Calibration method for optical inspection device, and method for manufacturing reflective mask blank.

Abstract

This technology provides a method for accurately measuring the dimensions of defects on the surface of a target film that constitutes a reflective mask blank. [Solution] The calibration method for an optical inspection device comprises the following steps: Prepare a first calibration substrate on which a standard defect is formed on its surface, having a rectangular shape in plan view and a side length greater than or equal to a threshold. Prepare a second calibration substrate on which standard particles with a particle size less than the threshold are attached to its surface. Prepare measurement data of the side length of the standard defect and the particle size of the standard particle, measured by an inspection device other than the optical inspection device. Measure the side length of the standard defect and the particle size of the standard particle with the optical inspection device. Create a first equation, which is a correlation equation between the measurement data of the optical inspection device and the measurement data of the other inspection device regarding the side length of the standard defect. Create a second equation, which is a correlation equation between the measurement data of the optical inspection device and the measurement data of the other inspection device regarding the particle size of the standard particle.

Description

Technical Field

[0001] The present disclosure relates to a calibration method for an optical inspection apparatus and a method for manufacturing a reflective mask blank.

Background Art

[0002] In recent years, with the miniaturization of semiconductor devices, extreme ultraviolet (EUV) lithography (EUVL), which is an exposure technique using extreme ultraviolet light, has been developed. EUV includes soft X-rays and vacuum ultraviolet rays, and specifically refers to light having a wavelength of about 0.2 nm to 100 nm. At present, EUV with a wavelength of about 13.5 nm is mainly being considered.

[0003] In EUVL, a reflective mask is used. The reflective mask has, for example, a conductive film, a glass substrate, a multilayer reflective film, a protective film, and an absorption film in this order. The conductive film is used to adsorb the reflective mask to the electrostatic chuck of the exposure apparatus. The multilayer reflective film reflects EUV light. The protective film protects the multilayer reflective film when forming an opening pattern in the absorption film. The absorption film absorbs EUV light. In EUVL, the opening pattern of the absorption film is transferred to a target substrate such as a semiconductor substrate. Transferring includes reducing and transferring.

[0004] The method for manufacturing a reflective mask includes preparing a reflective mask blank and forming an opening pattern in the absorption film. The reflective mask blank is configured in the same manner as the reflective mask, except that it does not have an opening pattern in the absorption film. The reflective mask blank has, for example, a conductive film, a glass substrate, a multilayer reflective film, a protective film, and an absorption film in this order. Before manufacturing the reflective mask, a defect inspection of the reflective mask blank is performed.

[0005] Patent Document 1 discloses a method for adjusting the optical axis of a defect inspection device used in the manufacturing process of a photomask blank. The method described in Patent Document 1 involves capturing an image of a square defect formed on the surface of a substrate, creating a cross-sectional profile of the defect intensity in the image, and adjusting the optical axis of the defect inspection device based on the symmetry of the cross-sectional profile.

[0006] Patent Document 2 discloses a method for correcting the dimensions of defects measured by a defect inspection device according to separately determined defect dimensions. The correction of defect dimensions is performed, for example, using a linear equation (y=ax+b). x is the dimension before correction, y is the dimension after correction, a is the correction coefficient, and b is the offset value. a and b are determined from the relationship between the defect dimensions measured by the defect inspection device and the defect dimensions measured using a SEM. When determining a and b, a standard wafer with defects fabricated in it, or a product wafer with standard particles scattered on it, is used. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-16629 [Patent Document 2] Japanese Patent Publication No. 2007-24737 [Overview of the project] [Problems that the invention aims to solve]

[0008] During the manufacturing process of a reflective mask blank, a defect inspection is performed on the target films that make up the reflective mask blank. A reflective mask blank, for example, has a conductive film, a glass substrate, a multilayer reflective film, a protective film, an absorbent film, and a hard mask film in this order. The films targeted for defect inspection are, for example, at least one of the conductive film, multilayer reflective film, protective film, absorbent film, and hard mask film. The hard mask film can have any configuration and may be omitted.

[0009] One embodiment of this disclosure provides a technique for accurately measuring the dimensions of defects in a target film constituting a reflective mask blank. [Means for solving the problem]

[0010] One embodiment of the present disclosure is a calibration method for an optical inspection device that measures the dimensions of defects on the surface of a target film by capturing an image of the surface of the target film constituting a reflective mask blank. The calibration method comprises the following steps: Prepare a first calibration substrate on which a standard defect having a rectangular shape in plan view and a side length greater than or equal to a threshold is formed on its surface. Prepare a second calibration substrate on which standard particles having a particle size less than the threshold are attached to its surface. Prepare measurement data of the side length of the standard defect and the particle size of the standard particle, measured by an inspection device other than the optical inspection device. Measure the side length of the standard defect and the particle size of the standard particle with the optical inspection device. Create a first equation, which is a correlation equation between the measurement data of the optical inspection device and the measurement data of the other inspection device regarding the side length of the standard defect. Create a second equation, which is a correlation equation between the measurement data of the optical inspection device and the measurement data of the other inspection device regarding the particle size of the standard particle. [Effects of the Invention]

[0011] According to one embodiment of the present disclosure, the dimensions of defects in a target film constituting a reflective mask blank can be measured with high accuracy. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a cross-sectional view showing a reflective mask blank according to one embodiment. [Figure 2] Figure 2 is a flowchart showing a method for manufacturing a reflective mask blank according to one embodiment. [Figure 3] Figure 3 is a cross-sectional view showing a reflective mask according to one embodiment. [Figure 4] Figure 4 is a flowchart showing a method for manufacturing a reflective mask according to one embodiment. [Figure 5]FIG. 5(A) is a cross-sectional view showing an example of S201, FIG. 5(B) is a cross-sectional view showing an example of S202, and FIG. 5(C) is a cross-sectional view showing an example of S203. [Figure 6] FIG. 6 is a cross-sectional view showing an example of EUV light reflected by the reflective mask of FIG. 3. [Figure 7] FIG. 7 is a diagram showing an optical inspection apparatus according to an embodiment. [Figure 8] FIG. 8 is a flowchart showing a calibration method of an optical inspection apparatus according to an embodiment. [Figure 9] FIG. 9 is a cross-sectional view showing an example of a first calibration substrate. [Figure 10] FIG. 10 is a plan view showing an example of a standard defect. [Figure 11] FIG. 11 is a cross-sectional view showing an example of a second calibration substrate. [Figure 12] FIG. 12 is a diagram showing the sizes of standard defects or standard particles measured by an uncalibrated optical inspection apparatus and a CD-SEM or a TEM. [Figure 13] FIG. 13 is a diagram showing the sizes of standard defects or standard particles measured by a calibrated optical inspection apparatus using the calibration formula shown in FIG. 12 and a CD-SEM or a TEM. [Figure 14] FIG. 14 is a diagram showing the sizes of actual defects existing in a conductive film measured by a calibrated optical inspection apparatus using the calibration formula shown in FIG. 12 and an AFM. [Figure 15] FIG. 15 is a diagram showing the same data as FIG. 14 in another format.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and the description thereof may be omitted. In the specification, "~" indicating a numerical range means that the numerical values described before and after it are included as the lower limit value and the upper limit value. The numerical range includes the rounded range.

[0014] In each drawing, the X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to each other. The Z-axis direction is perpendicular to the first principal surface 10a of the substrate 10. The X-axis direction is perpendicular to the incident surface of EUV light (the surface including the incident ray and the reflected ray). As shown in FIG. 6, the incident ray is inclined in the positive Y-axis direction as it goes in the negative Z-axis direction, and the reflected ray is inclined in the positive Y-axis direction as it goes in the positive Z-axis direction.

[0015] Referring to FIG. 1, a reflective mask blank 1 according to an embodiment will be described. The reflective mask blank 1 has, for example, a substrate 10, a multilayer reflective film 11, a protective film 12, an absorption film 13, and a hard mask film 14 in this order. The multilayer reflective film 11, the protective film 12, the absorption film 13, and the hard mask film 14 are formed on the first principal surface 10a of the substrate 10 in this order. The multilayer reflective film 11 reflects EUV light. The protective film 12 protects the multilayer reflective film 11 from the first etching gas during the processing of the absorption film 13. The absorption film 13 absorbs EUV light. The absorption film 13 may not only absorb EUV light but also shift the phase of EUV light. That is, the absorption film 13 may be a phase shift film. The hard mask film 14 protects a part of the absorption film 13 from the first etching gas during the processing of the absorption film 13.

[0016] The reflective mask blank 1 may have a conductive film 15 on the side opposite to the multilayer reflective film 11 with respect to the substrate 10. That is, the reflective mask blank 1 may have the conductive film 15, the substrate 10, the multilayer reflective film 11, the protective film 12, the absorption film 13, and the hard mask film 14 in this order. The conductive film 15 is formed on the second principal surface 10b of the substrate 10. The second principal surface 10b is a surface opposite to the first principal surface 10a. The conductive film 15 is used, for example, to adsorb the reflective mask 2 to the electrostatic chuck of the exposure apparatus.

[0017] The reflective mask blank 1 may further have a functional film not shown in FIG. 1. For example, the reflective mask blank 1 may have a diffusion barrier film (not shown) between the multilayer reflective film 11 and the protective film 12. The diffusion barrier film suppresses the diffusion of the metal element contained in the protective film 12 into the multilayer reflective film 11.

[0018] The reflective mask blank 1, although not shown, may have a buffer film between the protective film 12 and the absorption film 13. The buffer film protects the protective film 12 from the first etching gas that forms the opening pattern 13a in the absorption film 13. The buffer film is etched more slowly than the absorption film 13. Unlike the protective film 12, the buffer film ultimately has the same opening pattern as the opening pattern 13a of the absorption film 13.

[0019] Next, with reference to Figure 2, a method for manufacturing a reflective mask blank 1 according to one embodiment will be described. The method for manufacturing a reflective mask blank 1 includes, for example, steps S101 to S109 shown in Figure 2. In step S101, a substrate 10 is prepared. In step S102, a conductive film 15 is formed on the second main surface 10b of the substrate 10. In step S103, the dimensions of defects in the conductive film 15 are measured using an optical inspection device calibrated by a calibration method described later. The defects in the conductive film 15 may be concave or convex. The measurement result in step S103 is used, for example, to determine whether the reflective mask blank 1 is good or bad.

[0020] In step S104, a multilayer reflective film 11 is formed on the first main surface 10a of the substrate 10. In step S105, a protective film 12 is formed on the multilayer reflective film 11. In step S106, a defect inspection of the protective film 12 is performed. The defect inspection of the protective film 12 may also serve as a defect inspection of the multilayer reflective film 11, because defects from the multilayer reflective film 11 are transferred to the protective film 12.

[0021] When the multilayer reflective film 11 and the protective film 12 are deposited continuously using the same deposition apparatus, the defect inspection of the protective film 12 also serves as the defect inspection of the multilayer reflective film 11. However, if the multilayer reflective film 11 and the protective film 12 are deposited using different deposition apparatuses, the inspection of the multilayer reflective film 11 and the inspection of the protective film 12 may be performed separately. The inspection of the multilayer reflective film 11 may be performed before the formation of the protective film 12.

[0022] In step S106, the dimensions of the defect in the protective film 12 are measured using an optical inspection device calibrated by the calibration method described later. In step S106, not only the dimensions of the defect in the protective film 12 but also the location of the defect in the protective film 12 may be measured. The defect in the protective film 12 may be concave or convex. The measurement results in step S106 are used, for example, to determine the quality of the reflective mask blank 1 or to correct the formation position of the aperture pattern 13a of the absorption film 13.

[0023] In step S107, an absorption film 13 is formed on the protective film 12. In step S108, the dimensions of defects in the absorption film 13 are measured using an optical inspection device calibrated by a calibration method described later. In step S108, not only the dimensions of the defects in the absorption film 13 but also the location of the defects in the absorption film 13 may be measured. The defects in the absorption film 13 may be concave or convex. The measurement results in step S108 are used, for example, to determine the quality of the reflective mask blank 1 or to correct the formation position of the aperture pattern 13a of the absorption film 13.

[0024] In step S109, a hard mask film 14 is formed on the absorption film 13. In step S110, the dimensions of defects in the hard mask film 14 are measured using an optical inspection device calibrated by a calibration method described later. In step S110, not only the dimensions of the defects in the hard mask film 14 but also the location of the defects in the hard mask film 14 may be measured. The defects in the hard mask film 14 may be concave or convex. The measurement results in step S110 are used, for example, to determine the quality of the reflective mask blank 1, or to correct the formation position of the aperture pattern of the hard mask film 14 (and consequently the aperture pattern 13a of the absorption film 13).

[0025] Note that the order of steps S101 to S110 is not limited to the order shown in Figure 2. For example, the order of steps S102 to S103 and steps S104 to S110 may be reversed. Also, the method for manufacturing the reflective mask blank 1 does not have to include all of steps S101 to S110. Furthermore, the method for manufacturing the reflective mask blank 1 may further include a step of forming a functional film, which is not shown in Figure 2.

[0026] Next, with reference to Figure 3, a reflective mask 2 according to one embodiment will be described. The reflective mask 2 is fabricated, for example, using the reflective mask blank 1 shown in Figure 1, and includes an aperture pattern 13a in the absorption film 13. In EUVL, the aperture pattern 13a of the absorption film 13 is transferred to a target substrate such as a semiconductor substrate. Transfer includes transfer with reduction. Note that the hard mask film 14 shown in Figure 1 is not included in the reflective mask 2.

[0027] Next, a method for manufacturing a reflective mask 2 according to one embodiment will be described with reference to Figures 4 and 5. The method for manufacturing a reflective mask 2 has steps S201 to S204 shown in Figure 4. In step S201, a reflective mask blank 1 is prepared as shown in Figure 5(A). The reflective mask blank 1 includes a resist film 16 as shown in Figure 5(A). The resist film 16 is formed on a hard mask film 14. The resist film 16 has an opening pattern formed on it that is to be transferred to the absorption film 13.

[0028] In step S202, as shown in Figure 5(B), the hard mask film 14 is processed using a resist film 16 having an opening pattern. At the openings in the resist film 16, the hard mask film 14 is exposed to a second etching gas, and the second etching gas etches the hard mask film 14. At the end of step S202, the resist film 16 remains. As a result, the opening pattern of the resist film 16 is transferred to the hard mask film 14.

[0029] The second etching gas is selected according to the combination of the materials of the resist film 16 and the hard mask film 14, and is not particularly limited, but includes, for example, a fluorine-based gas. The fluorine-based gas includes, for example, at least one selected from CF4 gas, CHF3 gas, C2F6 gas, C3F6 gas, C4F6 gas, C4F8 gas, CH2F2 gas, CH3F gas, C3F8 gas, F2 gas, SF6 gas, and NF3 gas. In addition to the fluorine-based gas, the second etching gas may also include an active gas or an inert gas. The active gas includes, for example, O2 gas. The inert gas includes, for example, at least one selected from N2 gas, He gas, and Ar gas. The second etching gas is preferably plasma-generated.

[0030] In step S203, the absorption film 13 is processed using a hard mask film 14 having an opening pattern, as shown in Figure 5(C). At the openings of the hard mask film 14, the absorption film 13 is exposed to a first etching gas, and the first etching gas etches the absorption film 13. The hard mask film 14 has higher resistance to the first etching gas than the absorption film 13. At the end of step S203, the hard mask film 14 remains. As a result, the opening pattern of the hard mask film 14 is transferred to the absorption film 13.

[0031] The first etching gas is selected according to the combination of the material of the hard mask film 14 and the material of the absorption film 13, and is not particularly limited, but includes, for example, a chlorine-based gas and an oxygen-based gas. The chlorine-based gas includes, for example, at least one selected from Cl2 gas, SiCl4 gas, CHCl3 gas, CCl4 gas, and BCl3 gas. The oxygen-based gas includes, for example, at least one selected from O2 gas and O3 gas. In addition to the chlorine-based gas and oxygen-based gas, the first etching gas may also include an inert gas. The inert gas includes, for example, at least one selected from N2 gas, He gas, and Ar gas. The first etching gas is preferably plasma-generated.

[0032] In step S204, although not shown, the hard mask film 14 is removed. For example, a third etching gas is used to remove the hard mask film 14. The third etching gas, like the second etching gas, includes, for example, a fluorine-based gas. Preferably, the third etching gas is plasma-generated. Chemical solutions may also be used to remove the hard mask film 14.

[0033] Next, referring again to Figure 1, the substrate 10, multilayer reflective film 11, protective film 12, absorption film 13, hard mask film 14, and conductive film 15 will be explained in this order.

[0034] The substrate 10 is, for example, a glass substrate. The material of the substrate 10 is preferably quartz glass containing TiO2. Compared to general soda-lime glass, quartz glass has a smaller coefficient of linear expansion and less dimensional change due to temperature changes. The quartz glass may contain 80% to 95% by mass of SiO2 and 4% to 17% by mass of TiO2. When the TiO2 content is 4% to 17% by mass, the coefficient of linear expansion at room temperature is almost zero, and there is almost no dimensional change at room temperature. The quartz glass may contain third components or impurities other than SiO2 and TiO2. The material of the substrate 10 may also be crystallized glass with a β-quartz solid solution precipitated, silicon, or metal, etc.

[0035] The substrate 10 has a first main surface 10a and a second main surface 10b facing the opposite direction from the first main surface 10a. A multilayer reflective film 11 or the like is formed on the first main surface 10a. In plan view (viewed along the Z-axis), the size of the substrate 10 is, for example, 152 mm in length and 152 mm in width. The length and width dimensions may be 152 mm or more. The first main surface 10a and the second main surface 10b each have, for example, a square quality assurance area in the center. The size of the quality assurance area is, for example, 142 mm in length and 142 mm in width. The length and width dimensions may be 142 mm or more. The quality assurance area of ​​the first main surface 10a preferably has a root mean square roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less. Furthermore, it is preferable that the quality assurance area of ​​the first main surface 10a does not have defects that cause phase defects.

[0036] The multilayer reflective film 11 reflects EUV light. The multilayer reflective film 11 is, for example, made by alternately stacking high refractive index layers and low refractive index layers. The material of the high refractive index layer is, for example, silicon (Si), and the material of the low refractive index layer is, for example, molybdenum (Mo), and a Mo / Si multilayer reflective film is used. In addition, 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, Si / Ru / Mo / Ru multilayer reflective films, and Si / Ru / Mo multilayer reflective films can also be used as the multilayer reflective film 11.

[0037] The film thickness of each layer constituting the multilayer reflective film 11 and the number of repeating units of the layer can be appropriately selected according to the material of each layer and its reflectance to EUV light. In the case of a Mo / Si multilayer reflective film 11, to achieve a reflectance of 60% or more for EUV light with an incident angle θ (see Figure 6) of 6°, 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 should be stacked so that the number of repeating units is between 30 and 60. Preferably, the multilayer reflective film 11 has a reflectance of 60% or more for EUV light with an incident angle θ of 6°. More preferably, the reflectance is 65% or more.

[0038] The protective film 12 is formed between the multilayer reflective film 11 and the absorption film 13, protecting the multilayer reflective film 11. The protective film 12 protects the multilayer reflective film 11 from the first etching gas during the processing of the absorption film 13, i.e., in step S203. The protective film 12 remains on the multilayer reflective film 11 without being removed even when exposed to the first etching gas.

[0039] The protective film 12 contains at least one element selected from, for example, Ru, Rh, and Si. If the protective film 12 contains Rh, it may contain only Rh, or it may contain an Rh compound. The Rh compound may contain, in addition to Rh, at least one element selected from the group consisting of Ru, Nb, Mo, Ta, Ir, Pd, Zr, Y, and Ti.

[0040] The protective film 12 may be a single-layer film or a multilayer film having a lower layer and an upper layer. The lower and upper layers constituting the protective film 12 are formed on the multilayer reflective film 11 in this order. The uppermost layer of the protective film 12 is the layer furthest from the multilayer reflective film 11. By making the protective film 12 a multilayer structure in this way, materials with superior properties for a given function can be used in each layer, thereby enabling multifunctionality of the entire protective film 12.

[0041] The uppermost layer of the protective film 12 preferably contains at least one element selected from Ru and Rh, more preferably Rh, and even more preferably a Rh compound. The lower layer of the protective film 12 preferably contains at least one element selected from Ru, Rh, Nb, Mo, Zr, Y, and Si, and more preferably Ru. Furthermore, to suppress the crystallinity of the protective film 12, the lower layer of the protective film 12 preferably contains, in addition to these elements, at least one element selected from C, N, and B. If the protective film 12 is a multilayer film, the thickness of the protective film 12 below refers to the total thickness of the multilayer film. A mixing layer may be formed between the multilayer reflective film 11 and the lower layer of the protective film 12 by mixing the components contained in the multilayer reflective film 11 and the components contained in the lower layer of the protective film 12.

[0042] The thickness of the protective film 12 is preferably 1.0 nm to 4.0 nm, more preferably 2.0 nm to 3.5 nm, and even more preferably 2.5 nm to 3.0 nm. If the thickness of the protective film 12 is 1.0 nm or more, etching resistance is good. Also, if the thickness of the protective film 12 is 4.0 nm or less, reflectivity to EUV light is good.

[0043] The absorption film 13 absorbs EUV light. The absorption film 13 is a film on which an aperture pattern 13a is to be formed. The aperture pattern 13a is not formed in the manufacturing process of the reflective mask blank 1, but is formed in the manufacturing process of the reflective mask 2. The absorption film 13 may not only absorb EUV light, but also shift the phase of the EUV light. In other words, the absorption film 13 may be a phase-shifting film. A phase-shifting film shifts the phase of the second EUV light L2 with respect to the first EUV light L1 shown in Figure 6.

[0044] The first EUV light L1 is light that passes through the aperture pattern 13a without passing through the absorption film 13, is reflected by the multilayer reflective film 11, and passes through the aperture pattern 13a again without passing through the absorption film 13. The second EUV light L2 is light that is absorbed by the absorption film 13, passes through the absorption film 13, is reflected by the multilayer reflective film 11, and is absorbed by the absorption film 13 again, while passing through the absorption film 13.

[0045] The phase difference (≧0) 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 absorption film 13 improves the contrast of the transferred image by utilizing the interference of the first EUV light L1 and the second EUV light L2. The transferred image is an image obtained by transferring the aperture pattern 13a of the absorption film 13 onto the target substrate.

[0046] In EUVL, a so-called projection effect (shadowing effect) occurs. The shadowing effect is caused by the fact that the incident angle θ of the EUV light is not 0° (for example, 6°), resulting in a region near the side wall of the aperture pattern 13a where the EUV light is blocked by the side wall, causing a positional or dimensional shift in the transferred image. To reduce the shadowing effect, it is effective to lower the height of the side wall of the aperture pattern 13a, and thus to thin the absorption film 13.

[0047] The thickness of the absorption film 13 is, for example, 60 nm or less, preferably 50 nm or less, in order to reduce the shadowing effect. The thickness of the absorption film 13 is preferably 20 nm or more, more preferably 30 nm or more, in order to ensure a phase difference between the first EUV light L1 and the second EUV light L2.

[0048] To reduce the shadowing effect while maintaining a phase difference between the first EUV light L1 and the second EUV light L2, it is effective to reduce the thickness of the absorption film 13 by decreasing the refractive index n of the absorption film 13. Furthermore, to reduce the reflectance to EUV light, it is effective to increase the extinction coefficient k of the absorption film 13. Thus, the absorption film 13 is required to have excellent optical properties.

[0049] The absorption film 13 preferably contains at least one metallic element selected from Cr, Ta, Ir, Pt, Pd, W, Au, and Ru. Since these metallic elements have relatively small refractive indices, the thickness of the absorption film 13 can be reduced while ensuring a phase difference. The absorption film 13 preferably contains a compound of the metallic element. The compound of the metallic element preferably contains at least one element selected from O, B, C, and N. By adding at least one element selected from O, B, C, and N, crystallization can be suppressed while suppressing a decrease in optical properties, and the roughness of the sides of the aperture pattern 13a can be reduced.

[0050] In this embodiment, the absorption film 13 is a single-layer film, but it may also be a multilayer film having a lower layer and an upper layer. The lower and upper layers constituting the absorption film 13 are formed on the protective film 12 in this order. The uppermost layer of the absorption film 13 is the layer furthest from the protective film 12. The uppermost layer of the absorption film 13 preferably contains at least one metal element selected from Cr, Ta, Ir, Pt, Pd, W, Au, and Ru, and more preferably contains a compound of the metal element. If the absorption film 13 is a multilayer film, the thickness of the absorption film 13 means the total film thickness of the multilayer film.

[0051] The hard mask film 14 is formed on the opposite side of the protective film 12 from the absorption film 13, and is used to form an opening pattern 13a in the absorption film 13. The hard mask film 14 enables the thinning of the resist film 16.

[0052] The hard mask film 14 preferably contains at least one metallic or metalloid element selected from Al, Hf, Y, Cr, Nb, Ti, Mo, Ta, and Si. The hard mask film 14 preferably contains a compound of the above metallic or metalloid element. The compound preferably contains at least one element selected from O, N, C, and B.

[0053] The thickness of the hard mask film 14 is preferably 2 nm to 30 nm, more preferably 2 nm to 25 nm, and even more preferably 2 nm to 10 nm.

[0054] The conductive film 15 is formed on the side opposite to the multilayer reflective film 11 with respect to the substrate 10 and is used to adsorb the reflective mask 2 to the electrostatic chuck of the exposure apparatus. The conductive film 15 preferably contains at least one metallic element selected from Cr and Ta. The conductive film 15 preferably contains a compound of the above metallic elements. The compound preferably contains at least one element selected from O, N, C and B.

[0055] In this embodiment, the conductive film 15 is a single-layer film, but it may also be a multilayer film having a lower layer and an upper layer. The lower and upper layers constituting the conductive film 15 are formed on the substrate 10 in this order. The uppermost layer of the conductive film 15 is the layer furthest from the substrate 10. The uppermost layer of the conductive film 15 preferably contains at least one metal element selected from Cr and Ta, and more preferably contains a compound of the above metal element. If the conductive film 15 is a multilayer film, the thickness of the conductive film 15 means the total thickness of the multilayer film.

[0056] The thickness of the conductive film 15 is preferably 5 nm to 500 nm, more preferably 10 nm to 450 nm, and even more preferably 20 nm to 400 nm.

[0057] Next, an optical inspection apparatus 100 according to one embodiment will be described with reference to Figure 7. The optical inspection apparatus 100 measures the dimensions of a defect in at least one of steps S103, S106, S108, and S110, for example, as shown in Figure 2. That is, the target film for defect inspection is at least one of, for example, a conductive film 15, a multilayer reflective film 11, an absorbing film 13, and a hard mask film 14. The optical inspection apparatus 100 includes, for example, a light source 110, a beam splitter 120, a first lens system 121, an objective lens 122, a second lens system 123, a stage 130, an image detector 140, and an image processing device 150. The optical inspection apparatus 100 may further include an aperture filter 161 and a spatial filter 162.

[0058] The light source 110 irradiates light onto the position where the image is to be captured. The wavelength of the light is preferably 200 nm to 800 nm. The light passes through the first lens system 121, the aperture filter 161, the beam splitter 120, and the objective lens 122 in that order, and is reflected off the surface of the target substrate held by the stage 130. The target substrate is a reflective mask blank 1 in the process of being manufactured, a first calibration substrate 201, or a second calibration substrate 301. The light reflected off the surface of the target substrate passes through the objective lens 122, the beam splitter 120, the spatial filter 162, and the second lens system 123 in that order, and reaches the image detector 140. The image detector 140 captures an image. The image detector 140 may be either an area sensor camera or a line sensor camera. The image processing device 150 is composed of, for example, a computer. The image processing device 150 measures the dimensions of the defect by processing the image captured by the image detector 140. The image processing device 150 may measure the location of the defect in addition to its dimensions.

[0059] The optical inspection device 100 is not limited to the configuration shown in Figure 7. The optical inspection device 100 can be any device that can inspect the surface of a target substrate non-destructively using light. In this embodiment, the light is shone perpendicularly onto the surface of the target substrate, reflected perpendicularly from the surface of the target substrate, and reaches the image detector 140. However, the light may also be shone obliquely onto the surface of the target substrate, reflected perpendicularly or obliquely from the surface of the target substrate, and reach the image detector 140.

[0060] Next, a calibration method for an optical inspection apparatus 100 according to one embodiment will be described with reference to Figures 8 to 11. The calibration method includes, for example, steps S301, S302, S303, S304, S311, S312, S313, and S314 shown in Figure 8. Note that the order of steps S302 and S303 may be reversed. Also, the order of steps S312 and S313 may be reversed.

[0061] In step S301, a first calibration substrate 201 is prepared. The first calibration substrate 201 is used to create a correction formula, more specifically, the first formula, which corrects the dimensions of defects in the target film that constitutes the reflective mask blank 1. The target film is, for example, at least one of the conductive film 15, multilayer reflective film 11, protective film 12, absorption film 13, and hard mask film 14.

[0062] Preferably, the surface of the target film and the surface of the first calibration substrate 201 contain one or more of the same elements. This allows the background of the defects visible in the image to be the same or similar, and the measurement conditions for the dimensions of the defects visible in the image can be standardized. Therefore, the dimensions of the defects can be corrected with high accuracy, and the measurement accuracy of the defects can be improved.

[0063] It is more preferable that the surface of the target film and the surface of the first calibration substrate 201 have the same composition. Specifically, it is more preferable that the most abundant element on the surface of the target film and the surface of the first calibration substrate 201 is the same, and that the difference (absolute value) in the content of that most abundant element is 0 at% to 3 at%. The above difference is preferably 0 at% to 1 at% and more preferably 0 at% to 0.5 at%.

[0064] It is even more preferable that the first calibration substrate 201 has the same film as the film to be inspected for defects. Specifically, for example, if the film to be inspected for defects is the absorption film 13, it is preferable that the first calibration substrate 201 comprises at least a substrate 210 and an absorption film 213, as shown in Figure 9, with the surface of the absorption film 213 exposed. The substrate 210 is configured in the same way as the substrate 10, and the absorption film 213 is configured in the same way as the absorption film 13.

[0065] When the film to be inspected for defects is a multilayer reflective film 11, the first calibration substrate 201 comprises at least a substrate 210 and a multilayer reflective film 211, and although not shown, it is preferable that the surface of the multilayer reflective film 211 is exposed. The multilayer reflective film 211 is constructed in the same manner as the multilayer reflective film 11.

[0066] When the film to be inspected for defects is the protective film 12, the first calibration substrate 201 comprises at least the substrate 210 and the protective film 212, and it is preferable that the surface of the protective film 212 is exposed, although this is not shown. The protective film 212 is configured in the same way as the protective film 12.

[0067] When the film to be inspected for defects is the hard mask film 14, the first calibration substrate 201 preferably comprises at least the substrate 210 and a hard mask film (not shown), with the surface of the hard mask film (not shown) exposed. The hard mask film (not shown) is configured in the same manner as the hard mask film 14.

[0068] When the film to be inspected for defects is the conductive film 15, the first calibration substrate 201 comprises at least the substrate 210 and the conductive film 215, and although not shown, it is preferable that the surface of the conductive film 215 is exposed. The conductive film 215 is configured in the same way as the conductive film 15.

[0069] It is particularly preferable that the first calibration substrate 201 has the same structure as the reflective mask blank 1 that is to be inspected. Therefore, the first calibration substrate 201 may have various functional films between the same film as the film to be inspected for defects and the substrate 210.

[0070] A standard defect 220 is formed on the surface of the first calibration substrate 201, having a rectangular shape in plan view and a side length greater than or equal to a threshold TH. As shown in Figure 10, it is more preferable that the plan view shape of the standard defect 220 is square. The optical inspection device 100 measures the side length L of the standard defect 220. It is preferable that multiple standard defects 220 with different lengths L are formed on the surface of the first calibration substrate 201. The plan view shape of the standard defect 220 may have minute chamfers at the corners or minute irregularities on the edges, to the extent that they do not affect the measurement of the side length L of the standard defect 220.

[0071] The side length L of the standard defect 220 is preferably 0.55 μm or more and 10 μm or less. As will be described in detail later, if the side length L of the standard defect 220 is 0.55 μm or more, the dimensions of the defect can be corrected with good accuracy, and the measurement accuracy of the dimensions of the defect can be improved. The side length L of the standard defect 220 is more preferably 0.60 μm or more, and even more preferably 1.00 μm or more.

[0072] The calibration method may include a step of forming a standard defect 220 on the first calibration substrate 201 by dry etching or wet etching. Dry etching can improve the dimensional accuracy of the standard defect 220 compared to wet etching. Dry etching is preferably a process using a focused ion beam (FIB). In this embodiment, the standard defect 220 is concave, but it may be convex. For example, the calibration method may include a step of forming the standard defect 220 on the first calibration substrate 201 by localized film deposition.

[0073] In step S302, measurement data of the side length L of the standard defect 220 is prepared, measured with an inspection device other than the optical inspection device 100. The other inspection device is at least one selected from, for example, a critical dimension-scanning electron microscope (CD-SEM), a transmission electron microscope (TEM), and an atomic force microscope (AFM).

[0074] In step S303, the length L of one side of the standard defect 220 is measured by the optical inspection device 100. The optical inspection device 100 and another inspection device measure the length L of one side of the same standard defect 220. It is preferable that multiple standard defects 220 with different lengths L are formed on the surface of a single first calibration substrate 201. The optical inspection device 100 and the other inspection device measure the length L multiple times for each standard defect 220. It is preferable to use the average value as the measurement data. This reduces errors due to disturbances.

[0075] In the image captured by the optical inspection device 100, it is preferable that the ratio (I1 / I2) of the brightness of the standard defect 220 (I1) to the brightness of the background (I2) of the standard defect 220 is 0.1 to 0.9 or 1.1 to 10. The background of the standard defect 220 is the region that does not include the standard defect 220. The background of the standard defect 220 is the region outside the standard defect 220. If the ratio (I1 / I2) is 0.1 to 0.9 or 1.1 to 10, the contour of the standard defect 220 can be detected with high accuracy, and the dimensions of the standard defect 220 can be measured with high accuracy.

[0076] In step S304, a first equation is created that represents the correlation between the measurement data from the optical inspection device 100 and the measurement data from another inspection device, with respect to the side length L of the standard defect 220. The first equation is, for example, a linear equation (y = ax + b), where x is the measurement data from the optical inspection device 100, y is the measurement data from the other inspection device, a is the correction coefficient, and b is the offset value.

[0077] To create a linear equation, it is sufficient to have two standard defects 220 with different lengths L. Preferably, the two standard defects 220 with different lengths L are formed on the surface of one first calibration substrate 201, but they may also be formed on the surfaces of separate first calibration substrates 201. From the viewpoint of improving the accuracy of the first equation, it is preferable that the number of standard defects 220 with different lengths L be three or more. While a larger number of standard defects 220 with different lengths L is preferable, from a cost viewpoint, it may be 20 or less.

[0078] Note that the first equation is not limited to a linear equation. The first equation may be an algebraic equation of degree 2 or higher. The first equation can be found, for example, by the least squares method. If using an algebraic equation of degree 2 or higher results in a higher correlation coefficient than using a linear equation, then it is preferable to use an algebraic equation of degree 2 or higher.

[0079] Formula 1 is used as a correction formula in steps S103, S106, S108, or S110, for example, as shown in Figure 2. The correction formula is used to correct the dimensions of defects on the surface of the target film that constitutes the reflective mask blank 1. In the correction formula, x is the dimension before correction and y is the dimension after correction. Formula 1 is used as the correction formula when x is greater than or equal to the threshold TH.

[0080] In step S311, a second calibration substrate 301 is prepared. The second calibration substrate 301 is used to create a correction formula, more specifically a second formula, for correcting the dimensions of defects in the target film that constitutes the reflective mask blank 1. The target film is, for example, at least one of the conductive film 15, multilayer reflective film 11, protective film 12, absorption film 13, and hard mask film 14.

[0081] Preferably, the surface of the target film and the surface of the second calibration substrate 301 contain one or more of the same elements. This allows the background of the defects visible in the image to be the same or similar, and the measurement conditions for the dimensions of the defects visible in the image can be standardized. Therefore, the dimensions of the defects can be corrected with high accuracy, and the measurement accuracy of the defects can be improved.

[0082] It is more preferable that the surface of the target film and the surface of the second calibration substrate 301 have the same composition. Specifically, it is more preferable that the most abundant element on the surface of the target film and the surface of the second calibration substrate 301 is the same, and that the difference (absolute value) in the content of that most abundant element is 0 at% to 3 at%. The above difference is preferably 0 at% to 1 at%.

[0083] It is even more preferable that the second calibration substrate 301 has the same film as the film to be inspected for defects. Specifically, for example, if the film to be inspected for defects is the absorption film 13, as shown in Figure 11, the second calibration substrate 301 preferably comprises at least a substrate 310 and an absorption film 313, with the surface of the absorption film 313 exposed. The substrate 310 is configured similarly to the substrate 10, and the absorption film 313 is configured similarly to the absorption film 13.

[0084] Furthermore, if the film to be inspected for defects is the multilayer reflective film 11, the second calibration substrate 301 comprises at least the substrate 310 and the multilayer reflective film 311, and although not shown, it is preferable that the surface of the multilayer reflective film 311 is exposed. The multilayer reflective film 311 is constructed in the same manner as the multilayer reflective film 11.

[0085] When the film to be inspected for defects is the protective film 12, the second calibration substrate 301 comprises at least the substrate 310 and the protective film 312, and it is preferable that the surface of the protective film 312 is exposed, although this is not shown. The protective film 312 is configured in the same way as the protective film 12.

[0086] When the film to be inspected for defects is the hard mask film 14, the second calibration substrate 301 preferably comprises at least the substrate 310 and a hard mask film (not shown), with the surface of the hard mask film (not shown) exposed. The hard mask film (not shown) is configured in the same manner as the hard mask film 14.

[0087] When the film to be inspected for defects is the conductive film 15, the second calibration substrate 301 comprises at least the substrate 310 and the conductive film 315, and although not shown, it is preferable that the surface of the conductive film 315 is exposed. The conductive film 315 is configured in the same way as the conductive film 15.

[0088] It is particularly preferable that the second calibration substrate 301 has the same structure as the reflective mask blank 1 that is to be inspected. Therefore, the second calibration substrate 301 may have various functional films between the same film as the film to be inspected for defects and the substrate 310.

[0089] Standard particles 320 having a particle size less than the threshold TH are attached to the surface of the second calibration substrate 301. The standard particles 320 are preferably approximately spherical. The standard particles 320 are preferably SiO2-containing. The SiO2 content in the standard particles 320 is preferably 90% to 100% by mass. It is preferable that multiple standard particles 320 with different particle sizes (diameters) are formed on the surface of one second calibration substrate 301. The threshold TH is preferably the minimum length of one side L of the standard defect 220.

[0090] The maximum particle size of the standard particle 320 is smaller than the minimum side length L of the standard defect 220. The particle size of the standard particle 320 is preferably 0.01 μm or more and less than 0.55 μm. As will be described in detail later, if the particle size of the standard particle 320 is less than 0.55 μm, the dimensions of the defect can be corrected with good accuracy, and the measurement accuracy of the defect dimensions can be improved. The particle size of the standard particle 320 is more preferably 0.50 μm or less, and even more preferably 0.40 μm or less.

[0091] In step S312, measurement data for the particle size of standard particles 320 is prepared, measured using an inspection device other than the optical inspection device 100. The other inspection device is, for example, at least one selected from a CD-SEM, a transmission electron microscope (TEM), and an atomic force microscope (AFM). The measurement data prepared in step S312 may be measured using the same inspection device as the measurement data prepared in step S302, or it may be measured using a different inspection device.

[0092] In step S313, the particle size of the standard particle 320 is measured by the optical inspection device 100. The optical inspection device 100 and another inspection device measure the particle size of the same standard particle 320. It is preferable that multiple standard particles 320 with different particle sizes are attached to the surface of a single second calibration substrate 301. The optical inspection device 100 and the other inspection device measure the particle size of each standard particle 320 multiple times. It is preferable to use the average value as the measurement data. This reduces errors due to disturbances.

[0093] In step S314, a second equation is created, which is a correlation equation between the measurement data from the optical inspection device 100 and the measurement data from another inspection device regarding the particle size of the standard particle 320. The second equation is, for example, a linear equation (y = ax + b). Here, x is the measurement data from the optical inspection device 100, y is the measurement data from the other inspection device, a is the correction coefficient, and b is the offset value.

[0094] To create a linear equation, two standard particles 320 with different particle sizes are sufficient. The two standard particles 320 with different particle sizes are preferably formed on the surface of one second calibration substrate 301, but they may also be formed on the surfaces of separate second calibration substrates 301. From the viewpoint of improving the accuracy of the second equation, it is preferable that the number of standard particles 320 with different particle sizes be three or more. While a larger number of standard particles 320 with different particle sizes is preferable, from a cost viewpoint, it may be 20 or less.

[0095] Note that the second equation is not limited to a linear equation. The second equation may be an algebraic equation of degree 2 or higher. The second equation can be found, for example, by the least squares method. If using an algebraic equation of degree 2 or higher results in a higher correlation coefficient than using a linear equation, then it is preferable to use an algebraic equation of degree 2 or higher.

[0096] The second formula is used as a correction formula in steps S103, S106, S108, or S110, for example, as shown in Figure 2. The correction formula is used to correct the dimensions of defects on the surface of the target film that constitutes the reflective mask blank 1. In the correction formula, x is the dimension before correction and y is the dimension after correction. If x is less than the threshold TH, the second formula is used as the correction formula.

[0097] According to this embodiment, the first formula is created using standard defects 220 whose side length L is greater than or equal to the threshold TH, and the second formula is created using standard particles 320 whose particle size is less than the threshold TH. As will be described in detail in the Examples section, by using the first or second formula and calibrating the measurement data of the optical inspection device, the dimensions of actual defects present on the surface of the target film can be measured with high accuracy.

[0098] When the film to be inspected for defects is an absorption film 13, it is preferable that the surface of the absorption film 13, the surface of the first calibration substrate 201, and the surface of the second calibration substrate 301 each contain one or more of the same elements selected from Cr, Ta, Ir, Pt, Pd, W, Au, and Ru.

[0099] When the film to be inspected for defects is a conductive film 15, it is preferable that the surface of the conductive film 15, the surface of the first calibration substrate 201, and the surface of the second calibration substrate 301 each contain one or more of the same element selected from Cr and Ta.

[0100] When the film to be inspected for defects is a multilayer reflective film 11, it is preferable that the surface of the multilayer reflective film 11, the surface of the first calibration substrate 201, and the surface of the second calibration substrate 301 each contain one or more of the same element selected from Mo and Si.

[0101] When the film to be inspected for defects is the protective film 12, it is preferable that the surface of the protective film 12, the surface of the first calibration substrate 201, and the surface of the second calibration substrate 301 each contain one or more of the same elements selected from Ru, Rh, and Si.

[0102] When the film to be inspected for defects is a hard mask film 14, it is preferable that the surface of the hard mask film 14, the surface of the first calibration substrate 201, and the surface of the second calibration substrate 301 each contain one or more of the same elements selected from Al, Hf, Y, Cr, Nb, Ti, Mo, Ta, and Si.

[0103] [Example 1] In Example 1, a first calibration substrate was prepared by depositing a conductive film (Cr-based film) on an SiO2-TiO2 glass substrate, and then forming square standard defects on the surface of the conductive film using a focused ion beam (FIB). The side length L of the standard defects was 0.6 μm to 3.1 μm. The depth of the standard defects was 0.05 μm or less. In addition, a second calibration substrate was prepared by depositing a conductive film (Cr-based film) on an SiO2-TiO2 glass substrate, and then attaching standard particles (SiO2-based) to the surface of the conductive film. The particle size of the standard particles was 0.08 μm to 0.5 μm.

[0104] In Example 1, the length L of one side of the same standard defect was measured using the optical inspection device 100 shown in Figure 7 and a CD-SEM. The particle size of the same standard particle was also measured using the optical inspection device 100 shown in Figure 7 and a TEM. The measurement results are shown in Figure 12. As shown in Figure 12, the first correlation equation between the measurement data from the uncalibrated optical inspection device and the measurement data from the CD-SEM was (y=0.9825x+0.3380). The second correlation equation between the measurement data from the uncalibrated optical inspection device and the measurement data from the TEM was (y=0.9820x+0.0109).

[0105] Figure 13 shows the sizes of standard defects or standard particles measured using an optical inspection device calibrated with either formula 1 or 2 (as shown in Figure 12) and a CD-SEM or TEM. Figure 13 was created using the same data as Figure 12, except that the measurement data from the optical inspection device was corrected using either formula 1 or 2. As shown in Figure 13, the measurement data from the calibrated optical inspection device and the measurement data from the CD-SEM or TEM were in close agreement. In other words, the measurement data from the two different devices were in close agreement.

[0106] In Example 1, a reflective mask blank was prepared by depositing a conductive film (Cr-based film) on an SiO2-TiO2 glass substrate. The size of actual defects (maximum fillet diameter) on the surface of the conductive film was measured using an optical inspection device calibrated by either formula 1 or 2 shown in Figure 12, and an AFM. The measurement results are shown in Figure 14. As shown in Figure 14, the measurement data from the calibrated optical inspection device and the measurement data from the AFM were in near agreement. In other words, the measurement data from the two different devices were in near agreement.

[0107] [Comparative Example 1] In Comparative Example 1, only a first calibration substrate was prepared, and a second calibration substrate was not prepared. In Comparative Example 1, as the first calibration substrate, a conductive film (Cr-based film) was deposited on an SiO2-TiO2 glass substrate, and then square standard defects were formed on the surface of the conductive film using a focused ion beam (FIB). The length L of one side of the standard defects was 0.2 μm to 3.1 μm. The depth of the standard defects was 0.05 μm or less.

[0108] In Comparative Example 1, the length L of one side of the same standard defect was measured using the optical inspection device 100 shown in Figure 7 and a CD-SEM. The measurement results are shown in Figure 12. As shown in Figure 12, the first equation, which is the correlation equation between the measurement data of the uncalibrated optical inspection device and the measurement data of the CD-SEM, was (y=0.9782x-0.3269).

[0109] Figure 13 shows the standard defect sizes measured using an optical inspection device calibrated with the first formula shown in Figure 12, and a CD-SEM. Figure 13 was created using the same data as in Figure 12, except that the measurement data from the optical inspection device was corrected with the first formula. As shown in Figure 13, the measurement data from the calibrated optical inspection device and the measurement data from the CD-SEM were in close agreement. In other words, the measurement data from the two different devices were in close agreement.

[0110] In Comparative Example 1, a reflective mask blank in the process of being fabricated was prepared by depositing a conductive film (Cr-based film) on an SiO2-TiO2 glass substrate. The size of actual defects (maximum fillet diameter) present on the surface of the conductive film was measured using an optical inspection device calibrated by Equation 1 shown in Figure 12 and an AFM. The measurement results are shown in Figure 14. As shown in Figure 14, the measurement data from the calibrated optical inspection device and the measurement data from the AFM were in almost agreement. In other words, the measurement data from the two different devices were in almost agreement. However, the coefficient of determination R 2 As is clear from this, Comparative Example 1 had lower accuracy than Example 1.

[0111] [Comparative Example 2] In Comparative Example 2, only the second calibration substrate was prepared, and the first calibration substrate was not prepared. In Comparative Example 2, the second calibration substrate was prepared by depositing a conductive film (Cr-based film) on an SiO2-TiO2 glass substrate, and attaching standard particles (SiO2-based) to the surface of the conductive film. The particle size of the standard particles was 0.08 μm to 1.0 μm.

[0112] In Comparative Example 2, the particle size of the same standard particles was measured using the optical inspection device 100 shown in Figure 7 and a TEM. The measurement results are shown in Figure 12. As shown in Figure 12, the second equation, which is the correlation equation between the measurement data of the uncalibrated optical inspection device and the measurement data of the TEM, was (y = 1.0097x - 0.0018).

[0113] Figure 13 shows the sizes of standard defects or standard particles measured using an optical inspection device calibrated with the second equation shown in Figure 12, and a TEM. Figure 13 was created using the same data as in Figure 12, except that the measurement data from the optical inspection device was corrected with the second equation. As shown in Figure 13, the measurement data from the calibrated optical inspection device and the measurement data from the TEM were in close agreement. In other words, the measurement data from the two different devices were in close agreement.

[0114] In Comparative Example 2, a reflective mask blank was prepared by depositing a conductive film (Cr-based film) on an SiO2-TiO2 glass substrate. The size of actual defects (maximum fillet diameter) on the surface of the conductive film was measured using an optical inspection device calibrated by the second equation shown in Figure 12, and an AFM. The measurement results are shown in Figure 14. As shown in Figure 14, there was a large discrepancy between the measurement data from the calibrated optical inspection device and the measurement data from the AFM.

[0115] Figure 15 shows the same data as in Figure 14, but in a different format. Figure 15 shows the ratio of measurement data from an optical inspection device calibrated using standard defects to measurement data from an AFM, and the ratio of measurement data from an optical inspection device calibrated using standard particles to measurement data from an AFM. The closer these ratios are to 1, the better the measurement accuracy of the optical inspection device.

[0116] Figure 15 shows that standard defects are suitable for calibrating relatively large defects, while standard particles are suitable for calibrating relatively small defects. According to this disclosure, the first equation is created using standard defects 220 whose side length L is greater than or equal to the threshold TH, and the second equation is created using standard particles 320 whose particle size is less than the threshold TH. Therefore, the dimensions of actual defects can be measured with high accuracy.

[0117] Table 1 shows the experimental conditions and results for Example 1, Comparative Example 1, and Comparative Example 2.

[0118] [Table 1]

[0119] The calibration method for an optical inspection apparatus and the manufacturing method for a reflective mask blank described above have been explained, but this disclosure is not limited to the embodiments described above. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These also naturally fall within the technical scope of this disclosure. [Explanation of symbols]

[0120] 1 Reflective Mask Blank 100 Optical inspection device 201 1st calibration board 220 Standard Defects 301 2nd calibration board 320 standard particles

Claims

1. A calibration method for an optical inspection device that measures the dimensions of defects on the surface of a target film by capturing an image of the surface of the target film constituting a reflective mask blank, Prepare a first calibration substrate having a rectangular shape in plan view and standard defects formed on its surface where the length of one side is greater than or equal to a threshold, Prepare a second calibration substrate on which standard particles with a particle size less than the threshold are attached to the surface, Prepare measurement data of the length of one side of the standard defect and the particle size of the standard particle, measured using an inspection device separate from the optical inspection device. The length of one side of the standard defect and the particle size of the standard particle are measured using the optical inspection device, To create a first equation which is a correlation equation between the measurement data of the optical inspection device and the measurement data of the other inspection device regarding the length of one side of the standard defect, To create a second equation which is a correlation equation between the measurement data of the optical inspection device and the measurement data of the other inspection device regarding the particle size of the standard particles, A calibration method for an optical inspection device having [a specific characteristic].

2. The calibration method for an optical inspection apparatus according to claim 1, wherein the length of one side of the standard defect is 0.55 μm or more and 10 μm or less, and the particle size of the standard particle is 0.01 μm or more and less than 0.55 μm.

3. The calibration method for an optical inspection apparatus according to claim 1, wherein three or more of the standard defects, each having a rectangular shape in plan view and with a different side length, are formed on the surface of the first calibration substrate.

4. The calibration method for an optical inspection apparatus according to claim 1, wherein three or more of the standard particles with different particle sizes are attached to the surface of the second calibration substrate.

5. The aforementioned standard particle is SiO ２ A calibration method for an optical inspection apparatus according to claim 1, including the following:

6. A calibration method for an optical inspection apparatus according to claim 1, comprising forming the standard defects on the first calibration substrate by dry etching.

7. A calibration method for an optical inspection apparatus according to claim 1, comprising forming the standard defects on the first calibration substrate with a focused ion beam (FIB).

8. The calibration method for an optical inspection apparatus according to claim 1, wherein the other inspection apparatus is at least one selected from a critical dimension-scanning electron microscope (CD-SEM), a transmission electron microscope (TEM), and an atomic force microscope (AFM).

9. The calibration method for an optical inspection apparatus according to claim 1, wherein the first and second equations are linear equations.

10. The optical inspection apparatus has a light source that illuminates the position where the image is captured, The calibration method for an optical inspection apparatus according to claim 1, wherein the wavelength of the light is 200 nm to 800 nm.

11. A calibration method for an optical inspection apparatus according to claim 1, wherein in the image, the ratio (I1 / I2) of the brightness of the standard defect (I1) to the brightness of the background of the standard defect (I2) is 0.1 to 0.9 or 1.1 to 10.

12. A method for manufacturing a reflective mask blank having at least a substrate, a multilayer reflective film, a protective film, and an absorption film in this order, Calibrating the optical inspection device using the calibration method described in any one of claims 1 to 11, Forming the multilayer reflective film, the protective film, and the absorbing film, The dimensions of the surface defects of the absorption film are measured using the calibrated optical inspection device, It has, A method for manufacturing a reflective mask blank, wherein the surface of the absorption film, the surface of the first calibration substrate, and the surface of the second calibration substrate each contain one or more of the same element selected from Cr, Ta, Ir, Pt, Pd, W, Au, and Ru.

13. A method for manufacturing a reflective mask blank having at least a conductive film, a substrate, a multilayer reflective film, a protective film, and an absorption film in this order, Calibrating the optical inspection device using the calibration method described in any one of claims 1 to 11, Forming the conductive film, the multilayer reflective film, the protective film, and the absorbing film, The dimensions of the surface defects of the conductive film are measured using the calibrated optical inspection device, It has, A method for manufacturing a reflective mask blank, wherein the surface of the conductive film, the surface of the first calibration substrate, and the surface of the second calibration substrate each contain one or more of the same element selected from Cr and Ta.

14. A method for manufacturing a reflective mask blank having at least a substrate, a multilayer reflective film, a protective film, and an absorption film in this order, Calibrating the optical inspection device using the calibration method described in any one of claims 1 to 11, Forming the multilayer reflective film, the protective film, and the absorbing film, The dimensions of the surface defects of the multilayer reflective film are measured using the calibrated optical inspection device, It has, A method for manufacturing a reflective mask blank, wherein the surface of the multilayer reflective film, the surface of the first calibration substrate, and the surface of the second calibration substrate each contain one or more of the same element selected from Mo and Si.

15. A method for manufacturing a reflective mask blank having at least a substrate, a multilayer reflective film, a protective film, and an absorption film in this order, Calibrating the optical inspection device using the calibration method described in any one of claims 1 to 11, Forming the multilayer reflective film, the protective film, and the absorbing film, The dimensions of the surface defects of the protective film are measured using the calibrated optical inspection device, It has, A method for manufacturing a reflective mask blank, wherein the surface of the protective film, the surface of the first calibration substrate, and the surface of the second calibration substrate each contain one or more of the same element selected from Ru, Rh, and Si.

16. A method for manufacturing a reflective mask blank having at least a substrate, a multilayer reflective film, a protective film, an absorption film, and a hard mask film in this order, Calibrating the optical inspection device using the calibration method described in any one of claims 1 to 11, Forming the multilayer reflective film, the protective film, the absorption film, and the hard mask film, The dimensions of the surface defects of the hard mask film are measured using the calibrated optical inspection device, It has, A method for manufacturing a reflective mask blank, wherein the surface of the hard mask film, the surface of the first calibration substrate, and the surface of the second calibration substrate each contain one or more of the same element selected from Al, Hf, Y, Cr, Nb, Ti, Mo, Ta, and Si.

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