Reflection type mask blank and reflection type mask

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, which is a material for a reflective mask used in the manufacture of semiconductor devices such as LSIs, and a reflective mask. [Background technology]

[0002] In the manufacturing process of semiconductor devices (semiconductor device), photolithography technology is used in which exposure light is irradiated onto a transfer mask, and the 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 even finer patterns is required, EUV lithography technology using extreme ultraviolet (hereinafter referred to as "EUV") light, which has an even shorter wavelength than ArF excimer laser light, as exposure light is considered promising. EUV light is light with a wavelength of about 0.2 to 100 nm, more specifically, light with a wavelength of about 13.5 nm. This EUV light has extremely low permeability to materials, and conventional transmission type projection optical systems and masks cannot be used, so reflective optical elements are used. For this reason, reflective masks have been proposed as masks for pattern transfer. Reflective masks are generally used in which a multilayer reflective film that reflects EUV light is formed on a substrate, and an absorber film that absorbs EUV light is formed in a pattern on the multilayer reflective film, and a pattern is formed on a transfer target such as a silicon wafer by the difference in reflectance of the EUV light, which is the exposure light, caused by the presence or absence of the absorber film on the multilayer reflective film.

[0004] A reflective mask is manufactured using a reflective mask blank, which has a multilayer reflective film that reflects exposure light on a substrate, an absorber film with low reflectance to the exposure light on the multilayer reflective film, and a protective film generally between the multilayer reflective film and the absorber film. The multilayer reflective film is formed by alternately stacking layers with different refractive indices, and for example, for EUV light exposure, a layer in which molybdenum (Mo) layers and silicon (Si) layers are alternately stacked is used, and for the absorber film, for example, for EUV light exposure, a film in which nitrogen (N) is added to tantalum (Ta) is used (JP Patent Publication 2002-246299 (Patent Document 1)). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-246299 A Summary of the Invention [Problem to be solved by the invention]

[0006] In order to transfer a fine pattern to a semiconductor substrate or the like using a reflective mask, the absorber film of the reflective mask blank is partially removed to form a pattern. In order to transfer the fine pattern with high accuracy, the absorber film is required to have the following characteristics:

[0007] When forming a pattern of an absorber film by dry etching, if the etching rate is low, it is necessary to form a thick resist to form a pattern, and even if a hard mask film is used, the hard mask film may also be etched when etching the absorber film, so in order to form a pattern with high precision, it is preferable that the absorber film has a high etching rate. In addition, when the etching amount of an etching mask such as a resist film increases, the cross-sectional shape tends to deteriorate, so in order to form a pattern with a good cross-sectional shape, it is important that the etching rate of the absorber film is high. In order to further improve the processability of the absorber film, a material with a high etching rate is required as a material for the absorber film.

[0008] Also, if the absorber film is thick, the pattern resolution is reduced due to the shadowing effect. Therefore, the absorber film needs to be thin. Furthermore, when the absorber film is used as a film having a phase shift function, a material with a smaller refractive index n is required to make the absorber film thinner. Furthermore, in the case of an EUV reflective mask, since pulsed high-energy EUV light is irradiated during exposure, it is said that the absorber film on the reflective mask instantaneously becomes hot (for example, about 500°C), and the heat resistance of the absorber film is important. Therefore, a film whose film quality does not deteriorate due to oxidation or the like even at such high temperatures is required. On the other hand, if the sidewall roughness is large when forming a pattern, it may have an adverse effect on the resolution. However, in a material made of simple tungsten, the surface of the absorber film is uneven, and the sidewall roughness of the pattern is likely to become large.

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to provide a reflective mask blank in which pattern resolution is improved by a thinner absorber film with excellent processability, and a reflective mask manufactured using the reflective mask blank. [Means for solving the problem]

[0010] As a result of extensive research into solving the above problems, the inventors have found that if tungsten is used as a material for the absorber film, the etching rate is high, and even when used as a film having a phase shift function, the refractive index n is small, which is effective for making the absorber film thinner, and that tungsten is an excellent material for the absorber film.

[0011] Furthermore, the inventors have discovered that by using, together with tungsten, one or more types selected from metals and metalloids other than tungsten, or one or more types of light elements selected from nitrogen, oxygen, carbon and hydrogen, as the material for the absorber film, surface unevenness is improved, and in particular, by the absorber film containing, together with tungsten, one or more types selected from metals and metalloids other than tungsten, especially molybdenum or ruthenium, the film becomes resistant to oxidation even at high temperatures, and exhibits excellent heat resistance during exposure to EUV light, thereby completing the present invention.

[0012] Accordingly, the present invention provides the following reflective mask blank and reflective mask. 1. A reflective mask blank comprising a substrate, a multilayer reflective film formed on one main surface of the substrate and reflecting exposure light, and an absorber film formed on the multilayer reflective film and absorbing the exposure light, the mask blank being a material for a reflective mask used in EUV lithography using EUV light as the exposure light, The absorber film is (a) tungsten, (b) one or both of molybdenum and ruthenium, and (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen. Contains The total content of the (a) tungsten, the (b) one or both of molybdenum and ruthenium, and the (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen is 90 atomic % or more. A reflective mask blank comprising: 2. The reflective mask blank according to 1, wherein the content of one or both of (b) molybdenum and ruthenium is 1 atomic % or more and 80 atomic % or less. 3. The reflective mask blank according to 1 or 2, wherein the content of the one or more light elements (c) selected from nitrogen, oxygen, carbon and hydrogen is 10 atomic % or more and 80 atomic % or less. 4. The reflective mask blank according to any one of 1 to 3, wherein the content of (a) tungsten is 20 atomic % or more and 99 atomic % or less. 5. A reflective mask blank according to any one of 1 to 4, wherein the absorber film has a refractive index n of 0.94 or less at the exposure wavelength. 6. A reflective mask blank according to any one of 1 to 5, wherein the absorber film has a thickness of 70 nm or less. 7. A reflective mask blank described in any one of 1 to 6, 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 etching characteristics different from those of the absorber film. 8. A reflective mask blank according to any one of 1 to 7, further comprising a conductive film formed on the other main surface of the substrate. 9. The reflective mask blank according to any one of 1 to 8, further comprising a chromium-containing film formed on the absorber film as an etching mask. 10. A reflective mask produced from a reflective mask blank according to any one of 1 to 9. The present invention also relates to the following reflective mask blank and reflective mask. [1] A reflective mask blank comprising a substrate, a multilayer reflective film formed on one main surface of the substrate for reflecting exposure light, and an absorber film formed on the multilayer reflective film for absorbing exposure light, the mask blank being a material for a reflective mask used in EUV lithography using EUV light as exposure light, The absorber film is (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). A reflective mask blank comprising: [2] The absorber film, The reflective mask blank according to [1], characterized in that it comprises (a) tungsten and (b) one or more selected from metals and semi-metals other than tungsten. [3] The absorber film, The reflective mask blank according to [1], characterized in that it contains (a) tungsten, (b) one or more elements selected from metals and metalloids other than tungsten, and (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen. [4] The reflective mask blank according to [3], wherein a total of the (a) tungsten, the (b) one or more elements selected from metals and metalloids other than tungsten, and the (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen is 90 atomic % or more. [5] A reflective mask blank according to any one of [1] to [4], characterized in that the (b) one or more selected from metals and semi-metals other than tungsten is one or both of molybdenum and ruthenium. [6] The reflective mask blank according to any one of [1] to [5], characterized in that the content of the one or more elements selected from (b) metals and semi-metals other than tungsten is 1 atomic % or more and 80 atomic % or less. [7] The absorber film, The reflective mask blank according to [1], characterized in that it contains (a) tungsten and (c) one or more light elements selected from nitrogen, oxygen, carbon and hydrogen, and does not contain any metals or metalloids other than tungsten. [8] The reflective mask blank according to [7], wherein the content of the one or more light elements (c) selected from nitrogen, oxygen, carbon and hydrogen is 10 atomic % or more and 80 atomic % or less. [9] The reflective mask blank according to [7] or [8], wherein the sum of (a) tungsten and (c) one or more light elements selected from nitrogen, oxygen, carbon and hydrogen is 90 atomic % or more.

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

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

[10] , wherein the absorber film has a refractive index n of 0.94 or less at the exposure wavelength.

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

[11] , wherein the absorber film has a thickness of 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, the protective film being in contact with the multilayer reflective film and having etching characteristics different from those of the absorber film.

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

[13] , further comprising 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 comprising a chromium-containing film formed on the absorber film as an etching mask.

[16] A reflective mask produced from a reflective mask blank according to any one of [1] to

[15] . Effect 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 and at least one selected from metals and semimetals other than tungsten has good film stability (is less likely to oxidize) even at high temperatures. Therefore, by using the reflective mask of the present invention, it is possible to transfer a fine pattern to a semiconductor substrate or the like with high accuracy using EUV light or the like. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a reflective mask blank. [Diagram 2]FIG. 2 is a cross-sectional view showing another example of a reflective mask blank. [Diagram 3] FIG. 2 is a cross-sectional view showing another example of a reflective mask blank. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention will now be described in further detail. The reflective mask blank of the present invention includes a substrate, a multilayer reflective film formed on the substrate (on one main surface (front surface)) 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 reflectance. From a reflective mask blank (EUV reflective mask blank) that uses EUV light as exposure light, a reflective mask (EUV reflective mask) having an absorber pattern (absorber film pattern) formed by patterning the absorber film is manufactured. The wavelength of EUV light used in EUV lithography that uses EUV light as exposure light is 13 to 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 effect of the present invention is 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) having etching characteristics different from that of the absorber film may be provided between the multilayer reflective film and the absorber film, preferably in contact with the multilayer reflective film, more preferably in contact with 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. In addition, the protective film preferably has a function of protecting the multilayer reflective film when the absorber film is patterned by etching, and preventing the oxidation of the multilayer reflective film. Furthermore, a hard mask film (etching mask film for the absorber film) having etching characteristics different from that of the absorber film may be provided on the side of the absorber film that is separated from the substrate, preferably in contact with the absorber film. On the other hand, a conductive film used for electrostatically chucking a reflective mask to an exposure device may be provided under, and preferably in contact with, the other main surface (back surface) which is the surface opposite to the one main surface of the substrate. Note that, although the one main surface of the substrate is defined as the front surface and the upper side, and the other main surface is defined as the back surface and the lower side here, the front and back and the top and bottom of both are defined for convenience, and the one main surface and the other main surface are either of the two main surfaces (film formation surfaces) of the substrate, and the front and back and the top and bottom are interchangeable.

[0017] 1 to 3 show typical examples of the reflective mask blank of the present invention. Fig. 1 is a cross-sectional view showing one example of the reflective mask blank of the present invention, and this reflective mask blank 100 comprises a multilayer reflective film 102 formed on one main surface of a substrate 101 in contact with the one main surface, and an absorber film 103 formed in contact with the multilayer reflective film 102. Fig. 2 is a cross-sectional view showing another example of the reflective mask blank of the present invention, and this reflective mask blank 200 comprises a multilayer reflective film 102 formed on one main surface of a substrate 101 in contact with the one 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. FIG. 3 is a cross-sectional view showing another example of a reflective mask blank of the present invention, and this reflective mask blank 300 comprises a multilayer reflective film 102 formed on and in contact with one main surface of a substrate 101, 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 and in contact with the other main surface of the substrate 101.

[0018] The substrate may be, 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)). The substrate must reduce distortion of the pattern due to thermal expansion during exposure, and the thermal expansion coefficient of the substrate is preferably 30 ppb / °C or less, particularly 10 ppb / °C or less, in absolute value. Examples of such materials include titania-doped quartz glass (SiO 2 -TiO 2 Glasses containing fluorine, etc.

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

[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 tool, so in order to obtain sufficient pattern position accuracy, it is preferable that this surface of the substrate is also flat, with a flatness (flatness) of 1 μm or less.

[0021] The multilayer reflective film is a film that reflects exposure light such as EUV light in a reflective mask, and is made of a plurality of layers with different optical properties, for example, two layers (A layer and B layer) with different optical properties, which are alternately laminated, or more specifically, a plurality of layers with different refractive indexes, for example, a high refractive index layer and a low refractive index layer, which are periodically laminated. For EUV light, silicon (Si) is used as the material of the high refractive index layer, and molybdenum (Mo) is used as the material of the low refractive index layer, and an example of such a film is a Si / Mo laminate film in which silicon (Si) layers and molybdenum (Mo) layers are alternately laminated. The laminate of the plurality of layers is, for example, 2 cycles or more (2 layers or more each), particularly 40 cycles or more (40 layers or more each), and preferably 60 cycles or less (60 layers or less each). If the number of cycles is small, the reflectance may be low, and if the number of cycles is large, the film may be thick and the film stress may be large. In the case of a Si / Mo laminated film, the silicon (Si) layer and the molybdenum (Mo) layer are preferably formed of elemental silicon and elemental molybdenum, respectively, but may also be formed of a silicon compound and a molybdenum compound, respectively.

[0022] In the case of a Si / Mo laminated film, the layer closest to the substrate of the multilayer reflective film may be a Si layer or a Mo layer. The layer farthest from the substrate may also be a Si layer or a Mo layer, but is preferably a Si layer. The thicknesses of the high refractive index layer and the low refractive index layer of the multilayer reflective film are appropriately set according to the exposure wavelength. For example, when the exposure light is EUV light (exposure wavelength is 13 to 14 nm), it is preferable that the thickness of one period consisting of the high refractive index layer and the low refractive index layer is 6 to 8 nm, and the thickness of the high refractive index layer is 10 to 90% of the thickness of one period. In the multilayer reflective film, the thickness of each of the high refractive index layer and the low refractive index layer may be constant or may differ from one layer to another. The film thickness of the entire multilayer reflective film is usually about 240 to 320 nm. In a reflective mask blank (EUV reflective mask blank) and a reflective mask (EUV reflective mask), the reflectance of the multilayer reflective film with a multilayer reflective film or a protective film laminated thereon to EUV light is typically 65 to 67%.

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

[0024] Methods for depositing a multilayer reflective film include the sputtering method, in which electric power is supplied to a target, and the atmospheric gas is turned into plasma (ionized) by the supplied electric power to perform sputtering, and the ion beam sputtering method, in which an ion beam is irradiated onto a target. Sputtering methods include the DC sputtering method, in which a direct current voltage is applied to the target, and the RF sputtering method, in which a high frequency voltage is applied to the target.

[0025] The sputtering method is a film formation method in which a voltage is applied to a target while a gas such as Ar gas is introduced into a chamber, the gas is ionized, and the sputtering phenomenon caused by the gas ions is utilized. Magnetron sputtering is particularly advantageous in terms of productivity. Magnetron sputtering is a sputtering method in which a magnet is placed on the back side of the target, etc., and the plasma density directly above the target is increased by a magnetic field. When magnetron sputtering is applied, the plasma can be maintained even if the gas pressure (sputtering pressure) during discharge is low, and the film formation rate is high, so it is preferable. 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 reversed for a short period of time to prevent the target from charging up.

[0026] The multilayer reflective film can be formed by sputtering using, for example, a sputtering device capable of mounting multiple targets, specifically, a metal or metalloid target (e.g., Si target) constituting the A layer and a metal or metalloid target (e.g., Mo target) constituting the B layer are used, and a rare gas such as Ar gas or Kr gas is used as a sputtering gas, and the targets and the main surface of the substrate are made to face each other, and the metal or metalloid target constituting the A layer and the metal or metalloid target constituting the B layer are alternately sputtered to form the A layer and the B layer alternately. Sputtering is preferably performed while rotating the substrate along the main surface.

[0027] In the case of forming the silicon (Si) layer and the molybdenum (Mo) layer of the Si / Mo laminated film from a silicon compound and a molybdenum compound, respectively, the film can be formed by reactive sputtering using a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas, or a carbon-containing gas together with a rare gas as a sputtering gas. The target may be a silicon compound or a molybdenum compound.

[0028] The absorber film is a film formed on the multilayer reflective film, which absorbs the exposure light and reduces the reflectance of the exposure light, and in a reflective mask, a transfer pattern is formed by the difference in reflectance between the part where the absorber film is formed and the part where the absorber film is not formed. The absorber film of the present invention may be composed of a single layer or multiple layers.

[0029] In the present invention, the absorber film contains tungsten. A film containing tungsten has a high etching rate, and also when used as a film having a phase shift function, the refractive index n is small, so it is effective for making the absorber film thinner. On the other hand, a tungsten single film in particular has an uneven surface, and when a large diameter dent is observed with an atomic force microscope (AFM), for example, the grains are large. With such a film, a good shape cannot be obtained at the line edge of the pattern in pattern formation, and it may not be sufficient to meet the needs of a higher degree of accuracy in pattern formation. In addition, since the uneven surface reduces the defect detection sensitivity, it is preferable to make the surface of the absorber film smoother.

[0030] Therefore, it is preferable that the absorber film contains (a) tungsten, (b) one or more 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 tungsten together with one or more selected from metals and metalloids other than tungsten, or one or more light elements selected from nitrogen, oxygen, carbon and hydrogen, as the material of the absorber film, the depressions on the surface of the absorber film that can be observed with an atomic force microscope (AFM) can be made smaller or fewer than when tungsten is used alone, which is more effective.

[0031] As the metal or metalloid other than tungsten, tantalum, molybdenum, vanadium, zirconium, ruthenium, gold, platinum, rhodium, silicon, germanium, etc. are preferable. In particular, it is more preferable that the metal or metalloid other than tungsten contains one or both of molybdenum and ruthenium. When the absorber film contains molybdenum, the surface of the absorber film is small or reduced in depressions observed by an atomic force microscope (AFM), and the adsorption and intrusion of oxygen gas and water in the atmosphere, which cause oxidation, is reduced, which is considered to increase the heat resistance of the absorber film, especially the oxidation resistance at high temperatures. In addition, when the absorber film contains ruthenium, the surface can be made smoother. Furthermore, the refractive index n can be made smaller, and in particular, when the absorber film is made to have a phase shift function, not only can the film thickness be reduced, but the reflectance at a predetermined phase difference can be set high.

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

[0033] The refractive index n of the absorber film is preferably smaller than that of the exposure light, and the refractive index n at the exposure wavelength is preferably 0.94 or less, particularly 0.93 or less. The absorber film having a small refractive index n to the exposure light is preferable because it can be thinned when it is made into an absorber film having a phase shift function. The absorber film of the present invention is advantageous because it can be thinned, particularly when it is made into an absorber film having a phase shift function, compared with the absorber film of tantalum that has been used conventionally.

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

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

[0036] It is preferable that the absorber film can be dry etched with a fluorine-based gas that does not contain oxygen. If dry etching can be performed with a fluorine-based gas that does not contain oxygen, a protective film formed of a material containing ruthenium (Ru), as described below, can be used as the protective film for the multilayer reflective film. As an example of the fluorine-based gas that does not contain oxygen, CF 4 ,SCIENCE FICTION 6 When forming a pattern of the absorber film by dry etching, it is preferable that the etching rate is high, and the etching rate of the absorber film is preferably three times or more the etching rate of the protective film when the protective film is etched by the etching applied to the dry etching of the absorber film.

[0037] The absorber film is preferably such that, as a difference before and after forming the absorber film on the multilayer reflective film or protective film, when the substrate is a 6025 substrate (the size of the main surface is 152 mm square), the absolute value of the change in warp (ΔTIR) within a 142 mm square at the center of the substrate surface is 0.4 μm or less, particularly 0.3 μm or less. If the change in warp is small, a reflective mask blank having an absorber film with little shift in pattern position and little decrease in dimensional accuracy when a reflective mask is manufactured by patterning the absorber film is obtained. In addition, if the absorber film has a small change in warp (ΔTIR) immediately after film formation, it is possible to further reduce the change in warp (ΔTIR) by subsequent processing (e.g., heat treatment).

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

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

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

[0041] The phase difference (phase shift amount) of the 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 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 the multilayer reflective film and the protective film of the multilayer reflective film formed thereon). By utilizing the phase shift effect, the resolution can be increased.

[0042] A reflectance reduction film having a function of reducing reflectance against the inspection light used in the inspection of the absorber film may be formed on the side of the absorber film that is separated from the substrate. In this way, the inspection sensitivity during pattern inspection can be increased. If the reflectance reduction film is a film that can be etched with the same etchant as the absorber film, it has the advantage that it can be etched simultaneously with the absorber film. On the other hand, if the reflectance reduction film is a film that is resistant to the etchant of the absorber film, it has the advantage that the reflectance reduction film can be used as a hard mask. In addition, a layer for improving the irradiation resistance against the exposure light may be provided as the outermost layer on the side of the absorber film that is separated from the substrate.

[0043] The method for forming the absorber film is preferably a sputtering method using a target and a sputtering gas, and magnetron sputtering is suitable for the sputtering. Specific examples of the target include a tungsten target, one or more targets selected from metals and semimetals other than tungsten, and targets containing tungsten and one or more selected from metals and semimetals other than tungsten. Depending on the composition, one or more targets can be used. When multiple targets are used, targets with different compositions or composition ratios can also be used. On the other hand, specific examples of the sputtering gas that can be used include rare gases such as Ar gas and Kr gas. In addition to the rare gas, nitrogen gas (N 2 ), oxygen gas (O 2 ), nitrogen oxide gas (N 2 O, NO, NO 2 ) or the like, the film can be formed by reactive sputtering, which sputters a target. For example, when the absorber film is made of a nitride, nitrogen gas (N 2 ), and when it is oxide, oxygen gas (O 2 ) can be used. In addition, when making a nitride oxide, nitrogen gas (N 2 ) and oxygen gas (O 2 ), or nitrogen oxide gas (N 2 O, NO, NO 2) can be used. The pressure in the sputtering chamber (sputtering pressure) is preferably 0.15 Pa or more and less than 0.4 Pa, particularly 0.3 Pa or less. If the sputtering pressure is high, it becomes difficult to form a film with high crystallinity, but if the sputtering pressure is too high, not only does the surface roughness increase, but the film tends to be easily infiltrated by oxygen from the atmosphere, etc.

[0044] The material of the protective film includes a material containing ruthenium (Ru). Specific examples of the material containing ruthenium (Ru) include ruthenium (Ru) alone and ruthenium alloys containing metals such as titanium (Ti), niobium (Nb), molybdenum (Mo), and zirconium (Zr) in addition to ruthenium (Ru). The content of ruthenium 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 formed by, for example, ion beam sputtering or magnetron sputtering.

[0045] The conductive film preferably has a sheet resistance of 100Ω / □ or less, and there is no particular restriction on the material or film thickness. Examples of the material of the conductive film include materials containing chromium (Cr) or tantalum (Ta). The material containing chromium (Cr) or tantalum (Ta) may also contain oxygen (O), nitrogen (N), carbon (C), boron (B), and the like. Specific examples of the material containing chromium include Cr alone and chromium compounds such as CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCNB, CrCOB, and CrCONB. Examples of the material containing tantalum (Ta) include Ta alone and tantalum compounds such as 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 as an electrostatic chuck, but is usually about 5 to 50 nm. The conductive film is preferably formed as a reflective mask, specifically, after forming an absorber pattern, so that the film stress is balanced with 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 film side of the substrate, or after forming a part of the film on the multilayer reflective film side of the substrate, the conductive film may be formed, and then the remaining film on the multilayer reflective film side of the substrate may be formed. The conductive film can be formed, for example, by magnetron sputtering.

[0047] A hard mask film having etching characteristics different from those of the absorber film and functioning as an etching mask in etching when the absorber film is patterned may be provided on the absorber film. After the absorber pattern is formed, the hard mask film may be left as a reflectance reducing layer to be a part of the absorber film, or may be removed so as not to remain on the reflective mask. Materials for the hard mask film include materials containing chromium (Cr). When the reflectance reducing film is formed on the absorber film, the hard mask film may be formed on the reflectance reducing layer. The hard mask film may be formed by, for example, magnetron sputtering. The thickness of the hard mask film is not particularly limited, but is usually about 5 to 20 nm.

[0048] Furthermore, the reflective mask blank may have a resist film, such as a photoresist film used for patterning an absorber film, a hard mask film, etc., formed on the side farthest from the substrate. The photoresist film is preferably an electron beam (EB) resist. EXAMPLES

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

[0050] [Experimental Example 1] A 6025 quartz substrate measuring 152 mm square and 6.35 mm thick was placed in the chamber of the sputtering apparatus, and a tungsten (W) target and a molybdenum (Mo) target were used as the sputtering targets, and argon gas was used as the sputtering gas. A WMo film having a thickness of 30 nm was formed on the quartz substrate by magnetron sputtering.

[0051] The composition of the obtained WMo film was measured by X-ray photoelectron spectroscopy (XPS), and found to be 46.0 atomic % tungsten and 54.0 atomic % molybdenum. The surface of the obtained WMo film was observed in a 1 μm square area with an atomic force microscope (AFM) device, and 10 of the largest depressions (large areas in the observed image) were selected. The length of the 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 about 30°C to 500°C by thin film X-ray diffraction method (in-plane XRD method) to measure the diffraction spectrum. As a result, diffraction peaks attributable to cubic crystals of tungsten and molybdenum were confirmed at 2θ=40°, 59°, 74°, 88°, and 102° in the entire heating temperature range, and no tungsten oxide was detected in the WMo film heated to 500°C.

[0052] [Experimental Example 2] A WMo film having a thickness of 30 nm was formed 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) and found to be 71.6 atomic % tungsten and 28.4 atomic % molybdenum. The surface of the obtained WMo film was observed in an area of ​​1 μm square with an atomic force microscope (AFM) and 10 of the largest depressions (largest area in the observed image) were selected. The lengths of the depressions were measured and the average length was calculated to be 0.12 μm.

[0054] [Experimental Example 3] A WMo film having a thickness of 30 nm was formed 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) and found to be 25.8 atomic % tungsten and 74.2 atomic % molybdenum. The surface of the obtained WMo film was observed in an area of ​​1 μm square with an atomic force microscope (AFM) and 10 of the largest depressions (largest area in the observed image) were selected. The lengths of the depressions were measured and the average length was calculated to be 0.048 μm.

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

[0057] The composition of the obtained WRu film was measured by X-ray photoelectron spectroscopy (XPS), and found to be 43.9 atomic % tungsten and 56.1 atomic % ruthenium. The surface of the obtained WRu film was observed in a 1 μm square area with an atomic force microscope (AFM) device, and 10 of the largest depressions (large areas in the observed image) were selected. The length of the depressions was measured and the average length was calculated to be 0.033 μm. The obtained WRu film was heated in a nitrogen atmosphere from about 30°C to 500°C by thin film X-ray diffraction method (in-plane XRD method) to measure the diffraction spectrum. As a result, diffraction peaks attributable to cubic or hexagonal crystals of tungsten and ruthenium were confirmed at 2θ = 38°, 68°, and 80° in the entire heating temperature range, and the WRu film heated to 500°C contained tungsten oxide (WO 3) was detected, but its intensity was similar to that of tungsten oxide (WO) detected in the W film heated to 500°C when a 30 nm thick W film was similarly formed on a quartz substrate using only a tungsten (W) target and heated from about 30°C to 500°C in a nitrogen atmosphere. 3 ) was less than one-fifth of the strength of

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

[0059] The composition of the obtained WMoRu film was measured by X-ray photoelectron spectroscopy (XPS), and found to be 46.1 atomic % tungsten, 24.9 atomic % molybdenum, and 29.0 atomic % ruthenium. The surface of the obtained WMoRu film was observed in a 1 μm square area using an atomic force microscope (AFM) device, and 10 of the largest depressions (large areas in the observed image) were selected. The lengths of the depressions were measured and the average length was calculated to be 0.030 μm. The diffraction spectrum of the obtained WMoRu film was measured by heating it from about 30°C to 500°C in a nitrogen atmosphere using a thin film X-ray diffraction method (in-plane XRD method). As a result, diffraction peaks attributable to cubic or hexagonal crystals of tungsten, molybdenum, and ruthenium were confirmed at 2θ = 39°, 71°, and 84° over the entire heating temperature range, and no tungsten oxide was detected in the WMoRu film heated up to 500°C.

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

[0061] The composition of the obtained WMoN film was measured by X-ray photoelectron spectroscopy (XPS), and found to be 33.1 atomic % tungsten, 27.7 atomic % molybdenum, and 39.2 atomic % nitrogen. The surface of the obtained WMoN film was observed in a 1 μm square area using an atomic force microscope (AFM) device, and 10 large depressions (large areas in the observed image) were selected. The length of the 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 about 30°C to 500°C using a thin film X-ray diffraction method (in-plane XRD method) to measure the diffraction spectrum. As a result, diffraction peaks attributable to cubic crystals of WMoN were confirmed at 2θ = 37°, 43°, 62°, and 75° in the entire heating temperature range, and no tungsten oxide was detected in the WMoN film heated to 500°C.

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

[0063] The composition of the obtained WMoN film was measured by X-ray photoelectron spectroscopy (XPS), and found to be 25.0 atomic % tungsten, 22.9 atomic % molybdenum, and 52.1 atomic % nitrogen. The surface of the obtained WMoN film was observed in a 1 μm square area using an atomic force microscope (AFM) device, and 10 of the largest depressions (large areas in the observed image) were selected. The lengths of the depressions were measured and the average length was calculated to be 0.039 μm. The obtained WMoN film was heated in a nitrogen atmosphere from about 30°C to 500°C using thin film X-ray diffraction (in-plane XRD) to measure the diffraction spectrum. As a result, WMoN was found to have a large diffraction peak at 2θ=36°, 45°, 64°, and 75° in the entire heating temperature range. 2 Diffraction peaks attributable to hexagonal crystals were detected, confirming that WMoN is in a polycrystalline state with low orientation, and no tungsten oxide was detected in the WMoN film heated up to 500°C.

[0064] [Experimental Example 8] A 6025 quartz substrate measuring 152 mm square and 6.35 mm thick was placed in the chamber of the sputtering device, and a tungsten (W) target was used as the sputtering target, argon gas was used as the sputtering gas, and nitrogen gas was used as the reactive gas. A WN film having a thickness of 30 nm was formed on the quartz substrate by magnetron sputtering.

[0065] The composition of the obtained WN film was measured by X-ray photoelectron spectroscopy (XPS) and found to be 81.9 atomic % tungsten and 18.1 atomic % nitrogen. The surface of the obtained WN film was observed in an area of ​​1 μm square with an atomic force microscope (AFM) and 10 of the largest depressions (largest area in the observed image) were selected. The lengths of the depressions were measured and the average length was calculated to be 0.065 μm.

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

[0067] The composition of the obtained WN film was measured by X-ray photoelectron spectroscopy (XPS) and found to be 65.0 atomic % tungsten and 35.0 atomic % nitrogen. The surface of the obtained WN film was observed in an area of ​​1 μm square with an atomic force microscope (AFM) and 10 of the largest depressions (largest area in the observed image) were selected. The lengths of the depressions were measured and the average length was calculated to be 0.061 μm.

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

[0069] The composition of the obtained WN film was measured by X-ray photoelectron spectroscopy (XPS) and found to be 46.4 atomic % tungsten and 53.6 atomic % nitrogen. The surface of the obtained WN film was observed in an area of ​​1 μm square with an atomic force microscope (AFM) and 10 of the largest depressions (largest area in the observed image) were selected. The lengths of the depressions were measured and the average length was calculated to be 0.054 μm.

[0070] [Comparative experiment example] A 6025 quartz substrate measuring 152 mm square and 6.35 mm thick was placed in the chamber of the sputtering apparatus, and a tungsten (W) target was used as the sputtering target and argon gas was used as the sputtering gas to form a W film with a thickness of 30 nm on the quartz substrate by magnetron sputtering.

[0071] The surface of the obtained W film was observed in a 1 μm square area with an atomic force microscope (AFM) device, and 10 of the largest dents (large areas in the observed image) were selected. The lengths of the dents were measured and the average length was calculated to be 0.157 μm. The obtained W film was heated in a nitrogen atmosphere from about 30°C to 500°C by thin film X-ray diffraction method (in-plane XRD method) to measure the diffraction spectrum. As a result, diffraction peaks attributed to tungsten were confirmed at 2θ = 40°, 59°, 74°, 87°, and 101° in the entire heating temperature range, and the W film heated to 500°C contained tungsten oxide (WO 3) was detected. [Explanation of symbols]

[0072] 100, 200, 300 Reflective mask blanks 101 Substrate 102 Multilayer reflective film 103 Absorber membrane 104 Protective film 105 Conductive film

Claims

1. A reflective mask blank comprising a substrate, a multilayer reflective film formed on one main surface of the substrate and reflecting exposure light, and an absorber film formed on the multilayer reflective film and absorbing the exposure light, the mask blank being a material for a reflective mask used in EUV lithography using EUV light as exposure light, The absorber film is (a) tungsten, (b) one or both of molybdenum and ruthenium, and (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen. Contains The total content of (a) tungsten, (b) one or both of molybdenum and ruthenium, and (c) one or more light elements selected from nitrogen, oxygen, carbon, and hydrogen is 90 atomic % or more. A reflective mask blank comprising:

2. 2. The reflective mask blank according to claim 1, wherein the content of one or both of molybdenum and ruthenium (b) is 1 atomic % or more and 80 atomic % or less.

3. 3. The reflective mask blank according to claim 1, wherein the content of the one or more light elements (c) selected from nitrogen, oxygen, carbon and hydrogen is 10 atomic % or more and 80 atomic % or less.

4. 4. The reflective mask blank according to claim 1, wherein the content of the tungsten (a) is 20 atomic % or more and 99 atomic % or less.

5. 5. The reflective mask blank according to claim 1, wherein the absorber film has a refractive index n of 0.94 or less at an exposure wavelength.

6. 6. The reflective mask blank according to claim 1, wherein the absorber film has a thickness of 70 nm or less.

7. The reflective mask blank according to any one of claims 1 to 6, further comprising a protective film between the multilayer reflective film and the absorber film, the protective film being in contact with the multilayer reflective film and having etching characteristics different from those of the absorber film.

8. 8. The reflective mask blank according to claim 1, further comprising a conductive film formed on the other main surface of the substrate.

9. 9. The reflective mask blank according to claim 1, further comprising a chromium-containing film formed as an etching mask on the absorber film.

10. A reflective mask produced from the reflective mask blank according to claim 1 .

Images