Reflective photomask blank and method for manufacturing reflective photomask

Abstract

SOLUTION: The reflective photomask blank includes a substrate, a multilayer reflective film that reflects exposure light, a protective film for the multilayer reflective film, and a light-absorbing film that absorbs the exposure light and has a phase shift function, wherein the light-absorbing film contains 80 to 90 at% of ruthenium (Ru), 5 to 15 at% of tantalum (Ta), and 10 at% or less of N and does not contain O, the light-absorbing film has a thickness of 38 to 50nm, and the light-absorbing film has a reflectivity of 10 to 14% with respect to the exposure light and a retardation of 205 to 225 degrees with respect to the exposure light.EFFECT: It is possible to provide a reflective photomask blank having a thinner light absorbing film, which has high wafer transfer characteristics (large value of NILS) and is less affected by the shadowing effect when used as a reflective photomask, and for example, it is possible to obtain high wafer transfer characteristics (NILS) that provide a good pattern in a miniaturized line and space pattern on a wafer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a reflective photomask used in the manufacture of semiconductor devices and the like, and to a reflective photomask blank used as a material for the reflective photomask in the manufacture thereof. [Background technology]

[0002] As semiconductor devices become increasingly miniaturized, particularly with the increasing integration of large-scale integrated circuits, projection exposure requires high pattern resolution. To address this issue, phase-shift masks have been developed as a photomask technique for improving the resolution of transferred patterns. The principle of phase-shifting is to adjust the phase of transmitted light passing through an opening in the phase-shift film of the photomask so that it is approximately 180 degrees inverted relative to the phase of transmitted light passing through the portion of the phase-shift film adjacent to the opening. This causes interference between the transmitted light at the boundary between the opening and the adjacent portion, reducing the light intensity. As a result, the resolution and depth of focus of the transferred pattern are improved. Photomasks that use this principle are collectively called phase-shift masks. In this case, the phase-shift mask is a type of transmissive photomask that transmits exposure light.

[0003] The phase shift mask blank used to manufacture this phase shift mask, as the material for the phase shift mask, most commonly has a structure in which a phase shift film is laminated on a transparent substrate such as a glass substrate, and a film formed of a material containing chromium (Cr) is laminated on the phase shift film. Phase shift films typically have a phase difference of 175 to 185 degrees and a transmittance of approximately 6 to 30% with respect to the exposure light, and are primarily formed of silicon (Si)-containing films, particularly materials containing molybdenum (Mo) and silicon (Si). The film formed of the chromium (Cr)-containing material is typically adjusted to a thickness that, when combined with the phase shift film, achieves the desired optical density. The film formed of the chromium (Cr)-containing material is generally used as both a light-shielding film and an etching mask when etching the phase shift film.

[0004] A typical method for manufacturing a phase shift mask by patterning a phase shift film from a phase shift mask blank having a transparent substrate on which a phase shift film made of a silicon (Si)-containing material and a light-shielding film made of a chromium (Cr)-containing material are formed in this order is as follows: First, a resist film is formed on the light-shielding film made of a chromium (Cr)-containing material of the phase shift mask blank, and a pattern is written on the resist film using light or an electron beam and developed to form a resist pattern. Next, using the resist pattern as an etching mask, the light-shielding film made of a chromium (Cr)-containing material is dry-etched with a chlorine-based gas to form a light-shielding film pattern. Furthermore, using the light-shielding film pattern as an etching mask, the phase shift film made of a silicon (Si)-containing material is dry-etched with a fluorine-based gas to form a phase shift film pattern. The resist pattern is then removed, and the light-shielding film pattern is removed by dry-etching with a chlorine-based gas.

[0005] In this case, the light-shielding film is left outside the portion where the phase shift film pattern (circuit pattern) is formed, and the outer peripheral edge of the phase shift mask is made into a light-shielding portion (light-shielding pattern) with an optical density of 3 or more, combining the phase shift film and the light-shielding film. This is to prevent exposure light from leaking from the outer peripheral edge of the phase shift mask and irradiating the resist film on the adjacent chip of the wafer from the portion outside the circuit pattern when the circuit pattern is transferred to the wafer using a wafer exposure device. A typical method for forming such a light-shielding pattern involves forming a phase shift film pattern, removing the resist pattern, forming a new resist film, and then patterning and developing the resist pattern, leaving the resist film on the outer peripheral edge of the light-shielding film. Using this resist pattern as an etching mask, a film made of a material containing chromium (Cr) is etched, leaving the light-shielding film on the outer peripheral edge of the phase shift mask.

[0006] For phase-shift mask blanks, which require highly accurate pattern formation, dry etching using gas plasma is the mainstream method. For dry etching of films made of chromium (Cr)-containing materials, dry etching using chlorine-based gases (chlorine-based dry etching) is used. For dry etching of films made of silicon (Si)-containing materials or materials containing molybdenum and silicon, dry etching using fluorine-based gases (fluorine-based dry etching) is used. In particular, for dry etching of films made of chromium (Cr)-containing materials, it is known that using an etching gas in which 10 to 25 volume percent oxygen gas (O gas) is mixed with chlorine gas (Cl gas) increases chemical reactivity and improves the etching rate.

[0007] As circuit patterns become finer, technology is required to form finer circuit patterns on phase shift masks. In particular, the line pattern assist pattern, which supports the resolution of the main pattern of a phase shift mask, must be smaller than the main pattern so that it is not transferred to the wafer when the circuit pattern is transferred to the wafer using a wafer exposure tool. For phase shift masks of the generation in which the half pitch of the line and space pattern on the wafer is 10 nm, the line width of the assist pattern of the circuit line pattern on the phase shift mask is required to be approximately 40 nm.

[0008] Chemically amplified resists, which are capable of forming fine patterns, consist of a base resin, an acid generator, a surfactant, etc., and can be used in many reactions in which the acid generated by exposure acts as a catalyst, making it possible to achieve high sensitivity, and the use of chemically amplified resists makes it possible to form mask patterns such as fine phase shift film patterns with line widths of 0.1 μm or less. The resist is applied to a photomask blank by spin coating using a resist coater.

[0009] Furthermore, the higher pattern resolution required for projection exposure in recent years has become difficult to achieve even with transmission phase-shift masks. Therefore, for the logic 7nm generation and beyond, EUV lithography, which uses extreme ultraviolet light (EUV light) as the exposure light, has come to be used.

[0010] Extreme ultraviolet light is easily absorbed by all materials, making it impossible to use transmission lithography such as conventional photolithography using ArF excimer laser light. For this reason, EUV lithography uses a reflective optical system. The wavelength of extreme ultraviolet light used in EUV lithography is 13 to 14 nm, while the wavelength of conventional ArF excimer laser light is 193 nm. Therefore, compared to photolithography using conventional ArF excimer laser light, the exposure wavelength is shorter and it is possible to transfer finer patterns onto a photomask.

[0011] Photomasks used in EUV lithography are reflective photomasks in which exposure light is reflected by the photomask. They generally have a structure in which a reflective film that reflects extreme ultraviolet light, a protective film to protect the reflective film, and a light-absorbing film pattern that absorbs extreme ultraviolet light are formed in this order on a substrate such as a glass substrate. The reflective film is a multilayer reflective film, which is composed of alternating low-refractive index layers and high-refractive index layers to enhance reflectivity when extreme ultraviolet light is irradiated onto the surface of the reflective film. Typically, the low-refractive index layer of the multilayer reflective film is a molybdenum (Mo) layer, and the high-refractive index layer is a silicon (Si) layer. Ruthenium (Ru) films are typically used as protective films. Meanwhile, the light-absorbing film is made of a material with a high absorption coefficient for extreme ultraviolet light, specifically a material containing chromium (Cr) or tantalum (Ta) as its main component. Early-generation EUV lithography used binary reflective photomasks, which did not reflect light from the light-absorbing film.

[0012] A typical method for producing a reflective photomask by patterning a light-absorbing film from a reflective photomask blank having a substrate on which a reflective film that reflects extreme ultraviolet light, a protective film for protecting the reflective film, and a light-absorbing film that absorbs extreme ultraviolet light are formed in this order is as follows: First, a resist film is formed on the light-absorbing film, and a pattern is written on this resist film using light or an electron beam, and developed to form a resist pattern. Next, the light-absorbing film is dry-etched using the resist pattern as an etching mask to form a pattern of the light-absorbing film, and then the resist pattern is removed.

[0013] In EUV lithography, for logic 3nm generation and beyond, reflective photomasks (reflective phase-shift photomasks) equipped with a light-absorbing film pattern with phase-shifting functionality are used to form finer patterns on wafers. By using a reflective phase-shift photomask, better wafer transfer characteristics can be obtained than with a binary reflective photomask. The wafer transfer characteristics can be expressed by NILS (Normalized Image Log Slope), which corresponds to the contrast of the light intensity transferred onto the wafer, and NILS is expressed by the following formula: NILS=(dI / dx) / (W×Ith) (Where W is the desired pattern dimension, Ith is the light intensity threshold that gives W, and dI / dx is the aerial image gradient.) When the NILS value is large, the optical image becomes steeper, improving the dimensional controllability of the resist pattern on the wafer. Therefore, a large NILS value is effective in forming finer patterns on the wafer, and reflective phase-shift photomasks, which can achieve a larger NILS value than binary reflective photomasks, are used.

[0014] NILS is affected by the size of the pattern on the wafer, the pattern pitch, the reflectivity of the reflective phase-shift photomask to the exposure light, and the phase difference to the exposure light. For example, in a line and space pattern on the wafer, if the line and space sizes are each 18 nm, a good NILS value will be obtained when the reflectivity to the exposure light is about 12% and the phase difference to the exposure light is about 215 degrees.

[0015] Furthermore, the phase shift film must have a certain thickness or more to absorb some of the exposure light and achieve a predetermined reflectance. However, in a reflective phase shift photomask, the exposure light enters the reflective photomask at an angle and is reflected at an angle. Therefore, if the phase shift film is thick, the influence of the shadowing effect, in which the exposure light is blocked by the phase shift film when it enters and is reflected, becomes greater. Therefore, in order to reduce the influence of the shadowing effect, a thinner phase shift film that provides a predetermined reflectance is advantageous.

[0016] For example, Japanese Patent Laid-Open Publication No. 2022-24617 (Patent Document 1) describes a reflective mask blank for EUV lithography in which a multilayer reflective film that reflects EUV light and a phase shift film that shifts the phase of EUV light are formed in this order on a substrate, and the phase shift film has a layer containing ruthenium (Ru) and at least one selected from the group consisting of oxygen (O) and nitrogen (N). The reflective mask blank for EUV lithography described in Japanese Patent Laid-Open Publication No. 2022-24617 (Patent Document 1) describes that the crystalline structure of the phase shift film is amorphous, specifically, that the full width at half maximum (FWHM) of the most intense peak among the diffraction peaks derived from the phase shift film observed at 2θ: 20° to 50° by out-of-plane XRD is 1.0° or more, and that the amorphous crystalline structure of the phase shift film increases the smoothness of the phase shift film surface. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Publication No. 2022-24617 Summary of the Invention [Problem to be solved by the invention]

[0018] Japanese Patent Application Laid-Open Publication No. 2022-24617 (Patent Document 1) describes a phase shift film containing ruthenium (Ru) and at least one selected from the group consisting of oxygen (O) and nitrogen (N), such as a layer containing 40 to 99 at% Ru and 1 to 60 at% O, or a layer containing 30 to 98 at% Ru, 1 to 69 at% O, and 1 to 69 at% N. However, phase shift films with a reflectivity to the exposure light that deviates from about 12% or a phase difference to the exposure light that deviates from about 215 degrees cannot achieve high wafer transfer characteristics (NILS) in line and space patterns on a wafer. Furthermore, even with a phase shift film with a reflectivity to the exposure light of about 12% and a phase difference to the exposure light of about 215 degrees, if the phase shift film is thick, sufficient light intensity contrast cannot be obtained due to the shadowing effect.

[0019] The present invention has been made to solve the above-mentioned problems, and has an object to provide a reflective photomask blank having a thinner light-absorbing film that, when made into a reflective photomask, has high wafer transfer characteristics (large NILS value) and is less affected by the shadowing effect, and to provide a method for producing a reflective photomask from such a reflective photomask blank. [Means for solving the problem]

[0020] In order to solve the above-mentioned problems, the present inventors have conducted extensive research into reflective photomask blanks and light-absorbing films having a phase-shift function for reflective photomasks. As a result, they have found that by making the light-absorbing film a film containing ruthenium (Ru), tantalum (Ta) and nitrogen (N) but not containing oxygen (O), with the ruthenium content being 80 atomic % or more and 90 atomic % or less, the tantalum content being 5 atomic % or more and 15 atomic % or less, and the nitrogen content being 10 atomic % or less, even a thin film can be made to have a reflectance to the exposure light of about 12%, a phase difference to the exposure light of about 215 degrees, and a light-absorbing film having a phase-shift function with high wafer transfer characteristics (large NILS value), thereby solving the above-mentioned problems and have completed the present invention.

[0021] Therefore, the present invention provides the following reflective photomask blank and method for producing a reflective photomask. 1. A substrate; a multilayer reflective film formed on the substrate and reflecting exposure light in the extreme ultraviolet region; a protective film formed on the multilayer reflective film to protect the multilayer reflective film; a light absorbing film formed on the protective film, absorbing the exposure light and having a phase shift function; Equipped with the light-absorbing film contains ruthenium (Ru), tantalum (Ta) and nitrogen (N), and does not contain oxygen (O); The content of the ruthenium (Ru) is 80 atomic % or more and 90 atomic % or less, the content of the tantalum (Ta) is 5 atomic % or more and 15 atomic % or less, and the content of the nitrogen (N) is 10 atomic % or less, The thickness of the light absorbing film is 38 nm or more and 50 nm or less, The light absorbing film has a reflectance of 10% or more and 14% or less for the exposure light, and a phase difference of 205 degrees or more and 225 degrees or less for the exposure light. A reflective photomask blank characterized by: 2. The reflective photomask blank according to 1, wherein the light absorbing film further contains niobium (Nb), and the content of the niobium (Nb) is 4% or less. 3. The reflective photomask blank according to 1, wherein the thickness of the protective film is 1 nm or more and 6 nm or less. 4. A method for producing a reflective photomask having a pattern of the light-absorbing film from the reflective photomask blank according to any one of 1 to 3, comprising the steps of: (A) forming a resist film in contact with the side of the light absorbing film that is away from the substrate; (B) patterning the resist film to form a resist pattern; (C) patterning the light absorbing film by dry etching using a chlorine-based gas using the resist pattern as an etching mask to form a light absorbing film pattern; (D) removing the resist pattern; A method for manufacturing a reflective photomask, comprising: [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a reflective photomask blank having a thinner light-absorbing film that, when used as a reflective photomask, has high wafer transfer characteristics (large NILS value) and is less affected by the shadowing effect, and it is possible to obtain high wafer transfer characteristics (NILS) that give a good pattern in, for example, a fine line and space pattern on a wafer. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a cross-sectional view showing an example of a reflective photomask blank of the present invention. [Figure 2] 1 is a cross-sectional view showing an example of a reflective photomask of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention will be described in more detail below. The reflective photomask blank of the present invention comprises a substrate, a multilayer reflective film formed on the substrate, a protective film formed on the multilayer reflective film, and a light-absorbing film formed on the protective film.

[0025] When a reflective photomask is held on a mask stage of an exposure tool, it is usually fixed by an electrostatic chuck. Therefore, the reflective photomask blank and reflective photomask of the present invention may be provided with a conductive film (rear film) on the rear surface of the substrate (the surface opposite to the front surface on which the multilayer reflective film or the like is formed) for fixing the reflective photomask by an electrostatic chuck. Furthermore, the reflective photomask blank of the present invention may further be provided with a resist film formed on the light-absorbing film directly or via another film.

[0026] From the reflective photomask blank of the present invention, it is possible to obtain, for example, a reflective photomask comprising a substrate, a multilayer reflective film formed on the substrate, a protective film formed on the multilayer reflective film, and a pattern of a light-absorbing film formed on the protective film (circuit pattern or photomask pattern).

[0027] The structures of the reflective photomask blank and reflective photomask of the present invention will be described below with reference to the drawings. In the description of the drawings, the same components are given the same reference numerals and their description may be omitted. Furthermore, the drawings may be enlarged for convenience, and the dimensional ratios of the components may not necessarily be the same as in reality.

[0028] 1 is a cross-sectional view showing an example of a reflective photomask blank of the present invention. This reflective photomask blank 100 has a substrate 1, a multilayer reflective film 2 formed on and in contact with the substrate 1, a protective film 3 formed on and in contact with the multilayer reflective film 2, and a light-absorbing film 4 formed on and in contact with the protective film 3.

[0029] 2 is a cross-sectional view showing an example of a reflective photomask of the present invention. This reflective photomask 200 has a substrate 1, a multilayer reflective film 2 formed on and in contact with the substrate 1, a protective film 3 formed on and in contact with the multilayer reflective film 2, and a light-absorbing film pattern 4a formed on and in contact with the protective film 3.

[0030] There are no particular limitations on the type or size of the substrate, and the substrate of the reflective photomask blank and the reflective photomask may or may not be transparent at the exposure wavelength. For example, a glass substrate such as a quartz substrate can be used as the substrate. Furthermore, a substrate known as a 6025 substrate, which is 6 inches square and 0.25 inches thick as specified in the SEMI standard, is suitable as the substrate. In the SI unit system, a 6025 substrate is usually expressed as a substrate with a 152 mm square and a thickness of 6.35 mm.

[0031] The multilayer reflective film is a film that reflects exposure light, which is extreme ultraviolet light. The multilayer reflective film is preferably formed in contact with the substrate. This extreme ultraviolet light is called EUV light, and the wavelength of EUV light is 13 to 14 nm, and EUV light usually has a wavelength of about 13.5 nm.

[0032] The material constituting the multilayer reflective film is preferably a material that is resistant to dry etching (chlorine-based dry etching) using a chlorine-based gas (for example, chlorine gas (Cl2 gas) alone or a mixed gas of chlorine gas (Cl2 gas) and oxygen gas (O2 gas)).

[0033] Specific examples of materials constituting the multilayer reflective film include silicon (Si), molybdenum (Mo), etc. As the multilayer reflective film, a laminated film (Si / Mo laminated film) in which silicon (Si) layers and molybdenum (Mo) layers are alternately stacked in about 20 to 60 layers is generally used.

[0034] The thickness of the multilayer reflective film is preferably 200 nm or more, more preferably 220 nm or more, and preferably 340 nm or less, more preferably 280 nm or less. The thickness of the silicon (Si) layer is preferably 2 nm or more, more preferably 3 nm or more, and preferably 6 nm or less, more preferably 5 nm or less. The thickness of the molybdenum (Mo) layer is preferably 1 nm or more, more preferably 2 nm or more, and preferably 5 nm or less, more preferably 4 nm or less.

[0035] The protective film is a film for protecting the multilayer reflective film. The protective film is preferably formed in contact with the multilayer reflective film. The protective film is provided to protect the multilayer reflective film, for example, during cleaning in processing into a reflective photomask, or during cleaning or repair of the reflective photomask. Furthermore, the protective film preferably has the function of protecting the multilayer reflective film when the light absorbing film is patterned by etching, and of preventing oxidation of the multilayer reflective film.

[0036] The material constituting the protective film is preferably a material having etching characteristics different from those of the light absorbing film, specifically, a material having resistance to chlorine-based dry etching, and a material having resistance to cleaning solutions containing sulfuric acid and alkali.

[0037] Specific examples of materials constituting the protective film include materials containing ruthenium (Ru). The material constituting the protective film may be ruthenium (Ru) alone or a ruthenium (Ru) compound containing ruthenium (Ru) and one or more elements selected from molybdenum (Mo), niobium (Nb), zirconium (Zr), yttrium (Y), boron (B), titanium (Ti), and lanthanum (La).

[0038] The protective film may be a single-layer film or a multilayer film (for example, a film composed of 2 to 4 layers). The protective film may also be a film having a gradient composition. The thinner the protective film, the higher the reflectance of the exposure light from the multilayer reflective film of the reflective photomask, and more exposure light is irradiated onto the wafer during exposure using the reflective photomask, improving productivity during exposure using the reflective photomask. On the other hand, if the protective film is too thin, it loses its function as a protective film to protect the multilayer reflective film. Therefore, the thickness of the protective film is preferably 1 nm or more, and preferably 6 nm or less, more preferably 4 nm or less.

[0039] The light-absorbing film is a film that absorbs exposure light in the extreme ultraviolet region, and is preferably formed in contact with the protective film.

[0040] The material constituting the light absorbing film is preferably a material that can be etched by dry etching using a chlorine-based gas containing oxygen (for example, dry etching using a mixed gas of chlorine gas (Cl2 gas) and oxygen gas (O2 gas)).

[0041] The light-absorbing film contains ruthenium (Ru), tantalum (Ta), and nitrogen (N). On the other hand, the light-absorbing film does not contain oxygen (O). In this case, the light-absorbing film is allowed to contain oxygen (O) to the extent that it is contained in a surface oxide layer formed on the surface of the light-absorbing film when the light-absorbing film comes into contact with the atmosphere after formation. The light-absorbing film of the present invention does not contain oxygen (O) in excess of the amount of impurities during and immediately after formation of the light-absorbing film.

[0042] Specific examples of materials constituting the light-absorbing film include ruthenium tantalum nitride (RuTaN). Furthermore, after the reflective photomask blank is made into a reflective photomask, the light-absorbing film is exposed to the atmosphere in storage and in the environment of use in a wafer exposure machine. Therefore, it is advantageous in terms of resistance to oxygen contained in the atmosphere for the light-absorbing film to contain niobium (Nb) in addition to ruthenium (Ru), tantalum (Ta), and nitrogen (N). Specific examples of materials containing niobium (Nb) include ruthenium tantalum niobium nitride (RuTaNbN).

[0043] The content of ruthenium (Ru) contained in the light-absorbing film is 80 atomic % or more, preferably 82 atomic % or more, and 90 atomic % or less, preferably 86 atomic % or less. The content of tantalum (Ta) contained in the light-absorbing film is 5 atomic % or more, preferably 10 atomic % or more, and 15 atomic % or less, preferably 13 atomic % or less. The content of nitrogen (N) contained in the light-absorbing film is 10 atomic % or less, preferably 6 atomic % or less, and preferably 1 atomic % or more, more preferably 2 atomic % or more. When the light-absorbing film contains niobium (Nb), the content of niobium (Nb) contained in the light-absorbing film is preferably 4 atomic % or less, more preferably 3 atomic % or less. In this case, the lower limit of the niobium (Nb) content is more than 0 atomic %, and is not particularly limited, but is preferably 1 atomic % or more.

[0044] In the present invention, the light-absorbing film is a film having a phase shift function, i.e., a phase shift film. The light-absorbing film having a phase shift function absorbs a part of the exposure light and reflects the remaining part with a phase change (shift) relative to the phase of the exposure light reflected from the multilayer reflective film, thereby obtaining a phase shift function due to the phase difference between the light reflected from the multilayer reflective film and the light reflected from the light-absorbing film.

[0045] The reflective photomask blank and reflective photomask of the present invention can be referred to as a reflective photomask blank having a phase shift function (reflective phase shift photomask blank) and a reflective photomask having a phase shift function (reflective phase shift photomask), respectively. The phase shift function of the light absorbing film can improve wafer transfer characteristics (NILS).

[0046] The light-absorbing film having a phase shift function (phase shift film) has a reflectance of 10% or more, preferably 11% or more, and 14% or less, preferably 13% or less, for exposure light in the extreme ultraviolet region. This reflectance is a relative reflectance for a portion where the light-absorbing film is not formed, and specifically, it is the ratio of the reflectance of light reflected from the light-absorbing film formed on the substrate via the multilayer reflective film and the protective film to the reflectance of light reflected from the multilayer reflective film and the protective film formed on the substrate.

[0047] A light-absorbing film having a phase shift function (phase shift film) has a phase difference with respect to exposure light, which is extreme ultraviolet region light, of 205 degrees or more, preferably 210 degrees or more, and 225 degrees or less, preferably 220 degrees or less. This phase difference is a relative phase difference with respect to a portion where the light-absorbing film is not formed, and specifically, is the difference between the phase of light reflected from a multilayer reflective film and a protective film formed on a substrate and the phase of light reflected from a light-absorbing film formed on the substrate via the multilayer reflective film and the protective film.

[0048] The light-absorbing film may be a single-layer film or a multi-layer film (for example, a film composed of 2 to 5 layers). The light-absorbing film may also be a film having a gradient composition. From the viewpoint of ensuring the light-absorbing function and the phase-shifting function and reducing the influence of the shadowing effect, the thickness of the light-absorbing film is 38 nm or more, preferably 40 nm or more, more preferably 42 nm or more, and 50 nm or less, preferably 48 nm or less, more preferably 46 nm or less.

[0049] The conductive film is preferably formed in contact with the substrate. The conductive film preferably has a sheet resistance of 100 Ω / □ or less, and there are no particular restrictions on the material. Examples of the material for the conductive film include materials containing tantalum (Ta) or chromium (Cr). Furthermore, materials containing tantalum (Ta) or chromium (Cr) may also contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. The thickness of the conductive film is not particularly limited as long as it functions as an electrostatic chuck, but is usually about 20 to 300 nm.

[0050] In the present invention, the resist film may be an electron beam resist that is written by an electron beam or a photoresist that is written by light, but a chemically amplified resist is preferred. The chemically amplified resist may be either a positive or negative type, and may, for example, contain a base resin such as a hydroxystyrene-based resin or a (meth)acrylic acid-based resin, an acid generator, and, if necessary, may contain a crosslinker, a quencher, a surfactant, etc.

[0051] The thickness of the resist film is preferably 150 nm or less, but from the viewpoint of making the resist pattern for forming a fine assist pattern less likely to collapse due to impact with the developer or impact with pure water during the rinsing process in the development step of forming the resist pattern, the thickness is preferably 100 nm or less. The lower limit of the thickness of the resist film is not particularly limited as long as it is a thickness that functions as an etching mask in etching, i.e., a thickness that leaves a resist pattern on the entire surface of the film to be etched after etching, but is preferably 50 nm or more, more preferably 70 nm or more.

[0052] Although the formation of the multilayer reflective film, protective film, light absorbing film, and conductive film of the present invention is not particularly limited, sputtering is preferred because it is easy to control and to form a film with predetermined properties. The sputtering method can be DC sputtering, RF sputtering, or the like, and is not particularly limited.

[0053] When a laminated film of a molybdenum (Mo) layer and a silicon (Si) layer is formed as the multilayer reflective film, a molybdenum (Mo) target and a silicon (Si) target can be used as the sputtering target.

[0054] When the protective film is formed from a material containing ruthenium (Ru), a ruthenium (Ru) target can be used as the sputtering target, and if necessary, targets of other elements that constitute the protective film can be used.

[0055] When forming a light-absorbing film made of a material containing ruthenium (Ru), tantalum (Ta), and nitrogen (N), a ruthenium (Ru) target or a tantalum (Ta) target can be used as the sputtering target. Alternatively, a target containing ruthenium (Ru) and nitrogen (N) but not containing oxygen (O), or a target containing tantalum (Ta) and nitrogen (N) but not containing oxygen (O) may be used. When forming a light-absorbing film made of a material containing niobium (Nb) in addition to ruthenium (Ru), tantalum (Ta), and nitrogen (N), a niobium (Nb) target or a target containing niobium (Nb) and nitrogen (N) but not containing oxygen (O) may be used as the sputtering target.

[0056] When the conductive film is formed from a material containing tantalum (Ta) or chromium (Cr), a tantalum (Ta) target or a chromium (Cr) target can be used as the sputtering target.

[0057] The power input to the sputtering target can be set appropriately depending on the size of the sputtering target, cooling efficiency, ease of control of film formation, etc., and is usually 50 to 3000 W / cm as the power per area of ​​the sputtering surface of the sputtering target. 2Furthermore, a rare gas such as helium gas (He gas), neon gas (Ne gas), or argon gas (Ar gas) is used as the sputtering gas, and when the film and the layers that make up the film are formed using only the elements of the target, only a rare gas may be used as the sputtering gas.

[0058] When the film and the layers that make up the film are formed from a material containing oxygen (O), nitrogen (N), or carbon (C), reactive sputtering is preferred. Sputtering gases used in reactive sputtering include rare gases such as helium gas (He), neon gas (Ne), and argon gas (Ar), and reactive gases. In particular, for a light-absorbing film containing nitrogen (N), reactive sputtering is preferred, using a reactive gas that contains nitrogen (N) but does not contain oxygen (O).

[0059] When the film and its constituent layers are formed from a material containing nitrogen (N), nitrogen gas (N2 gas) may be used as the reactive gas. When the film and its constituent layers are formed from a material containing oxygen (O), oxygen gas (O2 gas) may be used as the reactive gas. When the film and its constituent layers are formed from a material containing nitrogen (N) and oxygen (O), the reactive gas may be selected appropriately from oxygen gas (O2 gas), nitrogen gas (N2 gas), and nitrogen oxide gases such as nitric oxide gas (NO gas), nitrogen dioxide gas (NO2 gas), and nitrous oxide gas (NO2 gas). When the film and its constituent layers are formed from a material containing carbon, the reactive gas may be a carbon-containing gas such as methane gas (CH4), carbon monoxide gas (CO gas), or carbon dioxide gas (CO2 gas). When the film and the layers that make up the film are formed from a material containing nitrogen (N), oxygen (O), and carbon (C), reactive gases such as oxygen gas (O2 gas), nitrogen gas (N2 gas), and carbon dioxide gas (CO2) can be used simultaneously.

[0060] The pressure during formation of the film and the layers that make up the film may be appropriately set in consideration of film stress, chemical resistance, cleaning resistance, etc., and is preferably 0.01 Pa or more, more preferably 0.03 Pa or more, and preferably 1 Pa or less, more preferably 0.3 Pa or less, to particularly improve chemical resistance. The flow rate of each gas may be appropriately set to obtain the desired composition, and is usually 0.1 to 100 sccm.

[0061] In the manufacturing process of a reflective photomask blank, before forming a resist film, the substrate or the substrate and the film formed on the substrate may be subjected to a heat treatment. When performing the heat treatment, it is preferable to perform the heat treatment while the surface of the light-absorbing film is not exposed. The heat treatment method can be infrared heating, resistance heating, or the like, and the treatment conditions are not particularly limited. The heat treatment can be performed, for example, in a gas atmosphere containing oxygen (O). The concentration of the gas containing oxygen (O) is not particularly limited, and in the case of oxygen gas (O gas), for example, it can be 1 to 100% by volume. The heat treatment temperature is preferably 200°C or higher, more preferably 400°C or higher.

[0062] Furthermore, in the manufacturing process of a reflective photomask blank, films formed on the substrate other than the light-absorbing film may be subjected to ozone treatment or plasma treatment before forming a resist film, and the treatment conditions are not particularly limited. Either treatment can be performed for the purpose of increasing the oxygen concentration in the surface region of the film. In such cases, the treatment conditions can be appropriately adjusted to achieve a predetermined oxygen concentration. When forming a film by sputtering, the oxygen concentration in the surface region of the film can also be increased by adjusting the ratio of the rare gas in the sputtering gas to an oxygen-containing gas (oxidizing gas) such as oxygen gas (O gas), carbon monoxide gas (CO gas), or carbon dioxide gas (CO gas).

[0063] Furthermore, in the manufacturing process of a reflective photomask blank, a cleaning treatment may be performed before forming a resist film to remove defects present on the surface of the substrate or the film formed on the substrate. Cleaning can be performed using one or both of ultrapure water and functional water, which is ultrapure water containing ozone gas (O3 gas), hydrogen gas (H2 gas), etc. When performing a cleaning treatment on a light-absorbing film, it is preferable not to use functional water containing ozone gas (O3 gas). Furthermore, after cleaning with ultrapure water containing a surfactant, further cleaning may be performed using one or both of ultrapure water and functional water. Cleaning can be performed while irradiating with ultrasonic waves as necessary, and UV light irradiation can also be combined.

[0064] The method for forming the resist film (applying the resist) is not particularly limited, and known methods such as spin coating can be applied.

[0065] From the reflective photomask blank of the present invention, a reflective photomask comprising a substrate, a multilayer reflective film, a protective film, and a light absorbing film pattern can be produced.

[0066] In the manufacture of a reflective photomask, if a resist film is not formed on a reflective photomask blank, a resist film is formed in contact with the film furthest from the substrate of the reflective photomask blank, for example, the side of the light-absorbing film that is farthest from the substrate. The resist film is then patterned to obtain a resist pattern, which is used as an etching mask to pattern the light-absorbing film by dry etching using a chlorine-based gas containing oxygen, thereby producing a reflective photomask. In the manufacture of a reflective photomask, the resist pattern can be removed with sulfuric acid / hydrogen peroxide (SPM).

[0067] Specific examples of methods for producing a reflective photomask having a light-absorbing film pattern from the reflective photomask blank of the present invention include the following. First, if necessary, a resist film is formed in contact with the side of the light-absorbing film that is away from the substrate (step (A)). Next, the resist film is patterned to form a resist pattern (step (B)). Next, using the resist pattern as an etching mask, the light-absorbing film is patterned by dry etching using a chlorine-based gas, preferably dry etching using a chlorine-based gas containing oxygen, to form a light-absorbing film pattern (step (C)). Next, the resist pattern is removed (step (D)). [Example]

[0068] 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.

[0069] [Example 1] A reflective multilayer film, a protective film, and a light-absorbing film were laminated in this order on a quartz substrate measuring 152 mm square and approximately 6 mm thick to produce a reflective photomask blank as shown in FIG.

[0070] First, a molybdenum (Mo) target and a silicon (Si) target were used as the sputtering targets, and argon gas (Ar) was used as the sputtering gas. The power applied to the targets was adjusted, and the flow rate of the sputtering gas was also adjusted. Sputtering with the molybdenum (Mo) target and sputtering with the silicon (Si) target were alternately performed on a quartz substrate to form a multilayer reflective film (with a reflectivity of 65% for light with a wavelength of 13.5 nm) consisting of a laminated film (thickness 280 nm) in which molybdenum (Mo) layers and silicon (Si) layers were alternately stacked. The stacking of molybdenum (Mo) layers and silicon (Si) layers was performed 40 times (40 layers each of molybdenum (Mo) layers and silicon (Si) layers).

[0071] Next, a ruthenium (Ru) target was used as the target, and argon gas (Ar gas) was used as the sputtering gas. The power applied to the target was adjusted, and the flow rate of the sputtering gas was also adjusted. Sputtering was then performed using the ruthenium (Ru) target, forming a film (thickness 2 nm) made of ruthenium (Ru) alone as a protective film on the multilayer reflective film.

[0072] Next, a ruthenium (Ru) target and a tantalum (Ta) target were used as targets, and argon gas (Ar gas) and nitrogen gas (N gas) were used as sputtering gases. The power applied to the targets was adjusted, and the flow rate of the sputtering gas was also adjusted to perform sputtering. A light-absorbing film made of ruthenium tantalum nitride (RuTaN) was then formed on the protective film, thereby obtaining a reflective photomask blank.

[0073] The composition and thickness of the light-absorbing film, as well as the reflectivity (relative reflectivity to the multilayer reflective film and protective film) and phase difference (relative phase difference to the multilayer reflective film and protective film) for light with a wavelength of 13.5 nm are shown in Table 1. The composition of the light-absorbing film was measured using an X-ray photoelectron spectrometer (the same applies hereinafter). The thickness of the light-absorbing film was measured using an X-ray diffraction device (the same applies hereinafter). The reflectivity was measured using a reflectometer for light at an incident angle of 6 degrees (the same applies hereinafter). The phase difference was calculated from the refractive index n and extinction coefficient k measured using a refractive index / extinction coefficient measuring instrument (the same applies hereinafter).

[0074] [Examples 2 to 6, Comparative Examples 1 to 10] The multilayer reflective film and the protective film were formed in the same manner as in Example 1, and the light absorbing film was formed in the same manner as in Example 1 by changing the power applied to the target, the flow rate of the sputtering gas, and the sputtering time, to obtain a reflective photomask blank.

[0075] In Examples 5 and 6, a niobium (Nb) target was used together with a ruthenium (Ru) target and a tantalum (Ta) target. In Comparative Example 1, a ruthenium (Ru) target was not used. In Comparative Example 9, nitrogen gas (N2 gas) was not used. In Comparative Example 10, oxygen gas (O2 gas) was used together with argon gas (Ar gas) and nitrogen gas (N2 gas) as the sputtering gas. The composition and thickness of the light absorbing film, as well as the reflectance and phase difference for light with a wavelength of 13.5 nm, are shown in Table 1.

[0076] [Table 1]

[0077] The resulting reflective photomask blank was used to manufacture a reflective photomask as shown in Figure 2. First, a positive chemically amplified electron beam resist was spin-coated onto the light-absorbing film to form a resist film with a thickness of 150 nm.

[0078] Next, an electron beam lithography system was used to irradiate the substrate with a dose of 100 μC / cm 2 A line and space pattern (long side dimension 1000 nm, 100,000 line patterns) was written using the above method. The line pattern width was varied in 2-nm intervals within a range of 72 to 112 nm to give 21 different widths, and the space pattern width was varied in 2-nm intervals within a range of 72 to 168 nm to give 49 different widths, and various combinations of line pattern widths and space pattern widths were used to form line and space patterns.

[0079] Next, a heat treatment (PEB: Post Exposure Bake) was performed at 110°C for 14 minutes using a heat treatment device. Next, a development process was performed using a paddle development for 40 seconds to form a resist pattern. Next, using the obtained resist pattern as an etching mask, dry etching was performed on the light absorbing film using a chlorine-based gas containing oxygen under the following conditions to form a light absorbing film pattern.

[0080] <Conditions for dry etching of light absorbing film using chlorine-based gas containing oxygen> Equipment: ICP (Inductively Coupled Plasma) method Etching gas: Cl2 gas + O2 gas Gas pressure: 3.0 mTorr (0.40 Pa) ICP power: 350W

[0081] Next, the remaining resist pattern was removed by washing with sulfuric acid / hydrogen peroxide (a mixed solution of sulfuric acid and hydrogen peroxide (sulfuric acid:hydrogen peroxide=3:1 (volume ratio))), to obtain a reflective photomask.

[0082] For the obtained reflective photomask, the NILS of the line and space pattern of the light absorbing film was evaluated under the following conditions using a wafer transfer simulator capable of measuring the gradient of the aerial image. The wafer transfer simulator capable of measuring the gradient of the aerial image has an illumination system and a projection system that are almost equivalent to those of a wafer exposure tool, and can measure the gradient of the aerial image of a specific pattern by irradiating a minute area of ​​the reflective photomask with exposure light.

[0083] <Wafer transfer simulator setting conditions> NA (numerical aperture of wafer exposure machine): 0.33 Lighting conditions: Dipole Simga-in:0.7 Sigma-out: 0.9 Center angle: 0 degrees Blade angle: 30 degrees Wafer defocus: 0.03 μm

[0084] The dimensions of the line pattern and space pattern of the obtained reflective photomask were changed, and the NILS of all the line and space patterns was evaluated, and the maximum NILS value was evaluated. NILS is calculated by the following formula: NILS=(dI / dx) / (W×Ith) (Where W is the desired pattern dimension, Ith is the light intensity threshold that gives W, and dI / dx is the aerial image gradient.) Table 2 shows the NILS (maximum value) and the difference from the NILS (maximum value) of Comparative Example 1, which corresponds to a binary type reflective photomask.

[0085] [Table 2]

[0086] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any other configurations that are identical or substantially identical to the technical concept of the present invention and that provide the same or similar effects are included within the technical scope of the present invention. [Explanation of symbols]

[0087] 1 board 2 Multilayer reflective film 3 Protective film 4. Light-absorbing film 4a Light absorbing film pattern 100 Reflective Photomask Blanks 200 Reflective Photomask

Claims

1. A substrate; a multilayer reflective film formed on the substrate and reflecting exposure light in the extreme ultraviolet region; a protective film formed on the multilayer reflective film to protect the multilayer reflective film; a light absorbing film formed on the protective film, absorbing the exposure light and having a phase shift function; Equipped with the light absorbing film contains ruthenium (Ru), tantalum (Ta) and nitrogen (N) but does not contain oxygen (O); the content of the ruthenium (Ru) is 80 atomic % or more and 90 atomic % or less, the content of the tantalum (Ta) is 5 atomic % or more and 15 atomic % or less, and the content of the nitrogen (N) is 10 atomic % or less, the thickness of the light absorbing film is 38 nm or more and 50 nm or less; The light absorbing film has a reflectance of 10% or more and 14% or less for the exposure light and a phase difference of 205 degrees or more and 225 degrees or less for the exposure light. A reflective photomask blank characterized by:

2. 2. The reflective photomask blank according to claim 1, wherein the light absorbing film further contains niobium (Nb), and the content of the niobium (Nb) is 4% or less.

3. 2. The reflective photomask blank according to claim 1, wherein the protective film has a thickness of 1 nm or more and 6 nm or less.

4. A method for producing a reflective photomask having a pattern of the light-absorbing film from the reflective photomask blank according to any one of claims 1 to 3, comprising the steps of: (A) forming a resist film in contact with the side of the light absorbing film that is away from the substrate; (B) patterning the resist film to form a resist pattern; (C) patterning the light absorbing film by dry etching using a chlorine-based gas using the resist pattern as an etching mask to form a light absorbing film pattern; (D) removing the resist pattern; A method for manufacturing a reflective photomask, comprising:

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