Reflective mask blank, reflective mask, and method for producing reflective mask

Abstract

To provide a reflective mask blank including a phase shift film with low crystallinity and superior optical characteristics.SOLUTION: A reflective mask blank has, in this order, a substrate, a multilayer reflective film that reflects EUV light, a protective film, and a phase shift film, wherein the phase shift film contains Ru and B and at least one element selected from the group consisting of Cr, Nb, Mo, Sn, Ta, W, Re, Os, Ir, Pt, and Au; the content of N in the phase shift film is less than 10 atom% relative to all atoms in the phase shift film; and, regarding the composition of the phase shift film, the reflective mask blank satisfies the following formulas (1) and (2). Formula (1): PB>-0.45×PCr+16 and Formula (2): PB≥4. In formula (1), PCr represents the value of Cr content in the phase shift film, expressed in atom%. In formulas (1) and (2), PB represents the value of B content in the phase shift film, expressed in atom%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a reflective mask used in EUV (Extreme Ultra Violet) exposure, which is used in the exposure process of semiconductor manufacturing, a method for manufacturing the same, and a reflective mask blank, which is an original plate for the reflective mask. [Background technology]

[0002] In recent years, in order to further miniaturize semiconductor devices, EUV lithography, which uses EUV light with a central wavelength of around 13.5 nm as a light source, has been considered.

[0003] Due to the characteristics of EUV light, EUV exposure uses a reflective optical system and a reflective mask. A reflective mask has a multilayer reflective film that reflects EUV light formed on a substrate, and an absorber film that absorbs EUV light is patterned on the multilayer reflective film.

[0004] EUV light incident on a reflective mask from the illumination optical system of an exposure tool is reflected by areas without an absorber film (openings) and absorbed by areas with an absorber film (non-openings). As a result, the mask pattern is transferred as a resist pattern onto a wafer through the reduced projection optical system of the exposure tool, and subsequent processing is carried out. The absorber film may also be a phase shift film, which shifts the phase of EUV light to reduce the reflectance of EUV light. The phase shift film reduces the reflectance of EUV light by causing interference between the EUV light reflected by the surface of the absorber film opposite the multilayer reflective film side and the EUV light reflected by the surface of the absorber film facing the multilayer reflective film side. As materials for forming such a phase shift film, for example, Patent Document 1 discloses a material containing ruthenium (Ru) and chromium (Cr), and a material containing Ru, Cr, and nitrogen (N). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 225736 Summary of the Invention [Problem to be solved by the invention]

[0006] Phase shift films for reflective mask blanks are required to have low crystallinity in order to suppress variations in line width during patterning. When the present inventors investigated the phase shift film described in the above patent document, they found that it had high crystallinity, and it was desired to reduce this. Furthermore, it is desirable for the phase shift film of the reflective mask blank to have excellent optical properties in that it can shift the phase of EUV light with a thinner film thickness.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a reflective mask blank having a phase shift film with low crystallinity and excellent optical properties. Another object of the present invention is to provide a reflective mask and a method for manufacturing the reflective mask. [Means for solving the problem]

[0008] The present inventors have discovered that the above problems can be solved by making the phase shift film contain ruthenium and boron and adjusting the contents of boron and chromium in the phase shift film to fall within predetermined ranges, and have arrived at the present invention. That is, the inventors have found that the above problems can be solved by the following configuration. [1] A substrate; A multilayer reflective film that reflects EUV light, A protective film; a phase shift film in this order, the phase shift film contains ruthenium and boron, and at least one element selected from the group consisting of chromium, niobium, molybdenum, tin, tantalum, tungsten, rhenium, osmium, iridium, platinum, and gold; the nitrogen content in the phase shift film is less than 10 atomic % based on the total atoms in the phase shift film; A reflective mask blank, wherein the composition of the phase shift film satisfies the following formulas (1) and (2): Formula (1) P B > -0.45×P Cr +16 Formula (2) P B ≧4 In formula (1), P Cr is the value of the chromium content in the phase shift film, expressed in atomic percent. In formula (1) and formula (2), P B is the content of boron in the phase shift film, expressed in atomic percent. [2] The phase shift film contains chromium, The reflective mask blank according to [1], wherein the refractive index n and extinction coefficient k of the phase shift film at a wavelength of 13.5 nm satisfy the following formula (3): Equation (3) k < 0.5×n-0.434 [3] The reflective mask blank according to [1] or [2], wherein the phase shift film has a half-width of the maximum peak in an X-ray diffraction chart measured by an out-of-plane method of 1.3° or more. [4] The content of ruthenium in the phase shift film is 20 to 91 atomic % based on the total atoms in the phase shift film; the content of chromium in the phase shift film is 5 to 50 atomic % based on the total atoms in the phase shift film; The reflective mask blank according to any one of [1] to [3], wherein the content of boron in the phase shift film is 4 to 30 atomic % based on the total atoms in the phase shift film. [5] The reflective mask blank according to any one of [1] to [4], wherein the protective film contains rhodium. [6] A reflective mask having a phase shift film pattern formed by patterning the phase shift film of the reflective mask blank according to any one of [1] to [5]. [7] A method for producing a reflective mask, comprising a step of patterning the phase shift film of the reflective mask blank according to any one of [1] to [5]. [Effects of the Invention]

[0009] According to the present invention, a reflective mask blank can be provided which has a phase shift film with low crystallinity and excellent optical properties. The present invention also provides a reflective mask and a method for manufacturing the reflective mask. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing an example of an embodiment of the reflective mask blank of the present invention. [Figure 2] 1A to 1C are cross-sectional views showing an example of a manufacturing process for a reflective mask using the reflective mask blank of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below. The following description of the components may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment.

[0012] The meaning of each description in this specification is as follows. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, elements such as boron, carbon, nitrogen, oxygen, silicon, titanium, chromium, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, and platinum may be represented by their corresponding element symbols (B, C, N, O, Si, Ti, Cr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, and Pt, etc.).

[0013] <Reflective mask blank> The reflective mask blank of the present invention is a reflective mask blank having a substrate, a multilayer reflective film that reflects EUV light, a protective film, a buffer layer, and a phase shift film in this order. The phase shift film of the reflective mask blank of the present invention contains Ru and B and at least one element selected from the group consisting of Cr, Nb, Mo, Sn, Ta, W, Re, Os, Ir, Pt and Au, and the nitrogen content in the phase shift film is less than 10 atomic % based on the total atoms in the phase shift film. Furthermore, the composition of the phase shift film satisfies the following formulas (1) and (2). Formula (1) P B > -0.45×P Cr +16 Formula (2) P B ≧4 In formula (1), P Cr is the content of chromium in the phase shift film, expressed in atomic percent. In formula (1) and formula (2), P B is the content of boron in the phase shift film, expressed in atomic percent. The reflective mask blank of the present invention will be described with reference to the drawings.

[0014] Fig. 1 is a cross-sectional view showing one embodiment of a reflective mask blank of the present invention. The reflective mask blank 10 shown in Fig. 1 has a substrate 12, a multilayer reflective film 14, a protective film 16, and a phase shift film 18, in this order. The phase shift film 18 contains Ru and B, and the N content in the phase shift film 18 is less than 10 atomic % with respect to all atoms in the phase shift film 18. Furthermore, the phase shift film 18 satisfies the relationships of the above formulas (1) and (2). The reflective mask blank 10 shown in FIG. 1 may have a conductive film, which will be described later, on the side of the substrate 12 opposite to the multilayer reflective film 14 side. The reflective mask blank 10 may also have an etching mask film, which will be described later, on the side of the phase shift film 18 opposite to the substrate 12 side.

[0015] The mechanism by which the phase shift film of the reflective mask blank of the present invention exhibits low crystallinity and excellent optical properties is not entirely clear, but the present inventors speculate as follows. The phase shift film of the reflective mask blank of the present invention contains B and satisfies the relationship of formula (2) above, and therefore contains a predetermined amount of B. Furthermore, since the phase shift film satisfies the relationship of formula (1) above, when the phase shift film contains Cr, the Cr content is relatively high relative to the B content. When the phase shift film contains a predetermined amount of B and a certain amount or more of Cr relative to the B content, the bonding strength between Cr and B is relatively strong and the melting point of a compound containing Cr and B is generally high, which is thought to make the phase shift film prone to low crystallinity. Furthermore, the phase shift film of the reflective mask blank of the present invention contains Ru and at least one element selected from the above-mentioned predetermined group, and has a predetermined or less N content. When the phase shift film has the above composition, it is believed that the refractive index and extinction coefficient for EUV light can be easily adjusted to an appropriate range, and excellent optical properties are exhibited. Here, "exhibiting excellent optical properties" means that the refractive index n for EUV light is small and the extinction coefficient k is large. More specifically, "exhibiting excellent optical properties" means that the relationship of formula (3) described below is satisfied. Furthermore, if the phase shift film exhibits excellent optical properties, it is preferable because the reflectance of the phase shift film can be easily adjusted within a predetermined range, and the incident EUV light can be shifted to a desired phase with a thin film thickness, resulting in improved contrast for EUV exposure.

[0016] The structure of the reflective mask blank of the present invention will be described below.

[0017] [substrate] The substrate of the reflective mask blank of the present invention preferably has a small thermal expansion coefficient, which can prevent distortion of the phase shift film pattern due to heat generated during exposure to EUV light. The thermal expansion coefficient of the substrate is 0±1.0×10 at 20℃.-7 / ℃ is preferred, 0±0.3×10 -7 / °C is more preferred. Materials with a low thermal expansion coefficient include SiO2-TiO2-based glass, but are not limited to this. Substrates such as crystallized glass in which β-quartz solid solution is precipitated, quartz glass, metallic silicon, and metal can also be used. The SiO2-TiO2-based glass preferably uses silica glass containing 90-95% by mass of SiO2 and 5-10% by mass of TiO2. When the TiO2 content is 5-10% by mass, the linear expansion coefficient is approximately zero near room temperature, and there is almost no dimensional change near room temperature. Note that the SiO2-TiO2-based glass may contain trace components other than SiO2 and TiO2.

[0018] The surface of the substrate on which the multilayer reflective film is to be laminated (hereinafter also referred to as the "first principal surface") preferably has high surface smoothness. The surface smoothness of the first principal surface can be evaluated by surface roughness. The surface roughness of the first principal surface is preferably 0.15 nm or less in terms of root mean square roughness Rq. The surface roughness can be measured using an atomic force microscope, and will be described as the root mean square roughness Rq based on JIS-B0601. The first main surface is preferably surface-processed to have a predetermined flatness, which improves the pattern transfer accuracy and positional accuracy of a reflective mask obtained using the reflective mask blank. In a predetermined region of the first main surface (e.g., a 132 mm × 132 mm region), the substrate preferably has a flatness of 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less. The flatness can be measured using a Fujinon flatness measuring instrument. The size and thickness of the substrate are determined appropriately depending on the design values ​​of the mask, etc. For example, the outer shape is 6 inches (152 mm) square and the thickness is 0.25 inches (6.3 mm). The substrate is often rectangular or square. Furthermore, the substrate preferably has high rigidity to prevent deformation due to film stress of films (such as multilayer reflective films and phase shift films) formed on the substrate. For example, the substrate preferably has a Young's modulus of 65 GPa or more.

[0019] [Multilayer reflective film] The multilayer reflective film of the reflective mask blank of the present invention is not particularly limited as long as it has the desired properties as a reflective film for an EUV mask blank. The multilayer reflective film preferably has high reflectivity for EUV light. Specifically, when EUV light is incident on the surface of the multilayer reflective film at an incident angle of 6°, the maximum reflectivity for EUV light at a wavelength of about 13.5 nm is preferably 60% or more, more preferably 65% ​​or more. Similarly, even when a protective film is laminated on the multilayer reflective film, the maximum reflectivity for EUV light at a wavelength of about 13.5 nm is preferably 60% or more, more preferably 65% ​​or more.

[0020] Multilayer reflective films can achieve high reflectivity for EUV light, so multilayer reflective films are usually used that are made by alternately stacking high-refractive index layers that have a high refractive index for EUV light and low-refractive index layers that have a low refractive index for EUV light multiple times. The multilayer reflective film may be formed by stacking multiple periods, each period being a stack structure in which a high refractive index layer and a low refractive index layer are stacked in this order from the substrate side, or may be formed by stacking multiple periods, each period being a stack structure in which a low refractive index layer and a high refractive index layer are stacked in this order. The high refractive index layer can be a layer containing Si. As the Si-containing material, in addition to simple Si, a Si compound containing Si and one or more elements selected from the group consisting of B, C, N, and O can be used. By using a high refractive index layer containing Si, a reflective mask with excellent reflectance to EUV light can be obtained. The low refractive index layer may be a layer containing a metal selected from the group consisting of Mo, Ru, Rh, and Pt, or an alloy thereof. Si is commonly used for the high-refractive index layer, and Mo is commonly used for the low-refractive index layer. That is, Mo / Si reflective multilayer films are the most common. However, the reflective multilayer film is not limited to this, and Ru / Si reflective multilayer films, Mo / Be reflective multilayer films, Mo compound / Si compound reflective multilayer films, Si / Mo / Ru reflective multilayer films, Si / Mo / Ru / Mo reflective multilayer films, Si / Ru / Mo reflective multilayer films, and Si / Ru / Mo / Ru reflective multilayer films can also be used.

[0021] The thickness of each layer constituting the multilayer reflective film and the number of layer repeat units can be appropriately selected depending on the film material used and the EUV light reflectivity required for the reflective layer. Taking a Mo / Si multilayer reflective film as an example, a multilayer reflective film with a maximum EUV light reflectivity of 60% or more can be obtained by stacking a Mo film with a thickness of 2.3±0.1 nm and a Si film with a thickness of 4.5±0.1 nm so that the number of repeat units is 30 to 60. The multilayer reflective film preferably has a reflectivity of 60% or more for EUV light at an incident angle θ of 6°. The reflectivity is more preferably 65% ​​or more.

[0022] Each layer constituting the multilayer reflective film can be deposited to a desired thickness using a known deposition method, such as DC sputtering, magnetron sputtering, or ion beam sputtering. For example, when fabricating a multilayer reflective film using ion beam sputtering, ion particles are supplied from an ion source to a target of a high refractive index material and a target of a low refractive index material. When the multilayer reflective film is a Mo / Si multilayer reflective film, for example, a Si layer with a predetermined thickness is first deposited on a substrate using an ion beam sputtering method, for example, using a Si target. Then, a Mo layer with a predetermined thickness is deposited using a Mo target. This Si layer and Mo layer constitute one cycle, and for example, 30 to 60 cycles (preferably 40 to 50 cycles) are stacked to form a Mo / Si multilayer reflective film.

[0023] [Protective film] The reflective mask blank of the present invention has a protective film between the multilayer reflective film and the phase shift film, which is provided for the purpose of protecting the multilayer reflective film from damage during an etching process (usually a dry etching process) to form a pattern on the phase shift film. Materials that can achieve the above objective include materials containing at least one element selected from the group consisting of Si, Ru, and Rh. That is, the protective film preferably contains at least one element selected from the group consisting of Si, Ru, and Rh. Furthermore, the protective film preferably contains Rh. More specifically, the above-mentioned materials include Ru metal alone, Ru alloys containing Ru and one or more metals selected from the group consisting of Si, Y, Ti, Zr, Nb, Mo, Rh, Pd, Ta, and Ir, and Rh metal alone, Rh alloys containing Rh and one or more metals selected from the group consisting of Si, Y, Ti, Zr, Nb, Mo, Ru, Pd, Ta, and Ir. Adding Ru, Nb, Mo, Zr, Y, or Ti to Rh can reduce the extinction coefficient while suppressing an increase in the refractive index, and can easily improve the reflectance to EUV light. Also, adding Ta, Ir, Pd, or Y to Rh can easily improve resistance to etching processes. Further, examples of materials that can achieve the above object include Al and nitrides containing these metals and nitrogen, and Al2O3. Among these, the materials that can achieve the above object are preferably Ru metal alone, Ru alloys, Rh metal alone, or Rh alloys.

[0024] When the protective film contains Ru or Rh, the protective film may also contain at least one element selected from the group consisting of B, C, N, and O. Addition of such an element tends to reduce the crystallinity of the protective film and tends to improve the surface smoothness of the protective film on the buffer layer side. A protective film having low crystallinity refers to a small crystallite diameter calculated using a diffraction chart obtained by X-ray diffraction (XRD). The crystallite diameter is calculated using Scherrer's equation. The full half-width of the diffraction peak with the highest intensity in the 2θ range of 30 to 55° is used to calculate the crystallite diameter using Scherrer's equation. If no clear diffraction peak is observed in the diffraction chart, the protective film can be said to be amorphous. The diffraction chart is obtained by measurement using the out-of-plane method. The out-of-plane method will be described in detail later. The crystallite diameter of the protective film is preferably 10 nm or less, more preferably 6.0 nm or less, and even more preferably 5.0 nm or less. There is no particular lower limit to the crystallite diameter, but it is often 0.1 nm or more. The protective film may also be amorphous.

[0025] The thickness of the protective film is not particularly limited as long as it can function as a protective film. In order to maintain the reflectance of EUV light reflected by the multilayer reflective film, the thickness of the protective film is preferably 10.0 nm or less, more preferably 6.0 nm or less, even more preferably 5.0 nm or less, and particularly preferably 3.5 nm or less. Furthermore, in order to obtain good etching resistance, the thickness of the protective film is preferably 1.0 nm or more, more preferably 1.5 nm or more, and even more preferably 2.0 nm or more. It is also preferable that the material of the protective film is Ru metal alone, a Ru alloy, Rh metal alone, or a Rh alloy, and that the thickness of the protective film is the above-mentioned preferable thickness. The thickness of the protective film is determined by X-ray reflectivity (XRR).

[0026] The density of the protective film is preferably 10.0 to 14.0 g / cm 3 The density of the protective film is 10.0 g / cm 3 When the density of the protective film is 14.0 g / cm or more, good etching resistance is easily obtained. 3If it is equal to or less than this, it is easy to suppress a decrease in reflectance to EUV light. The density of the protective film is determined by X-ray reflectometry.

[0027] The protective film may be a film consisting of a single layer, or may be a multilayer film consisting of multiple layers. When the protective film is a multilayer film, each layer constituting the multilayer film is preferably made of the above-mentioned preferred material. Furthermore, when the protective film is a multilayer film, it is also preferable that the total thickness of the multilayer film is within the above-mentioned preferred range. When the protective film is a multilayer film, it is preferable that the layer of the multilayer film closest to the phase shift film contains Rh. Furthermore, when the layer of the multilayer film closest to the phase shift film contains Rh, it is preferable that at least one of the other layers contains Ru.

[0028] The protective film can be formed by known film formation methods such as DC sputtering, magnetron sputtering, ion beam sputtering, etc. When forming an Rh film by magnetron sputtering, it is preferable to use an Rh target as the target and Ar gas as the sputtering gas.

[0029] [Phase shift film] The phase shift film of the reflective mask blank of the present invention is required to have a high contrast between the EUV light reflected by the openings in the phase shift film (multilayer reflective film) and the EUV light reflected by the remaining portions of the phase shift film when the phase shift film is patterned to obtain a phase shift film pattern. Since the phase shift film pattern is used as a phase shift mask, the reflectance of the phase shift film to EUV light is preferably 2% or more. To obtain a sufficient phase shift effect, the reflectance of the phase shift film is preferably 9 to 15%. When a phase shift film is used as a phase shift mask, the contrast of the optical image on the wafer is improved, and the exposure margin is likely to increase.

[0030] The phase shift film contains Ru. The Ru content in the phase shift film is preferably 20 atomic % or more, more preferably 30 atomic % or more, even more preferably 40 atomic % or more, and particularly preferably 50 atomic % or more, based on the total atoms in the phase shift film. The Ru content in the phase shift film is preferably 91 atomic % or less, more preferably 80 atomic % or less, even more preferably 70 atomic % or less, and particularly preferably 65 atomic % or less, based on the total atoms in the phase shift film.

[0031] The phase shift film contains B in addition to Ru. The B content in the phase shift film is not particularly limited as long as it satisfies the above formulas (1) and (2), but to satisfy the above formula (2), the B content is 4 atomic % or more, preferably 8 atomic % or more, more preferably 10 atomic % or more, and even more preferably 11 atomic % or more, based on the total atoms in the phase shift film. The B content in the phase shift film is preferably 30 atomic % or less, more preferably 20 atomic % or less, and even more preferably 15 atomic % or less.

[0032] The phase shift film also contains at least one element (hereinafter also referred to as element X1) selected from the group consisting of Cr, Nb, Mo, Sn, Ta, W, Re, Os, Ir, Pt and Au. The phase shift film preferably contains at least Cr. When the phase shift film contains Cr, the Cr content in the phase shift film is preferably 5 atomic % or more, more preferably 15 atomic % or more, even more preferably 20 atomic % or more, particularly preferably 25 atomic % or more, and most preferably 30 atomic % or more. Also, when the phase shift film contains Cr, the Cr content in the phase shift film is preferably 50 atomic % or less, more preferably 45 atomic % or less, and even more preferably 40 atomic % or less. When the phase shift film contains Cr, the preferred range of the Ru content in the phase shift film is the same as the preferred range described above. When the phase shift film contains Cr, the preferred range of the B content in the phase shift film is the same as the preferred range described above. When the phase shift film contains Cr, it is also preferable that the Ru content is 20 to 91 atomic % of all atoms in the phase shift film, the Cr content is 5 to 50 atomic % of all atoms in the phase shift film, and the B content is 4 to 30 atomic % of all atoms in the phase shift film.

[0033] The phase shift film may contain an element X1 other than Cr. When the phase shift film contains an element X1 other than Cr, the total content of the element X1 is preferably 10 atomic % or more, more preferably 20 atomic % or more, and even more preferably 25 atomic % or more. When the phase shift film contains an element X1 other than Cr, the total content of the element X1 is preferably 60 atomic % or less, more preferably 55 atomic % or less, and even more preferably 60 atomic % or less. It is also preferable that the phase shift film does not contain any element X1 other than Cr.

[0034] The composition of the phase shift film satisfies the following formulas (1) and (2). Formula (1) P B > -0.45×P Cr +16 Formula (2) P B ≧4 In formula (1), P Cr is the value of the chromium content in the phase shift film, expressed in atomic percent. For example, when the chromium content in the phase shift film is 20 atomic percent, the above P Cr will be assigned the value "20". In formula (1) and formula (2), P B is the content of boron in the phase shift film, expressed in atomic percent. For example, when the content of boron in the phase shift film is 10 atomic percent, the above P B will be assigned the value "10". When formula (1) is satisfied, the value obtained by subtracting the value on the right side from the value on the left side exceeds 0, but the value is preferably 1.0 or more, more preferably 2.0 or more, and even more preferably 3.0 or more.

[0035] The N content in the phase shift film is less than 10 atomic % of all atoms in the phase shift film, preferably 5 atomic % or less, and more preferably 1 atomic % or less. It is also preferable that the phase shift film does not contain N. In other words, the N content may be 0 atomic % of all atoms in the phase shift film.

[0036] The phase shift film preferably further contains at least one element selected from the group consisting of C, O and Si (hereinafter also referred to as element X2). When the phase shift film contains the element X2, the content of the element X2 is preferably 1 atomic % or more, more preferably 3 atomic % or more, and even more preferably 5 atomic % or more, based on the total atoms of the phase shift film. Also, when the phase shift film contains the element X2, the content of the element X2 is preferably 15 atomic % or less, more preferably 10 atomic % or less, and even more preferably 5 atomic % or less. When the phase shift film contains two or more kinds of element X2, the content of the element X2 is the total content of the element X2. The phase shift film does not necessarily contain the element X2.

[0037] In this specification, the content of an element contained in a phase shift film is determined by analysis using X-ray photoelectron spectroscopy (XPS). For the XPS analysis, an analytical instrument "PHI 5000 VersaProbe" manufactured by ULVAC-PHI, Inc. is used. The instrument is calibrated in accordance with JIS K 0145. First, a measurement sample of approximately 1 cm square is cut out from a reflective mask blank, and the obtained measurement sample is set in a measurement holder so that the phase shift film side becomes the measurement surface. After the measurement holder is loaded into the apparatus, if another layer is disposed on the side of the phase shift film opposite the substrate side, the other layer is removed with an argon ion beam to expose the phase shift film. After exposing the phase shift film, the phase shift film is removed from the outermost surface by a thickness equal to half the thickness of the phase shift film. The sputtering rate during the removal can be measured using a separately prepared sample. After removing the top surface of the phase shift film, the removed area is irradiated with X-rays (monochromated AlKα rays) and analyzed at a photoelectron take-off angle (the angle between the surface of the measurement sample and the direction of the detector) of 45°. During the analysis, a neutralization gun is used to suppress charge buildup. The analysis begins with a wide scan in the binding energy range of 1000 to 0 eV to confirm the elements present, followed by a narrow scan depending on the elements present (e.g., Cr, B, and Ru). The narrow scan is performed with a pass energy of 58.7 eV, an energy step of 0.1 eV, a time step of 50 ms, and five accumulations. The wide scan is performed with a pass energy of 58.7 eV, an energy step of 1 eV, a time step of 50 ms, and two accumulations. The content of each element in the phase shift film is analyzed using the relative sensitivity coefficient specific to each element and each orbital from the spectrum obtained by narrow scanning when XPS analysis is performed according to the above procedure. Alternatively, a model sample formed under the same conditions as those for forming the phase shift film may be used to carry out the analysis in the same manner as above.

[0038] The thickness of the phase shift film is preferably 20.0 nm or more, more preferably 30.0 nm or more, and is preferably 60.0 nm or less, more preferably 55.0 nm or less, and even more preferably 50.0 nm or less, in order to reduce the shadowing effect. The thickness of the phase shift film is determined by X-ray reflectometry.

[0039] The refractive index n of the phase shift film at a wavelength of 13.5 nm is preferably 0.885 or more, and is preferably 0.935 or less, more preferably 0.920 or less, and even more preferably 0.915 or less, in order to enable the thickness of the phase shift film to be made thinner. The extinction coefficient k of the phase shift film at a wavelength of 13.5 nm is preferably 0.040 or less, more preferably 0.035 or less, and even more preferably 0.030 or less.The extinction coefficient k of the phase shift film at a wavelength of 13.5 nm is preferably 0.010 or more, more preferably 0.015 or more, and even more preferably 0.020 or more, in order to make it easier to adjust the reflectance of the phase shift film lower. The refractive index n and extinction coefficient k are determined by measuring the incidence angle dependency of reflectance using EUV light with a wavelength of 13.5 nm and performing fitting on the obtained profile using the refractive index n and extinction coefficient k as parameters.

[0040] It is also preferable that the refractive index n and extinction coefficient k of the phase shift film at a wavelength of 13.5 nm satisfy the following formula (3). Equation (3) k < 0.5×n-0.434 It is also preferable that the phase shift film contains Cr and satisfies the above formula (3). If the phase shift film contains Ru, Cr, and B and is adjusted to satisfy the above formulas (1) and (2), the relationship of the above formula (3) is easily satisfied. The larger the value obtained by subtracting the value on the left side of equation (3) from the value on the right side, the smaller the deviation from the refractive index n and extinction coefficient k expected for a binary system of Ru and Cr, and the smaller the impact of the inclusion of light elements on the optical properties. The smaller the effect of the light element on the optical properties, the smaller the refractive index n and the larger the extinction coefficient k. This makes it easier to adjust the reflectance of the phase shift film within a predetermined range and to shift the incident EUV light to the desired phase with a thin film thickness, resulting in improved contrast for EUV exposure.

[0041] It is also preferable that the half-width of the maximum peak of the phase shift film measured by the out-of-plane method is 1.3° or more. The half-width is more preferably 3.0° or more, even more preferably 4.0° or more, and particularly preferably 5.0° or more. It is also preferable that no clear diffraction peak appears. A half-width of the above value or more corresponds to a small crystallite diameter of the phase shift film. A smaller crystallite diameter of the phase shift film is preferable because it is less likely to cause rattle at the processed edge when processing the phase shift film and therefore tends to improve processing accuracy. The out-of-plane method is a measurement method using the so-called θ / 2θ scan (also called the focusing method), in which the X-ray irradiation direction and X-ray detection direction are scanned in a plane perpendicular to the main surface of a plate-shaped sample. Specifically, the X-ray irradiation direction and X-ray detection direction are scanned in a plane perpendicular to the first main surface of the substrate. The maximum peak often appears in the 2θ range of 30 to 55°. When peaks of other components of the reflective mask blank also appear, the diffraction peaks originating from the phase shift film are identified by comparing their shapes with those of a diffraction chart of a sample from which the phase shift film has been removed. The detailed method for obtaining an X-ray diffraction chart by the out-of-plane method follows the conditions in the examples described below.

[0042] The crystallite diameter of the phase shift film is preferably 10.0 nm or less, more preferably 6.0 nm or less, and even more preferably 4.0 nm or less. There is no particular lower limit to the crystallite diameter, but it is often 0.1 nm or more. The phase shift film of the present invention may also be amorphous. The method for measuring the crystallite diameter of the phase shift film is the same as the method for measuring the crystallite diameter of the protective film.

[0043] The phase shift film preferably has resistance to dissolution in cleaning solutions. When the phase shift film has resistance to dissolution in cleaning solutions, the phase shift film is less likely to be removed during the etching process of the etching mask film described later, making it easier to obtain a desired pattern. More specifically, it is preferable that the change in thickness of the phase shift film is small when the phase shift film is brought into contact with a sulfuric acid-hydrogen peroxide aqueous solution (SPM). For example, when the phase shift film is etched with SPM at 100° C. for 20 minutes, the change in film thickness between before and after the etching is preferably 1.0 nm or less, more preferably 0.5 nm or less, and even more preferably 0.2 nm or less. The lower limit of the change in film thickness is 0 nm or more.

[0044] The phase shift film may be a single layer film or a multilayer film made up of multiple films. When the phase shift film is a multilayer film made up of multiple films, the phase shift film may include a film that does not contain Ru or B.

[0045] The phase shift film can be formed by known film formation methods such as DC sputtering, magnetron sputtering, ion beam sputtering, etc. For example, when forming a RuCrB film as the phase shift film by magnetron sputtering, the phase shift film can be formed by sputtering using a Ru target and a CrB target and supplying a gas containing Ar gas. The ratio of elements contained in the phase shift film can be adjusted by the ratio of elements in the target used, the ratio of power input to the target, and the like. Moreover, instead of the CrB target, a Cr target and a B target may be used.

[0046] [Conductive film] The reflective mask blank of the present invention may have a conductive film on the surface (second main surface) opposite to the first main surface of the substrate. By providing the conductive film, the reflective mask blank can be handled by an electrostatic chuck. The conductive film preferably has a low sheet resistance, for example, preferably 200 Ω / sq. or less, and more preferably 100 Ω / sq. or less. The conductive film may be made of a wide range of materials, including those described in known literature. For example, the high-dielectric-constant coating described in JP-A-2003-501823, specifically a coating made of Si, Mo, Cr, CrON, or TaSi, may be used. The conductive film may also be made of a Cr compound containing Cr and one or more elements selected from the group consisting of B, N, O, and C, or a Ta compound containing Ta and one or more elements selected from the group consisting of B, N, O, and C. The thickness of the conductive film is preferably 10 to 1000 nm, more preferably 10 to 400 nm. The conductive film may also have a function of adjusting stress on the second main surface side of the reflective mask blank. That is, the conductive film can adjust the reflective mask blank to be flat by balancing the stress from various films formed on the first main surface side. The conductive film can be formed by using a known film formation method, for example, a sputtering method such as DC sputtering, magnetron sputtering, or ion beam sputtering, a CVD method, a vacuum deposition method, or an electrolytic plating method.

[0047] [Etching mask film] The reflective mask blank of the present invention may have an etching mask film on the side of the phase shift film opposite to the substrate side. The etching mask film is preferably made of a material that is highly resistant to dry etching. When an etching mask film is formed on a phase shift film, dry etching can be performed even if the minimum line width of the phase shift film pattern is small. Therefore, this is effective for miniaturizing the phase shift film pattern.

[0048] The etching mask film preferably contains one or more elements selected from the group consisting of Al, Si, Ti, Cr, Y, Nb, Mo, Ta, and Hf (hereinafter also referred to as "element X3"). That is, the material constituting the etching mask film preferably contains element X3. The etching mask film may further contain at least one element selected from the group consisting of B, N and O. Examples of materials constituting the etching mask film include a simple substance of element X3, and oxides, nitrides, oxynitrides, carbides, carbonitrides, carbonates, fluorides, and oxyfluorides of element X3. Note that the material constituting the etching mask film may also be a composite compound (e.g., composite oxide) containing two or more elements of element X3.

[0049] For example, Cr-based materials containing Cr as element X3 include materials containing Cr and one or more elements selected from the group consisting of Cr and O, N, C, and H, and more specifically, include CrO, CrN, and CrON. Note that the notation "CrON" represents a material containing Cr, O, and N, and similar notations below have the same meaning. Furthermore, examples of Si-based materials containing Si as the element X3 include materials containing Si and one or more elements selected from the group consisting of O, N, C, and H, and more specifically, include SiO2, SiON, SiN, SiO, Si, SiC, SiCO, SiCN, and SiCON.

[0050] The thickness of the etching mask film is preferably 2 nm or more, and is preferably 30 nm or less, more preferably 25 nm or less, and even more preferably 10 nm or less.

[0051] The etching mask film can be formed by using a known film formation method such as DC sputtering, magnetron sputtering, or ion beam sputtering.

[0052] <Reflective mask manufacturing method and reflective mask> The reflective mask of the present invention is obtained by patterning the phase shift film of the reflective mask blank of the present invention. One example of a method for producing a reflective mask will be described with reference to FIG.

[0053] 2(a) shows a state in which a resist pattern 40 has been formed on a reflective mask blank having, in this order, a substrate 12, a multilayer reflective film 14, a protective film 16, and a phase shift film 18. The resist pattern 40 can be formed by a known method, for example, by applying a resist to the phase shift film 18 of the reflective mask blank, and then exposing and developing the resist to form the resist pattern 40. The resist pattern 40 corresponds to a pattern formed on a wafer using a reflective mask. Thereafter, the phase shift film 18 is etched and patterned using the resist pattern 40 of FIG. 2(a) as a mask, and the resist pattern 40 is removed to obtain a laminate having the phase shift film pattern 18pt shown in FIG. 2(b). Next, as shown in Fig. 2(c), a resist pattern 41 corresponding to the frame of the exposure area is formed on the laminate of Fig. 2(b), and dry etching is performed using the resist pattern 41 of Fig. 2(c) as a mask. Dry etching is performed until it reaches the substrate 12. After dry etching, the resist pattern 41 is removed to obtain the reflective mask shown in Fig. 2(d).

[0054] The dry etching used to form the phase shift film pattern 18pt may be, for example, dry etching using a Cl-based gas or dry etching using an F-based gas. The resist pattern 40 or 41 may be removed by a known method, such as removal with a cleaning solution, such as sulfuric acid-hydrogen peroxide solution (SPM), sulfuric acid, ammonia water, ammonia-hydrogen peroxide solution (APM), OH radical cleaning water, or ozone water. When the reflective mask blank has an etching mask film as another film, the etching mask film may be patterned using the resist pattern 40 as a mask, and dry etching may be performed using the pattern of the etching mask film as a mask. When the reflective mask blank has an etching mask film as another film, a step of removing the etching mask film may be performed in the step of obtaining the reflective mask. Furthermore, the etching mask film may be removed simultaneously in the step of removing the resist pattern 40 or 41 described above.

[0055] The phase shift film of the reflective mask blank of the present invention has low crystallinity, which tends to reduce the edge roughness of the pattern of the reflective mask obtained by patterning. Furthermore, the phase shift film of the reflective mask blank of the present invention has excellent optical properties, which tends to exhibit the function of the phase shift film with a thinner film thickness, and tends to reduce the influence of shadowing. A reflective mask obtained by patterning the phase shift film of the reflective mask blank of the present invention can be suitably used as a reflective mask for exposure to EUV light. [Example]

[0056] The present invention will be described in more detail below with reference to examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the following examples. Examples 1 to 8 described below are working examples, and Examples 9 to 23 are comparative examples.

[0057] <Example 1> First, the procedure for obtaining the reflective mask blank of Example 1 will be described as a representative example.

[0058] [substrate] First, a SiO2-TiO2 glass substrate (6-inch (152 mm) square, 6.3 mm thick) was prepared as a substrate. This glass substrate has a thermal expansion coefficient of 0.02 × 10 at 20 °C. -7 / °C, Young's modulus is 67 GPa, Poisson's ratio is 0.17, and specific stiffness is 3.07 × 10 7 m 2 / s 2 The quality assurance area of ​​the first main surface of the substrate was polished to a root-mean-square roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less. A 100 nm thick Cr film was formed on the second main surface of the substrate using magnetron sputtering. The sheet resistance of the Cr film was 100 Ω / □.

[0059] [Multilayer reflective film] Next, a Mo / Si multilayer reflective film was formed on the first main surface of the substrate as a multilayer reflective film. The Mo / Si multilayer reflective film was obtained by repeating the process of depositing a Si film (4.5 nm thick) and a Mo film (2.3 nm thick) using ion beam sputtering 40 times, and after the 40th Mo film was formed, an additional Si film (4.5 nm thick) was deposited. The total thickness of the Mo / Si multilayer reflective film was 276.5 nm ((4.5 nm + 2.3 nm) × 40 + 4.5 nm).

[0060] [Protective film] On the multilayer reflective film formed by the above procedure, a Ru film (thickness: 1.0 nm) and a Rh film (thickness: 1.5 nm) were formed in this order as protective films. The Ru film and the Rh film were formed by ion beam sputtering under the following conditions. Ru film deposition conditions: Target: Ru target Sputtering gas: Ar gas Gas pressure: 0.027Pa Ion acceleration voltage: 600V ·Deposition speed: 0.056nm / sec Rh film deposition conditions: Target: Rh target Sputtering gas: Ar gas Gas pressure: 0.027Pa Ion acceleration voltage: 600V ·Deposition speed: 0.077nm / sec

[0061] [Phase shift film] On the protective film formed by the above procedure, a RuCrB film (thickness: 45 nm) was formed as a phase shift film by DC sputtering under the following conditions. Targets: Ru target, CrB target (Cr: 60 atomic %, B: 40 atomic %), and Cr target Sputtering gas: Ar gas Gas pressure: 2.0 x 10 -1 Pa Input power density per Ru target area: 7.4W / cm 2 Input power density per CrB target area: 9.4W / cm 2 Input power density per Cr target area: 3.0W / cm 2 The composition of the RuCrB film formed in Example 1 was analyzed by the above-mentioned method (XPS method), and the Ru content was 62 atomic %, the Cr content was 24 atomic %, and the B content was 14 atomic %.

[0062] Through the above procedure, the reflective mask blank of Example 1 was obtained.

[0063] <Evaluation> [Optical properties] For the phase shift film of the reflective mask blank of Example 1, the optical properties (refractive index n and extinction coefficient k at a wavelength of 13.5 nm) were measured by the method described above.

[0064] [Half width] For the phase shift film of the reflective mask blank of Example 1, the half-value width of the maximum peak in the X-ray diffraction chart was measured by the procedure described above. The X-ray diffraction chart was obtained by performing XRD measurement according to the following procedure. The XRD measurement was performed using a "Mini Flex" manufactured by Rigaku. The X-ray source was CuKα radiation (including CuKα1 radiation and CuKα2 radiation), with a tube voltage of 30 kV and a tube current of 20 mA. A one-dimensional detector was used for the measurement. A 1.0 mm diameter microslit and a 1.0 mm diameter collimator were used on the X-ray source side. The step width was 0.02°, the step time was 0.2 s / step, and measurements were performed in the 2θ range of 20 to 80°.

[0065] <Examples 2-23> A reflective mask blank was obtained in the same manner as in Example 1, except that the film formation conditions for the phase shift film were adjusted so as to have the composition shown in the table below. Specifically, for example, in the reflective mask blank of Example 2, the input power density for each target was set to the value shown in the table, and a phase shift film that was a RuCrB film was formed. For the phase shift film containing N, N2 gas was introduced into the sputtering atmosphere and the amount introduced was adjusted to obtain the composition shown in the table below. In addition, in the same manner as in Example 1, the optical properties and half width of the reflective mask blank of each example were measured.

[0066] <Result> The composition of the phase shift film in the reflective mask blank of each example, and the measurement results of the optical properties and half-width are shown in Table 1 below. In Table 1, the notation "at%" means atomic %. In Table 1, the column "Equation (1)" indicates the value obtained by subtracting the value on the right side of the above-mentioned equation (1) from the value on the left side. Note that if the value in the above column is a positive value, it indicates that the above-mentioned equation (1) is satisfied. In Table 1, the column "Equation (3)" indicates the value obtained by subtracting the value on the left side of the above-mentioned equation (3) from the value on the right side. Note that if the value in the column is a positive value, it indicates that the above-mentioned equation (3) is satisfied.

[0067] [Table 1]

[0068] From the results shown in Table 1, the phase shift films of the reflective mask blanks of Examples 1 to 8 contained Ru and B and at least one element selected from the group consisting of Cr, Nb, Mo, Sn, Ta, W, Re, Os, Ir, Pt, and Au, and the nitrogen content in the phase shift film was less than 10 atomic % relative to all atoms in the phase shift film. It was also confirmed that the relationships of formulas (1) and (2) were satisfied. The phase shift films of the reflective mask blanks of Examples 1 to 8 had large half-width values ​​and positive values ​​in the column for "formula (3)," and were confirmed to have low crystallinity and excellent optical properties. On the other hand, it was confirmed that the phase shift films of the reflective mask blanks of Examples 9 to 23 did not contain B, had an N content of 10 atomic % or more, or did not satisfy formula (1) or formula (2). The phase shift films of such reflective mask blanks of Examples 9 to 23 were inferior in either crystallinity or optical properties. Furthermore, by comparing Examples 4 and 5 with Examples 1 to 3 and Examples 6 to 8, it was confirmed that when the B content was 8 atomic % or more, the half width was large and the crystallinity was lower. [Explanation of symbols]

[0069] 10 Reflective mask blanks 12 PCB 14 Multilayer reflective film 16 Protective film 18 Phase shift film 18pt phase shift film pattern 40,41 Resist pattern

Claims

1. A substrate; a multilayer reflective film that reflects EUV light; A protective film; a phase shift film in this order, the phase shift film contains ruthenium and boron, and at least one element selected from the group consisting of chromium, niobium, molybdenum, tin, tantalum, tungsten, rhenium, osmium, iridium, platinum, and gold; the nitrogen content in the phase shift film is less than 10 atomic % based on the total atoms in the phase shift film; A reflective mask blank, wherein the composition of the phase shift film satisfies the following formulas (1) and (2): Formula (1) P Ｂ > -0.45×P Ｃｒ +16 Formula (2) P Ｂ ≧4 In formula (1), P Ｃｒ is the content of chromium in the phase shift film, expressed in atomic percent. In formula (1) and formula (2), P Ｂ is the content of boron in the phase shift film, expressed in atomic percent.

2. the phase shift film contains chromium; 2. The reflective mask blank according to claim 1, wherein the refractive index n and extinction coefficient k of the phase shift film at a wavelength of 13.5 nm satisfy the following formula (3): Formula (3) k < 0.5×n-0.434

3. 3. The reflective mask blank according to claim 1, wherein the phase shift film has a half-width of the maximum peak in an X-ray diffraction chart measured by an out-of-plane method of 1.3° or more.

4. the content of ruthenium in the phase shift film is 20 to 91 atomic % based on the total atoms in the phase shift film; the content of chromium in the phase shift film is 5 to 50 atomic % based on the total atoms in the phase shift film; 3. The reflective mask blank according to claim 1, wherein the content of boron in said phase shift film is 4 to 30 atomic % based on all atoms in said phase shift film.

5. The reflective mask blank according to claim 1 , wherein the protective film contains rhodium.

6. A reflective mask having a phase shift film pattern formed by patterning the phase shift film of the reflective mask blank according to claim 1 or 2.

7. A method for manufacturing a reflective mask, comprising the step of patterning the phase shift film of the reflective mask blank according to claim 1 or 2.

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