Method for manufacturing reflective mask blanks and reflective masks

Abstract

The present invention provides a reflective mask blank, etc., in which a protective film made of rhodium (Rh), or a protective film formed from a material containing rhodium and ruthenium (Ru), is less susceptible to damage even when dry etching is performed using an oxygen (O)-containing gas during the mask manufacturing process. [Solution] The reflective mask blank 100 is a material for a reflective mask used in EUV lithography, which uses EUV light as the exposure light. The reflective mask blank comprises a substrate 1, a multilayer reflective film 2 formed on one of the main surfaces of the substrate that reflects exposure light, a protective film 3 formed on the multilayer reflective film that protects the multilayer reflective film, an absorption film 5 formed on the protective film that absorbs exposure light, and an etching-blocking film 4 containing niobium (Nb) provided between the protective film and the absorption film. The protective film has at least one layer containing rhodium. The layer in contact with the protective film in the multilayer reflective film contains molybdenum (Mo).

Description

Technical Field

[0001] The present invention relates to a reflective mask blank which is a material for manufacturing semiconductor devices such as LSIs, and a method for manufacturing a reflective mask from the reflective mask blank.

Background Art

[0002] In the manufacturing process of semiconductor devices (semiconductor apparatuses), photolithography technology is repeatedly 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) through a reduction projection optical system. Conventionally, the wavelength of exposure light has been mainly 193 nm using argon fluoride (ArF) excimer laser light, and by adopting a process called multi-patterning in which a plurality of exposure processes and processing processes are combined, finally, patterns with dimensions smaller than the exposure wavelength have been formed.

[0003] However, due to the continuous miniaturization of device patterns, the formation of further fine patterns has been required, and thus, extreme ultraviolet (Extreme Ultraviolet, hereinafter referred to as "EUV") lithography technology using EUV light with a wavelength shorter than that of ArF excimer laser light has come to be used. EUV light is light having a wavelength of about 0.2 to 100 nm, more specifically, light having a wavelength near 13.5 nm. Since EUV light has extremely low transparency to substances and conventional transmissive projection optical systems and masks cannot be used, reflective optical elements are used. Therefore, reflective masks are also used as masks for pattern transfer.

[0004] A reflective mask is constructed by forming a multilayer reflective film that reflects EUV light on a substrate, and then forming a pattern of an absorbing film that absorbs EUV light on top of the multilayer reflective film. On the other hand, the state before the absorbing film is patterned (including the state where a resist film has been formed) is called a reflective mask blank, and this is used as the material for a reflective mask. A reflective mask blank generally has a basic structure that includes a substrate with low thermal expansion, a multilayer reflective film that reflects EUV light formed on one of the two main surfaces of the substrate, and an absorbing film that absorbs EUV light formed on top of it.

[0005] As a multilayer reflective film, a multilayer reflective film is typically used that obtains the required reflectivity for EUV light by alternately stacking molybdenum (Mo) layers and silicon (Si) layers. On the other hand, as an absorbing film, tantalum (Ta), which has a relatively large extinction coefficient for EUV light, is used (Japanese Patent Publication No. 2002-246299 (Patent Document 1)).

[0006] Furthermore, a ruthenium (Ru) film or rhodium (Rh) film, as disclosed in Japanese Patent Publication No. 2002-122981 (Patent Document 2) and Japanese Patent Publication No. 2005-516182 (Patent Document 3), is formed on the multilayer reflective film as a protective film (capping film) to protect the multilayer reflective film during cleaning of the reflective mask, etc. In addition, a hard mask film containing chromium (Cr) may be formed on the absorption film as an etching mask when forming patterns on the absorption film. On the other hand, a conductive film is formed on the other main surface of the substrate. As a conductive film, metal nitride films have been proposed for electrostatic chucking, and films mainly containing chromium (Cr) and tantalum (Ta) are examples. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2002-246299 [Patent Document 2] Japanese Patent Publication No. 2002-122981 [Patent Document 3] Japanese Patent Publication No. 2002-516182 [Overview of the project] [Problems that the invention aims to solve]

[0008] The protective film is required to have the function of protecting the multilayer reflective film. Specifically, this includes functions such as protecting the multilayer reflective film from exposure to etching gases and cleaning solutions during pattern processing of absorption films, and suppressing the decrease in reflectivity that occurs with repeated exposures when using a reflective mask.

[0009] In the process of manufacturing a reflective mask using a reflective mask blank as the material, when forming a pattern on the absorption film by dry etching, a certain degree of over-etching is usually performed to control the pattern shape. When over-etching is performed, the protective film is exposed to etching and becomes damaged. When the absorption film is formed from a material that contains tantalum (Ta) and does not contain oxygen (O), a gas containing chlorine (Cl) and not oxygen (O) is preferably used as the etching gas. Therefore, the protective film is required to have resistance to dry etching using a gas that contains chlorine (Cl) and not oxygen (O).

[0010] Furthermore, when using a hard mask film pattern obtained by forming a pattern of a hard mask film made of a chromium (Cr)-containing material as an etching mask when forming a pattern on an absorption film, the hard mask film pattern is usually removed by dry etching using a gas containing chlorine (Cl) and oxygen (O) after the absorption film pattern has been formed. In this process, the protective film is also exposed to dry etching using a gas containing chlorine (Cl) and oxygen (O). Therefore, the protective film must also be resistant to dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0011] During dry etching in the manufacturing of reflective masks, damage to the protective film can occur, altering its quality and thickness, leading to problems such as the loss of its protective function against the multilayer reflective film. Therefore, it has been proposed to improve the resistance to dry etching and enhance the protective function of the protective film against the multilayer reflective film by adding additive elements such as niobium (Nb) to ruthenium (Ru)-containing protective films.

[0012] However, when a chromium (Cr)-based absorption film is laminated on top of a ruthenium (Ru)-based protective film, which is commonly used as a protective film for multilayer reflective films, dry etching using a gas containing chlorine (Cl) and oxygen (O), which is used for dry etching of chromium (Cr)-based films, etches the ruthenium (Ru) by the oxygen plasma. As a result, the ruthenium (Ru)-based film is also etched, damaging the ruthenium (Ru)-based protective film and causing it to become thinner.

[0013] Therefore, if Rh is included in the protective film instead of Ru, it has some resistance to dry etching using oxygen (O) gas, but there are problems such as the surface oxidizing and reducing reflectivity, or the protective film becoming thinner due to sputtering during dry etching.

[0014] The present invention was made to solve the above problems, and aims to provide a reflective mask blank that is less susceptible to damage to the protective film and can suppress a decrease in the thickness of the protective film and oxidation of the protective film, and a method for manufacturing a reflective mask using the reflective mask blank.

[0015] The inventors of this invention, after diligent research to solve the above problems, found that the above problems can be solved by having a protective film containing rhodium (Rh), making the uppermost layer of the multilayer reflective film in contact with the protective film Mo, and having a layer containing niobium (Nb) (etching-blocking film) between the protective film and the absorbing film, and thus conceived the present invention. [Means for solving the problem]

[0016] Therefore, the present invention provides the following reflective mask blank and a method for manufacturing a reflective mask.

[0017] [Concept 1] The reflective mask blank according to the present invention is a reflective mask blank that serves as a material for a reflective mask used in EUV lithography using EUV light as exposure light, a substrate, a multilayer reflective film formed above one main surface of the substrate to reflect exposure light, a protective film formed on the multilayer reflective film to protect the multilayer reflective film, an absorption film formed above the protective film to absorb exposure light, an etching stopper film containing niobium (Nb) provided between the protective film and the absorption film, and comprises the protective film has at least one layer containing rhodium (Rh), the layer in the multilayer reflective film that contacts the protective film may contain molybdenum (Mo).

[0018] [Concept 2] In the reflective mask blank according to Concept 1, the protective film may be made of rhodium (Rh).

[0019] [Concept 3] In the reflective mask blank according to Concept 1, the protective film may be made of a layer containing rhodium (Rh) and ruthenium (Ru).

[0020] [Concept 4] In the reflective mask blank according to Concept 1, the protective film may be made of a layer containing rhodium (Rh) and a layer containing ruthenium (Ru).

[0021] [Concept 5] In the reflective mask blank according to any one of Concepts 1 to 4, The etching-blocking film may consist of niobium (Nb) or a niobium (Nb) compound containing niobium (Nb) and oxygen (O).

[0022] [Concept 6] A reflective mask may be manufactured from a reflective mask blank according to any one of claims 1 to 5. [Effects of the Invention]

[0023] According to the present invention, when the uppermost layer of the multilayer reflective film in contact with the protective film formed from a rhodium (Rh)-containing material is made of Mo, a denser protective film can be formed. Furthermore, by having a layer containing niobium (Nb) between the protective film and the absorbing film, even when dry etching is performed using an oxygen (O)-containing gas, the protective film is less susceptible to damage, and a reduction in the thickness of the protective film and oxidation can be suppressed. [Brief explanation of the drawing]

[0024] [Figure 1] A cross-sectional view showing an example (first aspect) of a reflective mask blank according to an embodiment of the present invention. [Figure 2] A cross-sectional view showing another example (second aspect) of a reflective mask blank according to an embodiment of the present invention. [Figure 3] A cross-sectional view showing an example of a reflective mask according to an embodiment of the present invention. [Figure 4] A cross-sectional view showing yet another example (third aspect) of a reflective mask blank according to an embodiment of the present invention. [Modes for carrying out the invention]

[0025] The embodiments of the present invention will be described in more detail below.

[0026] The reflective mask blank 100 comprises a substrate 1, a multilayer reflective film 2 formed on one main surface (surface) of the substrate 1 that reflects exposure light, a protective film 3 formed on the multilayer reflective film 2, and an absorption film 5 formed above the protective film 3 that absorbs exposure light. The reflective mask blank 100 also has an etching-blocking film 4 between the protective film 3 and the absorption film 5.

[0027] The reflective mask blank 100 is suitable as a material for the reflective mask 110 (see Figure 3) used in EUV lithography, which uses EUV light as the exposure light. The wavelength of the EUV light used in EUV lithography is 13-14 nm, and is typically around 13.5 nm. The reflective mask blank 100 and the reflective mask 110, which use EUV light as the exposure light, are also called EUV mask blanks and EUV masks, respectively.

[0028] Figure 1 is a cross-sectional view showing an example (first aspect) of the reflective mask blank 100 of this embodiment. This reflective mask blank 100 comprises a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1, a protective film 3 formed in contact with the multilayer reflective film 2, and an absorption film 5 formed above the protective film 3, with an etching-blocking film 4 between the protective film 3 and the absorption film 5.

[0029] The substrate 1 is preferably made of materials with low thermal expansion properties for use in EUV light exposure, for example, a thermal expansion coefficient of ±2 × 10 -8 Within / ℃, preferably ±5 × 10 -9It is preferable that the substrate 1 be made of a material within the range of / ℃. Examples of such materials include titania-doped quartz glass (SiO2-TiO2 glass). Furthermore, it is preferable that the substrate 1 be made of a material with a sufficiently flat surface, and the surface roughness of the main surface of the substrate 1 is preferably 0.5 nm or less, more preferably 0.2 nm or less, in RMS value. Such surface roughness can be obtained by polishing the substrate 1. The size of the substrate 1 is preferably 152 mm square for the main surface and 6.35 mm thick. A substrate 1 of this size is a so-called 6025 substrate (a substrate with a main surface size of 6 inches square and a thickness of 0.25 inches).

[0030] The multilayer reflective film 2 is a film that reflects exposure light in the reflective mask 110 (see Figure 3). The multilayer reflective film 2 is preferably provided in contact with one main surface of the substrate 1, but other films such as an undercoat may be provided between it and one main surface of the substrate 1. As shown in Figure 4, the multilayer reflective film 2 has a periodic stacked structure in which a high refractive index layer 21 with a relatively high refractive index with respect to exposure light and a low refractive index layer 22 with a relatively low refractive index with respect to exposure light are alternately stacked.

[0031] The high refractive index layer 21 is preferably made of a material containing silicon (Si). The high refractive index layer 21 may also contain one or more additive elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H), and may be composed of a multilayer structure of a layer containing additive elements and a layer not containing additive elements. The thickness of the high refractive index layer 21 is preferably 3.5 nm or more, more preferably 4 nm or more, and preferably 4.9 nm or less, more preferably 4.4 nm or less.

[0032] The low refractive index layer 22 is preferably formed from a material containing molybdenum (Mo). Alternatively, the low refractive index layer 22 may be formed from a material containing ruthenium (Ru). A multilayer structure of Mo and Ru is also acceptable. The low refractive index layer 22 may contain one or more additive elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H), and may be composed of a multilayer structure of a layer containing additive elements and a layer not containing additive elements. The thickness of the low refractive index layer 22 is preferably 2.1 nm or more, more preferably 2.6 nm or more, and preferably 3.5 nm or less, more preferably 3 nm or less.

[0033] The periodic stacked structure only needs to include a high refractive index layer 21 and a low refractive index layer 22, and each period should contain one or more high refractive index layers 21 and one or more low refractive index layers 22. The number of layers included in the periodic stacked structure is two or more, and the periodic stacked structure can be composed of, for example, one high refractive index layer 21 and one low refractive index layer 22. Furthermore, it may include two or more high refractive index layers 21 with different compositions (for example, different composition ratios, different compositions due to the presence or absence of additive elements, etc.) and two or more low refractive index layers 22 with different compositions (for example, different composition ratios, different compositions due to the presence or absence of additive elements, etc.). In this case, the number of layers included in the periodic stacked structure is three or more, and may be four or more or five or more, but is preferably eight or less. The number of periods is preferably 20 or more, preferably 50 or less, and more preferably 40 or less.

[0034] The thickness of the multilayer reflective film 2 having a periodic stacked structure is adjusted according to the exposure wavelength and the angle of incidence of the exposure light, but is preferably 130 nm or more, 400 nm or less, and more preferably 290 nm or less.

[0035] Methods for forming the multilayer reflective film 2 include sputtering, which involves supplying power to a target to plasmaize (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. Sputtering is a film deposition method that utilizes the sputtering phenomenon caused by gas ions, by applying a voltage to the target while sputtering gas is introduced into a chamber, thereby ionizing the gas. Magnetron sputtering, in particular, offers advantages in terms of productivity. The power applied to the target can be DC or RF, and DC sputtering also includes pulse sputtering, where the negative bias applied to the target is briefly reversed to prevent charge-up of the target.

[0036] The multilayer reflective film 2 can be formed by sputtering, for example, using a sputtering apparatus that can be equipped with multiple targets. Specifically, the target can be appropriately selected from a molybdenum (Mo) target for forming a molybdenum (Mo) layer, a ruthenium (Ru) target for forming a ruthenium (Ru) layer, a silicon (Si) target for forming a silicon (Si) layer, etc., and the sputtering gas can be a rare gas such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas.

[0037] Furthermore, when sputtering is performed as reactive sputtering using a reactive gas, for example, when forming a film containing nitrogen (N), a nitrogen-containing gas such as nitrogen (N2) gas should be used; when forming a film containing oxygen (O), an oxygen-containing gas such as oxygen (O2) gas should be used; when forming a film containing nitrogen (N) and oxygen (O), nitrogen oxide gases such as nitrous oxide (N2O), nitric oxide (NO), and nitrogen dioxide (NO2) gas should be used; when forming a film containing carbon (C) and oxygen (O), carbon oxide gases such as carbon monoxide (CO) gas and carbon dioxide (CO2) gas should be used; when forming a film containing hydrogen (H), a hydrogen-containing gas such as hydrogen (H2) gas should be used; and when forming a film containing carbon (C) and hydrogen (H), a hydrocarbon gas such as methane (CH4) gas should be used, along with a noble gas.

[0038] Furthermore, when forming a boron (B)-containing layer, boron (B)-doped molybdenum (Mo) targets (molybdenum boride (MoB) targets), boron (B)-doped silicon (Si) targets (silicon boride (SiB) targets), etc., can be used.

[0039] In this embodiment, the uppermost layer of the multilayer reflective film 2 is a layer containing Mo (for example, a Mo layer). The thickness of this Mo-containing layer should be as thin as possible, preferably 2 nm or less, and more preferably 1 nm or less. The presence of molybdenum (Mo) in the layer in contact with the protective film 3 in the multilayer reflective film 2 is advantageous because it allows for the formation of a denser protective film 3.

[0040] The protective film 3 is also called the capping film. The protective film 3 is a film that protects the multilayer reflective film 2. The protective film 3 is usually provided in contact with the multilayer reflective film 2. The protective film 3 is made of a material containing rhodium (Rh).

[0041] Materials containing rhodium (Rh) include elemental rhodium (Rh), and alloys consisting of rhodium (Rh) and a metal or metalloid other than rhodium (Rh). Examples of metals or metalloids other than rhodium (Rh) include ruthenium (Ru), niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si). Among materials containing rhodium (Rh), elemental rhodium (Rh) is particularly preferred, and the protective film 3 is preferably made of rhodium (Rh). The content of a metal or metalloid other than rhodium (Rh) in the protective film 3 is preferably 50 atomic% or less, more preferably 30 atomic% or less, on average for the entire film. The lower limit of the content of a metal or metalloid other than rhodium (Rh) in the protective film 3 is not particularly limited, but is preferably 5 atomic% or more, more preferably 10 atomic% or more. Including rhodium (Rh) in protective film 3 is beneficial because it provides a certain degree of resistance to dry etching using oxygen (O)-containing gases.

[0042] The protective film 3 may be a single-layer structure or a multilayer structure combining multiple layers of different compositions. Furthermore, each layer constituting the single layer or multiple layers may have a gradient composition structure in which the composition changes continuously in the thickness direction. In particular, one or both of the side of the protective film 3 that is close to the multilayer reflective film 2 (in the case of a multilayer structure, the layer close to the multilayer reflective film 2) and the side that is furthest from the multilayer reflective film 2 (in the case of a multilayer structure, the layer furthest from the multilayer reflective film 2) may be made of rhodium (Rh).

[0043] Specifically, dry etching using a gas containing chlorine (Cl) and oxygen (O) can be exemplified by dry etching using a gas containing chlorine (Cl2) gas and oxygen (O2) gas. The gas containing chlorine (Cl) and oxygen (O) may also include noble gases such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas.

[0044] The thickness of the protective film 3 is preferably 1 nm or more, more preferably 2 nm or more, and also preferably 5 nm or less, more preferably 4 nm or less.

[0045] The protective film 3 is a mixture of two or more targets selected from rhodium (Rh), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), silicon (Si), ruthenium (Ru), niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si). The material can be formed by sputtering using a target that has been treated with rhodium (Rh), a target in which one or more metals or metalloids other than ruthenium (Ru) selected from ruthenium (Ru), niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si), and a rare gas such as helium (He), argon (Ar), krypton (Kr), or xenon (Xe) as the sputtering gas. Magnetron sputtering is preferred for sputtering.

[0046] The absorption film 5 is a film in the reflective mask 110 that absorbs exposure light and reduces reflectivity. In the reflective mask 110, the transfer pattern is formed by the difference in reflectivity between the areas where the absorption film 5 is formed and the areas where the absorption film 5 is not formed. The absorption film 5 may be a single layer or a multilayer, and an anti-reflective layer or the like may be formed on its surface.

[0047] The absorption film 5 is preferably mainly composed of tantalum (Ta), chromium (Cr), ruthenium (Ru), and platinum (Pt). The absorption film 5 is a film of a material that absorbs EUV light and can be patterned, and is preferably formed from a material containing tantalum (Ta) or a material containing chromium (Cr). In this embodiment, "main component" means the metal or metalloid element contained in the film that is present in the highest atomic percentage.

[0048] Materials containing tantalum (Ta) may also contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Specific examples of tantalum (Ta)-containing materials include elemental Ta and tantalum (Ta) compounds such as TaO, TaN, TaON, TaC, TaCO, TaCN, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCOB, TaCNB, and TaCONB. Note that the chemical formulas of metallic or metalloid compounds indicate the constituent elements of the compound, not their compositional ratios. (The same applies hereafter.)

[0049] Materials containing tantalum (Ta) can be etched by dry etching using a chlorine (Cl) gas if they do not contain oxygen (O). In this case, if nitrogen (N) is present, the etching rate of dry etching using a chlorine (Cl) gas increases. Furthermore, if a material containing tantalum (Ta) contains nitrogen (N) but not oxygen (O), the etching selectivity ratio to the etching-blocking film 4 in dry etching using a chlorine (Cl) gas increases. Therefore, it is preferable that the portion of the tantalum (Ta)-containing absorption film 5 in contact with the etching-blocking film 4 does not contain oxygen (O), and it is also preferable that it contains a large amount of nitrogen (N).

[0050] Specifically, dry etching using a chlorine (Cl)-containing gas can be described as dry etching using a chlorine (Cl2) gas. It is preferable that the chlorine (Cl)-containing gas does not contain an oxygen (O)-containing gas. The chlorine (Cl)-containing gas may also contain noble gases such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas.

[0051] Materials containing chromium (Cr) may also contain oxygen (O), nitrogen (N), carbon (C), etc. Specific examples of materials containing chromium (Cr) include elemental Cr and chromium (Cr) compounds such as CrO, CrN, CrON, CrC, CrCO, CrCN, and CrCON.

[0052] The absorption film 5 (each layer constituting the absorption film 5) can be formed by sputtering, and the sputtering method is preferably magnetron sputtering. Specifically, when forming with a material containing tantalum (Ta), a tantalum (Ta) target or a tantalum (Ta) compound target (a target containing tantalum (Ta) and oxygen (O), nitrogen (N), carbon (C), boron (B), etc.) is used, and when forming with a material containing chromium (Cr), a chromium (Cr) target or a chromium (Cr) compound target (a target containing chromium (Cr) and oxygen (O), nitrogen (N), carbon (C), etc.) is used, depending on the composition. The material can be formed by appropriately selecting and using a GET, and by sputtering with noble gases such as helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) as the sputtering gas, or by reactive sputtering using reactive gases such as oxygen-containing gases, nitrogen-containing gases, and carbon-containing gases, specifically oxygen (O2), nitrogen (N2), nitrogen oxide (N2O, NO, NO2) gas, and carbon oxide (CO, CO2) gas, along with noble gases.

[0053] As shown in Figure 2, an etching mask film 6 with different etching characteristics from the absorption film 5 can be provided on the side of the absorption film 5 that is separated from the substrate 1, as a hard mask film for the absorption film 5. This etching mask film 6 functions as a hard mask when dry etching the absorption film 5. It is preferable that the etching mask film 6 is provided in contact with the absorption film 5. The etching mask film 6 may be a single layer or a multilayer film.

[0054] Figure 2 is a cross-sectional view showing an example (second aspect) of the reflective mask blank 100 of this embodiment. This reflective mask blank 100 comprises a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1, a protective film 3 formed in contact with the multilayer reflective film 2, an etching-blocking film 4 formed in contact with the protective film 3, an absorption film 5 formed in contact with the etching-blocking film 4, and an etching mask film 6 formed in contact with the absorption film 5.

[0055] When the absorption film 5 contains tantalum (Ta), the etching mask film 6 preferably contains chromium (Cr), and the etching mask film 6 is preferably formed from a chromium (Cr)-containing material. A chromium (Cr)-containing material is preferable because, when processing the absorption film 5 formed from a tantalum (Ta)-containing material, it has different etching characteristics from the absorption film 5 and functions as an etching mask when dry etching the absorption film 5. For this reason, it is preferable that the chromium (Cr)-containing material of the etching mask film 6 does not contain tantalum (Ta). Examples of chromium (Cr)-containing materials include elemental Cr, CrO, CrN, CrON, CrC, CrOC, CrNC, and CrONC.

[0056] When the absorption film 5 contains chromium (Cr), the etching mask film 6 preferably contains tantalum (Ta), and the etching mask film 6 is preferably formed from a material containing tantalum (Ta). When processing the absorption film 5 formed from a material containing chromium (Cr), the etching mask film 6 formed from a material containing tantalum (Ta) has different etching characteristics from the absorption film 5 and functions as an etching mask when dry etching the absorption film 5. For this reason, it is preferable that the tantalum (Ta) material of the etching mask film 6 does not contain chromium (Cr). Examples of materials containing tantalum (Ta) include elemental Ta, TaO, TaN, TaON, TaC, TaOC, TaNC, and TaONC. The material containing tantalum (Ta) may further contain boron (B) or hydrogen (H).

[0057] The etching mask film 6 may be left on the reflective mask 110 after the pattern of the absorption film 5 has been formed, for example, as a reflectance reduction layer to reduce the reflectance at wavelengths of light used in inspections such as pattern inspection, or it may be removed so that it does not remain on the reflective mask 110.

[0058] The thickness of the etching mask film 6 is not particularly limited, but if it is too thin, it may not function as a hard mask, and if it is too thick, the processing characteristics may deteriorate. Therefore, it is preferably 1 nm or more, more preferably 2 nm or more, even more preferably 5 nm or more, and also preferably 20 nm or less, more preferably 10 nm or less.

[0059] The etching mask film 6 can be formed by sputtering. Specifically, when forming with a chromium (Cr)-containing material, a chromium (Cr) target or a chromium (Cr) compound target (a target containing chromium (Cr) and oxygen (O), nitrogen (N), carbon (C), etc.) is used. When forming with a tantalum (Ta)-containing material, a tantalum (Ta) target or a tantalum (Ta) compound target (a target containing tantalum (Ta) and oxygen (O), nitrogen (N), carbon (C), boron (B), etc.) is used. The target is appropriately selected and used according to the composition. Sputtering can be performed using noble gases such as helium (He), argon (Ar), krypton (Kr), and xenon (Xe) as the sputtering gas, or by reactive sputtering using reactive gases such as oxygen-containing gases, nitrogen-containing gases, and carbon-containing gases, specifically oxygen (O2), nitrogen (N2), nitrogen oxide (N2O, NO, NO2) gas, carbon oxide (CO, CO2) gas, hydrogen (H2) gas, and hydrocarbon gases (e.g., methane (CH4) gas) along with the noble gas. Magnetron sputtering is preferred for sputtering.

[0060] The etching-blocking film 4 is a film that protects the protective film 3 and prevents etching of the protective film 3 during dry etching using a gas containing chlorine (Cl) and oxygen (O). Therefore, the etching-blocking film 4 functions as an etching stopper against dry etching using a gas containing chlorine (Cl) and oxygen (O). The etching-blocking film 4 is a film containing niobium (Nb).

[0061] The niobium (Nb)-containing film is resistant to dry etching using chlorine (Cl) and oxygen (O) gases, which are used to etch chromium (Cr)-based films, and functions as a protective film for the protective film 3. Therefore, the niobium (Nb)-containing etching-blocking film 4 can prevent damage to the protective film 3 when patterning a chromium (Cr)-containing absorption film 5 by dry etching using chlorine (Cl) and oxygen (O) gases, or when patterning a tantalum (Ta)-containing absorption film 5 using the pattern of a chromium (Cr)-containing etching mask film 6, and then removing the chromium (Cr)-containing etching mask film 6 by dry etching using chlorine (Cl) and oxygen (O) gases.

[0062] The etching-blocking film 4 is preferably made of pure niobium (Nb), but may also be made of a niobium (Nb) compound containing niobium (Nb) and oxygen (O), such as niobium oxide (NbO). The niobium (Nb) compound containing oxygen (O) preferably has niobium (Nb) and oxygen (O) as its main components, and the total content of niobium (Nb) and oxygen (O) is preferably 70 atomic% or more, more preferably 80 atomic% or more, even more preferably 91 atomic% or more, and particularly preferably 100 atomic% on average for the entire film. Furthermore, the niobium (Nb) content is preferably 20 atomic% or more, more preferably 28 atomic% or more, and even more preferably 29 atomic% or more on average for the entire film.

[0063] The niobium (Nb) compound containing oxygen (O) may further contain elements or compounds that are etched by dry etching using a gas containing chlorine (Cl) or a gas containing fluorine (F), such as silicon (Si), nitrogen (N), and carbon (C), or compounds thereof. The total content of elements other than niobium (Nb) and oxygen (O) is preferably 30 atomic% or less, more preferably 20 atomic% or less, on average across the entire film. In this case, it is preferable that the total content of oxygen (O), nitrogen (N), and carbon (C) is 72 atomic% or less on average across the entire film.

[0064] The etching-blocking film 4 may be a single layer or multiple layers. Examples of multiple layers include combinations of layers containing niobium (Nb) with different compositions or composition ratios, such as a combination of a layer made of an oxygen (O)-containing niobium (Nb) compound and a layer made of niobium (Nb), or a combination of niobium (Nb) compound layers with different composition ratios of oxygen (O). Furthermore, each layer may be a single-composition layer or a gradient-composition layer having a gradient composition. If the etching-blocking film 4 contains oxygen (O), it is preferable to increase the oxygen (O) concentration on the front side (the side away from the substrate 1), or to make the front side a layer made of an oxygen (O)-containing niobium (Nb) compound and the substrate 1 side (back side) a layer made of niobium (Nb) or a layer containing niobium (Nb) but not oxygen (O).

[0065] In this embodiment, specific examples of dry etching using a gas containing fluorine (F) include dry etching using a gas containing carbon tetrafluoride (CF4) gas or sulfur hexafluoride (SF6) gas. The gas containing fluorine (F) may also include noble gases such as helium (He) gas, argon (Ar) gas, krypton (Kr) gas, and xenon (Xe) gas.

[0066] The thickness of the etching-blocking film 4 is preferably 0.5 nm or more, more preferably 1 nm or more, and also preferably 10 nm or less, more preferably 5 nm or less.

[0067] The etching-blocking film 4 can be formed by sputtering. The etching-blocking film 4 can be formed by sputtering using a niobium (Nb) target and, if necessary, a target of a different metal or metalloid from niobium (Nb), specifically a silicon (Si) target, and a rare gas such as helium (He), argon (Ar), krypton (Kr), or xenon (Xe) as the sputtering gas, or by reactive sputtering using a reactive gas such as an oxygen-containing gas, nitrogen-containing gas, or carbon-containing gas, specifically oxygen (O2), nitrogen (N2), nitrogen oxide (N2O, NO, NO2), or carbon oxide (CO, CO2) along with a rare gas. Magnetron sputtering is preferred for sputtering.

[0068] If the etching-blocking film 4 contains oxygen (O), niobium (Nb) is readily oxidized. Therefore, a film of elemental niobium (Nb) can be formed and oxidized by exposing it to an oxygen-containing atmosphere such as air to obtain an oxygen-containing niobium (Nb) compound. When oxidizing a film of elemental niobium (Nb), the film may be heat-treated.

[0069] On the other main surface (back surface) of the substrate 1, which is the surface opposite to one of the main surfaces, a conductive film (conductive film 50) may be provided, preferably in contact with the other main surface, for use in electrostatically chucking the reflective mask 110 to an exposure apparatus (e.g., an EUV scanner).

[0070] The conductive film 50 preferably has a sheet resistance of 100 Ω / □ or less, and there are no particular restrictions on the material. Examples of materials for the conductive film 50 include materials containing tantalum (Ta) or chromium (Cr). Furthermore, materials containing tantalum (Ta) may also contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc., and materials containing chromium (Cr) may also contain oxygen (O), nitrogen (N), carbon (C), etc. Examples of materials containing tantalum (Ta) include elemental Ta, TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, TaCONB, and other tantalum (Ta) compounds. Specific examples of materials containing chromium (Cr) include elemental Cr, CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, and other chromium (Cr) compounds.

[0071] The thickness of the conductive film 50 is not particularly limited, as long as it functions for electrostatic chucks, but is usually around 20 to 300 nm. The thickness of the conductive film 50 is preferably formed so that the film stress is balanced with the film and film pattern formed on one main surface (surface) side after it has been formed as a reflective mask 110, that is, after the pattern of the absorption film 5 has been formed. The conductive film 50 may be formed before forming the multilayer reflective film 2, or after all the films on the multilayer reflective film 2 side of the substrate 1 have been formed, or a portion of the films on the multilayer reflective film 2 side of the substrate 1 may be formed first, then the conductive film 50 may be formed, and then the remaining films on the multilayer reflective film 2 side of the substrate 1 may be formed. The conductive film 50 can be formed, for example, by magnetron sputtering.

[0072] As shown in Figure 4, the reflective mask blank 100 of this embodiment may have a resist film 9 formed on the side furthest from the substrate 1. The resist film 9 is preferably an electron beam (EB) resist.

[0073] From the reflective mask blank 100, for example, a reflective mask 110 can be manufactured having a substrate 1, a multilayer reflective film 2 formed on one main surface of the substrate 1, a protective film 3 formed in contact with the multilayer reflective film 2, a pattern of an etching-blocking film 4 formed in contact with the protective film 3, and a pattern of an absorption film 5 (absorption film pattern) 51 formed in contact with the pattern of the etching-blocking film 4. In the reflective mask 110, a transfer pattern is formed by the difference in reflectivity between the areas where the absorption film 5 is formed and the areas where the absorption film 5 is not formed.

[0074] Figure 3 is a cross-sectional view showing an example of a reflective mask 110 according to this embodiment. This reflective mask 110 comprises a substrate 1, a multilayer reflective film 2 formed on the substrate 1 in contact with the substrate 1, a protective film 3 formed in contact with the multilayer reflective film 2, a pattern 41 of an etching-blocking film 4 formed in contact with the protective film 3, and a pattern 51 of an absorption film 5 formed in contact with the pattern 41 of the etching-blocking film 4. In this reflective mask 110, the pattern 51 of the absorption film 5 is formed above the protective film 3 via the pattern 41 of the etching-blocking film 4.

[0075] The reflective mask 110 of this embodiment can be manufactured by a method that includes the steps of: preparing a reflective mask blank 100; optionally, forming a resist film 9 on an absorption film 5; forming a resist pattern from the resist film 9 on the absorption film 5; using the resist pattern as an etching mask to etch the absorption film 5 and form a pattern on the absorption film 5; removing the resist pattern; and removing the etching-blocking film 4 from the portion exposed after the absorption film 5 has been removed.

[0076] The absorption film 5, formed from a chromium (Cr)-containing material, can be etched by dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0077] In this case, the etching-blocking film 4 containing niobium (Nb) is not etched by dry etching using a gas containing chlorine (Cl) and oxygen (O), thus further preventing damage to the protective film 3.

[0078] The absorption film 5, formed from a material containing tantalum (Ta), can be etched by dry etching using a gas containing chlorine (Cl) or a gas containing fluorine (F).

[0079] In dry etching of the tantalum (Ta)-containing absorption film 5, dry etching using a fluorine (F) gas is preferable when etching the oxygen (O)-containing portions formed by spontaneous oxidation, and dry etching using a chlorine (Cl) gas is preferable when etching the oxygen-free portions. Therefore, it is preferable to pattern the tantalum (Ta)-containing absorption film 5 by initially using dry etching with a fluorine (F) gas, and then switching to dry etching with a chlorine (Cl) gas midway through the process. In this case, since the etching-blocking film 4 has low resistance to dry etching with a chlorine (Cl) gas, it is preferable to etch in a way that leaves the etching-blocking film 4 intact. To etch in a way that leaves the etching-blocking film 4 intact, for example, an endpoint detector attached to the etching apparatus can be used.

[0080] Furthermore, the reflective mask 110 can be manufactured by a method that includes the steps of: preparing a reflective mask blank 100; optionally, forming a resist film 9 on an etching mask film 6; forming a resist pattern from the resist film 9 on the etching mask film 6; using the resist pattern as an etching mask to etch the etching mask film 6 and form a pattern on the etching mask film 6; using the pattern on the etching mask film 6 as an etching mask to etch the absorption film 5 and form a pattern on the absorption film 5; removing the resist pattern; removing the pattern on the etching mask film 6; and removing the etching-blocking film 4 from the portion exposed after the absorption film 5 has been removed.

[0081] After forming the pattern of the absorption film 5, the pattern of the etching mask film 6 can be removed by dry etching using a gas containing chlorine (Cl) or fluorine (F) if the etching mask film 6 is made of a material containing tantalum (Ta), or by dry etching using a gas containing chlorine (Cl) and oxygen (O) if the etching mask film 6 is made of a material containing chromium (Cr).

[0082] If the absorption film 5 contains tantalum (Ta), the etching mask film 6 is made of a film containing chromium (Cr), and the etching mask film 6 is patterned by dry etching using a gas containing chlorine (Cl) and oxygen (O) to form a pattern on the etching mask film 6. After patterning the absorption film 5 using the pattern on the etching mask film 6 as an etching mask, the etching mask film 6 can be removed by dry etching using a gas containing chlorine (Cl) and oxygen (O).

[0083] In this case, the etching-blocking film 4 containing niobium (Nb) is not etched by dry etching using a gas containing chlorine (Cl) and oxygen (O), thus preventing damage to the protective film 3.

[0084] The resist pattern and the etching-blocking film 4 in the areas exposed after the absorption film 5 has been removed can be removed by sulfuric acid peroxide (SPM).

[0085] Furthermore, the etching-blocking film 4 in the area exposed after the absorption film 5 has been removed can also be removed by dry etching using a gas containing chlorine (Cl) or fluorine (F), but it is preferable to remove it with sulfuric acid peroxide (SPM). In this case, the etching-blocking film 4 can be removed simultaneously with the removal of the resist pattern.

[0086] The pattern of the absorption film 5 and the exposed protective film 3 can be subjected to treatments that involve contact with sulfuric acid peroxide (SPM), such as cleaning with sulfuric acid peroxide (SPM). [Examples]

[0087] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0088] [Example 1] On one main surface of a precisely polished, titania-doped, low-coefficient-of-thermal-expansion substrate 1, a multilayer reflective film 2 was formed by sputtering 40 alternating pairs (periods) of 3 nm thick molybdenum (Mo) and 4 nm thick silicon (Si) layers. The top layer of the multilayer reflective film 2 was made of 1 nm thick Mo. Next, a 1.2 nm thick ruthenium (Ru) film was deposited on the multilayer reflective film 2 as a protective film 3, followed by a 2 nm thick rhodium (Rh) film formed by sputtering. The reflectivity of this multilayer reflective film 2 and protective film 3 is 64% when EUV light with a wavelength of 13.5 nm is incident at an angle of incidence of 6°.

[0089] Next, a 2 nm thick niobium oxide (NbO) film (Nb:O=2:5 (atomic ratio)) was formed on the protective film 3 as an etching-blocking film 4. The niobium oxide (NbO) film was formed by first applying 750 W of power to a niobium (Nb) target and forming a niobium (Nb) film by sputtering while flowing argon (Ar) gas at a flow rate of 12 sccm, and then oxidizing the niobium (Nb) film by heat treatment at 150°C for 10 minutes in air.

[0090] Next, a chromium nitride (CrN) film with a thickness of 45 nm (Cr:N=4:1 (atomic ratio)) was formed on the etching-blocking film 4 as an absorption film 5. The chromium nitride (CrN) film was formed by sputtering while applying 1000 W of power to a chromium (Cr) target and flowing argon (Ar) gas at a flow rate of 20 sccm and nitrogen (N2) gas at 10 sccm.

[0091] Furthermore, a 70 nm thick tantalum nitride (TaN) film was formed as a conductive film 50 on the other main surface of the substrate 1 by sputtering to obtain a reflective mask blank 100.

[0092] A reflective mask 110 was manufactured from the obtained reflective mask blank 100. First, an electron beam (EB) resist was applied to the absorption film 5 to form a resist film 9. A pattern was drawn on the resist film 9 using an electron beam (EB), and the film was developed to form a resist pattern having a line-and-space (L / S) pattern with a line width of 200 nm.

[0093] Next, using the resist pattern as an etching mask, the absorption film 5 was patterned by dry etching using a gas containing chlorine (Cl2) gas and oxygen (O2) gas to form a pattern on the absorption film 5. Dry etching was performed using an inductively coupled plasma (ICP) method under the following conditions: Cl2 flow rate: 185 sccm, O2 flow rate: 55 sccm, He flow rate: 9.25 sccm, pressure: 6 mTorr (0.8 Pa), ICP power: 400 W, RIE voltage: 700 V, and over-etching: 454 seconds. At this stage, when the cross-section of the etched portion of the absorption film 5 was observed with a transmission electron microscope (TEM), the etching blocking film 4 remained with a thickness of 2 nm in all cases.

[0094] Next, the resist pattern was removed using sulfuric acid peroxide (SPM), and the etching-blocking film 4 in the exposed areas after the absorption film 5 was removed was also removed to obtain a reflective mask 110. When the cross-section of the area where the absorption film 5 had been etched was observed with a transmission electron microscope (TEM), the etching-blocking film 4 had been removed, but the protective film 3 remained undamaged in the same form as when it was deposited. Furthermore, good patterns of the absorption film 5 and etching-blocking film 4 were obtained.

[0095] [Example 2] After forming a multilayer reflective film 2 in the same manner as in Example 1, a rhodium (Rh) film with a thickness of 3 nm was deposited as a protective film 3. Then, in the same manner as in Example 1, an etching-blocking film 4 and an absorption film 5 were deposited, and a conductive film 50 was deposited on the other main surface of the substrate 1 to obtain a reflective mask blank 100. Next, a resist pattern was formed in the same manner as in Example 1. Then, in the same manner as in Example 1, the absorbance film 5 was patterned by dry etching using a gas containing chlorine (Cl2) gas and oxygen (O2) gas, using the resist pattern as an etching mask, to form a pattern of the absorption film 5.

[0096] Next, the resist pattern was removed using sulfuric acid peroxide (SPM), and the etching-blocking film 4 in the exposed areas after the absorption film 5 was removed was also removed to obtain a reflective mask 110. When the cross-section of the area where the absorption film 5 had been etched was observed with a transmission electron microscope (TEM), the etching-blocking film 4 had been removed, but the protective film 3 remained undamaged in the same form as when it was deposited. Furthermore, good patterns of the absorption film 5 and etching-blocking film 4 were obtained.

[0097] [Comparative Example 1] A reflective mask blank 100 was obtained in the same manner as in Example 1, except that a niobium oxide (NbO) film was not formed as the etching-blocking film 4. Next, a resist pattern was formed in the same manner as in Example 1. Then, in the same manner as in Example 1, the absorbance film 5 was patterned by dry etching using a gas containing chlorine (Cl2) gas and oxygen (O2) gas, with the resist pattern as an etching mask. When the cross-section of the etched portion of the absorbance film 5 was observed with a transmission electron microscope (TEM), it was found that the protective film 3 had become thinner and the surface had been oxidized. [Explanation of Symbols]

[0098] 1 circuit board 2 Multilayer reflective film 3 Protective film 4 Etching-blocking film 5 Absorption membrane 6 Etching mask film 41 Pattern of etching-blocking film 51 Absorption membrane patterns 100 Reflective Mask Blanks 110 Reflective Mask

Claims

1. A reflective mask blank that is used as the material for a reflective mask used in EUV lithography, which uses EUV light as the exposure light, circuit board and A multilayer reflective film that reflects exposure light is formed on one of the main surfaces of the substrate, A protective film formed on the multilayer reflective film to protect the multilayer reflective film, An absorption film that absorbs exposure light is formed above the protective film, An etching-blocking film containing niobium (Nb) is provided between the protective film and the absorption film, Equipped with, The protective film has at least one layer containing rhodium (Rh), A reflective mask blank characterized in that the layer in contact with the protective film in the multilayer reflective film contains molybdenum (Mo).

2. The reflective mask blank according to claim 1, characterized in that the protective film is made of rhodium (Rh).

3. The reflective mask blank according to claim 1, characterized in that the protective film consists of a layer containing rhodium (Rh) and ruthenium (Ru).

4. The reflective mask blank according to claim 1, characterized in that the protective film comprises a layer containing rhodium (Rh) and a layer containing ruthenium (Ru).

5. The etching-blocking film is characterized by being composed of niobium (Nb) or a niobium (Nb) compound containing niobium (Nb) and oxygen (O).

6. A method for manufacturing a reflective mask, comprising manufacturing a reflective mask from a reflective mask blank according to claim 1 or 2.

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