Reflection-type mask blank and method for manufacturing reflection-type mask blank

Abstract

This reflective mask blank is provided with at least: a substrate (10); a multilayer reflective film (50) formed on the substrate (10) and capable of reflecting exposure light; and a multilayer film (200) containing tantalum, the reflective mask blank being used in EUV lithography using EUV light as exposure light. The multilayer film (200) has a TaN part (210), a TaO part (230), and a Ta part (220) provided between the TaN part (210) and the TaO part (230). Wherein the density of the Ta part (220) is greater than the density of the TaN part (210) and the density of the oxygen TaO part (230), and the density of the Ta part (220) is 13 g / cm3 or more.

Description

Technical Field

[0001] The present invention relates to reflective mask blanks and a method for manufacturing reflective mask blanks as raw materials for the manufacture of reflective masks used in the manufacture of semiconductor devices such as LSIs. Background Technology

[0002] In the manufacturing process of semiconductor devices, photolithography is a technique that repeatedly exposes a transfer mask with light to transfer the circuit pattern formed on the mask onto the semiconductor substrate (semiconductor wafer) using a shrinking projection optical system. Previously, the wavelength of the exposure light was mainly 193nm using an argon fluoride (ArF) excimer laser. Through multiple patterning processes using combined exposure techniques or other processing methods, patterns smaller than the exposure wavelength are ultimately formed.

[0003] However, due to the continuous miniaturization of device patterns, further finer patterns are needed. Therefore, extreme ultraviolet (EUV) light, with a wavelength shorter than that of ArF excimer lasers, has gradually been adopted for exposure, leading to the development of EUV lithography. EUV light refers to light with a wavelength of approximately 0.2–100 nm, more specifically, light with a wavelength around 13.5 nm. This EUV light has extremely low transmittance to materials, making conventional transmissive projection optical systems or masks unsuitable. Therefore, reflective optical elements are used. Consequently, reflective masks are also used for pattern transfer.

[0004] A reflective mask is a structure in which a multilayer reflective film reflecting EUV light is formed on a substrate, and an absorber film absorbing EUV light is patterned on the multilayer reflective film. On the other hand, the film in the state before the pattern is formed on the absorber film (including the state in which a resist film has been formed) is called the reflective mask blank, which is used as the material of the reflective mask.

[0005] Reflective mask blanks generally have a basic structure including a substrate with low thermal expansion, a multilayer reflective film formed on one of the two main surfaces of the substrate to reflect EUV light, and an absorber film formed thereon to absorb EUV light. As the multilayer reflective film, a multilayer reflective film that achieves the necessary reflectivity for EUV light by alternately stacking molybdenum (Mo) layers and silicon (Si) layers is typically used. On the other hand, as the absorber film, tantalum (Ta) or similar materials with a relatively high extinction coefficient for EUV light are used (Japanese Patent Application Laid-Open No. 2002-246299). Furthermore, as a protective film for protecting the multilayer reflective film, as disclosed in Japanese Patent Application Laid-Open No. 2002-122981, a ruthenium (Ru) film is formed on the multilayer reflective film.

[0006] In addition, a hard mask film is sometimes formed on the absorber film as an etching mask when forming patterns on the absorber film. As a hard mask film, a material that can ensure the selectivity ratio of the absorber film and the etching is selected.

[0007] On the other hand, a back conductive film is formed on the other main surface (back side) of the substrate. As a back conductive film, metal nitride films are proposed for electrostatic chucking, and films mainly containing chromium (Cr), tantalum (Ta), etc. can be listed.

[0008] When a tantalum (Ta) film is used as an absorber film, and the absorber layer of the absorber film is tantalum nitride (TaN), sometimes a tantalum oxide (TaO) portion is formed on the surface used to reduce reflectivity at the inspection wavelength as a reflectivity-reducing layer, thus forming a tantalum oxide (TaO) portion and a tantalum nitride (TaN) portion. When forming a film containing both tantalum nitride (TaN) and tantalum oxide (TaO) portions, many TaON layers are formed at the interface between the tantalum nitride (TaN) and tantalum oxide (TaO) portions. However, near the interface forming this TaON composition, some elements may attempt to achieve a stable structure, resulting in crystal precipitation. Especially during film formation, when the film is formed in the same chamber and on the same target material, the TaON intermediate layer tends to be thicker, easily leading to crystal precipitation. When crystal precipitation occurs in the film, there are concerns about deterioration of the film's surface roughness, pattern shape, and warpage characteristics, therefore this is not preferred.

[0009] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a reflective mask blank and a method for manufacturing a reflective mask blank that can produce a reflective mask with small surface roughness and good defect inspection sensitivity. Summary of the Invention

[0010] The inventors have discovered that in a multilayer membrane containing TaN and TaO portions, by adding a component containing Ta with a density greater than that of the TaN and TaO portions and 13 g / cm³ between the TaN and TaO portions... 3 The Ta portion prevents crystals from precipitating at the interface between the TaN and TaO portions, thus enabling the formation of a smooth film.

[0011] Therefore, the present invention provides the following reflective mask blank.

[0012] [Concept 1]

[0013] The reflective mask blank of the present invention is used in EUV lithography using EUV light as the exposure light, and includes at least a substrate, a multilayer reflective film formed on the substrate to reflect the exposure light, and a multilayer film containing tantalum, characterized in that:

[0014] The multilayer film has a TaN portion, a TaO portion, and a Ta portion disposed between the TaN portion and the TaO portion.

[0015] The density of the Ta portion is greater than that of the TaN and TaO portions.

[0016] The density of the Ta portion is 13 g / cm³. 3 above.

[0017] [Concept 2]

[0018] In the concept 1 reflective mask blank

[0019] The multilayer film is stacked from the substrate side in the order of TaN, Ta, and TaO.

[0020] [Concept 3]

[0021] In the reflective mask blanks based on Concept 1 or 2

[0022] The thickness of the Ta portion is greater than 1 nm and less than 3 nm.

[0023] [Concept 4]

[0024] In reflective mask blanks based on any one of concepts 1 to 3,

[0025] The TaN portion is substantially oxygen-free, and tantalum (Ta) is less than 70 atoms, while nitrogen (N) is more than 30 atoms.

[0026] [Concept 5]

[0027] In reflective mask blanks based on any one of concepts 1 to 4,

[0028] The TaO portion is substantially nitrogen-free, and the tantalum (Ta) content is less than 70 atomic%, while the oxygen (O) content is greater than 30 atomic%, or

[0029] The TaO portion contains, in addition to tantalum (Ta) and oxygen (O), one or more of boron (B), carbon (C), hydrogen (H) and silicon (Si) in amounts less than 5 atomic percent.

[0030] [Concept 6]

[0031] In reflective mask blanks based on any one of concepts 1 to 5,

[0032] The Ta portion does not actually contain any elements other than tantalum (Ta), or

[0033] The total content of nitrogen (N) and oxygen (O) in the Ta portion is less than 20 atoms.

[0034] [Concept 7]

[0035] In reflective mask blanks based on any one of concepts 1 to 6,

[0036] The multilayer membrane functions as an absorber membrane.

[0037] [Concept 8]

[0038] In the concept 7 reflective mask blank

[0039] This further includes a hard mask film used as an etching mask during the processing of the multilayer film that functions as the absorber film.

[0040] The hard mask contains chromium (Cr).

[0041] [Concept 9]

[0042] In reflective mask blanks based on any one of concepts 1 to 6,

[0043] The multilayer film includes: a first multilayer film having a TaN portion, a TaO portion, and a Ta portion disposed between the TaN portion and the TaO portion; and a second multilayer film having a TaN portion, a TaO portion, and a Ta portion disposed between the TaN portion and the TaO portion.

[0044] The first multilayer membrane functions as an absorber membrane.

[0045] The second multilayer film functions as a hard mask film used as an etching mask during the processing of the first multilayer film, which serves as the absorber film.

[0046] The thickness of the first multilayer film is greater than 55 nm and less than 70 nm.

[0047] The thickness of the second multilayer film is less than 20 nm.

[0048] [Concept 10]

[0049] A method for manufacturing a reflective mask blank according to any one of concepts 1 to 9,

[0050] The Ta portion can be formed between the TaN portion and the TaO portion by forming a film of tantalum (Ta) in an oxygen- and nitrogen-free atmosphere.

[0051] [Concept 11]

[0052] In the manufacturing method of the reflective mask blank described in Concept 10,

[0053] After the TaN portion is formed, a Ta film is formed in an oxygen- and nitrogen-free atmosphere to form the Ta portion.

[0054] The TaO portion is formed by oxidizing the side of the Ta portion away from the substrate.

[0055] Invention Effects

[0056] According to the present invention, a reflective mask blank capable of producing reflective masks with low surface roughness and good defect inspection sensitivity can be provided. Attached Figure Description

[0057] Figure 1 This is a longitudinal cross-sectional view of the reflective mask substrate, i.e., the multilayer film, in the state where it functions as an absorber film according to an embodiment of the present invention.

[0058] Figure 2 This is a longitudinal cross-sectional view of the reflective mask substrate according to an embodiment of the present invention, in which the multilayer film functions as both an absorption film and a hard mask film.

[0059] Figure 3 This is a longitudinal cross-sectional view of an example of the structure of a multilayer membrane that functions as an absorber membrane according to an embodiment of the present invention.

[0060] Figure 4 This is a vertical cross-sectional view of another example of the construction of a multilayer membrane when it is used as an absorbent membrane, as described in an embodiment of the present invention.

[0061] Figure 5 This is a longitudinal cross-sectional view of an example of the structure of a multilayer film that functions as both an absorber film and a hard mask film according to an embodiment of the present invention.

[0062] Figure 6 This is a longitudinal cross-sectional view of the multilayer film according to an embodiment of the present invention, in which the TaN portion functions as an absorber film and the TaO portion functions as a hard mask film.

[0063] Figure 7 This is a longitudinal cross-sectional view of an embodiment of the present invention in which an auxiliary layer is provided on the lower surface of a multilayer film.

[0064] Figure 8 This is a view of an embodiment of the present invention in which an auxiliary layer is provided on the top surface of a multilayer film.

[0065] Figure 9 This is a longitudinal cross-sectional view of the reflective mask blank of the present invention, showing the presence of a resist film.

[0066] Figure 10 This is a longitudinal cross-sectional view of the patterning method of the resist film and hard mask film in the reflective mask substrate according to an embodiment of the present invention.

[0067] Figure 11 This is a cross-sectional view of the patterned state of the absorber film in the reflective mask blank according to an embodiment of the present invention. Detailed Implementation

[0068] Hereinafter, embodiments of the present invention will be described.

[0069] like Figure 1 and Figure 2 As shown, the reflective mask blank of this embodiment includes: a substrate 10, a multilayer reflective film 50 formed on a main surface (surface) of the substrate 10 and reflecting exposure light, and an absorber film 120 absorbing exposure light. A protective film 110 for the multilayer reflective film 50 may also be provided between the multilayer reflective film 50 and the absorber film 120. A hard mask film 130 may also be formed on the surface (upper surface) of the absorber film 120. A back conductive film 150 may be formed on the back side (lower surface) of the substrate 10. Furthermore, as... Figure 9 As shown, a resist film 140 can be formed on the surface (on top) of the hard mask film 130.

[0070] The reflective mask blank of this embodiment is suitable as a raw material for reflective masks used in EUV lithography, which uses EUV light as the exposure light. The wavelength of EUV light used in EUV lithography, which uses EUV light as the exposure light, is 13-14 nm, typically around 13.5 nm. The reflective mask blank and the reflective mask are also referred to as EUV mask blank and EUV mask, respectively.

[0071] The reflective mask blank used in EUV lithography, which uses EUV light as the exposure light in this embodiment, has at least: a substrate 10, a multilayer reflective film 50 formed on the substrate 10 to reflect the exposure light, and a multilayer film 200 containing tantalum.

[0072] like Figure 3 and Figure 4 As shown, 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 disposed between the TaN portion 210 and the TaO portion 230. The density of the Ta portion 220 is greater than that of the TaN portion 210 and the TaO portion 230. The density of the Ta portion 220 is 13 g / cm³. 3 That is all. In this way, the precipitation of crystals that form at the interface between the TaO section 230 and the TaN section 210 can be prevented, and the reduction of surface roughness can be prevented.

[0073] The TaN (tantalum nitride) section 210 is a layer mainly composed of tantalum and nitrogen, the TaO (tantalum oxide) section 230 is a layer mainly composed of tantalum and oxygen, and the Ta section 220 contains tantalum.

[0074] The Ta portion 220 is preferably a membrane with less oxygen than the TaO (tantalum oxide) portion 230 and less nitrogen than the TaN (tantalum nitride) portion 210.

[0075] The aforementioned tantalum-containing multilayer film 200 can be a patterned film, including absorber film 120 and hard mask film 130, etc. (see reference) Figure 10 and Figure 11 ).

[0076] In the multilayer film 200, it is preferable to sequentially stack TaN portion 210, Ta portion 220, and TaO portion 230 from the substrate 10 side (the back side of the reflective mask blank) (see reference). Figure 3 By forming it in this way, for example when used as an absorber film 120, the reflectivity is easily reduced at the inspection wavelength. In addition, the etching characteristics of the TaO portion 230 are different from those of the TaN portion 210, so the TaO portion 230 can be used as an etching mask (hard mask) for the TaN portion 210 during pattern formation.

[0077] However, it is not limited to this method. In the multilayer film 200, it is also possible to stack the layers in the order of TaO portion 230, Ta portion 220, and TaN portion 210, starting from the substrate 10 side (the back side of the reflective mask blank) (see reference). Figure 4 ).

[0078] The density of Ta portion 220 is preferably 13 g / cm³. 3 Above and 17g / cm 3 The preferred value is 16 g / cm³. 3 the following.

[0079] The density of TaN portion 210 is preferably 10 g / cm³. 3 Above, 12g / cm 3 the following.

[0080] The density of TaO portion 230 is preferably 3 g / cm³. 3 Above, 10g / cm 3 the following.

[0081] The thickness of the Ta portion 220 is preferably 1 nm or more and less than 3 nm. If the thickness of the Ta portion 220 becomes thinner than 1 nm, the film thickness becomes too thin, and the effect of preventing crystal precipitation weakens. On the other hand, when the thickness of the Ta portion 220 is 3 nm or more, Ta crystal growth will occur, which is detrimental to the film stress, surface roughness, and resistance to exposure light.

[0082] TaN 210 is preferably substantially oxygen-free, with tantalum (Ta) content less than 70 atomic% and nitrogen (N) content greater than 30 atomic%. Substantially oxygen-free means that the oxygen content is less than 2 atomic%.

[0083] The TaO component 230 is substantially free of nitrogen (N), and contains less than 70 atomic% tantalum (Ta) and more than 30% oxygen (O), or preferably 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). "Substantially free of nitrogen" means that the nitrogen content is less than 2 atomic%.

[0084] The composition of Ta section 220 preferably does not contain elements other than tantalum (Ta), or the total content of nitrogen (N) and oxygen (O) is less than 20 atomic percent. "Substantially does not contain elements other than tantalum (Ta)" means that the tantalum content is 95 atomic percent or more. Furthermore, from the viewpoint of reducing surface roughness, Ta section 220 is preferably designed to be substantially free of elements other than tantalum (Ta).

[0085] The absorber membrane 120 can be formed as a multilayer structure comprising at least the TaN portion 210, the Ta portion 220, and the TaO portion 230 (see reference). Figure 1 ).

[0086] Furthermore, the absorber film 120 and the hard mask film 130 can be formed as multilayer structures, each including a TaN portion 210, a Ta portion 220, and a TaO portion 230 (see reference). Figure 2 In this case, such as Figure 5 As shown, the multilayer film 200 comprises a first multilayer film 200a having a first TaN portion 210a, a first TaO portion 230a, and a first Ta portion 220a disposed between the first TaN portion 210a and the first TaO portion 230a; a second multilayer film 200b having a second TaN portion 210b, a second TaO portion 230b, and a second multilayer film 200b having a second Ta portion 220b disposed between the second TaN portion 210b and the second TaO portion 230b. The first multilayer film 200a can also function as an absorber film 120. The second multilayer film 200b can also function as a hard mask film 130 used as an etching mask when processing the first multilayer film 200a as an absorber film 120. When the first multilayer film 200a functions as an absorber film 120, the film 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 the hard mask film 130, the thickness of the second multilayer film 200b is preferably less than 20 nm.

[0087] Alternatively, the absorber film 120 may also be composed of a multilayer film 200 consisting only of TaN portions 210, Ta portions 220, and TaO portions 230. In this case, the hard mask film 130 used as an etching mask when processing the absorber film 120 may be a Cr-containing film (Cr-containing film) (see reference). Figure 3 and Figure 4 ).

[0088] Additionally, the TaN portion 210 and the TaO portion 230 can also function as the absorber film 120 for forming patterns and the hard mask film 130 used as an etching mask when processing the absorber film 120, respectively. In this way, it can be made to have etching selectivity.

[0089] Especially as Figure 6 As shown, the absorber membrane 120 can be composed of a TaN portion 210, and the hard mask membrane 130 can be composed of a TaO portion 230. In this case, the Ta portion 220 is used, for example, as part of the absorber membrane 120.

[0090] The absorber film 120 may have a phase-shifting function. Alternatively, it may be formed with a layer (buffer layer) at the bottom of the absorber film 120 that is resistant to the etching conditions during the formation of the upper pattern and the correction pattern.

[0091] When using a Ta-containing layer as the absorber film 120, the absorber film 120 may consist solely of a Ta-containing multilayer film 200, but it may also have layers containing any one or more of Ru, Rh, Ir, Pt, Nb, and Cr. The Ta-containing multilayer film 200 may also be disposed on the side of the layers 250 containing any one or more of Ru, Rh, Ir, Pt, Nb, and Cr that are away from the substrate 10 (see reference). Figure 7 Furthermore, a layer 250 comprising at least one of Ru, Rh, Ir, Pt, Nb, and Cr may be provided on the side of the multilayer film 200 away from the substrate 10 (see [link to documentation]). Figure 8 In this case, if the tantalum-containing multilayer film 200 disposed on one side of the substrate 10 is further disposed on the substrate 10 side with a layer 250 containing one or more of Ru, Rh, Ir, Pt, Nb and / or Cr, then the tantalum-containing multilayer film 200 can function as a buffer layer, and is therefore preferred.

[0092] The multilayer film 200 containing Ta can be formed by sputtering, preferably magnetron sputtering. For example, a tantalum (Ta) target can be used, with rare gases such as helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) as sputtering gases, and nitrogen (N2) or oxygen (O2) can be used in combination depending on the composition of the desired film, to form the film by reactive sputtering.

[0093] For example, Ta portion 220 can be formed by depositing a film of Ta between TaN (tantalum nitride) portion 210 and TaO (tantalum oxide) portion 230 in an atmosphere free of oxygen and nitrogen.

[0094] Furthermore, after forming the TaN (tantalum nitride) portion 210, a Ta film is formed in an atmosphere free of oxygen and nitrogen to form the Ta portion 220. Then, by oxidizing the side (surface) of the Ta portion 220 away from the substrate 10, a TaO (tantalum oxide) portion 230 can be formed on the surface of the Ta portion 220.

[0095] As a heat treatment, for example, it can be heated for 5 to 60 minutes in an oxygen-containing atmosphere, such as air, at a temperature of 120°C to 200°C, by a heating device such as a hot plate.

[0096] The substrate 10, used for EUV light exposure, preferably has low thermal expansion characteristics; for example, it is preferably composed of materials with a thermal expansion coefficient of ±2×10⁻⁶. -8 Within / ℃, preferably ±5×10 -9 Materials within a temperature range of / ℃ can be formed. Examples of such materials include titanium dioxide-doped quartz glass (SiO2-TiO2 type glass). Furthermore, the substrate 10 preferably uses a substrate with a sufficiently planarized 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 terms of RMS value. This surface roughness can be achieved by grinding the substrate 10, etc. The dimensions of the substrate 10 are preferably 152 mm square on the main surface and 6.35 mm thick. This size substrate 10 is what is known as a 6025 substrate 10 (a substrate 10 with a main surface size of 6 inches square and a thickness of 0.25 inches).

[0097] The multilayer reflective film 50 is a reflective exposure film in a reflective mask. The multilayer reflective film 50 is preferably disposed in contact with one main surface (surface) of the substrate 10, but other films such as a base film may also be disposed between it and one main surface of the substrate 10. The multilayer reflective film 50 has a periodic stacked structure 51 (see reference) formed by alternately stacking 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. Figure 1 and Figure 2 ).

[0098] The high refractive index layer 20 is preferably formed of a silicon (Si)-free material. 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 multiple layers containing additive elements and layers without 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 further preferably 4.9 nm or less, more preferably 4.4 nm or less.

[0099] The low refractive index layer 30 is preferably formed of a material containing molybdenum (Mo). Alternatively, the low refractive index layer 30 may also be formed of a material including ruthenium (Ru). The low refractive index layer 30 may include one or more additive elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B), and hydrogen (H), and may consist of multiple layers containing additive elements and layers 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 preferably 3.5 nm or less, more preferably 3 nm or less.

[0100] The periodic stacked structure 51 may include a high-refractive-index layer 20 and a low-refractive-index layer 30, and each period may include one or more high-refractive-index layers 20 and one or more low-refractive-index layers 30. The number of layers included in the periodic stacked structure 51 may be two or more, and the periodic stacked structure 51 may include, for example, one high-refractive-index layer 20 and one low-refractive-index layer 30. Alternatively, it may contain two or more high-refractive-index layers 20 with different compositions (e.g., different composition ratios, different compositions due to the presence or absence of added elements, etc.), and may also contain two or more low-refractive-index layers 30 with different compositions (e.g., different composition ratios, different compositions due to the presence or absence of added elements, etc.). In this case, the periodic stacked structure 51 contains three or more layers, four or more layers, or five or more layers, but preferably eight or fewer layers. The number of periods is preferably 30 or more, and preferably 50 or fewer, more preferably 40 or fewer. When the low refractive index layer 30 is formed of a material containing ruthenium (Ru), the layer (uppermost layer) of the periodic stacked structure 51 that is furthest from the substrate 10 is preferably the high refractive index layer 20.

[0101] The thickness of the multilayer reflective film 50 having a periodic stacked structure 51 is adjusted according to the exposure wavelength and the incident angle of the exposure light, preferably 200 nm or more, more preferably 270 nm or more, and preferably 400 nm or less, more preferably 290 nm or less.

[0102] Methods for forming the multilayer reflective film 50 include sputtering methods where electricity is supplied to the target, the supplied electricity is used to ionize the atmospheric gas, and sputtering is performed; and ion beam sputtering methods where an ion beam is irradiated onto the target. Sputtering methods include DC sputtering, where a direct current voltage is applied to the target, and RF sputtering, where a high-frequency voltage is applied to the target. Sputtering methods are film formation methods that utilize the gas ion sputtering phenomenon by applying a voltage to the target while the sputtering gas is introduced into a chamber, causing the gas to ionize. Magnetron sputtering, in particular, is advantageous in terms of productivity. The power applied to the target can be DC or RF, and DC includes pulsed sputtering, which briefly reverses to apply a negative bias to the target to prevent target charging.

[0103] The multilayer reflective film 50 can be formed, for example, by sputtering using a sputtering apparatus capable of mounting multiple targets. Specifically, the target can be appropriately selected from the following categories: molybdenum (Mo) targets for forming molybdenum (Mo) layers, ruthenium (Ru) targets for forming ruthenium (Ru) layers, silicon (Si) targets for forming silicon (Si) layers, etc.; the sputtering gas can be rare gases such as helium (He), argon (Ar), krypton (Kr), xenon (Xe), etc., thereby completing the formation of the multilayer reflective film 50.

[0104] Furthermore, if reactive sputtering with reactive gases is used, the specific gas selection is as follows: When forming a nitrogen (N) thin film, nitrogen-containing gases such as nitrogen (N2) can be used; when forming an oxygen (O) thin film, oxygen-containing gases such as oxygen (O2) can be used; when forming a thin film containing both nitrogen (N) and oxygen (O), nitrogen oxide gases such as nitrous oxide (N2O), nitric oxide (NO), and nitrogen dioxide (NO2) can be used; when forming a thin film containing carbon (C) and oxygen (O), carbon oxide gases such as carbon monoxide (CO) and carbon dioxide (CO2) can be used; when forming a hydrogen (H) thin film, hydrogen-containing gases such as hydrogen (H2) can be used; when forming a thin film containing both carbon (C) and hydrogen (H), hydrocarbon gases such as methane (CH4) can be used. All of the above reactive gases must be used in conjunction with rare gases.

[0105] In addition, when forming a boron (B)-containing layer, the following types of targets can be used: molybdenum (Mo) targets with added boron (B) (i.e., molybdenum boride (MoB) targets); silicon (Si) targets with added boron (B) (i.e., silicon boride (SiB) targets), etc.

[0106] like Figure 1 and Figure 2 As shown, a protective film 110 can be disposed above the multilayer reflective film 50. The protective film 110 is also called a cover film. The protective film 110 is used to protect the multilayer reflective film 50. The protective film 110 is typically disposed in contact with the multilayer reflective film 50. The protective film 110 is formed of a material containing ruthenium (Ru).

[0107] Materials containing ruthenium (Ru) include elemental ruthenium (Ru), ruthenium (Ru), and alloys composed of metals or half-metals different from ruthenium (Ru). Examples of metals or half-metals different from ruthenium (Ru) include niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si). The content of the metal or half-metal different from ruthenium (Ru) in the protective film 110 is preferably 30 atomic percent or less, more preferably 20 atomic percent or less. The lower limit of the content of the metal or half-metal different from ruthenium (Ru) in the protective film 110 is not particularly limited, but is preferably 5 atomic percent or more, more preferably 10 atomic percent or more.

[0108] The protective film 110 can be a single-layer structure or a multi-layer structure combining multiple layers with different compositions. Furthermore, the individual layers constituting the single layer or multiple layers can have an inclined composition structure whose composition continuously varies in the thickness direction. In particular, one or both of the sides of the protective film 110 closest to the multi-layer reflective film 50 (in the case of a multi-layer structure, the layer closest to the multi-layer reflective film 50) and furthest from the multi-layer reflective film 50 (in the case of a multi-layer structure, the layer furthest from the multi-layer reflective film 50) can be made of ruthenium (Ru).

[0109] Furthermore, when the protective film 110 has a multilayer structure or a tilted composition structure, it is preferable that the content of a metal or half-metal different from ruthenium (Ru) increases in a portion or all of the thickness direction of the protective film 110, from the side of the multilayer reflective film 50 to the side away from the multilayer reflective film 50. In particular, when the protective film contains a metal or half-metal niobium (Nb) different from ruthenium (Ru), the presence of niobium (Nb) also has a significant effect on improving resistance to "dry etching containing chlorine (Cl) and oxygen (O) gases". Therefore, it is ideal for the content of niobium (Nb) to increase in a portion or all of the thickness direction of the protective film 110 from the side closer to the multilayer reflective film 50 to the side away from the multilayer reflective film 50.

[0110] In this embodiment, as a dry etching process using a gas containing chlorine (Cl) and oxygen (O), specifically, a dry etching process using a gas containing chlorine (Cl2) and oxygen (O2) can be performed. Rare gases such as helium (He), argon (Ar), krypton (Kr), and xenon (Xe) can also be added to this mixture of chlorine (Cl) and oxygen (O).

[0111] The thickness of the protective film 110 is preferably 2 nm or more, more preferably 3 nm or more, and preferably 5 nm or less, more preferably 4 nm or less. When the thickness of the protective film 110 is less than 2 nm, the function of protecting the multilayer reflective film 50 becomes insufficient, and when it exceeds 5 nm, the reflectivity of EUV light decreases.

[0112] The protective film 110 can be formed by sputtering, specifically as follows: the target material can be appropriately selected from the following categories, including ruthenium (Ru) targets, metal or semi-metal targets different from ruthenium (Ru) (specifically niobium (Nb) targets, rhenium (Re) targets, zirconium (Zr) targets, titanium (Ti) targets, chromium (Cr) targets, silicon (Si) targets, and targets made by mixing two or more of niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si), as well as targets made by mixing one or more "metals or semi-metals different from ruthenium (Ru)" (selected from niobium (Nb), rhenium (Re), zirconium (Zr), titanium (Ti), chromium (Cr), and silicon (Si)) into ruthenium (Ru); the sputtering gas is a rare gas such as helium (He), argon (Ar), krypton (Kr), and xenon (Xe). Magnetron sputtering is preferred as the sputtering method.

[0113] After the formation of the multilayer reflective film 50 or the protective film 110, heat treatment can also be performed. By performing heat treatment, changes in properties such as reflectivity of EUV light due to heat generation during mask pattern formation can be suppressed. The heat treatment temperature is generally preferably between 120°C and 150°C. If the temperature is higher than 150°C, the reflectivity of EUV light decreases, so it is not preferred.

[0114] Heat treatment can be performed on either or both of the multilayer reflective film 50 and the protective film 110 after they are formed. However, from the viewpoint of concerns about defect adhesion or productivity, it is preferable to perform heat treatment less often and to perform heat treatment after the protective film 110 is formed.

[0115] On the other hand, when heat treatment is performed after the protective film 110 is formed, an oxide film may sometimes form on the surface of the protective film 110, thereby reducing the reflectivity of the pattern inspection light. In addition, even if heat treatment is not performed after the protective film 110 is formed, the surface of the protective film 110 may still oxidize after the pattern is formed. Therefore, the reflectivity of the absorption film to the pattern inspection light must be set based on the premise that the protective film 110 is oxidized.

[0116] like Figure 1 and Figure 2 As shown, on the opposite side surface of one main surface (front) of the substrate 10, i.e., the other main surface (back side), preferably at a position in contact with the other main surface, a conductive film (back conductive film 150) is provided for fixing the reflective mask to an exposure apparatus (e.g., an extreme ultraviolet scanning lithography machine (e.g., an EUV scanner)) by an electrostatic chuck.

[0117] 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 those containing tantalum (Ta) or chromium (Cr). Furthermore, materials containing tantalum (Ta) may also contain elements such as oxygen (O), nitrogen (N), carbon (C), and boron (B); materials containing chromium (Cr) may also contain elements such as oxygen (O), nitrogen (N), and carbon (C). Examples of materials containing tantalum (Ta) include elemental tantalum (Ta) and tantalum compounds (such as TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, TaCONB, etc.). Examples of materials containing chromium (Cr) include elemental chromium (Cr) and chromium compounds (such as CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, etc.).

[0118] The thickness of the back conductive film 150 is only required to achieve electrostatic adsorption and is not particularly limited, typically around 20–300 nm. The thickness of the back conductive film 150 is preferably formed after the formation of the reflective mask, i.e., after the formation of the absorption film pattern, in a manner that balances the film stress with the film and film pattern formed on one main surface (surface). The formation timing of the back conductive film 150 can be chosen in any of the following ways: it can be formed before the formation of the multilayer reflective film 50, or after the formation of all film layers on one side of the multilayer reflective film 50 on the substrate 10; alternatively, a portion of the film layers on one side of the multilayer reflective film 50 on the substrate 10 can be formed first, followed by the formation of the back conductive film 150, and then the formation of the remaining film layers on one side of the multilayer reflective film 50 on the substrate 10. The back conductive film 150 can be formed, for example, by magnetron sputtering.

[0119]

Example

[0120] The following describes experimental and comparative examples in detail, but the present invention is not limited to the experimental examples. Furthermore, according to the original function of the reflective mask blank, films should be formed on the multilayer reflective film 50, protective film 110, or absorber film 120. However, in the experimental examples, to compare the interface state of the multilayer structure, film formation was simply performed on the quartz substrate 10. The effects of the present invention can be reproduced unchanged whether on the quartz substrate 10 or on each layer.

[0121]

Example 1

[0122] On the main surface of a quartz glass substrate 10 measuring 152 mm square and 6.35 mm thick, a multilayer film 200 containing tantalum (Ta) is formed by DC pulsed magnetron sputtering while the substrate 10 is rotating. This multilayer film 200 can function as one of three components: the absorber film 120, the hard mask film 130, and the buffer layer in the absorber film 120 of the reflective mask blank. Furthermore, the buffer film prevents the lower film from being directly exposed to the etching gas during etching of the upper film, thereby suppressing the thinning of the lower film.

[0123] A quartz glass substrate 10 is placed in a chamber. Argon (Ar, 40% by volume) and nitrogen (N2, 60% by volume) are first introduced to adjust the chamber pressure to 0.48 Pa. An electric current of 1800 W is applied to the tantalum (Ta) target to form a tantalum nitride layer (TaN portion 210). Next, while the substrate 10 remains in place within the chamber, pure argon (Ar, 100% by volume) is introduced to adjust the chamber pressure to 0.07 Pa. The pressure is then switched to apply an electric current of 500 W to the tantalum (Ta) target to form a tantalum layer (Ta portion 220) with a thickness of 1 nanometer (nm). Subsequently, argon (Ar, 30% by volume) and oxygen (O2, 70% by volume) were introduced into the same chamber, and the pressure in the chamber was adjusted to 0.15 Pa. The conditions were then switched to apply 500 watts (W) of electricity to the tantalum (Ta) target to form a tantalum oxide layer (TaO part 230) with a thickness of 4.5 nanometers (nm).

[0124] The density and thickness of each layer of the obtained tantalum (Ta) multilayer film 200 were determined by X-ray diffraction (XRR) using a Rigaku SmartLab instrument. The results are as follows: the tantalum nitride (TaN) layer has a thickness of 20.7 nm and a density of 11.0 g / cm³. 3 The tantalum (Ta) layer has a thickness of 1.0 nm and a density of 13.0 g / cm³. 3 The tantalum oxide (TaO) layer has a thickness of 4.8 nm and a density of 8.2 g / cm³. 3 .

[0125] The composition of the obtained tantalum (Ta) multilayer film 200 was determined using X-ray photoelectron spectroscopy (XPS) (Thermo Fisher Scientific, model K-Alpha). The results are as follows: In the tantalum nitride (TaN) layer, based on the total number of tantalum (Ta) and nitrogen (N) atoms, tantalum (Ta) accounts for 45 atomic% and nitrogen (N) accounts for 55 atomic%; In the tantalum oxide (TaO) layer, based on the total number of tantalum (Ta) and oxygen (O) atoms, tantalum (Ta) accounts for 34 atomic% and oxygen (O) accounts for 66 atomic%.

[0126] The obtained multilayer film 200 was sectioned using a focused ion beam (FIB) instrument (FEI Corporation, Helios G4CX), and the cross-section including a portion of the substrate 10 and the entire multilayer film 200 was then observed using a transmission electron microscope (TEM) instrument (Nippon Electric Corporation, ARM200F). The results showed that no crystal precipitation or other phenomena were observed between the tantalum nitride (TaN) layer and the tantalum oxide (TaO) layer, and each layer was formed very smoothly. Because the surface roughness of the tantalum nitride (TaN) layer, the tantalum (Ta) layer, and the tantalum oxide (TaO) layer is reduced as a result, a better level of defect detection sensitivity can be achieved.

[0127]

Example 2

[0128] On the main surface of a quartz glass substrate 10 with a cross-section of 152 mm and a thickness of 6.35 mm, except that the thickness of the tantalum layer (TaO part 230) is adjusted to 2 nanometers, the rest are formed according to the method of Example 1 to form a multilayer film 200 containing tantalum (Ta). The multilayer film 200 can function as one of the three functions of the absorber film 120, the hard mask film 130, and the buffer layer in the absorber film 120 of the reflective mask blank.

[0129] The obtained tantalum (Ta) multilayer film 200 was subjected to the same method as in Example 1, with the density and thickness of each layer determined by X-ray reflectance (XRR). The results are as follows: the tantalum nitride (TaN) layer has a thickness of 21.0 nm and a density of 10.9 g / cm³. 3 The tantalum (Ta) layer has a thickness of 1.1 nm and a density of 16.6 g / cm³. 3 The tantalum oxide (TaO) layer has a film thickness of 4.5 nanometers (nm) and a density of 8.3 g / cm³. 3 .

[0130] Similar to Example 1, no crystallization or precipitation was found between the TaN and TaO layers using a transmission electron microscope, and each layer was formed very smoothly. This reduces the surface roughness of the TaN, Ta, and TaO layers, thus improving the sensitivity of defect inspection.

[0131]

Example 3

[0132] On the main surface of a quartz glass substrate 10 with a diameter of 152 mm and a thickness of 6.35 mm, a multilayer film 200 containing tantalum (Ta) is formed. This multilayer film 200 can function as one of the three functions of the absorber film 120, the hard mask film 130, and the buffer layer in the absorber film 120 of the reflective mask blank.

[0133] First, a TaN layer was formed under the same conditions as in Example 1. Similarly, a Ta layer was formed with a film thickness of 2 nm under the same conditions as in Example 1. Then, without forming a TaO layer, a heat treatment was performed at 150°C for 15 minutes in an atmospheric atmosphere using a hot plate heating device to oxidize the surface of the protective film 110, thereby forming a TaO layer.

[0134] 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 results showed that the thickness of the TaN layer was 29.5 nm and the density was 11.2 g / cm³. 3 The Ta layer has a thickness of 2.2 nm and a density of 16.6 g / cm³. 3 The TaO layer has a thickness of 1.3 nm and a density of 3.7 g / cm³. 3 .

[0135] Similar to Example 1, when observed with a transmission electron microscope, no crystal precipitation or other abnormalities were found between the TaN and TaO layers, and each layer was formed very smoothly. This reduces the surface roughness of the TaN, Ta, and TaO layers, thus improving the sensitivity of defect detection.

[0136]

Comparative Example 1

[0137] On the main surface of a quartz glass substrate 10 with a square diameter of 152 mm and a thickness of 6.35 mm, a multilayer film 200 containing Ta, in which any one of the absorber film 120 of the reflective mask blank, the hard mask film 130, and the buffer layer of the absorber film 120 functions, is formed. First, a TaN layer is formed under the same conditions as in Example 1. Then, without forming a Ta layer, a 4 nm TaO layer is formed under the same conditions as in Example 1.

[0138] 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 results showed that the thickness of the TaN layer was 21.9 nm and the density was 10.9 g / cm³. 3 The TaO layer has a thickness of 2.1 nm and a density of 8.4 g / cm³. 3 .

[0139] Similar to Example 1, observation using a transmission electron microscope revealed that the crystallized TaN and TaO layers formed layers of different densities, resulting in an uneven interface. This increased the surface roughness of both the TaN and TaO layers, thus reducing the sensitivity of defect detection.

[0140] [Comparative Example 2]

[0141] On the main surface of a quartz glass substrate 10 with a cross-section of 152 mm and a thickness of 6.35 mm, except that the thickness of the tantalum (Ta) layer is adjusted to 0.5 nanometers, the rest are formed according to the method of Example 1 to form a multilayer film 200 containing tantalum (Ta). The multilayer film 200 can function as one of the three functions of the absorber film 120, the hard mask film 130, and the buffer layer in the absorber film 120 of the reflective mask blank.

[0142] 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 results showed that the TaN layer had a thickness of 21.3 nm and a density of 10.9 g / cm³. The Ta layer had a thickness of 0.5 nm and a density of 12.0 g / cm³. 3 The TaO layer has a thickness of 4.8 nm and a density of 7.3 g / cm³. 3 .

[0143] Similar to Example 1, observation using a transmission electron microscope revealed that the crystallization of the TaN and TaO layers resulted in layers of varying densities and uneven interface formation. Consequently, the surface roughness of the TaN, Ta, and TaO layers increased, thus reducing the sensitivity of defect detection.

[0144] [Comparative Example 3]

[0145] On the main surface of a quartz glass substrate 10 with a diameter of 152 mm and a thickness of 6.35 mm, a multilayer film 200 containing tantalum (Ta) is formed. This multilayer film 200 can function as one of the three components: absorber film 120 of the reflective mask original, hard mask film 130, and buffer film in absorber film 120.

[0146] First, a tantalum nitride (TaN) layer was formed under the same conditions as in Example 1. Next, without forming a tantalum (Ta) layer, argon (Ar, 22% by volume), oxygen (O2, 56% by volume), and nitrogen (N2, 22% by volume) were introduced into the same chamber. The chamber pressure was adjusted to 0.18 Pa, and the conditions were switched to apply 500 watts (W) of electricity to the tantalum (Ta) target, forming a tantalum oxynitride (TaON) layer with a thickness of 4.7 nanometers (nm).

[0147] 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 results showed that the thickness of the TaN layer was 21.9 nm and the density was 11.0 g / cm³. 3 The TaON layer has a thickness of 4.7 nm and a density of 7.3 g / cm³. 3 .

[0148] Similar to Example 1, when observed with a transmission electron microscope, the TaON layer was found to be loosely formed, which was undesirable. Therefore, if the TaON layer becomes denser, the surface roughness will increase, thus reducing the sensitivity of defect inspection.

[0149] Symbol Explanation

[0150] 10 substrate

[0151] 20 High Refractive Index Layer

[0152] 30 Low Refractive Index Layer

[0153] 50 multilayer reflective film

[0154] 51 Periodic Stacked Structure

[0155] 110 Protective Film

[0156] 120 Absorbent membrane

[0157] 130 Hard Mask

[0158] 200 multilayer films

[0159] 200a First Multilayer Membrane (Absorber Membrane)

[0160] 200b second multilayer film (rigid mask film)

[0161] 210 TaN section

[0162] Part 220

[0163] 230 Department of TaO

Claims

1. A reflective mask blank for use in EUV lithography using EUV light as the exposure light, comprising at least a substrate, a multilayer reflective film formed on the substrate to reflect the exposure light, and a multilayer film containing tantalum, characterized in that: The multilayer film has a TaN portion, a TaO portion, and a Ta portion disposed between the TaN portion and the TaO portion. The density of the Ta portion is greater than that of the TaN and TaO portions. The density of the Ta portion is 13 g / cm³. 3 above.

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

3. The reflective mask blank according to claim 1, characterized in that: The thickness of the Ta portion is greater than 1 nm 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 oxygen-free, and tantalum (Ta) is less than 70 atoms, while nitrogen (N) is more than 30 atoms.

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

6. The reflective mask blank according to any one of claims 1 to 3, characterized in that: The Ta portion does not actually contain any elements other than tantalum (Ta), or The total content of nitrogen (N) and oxygen (O) in the Ta portion is less than 20 atoms.

7. The reflective mask blank according to any one of claims 1 to 3, characterized in that: The multilayer membrane functions as an absorber membrane.

8. The reflective mask blank according to claim 7, characterized in that: This further includes a hard mask film used as an etching mask during the processing of the multilayer film that functions as the absorber film. The hard mask contains chromium (Cr).

9. The reflective mask blank according to any one of claims 1 to 3, characterized in that: The multilayer film includes: a first multilayer film having a TaN portion, a TaO portion, and a Ta portion disposed between the TaN portion and the TaO portion; and a second multilayer film having a TaN portion, a TaO portion, and a Ta portion disposed between the TaN portion and the TaO portion. The first multilayer membrane functions as an absorber membrane. The second multilayer film functions as a hard mask film used as an etching mask during the processing of the first multilayer film, which serves as the absorber film. The thickness of the first multilayer film is greater than 55 nm and less than 70 nm. The thickness of the second multilayer film is less than 20 nm.

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

11. The method for manufacturing a reflective mask blank according to claim 10, characterized in that: After the TaN portion is formed, a Ta film is formed in an oxygen- and nitrogen-free atmosphere to form the Ta portion. The TaO portion is formed by oxidizing the side of the Ta portion away from the substrate.

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