Reflective mask blanks and reflective masks

Abstract

SOLUTION: A reflective mask blank used in EUV lithography, which includes a substrate, a multi-layer reflective film formed on one main surface of the substrate that reflects exposure light, and an absorbing film formed on the multi-layer reflective film that absorbs the exposure light, where the absorbing film contains tungsten, one or both of molybdenum and ruthenium, and one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen, with a total content ratio of 90 atomic percent or more and becomes a reflective mask blank that becomes a raw material of the reflective mask used in EU lithography with EUV light as an exposing light.EFFECT: A reflective mask obtained from a reflective mask blank with an absorbent film of the present invention has a good surface condition and favorable pattern characteristics. In particular, the absorbent film that contains one or more metals and metalloids other than tungsten, along with tungsten, exhibits good film stability even at high temperatures (and is less prone to oxidation). Therefore, by using the reflective mask of the present invention, it is possible to transfer fine patterns onto semiconductor substrates with high precision using EUV light and the like.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a reflective mask blank serving as a material for a reflective mask used in the manufacture of semiconductor devices such as LSIs, and a reflective mask.

Background Art

[0002] In the manufacturing process of semiconductor devices (semiconductor apparatuses), photolithography technology is used, in which exposure light is irradiated onto a transfer mask, and a circuit pattern formed on the mask is transferred onto a semiconductor substrate (semiconductor wafer) via a reduction optical system. At present, the wavelength of the exposure light is mainly 193 nm using argon fluoride (ArF) excimer laser light.

[0003] However, since the formation of further fine patterns has been required, EUV lithography technology using extreme ultraviolet (hereinafter referred to as "EUV") light having a wavelength shorter than that of ArF excimer laser light is regarded as promising. EUV light is light having a wavelength of about 0.2 to 100 nm, and more specifically, light having a wavelength of about 13.5 nm. Since this EUV light has extremely low permeability to substances and cannot use conventional transmissive projection optical systems or masks, reflective optical elements are used. Therefore, reflective masks have also been proposed as masks for pattern transfer. A reflective mask generally has a multilayer reflective film that reflects EUV light formed on a substrate, and an absorber film that absorbs EUV light formed in a pattern shape on the multilayer reflective film. A pattern is formed on a transfer object such as a silicon wafer by the difference in the reflectivity of EUV light, which is the exposure light, caused by the presence or absence of the absorber film on the multilayer reflective film.

[0004] Reflective masks are manufactured using reflective mask blanks, which have a multilayer reflective film on a substrate that reflects exposure light, and an absorber film on top of that that has low reflectivity to exposure light. Furthermore, generally, a protective film is provided between the multilayer reflective film and the absorber film. The multilayer reflective film is formed by alternately stacking layers with different refractive indices. For example, for EUV light exposure, a film is used in which molybdenum (Mo) layers and silicon (Si) layers are alternately stacked. For the absorber film, for example, for EUV light exposure, a film of tantalum (Ta) with nitrogen (N) added is used (Japanese Patent Publication No. 2002-246299 (Patent Document 1)). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2002-246299 [Overview of the initiative] [Problems that the invention aims to solve]

[0006] To transfer fine patterns onto semiconductor substrates using a reflective mask, the absorber film of the reflective mask blank is partially removed to form the pattern. However, in order to transfer fine patterns with high precision, the absorber film requires the following characteristics.

[0007] When forming absorber film patterns by dry etching, a low etching rate necessitates a thicker resist layer to form the pattern. Even when using a hard mask, the hard mask may be etched along with the absorber film. Therefore, a high etching rate for the absorber film is preferable for forming high-precision patterns. Furthermore, excessive etching of the etching mask, such as the resist film, tends to degrade the cross-sectional shape. Thus, a high etching rate for the absorber film is crucial for forming patterns with a good cross-sectional shape. To further improve the processability of absorber films, materials with high etching rates are in demand for the absorber film material.

[0008] Furthermore, if the absorber film is thick, the pattern resolution decreases due to the shadowing effect. Therefore, the absorber film needs to be thin. Moreover, when the absorber film is used as a film with a phase-shift function, a material with a smaller refractive index n is required for thinning. Furthermore, in EUV reflective masks, pulsed high-energy EUV light is irradiated during exposure, and it is said that the absorber film on the reflective mask can instantaneously reach high temperatures (e.g., around 500°C), making the heat resistance of the absorber film important. Therefore, a film is required that does not deteriorate in quality due to oxidation, etc., even at such high temperatures. On the other hand, if the sidewall roughness is large when forming a pattern, it can negatively affect the resolution. However, in materials made of pure tungsten, the surface of the absorber film has irregularities, and the sidewall roughness of the pattern tends to be large.

[0009] The present invention was made to solve the above problems, and aims to provide a reflective mask blank with excellent processability and improved pattern resolution due to a thinner absorbent film, and a reflective mask manufactured using the reflective mask blank. [Means for solving the problem]

[0010] The inventors of the present invention conducted extensive research to solve the above problems and found that using tungsten as the material for the absorber film results in a high etching rate, and also reduces the refractive index n when used as a film with a phase shift function, making it effective for thinning the absorber film. As a result, they discovered that tungsten is superior as a material for absorber films.

[0011] Furthermore, the inventors have discovered that by using tungsten along with one or more metals and metalloids other than tungsten, or one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen, as the material for the absorber film, the surface irregularities are improved. In particular, by including tungsten along with one or more metals and metalloids other than tungsten, especially molybdenum or ruthenium, the absorber film becomes less prone to oxidation even at high temperatures, exhibiting excellent heat resistance during exposure with EUV light. This led to the present invention.

[0012] Accordingly, the present invention provides the following reflective mask blanks and reflective masks. 1. A reflective mask blank that is used as a material for a reflective mask used in EUV lithography using EUV light as the exposure light, comprising a substrate, a multilayer reflective film formed on one main surface of the substrate that reflects exposure light, and an absorber film formed on the multilayer reflective film that absorbs exposure light, The absorbent membrane, (a) tungsten, (b) molybdenum and / or ruthenium, and (c) nitrogen Natural It contains, (a) The tungsten content is 20 atomic percent or more, (b) The content of one or both molybdenum and ruthenium is 1 atomic percent or more. (c) Nitrogen raw Content of 30 atomic percent or more 79 atomic% or less And, (a) tungsten, (b) molybdenum and ruthenium, or both, and (c) nitrogen Natural The total content is 90 atomic percent or more. A reflective mask blank characterized by the following features. 2The refractive index n of the absorber film at the exposure light wavelength is 0.94 or less. 1 The reflective mask blank according to the description. 3 The film thickness of the absorber film is 70 nm or less. or 2 The reflective mask blank according to 1. 4 Between the multilayer reflective film and the absorber film, there is a protective film that is in contact with the multilayer reflective film and has different etching characteristics from the absorber film. 3 The reflective mask blank according to any one of 1 to. 5 Furthermore, it has a conductive film formed on the other main surface of the substrate. 4 The reflective mask blank according to any one of 1 to. 6 Furthermore, on the absorber film, there is a film containing chromium formed as an etching mask. 5 The reflective mask blank according to any one of 1 to. 7 1 to 6 A reflective mask characterized by being manufactured from the reflective mask blank according to any one of. Also, the present invention relates to the following reflective mask blank and reflective mask. [1]. A reflective mask blank that has a substrate, a multilayer reflective film formed on one main surface of the substrate that reflects exposure light, and an absorber film formed on the multilayer reflective film that absorbs exposure light, and is used as a material for a reflective mask in EUV lithography using EUV light as exposure light. The absorber film is (a) Tungsten, (b) One or more selected from metals and semimetals other than tungsten, (c) One or more light elements selected from nitrogen, oxygen, carbon, and hydrogen, or both (b) and (c) The reflective mask blank characterized by containing. [2]. The absorber film is (a) tungsten, and (b) one or more selected from metals and semimetals other than tungsten, characterized in that it comprises a reflective mask blank according to [1]. [3]. The absorber film is (a) tungsten, (b) one or more selected from metals and semimetals other than tungsten, and (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen, characterized in that it contains a reflective mask blank according to [1]. [4]. The total of the above (a) tungsten, (b) one or more selected from metals and semimetals other than tungsten, and (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen is 90 atomic% or more, characterized in that it is a reflective mask blank according to [3]. [5]. One or more selected from metals and semimetals other than the above (b) tungsten is one or both of molybdenum and ruthenium, characterized in that it is a reflective mask blank according to any one of [1] to [4]. [6]. The content of one or more selected from metals and semimetals other than the above (b) tungsten is 1 atomic% or more and 80 atomic% or less, characterized in that it is a reflective mask blank according to any one of [1] to [5]. [7]. The absorber film is (a) tungsten and (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen, and does not contain metals and semimetals other than tungsten, characterized in that it is a reflective mask blank according to [1]. [8]. The content of one or more light elements selected from the above (c) nitrogen, oxygen, carbon, and hydrogen is 10 atomic% or more and 80 atomic% or less, characterized in that it is a reflective mask blank according to [7]. [9]. The total of the above (a) tungsten and (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen is 90 atomic% or more, characterized in that it is a reflective mask blank according to [7] or [8].

[10] . In the absorber film, the content of tungsten is 20 atomic% or more and 99 atomic% or less, characterized in that it is a reflective mask blank according to any one of [1] to [9].

[11] . A reflective mask blank according to any one of [1] to

[10] , characterized in that the refractive index n of the absorber film at the exposure wavelength is 0.94 or less.

[12] A reflective mask blank according to any one of [1] to

[11] , characterized in that the thickness of the absorber film is 70 nm or less.

[13] A reflective mask blank according to any one of [1] to

[12] , characterized in that a protective film is provided between the multilayer reflective film and the absorber film, in contact with the multilayer reflective film and having different etching characteristics from the absorber film.

[14] . A reflective mask blank according to any one of [1] to

[13] , further characterized by having a conductive film formed on another main surface of the substrate.

[15] . A reflective mask blank according to any one of [1] to

[14] , further characterized by having a chromium-containing film formed on the absorbent film as an etching mask. A reflective mask characterized by being manufactured from a reflective mask blank as described in any of [1] to

[15] . [Effects of the Invention]

[0013] The reflective mask obtained from the reflective mask blank having the absorber film of the present invention has a good surface condition and good pattern characteristics. In particular, the absorber film containing tungsten along with one or more metals and metalloids other than tungsten exhibits good film stability even at high temperatures (it is resistant to oxidation). Therefore, by using the reflective mask of the present invention, fine patterns can be transferred with high precision to semiconductor substrates and the like using EUV light. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional view showing an example of a reflective mask blank. [Figure 2] This is a cross-sectional view showing another example of a reflective mask blank. [Figure 3] This is a cross-sectional view showing another example of a reflective mask blank. [Modes for carrying out the invention]

[0015] The present invention will be described in more detail below. The reflective mask blank of the present invention comprises a substrate, a multilayer reflective film formed on the substrate (on one main surface (front side)) that reflects exposure light, specifically a multilayer reflective film that reflects exposure light such as extreme ultraviolet (EUV) light, and an absorber film formed on the multilayer reflective film that absorbs exposure light, specifically an absorber film that absorbs exposure light such as EUV light and reduces reflectivity. A reflective mask (EUV reflective mask) having an absorber pattern (pattern of the absorber film) formed by patterning the absorber film is manufactured from a reflective mask blank (EUV reflective mask blank) that uses EUV light as the exposure light. The wavelength of EUV light used in EUV lithography, which uses EUV light as the exposure light, is 13-14 nm, and is usually light with a wavelength of about 13.5 nm.

[0016] The multilayer reflective film is usually preferably provided in contact with one main surface of the substrate, but it is also possible to provide an undercoat film between the substrate and the multilayer reflective film, provided that the effects of the present invention are not lost. The absorber film may be formed in contact with the multilayer reflective film, but a protective film (protective film for the multilayer reflective film) with different etching characteristics from the absorber film may be provided between the multilayer reflective film and the absorber film, preferably in contact with the multilayer reflective film, and more preferably in contact with both the multilayer reflective film and the absorber film. The protective film is used to protect the multilayer reflective film during processing such as cleaning and correction. Furthermore, it is preferable that the protective film has the function of protecting the multilayer reflective film when the absorber film is patterned by etching, and preventing oxidation of the multilayer reflective film. In addition, on the side of the absorber film that is separated from the substrate, a hard mask film (etching mask film for the absorber film) with different etching characteristics from the absorber film may be provided, preferably in contact with the absorber film. On the other hand, a conductive film used for electrostatically chucking a reflective mask to an exposure apparatus may be provided on the other main surface (back surface), which is the surface opposite to one of the main surfaces of the substrate, preferably in contact with the other main surface. Here, one of the main surfaces of the substrate is referred to as the front surface and upper side, and the other main surface as the back surface and lower side. However, the front and back and top and bottom of these two surfaces are defined for convenience, and the one main surface and the other main surface are either of the two main surfaces (film-forming surfaces) of the substrate, and the front and back and top and bottom are interchangeable.

[0017] Figures 1 to 3 show typical examples of the reflective mask blanks of the present invention. Figure 1 is a cross-sectional view showing an example of the reflective mask blank of the present invention, which comprises a multilayer reflective film 102 formed on one main surface of a substrate 101 in contact with the main surface, and an absorber film 103 formed in contact with the multilayer reflective film 102. Figure 2 is a cross-sectional view showing another example of the reflective mask blank of the present invention, which comprises a multilayer reflective film 102 formed on one main surface of a substrate 101 in contact with the main surface, a protective film 104 formed in contact with the multilayer reflective film 102, and an absorber film 103 formed in contact with the protective film 104. Figure 3 is a cross-sectional view showing another example of the reflective mask blank of the present invention, which comprises a multilayer reflective film 102 formed on one main surface of a substrate 101 in contact with that main surface, a protective film 104 formed in contact with the multilayer reflective film 102, an absorber film 103 formed in contact with the protective film 104, and a conductive film 105 formed on the other main surface of the substrate 101 in contact with that main surface.

[0018] For example, a so-called 6025 substrate (6 inches x 6 inches x 0.25 inches thick (usually expressed as 152 mm x 152 mm x 6.35 mm thick in SI units)) can be used as the substrate. The substrate needs to reduce pattern distortion due to thermal expansion during exposure, and the thermal expansion coefficient of the substrate is preferably 30 ppb / °C or less in absolute value, and particularly preferably 10 ppb / °C or less. Examples of such materials include titania-doped quartz glass (SiO2-TiO2 glass).

[0019] The substrate is preferably flatter from the viewpoint of obtaining high positional accuracy in detecting defects in the multilayer reflective film, forming absorber patterns, and detecting defects in the absorber film. On the main surface on which the multilayer reflective film is formed, the flatness (planarity) in the exposure pattern formation area, for example, in the case of a 6025 substrate, in the central part of the main surface, for example, in a range of 132 mm × 132 mm, is preferably 0.1 μm or less, and particularly preferably 0.05 μm or less. Furthermore, in order to obtain high reflectivity on the main surface on which the multilayer reflective film is formed, the surface roughness is preferably low, and the surface roughness Rq (RMS, root mean square roughness) is preferably 0.15 nm or less, and particularly preferably 0.1 nm or less. In the present invention, the surface roughness Rq can be the value measured by an atomic force microscope (AFM) in a range of, for example, 1 μm square.

[0020] On the other hand, the main surface opposite to the main surface on which the multilayer reflective film is formed is usually the surface that is adsorbed when the reflective mask is set in the exposure apparatus. Therefore, in order to obtain sufficient pattern position accuracy, it is preferable that this surface of the substrate is also flat, and the flatness (planarity) is preferably 1 μm or less.

[0021] A multilayer reflective film is a film that reflects exposure light such as EUV light in a reflective mask. It consists of multiple layers with different optical properties, for example, two layers with different optical properties (layer A and layer B) stacked alternately. More specifically, it can consist of multiple layers with different refractive indices, for example, high refractive index layers and low refractive index layers stacked periodically. For EUV light, silicon (Si) is used as the material for the high refractive index layer, and molybdenum (Mo) is used as the material for the low refractive index layer. An example is a Si / Mo multilayer film in which silicon (Si) layers and molybdenum (Mo) layers are stacked alternately. The stacking of multiple layers is preferably, for example, two or more periods (two or more layers each), particularly 40 or more periods (40 or more layers each), and preferably 60 or fewer periods (60 or fewer layers each). If the number of periods is small, the reflectivity may be small, and if the number of periods is large, the film may become thicker and the film stress may increase. In the case of a Si / Mo multilayer film, the silicon (Si) layer and the molybdenum (Mo) layer are preferably formed from elemental silicon and elemental molybdenum, respectively, but they may also be formed from a silicon compound and a molybdenum compound, respectively.

[0022] In the case of a Si / Mo multilayer film, the layer closest to the substrate of the multilayer reflective film may be either a Si layer or a Mo layer. Similarly, the layer furthest from the substrate may also be either a Si layer or a Mo layer, but it is preferable to use a Si layer. The thicknesses of the high-refractive-index and low-refractive-index layers of the multilayer reflective film are appropriately set depending on the exposure wavelength. For example, if the exposure light is EUV light (exposure wavelength of 13-14 nm), it is preferable to set the thickness of one period, composed of the high-refractive-index and low-refractive-index layers, to 6-8 nm, and the thickness of the high-refractive-index layer to 10-90% of the total thickness of one period. Furthermore, the thicknesses of the high-refractive-index and low-refractive-index layers in the multilayer reflective film may be constant or may differ in each individual layer. The total film thickness of the multilayer reflective film is usually around 240-320 nm. In reflective mask blanks (EUV reflective mask blanks) and reflective masks (EUV reflective masks), the reflectivity of the multilayer reflective film to EUV light when a multilayer reflective film or protective film is laminated is typically 65-67%.

[0023] The reflectance of a multilayer reflective film depends on the composition and layer structure of the multilayer reflective film, but for example, it is preferable that the reflectance at an incident angle of 6° to extreme ultraviolet (EUV) light be 60% or more, and particularly 65% ​​or more.

[0024] Methods for depositing multilayer reflective films include sputtering, which involves supplying power to a target to plasma-enhance (ionize) the atmospheric gas and perform sputtering, and ion beam sputtering, which involves irradiating the target with an ion beam. Sputtering methods include DC sputtering, which applies a DC voltage to the target, and RF sputtering, which applies a high-frequency voltage to the target.

[0025] Sputtering is a film deposition method that utilizes the sputtering phenomenon caused by gas ions, by applying a voltage to a target while a gas such as Ar gas is introduced into a chamber, ionizing the gas. Magnetron sputtering, in particular, is advantageous in terms of productivity. Magnetron sputtering is a sputtering method in which a magnet is placed on the back side of the target, and the plasma density directly above the target is increased by the magnetic field. Applying magnetron sputtering is preferable because it allows the plasma to be maintained even with low gas pressure during discharge (sputtering pressure), and also increases the film deposition rate. The power applied to the target can be DC or RF, and DC sputtering also includes pulse sputtering, in which the negative bias applied to the target is briefly reversed to prevent the target from charging up.

[0026] Multilayer reflective films can be deposited by sputtering, for example, using a sputtering apparatus capable of mounting multiple targets. Specifically, a metal or metalloid target (e.g., a Si target) constituting layer A and a metal or metalloid target (e.g., a Mo target) constituting layer B are used, and a rare gas such as Ar gas or Kr gas is used as the sputtering gas. The targets are placed facing the main surface of the substrate, and the metal or metalloid targets constituting layer A and the metal or metalloid targets constituting layer B are alternately sputtered to form layers A and B alternately. Sputtering is preferably performed while the substrate is rotated along the main surface.

[0027] In Si / Mo multilayer films, when the silicon (Si) layer and molybdenum (Mo) layer are formed using silicon compounds and molybdenum compounds, respectively, the films can be deposited by reactive sputtering using a noble gas along with reactive gases such as oxygen-containing gases, nitrogen-containing gases, and carbon-containing gases as the sputtering gas. Alternatively, the target can be a silicon compound or a molybdenum compound.

[0028] The absorber film is formed on a multilayer reflective film and absorbs exposure light, reducing the reflectivity of the exposure light. In a reflective mask, the transfer pattern is formed by the difference in reflectivity between the areas where the absorber film is formed and the areas where the absorber film is not formed. The absorber film of the present invention may consist of a single layer or multiple layers.

[0029] In the present invention, the absorber film contains tungsten. Films containing tungsten have a high etching rate, and when used as films with a phase-shift function, the refractive index n is small, making them effective for thinning absorber films. On the other hand, tungsten films in particular have surface irregularities, and if large-diameter depressions are observed, for example, with an atomic force microscope (AFM), the grain is large. With such films, a good shape cannot be obtained at the line edges of the pattern during pattern formation, and it may not be able to adequately meet the requirements for higher accuracy in pattern formation. Also, surface irregularities reduce defect detection sensitivity, so it is preferable to make the surface of the absorber film as smooth as possible.

[0030] Therefore, it is preferable that the absorber membrane contains (a) tungsten, (b) one or more elements selected from metals and metalloids other than tungsten, (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen, or both (b) and (c). By using one or more elements selected from metals and metalloids other than tungsten, or one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen, along with tungsten as the material for the absorber membrane, the depressions on the surface of the absorber membrane that can be observed by an atomic force microscope (AFM) can be made smaller or less compared to when tungsten is used alone, making it more effective.

[0031] Other metals or metalloids besides tungsten include tantalum, molybdenum, vanadium, zirconium, ruthenium, gold, platinum, rhodium, silicon, and germanium. In particular, it is more preferable to include one or both of molybdenum and ruthenium as the other metals or metalloids besides tungsten. It is thought that the heat resistance of the absorber film, especially its oxidation resistance at high temperatures, is improved by reducing the size or number of depressions on the surface of the absorber film that can be observed with an atomic force microscope (AFM), thereby reducing the adsorption and penetration of oxygen gas and water from the atmosphere that cause oxidation. Furthermore, the surface of the absorber film can be made smoother by including ruthenium. In addition, the refractive index n can be made smaller, and in particular, when the absorber film is a film with a phase shift function, not only can the film thickness be reduced, but the reflectance at a predetermined phase difference can be set higher.

[0032] The tungsten content of the absorber membrane is preferably 20 atomic% or more, particularly 40 atomic% or more, less than 100 atomic%, particularly 99 atomic% or less, and especially 80 atomic% or less, if it contains other elements such as one or more selected from metals and metalloids other than tungsten, and one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen. On the other hand, if it contains one or more selected from metals and metalloids other than tungsten, the content of one or more selected from metals and metalloids other than tungsten is preferably more than 0%, particularly 1 atomic% or more, particularly 20 atomic% or more, 80 atomic% or less, and especially 60 atomic% or less. The absorber membrane may contain one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen, but if the absorber membrane contains light elements, the total content of the light elements is preferably more than 0 atomic% and 80 atomic% or less, less than 80 atomic%, particularly 79 atomic% or less, and especially 76 atomic% or less. The content of light elements is preferably 10 atomic% or more, more preferably 30 atomic% or more, and most preferably 50 atomic% or more. If the material contains one or more metals and metalloids other than tungsten and does not contain light elements, the total of tungsten and one or more metals and metalloids other than tungsten is preferably 90 atomic% or more, more preferably 99 atomic% or more, and most preferably 100 atomic% of the total components constituting the absorbent membrane. If the material contains light elements and does not contain metals and metalloids other than tungsten, the total of tungsten and light elements is preferably 90 atomic% or more, more preferably 99 atomic% or more, and most preferably 100 atomic% of the total components constituting the absorbent membrane. If the material contains both one or more metals and metalloids other than tungsten and light elements, the total of tungsten and one or more metals and metalloids other than tungsten and light elements is preferably 90 atomic% or more, more preferably 99 atomic% or more, and most preferably 100 atomic% of the total components constituting the absorbent membrane. The composition of the absorber membrane in the direction of film thickness may be constant, or it may be a gradient composition (a composition in which the composition ratio changes in the direction of film thickness).

[0033] The refractive index n of the absorber film is preferably small with respect to the exposure light, and the refractive index n at the exposure wavelength is preferably 0.94 or less, and particularly preferably 0.93 or less. An absorber film with a small refractive index n with respect to the exposure light is preferable because it can be made into a thin film when it is an absorber film with a phase shift function. Compared to conventionally used tantalum absorber films, the absorber film of the present invention is advantageous because it can be made into a thin film, especially when it is an absorber film with a phase shift function.

[0034] A thin absorber film is preferable. A thick absorber film is not only disadvantageous for pattern formation, but also reduces pattern resolution due to the shadowing effect during exposure. Therefore, the film thickness is preferably 70 nm or less, 60 nm or less, and more preferably 50 nm or less. On the other hand, the lower limit of the film thickness is 10 nm or more, and preferably 20 nm or more.

[0035] As the surface roughness of the absorber film increases, the defect detection sensitivity deteriorates. Therefore, the surface roughness Rq (RMS, root square roughness) of the absorber film is preferably 0.7 nm or less, 0.5 nm or less, and more preferably 0.3 nm or less.

[0036] It is preferable that the absorber film can be dry-etched with an oxygen-free fluorine-based gas. If dry etching is possible with an oxygen-free fluorine-based gas, a protective film formed from a ruthenium (Ru)-containing material, as described later, can be used as a protective film for the multilayer reflective film. Examples of oxygen-free fluorine-based gases include CF4 and SF6. When forming the pattern of the absorber film by dry etching, a high etching rate is preferable, but it is preferable that the etching rate of the absorber film is at least three times the etching rate of the protective film when the protective film is etched with the same etching method applied to the dry etching of the absorber film.

[0037] When the substrate is a 6025 substrate (main surface size is 152 mm square), it is preferable that the change in warpage (ΔTIR) within a 142 mm square area in the center of the substrate surface is 0.4 μm or less in absolute value, and particularly 0.3 μm or less, as the difference before and after deposition of the absorber film on a multilayer reflective film or protective film. If the substrate is a 6025 substrate (main surface size is 152 mm square), it is preferable that the change in warpage (ΔTIR) is 0.4 μm or less in absolute value, and particularly 0.3 μm or less. If the change in warpage is small, the reflective mask blank will have an absorber film that exhibits less pattern misalignment and less reduction in dimensional accuracy when the absorber film is patterned and a reflective mask is manufactured. Furthermore, if the change in warpage (ΔTIR) is small immediately after deposition, it is possible to further reduce the change in warpage (ΔTIR) through subsequent processing (e.g., heat treatment).

[0038] Here, the 142 mm square area in the center of the substrate surface is defined as the range more than 5 mm inward from the periphery of the surface (one main surface) on which the absorber film of the 152 mm square substrate is formed. This range is the region in which the photomask pattern used for exposure using a reflective mask is formed. The warpage of the substrate before the absorber film is formed (specifically, after the multilayer reflective film or multilayer reflective film and protective film are formed) and the warpage of the substrate after the absorber film is formed are defined by the flatness specified by the TIR (Total Indicator Reading) when the surface shape is measured with a flatness measuring instrument. ΔTIR, as the amount of change in TIR, is defined as the difference between the maximum or minimum value of the amount of change at each coordinate in the substrate plane, with the height of the center of the substrate when the surface shape of the substrate is measured as the origin in the height direction, and between the case where a film is present on the substrate and the case where it is not, on the same substrate. This warp and its change can be measured and calculated using a commercially available measuring device such as a grazing incidence interference flatness tester (e.g., the Tropel Ultra Flat 200 Mask from Corning).

[0039] The absorber film may have a phase-shift function. In a reflective mask, the reflectance of the absorber film formed on a multilayer reflective film or a protective film formed on a multilayer reflective film is preferably 2% or less, particularly 1.5% or less, with respect to the exposure light, which is EUV light, if it does not have a phase-shift function. On the other hand, in the case of an absorber film with a phase-shift function, the reflectance with respect to the exposure light, which is EUV light, is preferably 50% or less, particularly 30% or less. In this case, the reflectance may be greater than 2%, preferably 3% or more, and more preferably 3.5% or more.

[0040] If the absorbent film does not have a phase-shift function, in a reflective mask, the ratio of the reflectance of the absorbent film (absorbent pattern) portion to the reflectance of the portion without the absorbent film (the portion where the multilayer reflective film or its protective film is exposed) is preferably less than 3%, and more preferably 2% or less. On the other hand, if the absorbent film has a phase-shift function, the reflectance ratio is preferably 3% or more, particularly 5% or more, and also preferably 50% or less, particularly 30% or less.

[0041] The phase difference (amount of phase shift) of an absorber film having a phase-shift function is preferably 150° or more, particularly 170° or more, and 260° or less, particularly 250° or less, and especially 230° or less, as it is the phase difference between the light reflected from the region where the absorber film is formed and the light reflected from the region where the absorber film is not formed (such as a multilayer reflective film or a protective film formed on the multilayer reflective film thereon). By utilizing the phase-shift effect, the resolution can be increased.

[0042] A reflectance-reducing film may be formed on the side of the absorber film that is separated from the substrate. This film has the function of reducing reflectance to the inspection light used in inspecting the absorber film. This increases the inspection sensitivity during pattern inspection. If the reflectance-reducing film is a film that can be etched with the same etchant as the absorber film, it has the advantage of being etchable at the same time as the absorber film. On the other hand, if the reflectance-reducing film is a film that is resistant to the etchant of the absorber film, it has the advantage of being usable as a hard mask. In addition, a layer to improve irradiation resistance to exposure light may be provided as the outermost layer on the side of the absorber film that is separated from the substrate.

[0043] As a method for forming an absorber film, sputtering using a target and sputtering gas is preferred, and magnetron sputtering is preferred as the sputtering method. Specifically, examples of targets include tungsten targets, one or more targets selected from metals other than tungsten and metalloids, and targets containing tungsten and one or more selected from metals other than tungsten and metalloids. Depending on the composition, one or more targets can be used. When using multiple targets, targets with different compositions or composition ratios can also be used. Specifically, noble gases such as Ar gas and Kr gas can be used as the sputtering gas. In addition, the film can also be formed by reactive sputtering, in which nitrogen gas (N2), oxygen gas (O2), nitrogen oxide gas (N2O, NO, NO2), etc. are used as a reactive gas along with the noble gas to sputter the target. For example, when the absorber film is a nitride, nitrogen gas (N2) can be used, and when it is an oxide, oxygen gas (O2) can be used. Furthermore, when using nitride oxides, nitrogen gas (N2) and oxygen gas (O2), or nitrogen oxide gas (N2O, NO, NO2) can be used. The pressure inside the sputtering chamber (sputtering pressure) is preferably 0.15 Pa or higher, less than 0.4 Pa, and particularly preferably 0.3 Pa or lower. If the sputtering pressure is too high, it becomes difficult to form a highly crystalline film, but if it is too high, not only does the surface roughness increase, but the film tends to become more susceptible to oxygen penetration from the atmosphere.

[0044] Materials containing ruthenium (Ru) can be used for the protective film. Specifically, materials containing ruthenium (Ru) include elemental ruthenium (Ru), and ruthenium alloys containing ruthenium (Ru) along with metals such as titanium (Ti), niobium (Nb), molybdenum (Mo), and zirconium (Zr). The ruthenium content in the ruthenium alloy is preferably 50 atomic% or more and less than 100 atomic%. The thickness of the protective film is preferably 1 nm or more, 10 nm or less, and particularly preferably 5 nm or less. The protective film can be deposited, for example, by ion beam sputtering or magnetron sputtering.

[0045] The conductive film preferably has a sheet resistance of 100 Ω / □ or less, and there are no particular restrictions on the material or film thickness. Examples of conductive film materials include materials containing chromium (Cr) or tantalum (Ta). Materials containing chromium (Cr) or tantalum (Ta) may also contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Specific examples of chromium-containing materials include elemental Cr, CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCNB, CrCOB, and CrCONB. Examples of tantalum-containing materials include elemental Ta, TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, and TaCONB.

[0046] The thickness of the conductive film is not particularly limited, as long as it functions for electrostatic chucks, but it is usually around 5 to 50 nm. The conductive film is preferably formed as a reflective mask, specifically, after forming the absorber pattern, so that the film stress is balanced with that of the multilayer reflective film and the absorber pattern. The conductive film may be formed before forming the multilayer reflective film, or after forming all the films on the multilayer reflective side of the substrate, or a portion of the films on the multilayer reflective side of the substrate may be formed first, then the conductive film may be formed, and then the remaining films on the multilayer reflective side of the substrate may be formed. The conductive film can be deposited, for example, by magnetron sputtering.

[0047] A hard mask film may be provided on the absorber film, having different etching characteristics from the absorber film and functioning as an etching mask during the etching process for patterning the absorber film. After the absorber pattern is formed, this hard mask film may be left as part of the absorber film, for example, as a reflectance reduction layer, or it may be removed so that it does not remain on the reflective mask. Examples of materials for the hard mask film include materials containing chromium (Cr). When forming the reflectance reduction layer described above on the absorber film, the hard mask film can be formed on top of the reflectance reduction layer. The hard mask film can be deposited, for example, by magnetron sputtering. There are no particular restrictions on the thickness of the hard mask film, but it is usually around 5 to 20 nm.

[0048] Furthermore, the reflective mask blank may have a resist film, such as a photoresist film used for patterning, such as an absorber film or a hard mask film, formed on the side furthest from the substrate. Electron beam (EB) resist is preferred for the photoresist film. [Examples]

[0049] The present invention will be specifically described below with reference to experimental examples, but the present invention is not limited to the experimental examples described below.

[0050] [Experimental Example 1] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed inside the sputtering apparatus chamber. Using a tungsten (W) target and a molybdenum (Mo) target as sputtering targets, and argon gas as the sputtering gas, a 30 nm thick WMo film was deposited on the quartz substrate by magnetron sputtering.

[0051] The composition of the obtained WMo film was measured by X-ray photoelectron spectroscopy (XPS), revealing 46.0 atomic percent tungsten and 54.0 atomic percent molybdenum. The surface of the obtained WMo film was observed in a 1 μm square area using an atomic force microscope (AFM), and 10 depressions were selected, starting with the largest (largest area in the observed image). The length of these depressions was measured, and the average length was calculated to be 0.078 μm. The obtained WMo film was heated in a nitrogen atmosphere from approximately 30°C to 500°C using thin-film X-ray diffraction (In-Plane XRD), and the diffraction spectrum was measured. As a result, diffraction peaks attributed to cubic tungsten and molybdenum were confirmed at 2θ = 40°, 59°, 74°, 88°, and 102° across the entire heating temperature range. No tungsten oxide was detected in the WMo film heated to 500°C.

[0052] [Experimental Example 2] A 30 nm thick WMo film was deposited on a quartz substrate in the same manner as in Experimental Example 1, except that the power applied to the tungsten (W) target and the molybdenum (Mo) target was changed.

[0053] The composition of the obtained WMo film was measured by X-ray photoelectron spectroscopy (XPS), revealing that it contained 71.6 atomic percent tungsten and 28.4 atomic percent molybdenum. The surface of the obtained WMo film was observed using an atomic force microscope (AFM) in a 1 μm square area. Ten depressions were selected, starting with the largest (largest area in the observed image), and the length of each depression was measured. The average length was calculated to be 0.12 μm.

[0054] [Experimental Example 3] A 30 nm thick WMo film was deposited on a quartz substrate in the same manner as in Experimental Example 1, except that the power applied to the tungsten (W) target and the molybdenum (Mo) target was changed.

[0055] The composition of the obtained WMo film was measured by X-ray photoelectron spectroscopy (XPS), revealing that it contained 25.8 atomic percent tungsten and 74.2 atomic percent molybdenum. The surface of the obtained WMo film was observed using an atomic force microscope (AFM) in a 1 μm square area. Ten depressions were selected, starting with the largest (largest area in the observed image), and the length of each depression was measured. The average length was calculated to be 0.048 μm.

[0056] [Experimental Example 4] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed inside the sputtering apparatus chamber. Using a tungsten (W) target and a ruthenium (Ru) target as sputtering targets, and argon gas as the sputtering gas, a 30 nm thick WRu film was deposited on the quartz substrate by magnetron sputtering.

[0057] The composition of the obtained WRu film was measured by X-ray photoelectron spectroscopy (XPS), revealing that it contained 43.9 atomic percent tungsten and 56.1 atomic percent ruthenium. The surface of the obtained WRu film was observed in a 1 μm square area using an atomic force microscope (AFM), and 10 depressions were selected, starting with the largest (largest area in the observed image). The length of these depressions was measured, and the average length was calculated to be 0.033 μm. The diffraction spectrum of the obtained WRu film was measured by in-plane XRD after heating it in a nitrogen atmosphere from approximately 30°C to 500°C. As a result, diffraction peaks attributed to cubic or hexagonal tungsten and ruthenium were observed at 2θ = 38°, 68°, and 80° across the entire heating temperature range. Tungsten oxide (WO3) was detected in the WRu film heated to 500°C, but its intensity was less than 1 / 5 of the intensity of tungsten oxide (WO3) detected in a 30 nm thick W film similarly deposited on a quartz substrate using only a tungsten (W) target, when heated from approximately 30°C to 500°C in a nitrogen atmosphere.

[0058] [Experimental Example 5] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed inside the sputtering apparatus chamber. Using a tungsten (W) target, a molybdenum (Mo) target, and a ruthenium (Ru) target as sputtering targets, and argon gas as the sputtering gas, a WMoRu film with a thickness of 30 nm was deposited on the quartz substrate by magnetron sputtering.

[0059] The composition of the obtained WMoRu film was measured by X-ray photoelectron spectroscopy (XPS), revealing that it contained 46.1 atomic percent tungsten, 24.9 atomic percent molybdenum, and 29.0 atomic percent ruthenium. The surface of the obtained WMoRu film was observed in a 1 μm square area using an atomic force microscope (AFM), and 10 depressions were selected, starting with the largest (largest area in the observed image). The length of these depressions was measured, and the average length was calculated to be 0.030 μm. The obtained WMoRu film was heated in a nitrogen atmosphere from approximately 30°C to 500°C using thin-film X-ray diffraction (In-Plane XRD), and the diffraction spectrum was measured. As a result, diffraction peaks attributed to cubic or hexagonal tungsten, molybdenum, and ruthenium were observed at 2θ = 39°, 71°, and 84° across the entire heating temperature range, and no tungsten oxides were detected in the WMoRu film heated to 500°C.

[0060] [Experimental Example 6] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed inside the sputtering apparatus chamber. A tungsten (W) target and a molybdenum (Mo) target were used as sputtering targets, argon gas as the sputtering gas, and nitrogen gas as the reactive gas. A 30 nm thick WMoN film was deposited on the quartz substrate by magnetron sputtering.

[0061] The composition of the obtained WMoN film was measured by X-ray photoelectron spectroscopy (XPS), revealing 33.1 atomic percent tungsten, 27.7 atomic percent molybdenum, and 39.2 atomic percent nitrogen. The surface of the obtained WMoN film was observed in a 1 μm square area using an atomic force microscope (AFM), and 10 depressions were selected, starting with the largest (largest area in the observed image). The length of these depressions was measured, and the average length was calculated to be 0.051 μm. The obtained WMoN film was heated in a nitrogen atmosphere from approximately 30°C to 500°C using thin-film X-ray diffraction (In-Plane XRD), and the diffraction spectrum was measured. As a result, diffraction peaks attributable to the cubic crystal of WMoN were confirmed at 2θ = 37°, 43°, 62°, and 75° across the entire heating temperature range, and no tungsten oxide was detected in the WMoN film heated to 500°C.

[0062] [Experimental Example 7] A 30 nm thick WMoN film was deposited on a quartz substrate in the same manner as in Experimental Example 6, except that the flow rate of the reactive gas, nitrogen gas, was changed.

[0063] The composition of the obtained WMoN film was measured by X-ray photoelectron spectroscopy (XPS), revealing that it contained 25.0 atomic percent tungsten, 22.9 atomic percent molybdenum, and 52.1 atomic percent nitrogen. The surface of the obtained WMoN film was observed in a 1 μm square area using an atomic force microscope (AFM), and 10 depressions were selected, starting with the largest (largest area in the observed image). The length of these depressions was measured, and the average length was calculated to be 0.039 μm. The obtained WMoN film was heated in a nitrogen atmosphere from approximately 30°C to 500°C using thin-film X-ray diffraction (In-Plane XRD), and the diffraction spectrum was measured. As a result, diffraction peaks attributed to the hexagonal crystal structure of WN2 were detected at 2θ = 36°, 45°, 64°, and 75° across the entire heating temperature range, confirming that WMoN is in a polycrystalline state with low orientation. No tungsten oxides were detected in the WMoN film heated to 500°C.

[0064] [Experimental Example 8] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed inside the sputtering apparatus chamber. A tungsten (W) target was used as the sputtering target, argon gas as the sputtering gas, and nitrogen gas as the reactive gas. A 30 nm thick WN film was deposited on the quartz substrate by magnetron sputtering.

[0065] The composition of the obtained WN film was measured by X-ray photoelectron spectroscopy (XPS), revealing that it contained 81.9 atomic percent tungsten and 18.1 atomic percent nitrogen. The surface of the obtained WN film was observed using an atomic force microscope (AFM) in a 1 μm square area. Ten depressions were selected, starting with the largest ones (largest area in the observed image), and the length of each depression was measured. The average length was calculated to be 0.065 μm.

[0066] [Experimental Example 9] A 30 nm thick WN film was deposited on a quartz substrate in the same manner as in Experimental Example 8, except that the flow rate of the reactive gas, nitrogen gas, was changed.

[0067] The composition of the obtained WN film was measured by X-ray photoelectron spectroscopy (XPS), revealing that it contained 65.0 atomic percent tungsten and 35.0 atomic percent nitrogen. The surface of the obtained WN film was observed using an atomic force microscope (AFM) in a 1 μm square area. Ten depressions were selected, starting with the largest (largest area in the observed image), and the length of each depression was measured. The average length was calculated to be 0.061 μm.

[0068] [Experimental Example 10] A 30 nm thick WN film was deposited on a quartz substrate in the same manner as in Experimental Example 8, except that the flow rate of the reactive gas, nitrogen gas, was changed.

[0069] The composition of the obtained WN film was measured by X-ray photoelectron spectroscopy (XPS), revealing that it contained 46.4 atomic percent tungsten and 53.6 atomic percent nitrogen. The surface of the obtained WN film was observed in a 1 μm square area using an atomic force microscope (AFM), and 10 depressions were selected, starting with the largest (largest area in the observed image). The length of these depressions was measured, and the average length was calculated to be 0.054 μm.

[0070] [Example of comparative experiment] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed inside the sputtering apparatus chamber. Using a tungsten (W) target as the sputtering target and argon gas as the sputtering gas, a 30 nm thick W film was deposited on the quartz substrate by magnetron sputtering.

[0071] The surface of the obtained W film was observed in a 1 μm square area using an atomic force microscope (AFM). Ten depressions were selected, starting with the largest (largest area in the observed image), and their lengths were measured. The average length was calculated to be 0.157 μm. The obtained W film was heated in a nitrogen atmosphere from approximately 30°C to 500°C using thin-film X-ray diffraction (In-Plane XRD) and its diffraction spectrum was measured. As a result, diffraction peaks attributed to tungsten were confirmed at 2θ = 40°, 59°, 74°, 87°, and 101° across the entire heating temperature range, and tungsten oxide (WO3) was detected in the W film heated to 500°C. [Explanation of symbols]

[0072] 100, 200, 300 Reflective Mask Blanks 101 circuit board 102 Multilayer reflective film 103 Absorbing membrane 104 Protective film 105 Conductive film

Claims

1. A reflective mask blank that is used as a material for a reflective mask used in EUV lithography using EUV light as the exposure light, comprising a substrate, a multilayer reflective film formed on one main surface of the substrate that reflects exposure light, and an absorber film formed on the multilayer reflective film that absorbs exposure light, The absorbent membrane, (a) tungsten, (b) molybdenum and / or ruthenium, (c) nitrogen It contains, (a) The tungsten content is 20 atomic percent or more, (b) The content of one or both molybdenum and ruthenium is 1 atomic percent or more. The above (c) nitrogen content is 30 atomic percent or more and 79 atomic percent or less, The total content of (a) tungsten, (b) molybdenum and ruthenium (or both), and (c) nitrogen is 90 atomic percent or more. A reflective mask blank characterized by the following features.

2. The reflective mask blank according to claim 1, characterized in that the refractive index n of the absorber film at the exposure wavelength is 0.94 or less.

3. The reflective mask blank according to claim 1 or 2, characterized in that the thickness of the absorbent film is 70 nm or less.

4. A reflective mask blank according to any one of claims 1 to 3, characterized in that a protective film is provided between the multilayer reflective film and the absorber film, in contact with the multilayer reflective film and having different etching characteristics from the absorber film.

5. Furthermore, the reflective mask blank according to any one of claims 1 to 4, characterized in that it has a conductive film formed on another main surface of the substrate.

6. Furthermore, the reflective mask blank according to any one of claims 1 to 5, characterized in that it further has a chromium-containing film formed on the absorbent film as an etching mask.

7. A reflective mask characterized by being manufactured from a reflective mask blank according to any one of claims 1 to 6.

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