Photomask blank

Abstract

SOLUTION: A photomask blank includes a transparent substrate, and a light-shielding film formed on the transparent substrate, where the light-shielding film is formed by a material containing a transition metal, and silicon, the thickness of the light-shielding film is 30 nm or more and 80 nm or less, the light-shielding film is constituted by a multilayer including a protective layer formed by a material containing silicon and no transition metal, and disposed on a side most parted from the transparent substrate, and one or two or more light shielding layers formed by a material containing a transition metal, and silicon, and disposed on a transparent substrate side to the protective layer, the thickness of the protective layer is 1 nm or more and less than 8 nm, and the content of the transition metal in the light-shielding layer is 1 atom% or more.EFFECT: A light-shielding film of a photomask blank of the present invention has high SPM cleaning resistance, and light-shielding performance of the light-shielding film is hard to reduce even if repeating SPM cleaning to the light-shielding film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a photomask blank that serves as a material for photomasks used in the microfabrication of semiconductor integrated circuits, CCDs (charge-coupled devices), color filters for LCDs (liquid crystal displays), magnetic heads, etc., and in particular to a photomask blank that serves as a material for photomasks suitable for ArF excimer laser exposure. [Background technology]

[0002] In recent years, in semiconductor processing, particularly with the increasing integration density of large-scale integrated circuits, finer circuit patterns have become necessary, and there has been an increasing demand for technologies for finer wiring patterns that make up circuits and finer contact hole patterns for wiring between layers that make up cells. Therefore, in the manufacture of photomasks on which circuit patterns are written, which are used in optical lithography to form these wiring patterns and contact hole patterns, there is a demand for technologies that can write circuit patterns more finely and accurately.

[0003] To form a more accurate photomask pattern on a photomask substrate, it is first necessary to form a highly accurate resist pattern on a photomask blank. Because optical lithography for processing actual semiconductor substrates involves reduced projection, the photomask pattern is about four times the size of the actual required pattern, but this does not mean that precision is relaxed; higher precision is still required.

[0004] Furthermore, in current lithography, the circuit patterns to be drawn are sized much smaller than the wavelength of the light used, and if a photomask pattern that is four times the circuit shape is used, the exact shape of the photomask pattern will not be transferred to the resist film due to effects such as light interference that occur during actual optical lithography. Therefore, to reduce these effects, it may be necessary to process the photomask pattern into a shape that is more complex than the actual circuit pattern (a shape that applies so-called OPC: Optical Proximity Correction, etc.). Therefore, even in the lithography technology used to obtain photomask patterns, there is currently a demand for even more accurate processing methods.

[0005] When forming a pattern of a light-shielding film from a photomask blank, typically, a photoresist film is formed on a photomask blank having a light-shielding film on a transparent substrate, a pattern is drawn using an electron beam, and a resist pattern is obtained through development. The obtained resist pattern is then used as an etching mask to etch the light-shielding film and process it into a light-shielding pattern. However, when miniaturizing the light-shielding pattern, if an attempt is made to process it while maintaining the film thickness of the resist film the same as before miniaturization, the ratio of film thickness to the pattern, so-called aspect ratio, becomes high, which deteriorates the resist pattern shape and makes pattern transfer unsuccessful, and in some cases causes the resist pattern to collapse or peel off. Therefore, as the pattern becomes miniaturized, it is necessary to reduce the resist film thickness.

[0006] Many light-shielding films for photomask blanks have been proposed, but chromium compound films have been used as light-shielding film materials because there is a lot of knowledge about etching and standard processing methods have been established in practice. For example, Japanese Patent Laid-Open Publication No. 2003-195479 (Patent Document 1) describes a light-shielding film made of a chromium compound with a thickness of 50 to 77 nm as a light-shielding film for a photomask blank for ArF excimer laser exposure.

[0007] However, dry etching using chlorine-based gases containing oxygen, which is the general dry etching condition for chromium-based films such as chromium compound films, also etches the resist film to some extent, so when etching is performed with thinner resist films to transfer finer patterns, the resist film is damaged during etching, making it difficult to transfer the resist pattern accurately. Therefore, in order to achieve both finer patterning and high precision, it became necessary to reconsider materials that improve the processability of the light-shielding film, rather than relying solely on improving resist performance.

[0008] For example, Japanese Patent Application Laid-Open No. 2007-241060 (Patent Document 2) discloses that, in order to obtain even higher precision processability using a light-shielding film made of a material containing a transition metal and silicon, an etching mask film made of a chromium-based material is provided on the light-shielding film. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-195479 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-241060 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-78807 Summary of the Invention [Problem to be solved by the invention]

[0010] In mask blank manufacturing processes and lithography processes, cleaning using sulfuric acid and water (SPM (Sulfuric Acid-Hydrogen Peroxide Mixture) cleaning) is typically performed to clean the surfaces of photomask blanks and photomasks. However, repeated SPM cleaning of materials containing transition metals such as molybdenum, which are used to make the light-shielding film of photomask blanks, can cause film deterioration and film thinning, resulting in a decrease in light-shielding performance.

[0011] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a photomask blank having a light-shielding film formed from a material containing a transition metal such as molybdenum and silicon, in which the light-shielding performance of the light-shielding film is unlikely to deteriorate even after repeated SPM cleaning. [Means for solving the problem]

[0012] In order to solve the above-mentioned problems, the present inventors have conducted extensive research into light-shielding films of photomask blanks formed from a material containing a transition metal and silicon. As a result, they have found that a light-shielding film that combines high light-shielding properties with high SPM cleaning resistance can be obtained by configuring the light-shielding film to include a protective layer provided on the side furthest from the transparent substrate and a light-shielding layer provided on the transparent substrate side of the protective layer, and by forming the protective layer from a material that contains silicon but does not contain a transition metal, and by forming the light-shielding layer from a material that contains a transition metal and silicon, can be obtained, and have completed the present invention.

[0013] Accordingly, the present invention provides the following photomask blank. 1. A photomask blank having a transparent substrate and a light-shielding film formed on the transparent substrate, the light-shielding film is formed of a material containing a transition metal and silicon, the thickness of the light-shielding film is 30 nm or more and 80 nm or less, the light-shielding film is composed of multiple layers including a protective layer provided on the side farthest from the transparent substrate and formed of a material containing silicon but not containing a transition metal, and one or more light-shielding layers provided on the transparent substrate side of the protective layer and formed of a material containing a transition metal and silicon, the thickness of the protective layer is 1 nm or more and less than 8 nm, A photomask blank, wherein the content of the transition metal in the light-shielding layer is 1 atomic % or more. 2. The photomask blank according to 1, wherein the material containing a transition metal and silicon that forms the light-shielding film further contains one or more elements selected from oxygen, nitrogen, and carbon. 3. The photomask blank according to 1, wherein the material that forms the protective layer and contains silicon but no transition metal further contains one or both of oxygen and nitrogen. 4. The photomask blank according to 1, wherein the transition metal contained in the material forming the light-shielding film and light-shielding layer is molybdenum. 5. The photomask blank according to 1, wherein the protective layer and the light-shielding layer are both formed from materials that can be etched by dry etching using a fluorine-based gas. 6. When the above light-shielding film was brought into contact with an SPM cleaning solution prepared by mixing 96 mass % sulfuric acid and 30 mass % hydrogen peroxide solution at a volume ratio of sulfuric acid:hydrogen peroxide solution = 3:1 at 120°C for 18 minutes, The photomask blank according to 1, characterized in that the rate of variation in the optical density (OD) at the wavelength of the exposure light of the light-shielding film after contacting the SPM cleaning solution with respect to the optical density (OD) at the wavelength of the exposure light of the light-shielding film before contacting the SPM cleaning solution is less than 2%. 7. The photomask blank according to 1, which is a binary photomask blank. 8. The photomask blank according to 1, further comprising a hard mask film on the side of the light-shielding film that is away from the transparent substrate. [Effects of the Invention]

[0014] The light-shielding film of the photomask blank of the present invention has high resistance to SPM cleaning, and even if the light-shielding film is repeatedly subjected to SPM cleaning, the light-shielding performance of the light-shielding film is unlikely to deteriorate. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a first embodiment of the photomask blank of the present invention. [Figure 2]FIG. 2 is a cross-sectional view showing an example of a second embodiment of the photomask blank of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in more detail below. The photomask blank of the present invention has a transparent substrate and a light-shielding film formed on the transparent substrate. A photomask having a circuit pattern (photomask pattern) can be produced from the photomask blank of the present invention. The photomask blank of the present invention includes phase shift photomask blanks such as binary photomask blanks and halftone phase shift photomask blanks.

[0017] Generally, a photomask in which the circuit pattern (photomask pattern) is composed only of portions (light-shielding portions) that are formed by a light-shielding film and that substantially completely block the exposure light, and portions (transparent portions) that do not block the exposure light, and the light-shielding property of the circuit pattern is binary, either light-shielding or non-light-shielding, is called a binary photomask, and a material for producing a binary photomask is called a binary photomask blank. A binary photomask having a circuit pattern (photomask pattern) of a light-shielding film can be produced from the binary photomask blank.

[0018] On the other hand, when the photomask blank of the present invention is a phase shift photomask blank such as a halftone phase shift photomask blank, a phase shift film such as a halftone phase shift film can be provided between the transparent substrate and the light-shielding film. A phase shift photomask blank such as a halftone phase shift photomask blank serves as a material for phase shift photomasks such as halftone phase shift photomasks. A phase shift photomask having a circuit pattern (photomask pattern) of a phase shift film can be manufactured from the phase shift photomask blank.

[0019] Furthermore, when the photomask blank of the present invention is a phase shift photomask blank, a phase shift photomask can also be produced by engraving a transparent substrate to form a circuit pattern (photomask pattern) on the transparent substrate.

[0020] The exposure light (light used in exposure using a photomask) targeted by the photomask blank and photomask of the present invention is not particularly limited, but is preferably, for example, light having a wavelength of 250 nm or less, particularly light having a wavelength of 200 nm or less, such as an ArF excimer laser (wavelength: 193 nm).

[0021] 1 is a cross-sectional view showing an example of a first embodiment of the photomask blank of the present invention. This photomask blank 101 has a light-shielding film 2 formed on a transparent substrate 1 in contact with the transparent substrate 1. This photomask blank 101 is suitable as a binary photomask blank or a phase-shift photomask blank in which a circuit pattern (photomask pattern) is formed on the transparent substrate. The light-shielding film 2 is composed of a protective layer 21 provided on the side farthest from the transparent substrate 1, and a light-shielding layer 22 provided between the transparent substrate 1 and the protective layer 21 in contact with both of them.

[0022] The transparent substrate is not particularly limited in material or size, but is preferably a substrate that is transparent to exposure light and is used in transmission photomask blanks such as binary photomask blanks and phase-shift photomask blanks, and transmission photomasks such as binary photomasks and phase-shift photomasks, specifically a quartz substrate such as a synthetic quartz substrate. A suitable transparent substrate is, for example, a substrate known as a 6025 substrate, which is 6 inches square and 0.25 inches thick as specified in the SEMI standard. In SI units, a 6025 substrate is usually expressed as a substrate that is 152 mm square and 6.35 mm thick.

[0023] The light-shielding film is formed on a transparent substrate directly or via another film. When the photomask blank is a phase-shift photomask blank such as a halftone phase-shift photomask blank, a phase shift film such as a halftone phase-shift film can be provided as another film between the transparent substrate and the light-shielding film. In this case, it is preferable to provide an etching stopper film as another film between the light-shielding film and the phase shift film.

[0024] The light-shielding film is formed of a material containing a transition metal and silicon. The material containing a transition metal and silicon that forms the light-shielding film preferably further contains one or more light elements selected from oxygen, nitrogen, and carbon. The material that forms the light-shielding film is particularly preferably a material that contains a transition metal, silicon, and one or both of oxygen and nitrogen. The material that contains a transition metal, silicon, and one or both of oxygen and nitrogen may further contain carbon.

[0025] The transition metal material for forming the light-shielding film is preferably a transition metal other than chromium, specifically, molybdenum, tungsten, tantalum, titanium, zirconium, hafnium, etc., but molybdenum is particularly preferred from the viewpoint of processability by dry etching.

[0026] The light-shielding film is preferably made of a material that can be etched by dry etching using a fluorine-based gas (fluorine-based dry etching).Furthermore, the light-shielding film is preferably made of a material that is resistant to dry etching using a chlorine-based gas containing oxygen (chlorine-oxygen gas) (chlorine-based dry etching).

[0027] The thickness of the light-shielding film (the thickness of the entire light-shielding film) is preferably 20 nm or more, more preferably 30 nm or more, and even more preferably 40 nm or more, from the viewpoint of ensuring light-shielding properties against exposure light, and is preferably 90 nm or less, more preferably 80 nm or less, and even more preferably 70 nm or less, from the viewpoint of responding to miniaturization of patterns.

[0028] In particular, when the photomask blank is a binary photomask blank or a phase-shift photomask blank in which a circuit pattern (photomask pattern) is formed on a transparent substrate, the thickness of the light-shielding film (the total thickness of the light-shielding film) is preferably 30 nm or more, more preferably 40 nm or more, and preferably 90 nm or less, more preferably 80 nm or less. In this case, the optical density (OD) of the light-shielding film at the wavelength (193 nm) of exposure light, particularly an ArF excimer laser, is preferably 2.5 or more, more preferably 2.8 or more. Meanwhile, the upper limit of the optical density (OD) in this case is not particularly limited, but is usually 5 or less.

[0029] Furthermore, when the photomask blank is a phase shift photomask blank having a phase shift film such as a halftone phase shift film, the thickness of the light-shielding film (the total thickness of the light-shielding film) is preferably 20 nm or more, more preferably 30 nm or more, and preferably 80 nm or less, more preferably 70 nm or less. In this case, the optical density (OD) of the light-shielding film at the wavelength (193 nm) of exposure light, particularly an ArF excimer laser, is preferably 1 or more, more preferably 1.5 or more, and preferably 4.5 or less, more preferably 4 or less. Furthermore, the optical density (OD) of the light-shielding film combined with films (such as a phase shift film and an etching stopper film) provided between the transparent substrate and the light-shielding film at the wavelength (193 nm) of exposure light, particularly an ArF excimer laser, is preferably 2.5 or more, more preferably 2.8 or more. Meanwhile, the upper limit of the optical density (OD) in this case is not particularly limited, but is usually 5 or less.

[0030] The light-shielding film is composed of multiple layers (for example, 2 to 10 layers, preferably 2, 3, or 4 layers). The light-shielding film of the present invention includes, among the layers constituting the multiple layers, a protective layer provided on the side farthest from the transparent substrate. On the other hand, the light-shielding film includes, as a layer other than the protective layer, a light-shielding layer provided on the transparent substrate side of the protective layer, and it is preferable that at least the side closest to the transparent substrate is the light-shielding layer. The layers constituting the multiple layers may include layers other than the protective layer and the light-shielding layer, but are preferably composed of only the protective layer and the light-shielding layer.

[0031] Each layer constituting the multilayer light-shielding film may independently be a single-composition layer whose composition is constant in the thickness direction, or a gradient-composition layer whose composition changes continuously in the thickness direction. The multilayer light-shielding film may be a combination of only single-composition layers, a combination of only gradient-composition layers, or a combination of a single-composition layer and a gradient-composition layer.

[0032] From the viewpoint of reducing the reflectance of the exposure light, the multilayer light-shielding film preferably has a low optical density (OD) on the side of the light-shielding film away from the transparent substrate, and it is preferable that the entire layer other than the protective layer, preferably the entire light-shielding film including the protective layer, or the gradient composition layer, have a high content of light elements, particularly one or both of oxygen and nitrogen, on the side away from the transparent substrate. In this case, the optical density (OD) on the transparent substrate side can be increased, and the entire layer other than the protective layer, preferably the entire light-shielding film including the protective layer, or the gradient composition layer, have a high optical density (OD) on the side other than the side away from the transparent substrate, specifically, the content of light elements, particularly one or both of oxygen and nitrogen, can be reduced. Specific examples of such a light-shielding film include a three-layer structure consisting of, from the side away from the transparent substrate, a protective layer, a light-shielding layer with a low optical density (OD), and a light-shielding layer with a high optical density (OD).

[0033] Furthermore, from the viewpoint of reducing the reflectance of the exposure light, it is preferable that the optical density (OD) of the light-shielding film on the transparent substrate side is also low. It is more preferable that the content of light elements, particularly the content of one or both of oxygen and nitrogen, is high in the entire layer other than the protective layer or in the gradient composition layer on the transparent substrate side. In this case, the optical density (OD) on the side away from the transparent substrate and on the side other than the transparent substrate side can be made high, specifically, the content of light elements, particularly the content of one or both of oxygen and nitrogen, can be made low (the optical density (OD) of the central part in the thickness direction of the light-shielding film can be made high, specifically, the content of light elements, particularly the content of one or both of oxygen and nitrogen, can be made low). Specific examples of such light-shielding films include a four-layer structure consisting of, from the side away from the transparent substrate, a protective layer, a light-shielding layer with a low optical density (OD), a light-shielding layer with a high optical density (OD), and a light-shielding layer with a low optical density (OD).

[0034] The protective layer is formed of a material that contains silicon but does not contain transition metals (although the inclusion of transition metals as impurities is permitted). The protective layer of the present invention, which does not contain transition metals, is resistant to deterioration by SPM cleaning, and by providing the protective layer on the side farthest from the transparent substrate, high SPM cleaning resistance can be obtained for the light-shielding film. The protective layer may be composed of two or more sublayers (e.g., 2 to 5 layers). Each sublayer may be a single-composition layer or a gradient composition layer.

[0035] The material forming the protective layer, which contains silicon but does not contain a transition metal, preferably further contains one or more light elements selected from oxygen, nitrogen, and carbon. The material forming the protective layer more preferably contains one or both of oxygen and nitrogen, and particularly preferably contains silicon and oxygen.

[0036] Specific examples of materials for forming the protective layer include a material consisting of silicon only (Si), a material consisting of silicon and oxygen (SiO), a material consisting of silicon and nitrogen (SiN), and a material consisting of silicon, oxygen, and nitrogen (SiON). Of these, the material consisting of silicon and oxygen (SiO), the material consisting of silicon and nitrogen (SiN), and the material consisting of silicon, oxygen, and nitrogen (SiON) are preferred, and the material consisting of silicon and oxygen (SiO) is more preferred.

[0037] The material for forming the protective layer may be a material consisting only of silicon (Si) in terms of SPM cleaning resistance, but a material containing one or both of oxygen and nitrogen as a light element, particularly oxygen, and particularly a material consisting of silicon and oxygen (SiO), is preferable. The protective layer is the layer of the light-shielding film that is furthest from the transparent substrate, and the inclusion of a light element is also effective in reducing the reflectance of the light-shielding film to the exposure light, because this is the layer into which the exposure light is incident.

[0038] The silicon content of the material forming the protective layer is preferably 30 atomic % or more, and is preferably 99 atomic % or less, more preferably 60 atomic % or less, and even more preferably 50 atomic % or less.

[0039] When the material forming the protective layer contains oxygen, the oxygen content is preferably 1 atomic % or more, more preferably 40 atomic % or more, even more preferably 50 atomic % or more, and preferably 70 atomic % or less. When the material forming the protective layer contains nitrogen, the nitrogen content is preferably 1 atomic % or more, more preferably 20 atomic % or more, even more preferably 40 atomic % or more, and preferably 60 atomic % or less. Furthermore, when the material forming the protective layer contains both oxygen and nitrogen, the total content of oxygen and nitrogen is preferably 1 atomic % or more, more preferably 40 atomic % or more, even more preferably 50 atomic % or more, and preferably 70 atomic % or less.

[0040] The protective layer is preferably formed of a material that can be etched by dry etching using a fluorine-based gas (fluorine-based dry etching), and is also preferably formed of a material that is resistant to dry etching using a chlorine-based gas containing oxygen (chlorine-oxygen gas) (chlorine-based dry etching).

[0041] The thickness of the protective layer (when the protective layer is composed of two or more sublayers, the total thickness of all sublayers) is preferably thin, considering that it shortens the etching time when forming the light-shielding film pattern and obtains a good cross-sectional shape of the pattern, and is preferably less than 8 nm, more preferably 5 nm or less, and even more preferably 3 nm or less. On the other hand, if the thickness of the protective layer is too thin, sufficient SPM cleaning resistance cannot be obtained and it may be difficult to control the thickness when forming the protective layer, so it is preferably 1 nm or more. Furthermore, the optical density (OD) of the protective layer at the wavelength (193 nm) of the exposure light, particularly the ArF excimer laser, is preferably 1 or less, more preferably 0.5 or less, and even more preferably 0.05 or less.

[0042] The light-shielding layer is formed from a material containing a transition metal and silicon. The material containing a transition metal and silicon that forms the light-shielding layer preferably further contains one or more light elements selected from oxygen, nitrogen, and carbon. The material that forms the light-shielding layer is particularly preferably a material containing a transition metal, silicon, and nitrogen. In this case, the material containing a transition metal, silicon, and nitrogen may further contain one or both of oxygen and carbon.

[0043] The transition metal material for forming the light-shielding layer is preferably a transition metal other than chromium, such as molybdenum, tungsten, tantalum, titanium, zirconium, and hafnium, with molybdenum being particularly preferred from the viewpoint of processability by dry etching.

[0044] Specific examples of materials for forming the light-shielding layer include a material made of molybdenum, silicon, and nitrogen (MoSiN), a material made of molybdenum, silicon, oxygen, and nitrogen (MoSiON), a material made of molybdenum, silicon, nitrogen, and carbon (MoSiNC), and a material made of molybdenum, silicon, oxygen, nitrogen, and carbon (MoSiONC).

[0045] The transition metal content of the material forming the light-shielding layer is preferably 1 atomic % or more, more preferably 5 atomic % or more, even more preferably 10 atomic % or more, and is preferably 40 atomic % or less, more preferably 30 atomic % or less. On the other hand, the silicon content of the material forming the light-shielding layer is preferably 30 atomic % or more, more preferably 40 atomic % or more, even more preferably 50 atomic % or more, and is preferably 90 atomic % or less, more preferably 80 atomic % or less.

[0046] When the material forming the light-shielding layer contains nitrogen, the nitrogen content is preferably 3 atomic % or more, more preferably 5 atomic % or more, and preferably 50 atomic % or less, more preferably 40 atomic % or less. When the material forming the light-shielding layer contains oxygen, the oxygen content is preferably 0.5 atomic % or more, more preferably 1 atomic % or more, and preferably 50 atomic % or less, more preferably 30 atomic % or less. When the material forming the light-shielding layer contains carbon, the carbon content is preferably 0.2 atomic % or more, more preferably 0.4 atomic % or more, and preferably 10 atomic % or less, more preferably 5 atomic % or less. Furthermore, when the material forming the light-shielding layer contains one or more light elements selected from oxygen, nitrogen, and carbon, the total content of the light elements is preferably 0.5 atomic % or more, more preferably 5 atomic % or more, and preferably 60 atomic % or less, more preferably 50 atomic % or less.

[0047] The light-shielding layer is preferably made of a material that can be etched by dry etching using a fluorine-based gas (fluorine-based dry etching).Furthermore, the light-shielding layer is preferably made of a material that is resistant to dry etching using a chlorine-based gas containing oxygen (chlorine-oxygen gas) (chlorine-based dry etching).

[0048] The thickness of the light-shielding layer (when the light-shielding layer is composed of two or more layers, the total thickness of all the light-shielding layers) is the thickness obtained by subtracting the thickness of the protective layer from the thickness of the entire light-shielding film when the light-shielding film does not include any layers other than the protective layer and the light-shielding layer, but when the light-shielding film includes any layers other than the protective layer and the light-shielding layer, the thickness of the light-shielding layer is preferably 60% or more, more preferably 90% or more, and even more preferably 100% of the total thickness of the layers other than the protective layer in the light-shielding film, from the viewpoint of ensuring sufficient light-shielding properties. Furthermore, the optical density (OD) of the portion of the light-shielding film other than the protective layer in the exposure light is the optical density (OD) obtained by subtracting the optical density (OD) of the protective layer from the optical density (OD) of the light-shielding film.

[0049] The light-shielding film (each layer constituting the light-shielding film, such as the protective layer and the light-shielding layer, and each sub-layer constituting the protective layer) is preferably formed by a sputtering method, which can easily obtain a film (layer or sub-layer) with excellent homogeneity, and either DC sputtering or RF sputtering can be used. The target and sputtering gas are appropriately selected depending on the composition of the material that forms the light-shielding film.

[0050] The target may be appropriately selected from targets made of a transition metal such as a transition metal target (e.g., a molybdenum target), targets made of a transition metal and silicon such as a transition metal silicon target (e.g., a molybdenum silicide target), silicon targets (targets made of silicon), targets made of silicon and nitrogen such as a silicon nitride target and a target containing both silicon and silicon nitride, and the like.

[0051] As the sputtering gas, a rare gas (inert gas) such as helium gas, neon gas, or argon gas can be used, with argon gas being preferred as the rare gas. Furthermore, when forming a film using a material containing light elements such as oxygen, nitrogen, or carbon, reactive sputtering using a reactive gas together with the rare gas may be used. The content of the light elements can be adjusted by appropriately setting the amount of the reactive gas.

[0052] Examples of reactive gases that can be used include oxygen gas (O2 gas) when the material contains oxygen; nitrogen gas (N2 gas) when the material contains nitrogen; nitrogen oxide gases such as nitric oxide gas (NO gas), nitrogen dioxide gas (NO2 gas), and nitrous oxide gas (NO gas) when the material contains oxygen and nitrogen; and carbon oxide gases such as carbon monoxide gas (CO gas) and carbon dioxide gas (CO2 gas) when the material contains carbon and oxygen.

[0053] The sputtering pressure is preferably 0.01 Pa or more, more preferably 0.03 Pa or more, and is preferably 10 Pa or less, more preferably 0.1 Pa or less.

[0054] The light-shielding film of the present invention has high resistance to SPM cleaning. A specific example of an SPM cleaning solution used for SPM cleaning is a mixture of 96 mass % sulfuric acid (sulfuric acid aqueous solution) and 30 mass % hydrogen peroxide solution in a volume ratio of sulfuric acid:hydrogen peroxide = 3:1.

[0055] When the light-shielding film of the present invention is brought into contact with an SPM cleaning solution prepared by mixing 96% by mass of sulfuric acid (aqueous sulfuric acid solution) and 30% by mass of hydrogen peroxide solution in a volume ratio of sulfuric acid:hydrogen peroxide solution = 3:1 at 120°C for 18 minutes, the rate of variation in the optical density (OD) at the wavelength of the exposure light of the light-shielding film after contact with the SPM cleaning solution relative to the optical density (OD) at the wavelength of the exposure light of the light-shielding film before contact with the SPM cleaning solution is, for example, less than 2%, particularly 1% or less, and the light-shielding film has excellent SPM cleaning resistance.

[0056] A phase shift film is a film that has the function of increasing contrast by causing interference of exposure light due to the phase difference between the area where the phase shift film is present (phase shift portion) and the area where the phase shift film is not present. The phase shift film may be composed of a single layer or multiple layers.

[0057] The phase difference of the phase shift film relative to the exposure light, i.e., the phase difference between the exposure light that has passed through the phase shift film and the exposure light that has passed through an air layer of the same thickness as the phase shift film, is preferably 150° or more, more preferably 160° or more, even more preferably 175° or more, and is preferably 200° or less, more preferably 190° or less, even more preferably 185° or less.

[0058] The phase shift film is preferably a halftone phase shift film. The transmittance of the halftone phase shift film to the exposure light is not particularly limited, but is preferably 5% or more and 30% or less.

[0059] The phase shift film is preferably made of a material that can be etched by dry etching using a fluorine-based gas (fluorine-based dry etching), and is also preferably made of a material that is resistant to dry etching using a chlorine-based gas containing oxygen (chlorine-oxygen gas) (chlorine-based dry etching).

[0060] Examples of such materials include silicon compounds containing silicon and one or more elements selected from oxygen and nitrogen, and transition metal silicon compounds containing a transition metal, silicon, and one or more elements selected from oxygen, nitrogen, and carbon.

[0061] The transition metal material for forming the phase shift film is preferably a transition metal other than chromium, such as molybdenum, tungsten, tantalum, titanium, zirconium, and hafnium, with molybdenum being particularly preferred in terms of processability by dry etching.

[0062] When the material forming the phase shift film is a silicon compound, the silicon content is preferably 30 atomic % or more, more preferably 40 atomic % or more, and preferably 80 atomic % or less, more preferably 60 atomic % or less. The oxygen content is preferably 60 atomic % or less, more preferably 20 atomic % or less. The nitrogen content is preferably 10 atomic % or more, more preferably 30 atomic % or more, and preferably 65 atomic % or less, more preferably 60 atomic % or less.

[0063] On the other hand, when the material forming the phase shift film is a transition metal silicon compound, the transition metal content is preferably 0.1 atomic % or more, more preferably 1 atomic % or more, and preferably 30 atomic % or less, more preferably 20 atomic % or less. The silicon content is preferably 25 atomic % or more, more preferably 30 atomic % or more, and preferably 80 atomic % or less, more preferably 60 atomic % or less. The oxygen content is preferably 5 atomic % or more, and preferably 70 atomic % or less, more preferably 20 atomic % or less. The nitrogen content is preferably 10 atomic % or more, more preferably 25 atomic % or more, and preferably 60 atomic % or less, more preferably 57 atomic % or less. The carbon content is preferably 10 atomic % or less, more preferably 5 atomic % or less.

[0064] The thickness of the phase shift film is preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 70 nm or less. On the other hand, the lower limit of the thickness of the phase shift film is set within a range where necessary optical properties can be obtained at the wavelength of the exposure light, particularly the ArF excimer laser (193 nm), and is not particularly limited, but is usually 50 nm or more.

[0065] The phase shift film (each layer constituting the phase shift film) is preferably formed by sputtering, which can easily produce a film (layer) with excellent uniformity, and either DC sputtering or RF sputtering can be used. The target and sputtering gas are appropriately selected depending on the composition of the material that forms the phase shift film.

[0066] The target may be appropriately selected from targets made of a transition metal such as a transition metal target (e.g., a molybdenum target), targets made of a transition metal and silicon such as a transition metal silicon target (e.g., a molybdenum silicide target), silicon targets (targets made of silicon), targets made of silicon and nitrogen such as a silicon nitride target and a target containing both silicon and silicon nitride, and the like.

[0067] As the sputtering gas, a rare gas (inert gas) such as helium gas, neon gas, or argon gas can be used, with argon gas being preferred as the rare gas. Furthermore, when forming a film using a material containing a light element such as oxygen, nitrogen, or carbon, reactive sputtering using a reactive gas together with the rare gas may be used. The content of the light element can be adjusted by appropriately setting the amount of the reactive gas. The reactive gas may be the same as that exemplified in forming the light-shielding film.

[0068] The sputtering pressure is preferably 0.01 Pa or more, more preferably 0.03 Pa or more, and is preferably 10 Pa or less, more preferably 0.1 Pa or less.

[0069] The etching stopper film is a film that functions as an etching stopper when the light-shielding film is etched. The etching stopper film may be configured as a single layer or as a multilayer. The etching stopper film is preferably formed of a material that is resistant to dry etching using a fluorine-based gas (fluorine-based dry etching). Furthermore, the etching stopper film is preferably formed of a material that can be etched by dry etching using a chlorine-based gas containing oxygen (chlorine-oxygen gas) (chlorine-based dry etching).

[0070] Suitable examples of such materials include chromium-containing materials, such as elemental chromium and chromium compounds containing chromium and one or more selected from oxygen, nitrogen, and carbon, specifically chromium oxide (CrO), chromium nitride (CrN), chromium carbide (CrC), chromium oxynitride (CrON), chromium oxycarbide (CrOC), chromium nitride carbide (CrNC), and chromium oxynitride carbide (CrONC).

[0071] When the chromium-containing material is a chromium compound, the chromium content is preferably 30 atomic % or more, more preferably 35 atomic % or more, and less than 100 atomic %, preferably 90 atomic % or less. The oxygen content is preferably 60 atomic % or less, more preferably 50 atomic % or less. The nitrogen content is preferably 50 atomic % or less, more preferably 40 atomic % or less. The carbon content is preferably 30 atomic % or less, more preferably 20 atomic % or less. Furthermore, the total content of chromium, oxygen, nitrogen, and carbon in the chromium compound is preferably 95 atomic % or more, more preferably 99 atomic % or more, and even more preferably 100 atomic %. The thickness of the etching stopper film is preferably 1 nm or more, more preferably 3 nm or more, and preferably 20 nm or less, more preferably 10 nm or less.

[0072] The etching stopper film (each layer constituting the etching stopper film) is preferably formed by sputtering, which can easily produce a film (layer) with excellent uniformity, and either DC sputtering or RF sputtering can be used. The target and sputtering gas are appropriately selected depending on the composition of the material that forms the etching stopper film.

[0073] The target may be appropriately selected from targets made of chromium such as a chromium target, targets in which one or more species selected from oxygen, nitrogen, and carbon are added to chromium, and the like.

[0074] As the sputtering gas, a rare gas (inert gas) such as helium gas, neon gas, or argon gas can be used, with argon gas being preferred as the rare gas. Furthermore, when forming a film using a material containing a light element such as oxygen, nitrogen, or carbon, reactive sputtering using a reactive gas together with the rare gas may be used. The content of the light element can be adjusted by appropriately setting the amount of the reactive gas. The reactive gas may be the same as that exemplified in forming the light-shielding film.

[0075] The sputtering pressure is preferably 0.01 Pa or more, more preferably 0.03 Pa or more, and is preferably 10 Pa or less, more preferably 0.1 Pa or less.

[0076] The photomask blank of the present invention may further include a hard mask film on the side of the light-shielding film that is away from the transparent substrate, preferably in contact with the light-shielding film. The hard mask film functions as an etching assist film for the light-shielding film and contributes to improving the density dependency (reducing the loading effect), etc. By forming the hard mask film on the light-shielding film, the resist film used to form the pattern of the light-shielding film can be made thinner, allowing for more accurate formation of finer patterns. The hard mask film may be configured as a single layer or multiple layers.

[0077] 2 is a cross-sectional view showing an example of a second embodiment of the photomask blank of the present invention. This photomask blank 102 has, on a transparent substrate 1, a light-shielding film 2 formed in contact with the transparent substrate 1, and a hard mask film 3 formed in contact with the light-shielding film 2. This photomask blank 102 is suitable as a binary photomask blank or a phase-shift photomask blank in which a circuit pattern (photomask pattern) is formed on the transparent substrate. Furthermore, the light-shielding film 2 is composed of a protective layer 21 provided on the side farthest from the transparent substrate 1, and a light-shielding layer 22 provided between the transparent substrate 1 and the protective layer 21 in contact with both of them.

[0078] The hard mask film is preferably formed of a material having etching characteristics different from those of the light-shielding film, particularly the protective layer. The hard mask film is preferably formed of a material having resistance to dry etching using a fluorine-based gas (fluorine-based dry etching), which is suitably applied to etching the light-shielding film, particularly the protective layer. Furthermore, the hard mask film is preferably formed of a material that can be etched by dry etching using a chlorine-based gas containing oxygen (chlorine-oxygen gas) (chlorine-based dry etching).

[0079] The hard mask film is preferably formed of a material containing chromium, which may further contain one or more light elements selected from oxygen, nitrogen, and carbon.

[0080] Specific examples of materials for forming the hard mask film include chromium compounds such as elemental chromium (Cr), a material made of chromium and oxygen (CrO), a material made of chromium and nitrogen (CrN), a material made of chromium, oxygen and nitrogen (CrON), a material made of chromium and carbon (CrC), a material made of chromium, oxygen and carbon (CrOC), a material made of chromium, nitrogen and carbon (CrNC), and a material made of chromium, oxygen, nitrogen and carbon (CrONC).

[0081] When the material for forming the hard mask film is a chromium compound, the chromium content is preferably 30 atomic % or more, more preferably 35 atomic % or more, and less than 100 atomic %, preferably 99 atomic % or less, and more preferably 90 atomic % or less. The oxygen content is preferably 60 atomic % or less, more preferably 40 atomic % or less, and preferably 1 atomic % or more. The nitrogen content is preferably 50 atomic % or less, more preferably 40 atomic % or less, and preferably 1 atomic % or more. The carbon content is preferably 30 atomic % or less, more preferably 20 atomic % or less, and preferably 1 atomic % or more. When the material for forming the hard mask film contains chromium and one or more light elements selected from oxygen, nitrogen, and carbon, the total content of chromium and the light elements is preferably 95 atomic % or more, more preferably 99 atomic % or more, and even more preferably 100 atomic %.

[0082] The thickness of the hard mask film is preferably 1 nm or more, more preferably 2 nm or more, and is preferably 30 nm or less, more preferably 20 nm or less.

[0083] The hard mask film (each layer constituting the hard mask film) is preferably formed by a sputtering method, which can easily produce a film (layer) with excellent uniformity, and either DC sputtering or RF sputtering can be used. The target and sputtering gas are appropriately selected depending on the composition of the material that forms the hard mask film.

[0084] The target may be appropriately selected from targets made of chromium such as a chromium target, targets in which one or more species selected from oxygen, nitrogen, and carbon are added to chromium, and the like.

[0085] As the sputtering gas, a rare gas (inert gas) such as helium gas, neon gas, or argon gas can be used, with argon gas being preferred as the rare gas. Furthermore, when forming a film using a material containing a light element such as oxygen, nitrogen, or carbon, reactive sputtering using a reactive gas together with the rare gas may be used. The content of the light element can be adjusted by appropriately setting the amount of the reactive gas. The reactive gas may be the same as that exemplified in forming the light-shielding film.

[0086] The sputtering pressure is preferably 0.01 Pa or more, more preferably 0.03 Pa or more, and is preferably 10 Pa or less, more preferably 0.1 Pa or less. [Example]

[0087] EXAMPLES The present invention will be specifically explained below by showing examples and comparative examples, but the present invention is not limited to the following examples.

[0088] [Examples 1 to 5] Sputtering was performed on a transparent quartz substrate measuring 152 mm square and approximately 6 mm thick using a molybdenum target and a silicon target as targets and argon gas (Ar gas), oxygen gas (O2 gas), and nitrogen gas (N2 gas) as sputtering gases to form a light-shielding layer (MoSiON) made of a material consisting of molybdenum, silicon, oxygen, and nitrogen with an optical density (OD) of 3 (molybdenum: 11 atomic %, silicon: 42 atomic %, oxygen: 5 atomic %, nitrogen: 42 atomic %, thickness: 56 nm).

[0089] Next, a protective layer (thickness: 2 nm) made of a material consisting of silicon and oxygen (SiO), a material consisting of silicon and nitrogen (SiN), or a material consisting of silicon, oxygen, and nitrogen (SiON) was formed on the light-shielding layer by sputtering using a silicon target and argon gas as the sputtering gas, with either oxygen gas (O) or nitrogen gas (N), selected appropriately depending on the composition, to obtain a photomask blank. The increase in optical density after forming the protective layer was 0.05 or less in all cases. The composition of the protective layer is shown in Table 1.

[0090] [Comparative Example 1] A light-shielding layer was formed in the same manner as in Example 1 without forming a protective layer, to obtain a photomask blank having a light-shielding film consisting of only a light-shielding layer.

[0091] Next, the SPM cleaning resistance of the light-shielding films of the photomask blanks obtained in Examples 1 to 5 and Comparative Example 1 was evaluated. An SPM cleaning solution was used, which was a mixture of 96% by mass of sulfuric acid (aqueous sulfuric acid) and 30% by mass of hydrogen peroxide in a sulfuric acid:hydrogen peroxide ratio of 3:1 (volume ratio). The SPM cleaning solution was contacted with the surface of the light-shielding film of the photomask blank for 6 minutes at 120°C, the SPM cleaning solution was rinsed off with pure water for 1 minute, and the light-shielding film was dried for 4 minutes. This procedure from contact to drying was repeated three times, and the rate of change in optical density (OD) of the light-shielding film under ArF excimer laser irradiation (wavelength: 193 nm) before and after the three cycles was evaluated. Table 1 shows the optical density (OD) of the light-shielding film before evaluation and the rate of change in optical density.

[0092] [Table 1] [Explanation of symbols]

[0093] 1 Transparent substrate 2. Light-shielding film 21 Protective layer 22 Light blocking layer 3 Hard mask film 101, 102 Photomask blanks

Claims

1. A photomask blank having a transparent substrate and a light-shielding film formed on the transparent substrate, the light-shielding film is formed of a material containing a transition metal and silicon, the thickness of the light-shielding film is 30 nm or more and 80 nm or less, the light-shielding film is composed of multiple layers including a protective layer provided on the side farthest from the transparent substrate and formed of a material containing silicon but not containing a transition metal, and one or more light-shielding layers provided on the transparent substrate side of the protective layer and formed of a material containing a transition metal and silicon, the thickness of the protective layer is 1 nm or more and less than 8 nm, The content of the transition metal in the light-shielding layer is 1 atomic % or more. A photomask blank characterized by:

2. 2. The photomask blank according to claim 1, wherein the material containing a transition metal and silicon that forms the light-shielding film further contains at least one element selected from the group consisting of oxygen, nitrogen, and carbon.

3. 2. The photomask blank according to claim 1, wherein the material that forms the protective layer and contains silicon but no transition metal further contains one or both of oxygen and nitrogen.

4. 2. The photomask blank according to claim 1, wherein the transition metal contained in the material forming the light-shielding film and the light-shielding layer is molybdenum.

5. 2. The photomask blank according to claim 1, wherein the protective layer and the light-shielding layer are both formed from materials that can be etched by dry etching using a fluorine-based gas.

6. When the light-shielding film was brought into contact with an SPM cleaning solution prepared by mixing 96 mass % sulfuric acid and 30 mass % hydrogen peroxide solution at a volume ratio of sulfuric acid:hydrogen peroxide solution = 3:1 at 120°C for 18 minutes, 2. The photomask blank according to claim 1, wherein a variation rate of the optical density (OD) of the light-shielding film at the wavelength of exposure light after contacting the SPM cleaning solution relative to the optical density (OD) of the light-shielding film at the wavelength of exposure light before contacting the SPM cleaning solution is less than 2%.

7. 2. The photomask blank of claim 1, which is a binary photomask blank.

8. The photomask blank according to claim 1 , further comprising a hard mask film on the side of the light-shielding film that is away from the transparent substrate.

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