Reflective mask blank and method for manufacturing a reflective mask blank

Abstract

At the interface between the tantalum nitride (TaN) and tantalum oxide (TaO) portions, a TaON layer is inevitably formed, and if crystal precipitation occurs, there are concerns about deterioration of the film's surface roughness, pattern shape, and lithographic properties. [Solution] The reflective mask blank of the present invention comprises at least a substrate 10, a multilayer reflective film 50 formed on the substrate 10 that reflects exposure light, and a multilayer film 200 containing tantalum, and is used in EUV lithography using EUV light as the exposure light. The multilayer film 200 has a TaN portion, a TaO portion, and a Ta portion provided between the TaN portion and the TaO portion. The density of the Ta portion is greater than the density of the TaN portion and the TaO portion. The density of the Ta portion is 13 g / cm³ 3 That's all.

Description

[Technical Field]

[0001] This invention relates to a reflective mask blank, which is a material for reflective masks used in the manufacture of semiconductor devices such as LSIs, and a method for manufacturing a reflective mask blank. [Background technology]

[0002] In the manufacturing process of semiconductor devices (semiconductor devices), photolithography is repeatedly used, in which an exposure light is shone onto a transfer mask, and the circuit pattern formed on the mask is transferred onto a semiconductor substrate (semiconductor wafer) via a reduction projection optical system. Conventionally, the wavelength of the exposure light has mainly been 193 nm using argon fluoride (ArF) excimer laser light, and by employing a process called multi-patterning, which combines multiple exposure and processing processes, patterns with dimensions smaller than the exposure wavelength have ultimately been formed.

[0003] However, with the continuous miniaturization of device patterns, the formation of even finer patterns has become necessary. As a result, EUV lithography technology, which uses extreme ultraviolet (EUV) light with an even shorter wavelength than ArF excimer laser light as exposure light, has come into use. EUV light is light with a wavelength of approximately 0.2 to 100 nm, more specifically, light with a wavelength of around 13.5 nm. Because this EUV light has extremely low transmittance to materials, conventional transmission-type projection optics and masks cannot be used, and reflective optical elements are used instead. Therefore, reflective masks are also used for pattern transfer.

[0004] A reflective mask consists of a multilayer reflective film that reflects EUV light formed on a substrate, with an absorbent film that absorbs EUV light formed in a pattern on top of the multilayer reflective film. On the other hand, the state before patterning the absorbent film (including the state where a resist film has been formed) is called a reflective mask blank, and this is used as the material for the reflective mask.

[0005] 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 (the front surface), and an absorber film that absorbs EUV light formed on top of it. As the multilayer reflective film, a multilayer reflective film that obtains the required reflectivity for EUV light is usually used by alternately stacking molybdenum (Mo) layers and silicon (Si) layers. On the other hand, as the absorber film, tantalum (Ta), which has a relatively large extinction coefficient for EUV light, is used (Japanese Patent Application Publication No. 2002-246299 (Patent Document 1)). Furthermore, as a protective film to protect the multilayer reflective film, a ruthenium (Ru) film is formed on top of the multilayer reflective film, as disclosed in Japanese Patent Application Publication No. 2002-122981 (Patent Document 2).

[0006] In addition, a hard mask film may be formed on top of the absorber film as an etching mask when forming patterns on the absorber film. The hard mask film is selected from a material that ensures a sufficient selectivity ratio between the absorber film and etching.

[0007] On the other hand, a back-side conductive film is formed on the other main surface (back side) of the substrate. As the back-side conductive film, a metal nitride film has been proposed for electrostatic chucking, and films mainly containing chromium (Cr), tantalum (Ta), etc., are examples. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2002-246299 [Patent Document 2] Japanese Patent Publication No. 2002-122981 [Overview of the project] [Problems that the invention aims to solve]

[0009] When a film containing tantalum (Ta) is, for example, an absorber film, if the absorber layer of the absorber film is made of tantalum nitride (TaN), a tantalum oxide (TaO) portion may be formed on the surface as a reflectance reduction layer to reduce reflectance at the inspection wavelength, thus forming a tantalum oxide (TaO) portion and a tantalum nitride (TaN) portion. When forming a film containing a tantalum nitride (TaN) portion and a tantalum oxide (TaO) portion, a TaON layer will inevitably be formed at the interface between the tantalum nitride (TaN) portion and the tantalum oxide (TaO) portion. However, near this interface with a TaON composition, each element may attempt to adopt a stable structure in certain areas, which can lead to crystal precipitation. In particular, when forming a film in the same chamber and on the same target during film deposition, a thick TaON intermediate layer tends to form, making crystal precipitation more likely. When crystal precipitation occurs in the film, it is undesirable because it can lead to deterioration of the film's surface roughness, pattern shape, and lithography properties.

[0010] The present invention was made to solve the above-mentioned problems, and aims to provide a reflective mask blank and a method for manufacturing a reflective mask blank that can produce a reflective mask with low surface roughness and good defect inspection sensitivity. [Means for solving the problem]

[0011] The inventors of this application have provided a multilayer film containing a TaN portion and a TaO portion, wherein Ta is contained between the TaN portion and the TaO portion, and its density is greater than that of the TaN portion and the TaO portion, at 13 g / cm³. 3 By adding the above-mentioned Ta portion, we discovered that a smooth film can be formed without precipitating crystals at the interface between the TaN portion and the TaO portion, leading to the present invention.

[0012] Accordingly, the present invention provides the following reflective mask blank.

[0013] [Concept 1] The reflective mask blank according to the present invention is An EUV reflective mask blank used in EUV lithography with EUV light as exposure light, comprising at least a substrate, a multilayer reflective film formed on the substrate for reflecting the exposure light, and a multilayer film containing tantalum. The multilayer film has a TaN part, a TaO part, and a Ta part provided between the TaN part and the TaO part. The density of the Ta part is greater than the densities of the TaN part and the TaO part. The density of the Ta part may be 13 g / cm 3 or more.

[0014] [Concept 2] In the reflective mask blank according to Concept 1, the multilayer film may be laminated in the order of a TaN part, a Ta part, and a TaO part from the substrate side.

[0015] [Concept 3] In the reflective mask blank according to Concept 1 or 2, the film thickness of the Ta part may be 1 nm or more and less than 3 nm.

[0016] [Concept 4] In the reflective mask blank according to any one of Concepts 1 to 3, the TaN part may substantially not contain oxygen, the tantalum (Ta) may be less than 70 atomic%, and the nitrogen (N) may be more than 30 atomic%.

[0017] [Concept 5] In the reflective mask blank according to any one of Concepts 1 to 4, the TaO part may substantially not contain nitrogen, the tantalum (Ta) may be less than 70 atomic%, and the oxygen (O) may be more than 30 atomic%, or the TaO part may contain less than 5 atomic% of any one or more of boron (B), carbon (C), hydrogen (H), and silicon (Si) in addition to tantalum (Ta) and oxygen (O).

[0018] [Concept 6] In the reflective mask blank according to any one of Concepts 1 to 5, The Ta portion substantially contains no elements other than tantalum (Ta), or The total content of nitrogen (N) and oxygen (O) in the Ta portion may be less than 20 atomic percent.

[0019] [Concept 7] In a reflective mask blank based on any one of concepts 1 to 6, The aforementioned multilayer film may function as an absorbent film.

[0020] [Concept 8] In a reflective mask blank according to Concept 7, The system further comprises a hard mask used as an etching mask when processing the multilayer film that functions as an absorbent membrane, The hard mask film may contain chromium (Cr).

[0021] [Concept 9] In a reflective mask blank based on any one of concepts 1 to 6, The multilayer film comprises a first multilayer film having a TaN portion, a TaO portion, and a Ta portion provided between the TaN portion and the TaO portion, and a second multilayer film having a TaN portion, a TaO portion, and a Ta portion provided between the TaN portion and the TaO portion. The first multilayer film functions as an absorbent film, The second multilayer film functions as a hard mask used as an etching mask when processing the first multilayer film, which is the absorber film. The thickness of the first multilayer film is 55 nm or more and less than 70 nm. The thickness of the second multilayer film may be 20 nm or less.

[0022] [Concept 10] A method for manufacturing a reflective mask blank according to any one of concepts 1 to 9, The Ta portion may be formed between the TaN portion and the TaO portion by depositing a tantalum (Ta) film in an atmosphere free of oxygen and nitrogen.

[0023] [Concept 11] In the method for manufacturing a reflective mask blank described in Concept 10, After forming the TaN portion, Ta is deposited in an atmosphere free of oxygen and nitrogen to form the Ta portion. The TaO portion may be formed by oxidizing the surface of the Ta portion that is separated from the substrate. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide a reflective mask blank that can be used to produce a reflective mask with low surface roughness and good defect inspection sensitivity. [Brief explanation of the drawing]

[0025] [Figure 1] A longitudinal cross-sectional view showing a reflective mask blank according to an embodiment of the present invention, in which a multilayer film functions as an absorbent film. [Figure 2] A longitudinal cross-sectional view showing a reflective mask blank according to an embodiment of the present invention, in which the multilayer film functions as an absorber film and a hard mask film. [Figure 3] A longitudinal cross-sectional view showing an example of the configuration of a multilayer film according to an embodiment of the present invention, in which the multilayer film functions as an absorbent film. [Figure 4] A longitudinal cross-sectional view showing another example of the configuration of a multilayer film according to an embodiment of the present invention, in which the multilayer film functions as an absorbent film. [Figure 5] A longitudinal cross-sectional view showing an example of the configuration of a multilayer film according to an embodiment of the present invention, in which the multilayer film functions as an absorber film and a hard mask film. [Figure 6] A longitudinal cross-sectional view showing an embodiment of the present invention in which the TaN portion of the multilayer film functions as an absorber film and the TaO portion functions as a hard mask film. [Figure 7] A longitudinal cross-sectional view showing an embodiment of the present invention in which an auxiliary layer is provided on the lower surface of a multilayer film. [Figure 8] A longitudinal cross-sectional view showing an embodiment of the present invention in which an auxiliary layer is provided on the upper surface of a multilayer film. [Figure 9] A longitudinal cross-sectional view showing a reflective mask blank according to an embodiment of the present invention, in which a resist film is provided. [Figure 10] A longitudinal cross-sectional view showing a reflective mask blank according to an embodiment of the present invention, in which the resist film and the hard mask film are patterned. [Figure 11] A longitudinal cross-sectional view showing a reflective mask blank according to an embodiment of the present invention, in which the absorbent film is patterned. [Modes for carrying out the invention]

[0026] Embodiments of the present invention will be described below. As shown in Figures 1 and 2, the reflective mask blank of this embodiment includes a substrate 10, a multilayer reflective film 50 that reflects exposure light formed on one of the main surfaces (front surface) of the substrate 10, and an absorber film 120 that absorbs exposure light. A protective film 110 protecting the multilayer reflective film 50 may be provided between the multilayer reflective film 50 and the absorber film 120. A hard mask film 130 may be further formed on the front surface (upper surface) of the absorber film 120. A back surface conductive film 150 may be formed on the back surface (bottom surface) of the substrate 10. Furthermore, as shown in Figure 9, a resist film 140 may be formed on the front surface (upper surface) of the hard mask film 130.

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

[0028] The reflective mask blank used in EUV lithography using EUV light as the exposure light in this embodiment comprises at least a substrate 10, a multilayer reflective film 50 formed on the substrate 10 that reflects the exposure light, and a multilayer film 200 containing tantalum.

[0029] As shown in Figures 3 and 4, the tantalum-containing multilayer film 200 has a TaN (tantalum nitride) portion 210, a TaO (tantalum oxide) portion 230, and a Ta (tantalum) portion 220 located between the TaN portion 210 and the TaO portion 230. The density of the Ta portion 220 is greater than the densities of the TaN portion 210 and the TaO portion 230. The density of the Ta portion 220 is 13 g / cm³. 3 This concludes the explanation. By doing so, it is possible to prevent the precipitation of crystals at the interface between the TaO portion 230 and the TaN portion 210, thereby preventing a decrease in surface roughness.

[0030] The TaN (tantalum nitride) portion 210 is a layer mainly composed of tantalum and nitrogen, the TaO (tantalum oxide) portion 230 is a layer mainly composed of tantalum and oxygen, and the Ta portion 220 contains tantalum. Preferably, the Ta portion 220 is a film with less oxygen than the TaO (tantalum oxide) portion 230 and less nitrogen than the TaN (tantalum nitride) portion 210.

[0031] The multilayer film 200 containing tantalum described above can be used as a pattern-forming film, and pattern-forming films include absorber films 120 and hard mask films 130 (see Figures 10 and 11).

[0032] In the multilayer film 200, it is preferable that the TaN portion 210, Ta portion 220, and TaO portion 230 are stacked in that order from the substrate 10 side (the back side of the reflective mask blank) (see Figure 3). By forming it in this way, it becomes easier to reduce the reflectance at the inspection wavelength when used, for example, as an absorber film 120. Also, since the etching characteristics of the TaO portion 230 are different from those of the TaN portion 210, the TaO portion 230 can be used as an etching mask (hard mask) for the TaN portion 210 during pattern formation.

[0033] However, the configuration is not limited to this example, and in the multilayer film 200, the TaO portion 230, the Ta portion 220, and the TaN portion 210 may be laminated in that order from the substrate 10 side (the back side of the reflective mask blank) (see Figure 4).

[0034] The density of the Ta part 220 is 13 g / cm 3 or more and 17 g / cm 3 or less, more preferably 16 g / cm 3 or less. The density of the TaN part 210 is 10 g / cm 3 or more and 12 g / cm 3 or less. The density of the TaO part 230 is 3 g / cm 3 or more and 10 g / cm 3 or less.

[0035] The film thickness of the Ta part 220 is preferably 1 nm or more and less than 3 nm. If the film thickness of the Ta part 220 becomes thinner than 1 nm and the film thickness becomes too thin, the effect of preventing crystal precipitation becomes weak. On the other hand, if the film thickness of the Ta part 220 becomes 3 nm or more, crystal growth of Ta occurs, etc., which is disadvantageous in terms of an increase in film stress, deterioration of surface roughness, and deterioration of irradiation resistance to exposure light.

[0036] The TaN part 210 preferably contains substantially no oxygen, and the tantalum (Ta) is less than 70 atomic% and the nitrogen (N) is more than 30 atomic%. Containing substantially no oxygen means that the oxygen content is 2 atomic% or less.

[0037] The TaO part 230 preferably contains substantially no nitrogen, and the tantalum (Ta) is less than 70 atomic% and the oxygen (O) is more than 30%, or contains less than 5 atomic% of any one or more of boron (B), carbon (C), hydrogen (H), and silicon (Si) in addition to tantalum (Ta) and oxygen (O). Containing substantially no nitrogen means that the nitrogen content is 2 atomic% or less.

[0038] The composition of the Ta portion 220 is preferably substantially free of elements other than tantalum (Ta), or the total content of nitrogen (N) and oxygen (O) is less than 20 atomic percent. Substantially free of elements other than tantalum (Ta) means that the tantalum content is 95 atomic percent or more. Furthermore, from the viewpoint of reducing surface roughness, it is preferable that the Ta portion 220 is substantially free of elements other than tantalum (Ta).

[0039] The absorber membrane 120 can have a multilayer structure that includes at least all of the TaN portion 210, the Ta portion 220, and the TaO portion 230 (see Figure 1).

[0040] Furthermore, both the absorber film 120 and the hard mask film 130 can have a multilayer structure that includes all of the TaN portion 210, Ta portion 220, and TaO portion 230 (see Figure 2). In this case, as shown in Figure 5, the multilayer film 200 may have a first multilayer film 200a having a first TaN portion 210a, a first TaO portion 230a, and a first Ta portion 220a provided between the first TaN portion 210a and the first TaO portion 230a, and a second multilayer film 200b having a second TaN portion 210b, a second TaO portion 230b, and a second Ta portion 220b provided between the second TaN portion 210b and the second TaO portion 230b. The first multilayer film 200a may function as the absorber film 120. The second multilayer film 200b may function as the hard mask film 130 used as an etching mask when processing the first multilayer film 200a, which is the absorber film 120. When the first multilayer film 200a functions as an absorber film 120, the thickness of the first multilayer film 200a is preferably 55 nm or more and less than 70 nm. When the second multilayer film 200b functions as a hard mask film 130, the thickness of the second multilayer film 200b is preferably 20 nm or less.

[0041] Alternatively, the absorber film 120 may be composed solely of a multilayer film 200 consisting only of a TaN portion 210, a Ta portion 220, and a TaO portion 230. In this case, the hard mask film 130 used as an etching mask when processing the absorber film 120 may be a film containing Cr (Cr-containing film) (see Figures 3 and 4).

[0042] Furthermore, the TaN portion 210 and the TaO portion 230 may function as an absorber film 120 that forms a pattern and a hard mask film 130 used as an etching mask when processing the absorber film 120, respectively. This allows for etching selectivity. In particular, as shown in Figure 6, the absorber membrane 120 may be composed of the TaN portion 210 and the hard mask membrane 130 may be composed of the TaO portion 230. In this case, the Ta portion 220 will function, for example, as part of the absorber membrane 120.

[0043] The absorber film 120 may have a phase-shifting function. Furthermore, the absorber film 120 may have a structure with a buffer layer below it that is resistant to etching conditions during pattern formation and modification of the upper layer.

[0044] When a layer containing Ta is used as the absorber film 120, the absorber film 120 may consist only of a multilayer film 200 containing Ta, or it may have a layer containing one or more of Ru, Rh, Ir, Pt, Nb, and Cr. The multilayer film 200 containing Ta may be provided on the side of the layer 250 containing one or more of Ru, Rh, Ir, Pt, Nb, and Cr that is spaced away from the substrate 10 (see Figure 7). Alternatively, a layer 250 containing one or more of Ru, Rh, Ir, Pt, Nb, and Cr may be provided on the side of the multilayer film 200 that is spaced away from the substrate 10 (see Figure 8). In this case, the multilayer film 200 containing Ta provided on the substrate 10 side of the layer 250 containing one or more of Ru, Rh, Ir, Pt, Nb, and Cr can function as a buffer layer, which is preferable.

[0045] The Ta-containing multilayer film 200 can be formed by sputtering, and magnetron sputtering is preferred. For example, it can be formed by reactive sputtering using a tantalum (Ta) target and noble gases such as helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) as sputtering gases, along with nitrogen (N2) or oxygen (O2) gas depending on the film composition.

[0046] For example, the Ta portion 220 can be formed by depositing Ta between the TaN (tantalum nitride) portion 210 and the TaO (tantalum oxide) portion 230 in an atmosphere free of oxygen and nitrogen.

[0047] Alternatively, after forming the TaN (tantalum nitride) portion 210, a Ta film may be deposited in an atmosphere free of oxygen and nitrogen to form the Ta portion 220, and then the surface of the Ta portion 220 that is separated from the substrate 10 (the front surface) may be oxidized to form the TaO (tantalum oxide) portion 230 on the surface of the Ta portion 220. For heat treatment, the material may be heated in an oxygen-containing atmosphere, such as air, at a temperature of 120°C to 200°C for 5 to 60 minutes using, for example, a hot plate type heating device.

[0048] The substrate 10 preferably has low thermal expansion characteristics for use with EUV light exposure, for example, a thermal expansion coefficient of ±2 × 10 -8 Within / ℃, preferably ±5 × 10 -9It is preferable that the substrate is made of a material within a temperature range of / ℃ or less. Examples of such materials include titania-doped quartz glass (SiO2-TiO2 glass). Furthermore, it is preferable that the substrate 10 has a sufficiently flattened surface, and the surface roughness of the main surface of the substrate 10 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 10. The size of the substrate 10 is preferably 152 mm square for the main surface and 6.35 mm thick. A substrate 10 of this size is a so-called 6025 substrate 10 (a substrate 10 with a main surface size of 6 inches square and a thickness of 0.25 inches).

[0049] The multilayer reflective film 50 is a film that reflects exposure light in a reflective mask. The multilayer reflective film 50 is preferably provided in contact with one main surface (front surface) of the substrate 10, but other films, such as an undercoat, may be provided between it and the main surface of the substrate 10. The multilayer reflective film 50 has a periodic stacked structure 51 in which a high refractive index layer 20 with a relatively high refractive index to exposure light and a low refractive index layer 30 with a relatively low refractive index to exposure light are alternately stacked (see Figures 1 and 2).

[0050] The high refractive index layer 20 is preferably made of a material containing silicon (Si). The high refractive index layer 20 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 high refractive index layer 20 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.

[0051] The low refractive index layer 30 is preferably made of a material containing molybdenum (Mo). Alternatively, the low refractive index layer 30 may be made of a material containing ruthenium (Ru). The low refractive index layer 30 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 consisting of a layer containing additive elements and a layer not containing additive elements. The thickness of the low refractive index layer 30 is preferably 2.1 nm or more, more preferably 2.6 nm or more, and more preferably 3.5 nm or less, more preferably 3 nm or less.

[0052] The periodic stacked structure 51 only needs to include a high refractive index layer 20 and a low refractive index layer 30, and each period should contain one or more high refractive index layers 20 and one or more low refractive index layers 30. The number of layers in the periodic stacked structure 51 is two or more, and the periodic stacked structure 51 can be composed of, for example, one high refractive index layer 20 and one low refractive index layer 30. It may also contain two or more high refractive index layers 20 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 30 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 in the periodic stacked structure 51 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 30 or more, preferably 50 or less, and more preferably 40 or less. When the low refractive index layer 30 is formed of a material containing ruthenium (Ru), it is preferable that the layer furthest from the substrate 10 of the periodic stacked structure 51 (the uppermost layer) is the high refractive index layer 20.

[0053] The thickness of the multilayer reflective film 50 having a periodic stacked structure 51 is adjusted according to the exposure wavelength and the angle of incidence of the exposure light, but is preferably 200 nm or more, more preferably 270 nm or more, and also preferably 400 nm or less, more preferably 290 nm or less.

[0054] Methods for forming the multilayer reflective film 50 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.

[0055] The multilayer reflective film 50 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.

[0056] 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.

[0057] 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.

[0058] As shown in Figures 1 and 2, a protective film 110 may be provided above the multilayer reflective film 50. The protective film 110 is also called a capping film. The protective film 110 is a film for protecting the multilayer reflective film 50. The protective film 110 is usually provided in contact with the multilayer reflective film 50. The protective film 110 is made of a material containing ruthenium (Ru).

[0059] Materials containing ruthenium (Ru) include elemental ruthenium (Ru), and alloys consisting of ruthenium (Ru) and a metal or metalloid other than ruthenium (Ru). Examples of metals or metalloids other than ruthenium (Ru) include niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si). The content of the metal or metalloid other than ruthenium (Ru) in the protective film 110 is preferably 30 atomic% or less, more preferably 20 atomic% or less. The lower limit of the content of the metal or metalloid other than ruthenium (Ru) in the protective film 110 is not particularly limited, but is preferably 5 atomic% or more, more preferably 10 atomic% or more.

[0060] The protective film 110 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 110 that is close to the multilayer reflective film 50 (in the case of a multilayer structure, the layer close to the multilayer reflective film 50) and the side that is furthest from the multilayer reflective film 50 (in the case of a multilayer structure, the layer furthest from the multilayer reflective film 50) may be made of ruthenium (Ru).

[0061] Furthermore, if the protective film 110 has a multilayer structure or a gradient composition structure, it is preferable that the content of a metal or metalloid other than ruthenium (Ru) increases in part or all of the thickness direction of the protective film 110 from the multilayer reflective film 50 side toward the side away from the multilayer reflective film 50. In particular, if niobium (Nb) is included as the metal or metalloid other than ruthenium (Ru), the inclusion of niobium (Nb) is also effective in improving resistance to dry etching using a gas containing chlorine (Cl) and oxygen (O). Therefore, it is preferable that the content of niobium (Nb) increases in part or all of the thickness direction of the protective film 110 from the multilayer reflective film 50 side toward the side away from the multilayer reflective film 50.

[0062] In this embodiment, a specific example of dry etching using a gas containing chlorine (Cl) and oxygen (O) is 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.

[0063] The thickness of the protective film 110 is preferably 2 nm or more, more preferably 3 nm or more, and also preferably 5 nm or less, more preferably 4 nm or less. If the thickness of the protective film 110 is less than 2 nm, the protective function of the multilayer reflective film 50 will be insufficient, and if it exceeds 5 nm, the reflectivity of EUV light will decrease.

[0064] The protective film 110 is a target made of a ruthenium (Ru) target, a target made of a metal or metalloid other than ruthenium (Ru), specifically a niobium (Nb) target, a rhenium (Re) target, a zirconium (Zr) target, a titanium (Ti) target, a chromium (Cr) target, a silicon (Si) target, or a mixture of two or more selected from niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si). The material can be formed by appropriately selecting a target from among those containing ruthenium (Ru) mixed with one or more metals or metalloids other than ruthenium (Ru), selected from niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si), and sputtering with a noble gas such as helium (He), argon (Ar), krypton (Kr), or xenon (Xe) as the sputtering gas. Magnetron sputtering is preferred for sputtering.

[0065] Heat treatment may be performed after the formation of the multilayer reflective film 50 or the protective film 110. Heat treatment can suppress changes in properties such as reflectance to EUV light that occur when heat is applied during mask pattern formation. The heat treatment temperature is generally preferably between 120°C and 150°C, and temperatures higher than 150°C are undesirable because they reduce the reflectance to EUV light.

[0066] The heat treatment may be performed either after the formation of the multilayer reflective film 50 or the protective film 110, or both. However, fewer heat treatments are preferable from the viewpoint of concerns about defect adhesion and productivity, and it is preferable to perform the heat treatment after the formation of the protective film 110.

[0067] On the other hand, if heat treatment is performed after the formation of the protective film 110, an oxide film may form on the surface of the protective film 110, which may reduce its reflectivity to pattern inspection light. Furthermore, even if heat treatment is not performed after the formation of the protective film 110, oxidation of the surface layer of the protective film 110 after pattern formation is quite possible. Therefore, the reflectivity of the absorption film to pattern inspection light must be set to a reflectivity that takes into account the oxidation of the protective film 110.

[0068] As shown in Figures 1 and 2, a conductive film (back surface conductive film 150) may be provided on the other main surface (back surface), which is the surface opposite to one main surface (front surface) of the substrate 10, preferably in contact with the other main surface, for electrostatically chucking the reflective mask to the exposure apparatus (e.g., EUV scanner).

[0069] The back conductive film 150 preferably has a sheet resistance of 100 Ω / □ or less, and there are no particular restrictions on the material. Examples of materials for the back conductive film 150 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.

[0070] The thickness of the back conductive film 150 is not particularly limited, as long as it functions for electrostatic chucks, but is usually around 20 to 300 nm. The thickness of the back conductive film 150 is preferably formed so that the film stress is balanced with the film and film pattern formed on one of the main surfaces (front side) after it has been formed as a reflective mask, i.e., after the absorption film pattern has been formed. The back conductive film 150 may be formed before forming the multilayer reflective film 50, or after all the films on the multilayer reflective film 50 side of the substrate 10 have been formed, or a portion of the films on the multilayer reflective film 50 side of the substrate 10 may be formed first, then the back conductive film 150 may be formed, and then the remaining films on the multilayer reflective film 50 side of the substrate 10 may be formed. The back conductive film 150 can be formed, for example, by magnetron sputtering. [Examples]

[0071] The present invention will be explained in detail below with reference to experimental and comparative examples, but it is not limited to the experimental examples. Furthermore, depending on the original function of the reflective mask blank, the film should be deposited on a multilayer reflective film 50, a protective film 110, or an absorber film 120. However, in the experimental examples, the film was simply deposited on a quartz substrate 10 in order to compare the interface state of the multilayer structure. The effects of the present invention can be reproduced without change whether on the quartz substrate 10 or on each layer.

[0072] [Example 1] A multilayer film 200 containing Ta, which functions as either a reflective mask blank absorber film 120, a hard mask film 130, or a buffer layer in the absorber film 120, was deposited on the main surface of a 152 mm square, 6.35 mm thick quartz glass substrate 10 by DC pulsed magnetron sputtering while the substrate 10 was rotating. The buffer film is used to prevent the lower film from being directly exposed to etching gas when the upper film is etched, thereby suppressing film loss of the lower film.

[0073] A quartz glass substrate 10 was placed in the chamber. First, Ar gas (40 vol%) and N2 gas (60 vol%) were introduced, and the chamber pressure was set to 0.48 Pa. A power of 1,800 W was applied to the tantalum (Ta) target to form a TaN layer (TaN portion 210). Next, with the substrate 10 still in place in the chamber, Ar gas (100 vol%) was introduced, and the chamber pressure was set to 0.07 Pa. The conditions were changed to apply a power of 500 W to the tantalum (Ta) target to form a Ta layer (Ta portion 220) with a thickness of 1 nm. Subsequently, in the same chamber, Ar gas (30 vol%) and O2 gas (70 vol%) were introduced, and the chamber pressure was set to 0.15 Pa. The conditions were changed to apply a power of 500 W to the tantalum (Ta) target to deposit a TaO layer (TaO portion 230) with a thickness of 4.5 nm.

[0074] The density and thickness of each layer of the obtained Ta-containing multilayer film 200 were determined using XRR (X-ray reflectivity method) with an X-ray diffractometer (SmartLab, Rigaku). The results showed that the thickness of the TaN layer was 20.7 nm and its density was 11.0 g / cm³.3 The Ta layer thickness was 1.0 nm, and its density was 13.0 g / cm³. 3 The TaO layer thickness was 4.8 nm, and its density was 8.2 g / cm³. 3 That was the case.

[0075] The composition of the obtained Ta-containing multilayer film 200 was measured using an X-ray photoelectron spectroscopy (XPS) instrument (Thermo Fisher SCIENTIFIC, K-Alpha). The TaN layer contained 45 atomic percent tantalum (Ta) and 55 atomic percent nitrogen (N) relative to the total of tantalum (Ta) and nitrogen (N), while the TaO layer contained 34 atomic percent tantalum (Ta) and 66 atomic percent oxygen (O) relative to the total of tantalum (Ta) and nitrogen (O).

[0076] When a cross-section of the obtained multilayer film 200, including a portion of the substrate 10 and the entire multilayer film 200, was cut using a focused ion beam (FIB) system (FEI, Helios G4 CX), and observed with a transmission electron microscope (TEM) system (JEOL Ltd., ARM200F), no crystal deposition was observed between the TaN layer and the TaO layer, and each layer was formed smoothly. As a result of the reduced surface roughness of the TaN layer, Ta layer, and TaO layer, the sensitivity for defect inspection can be improved.

[0077] [Example 2] A multilayer film 200 containing Ta, which functions as either a reflective mask blank absorber film 120, a hard mask film 130, or a buffer layer in the absorber film 120, was formed on the main surface of a 152 mm square, 6.35 mm thick quartz glass substrate 10, in the same manner as in Example 1, except that the thickness of the Ta layer (TaO portion 230) was 2 nm.

[0078] The resulting Ta-containing multilayer film 200 was subjected to XRR to determine the density and film thickness of each layer, similar to Example 1. The TaN layer had a film thickness of 21.0 nm and a density of 10.9 g / cm³. 3 The Ta layer thickness was 1.1 nm, and its density was 16.6 g / cm³. 3The TaO layer thickness was 4.5 nm, and its density was 8.3 g / cm³. 3 That was the case.

[0079] Similar to Example 1, no crystal precipitation was observed between the TaN layer and the TaO layer using a transmission electron microscope, and each layer was smoothly formed. Because the surface roughness of the TaN layer, Ta layer, and TaO layer is reduced in this way, the sensitivity for defect inspection can be improved.

[0080] [Example 3] A multilayer film 200 containing Ta, which functions as either a reflective mask blank absorber film 120, a hard mask film 130, or a buffer layer within the absorber film 120, was formed on the main surface of a 152 mm square, 6.35 mm thick quartz glass substrate 10.

[0081] First, a TaN layer was formed under the same conditions as in Example 1. Similarly, a Ta layer was formed with a thickness of 2 nm under the same conditions as in Example 1. Then, without forming a TaO layer, the surface of the protective film 110 was oxidized by heat treatment at 150°C for 15 minutes in an air atmosphere using a hot plate heating device to form the TaO layer.

[0082] The density and thickness of each layer of the obtained Ta-containing multilayer film 200 were determined using XRR in the same manner as in Example 1. The result showed that the thickness of the TaN layer was 29.5 nm and the density was 11.2 g / cm³. 3 The Ta layer thickness was 2.2 nm, and the density was 16.6 g / cm³. 3 The TaO layer thickness was 1.3 nm, and its density was 3.7 g / cm³. 3 That was the case.

[0083] Observation using a transmission electron microscope, similar to Example 1, revealed no crystal precipitation between the TaN layer and the TaO layer, indicating that each layer was smoothly formed. This reduction in surface roughness between the TaN, Ta, and TaO layers improves the sensitivity of defect inspection.

[0084] [Comparative Example 1] A multilayer film 200 containing Ta, which functions as either a reflective mask blank absorber film 120, a hard mask film 130, or a buffer layer in the absorber film 120, was formed on the main surface of a 152 mm square, 6.35 mm thick quartz glass substrate 10. First, a TaN layer was formed under the same conditions as in Example 1. Next, without forming a Ta layer, a 4 nm TaO layer was formed under the same conditions as in Example 1.

[0085] The density and thickness of each layer of the obtained Ta-containing multilayer film 200 were determined using XRR in the same manner as in Example 1. The result showed that the thickness of the TaN layer was 21.9 nm and the density was 10.9 g / cm³. 3 The TaO layer thickness was 2.1 nm, and its density was 8.4 g / cm³. 3 That was the case.

[0086] Observation using a transmission electron microscope, similar to Example 1, revealed the formation of layers with different densities in both the TaN and TaO layers, which appear to be crystal precipitation, resulting in a non-uniform interface. This increased surface roughness of the TaN and TaO layers leads to poor defect inspection sensitivity.

[0087] [Comparative Example 2] A multilayer film 200 containing Ta, which functions as either a reflective mask blank absorber film 120, a hard mask film 130, or a buffer layer in the absorber film 120, was formed on the main surface of a 152 mm square, 6.35 mm thick quartz glass substrate 10, in the same manner as in Example 1, except that the thickness of the Ta layer was 0.5 nm.

[0088] The resulting Ta-containing multilayer film 200 was subjected to XRR to determine the density and film thickness of each layer, similar to Example 1. The TaN layer had a film thickness of 21.3 nm and a density of 10.9 g / cm³. 3 The Ta layer thickness was 0.5 nm, and its density was 12.0 g / cm³. 3 The TaO layer thickness was 4.8 nm, and its density was 7.3 g / cm³. 3 That was the case.

[0089] As in Example 1, observation using a transmission electron microscope revealed that layers with different densities had formed in both the TaN layer and the TaO layer, which appeared to be crystal precipitation, and the interface was formed unevenly. As a result of the increased surface roughness of the TaN layer, Ta layer, and TaO layer, the defect inspection sensitivity was poor.

[0090] [Comparative Example 3] A multilayer film 200 containing Ta, which functions as either a reflective mask blank absorber film 120, a hard mask film 130, or a buffer film within the absorber film 120, was formed on the main surface of a 152 mm square, 6.35 mm thick quartz glass substrate 10.

[0091] First, a TaN layer was formed under the same conditions as in Example 1. Next, without depositing a Ta layer, Ar gas (22 vol%), O2 gas (56 vol%), and N2 gas (22 vol%) were introduced into the same chamber, the chamber pressure was set to 0.18 Pa, and a tantalum (Ta) target was subjected to a 500 W power supply. This was then used to deposit a 4.7 nm thick TaON layer.

[0092] The density and thickness of each layer of the obtained Ta-containing multilayer film 200 were determined using XRR in the same manner as in Example 1. The result showed that the thickness of the TaN layer was 21.9 nm and the density was 11.0 g / cm³. 3 The TaON layer thickness was 4.7 nm, and its density was 7.3 g / cm³. 3 That was the case.

[0093] Observation using a transmission electron microscope, similar to Example 1, revealed that the entire TaON layer was formed with uneven density, which is undesirable. When the TaON layer is formed with uneven density in this manner, the surface roughness increases, resulting in poor defect inspection sensitivity. [Explanation of symbols]

[0094] 10 circuit boards 20 High refractive index layer 30 Low refractive index layer 50 Multilayer reflective coating 51 Periodic laminated structure part 110 Protective film 120 Absorbing membrane 130 Hard mask film 200 Multilayer film 200a First multilayer membrane (absorber membrane) 200b Second multilayer film (hard mask film) 210 TaN part 220 Ta section 230 TaO Club

Claims

1. A reflective mask blank used in EUV lithography using EUV light as the exposure light, comprising at least a substrate, a multilayer reflective film formed on the substrate that reflects exposure light, and a multilayer film containing tantalum, The multilayer film has a TaN portion, a TaO portion, and a Ta portion provided between the TaN portion and the TaO portion. The density of the Ta portion is greater than the density of the TaN portion and the TaO portion. The density of the Ta portion is 13 g / cm³. 3 A reflective mask blank characterized by the above features.

2. The reflective mask blank according to claim 1, characterized in that the multilayer film is stacked in the order of TaN portion, Ta portion, and TaO portion from the substrate side.

3. The reflective mask blank according to claim 1, characterized in that the film thickness of the Ta portion is 1 nm or more and less than 3 nm.

4. The reflective mask blank according to any one of claims 1 to 3, characterized in that the TaN portion is substantially free of oxygen, has less than 70 atomic percent tantalum (Ta), and has more than 30 atomic percent nitrogen (N).

5. The TaO portion is substantially nitrogen-free, contains less than 70 atomic percent tantalum (Ta), and contains more than 30 atomic percent oxygen (O), or The reflective mask blank according to any one of claims 1 to 3, characterized in that the TaO portion contains less than 5 atomic percent of one or more of the following: boron (B), carbon (C), hydrogen (H), and silicon (Si), in addition to tantalum (Ta) and oxygen (O).

6. The Ta portion substantially contains no elements other than tantalum (Ta), or The reflective mask blank according to any one of claims 1 to 3, characterized in that the total content of nitrogen (N) and oxygen (O) in the Ta portion is less than 20 atomic percent.

7. The reflective mask blank according to any one of claims 1 to 3, characterized in that the multilayer film functions as an absorbent film.

8. The system further comprises a hard mask used as an etching mask when processing the multilayer film that functions as an absorbent membrane, The reflective mask blank according to claim 7, characterized in that the hard mask film contains chromium (Cr).

9. The multilayer film comprises a first multilayer film having a TaN portion, a TaO portion, and a Ta portion provided between the TaN portion and the TaO portion, and a second multilayer film having a TaN portion, a TaO portion, and a Ta portion provided between the TaN portion and the TaO portion. The first multilayer film functions as an absorbent film, The second multilayer film functions as a hard mask used as an etching mask when processing the first multilayer film, which is the absorber film. The thickness of the first multilayer film is 55 nm or more and less than 70 nm. The reflective mask blank according to any one of claims 1 to 3, characterized in that the thickness of the second multilayer film is 20 nm or less.

10. A method for manufacturing a reflective mask blank according to claim 1, A method for manufacturing a reflective mask blank, characterized by forming a tantalum (Ta) film in an atmosphere free of oxygen and nitrogen, thereby forming the Ta portion between the TaN portion and the TaO portion.

11. After forming the TaN portion, Ta is deposited in an atmosphere free of oxygen and nitrogen to form the Ta portion. The method for manufacturing a reflective mask blank according to claim 10, characterized in that the Ta portion is formed by oxidizing the surface of the Ta portion that is separated from the substrate.

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