

[0137] <Conditions for oxygen-free chlorine-based dry etching of the absorption layer 42 of the light-absorbing film (Condition 5)> Equipment: ICP (Inductively Coupled Plasma) system Gas: Cl2 gas Gas pressure: 3.0 mTorr (0.40 Pa) ICP power: 350W [Table 2] Furthermore, the etching clear time when 1 / 2 the thickness of the absorption layer 42 of the light-absorbing film is dry-etched with a fluorine-based etchant is approximately half or half of the clear time of the absorption layer 42 of the light-absorbing film shown in Table 2 above. Therefore, given that the "clear time" of the absorption layer 42 of the light-absorbing film when dry-etched with a fluorine-based etchant is "65 seconds", the etching clear time when 1 / 2 the thickness of the absorption layer 42 of the light-absorbing film is dry-etched with a fluorine-based etchant is approximately "32.5 seconds".

[0138] [Reduction in resist film thickness during fluorine-based dry etching of the upper hard mask layer 52 of the first layer 51 and the second layer] Using the reflective photomask blanks obtained in Examples 1 to 10, the amount (thickness) of the resist film reduced until the hard mask layer 52 above the first and second layers disappeared was measured by fluorine-based dry etching. First, a 60 nm thick resist film was formed on the first layer 51 by spin-coating a positive-type chemically amplified electron beam resist. Next, an electron beam lithography system was used with a dose of 100 μC / cm². 2 Next, 20 isolated line patterns with a long side of 100,000 nm and a short side of 60 nm were drawn. Then, heat treatment (PEB: Post Exposure Bake) was performed at 115°C for 14 minutes using a heat treatment apparatus. Next, development was performed for 40 seconds using paddle development to form a resist pattern. Then, using the resist pattern as an etching mask, fluorine-based dry etching was performed on the first layer 51 and the upper hard mask layer 52 of the second layer under the conditions described above, and the pattern of the first layer 51 and the upper hard mask layer pattern of the second layer were formed simultaneously. After that, the thickness of the resist pattern remaining on the first layer pattern was measured and the thickness reduction was calculated. The results are shown in Table 3. The thickness of the resist pattern was measured using an atomic force microscope (AFM), and the measurement range was a 200 nm × 200 nm square area (the same applies below).

[0139] Furthermore, from the obtained reduction amount, the required thickness of the resist film to remain with a thickness of 15 nm after etching the upper hard mask layer 52 of the second layer was calculated as a fluorine-based dry etching of the first layer 51 and the upper hard mask layer 52 of the second layer. The results are shown in Table 3. The thickness is the minimum required thickness of the resist film in the manufacturing of reflective photomasks using the reflective photomask blanks of Examples 1 to 10, which will be described later. If the thickness of the resist pattern remaining after etching is too thin, the fluorine-based plasma will reach the first layer 51 and pinhole defects will be formed. Therefore, the thickness of the resist pattern remaining after dry etching was set to 15 nm. The results are shown in Table 3. [Reduction in resist film thickness during fluorine-based dry etching of the first layer 51] Using the reflective photomask blanks obtained in Comparative Examples 1 and 2, the amount (thickness) of the resist film reduced until the first layer 51 disappeared by fluorine-based dry etching was measured. First, a 60 nm thick resist film was formed on the first layer 51 by spin-coating a positive-type chemically amplified electron beam resist. Next, an electron beam lithography system was used with a dose of 100 μC / cm². 2 Next, 20 isolated line patterns with a long side of 100,000 nm and a short side of 60 nm were drawn. Then, heat treatment (PEB: Post Exposure Bake) was performed at 115°C for 14 minutes using a heat treatment device. Next, development was performed for 40 seconds using paddle development to form a resist pattern. Then, using the resist pattern as an etching mask, fluorine-based dry etching was performed on the first layer 51 under the conditions described above to form the pattern of the first layer 51. The thickness of the resist pattern remaining on the first layer pattern was measured and the thickness reduction was calculated. The results are shown in Table 3. The thickness of the resist pattern was measured using an atomic force microscope (AFM), and the measurement range was a 200 nm × 200 nm square area (the same applies below).

[0140] [Reduction in resist film thickness during fluorine-based dry etching of the upper hard mask layer 52 of the second layer] Using the reflective photomask blank obtained in Example 11, the amount (thickness) of the resist film reduced until the upper hard mask layer 52 of the second layer disappeared was measured by fluorine-based dry etching. First, a 60 nm thick resist film was formed on the upper hard mask layer 52 of the second layer by spin-coating a positive-type chemically amplified electron beam resist. Next, using an electron beam lithography system, at a dose of 100 μC / cm², the resist film was measured. 2 Next, 20 isolated line patterns with a long side of 100,000 nm and a short side of 60 nm were drawn. Then, a heat treatment (PEB: Post Exposure Bake) was performed at 115°C for 14 minutes using a heat treatment device. After that, a development process was performed using paddle development 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 upper hard mask layer 52 of the second layer under the conditions described in condition 1, simultaneously forming the upper hard mask layer pattern of the second layer. Subsequently, the thickness of the resist pattern remaining on the upper hard mask layer pattern of the second layer was measured, and the reduced thickness was calculated. The results are shown in Table 3. The thickness of the resist pattern was measured using an atomic force microscope (AFM), and the measurement range was a 200 nm × 200 nm square area (the same applies hereafter).

[0141] Furthermore, based on the obtained reduction amount, the required thickness of the resist film to remain with a thickness of 15 nm after etching the upper hard mask layer 52 of the second layer was calculated as a fluorine-based dry etching of the upper hard mask layer 52 of the second layer. The results are shown in Table 3. The thickness is the minimum required thickness of the resist film in the manufacturing of a reflective photomask using the reflective photomask blank of Example 11, which will be described later. If the thickness of the resist pattern remaining after etching is too thin, the fluorine-based plasma will reach the upper hard mask layer 52 of the second layer, and pinhole defects will be formed. Therefore, the thickness of the resist pattern remaining after dry etching was set to 15 nm here. The results are shown in Table 3.

[0142] [Reduction in resist film thickness during chlorine-based dry etching of the hard mask layer of the second layer] Using the reflective photomask blanks obtained in Comparative Examples 3 and 4, the amount (thickness) of the resist film reduced until the hard mask layer of the second layer disappeared was measured by chlorine-based dry etching. First, a 60 nm thick resist film was formed on the second layer by spin-coating a positive-type chemically amplified electron beam resist. Next, an electron beam lithography system was used with a dose of 100 μC / cm². 2Next, 20 isolated line patterns with a long side of 100,000 nm and a short side of 60 nm were drawn. Then, heat treatment (PEB: Post Exposure Bake) was performed at 115°C for 14 minutes using a heat treatment device. Next, development was performed using paddle development for 40 seconds to form a resist pattern. Then, using the resist pattern as an etching mask, chlorine-based dry etching was performed on the second layer hard mask layer under the aforementioned condition 2 with 300% over-etching to form the second layer pattern. After that, the thickness of the resist pattern remaining on the second layer pattern was measured and the thickness reduction was calculated. The results are shown in Table 3.

[0143] Furthermore, based on the obtained reduction amount, the required thickness of the resist film to leave a 15 nm thick resist pattern after 300% over-etching as a chlorine-based dry etching of the second layer was calculated. The results are shown in Table 3. This thickness is the minimum required resist film thickness for the manufacturing of reflective photomasks using the reflective photomask blanks of Comparative Examples 3 and 4, which will be described later. If the thickness of the resist pattern remaining after etching is too thin, the chlorine-based plasma will reach the second layer and pinhole defects will be formed. Therefore, the thickness of the resist pattern remaining after dry etching was set to 15 nm in this case.

[0144] [Table 3]

[0145] [Examples 12-21] A positive-type chemically amplified electron beam resist was spin-coated onto the first layer 51 of the reflective photomask blanks obtained in Examples 1 to 10 to form a resist film, thereby obtaining a reflective photomask blank with a resist film (a reflective photomask blank of the second embodiment) as shown in Figure 2. The thickness of this resist film was set to a thickness of 40 nm or more, which is the lower limit of the thickness at which a resist film can be formed stably with the resist material used, and is such that a 15 nm thick resist pattern remains after fluorine-based dry etching as described above. The thickness of the resist film is shown in Table 4.

[0146] To evaluate the resolution limit of the fine pattern corresponding to the assist pattern of the isolated line pattern, a reflective photomask was fabricated using a reflective photomask blank having the obtained resist film. First, using an electron beam lithography system, at a dose of 100 μC / cm², the photomask was fabricated. 2 As test patterns equivalent to assist patterns for line patterns, a total of 200,000 isolated patterns with different short side dimensions were drawn, with the long side dimension being 80 nm and the short side dimension being varied by 1 nm increments from 10 nm to 60 nm. Next, heat treatment (PEB: Post Exposure Bake) was performed at 110°C for 14 minutes using a heat treatment apparatus. Then, development was performed for 40 seconds using paddle development to form a resist pattern. Next, using the obtained resist pattern as an etching mask, fluorine-based dry etching was performed on the first layer 51 and the upper hard mask layer 52 of the second layer under the conditions 1 described above to form the first layer pattern and the upper hard mask layer pattern of the second layer. Next, the remaining resist pattern was removed by washing with sulfuric acid and hydrogen peroxide (a mixture of sulfuric acid and hydrogen peroxide in a 3:1 ratio). Then, using the first layer pattern and the upper hard mask layer pattern of the second layer as etching masks, oxygen-free chlorine-based dry etching was performed on the lower hard mask layer 53 of the second layer under the aforementioned condition 3, resulting in 100% overetching and the formation of the lower hard mask layer pattern of the second layer.

[0147] Next, using the first layer pattern, the upper hard mask layer pattern of the second layer, and the lower hard mask layer pattern of the second layer as hard masks, fluorine-based dry etching was performed on the oxide layer 41 of the light-absorbing film under the aforementioned condition 4, thereby forming the oxide layer 41 pattern and a portion of the absorption layer pattern of the light-absorbing film, while simultaneously removing a portion of the first layer pattern, the upper hard mask layer pattern of the second layer, and the lower hard mask layer pattern of the second layer.

[0148] Next, using the lower hard mask layer pattern of the second layer and the oxide layer 41 pattern of the light-absorbing film as etching masks, the light absorption pattern of the light-absorbing film remaining from the above process was dry-etched using an oxygen-free chlorine-based gas to form the absorption layer pattern of the light-absorbing film, while simultaneously removing the lower hard mask layer 53 of the second layer to obtain a reflective photomask.

[0149] Next, the resolution limit of the test patterns of the obtained photomasks was evaluated using a mask visual inspection device. For all isolated patterns, pattern disappearance, pattern collapse, and pattern shape defects were evaluated. Isolated patterns in which the visual inspection device detected any of these were considered defective, and the resolution limit was defined as the smallest short side dimension in which no defective isolated patterns were detected. In addition, the thickness of the protective film of the reflective photomasks obtained by the above mask manufacturing process was measured using an X-ray diffractometer, and the thickness of the protective film that disappeared during the mask process was evaluated. The results are then shown in Table 4.

[0150] [Example 22] A positive-type chemically amplified electron beam resist was spin-coated onto the upper hard mask layer 52 of the second layer of the reflective photomask blank obtained in Example 11 to form a resist film, thereby obtaining a reflective photomask blank with a resist film (a reflective photomask blank of the second embodiment) as shown in Figure 2. The thickness of this resist film was set to a thickness of 40 nm or more, which is the lower limit of the thickness at which a resist film can be formed stably with the resist material used, and is such that a 15 nm thick resist pattern remains after fluorine-based dry etching as described above. The thickness of the resist film is shown in Table 4.

[0151] To evaluate the resolution limit of the fine pattern corresponding to the assist pattern of the isolated line pattern, a reflective photomask was fabricated using a reflective photomask blank having the obtained resist film. First, using an electron beam lithography system, at a dose of 100 μC / cm², the photomask was fabricated. 2 As a test pattern equivalent to an assist pattern for the line pattern, a total of 200,000 isolated patterns with different short side dimensions were drawn, with the long side dimension being 80 nm and the short side dimension being varied by 1 nm increments from 10 nm to 60 nm. Next, heat treatment (PEB: Post Exposure Bake) was performed at 110°C for 14 minutes using a heat treatment device. Next, development was performed for 40 seconds using paddle development to form a resist pattern. Next, using the obtained resist pattern as an etching mask, fluorine-based dry etching was performed on the upper hard mask layer 52 of the second layer under the aforementioned condition 1 to form the upper hard mask layer pattern of the second layer. Next, the remaining resist pattern was removed by washing with sulfuric acid peroxide (a mixture of sulfuric acid and hydrogen peroxide (sulfuric acid:hydrogen peroxide = 3:1)). Next, using the upper hard mask layer pattern of the second layer as an etching mask, oxygen-free chlorine-based dry etching was performed on the lower hard mask layer 53 of the second layer under the aforementioned condition 3 to 100% over-etch the lower hard mask layer pattern of the second layer.

[0152] Next, using the upper hard mask layer pattern and the lower hard mask layer pattern of the second layer as hard masks, fluorine-based dry etching was performed on the oxide layer 41 of the light-absorbing film under the aforementioned condition 4, thereby forming the oxide layer 41 pattern and a portion of the absorption layer pattern of the light-absorbing film, while simultaneously removing a portion of the upper hard mask layer pattern and the lower hard mask layer pattern of the second layer.

[0153] Next, using the lower hard mask layer pattern of the second layer and the oxide layer 41 pattern of the light-absorbing film as etching masks, the light absorption pattern of the light-absorbing film remaining from the above process was dry-etched using an oxygen-free chlorine-based gas to form the absorption layer pattern of the light-absorbing film, while simultaneously removing the lower hard mask layer 53 of the second layer to obtain a reflective photomask.

[0154] Next, the resolution limit of the test patterns of the obtained photomasks was evaluated using a mask visual inspection device. For all isolated patterns, pattern disappearance, pattern collapse, and pattern shape defects were evaluated. Isolated patterns in which the visual inspection device detected any of these were considered defective, and the resolution limit was defined as the smallest short side dimension in which no defective isolated patterns were detected. In addition, the thickness of the protective film of the reflective photomasks obtained by the above mask manufacturing process was measured using an X-ray diffractometer, and the thickness of the protective film that disappeared during the mask process was evaluated. The results are then shown in Table 4.

[0155] [Comparative Example 5, Comparative Example 6] A positive-type chemically amplified electron beam resist was spin-coated onto the hard mask layer (second layer) of the reflective photomask blanks obtained in Comparative Examples 1 and 2 to form a resist film, thereby obtaining a reflective photomask blank with a resist film (a reflective photomask blank of the second embodiment) as shown in Figure 2. The thickness of this resist film was set to a thickness of 40 nm or more, which is the lower limit of the thickness at which a resist film can be formed stably with the resist material used, and is such that a 15 nm thick resist pattern remains after fluorine-based dry etching as described above. The thickness of the resist film is shown in Table 4.

[0156] To evaluate the resolution limit of the fine pattern corresponding to the assist pattern of the isolated line pattern, a reflective photomask was fabricated using a reflective photomask blank having the obtained resist film. First, using an electron beam lithography system, at a dose of 100 μC / cm², the photomask was fabricated. 2 As test patterns equivalent to assist patterns for line patterns, a total of 200,000 isolated patterns with different short side dimensions were drawn, with the long side dimension being 80 nm and the short side dimension being varied by 1 nm increments from 10 nm to 60 nm. Next, heat treatment (PEB: Post Exposure Bake) was performed at 110°C for 14 minutes using a heat treatment device. Next, development was performed for 40 seconds using paddle development to form a resist pattern. Next, using the obtained resist pattern as an etching mask, fluorine-based dry etching was performed on the first layer 51 under the conditions 1 described above to form the first layer pattern. Next, the remaining resist pattern was removed by washing with sulfuric acid peroxide (a mixture of sulfuric acid and hydrogen peroxide (sulfuric acid:hydrogen peroxide = 3:1)). Next, using the first layer pattern as an etching mask, oxygen-containing chlorine-based dry etching was performed on the second layer hard mask layer (chromium-based film) under the conditions 6 below, resulting in 300% overetching and forming the second layer hard mask layer pattern. <Conditions for oxygen-containing chlorine-based dry etching of the second layer hard mask (Condition 6)> Equipment: ICP (Inductively Coupled Plasma) system Gas: Cl2 gas + O2 gas Gas pressure: 3.0 mTorr (0.40 Pa) ICP power: 350W

[0157] Next, using the first layer pattern and the second layer hard mask layer (chromium-based film) as etching masks, fluorine-based dry etching was performed on the oxide layer 41 of the light-absorbing film under the aforementioned condition 3, thereby forming the oxide layer 41 pattern of the light-absorbing film and a portion of the pattern of the light-absorbing film, while simultaneously removing the first layer pattern.

[0158] Next, using the second hard mask layer (chromium-based film) as an etching mask, the light absorption pattern of the light absorption film remaining from the above process is dry-etched using an oxygen-free chlorine-based gas to form the absorption layer pattern of the light absorption film.

[0159] Next, dry etching was performed using a chlorine-based gas containing oxygen to remove the pattern of the second hard mask layer (chromium-based film), thereby obtaining a reflective photomask.

[0160] Next, the resolution limit of the test patterns of the obtained photomasks was evaluated using a mask visual inspection device. For all isolated patterns, pattern disappearance, pattern collapse, and pattern shape defects were evaluated. Isolated patterns in which the visual inspection device detected any of these were considered defective, and the resolution limit was defined as the smallest short side dimension in which no defective isolated patterns were detected. In addition, the thickness of the protective film of the reflective photomasks obtained by the above mask manufacturing process was measured using an X-ray diffractometer, and the thickness of the protective film that disappeared during the mask process was evaluated. The results are shown in Table 4.

[0161] [Comparative Example 7, Comparative Example 8] A reflective photomask blank with a resist film was obtained by spin-coating a positive-type chemically amplified electron beam resist onto the hard mask layer (chromium-based film) of the reflective photomask blanks obtained in Comparative Examples 3 and 4. The thickness of this resist film was set to a thickness of 40 nm or more, which is the lower limit of the thickness at which a resist film can be formed stably with the resist material used, and is such that a 15 nm thick resist pattern remains after fluorine-based dry etching as described above. The thickness of the resist film is shown in Table 4.

[0162] To evaluate the resolution limit of the fine pattern corresponding to the assist pattern of the isolated line pattern, a reflective photomask was fabricated using a reflective photomask blank having the obtained resist film.

[0163] To evaluate the resolution limit of the fine pattern corresponding to the assist pattern of the isolated line pattern, a reflective photomask was manufactured using a reflective photomask blank having the obtained resist film. First, using an electron beam lithography apparatus, at a dose of 100 μC / cm 2 with a long side dimension of 80 nm and short side dimensions changed from 10 nm to 60 nm by 1 nm increments, a total of 200,000 isolated patterns with different short side dimensions, corresponding to the assist pattern of the line pattern, were drawn. Next, using a heat treatment apparatus, post-exposure bake (PEB) was performed at 110 °C for 14 minutes. Next, paddle development was used to perform a development process for 40 seconds to form a resist pattern. Next, using the obtained resist pattern as an etching mask, chlorine-based dry etching containing oxygen was performed on the hard mask layer (chromium-based film) under the aforementioned condition 6 to form a hard mask layer pattern. Next, the remaining resist pattern was removed by washing with sulfuric acid and hydrogen peroxide water (a mixed solution of sulfuric acid and hydrogen peroxide water with a ratio of sulfuric acid: hydrogen peroxide water = 3:1).

[0164] Next, using the hard mask layer (chromium-based film) pattern as an etching mask, fluorine-based dry etching was performed on the oxide layer 41 of the light absorption film under the aforementioned condition 3 to form a pattern of the oxide layer 41 of the light absorption film and a part of the pattern of the light absorption film.

[0165] Next, using the hard mask layer (chromium-based film) pattern and the pattern of the oxide layer 41 of the light absorption film as etching masks, dry etching using a chlorine-based gas not containing oxygen was performed on the light absorption pattern of the light absorption film remaining in the above process to form a pattern of the absorption layer of the light absorption film.

[0166] Next, dry etching using a chlorine-based gas containing oxygen was performed to remove the hard mask layer (chromium-based film) pattern and obtain a reflective photomask.

[0167] Next, the resolution limit of the test patterns of the obtained photomasks was evaluated using a mask visual inspection device. For all isolated patterns, pattern disappearance, pattern collapse, and pattern shape defects were evaluated. Isolated patterns in which the visual inspection device detected any of these were considered defective, and the resolution limit was defined as the smallest short side dimension in which no defective isolated patterns were detected. In addition, the thickness of the protective film of the reflective photomasks obtained by the above mask manufacturing process was measured using an X-ray diffractometer, and the thickness of the protective film that disappeared during the mask process was evaluated. The results are shown in Table 4.

[0168] [Table 4]

[0169] As shown in Table 4, the hard masks of the reflective photomask blanks in Examples 1 to 10 have a first layer 51 formed on the side furthest from the substrate, which is made of a material that can be removed by fluorine-based dry etching. The hard mask of the reflective photomask blank in Example 11 has an upper hard mask layer 52 formed on the side furthest from the substrate, which is made of a material that can be removed by fluorine-based dry etching. Compared to the reflective photomask blanks in Comparative Examples 3 and 4, the reflective photomask blanks in Examples 1 to 11 can have thinner resist films, and a particularly good resolution limit can be obtained. This is thought to be because, because the resist film is thin, even with patterns with narrow line widths, the impact of the developer during the development process for resist pattern formation, or the impact of pure water during the rinsing process, reduces the likelihood of the resist pattern collapsing. Furthermore, in Examples 1 to 11, a film formed from a material that can be removed by oxygen-free chlorine-based dry etching is used beneath the first layer 51 of the reflective photomask blanks. It can be seen that the reflective photomask blanks of Examples 1 to 10 show particularly good resolution compared to the reflective photomask blanks of Comparative Examples 1 and 2. This is thought to be because the upper hard mask layer 52 of the second layer and the hard mask layer of the second layer are removed by oxygen-free chlorine-based dry etching, which does not cause large side etching and reduces the disappearance of the pattern during etching. Furthermore, it can be seen that the reflective photomask blanks of Examples 1 to 11 retain a particularly large amount of protective film after the fabrication of the reflective photomask compared to the reflective photomask blanks of Comparative Examples 1 to 4. This is thought to be because, since the upper hard mask layer 52 of the second layer and the hard mask layer of the second layer are used with oxygen-free chlorine-based dry etching, it is possible to pattern the absorption layer pattern of the light absorption film with oxygen-free chlorine-based dry etching, thus minimizing damage to the protective film.

[0170] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are merely examples, and any configuration that is identical or substantially identical to the technical concept of the present invention and that produces the same or similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0171] 1 circuit board 2 Multilayer reflective film 3 Protective film 4. Light-absorbing film 4a Pattern of light-absorbing film 41a Oxidation layer pattern of light-absorbing film 42a Absorption layer pattern of light-absorbing film 51 1st layer 52 Upper hard mask layer A of the second layer 53 Lower hard mask layer B of the second layer 51a First layer pattern 52a Upper hard mask layer pattern of the second layer 53a Lower hard mask layer pattern of the second layer 100 Reflective Photomask Blanks 200 Reflective Photomasks

Claims

1. circuit board and A multilayer reflective film formed on the substrate that reflects exposure light, which is light in the extreme ultraviolet region, A protective film formed on the multilayer reflective film for protecting the multilayer reflective film, A light-absorbing film formed on the protective film and absorbing the exposure light, A hard mask film provided on the light absorption film, Equipped with, The light-absorbing film is composed of a multilayer including an absorption layer and an oxygen-containing oxide layer provided on the side away from the substrate. The oxide layer of the light-absorbing film is formed from a material containing tantalum (Ta) and oxygen (O). The light-absorbing layer of the aforementioned light-absorbing film is formed from a material containing pure tantalum (Ta), or tantalum (Ta) and one or more of nitrogen (N) and boron (B). The hard mask film consists of a multilayer film comprising a second layer, or a second layer and a first layer formed on the side of the second layer that is separated from the substrate. If the first layer is included, the first layer is formed of a material containing silicon (Si) and one or more elements selected from oxygen (O), nitrogen (N), and carbon (C). The second layer is composed of a multilayer including an upper hard mask layer 2A and a lower hard mask layer 2B containing oxygen, which are provided on the side away from the substrate. The upper hard mask layer 2A of the second layer is formed of a material containing tantalum (Ta) and oxygen (O), The lower hard mask layer 2B of the second layer is formed of pure tantalum (Ta), or a material containing tantalum (Ta) and one or more of nitrogen (N) and boron (B). If the first layer is not included, the etching clear time when the upper hard mask layer 2A of the second layer is dry-etched with a fluorine-based system under one condition is shorter than the etching clear time when half the thickness of the absorption layer of the light-absorbing film is dry-etched with a fluorine-based system under one condition. A reflective photomask blank, characterized in that, when the first layer is included, the sum of the etching clear time when the first layer is dry-etched with a fluorine-based system under one condition and the etching clear time when the upper hard mask layer 2A of the second layer is dry-etched with a fluorine-based system under one condition is shorter than the sum of the etching clear time when the oxide layer of the light-absorbing film is dry-etched with a fluorine-based system under one condition and the etching clear time when half the thickness of the absorption layer of the light-absorbing film is dry-etched with a fluorine-based system under one condition.

2. The hard mask film includes the first layer, The reflective photomask blank according to claim 1, characterized in that when the absorption layer of the light-absorbing film and the first layer are dry-etched with a fluorine-based system under the conditions of claim 1, the ratio of the etching rate of the first layer to the etching rate of the absorption layer of the light-absorbing film is 0.4 or more and 2.0 or less.

3. The reflective photomask blank according to claim 1, characterized in that when the absorption layer of the light-absorbing film and the lower hard mask layer 2B of the second layer are dry-etched with a fluorine-based etchant under the conditions of claim 1, the ratio of the etching rate of the lower hard mask layer 2B of the second layer to the etching rate of the absorption layer of the light-absorbing film is 0.7 or more and 1.3 or less.

4. The reflective photomask blank according to claim 1, characterized in that when the absorption layer of the light-absorbing film and the lower hard mask layer 2B of the second layer are dry-etched with an oxygen-free chlorine-based system under the conditions of claim 1, the ratio of the etching rate of the lower hard mask layer 2B of the second layer to the etching rate of the absorption layer of the light-absorbing film is 0.7 or more and 1.3 or less.

5. The hard mask film includes the first layer, The reflective photomask blank according to claim 1, characterized in that the first layer is formed of a material that contains silicon and does not contain chromium.

6. The reflective photomask blank according to claim 1, characterized in that the upper hard mask layer 2A and the lower hard mask layer 2B of the second layer are made of a material containing tantalum.

7. The hard mask film includes the first layer, The reflective photomask blank according to claim 1, characterized in that the thickness of the first layer is 2 nm or more and 12 nm or less.

8. The reflective photomask blank according to claim 1, characterized in that the total thickness of the upper hard mask layer 2A and the lower hard mask layer 2B of the second layer is 8 nm or more and 30 nm or less.

9. The hard mask film includes the first layer, The reflective photomask blank according to claim 1, characterized in that the difference between the thickness of the first layer and the sum of the thickness of the oxide layer of the light-absorbing film and the thickness of the absorption layer of the light-absorbing film is 30 nm or more.

10. The reflective photomask blank according to claim 1, characterized in that the oxide layer and the absorption layer of the light-absorbing film are formed of a material containing tantalum.

11. A method for manufacturing a reflective photomask having an oxide layer pattern of the light-absorbing film and an absorption layer pattern of the light-absorbing film from a reflective photomask blank according to any one of claims 1 to 10, (A) A step of forming a resist film in contact with the side of the first layer that is separated from the substrate, (B) A step of patterning the resist film to form a resist pattern, (C) Using the resist pattern as an etching mask, the upper hard mask layer 2A of the first and second layers is simultaneously patterned by dry etching using a fluorine-based gas to simultaneously form the first layer pattern and the upper hard mask layer pattern of the second layer. (D) A step of removing the resist pattern, (E) Using the first layer pattern and the upper hard mask layer pattern of the second layer as etching masks, the lower hard mask layer 2B of the second layer is patterned by dry etching using an oxygen-free chlorine-based gas to form the lower hard mask layer pattern of the second layer. (F) Using the first layer pattern, the upper hard mask layer pattern of the second layer, and the lower hard mask layer pattern of the second layer as etching masks, a portion of the oxide layer and the absorption layer of the light-absorbing film is patterned by dry etching using a fluorine-based gas to form a portion of the oxide layer pattern and the absorption layer pattern of the light-absorbing film, while simultaneously removing a portion of the first layer pattern, the upper hard mask layer pattern of the second layer, and the lower hard mask layer pattern of the second layer. (G) A method for manufacturing a reflective photomask, comprising the steps of: (G) using a portion of the lower hard mask layer pattern of the second layer as an etching mask, patterning the absorption layer of the light absorption film by dry etching using an oxygen-free chlorine-based gas, and simultaneously removing a portion of the lower hard mask layer pattern of the second layer.

12. The manufacturing method according to claim 11, characterized in that the thickness of the resist film is 70 nm or less.

13. The manufacturing method according to claim 11, characterized in that the pattern of the light-absorbing film includes a line pattern with a width of 20 nm or less.

Images