Reflective photomask blank and method for manufacturing a reflective photomask

Abstract

A reflective photomask blank comprising 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 exposure light and has a phase-shift function, wherein the light-absorbing film contains 5 to 15 atomic percent of ruthenium (Ru) and 85 to 95 atomic percent of chromium (Cr), does not contain oxygen (O) or nitrogen (N), has a thickness of 40 to 56 nm, the reflectance of the light-absorbing film to exposure light is 2 to 5%, and the phase difference to exposure light is 200 to 230 degrees. [Effects] When used as a reflective photomask, it is possible to provide a reflective photomask blank with high wafer transfer characteristics (large NILS value), low shadowing effect, a thinner light absorption film, and a small deviation of the optimal focus value depending on the pitch of the line and space pattern on the wafer. For example, it provides a good pattern in a miniaturized line and space pattern on a wafer.

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 a reflective photomask blank used for the manufacture thereof as a material for the reflective photomask.

Background Art

[0002] With the miniaturization of semiconductor devices, particularly due to the high integration of large-scale integrated circuits, high pattern resolution is required for projection exposure. Therefore, as a method for improving the resolution of the transfer pattern in a photomask, a phase shift mask has been developed. The principle of the phase shift method is to adjust the phase of the transmitted light passing through the opening of the phase shift film of the photomask so that it is inverted by approximately 180 degrees with respect to the phase of the transmitted light passing through the portion of the phase shift film adjacent to the opening. As a result, at the boundary between the opening and the portion adjacent to the opening, the transmitted light interferes and the light intensity decreases. Consequently, the resolution and depth of focus of the transfer pattern are improved. A photomask using this principle is generally called a phase shift mask. In this case, the phase shift mask is a type of transmissive photomask that transmits exposure light.

[0003] The phase shift mask blank as a material for the phase shift mask used in the manufacture of this phase shift mask generally 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. The phase shift film usually has a phase difference of 175 to 185 degrees and a transmittance of about 6 to 30% with respect to exposure light, and a film containing silicon (Si), particularly a film formed of a material containing molybdenum (Mo) and silicon (Si), is the mainstream. In addition, the film formed of a material containing chromium (Cr) is adjusted to a thickness that provides a desired optical density in combination with the phase shift film, and the film formed of a material containing chromium (Cr) is generally used as a light-shielding film and an etching mask when etching the phase shift film.

[0004] A common method for manufacturing a phase-shift mask is to pattern a phase-shift film from a phase-shift mask blank, which has a phase-shift film made of silicon (Si) material and a light-shielding film made of chromium (Cr) material formed in that order on a transparent substrate. Specifically, the following method is generally used: First, a resist film is formed on the light-shielding film made of chromium (Cr) material of the phase-shift mask blank. A pattern is drawn on this resist film using light or an electron beam, and then developed to form a resist pattern. Next, using the resist pattern as an etching mask, the light-shielding film made of chromium (Cr) material is dry-etched using a chlorine-based gas to form a pattern for the light-shielding film. Furthermore, using the pattern for the light-shielding film as an etching mask, the phase-shift film made of silicon (Si) material is dry-etched using a fluorine-based gas to form a pattern for the phase-shift film. After that, the resist pattern is removed, and the pattern for the light-shielding film is removed by dry etching using a chlorine-based gas.

[0005] In this case, a light-shielding film is left outside the area where the phase-shift film pattern (circuit pattern) is formed, so that the outer edge of the phase-shift mask becomes a light-shielding area (light-shielding pattern) with a combined optical density of 3 or more from the phase-shift film and the light-shielding film. This is to prevent exposure light from leaking from the outer edge of the phase-shift mask when transferring the circuit pattern to the wafer using a wafer exposure apparatus, and from irradiating the resist film on adjacent chips on the wafer from the area located outside the circuit pattern. A common method for forming such a light-shielding pattern is to form a phase-shift film pattern, remove the resist pattern, then form a new resist film, and by pattern drawing and development, form a resist pattern in which the resist film remains on the outer edge of the light-shielding film. This resist pattern is then used as an etching mask to etch a film formed from a chromium (Cr)-containing material, leaving the light-shielding film on the outer edge of the phase-shift mask.

[0006] For phase-shift mask blanks, where high-precision pattern formation is required, dry etching using gas plasma is the mainstream method. Dry etching of films formed from chromium (Cr) materials is performed using chlorine-based gas (chlorine-based dry etching), while dry etching of films formed from silicon (Si) materials or from materials containing molybdenum and silicon is performed using fluorine-based gas (fluorine-based dry etching). In particular, for dry etching of films formed from chromium (Cr) materials, it is known that the chemical reactivity is increased and the etching rate is improved by using an etching gas that is a mixture of chlorine gas (Cl2 gas) and oxygen gas (O2 gas) at a ratio of 10 to 25 volume percent.

[0007] As circuit patterns become smaller, techniques for forming finer circuit patterns on phase shift masks are also required. In particular, the assist patterns of line patterns that support the resolution of the main pattern of the phase shift mask need to be formed smaller than the main pattern so that they are not transferred to the wafer when the circuit pattern is transferred to the wafer using a wafer exposure apparatus. In the generation of phase shift masks where the half-pitch of the line and space pattern on the wafer is 10 nm, the line width of the assist patterns of the circuit lines on the phase shift mask needs to be around 40 nm.

[0008] Chemically amplified resists, capable of forming fine patterns, consist of a base resin, an acid generator, a surfactant, and other components. Because many reactions in which the acid generated by exposure acts as a catalyst are applicable, high sensitivity is possible. Using chemically amplified resists enables the formation of mask patterns, such as fine phase-shift film patterns with line widths of 0.1 μm or less. The resist is applied onto a photomask blank by spin coating using a resist coating machine.

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

[0010] Extreme ultraviolet (EUV) light is readily absorbed by all materials, making it impossible to use transmission lithography like conventional photolithography using ArF excimer laser light. Therefore, EUV lithography employs a reflective optical system. The wavelength of extreme ultraviolet light used in EUV lithography is 13-14 nm, while the wavelength of conventional ArF excimer laser light is 193 nm. Compared to conventional photolithography using ArF excimer laser light, EUV lithography has a shorter exposure wavelength, making it possible to transfer finer patterns on the photomask.

[0011] The photomasks used in EUV lithography are reflective photomasks in which exposure light is reflected by the photomask. Generally, they 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 that absorbs extreme ultraviolet light are formed in this order on a substrate such as a glass substrate. As the reflective film, a multilayer reflective film is used in which the reflectivity when extreme ultraviolet light is irradiated onto the surface of the reflective film is increased by alternately stacking low refractive index layers and high refractive index layers. Typically, a molybdenum (Mo) layer is used as the low refractive index layer of the multilayer reflective film, and a silicon (Si) layer is used as the high refractive index layer. A ruthenium (Ru) film is usually used as the protective film. On the other hand, the light-absorbing film uses a material with a high absorption coefficient for extreme ultraviolet light, specifically, a material containing chromium (Cr) or tantalum (Ta) as the main component. In early generations of EUV lithography, a binary type reflective photomask was used in which there was no light reflection from the light-absorbing film.

[0012] A common method for manufacturing a reflective photomask is to pattern a light-absorbing film from a reflective photomask blank, which has a reflective film that reflects extreme ultraviolet light, a protective film to protect the reflective film, and a light-absorbing film that absorbs extreme ultraviolet light formed in this order on a substrate. Specifically, the following method is generally used: First, a resist film is formed on the light-absorbing film, a pattern is drawn on this resist film using light or an electron beam, and then developed to form a resist pattern. Next, the resist pattern is used as an etching mask to dry etch the light-absorbing film to form a pattern on the light-absorbing film, and then the resist pattern is removed.

[0013] In EUV lithography, from the logic 3nm generation onward, reflective photomasks (reflective phase-shift photomasks) with a light-absorbing film pattern that has a phase-shift function are used to form finer patterns on the wafer. By using a reflective phase-shift photomask, higher wafer transfer characteristics can be obtained compared to binary-type reflective photomasks. Wafer transfer characteristics can be expressed by NILS (Normalized Image Log Slope), which corresponds to the contrast of the light intensity transferred to the wafer, and NILS is given by the following formula NILS = (dI / dx) / (W×Ith) (In the formula, W is the desired pattern dimension, Ith is the threshold light intensity that gives W, and dI / dx is the gradient of the spatial image.) This can be determined by [the formula used]. 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 a reflective phase-shift photomask, which can achieve a larger NILS value than a binary reflective photomask, is used.

[0014] Furthermore, while a phase-shift film requires a certain thickness to absorb some of the exposure light and achieve a predetermined reflectivity, in a reflective phase-shift photomask, the exposure light is incident on the reflective photomask at an oblique angle and reflected at an oblique angle. Therefore, if the phase-shift film is thick, the shadowing effect, where the exposure light is blocked by the phase-shift film when it is incident and when it is reflected, becomes significant. To minimize the shadowing effect, a thinner phase-shift film that provides the predetermined reflectivity is advantageous.

[0015] For example, Japanese Patent Publication No. 2022-24617 (Patent Document 1) describes a layer 1 as a phase-shift film layer for a reflective mask blank for EUV lithography, which includes ruthenium (Ru) and at least one selected from the group consisting of oxygen (O) and nitrogen (N). This layer 1 contains Ru in the range of 40-99 at%, O in the range of 1-60 at%, and further includes an element (X) such as chromium (Cr), with a composition ratio of Ru:X The document describes layers with a composition ratio (at%) of 20:1 to 1:5, where the total of Ru and X is 40 to 99 at%, and O is 1 to 60 at%, and layers containing Ru in the range of 30 to 98 at%, O in the range of 1 to 69 at%, and N in the range of 1 to 69 at%, and further containing elements (X) such as chromium (Cr), where the composition ratio of Ru to X (Ru:X) (at%) is 20:1 to 1:5, where the total of Ru and X is 30 to 98 at%, O in the range of 1 to 69 at%, and N in the range of 1 to 69 at%. [Prior art documents] [Patent Documents]

[0016] [Patent Document 1] Japanese Patent Publication No. 2022-24617 [Overview of the Initiative] [Problems that the invention aims to solve]

[0017] When forming fine line-and-space patterns on a wafer using a reflective phase-shift mask, for example, when attempting to form line-and-space patterns with different pitches in the range of 16 to 60 nm, the optimal focus value differs depending on the pitch of the line-and-space pattern. Therefore, accurately transferring the circuit pattern of a reflective phase-shift mask containing two or more line-and-space patterns with different pitches onto the wafer is a challenge in EUV lithography.

[0018] In the phase-shift film of the reflective mask blank for EUV lithography described in Japanese Patent Publication No. 2022-24617 (Patent Document 1), the lowest relative reflectance in the EUV wavelength region is 6.1%. However, in phase-shift films having fine line-and-space patterns, if the relative reflectance is high, the optimal focus value differs significantly between line-and-space patterns with narrow pitches and those with wide pitches.

[0019] The present invention was made to solve the above problems, and aims to provide a reflective photomask blank that has a thinner light absorption film, high wafer transfer characteristics (large NILS value), low shadowing effect, and small deviation of the optimal focus value due to the pitch of the line and space pattern on the wafer, when used as a reflective photomask, and also to provide a method for manufacturing a reflective photomask from such a reflective photomask blank. [Means for solving the problem]

[0020] By reducing the reflectivity of a reflective photomask blank and a light absorption film having a phase shift function of a reflective photomask with respect to light in the extreme ultraviolet region, even for a fine line and space pattern, the optimal focus value for a line and space pattern with a narrow pitch and the optimal focus value for a line and space pattern with a wide pitch become approximately the same. Even for a reflective phase shift mask in which line and space patterns having two or more different pitches are mixed, the circuit pattern can be accurately transferred onto the wafer.

[0021] Therefore, in order to solve the above problems, the present inventor intensively studied a light absorption film having a phase shift function. As a result, the light absorption film is a film containing ruthenium (Ru) and chromium (Cr) and not containing oxygen (O) and nitrogen (N). By setting the content rate of ruthenium (Ru) to 5 atomic % or more and 15 atomic % or less and the content rate of chromium (Cr) to 85 atomic % or more and 95 atomic % or less, even for a thin film, the deviation of the optimal focus value due to the pitch of the line and space pattern on the wafer is small. It becomes a light absorption film having a phase shift function with a reflectivity with respect to exposure light of 5% or less and a phase difference with respect to exposure light of around 215 degrees, and having high wafer transfer characteristics (a large NILS value), and the present inventor found that the above problems can be solved, and thus completed the present invention.

[0022] Therefore, the present invention provides the following reflective photomask blank and a method for manufacturing a reflective photomask. 1. A substrate, A multilayer reflective film formed on the substrate and reflecting exposure light which is light in the extreme ultraviolet region, A protective film formed on the multilayer reflective film for protecting the multilayer reflective film, A light absorption film formed on the protective film, absorbing the exposure light and having a phase shift function and comprising, where the light absorption film contains ruthenium (Ru) and chromium (Cr) and does not contain oxygen (O) and nitrogen (N), The content ratio of ruthenium (Ru) is 5 atomic % or more and 15 atomic % or less, and the content ratio of chromium (Cr) is 85 atomic % or more and 95 atomic % or less, the thickness of the light absorption film is 40 nm or more and 56 nm or less, the reflectance of the light absorption film with respect to exposure light is from 2% to 5%, and the phase difference with respect to exposure light is from 200 degrees to 230 degrees characterizing a reflective photomask blank. 2. The reflective photomask blank according to 1, wherein the light absorption film further contains niobium (Nb), and the content ratio 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 manufacturing a reflective photomask including a pattern of the light absorption film from the reflective photomask blank according to any one of 1 to 3, (A) A step of forming a resist film in contact with the side of the light absorption film away from the substrate; (B) A step of patterning the resist film to form a resist pattern; (C) A step of patterning the light absorption film by dry etching using a chlorine-based gas with the resist pattern as an etching mask to form a light absorption film pattern; (D) A step of removing the resist pattern characterizing a method for manufacturing a reflective photomask.

Advantages of the Invention

[0023] According to the present invention, when a reflective photomask is formed, a reflective photomask blank having a higher wafer transfer characteristic (a larger NILS value), a smaller influence of the shadowing effect, a thinner light absorption film, and a smaller deviation of an optimal focus value due to the pitch of a line and space pattern on the wafer can be provided. For example, in a fine line and space pattern on the wafer, a good pattern can be provided.

Brief Description of the Drawings

[0024] [Figure 1] This is a cross-sectional view showing an example of a reflective photomask blank of the present invention. [Figure 2] This is a cross-sectional view showing an example of a reflective photomask of the present invention. [Modes for carrying out the invention]

[0025] 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.

[0026] Reflective photomasks are typically fixed to the mask stage of an exposure apparatus using an electrostatic chuck. Therefore, the reflective photomask blank and reflective photomask of the present invention may have a conductive film (back surface film) on the back surface of the substrate (the surface opposite to the surface on which the multilayer reflective film is formed) for fixing the reflective photomask with an electrostatic chuck. Furthermore, the reflective photomask blank of the present invention may further have a resist film formed directly or via another film on the light-absorbing film.

[0027] From the reflective photomask blank of the present invention, for example, a reflective photomask can be obtained comprising a substrate, a multilayer reflective film formed on the substrate, a protective film formed on the multilayer reflective film, and a pattern (circuit pattern or photomask pattern) of a light-absorbing film formed on the protective film.

[0028] The structure 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, identical components may be given the same reference numerals and their description may be omitted. Also, for convenience, the drawings may be shown in an enlarged form, and the dimensional ratios of each component may not necessarily be the same as in reality.

[0029] Figure 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 the substrate 1 in contact with the substrate 1, a protective film 3 formed on the multilayer reflective film 2 in contact with the multilayer reflective film 2, and a light-absorbing film 4 formed on the protective film 3 in contact with the protective film 3.

[0030] Figure 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 the substrate 1 in contact with the substrate 1, a protective film 3 formed on the multilayer reflective film 2 in contact with the multilayer reflective film 2, and a pattern 4a of a light-absorbing film formed on the protective film 3 in contact with the protective film 3.

[0031] There are no particular restrictions on the type or size of the substrate, and the substrates for the reflective photomask blank and reflective photomask may be transparent or opaque at the exposure wavelength. For example, glass substrates such as quartz substrates can be used. Alternatively, a substrate called a 6025 substrate, which is 6 inches square and 0.25 inches thick as defined in the SEMI standard, is preferred. When using the SI unit system, a 6025 substrate is usually described as a substrate with dimensions of 152 mm square and 6.35 mm thickness.

[0032] A multilayer reflective film is a film that reflects exposure light, which is light in the extreme ultraviolet region. Preferably, the multilayer reflective film is formed in contact with the substrate. This extreme ultraviolet region light is called EUV light, and the wavelength of EUV light is 13-14 nm, typically around 13.5 nm.

[0033] The materials constituting the multilayer reflective film are preferably materials that are resistant to dry etching using chlorine-based gases (for example, chlorine gas (Cl2 gas) alone, or a mixed gas of chlorine gas (Cl2 gas) and oxygen gas (O2 gas)).

[0034] Examples of materials that make up a multilayer reflective film include silicon (Si) and molybdenum (Mo). In this case, a multilayer film (Si / Mo multilayer film) is generally used, in which silicon (Si) layers and molybdenum (Mo) layers are stacked alternately in a number of layers of about 20 to 60.

[0035] When the multilayer reflective film is a Si / Mo multilayer film, the thickness of the multilayer reflective film is preferably 200 nm or more, more preferably 220 nm or more, and also 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 also 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 also preferably 5 nm or less, more preferably 4 nm or less.

[0036] Furthermore, silicon (Si) and ruthenium (Ru) can also be used as materials to constitute a multilayer reflective film. In this case, a multilayer film (Si / Ru multilayer film) in which silicon (Si) layers and ruthenium (Ru) layers are alternately stacked is generally used as the multilayer reflective film.

[0037] The protective film is a film for protecting the multilayer reflective film. Preferably, the protective film is formed in contact with the multilayer reflective film. The protective film is provided, for example, to protect the multilayer reflective film during cleaning in processing a reflective photomask, or during cleaning and repair of a reflective photomask. Furthermore, it is preferable that the protective film has the function of protecting the multilayer reflective film when patterning a light-absorbing film by etching, and preventing oxidation of the multilayer reflective film.

[0038] The material constituting the protective film is preferably a material with different etching properties from the light-absorbing film, and specifically, it is preferable that it is a material resistant to chlorine-based dry etching. Furthermore, the material constituting the protective film is preferably a material resistant to cleaning solutions containing sulfuric acid or alkali.

[0039] Specific examples of materials that constitute the protective film include materials containing ruthenium (Ru). The material that constitutes the protective film may be pure ruthenium (Ru), or it may be a ruthenium (Ru) compound containing ruthenium (Ru) and one or more elements selected from molybdenum (Mo), niobium (Nb), zirconium (Zr), yttrium (Y), boron (B), rhodium (Rh), titanium (Ti), and lanthanum (La).

[0040] The protective film may be a single layer or a multilayer film (for example, a film composed of 2 to 4 layers). The protective film may also have a gradient composition. A thinner protective film results in higher reflectivity of exposure light from the multilayer reflective film of the reflective photomask, allowing more exposure light to reach the wafer during exposure using a reflective photomask, thus improving productivity. On the other hand, if the film is too thin, it loses its function of protecting the multilayer reflective film. Therefore, the thickness of the protective film is preferably 1 nm or more, preferably 6 nm or less, and more preferably 4 nm or less.

[0041] A light-absorbing film is a film that absorbs exposure light, which is light in the extreme ultraviolet region. Preferably, the light-absorbing film is formed in contact with a protective film.

[0042] The material constituting the light-absorbing film is preferably a material that can be etched using dry etching with an oxygen-containing chlorine-based gas (for example, dry etching using a mixed gas of chlorine gas (Cl2 gas) and oxygen gas (O2 gas)).

[0043] The light-absorbing film contains ruthenium (Ru) and chromium (Cr). On the other hand, the light-absorbing film does not contain oxygen (O) or nitrogen (N). In this case, the content of oxygen (O) in the light-absorbing film is acceptable to the extent that it is contained in the surface oxide layer formed on the surface of the light-absorbing film when the light-absorbing film comes into contact with the atmosphere after its formation. The light-absorbing film of the present invention does not contain oxygen (O) and nitrogen (N) in amounts exceeding the amount of impurities at the time of formation and immediately after formation.

[0044] Specific examples of materials that constitute a light-absorbing film include ruthenium-chromium (RuCr). Furthermore, since the light-absorbing film is exposed to the atmosphere in storage environments and wafer exposure environments after being made from a reflective photomask blank into a reflective photomask, it is advantageous for the light-absorbing film to contain niobium (Nb) along with ruthenium (Ru) and chromium (Cr) in order to have resistance to oxygen in the atmosphere. Specific examples of materials containing niobium (Nb) include ruthenium-chromium-niobium (RuCrNb).

[0045] The ruthenium (Ru) content in the light-absorbing film is 5 atomic percent or more, preferably 8 atomic percent or more, and 15 atomic percent or less, preferably 12 atomic percent or less. The chromium (Cr) content in the light-absorbing film is 85 atomic percent or more, preferably 87 atomic percent or more, and 95 atomic percent or less, preferably 93 atomic percent or less. If the light-absorbing film contains niobium (Nb), the niobium (Nb) content in the light-absorbing film is preferably 4 atomic percent or less, more preferably 3 atomic percent or less. In this case, the lower limit of the niobium (Nb) content is greater than 0 atomic percent and is not particularly limited, but it is preferably 1 atomic percent or more.

[0046] In the present invention, the light-absorbing film is a film having a phase-shift function, that is, a phase-shift film. The light-absorbing film having a phase-shift function absorbs a portion of the exposure light, and reflects the remainder with its phase changed (shifted) 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.

[0047] The reflective photomask blank and reflective photomask of the present invention can be described 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. By having a light-absorbing film with a phase-shift function, wafer transfer characteristics (NILS) can be improved.

[0048] A light-absorbing film (phase-shift film) having a phase-shift function has a reflectance of 2% or more, preferably 3% or more, and 5% or less, preferably 4% or less, to exposure light, which is in the extreme ultraviolet region. This reflectance is the relative reflectance to the 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 protective film to the reflectance of light reflected from the multilayer reflective film and protective film formed on the substrate. By setting the reflectance to exposure light, which is in the extreme ultraviolet region, to 2% or more and 5% or less, a phase-shift function is ensured, and the light-absorbing film (phase-shift film) has a small deviation from the optimal focus value due to the pitch of the line-and-space pattern on the wafer.

[0049] A light-absorbing film having a phase-shift function (phase-shift film) has a phase difference of 200 degrees or more, preferably 205 degrees or more, with respect to exposure light, which is in the extreme ultraviolet region, and 230 degrees or less, preferably 225 degrees or less. This phase difference is the relative phase difference with respect to the portion where the light-absorbing film is not formed, and specifically, it is the difference between the phase of light reflected from the multilayer reflective film and protective film formed on the substrate and the phase of light reflected from the light-absorbing film formed on the substrate via the multilayer reflective film and protective film.

[0050] The light-absorbing film may be a single layer or a multilayer film (for example, a film composed of 2 to 5 layers). Furthermore, the light-absorbing film may have a gradient composition. From the viewpoint of ensuring light absorption and phase shift functions while minimizing the influence of shadowing effects, the thickness of the light-absorbing film is 40 nm or more, preferably 42 nm or more, more preferably 44 nm or more, and also 56 nm or less, preferably 54 nm or less, more preferably 52 nm or less.

[0051] 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 materials 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 for electrostatic chuck, but it is usually around 20 to 300 nm.

[0052] In the present invention, the resist film may be an electron beam resist drawn with an electron beam or a photoresist drawn with light, but a chemically amplified resist is preferred. The chemically amplified resist may be positive or negative, and examples include a base resin such as a hydroxystyrene resin or a (meth)acrylic acid resin, and an acid generator, with the addition of a crosslinking agent, quencher, surfactant, etc. as needed.

[0053] 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 during the development process for forming the resist pattern less susceptible to damage from the developer or the pure water during the rinsing process, it is preferable that the thickness be 100 nm or less. The lower limit of the resist film thickness is not particularly limited, as long as it is a thickness that functions as an etching mask in etching, that is, a thickness that leaves a resist pattern over the entire surface of the film to be etched after etching, but it is preferably 50 nm or more, more preferably 70 nm or more.

[0054] The formation of the multilayer reflective film, protective film, light-absorbing film, and conductive film of the present invention is not particularly limited, but formation by sputtering is preferred because it offers good controllability and makes it easy to form films with predetermined properties. The sputtering method can be DC sputtering, RF sputtering, etc., and is not particularly limited.

[0055] When forming a multilayer reflective film consisting of a molybdenum (Mo) layer and a silicon (Si) layer, a molybdenum (Mo) target and a silicon (Si) target can be used as the sputtering target. Similarly, when forming a multilayer reflective film consisting of a ruthenium (Ru) layer and a silicon (Si) layer, a ruthenium (Ru) target and a silicon (Si) target can be used as the sputtering target.

[0056] When forming a protective film with a material containing ruthenium (Ru), a ruthenium (Ru) target can be used as the sputtering target, and targets of other elements that make up the protective film can be used as needed.

[0057] When forming a light-absorbing film made from a material containing ruthenium (Ru) and chromium (Cr), a ruthenium (Ru) target and a chromium (Cr) target can be used as sputtering targets. When forming a light-absorbing film made from a material containing niobium (Nb) along with ruthenium (Ru) and chromium (Cr), a niobium (Nb) target can also be used as a sputtering target.

[0058] When forming a conductive film with a material containing tantalum (Ta) or chromium (Cr), a tantalum (Ta) target or a chromium (Cr) target can be used as the sputtering target.

[0059] The power supplied to the sputtering target should be set appropriately depending on the size of the sputtering target, cooling efficiency, and ease of controlling film formation. Typically, the power per unit area of ​​the sputtering surface of the sputtering target is 50 to 3000 W / cm². 2 This is sufficient. Furthermore, noble gases such as helium (He), neon (Ne), and argon (Ar) are used as sputtering gases, and if the film and the layers constituting the film are to be formed using only the target element, then only noble gases should be used as sputtering gases.

[0060] When forming a film and its constituent layers from a material containing oxygen (O), nitrogen (N), or carbon (C), reactive sputtering is preferred. For reactive sputtering, noble gases such as helium (He), neon (Ne), and argon (Ar) are used as sputtering gases, along with reactive gases. In particular, for light-absorbing films containing nitrogen (N), it is preferable to use reactive sputtering with a reactive gas that contains nitrogen (N) but not oxygen (O).

[0061] When forming the membrane and its constituent layers with a nitrogen (N)-containing material, nitrogen gas (N2 gas) may be used as the reactive gas. When forming the membrane and its constituent layers with an oxygen (O)-containing material, oxygen gas (O2 gas) may be used as the reactive gas. When forming the membrane and its constituent layers with a nitrogen (N) and oxygen (O)-containing material, the reactive gas may be appropriately selected from oxygen gas (O2 gas), nitrogen gas (N2 gas), and nitrogen oxide gases such as nitric oxide (NO gas), nitrogen dioxide gas (NO2 gas), and nitrous oxide gas (N2O gas). When forming the membrane and its constituent layers with a carbon-containing material, 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 forming a film and its constituent layers from a material containing nitrogen (N), oxygen (O), and carbon (C), the reactive gases can be, for example, oxygen gas (O2 gas), nitrogen gas (N2 gas), and carbon dioxide gas (CO2) used simultaneously.

[0062] The pressure during the formation of the membrane and its constituent layers should be set appropriately considering membrane stress, chemical resistance, and wash resistance, preferably 0.01 Pa or higher, more preferably 0.03 Pa or higher, and more preferably 1 Pa or lower, more preferably 0.3 Pa or lower, which particularly improves chemical resistance. The flow rates of each gas should be set appropriately to achieve the desired composition, and are usually between 0.1 and 100 sccm.

[0063] In the manufacturing process of a reflective photomask blank, the substrate or the substrate and the film formed on the substrate may be heat-treated before forming the resist film. When heat treatment is performed, 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, etc., and there are no particular restrictions on the treatment conditions. The heat treatment can be performed, for example, in a gas atmosphere containing oxygen (O). There are no particular restrictions on the concentration of the gas containing oxygen (O); for example, in the case of oxygen gas (O2 gas), it can be 1 to 100 volume%. The heat treatment temperature is preferably 200°C or higher, more preferably 400°C or higher.

[0064] Furthermore, in the manufacturing process of reflective photomask blanks, before forming the resist film, the film formed on the substrate other than the light-absorbing film may be subjected to ozone treatment, plasma treatment, or the like, and there are no particular restrictions on the treatment conditions. Any of these treatments can be performed with the aim of increasing the oxygen concentration on the surface of the film, and in that case, the treatment conditions should be adjusted as appropriate to achieve a predetermined oxygen concentration. When forming the film by sputtering, it is also possible to increase the oxygen concentration on the surface of the film by adjusting the ratio of the noble gas in the sputtering gas to oxygen-containing gases (oxidizing gases) such as oxygen gas (O2 gas), carbon monoxide gas (CO gas), and carbon dioxide gas (CO2 gas).

[0065] Furthermore, in the manufacturing process of reflective photomask blanks, a cleaning treatment may be performed to remove defects present on the surface of the substrate or the film formed on the substrate before forming the resist film. The cleaning can be performed using either or both ultrapure water and functional water, which is ultrapure water containing ozone gas (O3 gas), hydrogen gas (H2 gas), etc. When performing the cleaning treatment on a light-absorbing film, it is preferable not to use functional water containing ozone gas (O3 gas). Alternatively, after cleaning with ultrapure water containing a surfactant, further cleaning may be performed using either or both ultrapure water and functional water. The cleaning can be performed while irradiating with ultrasound as needed, and UV light irradiation can also be combined with the cleaning.

[0066] The method for forming the resist film (coating the resist) is not particularly limited, and known techniques such as spin coating can be applied.

[0067] A reflective photomask can be manufactured from the reflective photomask blank of the present invention, comprising a substrate, a multilayer reflective film, a protective film, and a pattern of light-absorbing films.

[0068] In the manufacturing of reflective photomasks, if a resist film is not formed on the reflective photomask blank, a resist film is formed in contact with the film furthest from the substrate on the reflective photomask blank, for example, the light-absorbing film, on the side furthest from the substrate. Subsequently, the resist pattern obtained by patterning the resist film is used as an etching mask, and the light-absorbing film is patterned by dry etching using a chlorine-based gas containing oxygen, thereby manufacturing the reflective photomask. In the manufacturing of reflective photomasks, the resist pattern can be removed with sulfuric acid peroxide (SPM).

[0069] A specific method for manufacturing a reflective photomask having a light-absorbing film pattern from a reflective photomask blank of the present invention is as follows: First, a resist film is formed in contact with the side of the light-absorbing film that is separated from the substrate, if necessary (Step (A)). Next, the resist film is patterned to form a resist pattern (Step (B)). Next, the resist pattern is used as an etching mask to pattern the light-absorbing film 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)). [Examples]

[0070] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0071] [Example 1] A reflective photomask blank, as shown in Figure 1, was manufactured by sequentially layering a multilayer reflective film, a protective film, and a light-absorbing film on a quartz substrate measuring 152 mm square and approximately 6 mm thick.

[0072] First, using molybdenum (Mo) and silicon (Si) targets, and argon gas (Ar) as the sputtering gas, the applied power to the targets and the flow rate of the sputtering gas were adjusted, and sputtering with the molybdenum (Mo) target and sputtering with the silicon (Si) target were performed alternately to form a multilayer reflective film (280 nm thick) on a quartz substrate, in which molybdenum (Mo) layers and silicon (Si) layers were alternately stacked (reflectance of 65% for light with a wavelength of 13.5 nm). The stacking of the molybdenum (Mo) layer and silicon (Si) layer was performed for 40 cycles (40 layers each of molybdenum (Mo) and silicon (Si) layers).

[0073] Next, using a ruthenium (Ru) target as the target and argon gas (Ar gas) as the sputtering gas, sputtering was performed with the ruthenium (Ru) target by adjusting the power applied to the target and the flow rate of the sputtering gas, thereby forming a protective film (2 nm thick) made of pure ruthenium (Ru) on top of the multilayer reflective film.

[0074] Next, using ruthenium (Ru) and chromium (Cr) targets, and argon (Ar) gas as the sputtering gas, sputtering was performed by adjusting the power applied to the targets and the flow rate of the sputtering gas to form a light-absorbing film on the protective film, thereby obtaining a reflective photomask blank.

[0075] Table 1 shows the composition, thickness, and reflectance (relative reflectance to the multilayer reflective film and protective film) and phase difference (relative phase difference to the multilayer reflective film and protective film) of the light-absorbing film for light with a wavelength of 13.5 nm. The composition of the light-absorbing film was measured using an X-ray photoelectron spectroscopy analyzer (the same applies below). The thickness of the light-absorbing film was measured using an X-ray diffractometer (the same applies below). The reflectance was measured using a reflectometer for light at an incident angle of 6 degrees (the same applies below). The phase difference was calculated from the measured values ​​of the refractive index n and extinction coefficient k using a refractive index / extinction coefficient meter (the same applies below).

[0076] [Examples 2-7, Comparative Examples 1-9] The multilayer reflective film and 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, but with changes to the power applied to the target, the flow rate of the sputtering gas, and the sputtering time, to obtain a reflective photomask blank.

[0077] In Examples 5-7 and Comparative Example 8, a niobium (Nb) target was used along with ruthenium (Ru) and chromium (Cr) targets. In Comparative Example 1, a tantalum (Ta) target was used instead of ruthenium (Ru) and chromium (Cr) targets. In Comparative Example 9, a tantalum (Ta) target was used along with a ruthenium (Ru) target, but no chromium (Cr) target was used. In Comparative Examples 1, 4, 6, 7, and 9, nitrogen (N2) gas was used along with argon (Ar) gas as the sputtering gas. In Comparative Examples 5 and 6, oxygen (O2) gas was used along with argon (Ar) gas as the sputtering gas. The composition, thickness, reflectance, and phase difference of the light-absorbing film for light at a wavelength of 13.5 nm are shown in Table 1.

[0078] [Table 1]

[0079] Using the obtained reflective photomask blank, a reflective photomask as shown in Figure 2 was fabricated. First, a 150 nm thick resist film was formed by spin-coating a positive-type chemically amplified electron beam resist onto the light-absorbing film.

[0080] Next, using an electron beam lithography apparatus, a dose of 100 μC / cm² was used. 2 Next, a line and space pattern (long side dimension 1000 nm, 100,000 lines) was drawn. The widths of the line and space patterns were set to 21 different widths for the line pattern (changed in 2 nm intervals within the range of 72 to 112 nm) and 49 different widths for the space pattern (changed in 2 nm intervals within the range of 72 to 168 nm). The line and space patterns were formed by various combinations of line and space pattern widths.

[0081] Next, a heat treatment (PEB: Post Exposure Bake) was performed at 110°C for 14 minutes using a heat treatment apparatus. Then, a development treatment was performed using 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 absorption film using a chlorine-based gas containing oxygen under the following conditions to form a light absorption film pattern.

[0082] <Conditions for dry etching of light-absorbing films using oxygen-containing chlorine-based gases> Equipment: ICP (Inductively Coupled Plasma) system Etching gas: Cl2 gas + O2 gas Gas pressure: 3.0 mTorr (0.40 Pa) ICP power: 350W

[0083] Next, the remaining resist pattern was washed away with sulfuric acid peroxide (a mixture of sulfuric acid and hydrogen peroxide in a 3:1 volume ratio) to obtain a reflective photomask.

[0084] The NILS of the line-and-space pattern of the light-absorbing film was evaluated for the obtained reflective photomask under the following conditions using a wafer transfer simulator capable of measuring the gradient of the spatial image. The wafer transfer simulator capable of measuring the gradient of the spatial image has an illumination system and projection system that are almost equivalent to those of a wafer exposure apparatus, and it is possible to measure the gradient of the spatial image of a specific pattern by illuminating a minute area of ​​the reflective photomask with exposure light.

[0085] <Wafer Transfer Simulator Settings> NA (Natural Aperture of Wafer Lithography 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

[0086] The NILS of all line and space patterns obtained by varying the dimensions of the line and space patterns of the reflective photomask was evaluated, and the maximum value of NILS was evaluated. NILS is calculated using the following formula: NILS = (dI / dx) / (W×Ith) (In the formula, W is the desired pattern dimension, Ith is the threshold light intensity that gives W, and dI / dx is the gradient of the spatial image.) This was determined by [method / method]. Table 2 shows the difference between the NILS (maximum value) and the NILS (maximum value) of Comparative Example 1, which corresponds to a binary type reflective photomask.

[0087] [Table 2]

[0088] For all line and space patterns obtained by varying the dimensions of the line and space patterns of the reflective photomask, the optimal focus value for each line and space pattern was evaluated, and the range of focus values ​​for all line and space patterns was evaluated. The range of focus values ​​and the difference from the range of focus values ​​of a phase-shift film with a reflectivity of approximately 12% (Comparative Example 9) are shown in Table 3.

[0089] [Table 3]

[0090] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are merely examples, and any configuration that is identical or substantially identical to the technical concept of the present invention and that produces the same or similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0091] 1 circuit board 2 Multilayer reflective film 3 Protective film 4. Light-absorbing film 4a Pattern of light-absorbing film 100 Reflective Photomask Blanks 200 Reflective Photomasks

Claims

1. circuit board and A multilayer reflective film formed on the substrate that reflects exposure light, which is light in the extreme ultraviolet region, A protective film formed on the multilayer reflective film for protecting the multilayer reflective film, A light-absorbing film formed on the protective film, which absorbs the exposure light and has a phase-shift function, Equipped with, The light-absorbing film contains ruthenium (Ru) and chromium (Cr), and does not contain oxygen (O) and nitrogen (N). The ruthenium (Ru) content is 5 atomic% or more and 15 atomic% or less, and the chromium (Cr) content is 85 atomic% or more and 95 atomic% or less. The thickness of the light-absorbing film is 40 nm or more and 56 nm or less. The light-absorbing film has a reflectance of 2% to 5% with respect to exposure light, and a phase difference of 200 degrees to 230 degrees with respect to exposure light. A reflective photomask blank characterized by the following features.

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

3. The reflective photomask blank according to claim 1, characterized in that the thickness of the protective film is 1 nm or more and 6 nm or less.

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

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