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

Abstract

The invention provides a reflective photomask blank and a method for manufacturing a reflective photomask. Provided is a reflective photomask blank including a substrate, a multilayer reflective film, a protective film, and a light absorbing film having a phase shift function. The light-absorbing film contains ruthenium and chromium and does not contain oxygen and nitrogen, and has a ruthenium content of 64-74 at%, a chromium content of 26-36 at%, a thickness of 40-44 nm, a reflectance of 12-15% with respect to exposure light that is light in the extreme ultraviolet range, and a phase shift of 200-230 degrees.

Description

Technical Field

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

[0002] High pattern resolution is required for projection exposure to address the miniaturization of semiconductor devices, particularly the high integration density of large-scale integrated circuits. Therefore, phase-shifting masks have been developed as a means to improve the resolution of transferred patterns. The principle of the phase-shifting method is that by adjusting the phase of the transmitted light that has passed through the opening of the phase-shifting film in the photomask to be approximately 180 degrees phase-reversed relative to the transmitted light that has passed through the portion of the phase-shifting film adjacent to the opening, interference between the transmitted light and the portion adjacent to the opening is reduced, thus improving the light intensity at the boundary. As a result, the resolution and depth of focus of the transferred pattern are improved. Photomasks utilizing this principle are generally called phase-shifting masks. In this case, the phase-shifting mask is a type of transmission-type photomask that transmits exposure light.

[0003] The most commonly used phase-shift mask preform (as the material of the phase-shift mask) for manufacturing phase-shift masks has the following structure, wherein a phase-shift film is stacked on a transparent substrate such as a glass substrate, and a film composed of a chromium (Cr)-containing material is stacked on top of the phase-shift film. Phase-shift films typically have a phase shift of about 175 to 185 degrees and a transmittance of about 6 to 30% for exposure light, and mainstream phase-shift films are composed of silicon (Si)-containing materials, particularly those containing molybdenum (Mo) and silicon (Si). Typically, the film composed of a chromium (Cr)-containing material is adjusted to have a thickness that, together with the phase-shift film, provides the desired optical density, and the film composed of a chromium (Cr)-containing material is provided as a light-shielding film and also used as an etching mask in etching the phase-shift film.

[0004] As a general method for manufacturing a phase-shifting mask by patterning a phase-shifting film from a phase-shifting mask blank, an example is the following method, in which a phase-shifting film composed of a silicon (Si) material and a light-shielding film composed of a chromium (Cr) material are sequentially formed on a transparent substrate in the phase-shifting mask blank. First, a photoresist film is formed on the light-shielding film composed of the chromium (Cr) material of the phase-shifting mask blank, and a photoresist pattern is formed by drawing a pattern on the photoresist film with light or an electron beam and developing it. Next, using the photoresist pattern as an etching mask, the light-shielding film composed of the chromium (Cr) material is dry-etched using a chlorine-based gas to form a pattern of the light-shielding film. Furthermore, using the pattern of the light-shielding film as an etching mask, the phase-shifting film composed of the silicon (Si) material is dry-etched using a fluorine-based gas to form a pattern of the phase-shifting film. Then, the photoresist pattern is removed, and the pattern of the light-shielding film is removed by dry etching using a chlorine-based gas.

[0005] In this configuration, the light-shielding film remains outside the portion of the pattern (circuit pattern) forming the phase-shifting film, and a light-shielding portion (light-shielding pattern) is formed on the outer periphery of the phase-shifting mask. This light-shielding portion has an optical density of not less than 3 in the combination of the phase-shifting film and the light-shielding film. This is to prevent exposure light leakage from the portion outside the circuit pattern on the outer periphery of the phase-shifting mask, which would otherwise cause exposure light to reach the resist film on an adjacent chip on the wafer, when the circuit pattern is transferred onto the wafer using a wafer exposure apparatus. In a general method for forming such a light-shielding pattern, after forming the pattern of the phase-shifting film and removing the resist pattern, the resist film is re-formed, and the resist pattern retained on the outer periphery of the light-shielding film is formed by drawing a pattern and developing. Then, the resist pattern is used as an etching mask to etch a film composed of a chromium (Cr)-containing material to leave a light-shielding film on the outer periphery of the phase-shifting mask.

[0006] The mainstream etching method in phase-shift mask preforms requiring highly precise patterning is dry etching using gas plasma. Dry etching using chlorine-based gases (chlorine-based dry etching) is used for films composed of materials containing chromium (Cr), and dry etching using fluorine-based gases (fluorine-based dry etching) is used for films containing silicon (Si) and films containing molybdenum and silicon. In particular, it is known that in dry etching of films composed of materials containing chromium (Cr), chemical reactivity and etching rate are increased by applying an etching gas consisting of chlorine (Cl2 gas) mixed with 10 to 25% by volume oxygen (O2 gas).

[0007] As circuit patterns become more miniaturized, the circuit patterns of phase-shift masks also require techniques for fine patterning. Specifically, auxiliary patterns for line patterns need to be formed smaller than the main pattern so that they are not transferred onto the wafer when the circuit pattern is transferred to the wafer using a wafer exposure apparatus. These auxiliary patterns contribute to the resolution of the main pattern of the phase-shift mask. In generational phase-shift masks with a half-pitch of 10 nm for both line and space patterns on the wafer, the linewidth of the auxiliary patterns for the line patterns in the circuitry on the phase-shift mask is required to be approximately 40 nm.

[0008] Chemically amplified resists, capable of forming fine patterns, consist of a base resin, an acid-generating agent, and a surfactant, and can be applied to many reactions in which the acid generated by exposure acts as a catalyst. Therefore, chemically amplified resists can exhibit high sensitivity. By using chemically amplified resists, mask patterns, such as those with phase-shifted films having linewidths of 0.1 μm or less, can be formed. The resist is applied to the photomask preform using a resist applicator via spin coating.

[0009] Furthermore, the higher pattern resolution required for projection exposure, as a desired pattern resolution, has become difficult to achieve even when using transmissive phase-shift masks. Therefore, for the logic 7nm generation and beyond, EUV lithography, which uses light in the extreme ultraviolet (EUV) range as the exposure light, has begun to be used.

[0010] Light in the extreme ultraviolet (EUV) range is readily absorbed by all materials, and transmission lithography, such as that using ArF excimer lasers, cannot be used. Therefore, reflective optics are used in EUV lithography. EUV lithography uses light in the extreme ultraviolet range with wavelengths of 13 to 14 nm, while conventional ArF excimer lasers have a wavelength of 193 nm. Therefore, compared to lithography using conventional ArF excimer lasers, the exposure wavelength is shorter, and finer patterns can be transferred in the photomask.

[0011] The photomasks used in EUV lithography are reflective photomasks in which exposure light is reflected by the photomask, and typically have the following structure: a pattern of a reflective film that reflects light in the extreme ultraviolet (EUV) range, a protective film for protecting the reflective film, and a light-absorbing film that absorbs light in the EUV range are sequentially formed on a substrate, such as a glass substrate. As the reflective film, a multilayer reflective film is used, in which low-refractive-index layers and high-refractive-index layers are stacked alternately to increase reflectivity when EUV light shines on the surface of the reflective film. Typically, for multilayer reflective films, a molybdenum (Mo) layer and a silicon (Si) layer are used as the low-refractive-index layer and the high-refractive-index layer, respectively. As the protective film, a ruthenium (Ru) film is typically used. On the other hand, for the light-absorbing film, a material with a high absorption coefficient for light in the EUV range is used, particularly a material containing, for example, chromium (Cr) or tantalum (Ta) as the main component. In earlier generations of EUV lithography, binary reflective photomasks were used, in which light was not reflected by the light-absorbing film.

[0012] As a general method for manufacturing a reflective photomask by patterning a light-absorbing film from a reflective photomask preform, specifically, the following method is exemplified, wherein a reflective film for reflecting light in the extreme ultraviolet (EUV) range, a protective film for protecting the reflective film, and a light-absorbing film for absorbing light in the EUV range are sequentially formed on a substrate in the reflective photomask preform. First, a photoresist film is formed on the light-absorbing film, and a pattern is drawn on the photoresist film by using light or an electron beam and then developed to form a photoresist pattern. Next, the photoresist pattern is used as an etching mask to dry etch the light-absorbing film to form the pattern of the light-absorbing film, and then the photoresist pattern is removed.

[0013] In EUV lithography, for logic 3nm and beyond, reflective photomasks (reflective phase-shift photomasks) with patterns including light-absorbing films with phase-shifting capabilities are used to form finer patterns on the wafer. Compared to binary reflective photomasks, reflective phase-shift photomasks offer superior wafer transfer characteristics. These characteristics can be represented by NILS (Normalized Image Logarithmic Slope), which corresponds to the contrast of light intensity transferred to the wafer, and NILS can be calculated using the following expression:

[0014] NILS = (dI / dx) / (W×Ith),

[0015] Where W is the desired pattern size, Ith is the threshold for the light intensity providing W, and dI / dx is the gradient of the spatial image. A large NILS value results in a steeper optical image, improving the dimensional controllability of the resist pattern on the wafer. Therefore, a large NILS value is effective for forming finer patterns on the wafer, and a reflective phase-shifting photomask that can provide a larger NILS value than a binary reflective photomask is used.

[0016] Furthermore, the phase-shift film must have a certain thickness to provide a predetermined reflectivity and absorb a portion of the exposure light. However, in a reflective phase-shift photomask, the exposure light is incident at an angle and reflected at an angle. Therefore, when the phase-shift film is thick, the shadowing effect, where the exposure light is blocked by the phase-shift film during incident and reflection, increases. Therefore, to reduce the shadowing effect, it is advantageous to provide a thinner phase-shift film with a predetermined reflectivity.

[0017] For example, JP 2022-24617 A (Patent Document 1) discloses a layer as a phase shift film in a reflective mask blank for EUV lithography, wherein layer 1 comprises ruthenium (Ru) and at least one selected from oxygen (O) and nitrogen (N). JP 2022-24617 A (Patent Document 1) discloses a layer as layer 1 containing Ru in the range of 40 to 99 at% and O in the range of 1 to 60 at% and also containing an element (X) such as chromium (Cr), and having a Ru:X (at%) composition ratio of Ru:X (at%) of 20:1 to 1:5, a total Ru and X content of 40 to 99 at%, and an O content of 1 to 60 at%; and a layer 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 also containing an element (X) such as chromium (Cr), and having a Ru:X (at%) composition ratio of Ru:X (at%) of 20:1 to 1:5, a total Ru and X content of 30 to 98 at%, and an O content of 1 to 69 at% and an N content of 1 to 69 at%.

[0018] Reference List

[0019] Patent Document 1: JP 2022-24617 A Summary of the Invention

[0020] When fine line and space patterns are formed on a wafer using a reflective phase-shift mask, phase-shift films with a reflectivity significantly deviating from the exposure light by about 12.5% ​​or a phase shift significantly deviating from the exposure light by about 215 degrees cannot provide high wafer transfer characteristics (NILS) in the line and space patterns on the wafer. Furthermore, even when the phase-shift film has a reflectivity of about 12.5% ​​and a phase shift of about 215 degrees relative to the exposure light, a thick phase-shift film cannot provide sufficient contrast in light intensity due to shading effects.

[0021] The present invention aims to solve the above-mentioned problems. The object of the present invention is to provide a reflective photomask preform that can provide a reflective photomask including a thin light-absorbing film, which has good wafer transfer characteristics (high NILS value) and is not easily affected by shading effects, and to provide a method for manufacturing a reflective photomask from such a reflective photomask preform.

[0022] NILS is affected by the size of the pattern on the wafer, the spacing of the pattern, and the reflectivity and phase shift of the reflective phase-shifting photomask relative to the exposure light. For example, in line and space patterns on a wafer, when the size of both the line and space is 24 nm to 36 nm, a good NILS value is obtained when the reflectivity relative to the exposure light is about 12.5% ​​and the phase shift relative to the exposure light is about 215 degrees.

[0023] Regarding the light-absorbing film with phase-shifting function, the inventors conducted careful research to solve the aforementioned problems. As a result, the inventors discovered that the problems could be solved by using a light-absorbing film containing ruthenium (Ru) and chromium (Cr), free of oxygen (O) and nitrogen (N), and having a ruthenium (Ru) content of not less than 64 at% and not more than 74 at% and a chromium (Cr) content of not less than 26 at% and not more than 36 at%; furthermore, it was found that despite the thinness of the light-absorbing film, at a reflectance of approximately 12.5% ​​relative to the exposure light, the light-absorbing film exhibits a phase-shifting function with excellent wafer transfer characteristics (high NILS value) at a phase shift of approximately 215 degrees relative to the exposure light.

[0024] In one aspect, the present invention provides a reflective photomask preform comprising:

[0025] substrate,

[0026] A multilayer reflective film is formed on a substrate and reflects exposure light in the extreme ultraviolet range.

[0027] A protective film, formed on the multilayer reflective film to protect the multilayer reflective film, and

[0028] The light-absorbing film, formed on the protective film, absorbs exposure light and has a phase-shifting function.

[0029] light absorbing film

[0030] It contains ruthenium (Ru) and chromium (Cr) but no oxygen (O) or nitrogen (N), and

[0031] It has a ruthenium (Ru) content of not less than 64 at% and not more than 74 at% and a chromium (Cr) content of not less than 26 at% and not more than 36 at%.

[0032] A thickness of not less than 40nm and not more than 44nm

[0033] A reflectance of not less than 12% and not more than 15% relative to the exposed light, and a phase shift of not less than 200 degrees and not more than 230 degrees relative to the exposed light.

[0034] Preferably, the light-absorbing film also contains niobium (Nb) and has a niobium (Nb) content of no more than 4 at%.

[0035] Preferably, the protective film has a thickness of not less than 1 nm and not more than 6 nm.

[0036] In another aspect, the present invention provides a method for manufacturing a reflective photomask from a reflective photomask preform, the reflective photomask comprising a pattern of a light-absorbing film, wherein...

[0037] The method includes the following steps:

[0038] (A) A resist film is formed on the side away from the substrate in contact with the light-absorbing film.

[0039] (B) Patterning the resist film to form a resist pattern.

[0040] (C) The light-absorbing film is patterned by using dry etching with chlorine-based gases and a resist pattern as an etching mask to form a light-absorbing film pattern, and

[0041] (D) Remove the resist pattern.

[0042] Beneficial effects of the invention

[0043] According to the present invention, a reflective photomask preform can be provided, which can provide a reflective photomask including a thin light-absorbing film, having good wafer transfer characteristics (high NILS value) and being less susceptible to shading effects. For example, fine lines and good patterns in spatial patterns can be obtained on the wafer. Attached Figure Description

[0044] Figure 1This is a cross-sectional view showing an example of the reflective photomask blank of the present invention.

[0045] Figure 2 This is a cross-sectional view showing an example of the reflective photomask of the present invention. Detailed Implementation

[0046] The reflective photomask blank of the present invention includes 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.

[0047] When a reflective photomask is held on the mask stage of an exposure apparatus, it is typically secured by an electrostatic chuck. Therefore, the reflective photomask blank and reflective photomask of the present invention may include a conductive film (back-side film) on the back side of the substrate (the surface opposite to the front side on which multiple reflective films are formed) for securing the reflective photomask by an electrostatic chuck. Furthermore, the reflective photomask blank of the present invention may also include a resist film formed directly on the light-absorbing film or via another film.

[0048] From the reflective photomask blank of the present invention, for example, a reflective photomask can be obtained including a pattern (circuit pattern or photomask pattern) of 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.

[0049] The structure of the reflective photomask blank and the reflective photomask of the present invention will now be described with reference to the accompanying drawings. In the description of the drawings, the same components may be given the same reference numerals, and repeated descriptions may be omitted. Furthermore, for convenience, the drawings may be enlarged, and the dimensional ratios of the components may differ from the actual proportions.

[0050] Figure 1 This is a cross-sectional view showing an example of the reflective photomask blank of the present invention. The reflective photomask blank 100 includes 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.

[0051] Figure 2 This is a cross-sectional view showing an example of a reflective photomask of the present invention. The reflective photomask 200 includes 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 formed on the protective film 3 in contact with the protective film 3, and a pattern 4a.

[0052] There are no particular restrictions on the material or size of the substrate. The substrate for reflective photomask blanks and reflective photomasks can be transparent or opaque at the wavelength of the exposure light. Glass substrates, such as quartz substrates, can be used as substrates. Suitable substrates are, for example, those with dimensions of 6 inches square and 0.25 inches thick, referred to as 6025 substrates, as defined in the SEMI standard. A 6025 substrate typically indicates a substrate with dimensions of 152 mm square and 6.35 mm thick in the SI unit system.

[0053] A multilayer reflective film is a film that reflects exposure light in the extreme ultraviolet (EUV) range. Preferably, the multilayer reflective film is formed in contact with a substrate. The light in this extreme ultraviolet region is called EUV light, and EUV light has a wavelength of 13-14 nm, and typically has a wavelength of about 13.5 nm.

[0054] The material constituting the multilayer reflective film is preferably a material resistant to dry etching (chlorine-based dry etching) of chlorine-based gases (e.g., only chlorine (Cl2 gas), or a mixture of chlorine (Cl2 gas) and oxygen (O2 gas).

[0055] Examples of materials used to construct multilayer reflective films include silicon (Si) and molybdenum (Mo). In this case, a multilayer reflective film typically uses a laminated film in which approximately 20-60 silicon (Si) layers and molybdenum (Mo) layers are alternately stacked (Si / Mo laminated film).

[0056] When the multilayer reflective film is a laminated film (Si / Mo laminated film), the multilayer reflective film preferably has a thickness of not less than 200 nm, more preferably not less than 220 nm, and more preferably not greater than 340 nm, and more preferably not greater than 280 nm. The silicon (Si) layer preferably has a thickness of not less than 2 nm, more preferably not less than 3 nm, and more preferably not greater than 6 nm, and more preferably not greater than 5 nm. The molybdenum (Mo) layer preferably has a thickness of not less than 1 nm, more preferably not less than 2 nm, and more preferably not greater than 5 nm, and more preferably not greater than 4 nm.

[0057] In addition, silicon (Si) and ruthenium (Ru) are also examples of materials constituting multilayer reflective films. In this case, a multilayer reflective film in which silicon (Si) layers and ruthenium (Ru) layers are alternately stacked (Si / Ru multilayer film) is usually used.

[0058] A protective film is used to protect a multilayer reflective film. Preferably, the protective film is formed in contact with the multilayer reflective film. The protective film is provided to protect the multilayer reflective film, for example, during cleaning when processing into a reflective photomask, or during cleaning or correction of a reflective photomask. Furthermore, the protective film preferably has the function of protecting the multilayer reflective film when patterning the light-absorbing film by etching, or preventing oxidation of the multilayer reflective film.

[0059] The material constituting the protective film is preferably a material with different etching properties than the light-absorbing film, and particularly preferably 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.

[0060] Materials constituting the protective film include, for example, materials containing ruthenium (Ru). The material constituting the protective film may be ruthenium (Ru) alone, or a ruthenium (Ru) compound containing ruthenium (Ru) and at least one selected from molybdenum (Mo), niobium (Nb), zirconium (Zr), yttrium (Y), boron (B), rhodium (Rh), titanium (Ti), and lanthanum (La).

[0061] The protective film can be a single-layer film or a multi-layer film (e.g., a film composed of two to four layers). Furthermore, the protective film can also be a film with a gradient composition. When the protective film is thin, the reflectivity of the exposure light from the multi-layer reflective film of the reflective photomask is high, and more exposure light illuminates the wafer during exposure using the reflective photomask, thereby improving productivity. On the other hand, when the protective film is too thin, its function as a protective film for the multi-layer reflective film is lost. Therefore, the protective film preferably has a thickness of not less than 1 nm and preferably not more than 6 nm, more preferably not more than 4 nm.

[0062] A light-absorbing film is a film that absorbs exposure light in the extreme ultraviolet range. Preferably, the light-absorbing film is formed in contact with a protective film.

[0063] The material constituting the light-absorbing film is preferably a material that can be etched using a chlorine-based gas containing oxygen (e.g., dry etching using a mixture of chlorine (Cl2 gas) and oxygen (O2 gas)).

[0064] The light-absorbing film contains ruthenium (Ru) and chromium (Cr). On the other hand, the light-absorbing film does not contain oxygen (O) and nitrogen (N). In this case, the oxygen (O) content in the light-absorbing film is the amount permitted in the surface oxide layer formed at the surface portion of the light-absorbing film after its formation by contacting the film with air. During and immediately after the formation of the light-absorbing film, the light-absorbing film of the present invention does not contain amounts of oxygen (O) and nitrogen (N) exceeding the amount of impurities.

[0065] As a material constituting the light-absorbing film, ruthenium-chromium (RuCr) is a prime example. Furthermore, after the reflective photomask preform is processed into a reflective photomask, the light-absorbing film is exposed to air in the environment used for storage or in the wafer exposure apparatus. Therefore, from the viewpoint of resistance to oxygen contained in air, light-absorbing films containing niobium (Nb) as well as ruthenium (Ru) and chromium (Cr) are advantageous. As a material containing niobium (Nb), ruthenium-chromium-niobium (RuCrNb) is a prime example.

[0066] The light-absorbing film has a ruthenium (Ru) content preferably not less than 64 at%, more preferably not less than 67 at%, and more preferably not more than 74 at%, and more preferably not more than 71 at%. The light-absorbing film has a chromium (Cr) content preferably not less than 26 at%, more preferably not less than 29 at%, and more preferably not more than 36 at%, and more preferably not more than 33 at%. When the light-absorbing film contains niobium (Nb), it preferably has a niobium (Nb) content of not more than 4 at%, and more preferably not more than 3 at%. In this case, the lower limit of the niobium (Nb) content is greater than 0 at%, and the niobium (Nb) content is preferably not less than 1 at%, but is not particularly limited thereto.

[0067] In this invention, the light-absorbing film is a film with phase-shifting function, i.e., a phase-shifting film. A light-absorbing film with phase-shifting function is a film that absorbs a portion of the exposure light and reflects the remaining portion, thereby changing (shifting) the phase of the exposure light relative to the phase of the exposure light reflected from the multilayer reflective film. As a result, the phase-shifting function is obtained due to the phase shift between the light reflected from the multilayer reflective film and the light reflected from the light-absorbing film.

[0068] The reflective photomask blank and reflective photomask of the present invention can be referred to as a reflective photomask blank with phase-shifting function (reflective phase-shifting photomask blank) and a reflective photomask with phase-shifting function (reflective phase-shifting photomask), respectively. The phase-shifting function of the light-absorbing film can improve the wafer transfer characteristics (NILS).

[0069] The phase-shifting absorber film (phase-shifting film) has a reflectance of preferably not less than 12%, more preferably not less than 13%, and more preferably not more than 15%, and more preferably not more than 14%, for exposure light in the extreme ultraviolet range. Reflectance is the relative reflectance relative to the portion where no absorber film is formed. Specifically, reflectance is the ratio of the reflectance of light reflected from the absorber film formed on the substrate via a multilayer reflective film and a protective film to the reflectance of light reflected from the multilayer reflective film and the protective film formed on the substrate.

[0070] A phase-shifting light-absorbing film (phase-shifting film) has a phase shift of preferably not less than 200 degrees, more preferably not less than 205 degrees, and more preferably not greater than 230 degrees, and more preferably not greater than 225 degrees, for exposure light in the extreme ultraviolet range. The phase shift is the relative phase shift with respect to the portion where no light-absorbing film is formed. Specifically, the phase shift is the difference between the phase shift of light reflected from the multilayer reflective film and protective film formed on the substrate and the phase shift of light reflected from the light-absorbing film formed on the substrate via the multilayer reflective film and protective film.

[0071] The light-absorbing film can be a single-layer film or a multi-layer film (e.g., a film composed of two to five layers). Furthermore, the light-absorbing film can also be a film with a gradient composition. From the viewpoint of ensuring light absorption and phase shift functions while reducing the influence of shading effects, the light-absorbing film preferably has a thickness of not less than 36 nm, more preferably not less than 38 nm and more preferably not greater than 52 nm, more preferably not greater than 50 nm, and even more preferably not greater than 48 nm. In particular, from the viewpoint of ensuring light absorption and phase shift functions while reducing shading effects, the light-absorbing film further preferably has a thickness of not less than 40 nm, most preferably not less than 41 nm and further preferably not greater than 44 nm, and most preferably not greater than 43 nm.

[0072] The conductive film is preferably formed in contact with the substrate. The conductive film preferably has a sheet resistance of no more than 100 Ω / □, and there are no limitations on the material of the conductive film. Examples of materials for the conductive film include those containing tantalum (Ta) or chromium (Cr). Furthermore, materials containing tantalum (Ta) or chromium (Cr) may contain oxygen (O), nitrogen (N), carbon (C), boron (B), or others. The conductive film has a thickness sufficient for use in an electrostatic chuck, and typically has a thickness of about 20-300 nm, but is not particularly limited thereto.

[0073] In this invention, electron beam resists drawn with an electron beam or photoresists drawn with light can be used in resist films, and chemically amplified resists are preferred. Chemically amplified resists can be positive or negative, and examples of resists include resists containing a base resin (e.g., hydroxystyrene-based or (meth)acrylic resin) and an acid-generating agent, and optionally containing a crosslinking agent, a quencher, a surfactant, or other components.

[0074] The resist film preferably has a thickness of no more than 150 nm. In the development step for the resist pattern, to form a resist pattern that is difficult to be damaged by the impact of the developer or by the impact of pure water during rinsing, the resist film preferably has a thickness of no more than 100 nm, especially when forming fine auxiliary patterns. The resist film has a lower limit for its use as an etching mask in etching, that is, a thickness that allows the resist pattern to be maintained across the entire surface of the film to be etched after etching. The lower limit is preferably no less than 50 nm, more preferably no less than 70 nm, but is not particularly limited thereto.

[0075] In this invention, the multilayer reflective film, protective film, light-absorbing film, and conductive film are preferably formed by sputtering, because sputtering has good controllability and is easy to form films with predetermined properties, but it is not particularly limited thereto. As the sputtering system, a DC sputtering system or an RF sputtering system can be used, but it is not particularly limited thereto.

[0076] When a multilayer reflective film is formed by stacking molybdenum (Mo) and silicon (Si) layers, a molybdenum (Mo) target and a silicon (Si) target can be used as sputtering targets. Similarly, when a multilayer reflective film is formed by stacking ruthenium (Ru) and silicon (Si) layers, a ruthenium (Ru) target and a silicon (Si) target can be used as sputtering targets.

[0077] When the protective film is composed of a material containing ruthenium (Ru), a ruthenium (Ru) target can be used as a sputtering target, and targets of other elements constituting the protective film can be used if necessary.

[0078] When the light-absorbing film is composed of a material containing ruthenium (Ru) and chromium (Cr), a ruthenium (Ru) target and a chromium (Cr) target can be used as sputtering targets. Furthermore, when the light-absorbing film is composed of a material containing niobium (Nb) in addition to ruthenium (Ru) and chromium (Cr), a niobium (Nb) target can be used as a sputtering target.

[0079] When the conductive film is composed of a material containing tantalum (Ta) or chromium (Cr), a tantalum (Ta) target or a chromium (Cr) target can be used as a sputtering target.

[0080] The power supplied to the sputtering target can be appropriately set according to the target's size, cooling efficiency, and the controllability of film formation. The power is typically 50-3000 W / cm². 2 This refers to the power of the sputtering surface per unit area of ​​the sputtering target. Furthermore, rare gases such as helium (He), neon (Ne), and argon (Ar) can be used as sputtering gases. When forming a film or layer containing only the elements constituting the target, only rare gases can be used as sputtering gases.

[0081] When the film or the layers constituting the film are composed of materials containing oxygen (O), nitrogen (N), or carbon (C), sputtering is preferably reactive sputtering. Rare gases and reactive gases such as helium (He), neon (Ne), and argon (Ar) are used as sputtering gases for reactive sputtering. In particular, to form a light-absorbing film containing nitrogen (N), sputtering is preferably reactive sputtering, and a nitrogen (N) reactive gas that does not contain oxygen (O) is used.

[0082] When the membrane or the layers constituting the membrane are composed of a nitrogen-containing (N) material, nitrogen gas (N2) can be used as the reactive gas. When the membrane or the layers constituting the membrane are composed of an oxygen-containing (O) material, oxygen gas (O2) can be used as the reactive gas. When the membrane or the layers constituting the membrane are composed of a material containing both nitrogen (N) and oxygen (O), reactive gases can be appropriately selected and used from oxygen gas (O2), nitrogen gas (N2), and nitrogen oxide gases such as nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O). When the membrane or the layers constituting the membrane are composed of a carbon-containing material, carbon-containing gases such as methane gas (CH4), carbon monoxide gas (CO), and carbon dioxide gas (CO2) can be used as the reactive gas. When the membrane or the layers constituting the membrane are composed of a material containing nitrogen (N), oxygen (O), and carbon (C), for example, nitrogen gas (N2), oxygen gas (O2), and carbon dioxide gas (CO2) can be used simultaneously.

[0083] The pressure during membrane formation or the formation of layers of the membrane can be appropriately set taking into account membrane stress, chemical resistance, and cleaning resistance. In particular, chemical resistance can be improved by preferably setting the pressure to not less than 0.01 Pa, more preferably not less than 0.03 Pa, and preferably not more than 1 Pa, more preferably not more than 0.3 Pa. Furthermore, the flow rate of each gas can be appropriately set to obtain the desired composition, and can typically be set from 0.1 to 100 sccm.

[0084] In the manufacturing process of a reflective photomask preform, the substrate or the substrate and the film formed on the substrate may be heat-treated before the resist film is formed. When heat-treating, it is preferable to perform the heat treatment while the surface of the light-absorbing film is not exposed. Infrared heating, resistance heating, etc., can be used as heat treatment methods, and there are no particular limitations on the treatment conditions. Heat treatment can be performed in an atmosphere containing, for example, oxygen (O). The oxygen (O)-containing gas has a concentration of, for example, 1 to 100 vol% in the case of oxygen (O2 gas), but is not particularly limited thereto. Heat treatment is preferably performed at a temperature of not less than 200°C, and more preferably not less than 400°C.

[0085] In the manufacturing process of a reflective photomask preform, before forming the resist film, the film formed on the substrate, excluding the light-absorbing film, can be subjected to ozone treatment or plasma treatment, and there are no particular limitations on the treatment conditions. Each treatment can be performed to increase the oxygen concentration in the surface portion of the film. In this case, the treatment conditions can be appropriately adjusted to obtain a predetermined oxygen concentration. Alternatively, in the case of film formation by sputtering, the oxygen concentration in the surface portion of the film can also be increased by adjusting the ratio of rare gases to oxygen-containing gases (oxidizing gases) such as oxygen (O2 gas), carbon monoxide gas (CO gas), and carbon dioxide gas (CO2 gas) in the sputtering gas.

[0086] In the manufacturing process of a reflective photomask preform, a cleaning process can be performed before forming the resist film to remove defects present on the substrate or the surface of the film formed on the substrate. Cleaning can be performed using either or both of ultrapure water and functional water, wherein the functional water is ultrapure water containing ozone gas (O3 gas), hydrogen gas (H2 gas), etc. When cleaning the light-absorbing film, it is preferable not to use functional water containing ozone gas (O3 gas). Alternatively, cleaning can be performed using ultrapure water containing surfactants, followed by cleaning with either or both of ultrapure water and functional water. If necessary, cleaning can be performed simultaneously with ultrasonic irradiation, and can be further combined with UV light irradiation for cleaning.

[0087] There are no particular restrictions on the method of forming the resist film (applying the resist), and known methods such as spin coating can be applied.

[0088] The reflective photomask blank of the present invention can be used to manufacture a reflective photomask including a pattern of a substrate, a multilayer reflective film, a protective film and a light-absorbing film.

[0089] In manufacturing a reflective photomask, when no resist film is formed in the reflective photomask blank, a resist film is formed in contact with the substrate on the side of the film (e.g., the light-absorbing film) furthest from the substrate in the reflective photomask blank. Then, by using an oxygen-containing chlorine gas and a resist pattern obtained through patterning the resist film as an etching mask, the light-absorbing film is patterned by dry etching, thereby manufacturing the reflective photomask. During the manufacturing of the reflective photomask, the resist pattern can be removed using a sulfuric acid-hydrogen peroxide mixture (SPM).

[0090] Specifically, as a method for manufacturing a reflective photomask including a pattern of a light-absorbing film from a reflective photomask blank of the present invention, the following method is exemplified. First, if necessary, a resist film is formed in contact with the light-absorbing film on the side away from the substrate (step (A)). Next, the resist film is patterned to form a resist pattern (step (B)). Next, the light-absorbing film is patterned to form a pattern of the light-absorbing film by using dry etching with a chlorine-based gas, preferably dry etching with an oxygen-containing chlorine-based gas, and using the resist pattern as an etching mask (step (C)). Next, the resist pattern is removed (step (D)).

[0091] Example

[0092] The embodiments of the present invention are given below by way of illustration rather than limitation.

[0093] Example 1

[0094] By sequentially stacking multiple layers of reflective film, protective film, and light-absorbing film on a quartz substrate with dimensions of 152 mm square and a thickness of approximately 6 mm, a material like... Figure 1 The reflective photomask blank shown.

[0095] First, using molybdenum (Mo) and silicon (Si) targets as targets and argon (Ar) gas as sputtering gas, a multilayer reflective film is formed on a quartz substrate by alternately sputtering the Mo and Si targets and adjusting the power applied to the targets and the flow rate of the sputtering gas. This multilayer reflective film is a stacked film (thickness: 280 nm) in which molybdenum (Mo) layers and silicon (Si) layers are alternately stacked, and it has a reflectivity of 65% for light with a wavelength of 13.5 nm. The molybdenum (Mo) layers and silicon (Si) layers are stacked for 40 cycles (40 molybdenum (Mo) layers and 40 silicon (Si) layers, respectively).

[0096] Next, using a ruthenium (Ru) target as the target and argon (Ar) gas as the sputtering gas, a film (thickness: 2nm) composed of monomeric ruthenium (Ru) film is formed on the multilayer reflective film as a protective film by sputtering the ruthenium (Ru) target and adjusting the power applied to the target and the flow rate of the sputtering gas.

[0097] Next, using ruthenium (Ru) and chromium (Cr) targets and argon (Ar) gas as sputtering gas, a light-absorbing film was formed on the protective film by sputtering and adjusting the power applied to the targets and the flow rate of the sputtering gas. As a result, a reflective photomask preform was obtained.

[0098] Regarding the light-absorbing film, its composition, thickness, reflectance (relative to the multilayer reflective film and the protective film) and phase shift (relative to the multilayer reflective film and the protective film) with respect to light having a wavelength of 13.5 nm are shown in Table 1. The composition of the light-absorbing film was determined by X-ray photoelectron spectroscopy, and the same method was applied below. The thickness of the light-absorbing film was determined by X-ray diffraction, and the same method was applied below. The reflectance was determined by a reflectometer for light with an incident angle of 6 degrees, and the same method was applied below. Furthermore, the refractive index n and extinction coefficient k were determined by a refractive index / extinction coefficient meter, and the phase shift was calculated from these measurements, and the same method was applied below.

[0099] Examples 2 to 6 and Comparative Examples 1 to 9

[0100] In addition to changing one or more of the power applied to the target, the flow rate of the sputtering gas, and the sputtering time, a reflective photomask blank is obtained by forming a multilayer reflective film and a protective film in the same manner as in Example 1, and by forming a light-absorbing film in the same manner as in Example 1.

[0101] In Examples 5 and 6 and Comparative Example 8, a niobium (Nb) target was used in addition to the ruthenium (Ru) and chromium (Cr) targets. In Comparative Example 1, neither a ruthenium (Ru) nor a chromium (Cr) target was used, and a tantalum (Ta) target was used in addition to the ruthenium target. In Comparative Examples 1, 4, 6, 7, and 9, nitrogen (N2) gas was used in addition to argon (Ar) gas as the sputtering gas. In Comparative Examples 5 and 6, oxygen (O2) gas was used in addition to argon (Ar) gas as the sputtering gas. The composition and thickness of the light-absorbing film, as well as the reflectivity and phase shift relative to light with a wavelength of 13.5 nm, are shown in Table 1.

[0102] Table 1

[0103]

[0104] Using the obtained reflective photomask preform, a fabrication was made as follows: Figure 2 The reflective photomask shown is first spin-coated with a positive chemical amplified electron beam resist on the light-absorbing film to form a resist film with a thickness of 150 nm.

[0105] Next, electron beam lithography was performed at 100 μC / cm. 2The dose was used to plot line and space patterns (long side dimension: 1000nm, 100,000 line patterns). Regarding the width of the line and space patterns, the line pattern width was set to 13 different widths varying in 2nm intervals within the range of 48 to 72nm, and the space pattern width was set to 49 different widths varying in 2nm intervals within the range of 48 to 144nm. The widths of the line and space patterns were varied in various combinations to form the line and space patterns.

[0106] Next, a heat treatment (PEB: post-exposure baking) is performed at 110°C for 14 minutes using a heat treatment apparatus. Next, a paddle-type development process is performed for 40 seconds to form a resist pattern. Next, the light-absorbing film is dry-etched using an oxygen-chlorine gas under the following conditions, using the obtained resist pattern as an etching mask, to form a light-absorbing film pattern.

[0107] [Conditions for dry etching of light-absorbing films using oxychlorine-based gases]

[0108] Apparatus: ICP (Inductively Coupled Plasma) system

[0109] Etching gases: Cl2 and O2

[0110] Gas pressure: 3.0 mTorr (0.40 Pa)

[0111] ICP power: 350W

[0112] Next, the remaining resist pattern is removed by washing with a sulfuric acid-hydrogen peroxide mixture (a mixture of sulfuric acid and hydrogen peroxide (sulfuric acid / hydrogen peroxide = 3 / 1 (volume ratio))) to obtain a reflective photomask.

[0113] The NILS of the lines and spatial patterns of the light-absorbing film in a reflective photomask is evaluated under the following conditions using a wafer transfer simulator capable of measuring spatial image gradients. The wafer transfer simulator capable of measuring spatial image gradients has an illumination and projection system almost identical to that of a wafer exposure apparatus, and can measure the spatial image gradient of a specific pattern by illuminating a small area of ​​the reflective photomask with exposure light.

[0114] [Setup requirements for the chip transfer simulator]

[0115] NA (numerical aperture of the wafer exposure device): 0.33

[0116] Lighting conditions: Dipole

[0117] Simga-in: 0.7

[0118] Simga-out: 0.9

[0119] Center angle: 0 degrees

[0120] Leaf angle: 30 degrees

[0121] Crystal defocus: 0.03μm

[0122] For all line and spatial patterns (with variations in their dimensions), evaluate each NILS in the resulting reflective photomask, and evaluate the maximum NILS value. NILS is calculated using the following expression:

[0123] NILS = (dI / dx) / (W×Ith),

[0124] Where W is the desired pattern size, Ith is the threshold for the light intensity provided by W, and dI / dx is the gradient of the spatial image. The NILS (maximum value) and the difference between the NILS (maximum value) and Comparative Example 1 (which corresponds to the binary reflective photomask) are shown in Table 2.

[0125] Table 2

[0126]

[0127] This invention is not limited to the embodiments described above. The embodiments described above are examples, and any other embodiments having the same or substantially the same structure as the technical concept of this invention and having the same or similar effects can be considered as inventions included within the technical scope of this invention.

Claims

1. A reflective photomask preform, comprising: substrate; A multilayer reflective film is formed on the substrate and reflects exposure light as light in the extreme ultraviolet range; A protective film is formed on the multilayer reflective film to protect the multilayer reflective film; as well as A light-absorbing film, formed on the protective film, absorbs the exposure light and has a phase-shifting function, wherein... The light-absorbing film It contains ruthenium (Ru) and chromium (Cr) and does not contain oxygen (O) or nitrogen (N). It has a ruthenium (Ru) content of not less than 64 at% and not more than 74 at% and a chromium (Cr) content of not less than 26 at% and not more than 36 at%. A thickness of not less than 40nm and not more than 44nm A reflectance of not less than 12% and not more than 15% relative to the exposure light, and a phase shift of not less than 200 degrees and not more than 230 degrees relative to the exposure light.

2. The reflective photomask blank according to claim 1, wherein, The light-absorbing film also contains niobium (Nb) and has a niobium (Nb) content of no more than 4 at%.

3. The reflective photomask blank according to claim 1 or 2, wherein, The protective film has a thickness of not less than 1 nm and not more than 6 nm.

4. A method for manufacturing a reflective photomask from a reflective photomask preform according to any one of claims 1 to 3, wherein the reflective photomask includes a pattern of a light-absorbing film, wherein, The method includes the following steps: (A) A resist film is formed on the side away from the substrate in contact with the light-absorbing film. (B) Patterning the resist film to form a resist pattern. (C) The light-absorbing film is patterned by using dry etching with chlorine-based gases and the resist pattern as an etching mask to form a light-absorbing film pattern, and (D) Remove the resist pattern.

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