Reflective photomask substrate, reflective photomask, manufacturing method of reflective photomask substrate, and manufacturing method of reflective photomask.

Abstract

The reflective photomask substrate of the present invention sequentially comprises a substrate, a multilayer reflective film for reflecting EUV light, and a phase-shifting film for shifting the phase of the EUV light. The phase-shifting film is a predetermined film for forming an opening pattern. The phase-shifting film has a refractive index of 0.920 or less for EUV light, an extinction coefficient of 0.024 or more for EUV light, a film thickness of 50 nm or less, and when the line and gap pattern is formed on the target substrate, a normalized image log slope of the transferred image is 2.9 or more, and the focal depth margin of the transferred image is 60 nm or less.

Description

Technical Field

[0001] This invention relates to a reflective photomask substrate, a reflective photomask, a method for manufacturing a reflective photomask substrate, and a method for manufacturing a reflective photomask. Prior Technology

[0002] In recent years, with the miniaturization of semiconductor devices, an exposure technology using extreme ultraviolet (EUV) light has been developed, namely EUV lithography (EUVL). EUV includes soft X-rays and vacuum ultraviolet light, specifically light with wavelengths ranging from 0.2 nm to 100 nm. Currently, the industry is mainly researching EUV with wavelengths around 13.5 nm.

[0003] EUVL uses a reflective photomask. The reflective photomask comprises a substrate such as a glass substrate, a multilayer reflective film formed on the substrate, and a phase-shifting film formed on the multilayer reflective film. An opening pattern is formed on the phase-shifting film. Using EUVL, the opening pattern of the phase-shifting film is transferred to an object substrate such as a semiconductor substrate. The transfer includes scaling down the substrate before transfer.

[0004] In Embodiment 1 of Patent Document 1, a phase shift film alternately comprising Ta and Mo layers is disclosed. The refractive index of Ta is 0.943, and the extinction coefficient is 0.041 (paragraph 0045 of Patent Document 1). The refractive index of Mo is 0.921, and the extinction coefficient is 0.006 (paragraph 0046 of Patent Document 1).

[0005] In Embodiment 4 of Patent Document 1, a phase shifting film is disclosed that alternately comprises Ta and Ru layers. The refractive index of Ru is 0.888 and the extinction coefficient is 0.017 (paragraph 0046 of Patent Document 1).

[0006] In Example 4 of Patent Document 2, a phase shifting film comprising a RuNi alloy (Ru:Ni=0.65:0.35) is disclosed. The RuNi alloy (Ru:Ni=0.65:0.35) has a refractive index of 0.905 and an extinction coefficient of 0.035. [Previous Technical Documents] [Patent Literature]

[0007] Patent Document 1: Japanese Patent No. 6441012 Patent Document 2: Japanese Patent No. 6861095 Summary of the Invention

[0008] [The problem the invention aims to solve]

[0009] Previously, the chemical composition and structure of phase shift films for EUVL were studied, but the case where the opening pattern of the phase shift film includes logic patterns such as holes or lines and gaps has not been fully studied.

[0010] One aspect of the present invention provides a technique that improves the transfer accuracy of line and gap patterns transferred to a substrate using an EUV self-reflective photomask. [Technical means to solve the problem]

[0011] One embodiment of the present invention comprises a reflective photomask substrate, which sequentially includes a substrate, a multilayer reflective film for reflecting EUV light, and a phase-shifting film for shifting the phase of the EUV light. The phase-shifting film is a predetermined film for forming an opening pattern. The phase-shifting film has a refractive index of 0.920 or less for EUV light, an extinction coefficient of 0.024 or more for EUV light, a film thickness of 50 nm or less, and a normalized image log slope of the transferred image when a line and gap pattern is formed on the target substrate, which is 2.9 or more, and a focal depth margin of the transferred image, which is 60 nm or less. [Effects of the Invention]

[0012] According to one aspect of the present invention, the transfer accuracy of line and gap patterns transferred to a target substrate using an EUV self-reflective photomask can be improved. Simple Explanation of the Diagram

[0013] Figure 1 is a cross-sectional view of a reflective photomask substrate according to one embodiment. Figure 2 is a cross-sectional view of a reflective photomask according to one embodiment. Figure 3 is a cross-sectional view showing an example of EUV light reflected by the reflective diaphragm in Figure 2. Figure 4 is an example of the relationship between the chemical composition, refractive index, and extinction coefficient of a phase-shifting film. Figure 5 shows an example of the light intensity distribution in a transferred image. Figure 6 is a flowchart illustrating a method for manufacturing a reflective photomask substrate according to one embodiment. Figure 7 is a flowchart illustrating a method for manufacturing a reflective photomask according to one embodiment. Implementation

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding components are labeled with the same symbols, and their descriptions are sometimes omitted. In the specification, the "~" indicating a numerical range means that the values ​​before and after it are included as the lower limit and upper limit.

[0015] Referring to FIG1, a reflective photomask substrate 1 according to one embodiment will be described. The reflective photomask substrate 1, for example, sequentially includes a substrate 10, a multilayer reflective film 11, a protective film 12, a phase shift film 13, and an etch mask film 14. The multilayer reflective film 11, the protective film 12, the phase shift film 13, and the etch mask film 14 are sequentially formed on the first main surface 10a of the substrate 10. Furthermore, the reflective photomask substrate 1 may at least include a substrate 10, a multilayer reflective film 11, and a phase shift film 13.

[0016] The reflective photomask substrate 1 may further have a functional film (not shown). For example, the reflective photomask substrate 1 may have a conductive film located on the opposite side of the multilayer reflective film 11 when the substrate 10 is used as a reference. The conductive film is used, for example, to allow the reflective photomask 2 to be adsorbed onto the electrostatic chuck of the exposure apparatus. In the reflective photomask substrate 1, a diffusion barrier film (not shown) may be provided between the multilayer reflective film 11 and the protective film 12. The diffusion barrier film inhibits the diffusion of metal elements contained in the protective film 12 into the multilayer reflective film 11.

[0017] Next, referring to Figures 2 and 3, a reflective photomask 2 according to one embodiment will be described. In Figures 2 and 3, the X-axis, Y-axis, and Z-axis directions are mutually orthogonal. The Z-axis direction is perpendicular to the first main surface 10a of the substrate 10. The X-axis direction is the length direction of the lines and gap patterns. The Y-axis direction is the width direction of the lines.

[0018] The reflective mask 2 is fabricated, for example, using the reflective mask substrate 1 shown in FIG. 1, and the phase shift film 13 has an opening pattern 13a. The opening pattern 13a includes a pattern of lines and gaps. Furthermore, the etch mask film 14 shown in FIG. 1 is removed after the opening pattern 13a is formed on the phase shift film 13.

[0019] Using EUVL, the opening pattern 13a of the phase shift film 13 is transferred to a substrate such as a semiconductor substrate. The transfer includes transferring after shrinking. Hereinafter, the substrate 10, the multilayer reflective film 11, the protective film 12, the phase shift film 13, and the etching mask film 14 will be described in sequence.

[0020] The substrate 10 is, for example, a glass substrate. The substrate 10 is preferably made of quartz glass containing TiO₂. Compared to ordinary soda-lime glass, quartz glass has a smaller coefficient of linear expansion, resulting in less dimensional change due to temperature variations. The quartz glass can contain 80% to 95% by mass of SiO₂ and 4% to 17% by mass of TiO₂. If the TiO₂ content is 4% to 17% by mass, the coefficient of linear expansion near room temperature is approximately zero, and dimensional change occurs almost nonexistent near room temperature. The quartz glass may also contain a third component or impurity other than SiO₂ and TiO₂. Furthermore, the substrate 10 can be made of crystalline glass with precipitated β-quartz solid solution, silicon, or metal, etc.

[0021] The substrate 10 has a first main surface 10a and a second main surface 10b with the direction opposite to that of the first main surface 10a. A multilayer reflective film 11 is formed on the first main surface 10a. Viewed from above (Z-axis direction), the dimensions of the substrate 10 are, for example, 152 mm in length and 152 mm in width. The length and width may also be 152 mm or more. Each of the first main surface 10a and the second main surface 10b has a quality assurance region, for example, a square. The dimensions of the quality assurance region are, for example, 142 mm in length and 142 mm in width. Preferably, the quality assurance region of the first main surface 10a has a root mean square roughness (RMS) of less than 0.15 nm and a flatness of less than 100 nm. Furthermore, the quality assurance region of the first main surface 10a preferably does not have defects that would cause phase defects.

[0022] The multilayer reflective film 11 reflects EUV light. The multilayer reflective film 11 may be, for example, composed of alternating layers of high refractive index and low refractive index. The high refractive index layer may be made of, for example, silicon (Si), and the low refractive index layer may be made of, for example, molybdenum (Mo). A Mo / Si multilayer reflective film can be used. Furthermore, Ru / Si multilayer reflective films, Mo / Be multilayer reflective films, Mo compound / Si compound multilayer reflective films, Si / Mo / Ru multilayer reflective films, Si / Mo / Ru / Mo multilayer reflective films, and Si / Ru / Mo / Ru multilayer reflective films can also be used as the multilayer reflective film 11.

[0023] The film thickness of each layer constituting the multilayer reflective film 11 and the number of repeating units of the layers can be appropriately selected according to the material of each layer and the reflectivity for EUV light. When the multilayer reflective film 11 is a Mo / Si multilayer reflective film, in order to achieve a reflectivity of 60% or more for EUV light with an incident angle θ (refer to FIG. 3) of 6°, it is only necessary to stack a Mo layer with a film thickness of 2.3 ± 0.1 nm and a Si layer with a film thickness of 4.5 ± 0.1 nm in such a way that the number of repeating units is 30 or more and 60 or less. The multilayer reflective film 11 preferably has a reflectivity of 60% or more for EUV light with an incident angle θ of 6°. The reflectivity is more preferably 65% or more.

[0024] Examples of the film formation method for each layer of the multilayer reflective film 11 formed include a DC (Direct Current) sputtering method, a magnetron sputtering method, an ion beam sputtering method, etc. When forming a Mo / Si multilayer reflective film using the ion beam sputtering method, an example of the film formation conditions for each of the Mo layer and the Si layer is as described below. <Film formation conditions for the Si layer> Target: Si target Sputtering gas: Argon (Ar) Gas pressure: 1.3×10 -2 Pa to 2.7×10 -2 Pa Ion acceleration voltage: 300 V to 1500 V Film formation speed: 0.030 nm / sec to 0.300 nm / sec Film thickness of the Si layer: 4.5 ± 0.1 nm <Film formation conditions for the Mo layer> Target: Mo target Sputtering gas: Argon (Ar) Gas pressure: 1.3×10 -2 Pa to 2.7×10 -2 Pa Ion acceleration voltage: 300 V to 1500 V Film formation speed: 0.030 nm / sec to 0.300 nm / sec Film thickness of the Mo layer: 2.3 ± 0.1 nm <Repeating units of the Si layer and the Mo layer> Number of repeating units: 30 to 60 (preferably 40 to 50).

[0025] A protective film 12 is formed between the multilayer reflective film 11 and the phase shift film 13 to protect the multilayer reflective film 11 from the effects of the etching gas. The etching gas is used to form an opening pattern 13a on the phase shift film 13 (see Figure 2). The etching gas is, for example, a halogen-based gas, an oxygen-based gas, or a mixture thereof. The etching gas will be described in detail later. The protective film 12 will not be removed even when exposed to the etching gas and will remain on the multilayer reflective film 11.

[0026] The protective film 12 is resistant to the sulfuric acid-hydrogen peroxide mixture (SPM) used as a cleaning solution, and is used to protect the multilayer reflective film 11 from the influence of the SPM mixture. The SPM mixture is used, for example, for the removal of resist films (not shown) or the cleaning of reflective photomasks 2. The resist film is formed on the etching mask film 14 (or the phase shift film 13 if the etching mask film 14 is not present).

[0027] The protective film 12 may contain, for example, at least one element selected from ruthenium (Ru), rhodium (Rh), and silicon (Si). When the protective film 12 contains rhodium, it may contain only rhodium, but in addition to rhodium, it may also contain elements selected from the group consisting of nitrogen (N), oxygen (O), carbon (C), boron (B), ruthenium (Ru), niobium (Nb), molybdenum (Mo), tantalum (Ta), iridium (Ir), palladium (Pd), zirconium (Zr), yttrium (Y), and titanium (Ti).

[0028] The protective film 12 can be made of a rhodium alloy. Besides Rh, the rhodium alloy also contains at least one element X selected from the group consisting of Ru, Nb, Mo, Ta, Ir, Pd, Zr, Ti, and Y. When element X is Ru, Nb, Mo, Zr, Ti, or Y, the extinction coefficient k can be reduced without significantly increasing the refractive index n, thus improving the reflectivity to EUV light. When element X is Ru, Ta, Ir, Pd, or Y, the etching durability against specific gases or the cleaning durability can be improved. Preferably, element X is Ru, Nb, Mo, Y, or Zr.

[0029] The elemental ratio of X to Rh (X:Rh) is preferably 1:99 to 1:1. In this specification, the elemental ratio refers to the molar ratio. If the ratio (X / Rh) is 1 / 99 or higher, the reflectivity to EUV light is good. If the ratio (X / Rh) is 1 or lower, the protective film 12 has good durability against etching gases. The elemental ratio of X to Rh (X:Rh) is more preferably 3:10 to 1:1.

[0030] In addition to Rh, the protective film 12 may also contain at least one element Z selected from the group consisting of N, O, C, and B. The element Z reduces the durability of the protective film 12 against etching gases, but on the other hand, reduces the crystallinity of the protective film 12, thereby improving the smoothness of the protective film 12. The protective film 12 containing the element Z has an amorphous structure or a microcrystalline structure. When the protective film 12 has an amorphous structure or a microcrystalline structure, the X-ray diffraction pattern of the protective film 12 does not have a clear peak.

[0031] When, in addition to Rh, the protective film 12 also contains Z, preferably the content of Rh or the total content of Rh and X is 40 at% to 99 at% and the total content of Z is 1 at% to 60 at%. When, in addition to Rh, the protective film 12 also contains Z, more preferably the content of Rh or the total content of Rh and X is 80 at% to 99 at% and the total content of Z is 1 at% to 20 at%.

[0032] When the protective film 12 contains 90 at% or more of Rh, contains at least one of X and Z, and has a film density of 10.0 g / cm 3 to 14.0 g / cm 3, the protective film 12 has an amorphous structure or a microcrystalline structure. The film density of the protective film 12 is preferably 11.0 g / cm 3 to 13.0 g / cm 3. Furthermore, when the protective film 12 contains 100 at% of Rh and has a film density of 11.0 g / cm 3 to 12.0 g / cm 3, the protective film 12 has an amorphous structure or a microcrystalline structure. Furthermore, the film density of the protective film 12 is measured by the X-ray reflectivity method.

[0033] The film thickness of the protective film 12 is preferably 1.0 nm or more and 10.0 nm or less, more preferably 2.0 nm or more and 3.5 nm or less.

[0034] The root mean square roughness (RMS) of the protective film 12 is preferably 0.3 nm or less, more preferably 0.1 nm or less.

[0035] The film formation method of the protective film 12 is, for example, a DC sputtering method, a magnetron sputtering method, or an ion beam sputtering method. When forming a Rh film using the DC sputtering method, an example of the film formation conditions is as described below. <Film formation conditions of Rh film> Target: Rh target Sputtering gas: argon (Ar) Air pressure: 1.0×10 -2Pa~1.0×10 0Pa Input power density per unit target area: 1.0 W / cm 2~8.5 W / cm 2 Film formation rate: 0.020 nm / sec~1.000 nm / sec Film thickness of Rh film: 1 nm~10 nm.

[0036] Furthermore, when forming the Rh film, nitrogen gas (N 2), or a mixed gas of argon gas and nitrogen gas can be used as the sputtering gas. The volume ratio of nitrogen gas in the sputtering gas (N 2 / (Ar+N 2)) is 0.05 or more and 1.0 or less.

[0037] When forming the RhO film using the DC sputtering method, an example of the film formation conditions is as described below. <Film formation conditions of RhO film> Target: Rh target Sputtering gas: oxygen gas (O 2), or a mixed gas of argon gas and oxygen gas Volume ratio of oxygen gas in the sputtering gas (O 2 / (Ar+O 2)): 0.05~1.0 Air pressure: 1.0×10 -2Pa~1.0×10 0Pa Input power density per unit target area: 1.0 W / cm 2~8.5 W / cm 2 Film formation rate: 0.020 nm / sec~1.000 nm / sec Film thickness of RhO film: 1 nm~10 nm.

[0038] When forming the RhRu film using the DC sputtering method, an example of the film formation conditions is as described below. <Film formation conditions of RhRu film> Target: Rh target and Ru target (or RhRu target) Sputtering gas: argon gas (Ar) Air pressure: 1.0×10 -2Pa~1.0×10 0Pa Input power density per unit target area: 1.0 W / cm 2~8.5 W / cm 2 Film formation rate: 0.020 nm / sec~1.000 nm / sec Film thickness of RhRu film: 1 nm~10 nm.

[0039] The phase-shifting film 13 is a predetermined film for forming the opening pattern 13a. The opening pattern 13a is formed during the manufacturing process of the reflective photomask 2, but not during the manufacturing process of the reflective photomask substrate 1. The phase-shifting film 13 shifts the phase of the second EUV light L2 relative to the first EUV light L1 shown in FIG. 3. The first EUV light L1 passes through the opening pattern 13a without passing through the phase-shifting film 13, is reflected by the multilayer reflective film 11, and then passes through the opening pattern 13a again without passing through the phase-shifting film 13. The second EUV light L2 passes through the phase-shifting film 13 while being absorbed by it, is reflected by the multilayer reflective film 11, and then passes through the phase-shifting film 13 again while being absorbed by it. The phase difference between the first EUV light L1 and the second EUV light L2 is, for example, 170° to 250°. The phase of the first EUV light L1 may lead or lag behind the phase of the second EUV light L2. The phase difference between the first EUV light L1 and the second EUV light L2 is preferably 170°~250°, more preferably 180°~245°, further preferably 190°~240°, and even more preferably 190°~235°. The phase shift film 13 utilizes the interference between the first EUV light L1 and the second EUV light L2 to enhance the contrast of the transferred image. The transferred image is obtained by transferring the opening pattern 13a of the phase shift film 13 onto the target substrate.

[0040] Previously, the chemical composition and structure of the phase shift film 13 for EUVL were studied, but the case where the opening pattern 13a includes line and gap patterns was not fully studied.

[0041] The inventors focused on the refractive index n of the phase-shifting film 13 for EUV light and the extinction coefficient k of the phase-shifting film 13 for EUV light. The refractive index and extinction coefficient of each element that may be included in the phase-shifting film 13 are shown in Figure 4. The inventors discovered that within a certain range where the refractive index n is below 0.920 and the extinction coefficient k is above 0.024, there exists a range that can improve the transfer accuracy of the line and gap patterns (for example, range A shown in Figure 4), details of which are described in the Examples section.

[0042] The optical properties (refractive index n and extinction coefficient k) of the phase-shifting film 13 were obtained from the databases of the Center for X-Ray Optics and Lawrence Berkeley National Laboratory, or calculated based on the "incidence angle dependence" of the reflectance described below.

[0043] The incident angle θ of EUV light, the reflectivity R of EUV light, the refractive index n of phase shift film 13, and the extinction coefficient k of phase shift film 13 satisfy the following equation (1). R=|(sinθ-((n+ik) 2-cos 2θ) 1 / 2) / (sinθ+((n+ik) 2-cos 2θ) 1 / 2)| ……(1) The refractive index n and extinction coefficient k are calculated using the least squares method, which takes into account a complex number of combinations of incident angle θ and reflectivity R, with the error between the complex number of measured data and equation (1) being minimized.

[0044] The phase-shifting film 13 has a refractive index n of 0.920 or less, an extinction coefficient k of 0.024 or more, a film thickness t of 50 nm or less, a normalized imaging logarithmic slope NILS of the transferred image of 2.90 or more, and a focal depth margin m of the transferred image of 60 nm or less. The transferred image is obtained by transferring the line and gap patterns contained in the opening pattern 13a to the target substrate.

[0045] The normalized imaging log slope NILS of the transferred image represents the contrast of the transferred image and is calculated using the following formula (1).

[0046] [Formula 1] In the above formula (1), I(x) is the light intensity of the transferred image (intensity normalized to maximum intensity, dimensionless quantity), x is the position of the width direction of the transferred image (the direction orthogonal to the line, equivalent to the Y-axis direction in Figure 3) (unit: nm), and CD is the critical dimension of the transferred image.

[0047] I(x) is derived using lithography simulation based on optical imaging theory. The simulation based on optical imaging theory is, for example, based on a well-known document (Koichi Matsumoto, "Lithography Optics", journal "Optics", Optical Society of Japan, March 2001, Vol. 30, No. 3, pp. 40-47). <Simulation Conditions> EUV light wavelength: 13.5 nm Angle of incidence θ: 6° Numerical aperture (NA) of the EUV exposure apparatus: 0.33 Opening pattern of phase shift film: lines and gaps Image reduction ratio for pattern transfer: 4x Line spacing p of transferred images: 26 nm, 28 nm, 32 nm, 36 nm Duty ratio of transferred image (ratio of line width to gap width): 1:1 Critical image transfer dimensions (CD): 13 nm, 14 nm, 16 nm, 18 nm EUV exposure apparatus illumination system: bipolar illumination (σ0.7 / 0.5).

[0048] Furthermore, to reflect the following projection effect in I(x), as shown in Figure 3, the closer the optical axis of EUV light is to the Z-axis, the more it tilts towards the Y-axis. As shown in Figure 3, the closer the incident ray is to the negative Z-axis, the more it tilts towards the positive Y-axis, and the closer the reflected ray is to the positive Z-axis, the more it tilts towards the positive Y-axis. When viewed from the X-axis, the optical axis of EUV light is tilted, but when viewed from the Y-axis, the optical axis of EUV light is perpendicular. The X-axis is orthogonal to the incident surface of EUV light (the surface containing both the incident and reflected rays).

[0049] In the simulation, the calculation in the ZY plane was illustrated above. However, the incident light inclined in the ZX plane in Figure 3 can also be calculated. In this case, eight types of I(x) can be obtained.

[0050] Regarding the Normalized Imaging Logarithmic Slope (NILS) of the transferred image, as shown in Figure 5, the slope of lnI(x) (the natural logarithm of I(x)) is calculated with the width of the peak of I(x) equal to x of CD (x=x1). The calculated slope is then multiplied by CD, and the product is taken as the NILS. The larger the NILS, the greater the contrast of the transferred image. For example, when the line spacing of the transferred image is 32 nm and the critical size CD of the transferred image is 16 nm, the NILS is 2.9 or higher, preferably 3.0 or higher. Furthermore, there is no particular upper limit to the NILS, but it is preferably 4.5 or lower, and more preferably 3.5 or lower. I(x) is the value at the optimal focal point described below.

[0051] The depth-of-focus margin range *m* of the transferred image is the difference between the maximum and minimum values ​​of the optimal focal length when the line spacing *p* of the transferred image is 26 nm, 28 nm, 32 nm, and 36 nm. The optimal focal length is the focal position of the EUV exposure device where I(x) reaches its maximum when x = x1. The smaller the margin range *m*, the easier it is to focus on multiple line spacings *p* simultaneously. The upper limit of the margin range *m* is preferably below 60 nm, and more preferably below 55 nm. There is no particular limitation on the lower limit of the margin range *m*, but the margin range *m* should be above 0 nm, and preferably above 5 nm.

[0052] The smaller the refractive index n of the phase shifting film 13, the larger the normalized imaging logarithmic slope NILS will be, even if the film thickness t of the phase shifting film 13 is small. The refractive index n is, for example, 0.920 or less, preferably 0.910 or less, and more preferably 0.900 or less. Furthermore, the refractive index n is preferably 0.880 or more, and more preferably 0.885 or more.

[0053] The larger the extinction coefficient k of the phase shift film 13, the smaller the margin range m of the focal depth, which can improve the normalized imaging logarithmic slope NILS. On the other hand, if the extinction coefficient k is too large, the normalized imaging logarithmic slope NILS of lines and gaps with large spacing will decrease. The extinction coefficient k is, for example, 0.024 or more, preferably 0.030 or more, more preferably 0.035 or more, and even more preferably 0.040 or more. Furthermore, the extinction coefficient k is preferably 0.065 or less, more preferably 0.060 or less, even more preferably 0.055 or less, and especially preferably 0.050 or less.

[0054] The smaller the thickness t of the phase shift film 13, the lower the projection effect (masking effect). For example, as shown in Figure 3, the masking effect refers to the area formed near the opening edge of the opening pattern 13a where the EUV light is blocked by the phase shift film 13 because the incident angle θ of EUV light is not 0° (for example, 6°), thus causing the size of the transferred image to deviate from the required size.

[0055] Furthermore, the smaller the film thickness t of the phase shift film 13, the better the processing accuracy of the opening pattern 13a.

[0056] The film thickness t of the phase shift film is, for example, 50 nm or less, preferably 45 nm or less, and more preferably 35 nm or less. Furthermore, the film thickness t is preferably 15 nm or more, and more preferably 20 nm or more.

[0057] The reflectivity of the phase-shifting film 13 is preferably 12% or less, more preferably 11% or less, and even more preferably 10% or less. Furthermore, there is no particular limitation on the lower limit of the reflectivity of the phase-shifting film 13, but it is preferably 1.2% or more, and more preferably 2.0% or more. Here, the reflectivity of the phase-shifting film 13 is the relative reflectivity of the second EUV light L2 relative to the first EUV light L1 as shown in Figure 3 (the reflectivity of the second EUV light when the reflectivity of the first EUV light L1 is set to 100%).

[0058] The phase shift film 13 contains, for example, at least one element selected from Group 1, consisting of iridium (Ir), platinum (Pt), gold (Au), silver (Ag), osmium (Os), and rhenium (Re). Ir, Pt, Au, Os, and Re can improve the etching rate of the phase shift film 13. Furthermore, Ir and Pt can improve the tolerance to sulfuric acid-hydrogen peroxide-water mixtures.

[0059] In addition to one element selected from Group 1 above, the phase shift film 13 may also contain at least one element selected from Group 2, consisting of ruthenium (Ru), silicon (Si), tantalum (Ta), niobium (Nb), tungsten (W), and chromium (Cr). Ru, Si, Ta, Nb, W, and Cr can improve the etching rate of the phase shift film 13. Furthermore, Ru, Si, and Ta can improve the tolerance to sulfuric acid-hydrogen peroxide-water mixtures.

[0060] The phase shift film 13 can be either a monolayer or a laminated film. A monolayer film comprises a single metal or an alloy. The alloy may, for example, comprise two or more elements selected from Group 1 above, two or more elements selected from Group 2 above, or one or more elements selected from Group 1 above and one or more elements selected from Group 2 above. A laminated film comprises at least a first layer and a second layer with a different chemical composition from the first layer. Both the first and second layers comprise a single metal or an alloy. The laminated film may repeatedly comprise the first and second layers.

[0061] When the phase shift film 13 includes a first layer and a second layer, the refractive index n of the phase shift film 13 is calculated according to the following formula (2).

[0062] [Formula 2] In the above formula (2), n1 is the refractive index of the first layer, n2 is the refractive index of the second layer, t1 is the film thickness of the first layer, t2 is the film thickness of the second layer, d1 is the density of the first layer, d2 is the density of the second layer, M1 is the atomic weight of the first layer, and M2 is the atomic weight of the second layer.

[0063] When the phase shift film 13 includes a first layer and a second layer, the extinction coefficient k of the phase shift film 13 is calculated according to the following formula (3).

[0064] [Formula 3] In the above formula (3), k1 is the extinction coefficient of the first layer, k2 is the extinction coefficient of the second layer, t1 is the film thickness of the first layer, t2 is the film thickness of the second layer, d1 is the density of the first layer, d2 is the density of the second layer, M1 is the atomic weight of the first layer, and M2 is the atomic weight of the second layer.

[0065] Furthermore, in addition to the first and second layers, the phase shift film 13 may also include a third layer with a different chemical composition from the first and second layers. In the case where the third layer is included, the refractive index n and the extinction coefficient k can be calculated using the same formulas as those in equations (2) and (3) above.

[0066] The phase shift film 13 may contain Ir or a mixture of Ir and Re. Preferably, the elemental ratio of Re to Ir (Re:Ir) is 0:1 to 1:1. The phase shift film 13 may contain only Ir, but more preferably, it contains Re in addition to Ir. Re can improve the etching rate of the phase shift film 13 without damaging its optical properties (refractive index n and extinction coefficient k). If the ratio (Re / Ir) is less than 1, the phase shift film 13 exhibits good durability against sulfuric acid-hydrogen peroxide-water mixtures. The elemental ratio of Re to Ir (Re:Ir) is preferably 1:9 to 5:5, more preferably 2:8 to 4:6.

[0067] The phase-shifting film 13 may contain Ir, or may contain both Ir and Ru. Preferably, the elemental ratio of Ru to Ir (Ru:Ir) is 0:1 to 1:1. The phase-shifting film 13 may contain only Ir, but more preferably, it contains Ru in addition to Ir. Ru can reduce the refractive index n of the phase-shifting film 13 and decrease the film thickness t, thereby improving NILS. If the ratio (Ru / Ir) is less than 1, the decrease in the extinction coefficient k of the phase-shifting film 13 can be suppressed, and the margin range m of the focal depth can be suppressed from becoming too large. The elemental ratio of Ru to Ir (Ru:Ir) is preferably 1:9 to 5:5, more preferably 2:8 to 4:6.

[0068] The phase shifting film 13 may contain Ir, Re, and Ru. Preferably, the elemental ratio of Re to Ir (Re:Ir) is 1:99 to 80:20, and the elemental ratio of Ru to Ir (Ru:Ir) is 1:99 to 80:20. More preferably, the elemental ratio of Re to Ir (Re:Ir) is 1:9 to 5:5, and even more preferably, 2:8 to 3:7. More preferably, the elemental ratio of Ru to Ir (Ru:Ir) is 1:9 to 4:6, and even more preferably, 1:9 to 2:8.

[0069] When the phase shift film 13 contains Re and Ru, it may or may not contain Ir. In this case, the elemental ratio of Ru to Re (Ru:Re) is preferably 3:7 to 7:3. By adding Ru to Re, the durability of the sulfuric acid-hydrogen peroxide-water mixture is improved, but on the other hand, the extinction coefficient k will decrease. If the ratio (Ru / Re) is 3 / 7 or higher, the phase shift film 13 has good durability for the sulfuric acid-hydrogen peroxide-water mixture. If the ratio (Ru / Re) is 7 / 3 or lower, the decrease in the extinction coefficient k of the phase shift film 13 can be suppressed, and the margin range m of the depth of focus can be prevented from becoming too large. The elemental ratio of Ru to Re (Ru:Re) is more preferably 5:5 to 6:4.

[0070] As described above, an etching gas is used in the formation of the opening pattern 13a of the phase shift film 13. The etching gas is, for example, a halogen gas, an oxygen gas, or a mixture of the above.

[0071] Examples of halogen-based gases include chlorine-based gases and fluorine-based gases. Chlorine-based gases include, for example, chlorine (Cl₂), SiCl₄, CHCl₃, CCl₄, BCl₃, or mixtures thereof. Fluorine-based gases include, for example, CF₄, CHF₃, SF₆, BF₃, XeF₂, or mixtures thereof. Oxygen-based gases include oxygen (O₂), O₃, or mixtures thereof.

[0072] When the phase shift film 13 contains Ir, a fluorine-based gas is preferred as the halogen-based gas. It is preferable to use a fluorine-based gas as a mixture with an oxygen-based gas rather than using a fluorine-based gas alone. The volume ratio of the oxygen-based gas to the fluorine-based gas (oxygen-based gas:fluorine-based gas) is preferably 10:90 to 50:50, more preferably 20:80 to 40:60.

[0073] The ratio of the etching rate of the phase shift film 13 using etching gas to the etching rate of the protective film 12 using etching gas is also called the selectivity ratio. A selectivity ratio of 5 or higher is preferred. The higher the selectivity ratio, the better the etching resistance of the protective film 12. A selectivity ratio of 200 or lower is preferred, and more preferably 100 or lower.

[0074] The etching rate of the phase shift film 13 using a sulfuric acid-hydrogen peroxide-water mixture is 0 nm / min to 0.05 nm / min. The sulfuric acid-hydrogen peroxide-water mixture can be used for removing resist films or cleaning reflective photomasks 2. If the etching rate of the phase shift film 13 using the sulfuric acid-hydrogen peroxide-water mixture is 0.05 nm / min, damage to the phase shift film 13 during cleaning can be suppressed.

[0075] The phase-shifting film 13 can be formed by methods such as DC sputtering, magnetron sputtering, or ion beam sputtering.

[0076] An etch mask 14 is formed on a phase shift film 13 to form an opening pattern 13a on the phase shift film 13. A resist film (not shown) is disposed on the etch mask 14. In the manufacturing steps of the reflective photomask 2, a first opening pattern is first formed on the resist film, then a second opening pattern is formed on the etch mask 14 using the first opening pattern, and then a third opening pattern 13a is formed on the phase shift film 13 using the second opening pattern. The first, second, and third opening patterns 13a have the same size and shape when viewed from above (Z-axis direction). The etch mask 14 enables the thinning of the resist film.

[0077] The etching mask film 14 contains at least one element selected from the group consisting of Ru, Al, Hf, Y, Cr, Nb, Ti, Mo, Ta, and Si. In addition to the elements mentioned above, the etching mask film 14 may also contain at least one element selected from the group consisting of O, N, C, and B. Preferably, the etching mask film 14 contains at least one element selected from the group consisting of O, N, and B, and more preferably, it contains at least one element selected from the group consisting of O and N.

[0078] The thickness of the etched mask film 14 is preferably 2 nm or more and 30 nm or less, more preferably 2 nm or more and 25 nm or less, and even more preferably 2 nm or more and 10 nm or less.

[0079] The etching mask film 14 can be formed by methods such as DC sputtering, magnetron sputtering, or ion beam sputtering.

[0080] Next, referring to FIG6, a method for manufacturing a reflective photomask substrate 1 according to one embodiment will be described. The method for manufacturing the reflective photomask substrate 1 includes, for example, steps S101 to S105 shown in FIG6. In step S101, a substrate 10 is prepared. In step S102, a multilayer reflective film 11 is formed on the first main surface 10a of the substrate 10. In step S103, a protective film 12 is formed on the multilayer reflective film 11. In step S104, a phase shift film 13 is formed on the protective film 12. In step S105, an etching mask film 14 is formed on the phase shift film 13. Furthermore, the method for manufacturing the reflective photomask substrate 1 may include at least steps S101, S102, and S104. The method for manufacturing the reflective photomask substrate 1 may further include a step for forming a functional film (not shown).

[0081] Next, referring to FIG7, a method for manufacturing a reflective photomask 2 according to one embodiment will be described. The method for manufacturing the reflective photomask 2 includes steps S201 to S204 shown in FIG7. In step S201, a reflective photomask substrate 1 is prepared. In step S202, an etch mask film 14 is processed. A resist film (not shown) is provided on the etch mask film 14. First, a first opening pattern is formed on the resist film, and then a second opening pattern is formed on the etch mask film 14 using the first opening pattern. In step S203, a third opening pattern 13a is formed on the phase shift film 13 using the second opening pattern. In step S203, the phase shift film 13 is etched using an etching gas. In step S204, the resist film and the etch mask film 14 are removed. The removal of the resist film uses, for example, a mixture of sulfuric acid, hydrogen peroxide, and water. The removal of the etch mask film 14 uses, for example, an etching gas. The etching gas used in step S204 (removal of the etching mask 14) can be the same type as the etching gas used in step S203 (formation of the opening pattern 13a). Furthermore, the manufacturing method of the reflective photomask 2 only needs to include steps S201 and S203. [Example]

[0082] The experimental data are described below. Examples 1 to 8 and 10 below are examples, and examples 9 and 11 below are comparative examples.

[0083] In Example 1, an EUV photomask substrate comprising a substrate, a multilayer reflective film, a protective film, and a phase shift film is fabricated.

[0084] A SiO₂-TiO₂ glass substrate (6 inches (152 mm) square, 6.3 mm thick) was prepared as the substrate. The glass substrate had a coefficient of thermal expansion of 0.02 × 10⁻⁷ / ℃ at 20°C, a Young's modulus of 67 GPa, a Poisson's ratio of 0.17, and a specific modulus of 3.07 × 10⁷ m² / s². The quality assurance area of ​​the first main surface of the substrate was polished to achieve a root mean square roughness (RMS) of less than 0.15 nm and a flatness of less than 100 nm. A 100 nm thick Cr film was deposited on the second main surface of the substrate using magnetron sputtering. The sheet resistivity of the Cr film was 100 Ω / □.

[0085] A Mo / Si multilayer reflective film was formed as a multilayer reflective film. The Mo / Si multilayer reflective film was formed by repeating the process of depositing a Si layer (film thickness 4.5 nm) and a Mo layer (film thickness 2.5 nm) using ion beam sputtering 40 times. The total film thickness of the Mo / Si multilayer reflective film is 272 nm ((4.5 nm + 2.3 nm) × 40).

[0086] A 2.5 nm thick Rh film was formed as a protective film. The Rh film was formed using DC sputtering. The reflectivity of the multilayer reflective film after the formation of the protective film for EUV light, i.e., the maximum reflectivity of the first EUV light L1 shown in Figure 3, is 64.5%.

[0087] In Example 1, an Ir film (32 nm thick, 100 at%) was formed as a phase shifting film. The Ir film was formed using DC sputtering. The characteristics of the phase shifting film are shown in Table 1.

[0088] In Examples 2 to 11, EUV photomask substrates were fabricated under the same conditions as in Example 1, except for the chemical composition and thickness of the phase-shifting film. The characteristics of the phase-shifting film are shown in Table 1. Furthermore, the phase-shifting film in Examples 2 to 8 and Example 11 was an alloy film, and in Examples 9 and 10 it was a single-metal film.

[0089] [Table 1] Composition (at%) Optical properties SPM Tolerance EUVL characteristics ER (nm / min) Gas flow rate CF 4 / O 2 (sccm) Ir Ru Re Refractive index n matte coefficient k film thickness t (nm) reflectivity (%) Phase difference (°) Margin scope m (nm) NILS Example 1 100 0 0 0.905 0.044 ○ 32 7.3 180.9 45 2.9 11.19 24 / 8 Example 2 70 0 30 0.908 0.043 ○ 32 7.4 175.4 40 2.9 13.32 24 / 8 Example 3 80 20 0 0.901 0.039 ○ 33 6.6 193.2 45 2.9 8.66 24 / 8 Example 4 56 14 30 0.905 0.039 ○ 33 6.3 184.7 50 2.9 12.91 24 / 8 Example 5 0 70 30 0.895 0.024 ○ 42 9.5 244.8 30 2.9 35.06 4 / 28 Example 6 30 49 twenty one 0.898 0.030 ○ 35 8.9 190.2 60 3.0 8.85 24 / 8 Example 7 0 50 50 0.901 0.028 ○ 41 8.1 232.1 twenty five 2.9 41.01 4 / 28 Example 8 30 35 35 0.902 0.033 ○ 34 7.3 186.8 50 2.9 11.48 24 / 8 Example 9 0 100 0 0.886 0.017 ○ 30 39.7 179.9 95 2.4 Example 10 Pd 0.876 0.046 × 33 8.4 195.0 40 3.0 Example 11 TaSn 0.955 0.055 ○ 38 1.1 109.5 2.8 In Table 1, the SPM tolerance of the phase shift film and the etching rate ER of the phase shift film are measured under the following conditions.

[0090] The SPM tolerance of the phase shift film is evaluated as follows: The EUV mask substrate is immersed in a sulfuric acid-hydrogen peroxide water mixture at 100 °C for 20 minutes, and the change in the film thickness of the phase shift film is measured by X-ray reflectometry (XRR: X-ray Reflectometry), and the etching rate of the phase shift film relative to the sulfuric acid-hydrogen peroxide water mixture is evaluated. The sulfuric acid-hydrogen peroxide water mixture is obtained by mixing concentrated sulfuric acid and hydrogen peroxide solution at 75 vol%:25 vol% (concentrated sulfuric acid: hydrogen peroxide solution). The concentrated sulfuric acid contains 96 vol% sulfuric acid and 4 vol% water. The hydrogen peroxide solution contains 30 vol% - 35 vol% hydrogen peroxide and 65 vol% - 70 vol% water. An SPM tolerance of "○" means that the etching rate of the phase shift film relative to the sulfuric acid-hydrogen peroxide water mixture is 0.05 nm / min or less. An SPM tolerance of "×" means that the etching rate of the phase shift film relative to the sulfuric acid-hydrogen peroxide water mixture is greater than 0.05 nm / min.

[0091] The etching rate ER of the phase shift film is obtained as follows: The EUV mask substrate is placed on the sample stage of an ICP (inductively coupled mode) plasma etching apparatus, and ICP plasma etching is performed under the following conditions. <Conditions for ICP Plasma Etching> ICP antenna bias: 200 W Substrate bias: 40 W Trigger pressure: 3.5×10 0Pa Etching pressure: 3.0×10 -1Pa Etching gas: Mixed gas of O 2 and CF 4 Gas flow rate (CF 4 / O 2): 24 / 8 sccm - 4 / 28 sccm.

[0092] Furthermore, in Table 1, the reflectivity of the phase shift film is the relative reflectivity of the second EUV light L2 to the first EUV light L1 shown in Figure 3 (the reflectivity of the second EUV light when the reflectivity of the first EUV light L1 is set to 100%).

[0093] As shown in Table 1, according to Examples 1-8 and Example 10, the refractive index n of the phase-shifting film is 0.920 or less, the extinction coefficient k of the phase-shifting film is 0.024 or more, the film thickness t of the phase-shifting film is 50 nm or less, the normalized imaging logarithmic slope NILS of the transferred image is 2.9 or more, and the depth-of-focus margin m of the transferred image is 60 nm or less. However, in Example 10, because a Pd film was used as the phase-shifting film, the SPM tolerance was poor.

[0094] According to Example 9, the extinction coefficient k of the phase-shifting film did not reach 0.024, the normalized imaging logarithmic slope NILS of the transferred image did not reach 2.9, and the depth of focus margin m of the transferred image exceeded 60 nm.

[0095] According to Example 11, the refractive index n of the phase-shifting film exceeds 0.920, and the normalized imaging log slope NILS of the transferred image does not reach 2.9.

[0096] The above describes the reflective photomask substrate, the reflective photomask, the manufacturing method of the reflective photomask substrate, and the manufacturing method of the reflective photomask of the present invention. However, the present invention is not limited to the above-described embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations can be made within the scope of the claims. These naturally also fall within the technical scope of the present invention.

[0097] This application claims priority based on Japan Patent Application No. 2021-125887, filed with the Japan Patent Office on July 30, 2021, and the entire contents of Japan Patent Application No. 2021-125887 are incorporated herein by reference.

[0098] 1: Reflective photomask substrate 2: Reflective photomask 10:Substrate 10a: 1st main side 10b: 2nd main side 11: Multilayer reflective film 12: Protective film 13: Phase shifting film 13a: Opening pattern 14: Etching mask film L1: First EUV light L2: Second EUV light X, Y, Z: Axis directions θ: Angle of incidence of EUV light

Claims

1. A reflective photomask substrate, comprising, in sequence, a substrate, a multilayer reflective film for reflecting EUV light, and a phase-shifting film for shifting the phase of the EUV light, wherein the phase-shifting film is a predetermined film for forming an opening pattern, the phase-shifting film has a refractive index of 0.920 or less for the EUV light, an extinction coefficient of 0.024 or more for the EUV light, a film thickness of 50 nm or less, and a normalized image log slope of the transferred image when a line and gap pattern is formed on a target substrate is 2.9 or more, and the focal depth margin of the transferred image is 60 nm or less, wherein the focal depth margin of the transferred image is the difference between the maximum and minimum values ​​of the optimal focal point when the line spacing of the transferred image is 26 nm, 28 nm, 32 nm, and 36 nm, and the optimal focal point is the focal position of the EUV exposure apparatus where the light intensity of the transferred image reaches its maximum.

2. The reflective photomask substrate of claim 1, wherein the phase shift film comprises at least one element selected from the first group consisting of Ir, Pt, Au, Ag, Os and Re.

3. The reflective photomask substrate of claim 1, wherein the phase shifting film comprises at least one element selected from the first group consisting of Ir, Pt, Au, Os and Re.

4. The reflective photomask substrate of claim 2 or 3, wherein the phase shift film contains, in addition to at least one element selected from the first group, at least one element selected from the second group consisting of Ru, Si, Ta, Nb, W and Cr.

5. The reflective photomask substrate of claim 2 or 3, wherein the phase shift film comprises Ir, or Ir and Re, wherein the elemental ratio of Re to Ir (Re:Ir) is 0:1 to 1:

1.

6. The reflective photomask substrate of claim 2 or 3, wherein the phase shifting film comprises Ir, or Ir and Ru, wherein the elemental ratio of Ru to Ir (Ru:Ir) is 0:1 to 1:

1.

7. The reflective photomask substrate of claim 2 or 3, wherein the phase shifting film comprises Ir, Re and Ru, wherein the elemental ratio of Re to Ir (Re:Ir) is 1:99 to 80:20, and the elemental ratio of Ru to Ir (Ru:Ir) is 1:99 to 80:

20.

8. The reflective photomask substrate of claim 2 or 3, wherein the phase shift film comprises Re and Ru, and the elemental ratio of Ru to Re (Ru:Re) is 3:7 to 7:

3.

9. The reflective photomask substrate of any one of claims 1 to 3, wherein the etching rate of the phase shift film using a mixture of sulfuric acid, hydrogen peroxide, and water is 0 nm / min to 0.05 nm / min.

10. A reflective photomask substrate as claimed in any one of claims 1 to 3, wherein a protective film is provided between the multilayer reflective film and the phase shift film, the protective film being used to protect the multilayer reflective film from the effects of the etching gas used to form the opening pattern on the phase shift film, and the ratio of the etching rate of the phase shift film using the etching gas to the etching rate of the protective film using the etching gas is 5 or more.

11. The reflective photomask substrate of claim 10, wherein the protective film comprises at least one element selected from Ru, Rh and Si.

12. The reflective photomask substrate of any one of claims 1 to 3, wherein the phase shift film has a refractive index of 0.885 or higher for the EUV light.

13. The reflective photomask substrate of any one of claims 1 to 3, wherein an etch mask film is provided on the phase shift film, the etch mask film comprising at least one element selected from the group consisting of Ru, Al, Hf, Y, Cr, Nb, Ti, Mo, Ta and Si.

14. A reflective photomask having a reflective photomask substrate as claimed in any one of claims 1 to 3, wherein the phase shift film has the aforementioned opening pattern.

15. A method for manufacturing a reflective photomask substrate, comprising: The process includes the steps of forming a multilayer reflective film on a substrate to reflect EUV light, and forming a phase-shifting film on the multilayer reflective film to shift the phase of the EUV light. The phase-shifting film is a predetermined film for forming an opening pattern. The phase-shifting film has a refractive index of 0.920 or less for EUV light, an extinction coefficient of 0.024 or more for EUV light, a film thickness of 50 nm or less, a normalized image log slope of the transfer image when the line and gap pattern is formed on the target substrate, a normalized image log slope of 2.9 or more, and a focal depth margin of the transfer image of 60 nm or less. The focal depth margin of the transfer image is the difference between the maximum and minimum values ​​of the optimal focal point when the line spacing of the transfer image is 26 nm, 28 nm, 32 nm, and 36 nm. The optimal focal point is the focal position of the EUV exposure apparatus where the light intensity of the transfer image reaches its maximum.

16. A method for manufacturing a reflective photomask, comprising: Steps for preparing a reflective photomask substrate to be manufactured using the manufacturing method as described in claim 15; The step of forming the opening pattern on the phase offset film.

Images