Reflective photomask blank and method for manufacturing reflective photomask

Abstract

SOLUTION: A reflective photomask blank comprises a substrate, a multilayer reflective film reflecting exposure light which is extreme ultraviolet region light, a protective film for protecting the multilayer reflection film, a light absorption film absorbing the exposure light, and a hard mask film formed by coming into contact with the light absorption film. The hard mask film is a multilayer including a first layer with resistance to chlorine-based dry etching, formed of a material which can be removed by fluorine-based dry etching, and a second layer with resistance to fluorine-based dry etching, formed of a material which can be removed by chlorine-based dry etching. The light absorption film has longer etching clear time than the first layer when performing fluorine-based dry etching on the light absorption film and the first layer under the same condition.EFFECT: The thickness of a resist film can be made thinner, an assist pattern with about 30 nm of a line width can be excellently formed by reducing an aspect ratio of a resist pattern, and high resolution can be attained in a transfer pattern of a reflective photomask.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] With the miniaturization of semiconductor devices, particularly due to the high integration of large-scale integrated circuits, high pattern resolution is required for projection exposure. Therefore, as a method for improving the resolution of the transferred pattern in a photomask, a phase shift mask has been developed. The principle of the phase shift method is to adjust the phase of the transmitted light passing through the opening of the phase shift film of the photomask so that it is inverted by about 180 degrees with respect to the phase of the transmitted light passing through the portion of the phase shift film adjacent to the opening. By doing so, at the boundary between the opening and the portion adjacent to the opening, the transmitted light interferes and the light intensity decreases. As a result, the resolution and depth of focus of the transferred pattern are improved. A photomask using this principle is generally called a phase shift mask.

[0003] A phase shift mask blank, which is a material for a phase shift mask used in the manufacture of a phase shift mask, typically has a structure in which a phase shift film is laminated on a transparent substrate such as a glass substrate, and a film formed of a material containing chromium (Cr) is laminated on the phase shift film. The phase shift film usually has a phase difference of 175 to 185 degrees and a transmittance of about 6 to 30% with respect to the exposure light, and a film containing silicon (Si), particularly a film formed of a material containing molybdenum (Mo) and silicon (Si), is the mainstream. In addition, the film formed of a material containing chromium is adjusted to a thickness that provides a desired optical density in combination with the phase shift film, and the film formed of a material containing chromium is generally used as a light-shielding film and a hard mask film when etching the phase shift film.

[0004] As a method for manufacturing a phase shift mask by patterning a phase shift film from a phase shift mask blank in which a phase shift film formed of a silicon-containing material and a light-shielding film formed of a chromium-containing material are formed in this order on a transparent substrate, specifically, the following method is common. First, a resist film is formed on the light-shielding film formed of the chromium-containing material of the phase shift mask blank, a pattern is drawn on this resist film by light or an electron beam, and developed to form a resist pattern. Next, using the resist pattern as an etching mask, the light-shielding film formed of the chromium-containing material is etched using a chlorine-based gas to form a pattern of the light-shielding film. Further, using the pattern of the light-shielding film as an etching mask, the phase shift film formed of the silicon-containing material is etched using a fluorine-based gas to form a pattern of the phase shift film. Then, the resist pattern is removed, and the pattern of the light-shielding film is etched and removed using a chlorine-based gas.

[0005] In this case, the light-shielding film is left to remain outside the portion where the pattern (circuit pattern) of the phase shift film is formed, and the outer peripheral edge portion of the phase shift mask is made into a light-shielding portion (light-shielding pattern) having an optical density of 3 or more when the phase shift film and the light-shielding film are combined. This is to prevent exposure light from leaking from the outer peripheral edge portion of the phase shift mask and irradiating the resist film on the adjacent chip of the wafer from the portion located outside the circuit pattern when transferring the circuit pattern to the wafer using a wafer exposure apparatus. As a method for forming such a light-shielding pattern, after forming the pattern of the phase shift film and removing the resist pattern, a resist film is newly formed, and a resist pattern with the resist film remaining at the outer peripheral edge portion of the phase shift mask is formed by pattern drawing and development. Then, using this resist pattern as an etching mask, the film formed of the chromium-containing material is etched to leave the light-shielding film at the outer peripheral edge portion of the phase shift mask, which is a common method.

[0006] In a phase shift mask that requires high-precision pattern formation, dry etching using gas plasma is the mainstream. For dry etching of a film formed of a chromium-containing material, dry etching using a chlorine-based gas (chlorine-based dry etching) is used, and for dry etching of a film containing silicon or a film containing molybdenum and silicon, dry etching using a fluorine-based gas (fluorine-based dry etching) is used. In particular, in dry etching of a film formed of a chromium-containing material, by using an etching gas that is a mixture of chlorine gas (Cl 2 gas) and oxygen gas (O 2 gas) at 10 to 25% by volume, it is known that the chemical reactivity increases and the etching rate improves.

[0007] With the miniaturization of circuit patterns, techniques for finely forming circuit patterns on phase shift masks are also required. In particular, an assist pattern of a line pattern that supplements the resolution of the main pattern of a phase shift mask needs to be formed smaller than the main pattern so as not to be transferred to the wafer when transferring the circuit pattern to the wafer using a wafer exposure apparatus. In a phase shift mask of a generation 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 pattern of the line pattern of the circuit on the phase shift mask is required to be about 40 nm.

[0008] A chemically amplified resist capable of forming a fine pattern is composed of a base resin, an acid generator, a surfactant, etc. Since many reactions in which the acid generated by exposure acts as a catalyst can be applied, high sensitivity can be achieved, and by using a chemically amplified resist, it is possible to form mask patterns such as patterns of a fine phase shift film with a line width of 0.1 μm or less. The resist is applied onto a photomask blank by spin coating using a resist coater.

[0009] The thickness of the resist film used for the phase shift mask blank of the advanced product is 100 to 150 nm. The reason why it is difficult to form a finer assist pattern on the phase shift mask is that the aspect ratio of the resist pattern for forming the assist pattern, which is formed on the light-shielding film made of a chromium-containing material, is high. Therefore, 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.

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

[0011] Therefore, in order to solve this problem, a hard mask film made of a silicon-containing material is further provided on the light-shielding film made of a chromium-containing material. In this case, the hard mask film made of a silicon-containing material is a thin film with a thickness of 5 to 15 nm, and the thickness of the resist film formed on the hard mask film is reduced to 80 to 110 nm.

[0012] When dry-etching a light-shielding film formed of a chromium-containing material using a chlorine-based gas, in addition to the clear time when the light-shielding film formed of the chromium-containing material disappears, it is necessary to perform over-etching of 100 to 300% of the clear time. This is because chlorine-based dry-etching is an isotropic etching dominated by chemical components, and the pattern of the light-shielding film formed of a chromium-containing material becomes under-etched at the boundary with the phase-shifting film, resulting in a trailing shape and preventing the desired pattern width from being stably formed.

[0013] Also, because it is an isotropic etching dominated by chemical components, the chlorine-based plasma moves in the vertical and horizontal directions with respect to the substrate, causing side-etching on the pattern of the light-shielding film formed of a chromium-containing material. To make the CD (Critical Dimension), which is the pattern line width, uniform across the entire mask surface, it is necessary to obtain an equivalent side-etching amount across the entire mask surface. For this purpose, a long dry-etching time is required until the side-etching amount saturates and stabilizes.

[0014] On the other hand, when dry-etching a phase-shifting film formed of a silicon-containing material using a fluorine-based gas, in addition to the clear time when the phase-shifting film formed of a silicon-containing material disappears, over-etching of about up to 20% of the clear time (for example, a short over-etching of 1 to 6 seconds) is performed. By dry-etching, the transparent substrate in contact with the phase-shifting film is also slightly etched to adjust the phase difference to 175 to 185 degrees with respect to the exposure light. In this case, the phase-shifting film formed of a silicon-containing material has an initial phase difference set to 175 to 179 degrees, and a method of making the desired phase difference, that is, 175 to 185 degrees, by digging into the transparent substrate by over-etching is common.

[0015] In fluorine-based dry etching, overetching can be done in a short time because fluorine-based dry etching is anisotropic etching dominated by physical components. For a phase shift mask pattern formed of a silicon-containing material, the pattern will not have a scalloped shape at the boundary with the substrate. Also, fluorine-based plasma moves in a direction perpendicular to the substrate surface, and the CD of the light-shielding film formed of a chromium-containing material that functions as an etching mask is faithfully reproduced, so long-time overetching is not required.

[0016] Since fluorine-based dry etching is anisotropic etching dominated by physical components, the amount of resist disappearance is generally larger than that in chlorine-based dry etching. Therefore, a resist film for forming a pattern of a hard mask film formed of a silicon-containing material requires an appropriate thickness. However, a hard mask film formed of a silicon-containing material functions as an etching mask when dry etching a light-shielding film formed of a chromium-containing material using a chlorine-based gas and has sufficient etching resistance to chlorine-based gas. Thus, it is possible to make the hard mask film formed of a silicon-containing material thinner. If the hard mask film formed of a silicon-containing material is thinner, the time for fluorine-based dry etching of the hard mask film will be shorter. As a result, the resist film required for forming a pattern of the hard mask film formed of a silicon-containing material can also be made thinner. For these reasons, by using a hard mask film formed of a silicon-containing material, it becomes possible to thin the resist film used for etching the hard mask film, that is, the resist film initially used for the phase shift mask blank. And by thinning the resist film, the aspect ratio of the resist pattern becomes lower. Therefore, the influence of the impact by the developer or the impact by pure water during the rinse process in the development process of resist pattern formation is reduced, and a good assist pattern can be formed, making it possible to achieve high resolution of the transferred pattern.

[0017] As a method of manufacturing a phase shift mask by patterning a phase shift film from a phase shift mask blank in which a phase shift film formed of a silicon-containing material, a light-shielding film formed of a chromium-containing material, and a hard mask film formed of a silicon-containing material are 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 film, and a pattern is drawn on this resist film by light or an electron beam and developed to form a resist pattern. Next, using the resist pattern as an etching mask, the hard mask film formed of a silicon-containing material is dry-etched using a fluorine-based gas to form a pattern of the hard mask film, and then the resist pattern is removed. Next, using the pattern of the hard mask film as an etching mask, the light-shielding film formed of a chromium-containing material is dry-etched using a chlorine-based gas to form a pattern of the light-shielding film. Further, using the pattern of the light-shielding film as an etching mask, the phase shift film formed of a silicon-containing material is dry-etched using a fluorine-based gas to form a phase shift film pattern, and at the same time, the pattern of the hard mask film is removed, and then the pattern of the light-shielding film is etched and removed using a chlorine-based gas.

[0018] Furthermore, the higher pattern resolution that has been demanded in projection exposure in recent years cannot obtain the desired pattern resolution even with a phase shift mask. Therefore, EUV lithography using light in the extreme ultraviolet region for exposure light has come to be used.

[0019] Light in the extreme ultraviolet region is easily absorbed by all substances, and transmissive lithography such as conventional photolithography using ArF excimer laser light cannot be used. Therefore, in EUV lithography, a reflective optical system is used. The wavelength of the light in the extreme ultraviolet region used in EUV lithography is 13 to 14 nm, and the wavelength of conventional ArF excimer laser light is 193 nm. Therefore, compared with photolithography using conventional ArF excimer laser light, the exposure wavelength is short, and it is 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 light in the extreme ultraviolet region, a protective film for protecting the reflective film, and a light absorption film that absorbs light in the extreme ultraviolet region are formed in this order on a substrate such as a glass substrate. As the reflective film, a multilayer reflective film in which a low refractive index layer and a high refractive index layer are alternately laminated to increase the reflectivity when light in the extreme ultraviolet region is irradiated on the surface of the reflective film is used. Usually, 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. As the protective film, a ruthenium (Ru) film is usually used. On the other hand, for the light absorption film, a material having a high absorption coefficient for EUV light, specifically, a material containing, for example, chromium (Cr) or tantalum (Ta) as a main component is used.

[0021] As a method for manufacturing a reflective photomask by patterning a light absorption film from a reflective photomask blank in which a reflective film that reflects light in the extreme ultraviolet region, a protective film for protecting the reflective film, and a light absorption film that absorbs light in the extreme ultraviolet region are formed in this order on a substrate, specifically, the following method is common. First, a resist film is formed on the light absorption film, a pattern is drawn on this resist film by light or an electron beam, and developed to form a resist pattern. Next, a pattern of the light absorption film is formed, and then the resist pattern is removed.

[0022] In a reflective photomask required for EUV lithography, an assist pattern of a line pattern that aids in the resolution of the main pattern becomes smaller as the main pattern is miniaturized, and the line width of the assist pattern needs to be reduced to about 30 nm, particularly about 25 nm. Therefore, compared with a phase shift mask blank, a thinner resist film is required for a reflective photomask blank.

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

[0024] 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 a finer assist pattern, so in the development process of resist pattern formation, 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.

[0025] 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 having 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 in 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.

[0026] 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, using the pattern-formed resist film as a mask, etching by a chlorine-based gas process is performed to form a pattern on the hard mask layer. Next, using the pattern-formed hard mask layer as a mask, etching by a fluorine-based gas process is performed 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

[0027]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0028] 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 a hard mask layer, and a film containing tantalum is used as an absorption layer, and the absorption layer is patterned by fluorine-based dry etching. In this case, the films formed of materials containing chromium (CrNH film and CrOH film) have high resistance to fluorine-based dry etching, so the etching rate is slow, and the film mainly containing tantalum has low resistance to fluorine-based dry etching, so the etching rate is fast. Therefore, the hard mask layer can be made thinner. On the other hand, the film containing tantalum is patterned by chlorine-based dry etching. However, if the hard mask layer becomes thinner, the reduction amount of the resist film during dry etching also decreases, so the resist film formed on the hard mask layer can be made thinner. As a result, the aspect ratio of the resist pattern becomes low, and the influence of the impact by the developer or the impact by pure water during the rinse process in the development process of forming the resist pattern is reduced. Therefore, a good assist pattern can be formed by the hard mask layer.

[0029] However, as described above, when dry-etching a hard mask layer formed of a material containing chromium using a chlorine-based gas, in addition to the clear time when the hard mask layer formed of the material containing chromium disappears, it is necessary to perform over-etching of 100 to 300% of the clear time. In that case, the thickness of the resist film cannot be made 80 nm or less.

[0030] The present invention has been made to solve the above problems, and when manufacturing a reflective photomask from a reflective photomask blank including 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 absorption film that absorbs the exposure light, it is possible to satisfactorily form an assist pattern having a line width of about 30 nm, particularly about 25 nm. Specifically, even when the resist film is thin, for example, even when the resist film has a thickness of 80 nm or less, it is possible to satisfactorily form an assist pattern having a line width of about 30 nm, particularly about 25 nm. A first object of the present invention is to provide a reflective photomask blank. Furthermore, a second object of the present invention is to provide a method for manufacturing a reflective photomask from such a reflective photomask blank.

Means for Solving the Problems

[0031] As described above, in the conventional reflective photomask blank, there has been a problem that when the resist film has a thickness of 80 nm or less, the resist film does not remain after dry etching, and a fine assist pattern cannot be satisfactorily formed.

[0032] Therefore, as a result of intensive studies to solve the above problems, the present inventors have provided 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 absorption film that absorbs the exposure light. On the light absorption film of a reflective photomask blank including a light absorption film, a hard mask film that functions as a hard mask when patterning the light absorption film by dry etching is provided in contact with the light absorption film. The hard mask film is provided on the side farthest from the substrate and is formed of a material that is resistant to chlorine-based dry etching and removable by fluorine-based dry etching. The hard mask film includes a first layer and a second layer, where the first layer is formed of a material that is resistant to chlorine-based dry etching and removable by fluorine-based dry etching, and the second layer is formed of a material that is resistant to fluorine-based dry etching and removable by chlorine-based dry etching. By making the etching clearance time when the light absorption film is dry-etched under one condition longer than the etching clearance time when the first layer of the hard mask film is dry-etched under the same condition, the inventors have found that the above-described problems can be solved, and thus the present invention has been accomplished.

[0033] Accordingly, the present invention provides the following reflective photomask blank and method for manufacturing a reflective photomask. 1. A substrate, 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 absorption film formed on the protective film that absorbs the exposure light, A hard mask film formed on the light absorption film in contact with the light absorption film, which functions as a hard mask when patterning the light absorption film by dry etching A reflective photomask blank comprising: The hard mask film is composed of a multilayer including a first layer provided on the side farthest from the substrate and a second layer, The first layer is formed of a material that is resistant to chlorine-based dry etching and removable by fluorine-based dry etching, The second layer is formed of a material that is resistant to fluorine-based dry etching and can be removed by chlorine-based dry etching. A reflective photomask blank, characterized in that when the light absorption film is subjected to fluorine-based dry etching under a certain condition, the etching clearance time is longer than the etching clearance time when the first layer of the hard mask film is subjected to fluorine-based dry etching under the same condition. 2. The reflective photomask blank according to 1, characterized in that when the light absorption film and the first layer of the hard mask film are subjected to fluorine-based dry etching under the certain condition, the ratio of the etching rate of the light absorption film to the etching rate of the first layer of the hard mask film is 0.4 or more and 2 or less. 3. The reflective photomask blank according to 1, characterized in that the first layer is formed of a material containing silicon and not containing chromium. 4. The reflective photomask blank according to 1, characterized in that the second layer is formed of a material containing chromium and not containing silicon. 5. The reflective photomask blank according to 1, characterized in that the thickness of the first layer is 2 nm or more and 14 nm or less. 6. The reflective photomask blank according to 1, characterized in that the difference between the thickness of the first layer and the thickness of the light absorption film is 30 nm or more. 7. The reflective photomask blank according to 1, characterized in that the difference between the thickness of the first layer and the thickness of the second layer is 10 nm or less. 8. The reflective photomask blank according to 1, characterized in that the light absorption film is formed of a material containing tantalum. 9. A method for manufacturing a reflective photomask including a pattern of the light absorption film from the reflective photomask blank according to any one of 1 to 8, (A) A step of forming a resist film in contact with the side of the hard mask film away 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, patterning the first layer by dry etching using a fluorine-based gas to form a pattern of the first layer; (D) Removing the resist pattern; (E) Using the pattern of the first layer as an etching mask, patterning the second layer by dry etching using a chlorine-based gas to form a pattern of the second layer; (F) Using the pattern of the second layer as an etching mask, patterning the light absorption film by dry etching using a fluorine-based gas to form a pattern of the light absorption film, and at the same time removing the pattern of the first layer; (G) Removing the pattern of the second layer by dry etching using a chlorine-based gas A method for manufacturing a reflective photomask, comprising the steps of: 10. The manufacturing method according to 9, wherein the thickness of the resist film is 80 nm or less. 11. The manufacturing method according to 9, wherein the pattern of the light absorption film includes a line pattern having a width of 25 nm or less.

Effect of the Invention

[0034] According to the present invention, the thickness of the resist film can be reduced, the aspect ratio of the resist pattern can be lowered, and an assist pattern having a line width of about 30 nm, particularly about 25 nm, can be formed favorably. Therefore, high resolution can be obtained in the transfer pattern of the reflective photomask manufactured from the reflective photomask blank.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0036] Hereinafter, the present invention will be described in more detail. The reflective photomask blank of the first aspect of the present invention includes a substrate, a multilayer reflective film formed on the substrate and reflecting 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 absorption film formed on the protective film and absorbing exposure light which is light in the extreme ultraviolet region, and a hard mask film formed on the light absorption film in contact with the light absorption film and functioning as a hard mask when patterning the light absorption film by dry etching. This hard mask film is a film (laminated film) composed of multiple layers including a first layer provided on the side most distant from the substrate and a second layer.

[0037] The reflective photomask blank of the present invention may further include a resist film. The reflective photomask blank of the second aspect of the present invention includes a substrate, a multilayer reflective film formed on the substrate and reflecting 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 absorption film formed on the protective film and absorbing exposure light which is light in the extreme ultraviolet region, a hard mask film formed on the light absorption film in contact with the light absorption film and functioning as a hard mask when patterning the light absorption film by dry etching, and a resist film formed on the hard mask film in contact with the hard mask film. This hard mask film is a film (laminated film) composed of multiple layers including a first layer provided on the side most distant from the substrate and a second layer.

[0038] From the reflective photomask blanks of the first and second aspects, for example, a reflective photomask can be obtained which includes a substrate, a multilayer reflective film formed on the substrate and reflecting 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, and a pattern (circuit pattern or photomask pattern) of a light absorption film formed on the protective film and absorbing exposure light which is light in the extreme ultraviolet region.

[0039] Hereinafter, the structure of the reflective photomask blank and the reflective photomask of the present invention will be described with reference to the drawings. In the description of the drawings, the same reference numerals may be given to the same components and the description may be omitted. Further, the drawings may be shown in an enlarged manner for convenience, and the dimensional ratios of the respective components are not necessarily the same as the actual ones.

[0040] FIG. 1 is a cross-sectional view showing an example of the first aspect of the reflective photomask blank of the present invention. This reflective photomask blank 101 includes 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 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 for protecting the multilayer reflective film 2, a light absorption film 4 formed on the protective film 3 in contact with the protective film 3 and absorbing the exposure light, and a hard mask film 5 formed on the light absorption film 4 in contact with the light absorption film 4 and functioning as a hard mask when patterning the light absorption film 4 by dry etching. In this case, the hard mask film 5 is composed of two layers including a first layer 51 provided on the side most distant from the substrate and a second layer 52 provided on the substrate 1 side of the first layer 51. In other words, in this reflective photomask blank 101, from the substrate 1 side, the multilayer reflective film 2, the protective film 3, the light absorption film 4, the second layer 52 of the hard mask film 5, and the first layer 51 of the hard mask film 5 are laminated in this order.

[0041] FIG. 2 is a cross-sectional view showing an example of a second aspect of the reflective photomask blank of the present invention. This reflective photomask blank 102 includes a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1 and reflecting exposure light that 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 for protecting the multilayer reflective film 2, a light absorption film 4 formed on the protective film 3 in contact with the protective film 3 and absorbing the exposure light, a hard mask film 5 formed on the light absorption film 4 in contact with the light absorption film 4 and functioning as a hard mask when patterning the light absorption film 4 by dry etching, and a resist film 6 formed on the hard mask 5 film in contact with the hard mask 5 film. In this case, the hard mask film 5 is composed of two layers including a first layer 51 provided on the side farthest from the substrate and a second layer 52 provided on the substrate 1 side of the first layer 51. In other words, in this reflective photomask blank 102, from the substrate 1 side, the multilayer reflective film 2, the protective film 3, the light absorption film 4, the second layer 52 of the hard mask film 5, the first layer 51 of the hard mask film 5, and the resist film 6 are laminated in this order.

[0042] FIG. 3 is a cross-sectional view showing an example of the reflective photomask 200 of the present invention. This reflective photomask includes a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1 and reflecting exposure light that 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 for protecting the multilayer reflective film, and a pattern (circuit pattern or photomask pattern) 4a of a light absorption film formed on the protective film 3 in contact with the protective film 3 and absorbing the exposure light. In other words, in this reflective photomask 200, from the substrate 1 side, the multilayer reflective film 2, the protective film 3, and the pattern 4a of the light absorption film are laminated in this order.

[0043] [Substrate] There are no particular restrictions on the type and size of the substrate. The substrate of the reflective photomask blank and the reflective photomask may or may not be transparent at the exposure wavelength. For the substrate, for example, a glass substrate such as a quartz substrate can be used. Further, as the substrate, for example, a substrate called a 6025 substrate with a 6-inch square and a thickness of 0.25 inches defined in the SEMI standard is suitable. The 6025 substrate is usually expressed as a substrate with a 152 mm square and a thickness of 6.35 mm when using the SI unit system.

[0044] [Multilayer reflective film] The multilayer reflective film is a film that reflects exposure light which is light in the extreme ultraviolet region. The multilayer reflective film is preferably formed in contact with the substrate. This light in the extreme ultraviolet region is called EUV light, the wavelength of EUV light is 13 - 14 nm, and EUV light is usually light with a wavelength of about 13.5 nm. The material constituting the multilayer reflective film has resistance to dry etching (chlorine-based dry etching) using a chlorine-based gas (for example, only Cl 2 gas, or a mixed gas of Cl 2 gas and O 2 gas), and is preferably a material that can be removed by dry etching (fluorine-based dry etching) using a fluorine-based gas (for example, CF 4 gas or SF 6 gas). Specifically, examples of the material constituting the multilayer reflective film include molybdenum (Mo), silicon (Si), etc. As the multilayer reflective film, generally, a laminated film (Si / Mo laminated film) in which about 20 - 60 layers of molybdenum (Mo) layers and silicon (Si) layers are alternately laminated is used. The thickness of the multilayer reflective film is preferably 200 nm or more, particularly preferably 220 nm or more, and preferably 340 nm or less, particularly preferably 280 nm or less.

[0045] [Protective film] The protective film is 、multipleIt 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, for example, to protect the multilayer reflective film in cleaning during processing into a reflective photomask, correction of a reflective photomask, etc. Further, the protective film preferably has a function of protecting the multilayer reflective film when patterning the light absorption film by etching and preventing oxidation of the multilayer reflective film. The material constituting the protective film is preferably a material having etching characteristics different from those of the light absorption film, and specifically, a material having resistance to chlorine-based dry etching is preferable. Specifically, examples of the material constituting the protective film include a material containing ruthenium (Ru). The protective film may be a single-layer film, a multilayer film (for example, a film composed of 2 to 4 layers), or a film having a gradient composition. The thickness of the protective film is preferably 1 nm or more and preferably 20 nm or less.

[0046] [Light absorption film] The light absorption film is a film that absorbs exposure light which is light in the extreme ultraviolet region. The light absorption film is preferably formed in contact with the protective film. The light absorption film is preferably a material that has resistance to chlorine-based dry etching and can be removed by fluorine-based dry etching. The light absorption film is preferably formed of a material containing tantalum (Ta). Specific examples of the material containing tantalum include, for example, tantalum alone (Ta), and tantalum compounds containing tantalum (Ta) and one or more selected from oxygen (O), nitrogen (N), boron (B), etc. Examples of such materials include a material composed of tantalum (Ta), a material composed of tantalum and oxygen (TaO), a material composed of tantalum and nitrogen (TaN), a material composed of tantalum and boron (TaB), a material composed of tantalum, oxygen and nitrogen (TaON), a material composed of tantalum, oxygen and boron (TaOB), a material composed of tantalum, nitrogen and boron (TaNB), and a material composed of tantalum, oxygen, nitrogen and boron (TaONB). The light absorption film may be a single-layer film, a multilayer film (for example, a film composed of 2 to 4 layers), or a film having a gradient composition. The thickness of the light absorption film is preferably 30 nm or more, particularly preferably 40 nm or more, especially preferably 50 nm or more, and preferably 100 nm or less, particularly preferably 80 nm or less, especially preferably 74 nm or less.

[0047] [Hard mask film] The hard mask film of the present invention is composed of multiple layers including a first layer provided on the side farthest from the substrate and a second layer provided on a side other than the side farthest from the substrate. The hard mask film is not limited to being composed of two layers, and may be composed of three or more layers, for example, it may be composed of three, four or five layers. The second layer is preferably provided on the side closest to the substrate.

[0048] The first layer of the hard mask film is made of a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching. Due to such etching characteristics, the first layer functions as an etching mask in the etching of the second layer. As the material of the first layer, a material containing silicon (Si) and not containing chromium (Cr) is suitable.

[0049] On the other hand, the second layer of the hard mask film is made of a material that is resistant to fluorine-based dry etching and can be removed by chlorine-based dry etching. Due to such etching characteristics, the second layer functions as an etching mask in the etching of the light absorption film. As the material of the second layer, a material containing chromium (Cr) and not containing silicon (Si) is suitable.

[0050] [The first layer of the hard mask film] The first layer is the layer in contact with the resist film. Also, the first layer is the layer that functions as an etching mask (hard mask) in the etching of the second layer.

[0051] In addition to silicon, the material of the first layer may contain one or more selected from oxygen (O), nitrogen (N), and carbon (C). In particular, a material composed of silicon and one or more selected from oxygen, nitrogen, and carbon is preferable. When the material of the first layer contains elements other than silicon, the silicon content is less than 100 atomic%, preferably 80 atomic% or less, particularly preferably 60 atomic% or less. A lower silicon content results in a higher etching rate (etching speed) of the first layer in fluorine-based dry etching. On the other hand, the lower limit of the silicon content is usually 20 atomic% or more, preferably 30 atomic% or more.

[0052] The material of the first layer preferably contains nitrogen, and particularly, silicon nitride (SiN) composed of silicon and nitrogen is suitable. When the material of the first layer contains nitrogen, the silicon content is preferably 20 atomic % or more, particularly preferably 30 atomic % or more, and is preferably 80 atomic % or less, particularly preferably 60 atomic % or less. On the other hand, the nitrogen content is preferably 60 atomic % or less, particularly preferably 55 atomic % or less. The lower limit of the nitrogen content is not particularly limited, but is preferably 1 atomic % or more, particularly preferably 2 atomic % or more.

[0053] The material of the first layer preferably contains oxygen, and particularly, silicon oxide (SiO) composed of silicon and oxygen is suitable. When the material of the first layer contains oxygen, the silicon content is preferably 20 atomic % or more, particularly preferably 30 atomic % or more, and is preferably 80 atomic % or less, particularly preferably 60 atomic % or less. On the other hand, the oxygen content is preferably 20 atomic % or more, particularly preferably 25 atomic % or more, and is preferably 70 atomic % or less, particularly preferably 68 atomic % or less.

[0054] The material of the first layer preferably contains nitrogen together with oxygen, and particularly, silicon oxynitride (SiON) composed of silicon, oxygen, and nitrogen is suitable. When the material of the first layer contains oxygen and nitrogen, the silicon content, nitrogen content, and oxygen content are preferably in the ranges described above.

[0055] 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 thinner the layer, the shorter the etching time, the thickness of the first layer is preferably 14 nm or less, particularly preferably 13 nm or less, and especially preferably 12 nm or less. On the other hand, if it is too thin, the function as an etching mask in the etching of the second layer is lost, and the sensitivity of the defect inspection of the hard mask film decreases. Therefore, the thickness of the first layer is preferably 2 nm or more, particularly preferably 4 nm or more.

[0056] The silicon-containing and chromium-free material has resistance to chlorine-based dry etching of the second layer, and the pattern of the first layer functions as an etching mask in the etching of the second layer. Furthermore, since it can be etched by fluorine-based dry etching that does not require long-time over-etching, the thickness of the resist film used for etching the first layer can be reduced. In particular, a material containing oxygen together with silicon and not containing chromium, preferably a material containing each element at the aforementioned content rate, more preferably a material having a relatively high oxygen content composition, has high adhesion to the resist film, and is also difficult to dissolve in a mixed solution of sulfuric acid and hydrogen peroxide water, ammonia-added water, etc. compared to a chromium-containing material, and can stably maintain the optical characteristics required for defect inspection, etc. For these reasons, by using such a first layer on the side farthest from the substrate of the etching mask film, even a line pattern such as a fine assist pattern is difficult to be toppled by the impact of the developer or the impact of pure water during the rinse process in the development process of resist pattern formation, and a good resist pattern can be formed, and high resolution can be obtained.

[0057] Since the material of the first layer is a material that can be removed by fluorine-based dry etching, the pattern of the first layer can be removed simultaneously with the formation of the pattern of the light absorption film in fluorine-based dry etching when forming the pattern of the light absorption film. In particular, in fluorine-based dry etching when forming the pattern of the light absorption film, in order to remove the entire thickness direction of the pattern of the first layer simultaneously with the formation of the pattern of the light absorption film, it is necessary that the etching clear time when the light absorption film is fluorine-based dry etched under one condition is longer than the etching clear time when the first layer of the hard mask film is fluorine-based dry etched under the same condition (the same condition as the fluorine-based dry etching of the light absorption film).

[0058] In addition, when the first layer of the light absorption film and the hard mask film is subjected to fluorine-based dry etching under one condition, the ratio of the etching rate (nm / sec) of the light absorption film to the etching rate (nm / sec) of the first layer of the hard mask film is preferably 0.4 or more, particularly preferably 0.7 or more, and preferably 2 or less, particularly preferably 1.2 or less. Further, the difference between the thickness of the first layer and the thickness of the light absorption film is preferably 30 nm or more, particularly preferably 40 nm or more, and especially preferably 44 nm or more.

[0059] [Second layer of hard mask film] The second layer is a layer that functions as an etching mask (hard mask) in the etching of the light absorption film.

[0060] In addition to chromium, the material of the second layer may contain one or more selected from oxygen (O), nitrogen (N), and carbon (C). Particularly, a material composed of chromium and one or more selected from oxygen, nitrogen, and carbon is preferable. When the material of the second layer contains an element other than chromium, the chromium content is less than 100 atomic%, preferably 98 atomic% or less, particularly preferably 95 atomic% or less. A lower chromium content results in a higher etching rate in the chlorine-based dry etching of the second layer. On the other hand, the lower limit of the chromium content is usually 2 atomic% or more, preferably 5 atomic% or more.

[0061] The material of the second layer preferably contains nitrogen. Particularly, chromium nitride (CrN) composed of chromium and nitrogen is suitable. When the material of the second layer contains nitrogen, the chromium content is preferably 5 atomic% or more, particularly preferably 40 atomic% or more, and preferably 98 atomic% or less, particularly preferably 96 atomic% or less. On the other hand, the nitrogen content is preferably 3 atomic% or more, particularly preferably 5 atomic% or more, and preferably 60 atomic% or less, particularly preferably 52 atomic% or less, especially preferably 50 atomic% or less.

[0062] The second layer is patterned by chlorine-based dry etching using the pattern of the first layer formed in contact with the second layer as an etching mask. However, if the first layer is also exposed to chlorine-based dry etching and gradually thins, and when the first layer disappears, pinhole defects will be formed in the second layer. When dry etching the light absorption film using the second layer as an etching mask, the plasma during the etching of the light absorption film will reach the light absorption film through the pinhole defects, resulting in pinhole defects in the light absorption film. Therefore, it is preferable that the second layer is thinner with a shorter etching time, and the thickness of the second layer is preferably 16 nm or less, particularly preferably 10 nm or less. On the other hand, if it is too thin, the function as an etching mask in the etching of the light absorption film will be lost, and the sensitivity of the defect inspection of the hard mask film will decrease. Therefore, the thickness of the second layer is preferably 2 nm or more, particularly preferably 4 nm or more. In particular, the difference between the thickness of the first layer and the thickness of the second layer is preferably 10 nm or less, particularly preferably 4 nm or less.

[0063] A material containing chromium and not containing silicon has resistance to fluorine-based dry etching of the light absorption film, and the pattern of the second layer functions as an etching mask in the etching of the light absorption film. In particular, a material containing nitrogen and not containing silicon together with chromium, preferably a material containing each element at the aforementioned content rate, has a high etching rate and a short etching time. For these reasons, by providing the second layer together with the first layer on the etching mask film, high resolution can be obtained.

[0064] Since the material of the second layer can be removed by chlorine-based dry etching, if the light absorption film is formed of a material having resistance to chlorine-based dry etching, after forming the pattern of the light absorption film, the pattern of the second layer can be removed by chlorine-based dry etching, leaving the pattern of the light absorption film.

[0065] [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 a positive type or a negative type. For example, it contains a base resin such as a hydroxystyrene-based resin or a (meth)acrylic acid-based resin and an acid generator, and may contain a crosslinking agent, a quencher, a surfactant, etc. as necessary.

[0066] In the hard mask film of the present invention, a first layer is provided on the side most distant from the substrate, and the thickness of the resist film formed on this first layer can be made thin as described above. The thickness of the resist film is preferably 100 nm or less from the viewpoint of making the resist pattern for forming a fine assist pattern difficult to collapse against the impact of the developer or the impact of pure water during the rinse process in the development process of resist pattern formation. Also, from the viewpoint of favorably forming line patterns such as assist patterns having a width of about 30 nm, particularly about 25 nm, it is preferably 80 nm or less, particularly 60 nm or less. The lower limit of the thickness of the resist film is the thickness that functions as an etching mask in the etching of the first layer, and it is only necessary that the resist pattern remains entirely on the pattern of the first layer after etching, and it is not particularly limited, but it is preferably 30 nm or more, particularly 40 nm or more.

[0067] The formation of the multilayer reflection film, protective film, light absorption film, and hard mask film including the first layer and the second layer of the present invention is not particularly limited, but since it has good controllability and is easy to form a film having predetermined characteristics, formation by a sputtering method is preferred. As the sputtering method, DC sputtering, RF sputtering, etc. can be applied, and there is no particular limitation.

[0068] When forming a multilayer reflective film as a laminate of a molybdenum layer and a silicon layer, as a sputtering target, a molybdenum target and a silicon target can be used. When forming a film made of a material containing ruthenium as a protective film, as a sputtering target, a ruthenium target can be used. When forming a film made of a material containing tantalum as a light absorption film, as a sputtering target, a tantalum target can be used. When forming a first layer of a hard mask film made of a material containing silicon and not containing chromium and a second layer made of a material containing chromium and not containing silicon, as sputtering targets, a silicon target and a chromium target can be used respectively.

[0069] The power input to the sputtering target may be appropriately set according to the size of the sputtering target, the cooling efficiency, the ease of film formation control, etc. Usually, as the power per unit area of the sputtering surface of the sputtering target, 50 to 3000 W / cm 2 is sufficient. Also, as the sputtering gas, noble gases such as helium gas (He gas), neon gas (Ne gas), and argon gas (Ar gas) are used, and each film and the layers included in the film 、 When forming only with the elements of the target, only a noble gas may be used as the sputtering gas.

[0070] When forming each film and the layers included in the film with a material containing oxygen, nitrogen, or carbon, reactive sputtering is preferably used for sputtering. As the sputtering gas for reactive sputtering, a noble gas such as helium gas (He gas), neon gas (Ne gas), argon gas (Ar gas), and a reactive gas are used. For example, when forming with a material containing oxygen, oxygen gas (O 2 gas) is used, and when forming a film of a material containing nitrogen, nitrogen gas (N 2 gas) may be used. When forming with a material containing both nitrogen and oxygen, as the reactive gas, oxygen gas (O 2 gas), nitrogen gas (N 2gas), and nitric oxide gas (NO gas), nitrogen dioxide gas (NO 2 gas), nitrous oxide gas (N 2 O gas), etc., can be appropriately selected and used from nitrogen oxide gases. When forming with a carbon-containing material, as the reactive gas, methane gas (CH 4 ), carbon monoxide gas (CO gas), carbon dioxide gas (CO 2 gas), etc., can be used. When forming with a material containing oxygen, nitrogen, and carbon, as the reactive gas, for example, oxygen gas (O 2 gas) and nitrogen gas (N 2 gas) and carbon dioxide gas (CO 2 ) can be used simultaneously.

[0071] The pressure during the formation of each film and the layers contained in the film may be appropriately set in consideration of film stress, chemical resistance, cleaning resistance, etc. Usually, it is 0.01 Pa or more, particularly 0.03 Pa or more, and 1 Pa or less, particularly 0.3 Pa or less, so that the chemical resistance is improved. Also, each gas flow rate may be appropriately set so as to obtain a desired composition, and usually 0.1 to 100 sccm may be used.

[0072] In the manufacturing process of the reflective photomask blank, before forming the resist film, the substrate or the substrate and the film formed on the substrate may be heat-treated. As the heat treatment method, infrared heating, resistance heating, etc. can be applied, and the treatment conditions are not particularly limited. The heat treatment can be carried out, for example, in a gas atmosphere containing oxygen. The concentration of the gas containing oxygen is not particularly limited. For example, in the case of oxygen gas (O 2 gas), it can be 1 to 100 vol%. The heat treatment temperature is preferably 200 °C or more, particularly 400 °C or more.

[0073] Also, in the manufacturing process of the reflective photomask blank, before forming the resist film, the film formed on the substrate, particularly the hard mask film, may be subjected to ozone treatment, plasma treatment, etc., and the treatment conditions are not particularly limited. Any of these treatments can be carried out for the purpose of increasing the oxygen concentration in the surface portion of the film. In that case, the treatment conditions may be appropriately adjusted so as to obtain a predetermined oxygen concentration. When the film is formed by sputtering, the ratio of the rare gas in the sputtering gas to the oxygen-containing gas (oxidizing gas) such as oxygen gas (O 2 gas), carbon monoxide gas (CO gas), carbon dioxide gas (CO 2 gas), etc. can be adjusted to increase the oxygen concentration in the surface portion of the film.

[0074] Furthermore, in the manufacturing process of the reflective photomask blank, before forming the resist film, a cleaning process may be carried out to remove defects existing on the surface of the substrate or the film formed on the substrate. The cleaning can be carried out using one or both of ultrapure water and functional water which is ultrapure water containing ozone gas, hydrogen gas, etc. Also, after cleaning with ultrapure water containing a surfactant, further cleaning may be carried out using one or both of ultrapure water and functional water. The cleaning can be carried out while irradiating ultrasonic waves as necessary, and furthermore, UV light irradiation can also be combined.

[0075] The method of forming the resist film (applying the resist) is not particularly limited, and known techniques can be applied.

[0076] Next, a method for manufacturing a reflective photomask from a reflective photomask blank of the present invention will be described with reference to the drawings. When manufacturing a reflective photomask from the reflective photomask blank of the present invention, a resist pattern is formed from a resist film, and using the resist pattern as an etching mask, 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 the underlying film or layer according to the material forming the film or layer to form the pattern, and the pattern is removed in a timely manner. Also, in the manufacture of a reflective photomask, the resist film and the resist pattern can be removed with sulfuric acid peroxide.

[0077] FIG. 4 is a cross-sectional view for explaining the process of manufacturing a reflective photomask from a reflective photomask blank of the present invention. First, as shown in FIG. 4(A), a resist film 6 is formed in contact with the side of the hard mask film 5 of the reflective photomask blank 101 of the first aspect that is separated from the substrate 1 (i.e., in contact with the first layer 51) (step (A)).

[0078] Next, as shown in FIG. 4(B), the resist film 6 is patterned to form a resist pattern 6a (step (B)).

[0079] Next, as shown in FIG. 4(C), using the resist pattern 6a as an etching mask, the first layer 51 is patterned by dry etching using a fluorine-based gas to form a pattern 51a of the first layer (step (C)).

[0080] Next, as shown in FIG. 4(D), the resist pattern 6a is removed (step (D)).

[0081] Next, as shown in FIG. 4(E), using the pattern 51a of the first layer as an etching mask, the second layer 52 is patterned by dry etching using a chlorine-based gas to form the pattern 52a of the second layer (step (E)). Thereby, the pattern 5a of the hard mask film including the pattern 51a of the first layer and the pattern 52a of the second layer is formed.

[0082] Next, as shown in FIG. 4(F), using the pattern 52a of the second layer as an etching mask, the light absorption film 4 is patterned by dry etching using a fluorine-based gas to form the pattern 4a of the light absorption film, and at the same time, the pattern 51a of the first layer is removed (step (F)). Here, the pattern 51a of the first layer formed of a material containing silicon and not containing chromium is removed by fluorine-based dry etching, but the pattern 52a of the second layer formed of a material containing chromium and not containing silicon is resistant to fluorine-based dry etching, so it functions as an etching mask and remains on the pattern 4a of the light absorption film even after dry etching.

[0083] Next, as shown in FIG. 4(G), the pattern 52a of the second layer is removed by dry etching using a chlorine-based gas (step (G)).

[0084] When manufacturing a reflective photomask from the reflective photomask blank of the second aspect of the present invention, since the resist film is already formed, step (A) can be omitted, and steps (B) to (G) may be performed.

[0085] By such a method, a resist film is formed thinly, for example, with a thickness of 80 nm or less, on a reflective photomask blank, or a light absorption film is patterned from a reflective photomask blank on which a thin resist film with a thickness of, for example, 80 nm or less is formed, to obtain a reflective photomask on which a pattern of a light absorption film including line patterns such as assist patterns with a line width of 30 nm or less (30 nm or less than 30 nm), particularly 25 nm or less (25 nm or less than 25 nm) is formed. In the present invention, the lower limit of the width of line patterns such as assist patterns formed in the pattern of the light absorption film of the reflective photomask is usually 10 nm or more.

Example

[0086] Hereinafter, the present invention will be specifically described by showing examples and comparative examples, but the present invention is not limited to the following examples.

[0087] [Example 1] On a quartz substrate having a size of 152 mm square and a thickness of about 6 mm, a multilayer reflective film, a protective film, a light absorption film, and a hard mask film composed of a first layer and a second layer were sequentially laminated to manufacture a reflective photomask blank (reflective photomask blank of the first aspect) as shown in FIG. 1.

[0088] First, a molybdenum target and a silicon target were used as targets, argon gas was used as a sputtering gas, the applied power to the targets was adjusted, the flow rate of the sputtering gas was adjusted, and sputtering by the molybdenum target and sputtering by the silicon target were alternately performed to form a multilayer reflective film, which is a laminated film (thickness: 280 nm) in which molybdenum (Mo) and silicon (Si) layers having a reflectance of 67% with respect to light having a wavelength of 13.5 nm are alternately laminated on the quartz substrate.

[0089] Next, using ruthenium as the target and argon gas as the sputtering gas, while adjusting the applied power to the target and the flow rate of the sputtering gas, sputtering was performed to form a ruthenium (Ru) film (thickness 4 nm) as a protective film formed of a material containing ruthenium on the multilayer reflective film.

[0090] Next, using a tantalum target as the target and argon gas and nitrogen gas as the sputtering gases, while adjusting the applied power to the target and the flow rate of the sputtering gas, sputtering was performed to form a tantalum nitride (TaN) film (thickness 64 nm) as a light absorption film formed of a material containing tantalum on the protective film.

[0091] Next, using a chromium target as the target and argon gas and nitrogen gas as the sputtering gases, while adjusting the applied power to the target and the flow rate of the sputtering gas, sputtering was performed to form a chromium nitride (CrN) layer as the second layer of the hard mask film formed of a material containing chromium and not containing silicon on the light absorption film.

[0092] Furthermore, using a silicon target as the target and argon gas and nitrogen gas as the sputtering gases, while adjusting the applied power to the target and the flow rate of the sputtering gas, sputtering was performed to form a silicon nitride (SiN) layer as the first layer of the hard mask film formed of a material containing silicon and not containing chromium on the second layer, thereby obtaining a reflective photomask blank. The compositions of the first layer and the second layer and the thicknesses of the first layer and the second layer are shown in Table 1. The composition was measured using an X-ray photoelectron spectrometer, and the thickness was measured using an X-ray diffractometer (the same applies hereinafter).

[0093] [Example 2] A reflective photomask blank was obtained in the same manner as in Example 1, except that the formation of the first layer was changed as follows. For the first layer, a silicon target was used as the target, argon gas and oxygen gas were used as the sputtering gases, the applied power to the target was adjusted, and the flow rate of the sputtering gases was adjusted to perform sputtering. A silicon oxide (SiO) layer was formed as the first layer of the hard mask film, which contains silicon and does not contain chromium, on the second layer. The compositions of the first and second layers and the thicknesses of the first and second layers are shown in Table 1.

[0094] [Example 3] A reflective photomask blank was obtained in the same manner as in Example 1, except that the formation of the first layer was changed as follows. For the first layer, a silicon target was used as the target, argon gas, nitrogen gas, and oxygen gas were used as the sputtering gases, the applied power to the target was adjusted, and the flow rate of the sputtering gases was adjusted to perform sputtering. A silicon oxynitride (SiNO) layer was formed as the first layer of the hard mask film, which contains silicon and does not contain chromium, on the second layer. The compositions of the first and second layers and the thicknesses of the first and second layers are shown in Table 1.

[0095] [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 was changed. The compositions of the first and second layers and the thicknesses of the first and second layers are shown in Table 1.

[0096] [Comparative Example 1] A reflective photomask blank was obtained in the same manner as in Example 1, except that a hard mask film (corresponding to the hard mask film consisting only of the second layer) consisting only of a layer formed of a material containing chromium and not containing silicon was formed on the light absorption film. The composition and thickness of the hard mask film are shown in Table 1.

[0097] [Comparative Example 2] A reflective photomask blank was obtained in the same manner as in Comparative Example 1, except that the ratio of chromium to nitrogen in the hard mask film was changed. The compositions of the first and second layers, and the composition and thickness of the hard mask film are shown in Table 1.

[0098]

Table 1

[0099] [Clear time of fluorine-based dry etching of the first layer] Using the reflective photomask blanks obtained in Examples 1 to 4, the time (clear time) until the first layer disappeared by fluorine-based dry etching was measured. The clear time of fluorine-based dry etching was defined as the time until endpoint detection (time until the endpoint) when dry etching was performed on the first layer under the following conditions (Condition 1). The results are shown in Table 2.

[0100] <Conditions for fluorine-based dry etching of the first layer (Condition 1)> Apparatus: ICP (Inductively Coupled Plasma) method Gas: SF 6 Gas + He gas Gas pressure: 4.0 mTorr (0.53 Pa) ICP power: 400 W

[0101] [Clear time of chlorine-based dry etching of the second layer] For the reflective photomask blanks obtained in Examples 1 to 4 and Comparative Examples 1 and 2, after measuring the clear time of fluorine-based dry etching of the first layer, the time (clear time) until the second layer disappeared by chlorine-based dry etching was measured. The clear time of chlorine-based dry etching was defined as the time until endpoint detection (time until the endpoint) when dry etching was performed on the second layer under the following conditions (Condition 2). The results are shown in Table 2.

[0102] <Conditions for chlorine-based dry etching of the second layer (Condition 2)> Apparatus: ICP (Inductively Coupled Plasma) method Gas: Cl 2 Gas + O 2 Gas Gas pressure: 3.0 mTorr (0.40 Pa) ICP power: 350 W

[0103] [Clear time of fluorine-based dry etching of light absorption film] For the reflective photomask blanks obtained in Examples 1 to 4 and Comparative Examples 1 and 2, after measuring the clear time of the fluorine-based dry etching of the first layer and the clear time of the chlorine-based dry etching of the second layer, the time until the light absorption film disappeared (clear time) was measured. The clear time of the fluorine-based dry etching was defined as the time until the endpoint detection (time to the endpoint) when dry etching was performed on the light absorption film under the following conditions (Condition 3) same as Condition 1 above. The results are shown in Table 2.

[0104] [Conditions for fluorine-based dry etching of light absorption film (Condition 3)] Apparatus: ICP (Inductively Coupled Plasma) method Gas: SF 6 Gas + He gas Gas pressure: 4.0 mTorr (0.53 Pa) ICP power: 400 W

[0105]

Table 2

[0106] [Amount of resist film reduction in fluorine-based dry etching of the first layer] Using the reflective photomask blanks obtained in Examples 1 to 4, the amount (thickness) by which the resist film decreased until the first layer disappeared was measured by fluorine-based dry etching. First, a positive chemically amplified electron beam resist was spin-coated on the first layer to form a resist film with a thickness of 60 nm. Next, using an electron beam lithography apparatus, 20 isolated line patterns with a long side of 100,000 nm and a short side of 60 nm were drawn at a dose of 100 μC / cm 2 2. Next, using a heat treatment apparatus, heat treatment (PEB: Post Exposure Bake) was performed at 115 °C for 14 minutes. Next, paddle development was performed for 42 seconds to form a resist pattern. Next, using the resist pattern as an etching mask, fluorine-based dry etching was performed on the first layer under the above-mentioned condition 1 with 20% overetching to form a pattern of the first layer. Thereafter, the thickness of the resist pattern remaining on the pattern of the first layer was measured, and the decreased 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 set to a square region of 200 nm × 200 nm (the same applies hereinafter).

[0107] Also, from the obtained decrease amount, the thickness of the resist film required for the resist pattern to remain with a thickness of 20 nm after 20% overetching as the fluorine-based dry etching of the first layer was calculated. The results are shown in Table 3. This thickness is the minimum required thickness of the resist film in the manufacture of the reflective photomask using the reflective photomask blanks of Examples 1 to 4 described later. If the thickness of the resist pattern remaining after etching is too thin, the fluorine-based plasma reaches the first layer and pinhole defects are formed. Therefore, here, the thickness of the resist pattern remaining after dry etching was set to 20 nm 。

[0108] [Amount of decrease in resist film in chlorine-based dry etching of the second layer] Using the reflective photomask blanks obtained in Comparative Examples 1 and 2, by chlorine-based dry etching, the amount (thickness) by which the resist film decreased until the second layer disappeared was measured. First, a positive chemically amplified electron beam resist was spin-coated on the second layer to form a resist film with a thickness of 60 nm. Next, using an electron beam lithography apparatus, 20 isolated line patterns with a long side of 100,000 nm and a short side of 60 nm were drawn at a dose of 100 μC / cm 2 2 . Next, using a heat treatment apparatus, heat treatment (PEB: Post Exposure Bake) was performed at 115 °C for 14 minutes. Next, paddle development was used to perform a development process for 42 seconds to form a resist pattern. Next, using the resist pattern as an etching mask, chlorine-based dry etching was performed on the second layer under the aforementioned condition 2 with 300% overetching to form a pattern of the second layer. Thereafter, the thickness of the resist pattern remaining on the pattern of the second layer was measured, and the decreased thickness was calculated. The results are shown in Table 3.

[0109] Also, from the obtained reduction amount, as chlorine-based dry etching of the second layer, after 300% overetching, the thickness of the resist film required for the resist pattern to remain with a thickness of 20 nm was calculated. The results are shown in Table 3. This thickness is the minimum required thickness of the resist film in the manufacture of the reflective photomask using the reflective photomask blanks of Comparative Examples 1 and 2 described later. If the thickness of the resist pattern remaining after etching is too thin, the chlorine-based plasma reaches the second layer and pinhole defects are formed. Therefore, here, the thickness of the resist pattern remaining after dry etching was set to 20 nm.

[0110] [Table 3]

[0111] [Examples 5 to 8] On the hard mask film (first layer) of the reflective photomask blank obtained in Examples 1 to 4, a positive chemically amplified electron beam resist was spin-coated to form a resist film, and a reflective photomask blank having a resist film as shown in FIG. 2 (reflective photomask blank of the second aspect) was obtained. The thickness of this resist film was the thickness at which a resist pattern with a thickness of 20 nm remained after the fluorine-based dry etching described above, and was set to a thickness of 40 nm or more, which is the lower limit of the thickness at which a stable resist film could be formed with the resist material used. The thickness of the resist film is shown in Table 4.

[0112] 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 the obtained reflective photomask blank having a resist film. First, using an electron beam lithography apparatus, at a dose of 100 μC / cm 2 a total of 200,000 isolated patterns with different short side dimensions were drawn as test patterns corresponding to the assist pattern of the line pattern, with a long side dimension of 80 nm and the short side dimension changed from 20 nm to 60 nm in 1 nm increments. Next, using a heat treatment apparatus, post-exposure bake (PEB) was performed at 110 °C for 14 minutes. Next, paddle development was performed for 45 seconds 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 under the above-described condition 1 with 20% overetching to form a pattern of the first layer. Next, the remaining resist pattern was removed by washing with sulfuric acid and hydrogen peroxide solution (a mixed solution of sulfuric acid and hydrogen peroxide water (sulfuric acid: hydrogen peroxide water = 3:1)). Next, using the pattern of the first layer as an etching mask, chlorine-based dry etching was performed on the second layer under the above-described condition 2 with 300% overetching to form a pattern of the second layer.

[0113] Next, using the pattern of the second layer as an etching mask, fluorine-based dry etching was performed on the light absorption film under the above-described condition 3 to form a pattern of the light absorption film and at the same time remove the pattern of the first layer.

[0114] Next, chlorine-based dry etching was performed on the pattern of the second layer under the aforementioned condition 2 with 50% overetching to remove the pattern of the second layer, thereby obtaining a reflective photomask.

[0115] Next, using an appearance inspection apparatus, the resolution limit of the test pattern of the obtained photomask was evaluated. For all isolated patterns, pattern disappearance, pattern collapse, and pattern shape defects were evaluated. An isolated pattern in which the appearance inspection apparatus detected any of pattern disappearance, pattern collapse, and pattern shape defects was regarded as a defect, and the minimum short-side dimension without any detected isolated pattern with a defect was defined as the resolution limit. The results are shown in Table 4.

[0116] [Comparative Examples 3 and 4] A positive chemically amplified electron beam resist was spin-coated on the hard mask film of the reflective photomask blank obtained in Comparative Examples 1 and 2 to form a resist film, thereby obtaining a reflective photomask blank. The thickness of this resist film was the thickness at which a resist pattern with a thickness of 20 nm remained after chlorine-based dry etching as described above, and was set to a thickness of 40 nm or more, which is the lower limit of the thickness at which a stable resist film can be formed with the resist material used. The thickness of the resist film is shown in Table 4.

[0117] 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 the obtained reflective photomask blank having a resist film. First, a resist pattern was formed in the same manner as in the examples. Next, using the obtained resist pattern as an etching mask, chlorine-based dry etching was performed on the hard mask film under the aforementioned condition 2 with 300% overetching to form a pattern of the hard mask film. Next, the remaining resist pattern was removed by washing with sulfuric acid peroxide (a mixed solution of sulfuric acid and hydrogen peroxide water (sulfuric acid: hydrogen peroxide water = 3:1)).

[0118] Next, using the pattern of the hard mask film as an etching mask, fluorine-based dry etching was performed on the light absorption film under the above-described condition 3 to form a pattern of the light absorption film.

[0119] Next, chlorine-based dry etching was performed on the pattern of the hard mask film under the above-described condition 2 with 50% overetching to remove the pattern of the hard mask film, obtaining a reflective photomask. Using an appearance inspection apparatus, the resolution limit of the test pattern was evaluated in the same manner as in the examples. The results are shown in Table 4.

[0120]

Table 4

[0121] As shown in Table 4, the hard mask films of the reflective photomask blanks of Examples 1 to 4 are the first layers formed of a material having resistance to chlorine-based dry etching on the side most distant from the substrate and being removable by fluorine-based dry etching. In the reflective photomask blanks of Examples 1 to 4, it can be seen that compared with the reflective photomask blanks of Comparative Examples 1 and 2, the resist film can be made thinner, and particularly good resolution limits are obtained. This is presumably because since the resist film is thin, even for a pattern with a narrow line width, the collapse of the resist pattern due to the impact of the developer or the impact of pure water during the rinse process in the development process of forming the resist pattern is reduced.

[0122] Note that the present invention is not limited to the above-described embodiments. The above-described embodiments are examples, and any configuration having the same or substantially the same configuration as the technical idea of the present invention and exhibiting the same or similar operational effects is included in the technical scope of the present invention.

Explanation of Reference Numerals

[0123] 1 Substrate 2 Multilayer Reflective Film 3 Protective Film 4 Light Absorption Film Pattern of the 4a light absorption film 5 Hard mask film 5a Pattern of the hard mask film 51 First layer 51a Pattern of the first layer 52 Second layer 52a Pattern of the second layer 6 Resist film 6a Resist pattern 101, 102 Reflective photomask blank 200 Reflective photomask

Claims

1. A substrate, a multilayer reflective film formed on the substrate and reflecting 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 absorption film formed on the protective film and absorbing the exposure light, a hard mask film formed on the light absorption film in contact with the light absorption film and functioning as a hard mask when patterning the light absorption film by dry etching, A reflective photomask blank comprising: the hard mask film is composed of a multilayer including a first layer provided on the side farthest from the substrate and a second layer, the first layer is formed of a material having resistance to chlorine-based dry etching and removable by fluorine-based dry etching, the second layer is formed of a material having resistance to fluorine-based dry etching and removable by chlorine-based dry etching, A reflective photomask blank, characterized in that an etching clearance time when the light absorption film is dry-etched with fluorine under a certain condition is longer than an etching clearance time when the first layer of the hard mask film is dry-etched with fluorine under the same condition.

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

3. The reflective photomask blank according to claim 1, characterized in that the first layer is formed of a material containing silicon and not containing chromium.

4. The reflective photomask blank according to claim 1, characterized in that the second layer is formed of a material containing chromium and not containing silicon.

5. The reflective photomask blank according to claim 1, characterized in that a thickness of the first layer is 2 nm or more and 14 nm or less.

6. The reflective photomask blank according to claim 1, characterized in that a difference between a thickness of the first layer and a thickness of the light absorption film is 30 nm or more.

7. The reflective photomask blank according to claim 1, characterized in that a difference between a thickness of the first layer and a thickness of the second layer is 10 nm or less.

8. The reflective photomask blank according to claim 1, wherein the light absorption film is formed of a material containing tantalum.

9. A method for manufacturing a reflective photomask having a pattern of the light absorption film from the reflective photomask blank according to any one of claims 1 to 8, comprising: (A) forming a resist film in contact with the side of the hard mask film away from the substrate; (B) patterning the resist film to form a resist pattern; (C) using the resist pattern as an etching mask, patterning the first layer by dry etching using a fluorine-based gas to form a pattern of the first layer; (D) removing the resist pattern; (E) using the pattern of the first layer as an etching mask, patterning the second layer by dry etching using a chlorine-based gas to form a pattern of the second layer; (F) using the pattern of the second layer as an etching mask, patterning the light absorption film by dry etching using a fluorine-based gas to form a pattern of the light absorption film, and at the same time removing the pattern of the first layer; (G) removing the pattern of the second layer by dry etching using a chlorine-based gas. A method for manufacturing a reflective photomask, characterized by including the above steps.

10. The manufacturing method according to claim 9, wherein the thickness of the resist film is 80 nm or less.

11. The manufacturing method according to claim 9, wherein the pattern of the light absorption film includes a line pattern having a width of 25 nm or less.

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