Reflective mask blank, method for manufacturing the same, and method for inspecting reflective mask blank-associated substrate

Abstract

To provide a reflective mask blank capable of surely detecting a reference mark without erroneously detecting a defect as the reference mark, and to provide a method for manufacturing the same and a method for inspecting a reflective mask blank-related substrate.SOLUTION: A reflective mask blank comprising at least a substrate, a multilayer reflective film provided on the substrate and configured to reflect exposure light, and an absorber film provided on the multilayer reflective film and configured to absorb the exposure light, the reflective mask blank comprising a fiducial mark serving as a reference position for a defect position and a fiducial mark formation region for searching for the fiducial mark, the fiducial mark and the fiducial mark formation region being formed on a surface of the reflective mask blank on the same side as the multilayer reflective film, wherein the fiducial mark formation region is formed at a height different from that of a periphery of the fiducial mark formation region, and the fiducial mark is formed so that at least a part thereof is included in the fiducial mark formation region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a reflective mask blank used in the manufacture of semiconductor devices, a method for manufacturing the same, and a method for inspecting a substrate related to the reflective mask blank. [Background technology]

[0002] In the manufacturing process of semiconductor devices (semiconductor devices), photolithography technology is repeatedly used, in which exposure light is irradiated onto a transfer mask and the circuit pattern formed on the mask is transferred onto a semiconductor substrate (semiconductor wafer) via a reduced projection optical system. Conventionally, the wavelength of the exposure light has mainly been 193 nm, using argon fluoride (ArF) excimer laser light, and a process called multi-patterning, which combines exposure and processing processes multiple times, has been used to ultimately form patterns with dimensions smaller than the exposure wavelength.

[0003] However, as device patterns continue to become finer, the formation of even finer patterns is becoming necessary. Therefore, EUV lithography technology, which uses extreme ultraviolet (EUV) light, which has an even shorter wavelength than ArF excimer laser light, as exposure light, has begun to be used. EUV light is light with a wavelength of approximately 0.2 to 100 nm, and more specifically, light with a wavelength of approximately 13.5 nm. This EUV light has extremely low transmittance through materials, making conventional transmission-type projection optical systems and masks incompatible, so reflective optical elements are used. Reflective masks have also been proposed for pattern transfer.

[0004] A reflective mask has a multilayer reflective film that reflects EUV light formed on a substrate, and an absorber film that absorbs EUV light formed in a pattern on the multilayer reflective film (hereinafter referred to as an EUV reflective mask). On the other hand, the state before the absorber film is patterned (including the state where a resist film is formed) is called a reflective mask blank, and this is used as the material for reflective masks (hereinafter referred to as an EUV reflective mask blank).

[0005] If a concave or convex defect exists on the surface or in the film of an EUV reflective mask, the reflectivity of EUV light at the defect location decreases, preventing the desired transfer pattern from being obtained during wafer exposure. In particular, if a defect exists in the multilayer reflective film or between the multilayer reflective film and the substrate, even if the defect is only a few nanometers high, the periodic structure of the multilayer reflective film collapses around the defect, causing a phase shift in the reflected EUV light, resulting in a localized decrease in reflectivity and significantly affecting the pattern shape transferred to the wafer. Such defects are called phase defects. Because phase defects are located in or under the film, they are difficult to repair. On the other hand, defects on the multilayer reflective film or absorber film attenuate the intensity of the reflected EUV light, and are therefore called amplitude defects in contrast to phase defects.

[0006] To prevent the influence of phase defects and amplitude defects on the transferred pattern, Defect Mitigation (DM) technology has been proposed, which conceals phase defects with an absorber pattern. DM technology is realized by identifying defect positions in a coordinate system defined by fiducial marks fabricated on an EUV reflective mask blank through defect inspection, measuring the fiducial mark positions in the mask manufacturing process, and performing appropriate coordinate conversion to obtain defect position information on the EUV reflective mask blank in the coordinate system used in mask manufacturing. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2017-227936 Summary of the Invention [Problem to be solved by the invention]

[0008] Patent Document 1 describes forming a fiducial mark that is symmetrical in shape and has a portion with a width of 200 nm to 10 μm in the scanning direction of an electron beam or defect inspection light. One possible method for detecting a fiducial mark is to use a defect inspection machine to search the area around the design coordinates of the fiducial mark and identify an object within a certain area as a fiducial mark. However, the size of the fiducial mark proposed in Patent Document 1 is approximately the same as a defect that may exist on a reflective mask blank. Therefore, if such a defect exists around the fiducial mark, the defect may be erroneously detected as a fiducial mark. In such a case, the defect position in the coordinate system defined by the fiducial mark cannot be properly obtained, making it impossible to apply DM technology to the reflective mask manufacturing process.

[0009] The present invention has been made to solve the above-mentioned problems, and aims to provide a reflective mask blank that can reliably detect a reference mark without erroneously detecting a defect as a reference mark, a method for manufacturing the same, and a method for inspecting a reflective mask blank-related substrate. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides: A substrate; a multilayer reflective film provided on the substrate and reflecting exposure light; an absorber film provided on the multilayer reflective film and absorbing the exposure light; A reflective mask blank comprising at least a reference mark serving as a reference position for a defect position, formed on a surface of the reflective mask blank on the same side as the multilayer reflective film, and a reference mark forming area for searching for the reference mark, the reference mark formation area is formed at a height different from that of the surrounding area of ​​the reference mark formation area, The present invention provides a reflective mask blank, wherein the fiducial mark is formed so that at least a part of the fiducial mark is included in the fiducial mark forming region.

[0011] With the reflective mask blank of the present invention, when a defect inspection machine searches for a fiducial mark, it is possible to distinguish between a defect and a fiducial mark based on the presence or absence of a fiducial mark forming area. This makes it possible to provide a reflective mask blank that can reliably detect a fiducial mark without erroneously detecting a defect as a fiducial mark. Therefore, it is possible to appropriately identify the defect position from the detected fiducial mark.

[0012] In order to achieve the above object, the present invention provides: A substrate; a multilayer reflective film provided on the substrate and reflecting exposure light; an absorber film provided on the multilayer reflective film and absorbing the exposure light; A reflective mask blank comprising at least a reference mark serving as a reference position for a defect position, formed on a surface of the reflective mask blank on the same side as the multilayer reflective film, and a reference mark forming area for searching for the reference mark, the reference mark formation region is formed at a height different from that of the main pattern formation region, The present invention provides a reflective mask blank, wherein the fiducial mark is formed so that at least a part of the fiducial mark is included in the fiducial mark forming region.

[0013] With the reflective mask blank of the present invention, when a defect inspection machine searches for a fiducial mark, it is possible to distinguish between a defect and a fiducial mark based on the presence or absence of a fiducial mark forming area. This makes it possible to provide a reflective mask blank that can reliably detect a fiducial mark without erroneously detecting a defect as a fiducial mark. Therefore, it is possible to appropriately identify the defect position from the detected fiducial mark. The main pattern forming region is a region where a mask pattern is formed.

[0014] In this case, the absolute value of the difference in height between the reference mark formation region and the main pattern formation region can be 1 nm or more.

[0015] With this, when a defect inspection machine searches for the fiducial mark, it is possible to more reliably create a contrast with the surrounding area (main pattern forming area), thereby making it easier to determine whether or not the fiducial mark forming area exists.

[0016] The fiducial mark formation area may be smaller than the field of view of an optical image acquired by a defect inspection machine used when searching for the fiducial mark.

[0017] With this arrangement, when a defect inspection machine searches for a fiducial mark, the boundary of the fiducial mark formation region can be more reliably displayed within the field of view of the optical image, making it easier to determine whether or not the boundary is present.

[0018] The present invention also provides forming a multilayer reflective film on a substrate that reflects exposure light; forming an absorber film on the multilayer reflective film to absorb the exposure light; A method for manufacturing a reflective mask blank having at least forming a reference mark serving as a reference position for a defect position and a reference mark forming area for searching for the reference mark on the same surface of the reflective mask blank as the multilayer reflective film, In the step of forming the reference mark and the reference mark forming area, forming the reference mark forming region so as to have a height different from that of the surrounding area of ​​the reference mark forming region; The present invention provides a method for manufacturing a reflective mask blank, characterized in that the fiducial mark is formed so that at least a part of the fiducial mark is included in the fiducial mark forming region.

[0019] The method for manufacturing a reflective mask blank of the present invention can provide a reflective mask blank that can reliably detect fiducial marks without erroneously detecting defects as fiducial marks. The reason for preventing such erroneous detection is that, when a defect inspection machine searches for a fiducial mark, it is possible to distinguish between a defect and a fiducial mark based on the presence or absence of a fiducial mark formation region formed in the reflective mask blank. Furthermore, the position of the defect can be appropriately identified from the detected fiducial mark.

[0020] The present invention also provides forming a multilayer reflective film on a substrate that reflects exposure light; forming an absorber film on the multilayer reflective film to absorb the exposure light; A method for manufacturing a reflective mask blank having at least forming a reference mark serving as a reference position for a defect position and a reference mark forming area for searching for the reference mark on the same surface of the reflective mask blank as the multilayer reflective film, In the step of forming the reference mark and the reference mark forming area, forming the reference mark forming region to have a height different from that of the main pattern forming region; The present invention provides a method for manufacturing a reflective mask blank, characterized in that the fiducial mark is formed so that at least a part of the fiducial mark is included in the fiducial mark forming region.

[0021] The method for manufacturing a reflective mask blank of the present invention can provide a reflective mask blank that can reliably detect fiducial marks without erroneously detecting defects as fiducial marks. The reason for preventing such erroneous detection is that, when a defect inspection machine searches for a fiducial mark, it is possible to distinguish between a defect and a fiducial mark based on the presence or absence of a fiducial mark formation region formed in the reflective mask blank. Furthermore, the position of the defect can be appropriately identified from the detected fiducial mark.

[0022] At this time, in the step of forming the reference mark and the reference mark forming area, The reference mark forming region can be formed so that the absolute value of the difference in height between the reference mark forming region and the main pattern forming region is 1 nm or more.

[0023] This makes it possible to more reliably provide contrast with the surrounding area (main pattern forming area) when searching for the fiducial mark using a defect inspection machine, thereby making it easier to determine whether or not the fiducial mark forming area exists.

[0024] In addition, in the step of forming the reference mark and the reference mark forming area, The fiducial mark formation area can be formed to be smaller than the field of view of an optical image acquired by a defect inspection machine used when searching for the fiducial mark.

[0025] In this way, when a defect inspection machine searches for a fiducial mark, the boundary of the fiducial mark formation region can be more reliably displayed within the field of view of the optical image, making it easier to determine whether or not the boundary exists.

[0026] Furthermore, when forming the fiducial mark and the fiducial mark forming region, they can be formed by FIB processing.

[0027] In this way, the fiducial marks and the fiducial mark forming areas can be formed with high precision.

[0028] The present invention also provides A substrate; a multilayer reflective film provided on the substrate and reflecting exposure light; an absorber film provided on the multilayer reflective film and absorbing the exposure light; A method for inspecting a reflective mask blank-related substrate selected from a reflective mask blank and its manufacturing intermediate, comprising: an inspection target preparation step of preparing a reflective mask blank-related substrate to be inspected; an inspection process including searching for a reference mark formed on the prepared reflective mask blank-related substrate and specifying a defect position based on the reference mark; In the inspection object preparation step, the reflective mask blank-related substrate to be inspected comprises the reference mark, which serves as a reference position for a defect position, and a reference mark forming area for searching for the reference mark, both formed on a surface of the reflective mask blank on the same side as the multilayer reflective film, the reference mark formation area is formed at a height different from that of the surrounding area of ​​the reference mark formation area, preparing the reference mark formed so that at least a part of the reference mark is included in the reference mark forming area; In the inspection step, The present invention provides a method for inspecting a reflective mask blank-related substrate, characterized in that when searching for the reference mark, the reference mark and the defect are distinguished based on the presence or absence of the reference mark formation area.

[0029] The inspection method for reflective mask blank-related substrates of the present invention can reliably detect reference marks during the inspection process without erroneously detecting defects as reference marks, and can appropriately identify the defect position from the detected reference marks.

[0030] The present invention also provides A substrate; a multilayer reflective film provided on the substrate and reflecting exposure light; an absorber film provided on the multilayer reflective film and absorbing the exposure light; A method for inspecting a reflective mask blank-related substrate selected from a reflective mask blank and its manufacturing intermediate, comprising: an inspection target preparation step of preparing a reflective mask blank-related substrate to be inspected; an inspection process including searching for a reference mark formed on the prepared reflective mask blank-related substrate and specifying a defect position based on the reference mark; In the inspection object preparation step, the reflective mask blank-related substrate to be inspected comprises the reference mark, which serves as a reference position for a defect position, and a reference mark forming area for searching for the reference mark, both formed on a surface of the reflective mask blank on the same side as the multilayer reflective film, the reference mark formation region is formed at a height different from that of the main pattern formation region, preparing the reference mark formed so that at least a part of the reference mark is included in the reference mark forming area; In the inspection step, The present invention provides a method for inspecting a reflective mask blank-related substrate, characterized in that when searching for the reference mark, the reference mark and the defect are distinguished based on the presence or absence of the reference mark formation area.

[0031] The inspection method for reflective mask blank-related substrates of the present invention can reliably detect reference marks during the inspection process without erroneously detecting defects as reference marks, and can appropriately identify the defect position from the detected reference marks. [Effects of the Invention]

[0032] The reflective mask blank and its manufacturing method, as well as the inspection method for reflective mask blank-related substrates of the present invention, make it possible to distinguish between a reference mark and a defect based on the presence or absence of a reference mark forming area when searching for the reference mark, even if the defect and the reference mark that may be present on the reflective mask blank are of similar size, and it is possible to provide a reflective mask blank that can reliably detect the reference mark without erroneously detecting the defect as a reference mark, and ultimately can identify the defect position appropriately and reliably. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is an example of a cross-sectional schematic diagram of a reflective mask blank of the present invention in which a fiducial mark formation region is recessed. [Figure 2] FIG. 2 is an example of a cross-sectional schematic diagram of a reflective mask blank of the present invention in which the fiducial mark formation region is convex. [Figure 3] FIG. 2 is a plan view schematically illustrating an example of the arrangement of fiducial marks and fiducial mark forming regions on a reflective mask blank according to the present invention. [Figure 4] 3A and 3B are schematic plan views showing examples of the positional relationship between a reference mark and a reference mark forming area in the present invention. [Figure 5] 1 is a schematic diagram illustrating an example of a planar shape of a reference mark according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0034] As described above, there has been a demand for the establishment of a technology that can reliably detect fiducial marks on reflective mask blanks without erroneously detecting defects as fiducial marks when searching for the fiducial marks.

[0035] The present inventors have therefore conducted extensive research into reflective mask blanks and have found that a reflective mask blank (having at least a multilayer reflective film and an absorber film on a substrate) which is provided with a fiducial mark serving as a reference position for a defect position, formed on the same surface as the multilayer reflective film, and a fiducial mark forming area for searching for the fiducial mark, wherein the fiducial mark forming area is formed at a height different from that of the surrounding area of ​​the fiducial mark forming area, and the fiducial mark is formed so that at least a portion of the fiducial mark is included in the fiducial mark forming area, can be used to distinguish between a defect and a fiducial mark based on the presence or absence of the fiducial mark forming area in a fiducial mark search using a defect inspection machine or the like, thereby enabling a reflective mask blank to be obtained which is capable of reliably detecting the fiducial mark without erroneously detecting a defect as a fiducial mark, and has thus completed the present invention.

[0036] Furthermore, the present inventors have found that the manufacturing method also includes a step of forming a multilayer reflective film and an absorber film, and a step of forming a reference mark and a reference mark forming region on the same surface of the reflective mask blank as the multilayer reflective film, and that by forming the reference mark forming region in this step to have a height different from that of the surrounding area of ​​the reference mark forming region and by forming the reference mark so that at least a portion of the reference mark is included in the reference mark forming region, it is possible to manufacture a reflective mask blank with a reference mark, which can reduce the risk of erroneously detecting defects present around the reference mark as a reference mark, and have completed the present invention.

[0037] Furthermore, in a method for inspecting a reflective mask blank-related substrate (selected from the above-mentioned reflective mask blank and its manufacturing intermediates), in an inspection object preparation step, the reflective mask blank-related substrate to be inspected is provided with a fiducial mark serving as a reference position for a defect position, formed on the same surface as the multilayer reflective film of the reflective mask blank, and a fiducial mark forming area for searching for the fiducial mark, the fiducial mark forming area being formed at a height different from that of the surrounding area, and the fiducial mark being formed so that at least a part of the fiducial mark is included in the fiducial mark forming area, and in the inspection step, when searching for the fiducial mark, it has been found that by distinguishing between the fiducial mark and a defect depending on the presence or absence of the fiducial mark forming area, the fiducial mark can be reliably detected without erroneously detecting a defect as a fiducial mark, and the present invention has been completed.

[0038] Furthermore, the present inventors have found that, as one embodiment of the reflective mask blank of the present invention, a reflective mask blank (having at least a multilayer reflective film and an absorber film on a substrate) is provided with a fiducial mark serving as a reference position for a defect position, formed on the same surface as the multilayer reflective film, and a fiducial mark forming area for searching for the fiducial mark, wherein the fiducial mark forming area is formed at a height different from that of the main pattern forming area, and the fiducial mark is formed so that at least a portion of the fiducial mark is included in the fiducial mark forming area, and thus a reflective mask blank can be obtained that can distinguish between a defect and a fiducial mark based on the presence or absence of the fiducial mark forming area in a fiducial mark search using a defect inspection machine or the like, and can reliably detect the fiducial mark without erroneously detecting a defect as a fiducial mark, thereby completing the present invention.

[0039] Furthermore, the present inventors have found that the manufacturing method also includes a step of forming a multilayer reflective film and an absorber film, as well as a step of forming a reference mark and a reference mark forming region on the same surface of the reflective mask blank as the multilayer reflective film, and that by forming the reference mark forming region in this step to have a height different from that of the main pattern forming region and by forming the reference mark so that at least a portion of the reference mark is included in the reference mark forming region, it is possible to manufacture a reflective mask blank with a reference mark, which can reduce the risk of erroneously detecting defects present around the reference mark as a reference mark, and have completed the present invention.

[0040] Furthermore, in a method for inspecting a reflective mask blank-related substrate (selected from the above-mentioned reflective mask blank and its manufacturing intermediates), in an inspection object preparation step, the reflective mask blank-related substrate to be inspected is provided with a fiducial mark serving as a reference position for a defect position, formed on the same surface as the multilayer reflective film of the reflective mask blank, and a fiducial mark forming area for searching for the fiducial mark, the fiducial mark forming area being formed at a height different from that of the main pattern forming area, and the fiducial mark is formed so that at least a part of the fiducial mark is included in the fiducial mark forming area, and in the inspection step, by distinguishing between the fiducial mark and a defect depending on the presence or absence of the fiducial mark forming area, it has been found that the fiducial mark can be reliably detected without erroneously detecting a defect as a fiducial mark, and the present invention has been completed.

[0041] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. First, the reflective mask blank of the present invention will be described. FIGS. 1 and 2 show an example of a schematic diagram of a reflective mask blank according to the present invention. In FIG. 1, the fiducial mark formation region is concave, while in FIG. 2, the fiducial mark formation region is convex. An example for EUV will be described, but the present invention is not limited thereto. In FIGS. 1 and 2, the reflective mask blank 1 first includes a substrate 10, a multilayer reflective film 20 formed on the surface of the substrate 10 to reflect exposure light, an absorber film 30 formed on the multilayer reflective film 20 to absorb exposure light, a fiducial mark 40 (which serves as a reference position for defect positions) formed on the surface of the reflective mask blank, and a fiducial mark formation region 41 (which includes at least a portion of the fiducial mark 40) formed around the fiducial mark 40.

[0042] Here, fiducial mark formation region 41 is formed at a height different from the periphery of fiducial mark formation region 41. There are no particular limitations on the "periphery of fiducial mark formation region 41," but one example is main pattern formation region 50. In the following explanations of the reflective mask blank of the present invention, its manufacturing method, and the inspection method for reflective mask blank-related substrates, the "periphery of fiducial mark formation region 41" will be described taking the case where the "periphery of fiducial mark formation region 41" is main pattern formation region 50 as an example; however, the same can be said about the structure, procedure, effect, etc. even if the "periphery of fiducial mark formation region 41" is a region other than main pattern formation region 50.

[0043] The fiducial mark formation region 41 is formed at a different height than the main pattern formation region 50, which creates a contrast with the inspection light between the fiducial mark formation region 41 and its surroundings (main pattern formation region 50). For example, in Fig. 1, the fiducial mark formation region 41 is an area lower than the main pattern formation region 50, and in Fig. 2, the fiducial mark formation region 41 is an area higher than the main pattern formation region 50. In Fig. 2, a deposition layer 60 is formed between the multilayer reflective film 20 and the absorber film 30 so that the fiducial mark formation region 41 has a convex shape.

[0044] Although not shown in FIGS. 1 and 2 , a protective film may be formed between the multilayer reflective film 20 and the absorber film 30 to prevent damage to the multilayer reflective film 20 when a pattern is formed on the absorber film 30. Also, a hard mask film may be provided on the absorber film 30 to function as an etching mask when dry etching the absorber film 30. Also, a conductive film that functions as an antistatic layer during electrostatic chucking may be provided on the back side of the substrate 10. Other functional layers may also be provided.

[0045] Below, each part will be explained using the embodiment in FIG. 1 as an example, but unless otherwise specified, the same applies to the embodiment in FIG. 2. The substrate 10 preferably has low thermal expansion characteristics for use in EUV light exposure, and has a thermal expansion coefficient of, for example, ±2×10 -8 / °C, preferably ±5×10 -9 / °C. The substrate 10 preferably has a sufficiently flat surface, and the surface roughness of the main surface of the substrate 10 is preferably 0.5 nm or less, and more preferably 0.2 nm or less, in terms of RMS value. Such a surface roughness can be achieved by polishing the substrate 10, for example.

[0046] The multilayer reflective film 20 is generally a multilayer film in which low-refractive index materials and high-refractive index materials are alternately stacked. In this example, the multilayer reflective film 20 is a film that reflects EUV light, which is exposure light. In the embodiment shown in FIG. 1 , the multilayer reflective film 20 has a stacked portion 25 composed of multiple layers in which layers 21 having a relatively high refractive index for EUV light and layers 22 having a relatively low refractive index for EUV light are alternately stacked. In this stacked portion 25, Si (silicon) is preferably periodically stacked for the layer 21 having a relatively high refractive index for EUV light, and Mo (molybdenum) is preferably periodically stacked for the layer 22 having a relatively low refractive index for EUV light (in this case, the stacked portion 25 is a Si / Mo stacked portion). The Si layer 21 and the Mo layer 22 may be layers formed of elemental silicon and elemental molybdenum, respectively, or may contain other components. Furthermore, a diffusion prevention layer may be provided between the Si layer 21 and the Mo layer 22. The diffusion prevention layer may be provided entirely or partially between the Si layer 21 and the Mo layer 22. The multilayer reflective film 20 can be formed by, for example, ion beam sputtering or magnetron sputtering.

[0047] The number of stacked Si layers 21 and Mo layers 22 is preferably, for example, 40 periods or more (40 layers or more for each) and preferably 60 periods or less (60 layers or less for each). The thicknesses of the Si layer 21 and the Mo layer 22 of the Si / Mo laminated portion 25 are set appropriately depending on the exposure wavelength, with the Si layer 21 preferably being 5 nm or less and the Mo layer 22 preferably being 4 nm or less. The lower limit of the thickness of the Si layer 21 is not particularly limited, but is usually 1 nm or more. The lower limit of the thickness of the Mo layer 22 is not particularly limited, but is usually 1 nm or more. The thicknesses of the Si layer 21 and the Mo layer 22 may be set so as to obtain high reflectivity with respect to EUV light. The thicknesses of the Si layer 21 and the Mo layer 22 may be constant or may vary from layer to layer. The overall thickness of the Si / Mo laminated portion 25 is usually about 250 to 450 nm. The multilayer reflective film 20 may also have a structure including a Si / Ru stacked portion 25 formed of multiple layers in which Si (silicon) layers 21 and Ru (ruthenium) layers 22 are alternately stacked.

[0048] The material of the absorber film 30 is not limited as long as it absorbs exposure light and can be patterned. For example, a material containing tantalum (Ta) or chromium (Cr) is preferably used as the material of the absorber film 30. Furthermore, the material containing Ta or Cr may contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Examples of materials containing Ta include elemental Ta and tantalum compounds such as TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, and TaCONB. Examples of materials containing Cr include elemental Cr and chromium compounds such as CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCNB, CrCOB, and CrCONB. A multilayer structure composed of these materials may also be used. The absorber film 30 may also function as a phase shift mask. The absorber film 30 can be formed by, for example, ion beam sputtering or magnetron sputtering.

[0049] As described above, a protective film may be formed between the multilayer reflective film 20 and the absorber film 30. The protective film is required to have the function of protecting the multilayer reflective film 20 from various dry etchings and cleanings in the reflective mask manufacturing process, the exposure environment when the reflective mask is used, and cleaning treatments in the recycling process after use, and therefore a film made of ruthenium (Ru) containing an additive element such as niobium (Nb), zirconium (Zr), or titanium (Ti) to provide resistance to various processes is preferably used, or a multilayer structure made of these materials may be used. The protective film can be formed by, for example, ion beam sputtering or magnetron sputtering.

[0050] A hard mask film (an etching mask film for the absorber film 30) having etching characteristics different from those of the absorber film 30 may be provided on the side of the absorber film 30 that is away from the substrate 10, preferably in contact with the absorber film 30. This hard mask film functions as an etching mask when dry etching the absorber film 30. After the absorber pattern is formed, this hard mask film may be left as a part of the absorber film 30 as a reflectance reduction layer for reducing the reflectance at the wavelength of light used in inspections such as pattern inspection, or may be removed so that it does not remain on the EUV reflective mask. The hard mask film may be made of a material containing chromium (Cr), for example, and may have a multilayer structure. A hard mask film made of a material containing Cr is particularly suitable when the absorber film 30 is made of a material containing Ta but not Cr. The hard mask film can be formed by, for example, magnetron sputtering. The thickness of the hard mask film is not particularly limited, but is usually about 5 to 20 nm.

[0051] A conductive film may be provided on the back side of the substrate 10 as an antistatic layer for electrostatic chucking. The conductive film preferably has a sheet resistance of 100 Ω / □ or less, and there are no particular limitations on the material. Materials containing tantalum (Ta) or chromium (Cr) are suitable for the conductive film. Furthermore, materials containing Ta or Cr may contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Examples of materials containing Ta include elemental Ta and tantalum compounds such as TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, and TaCONB. Examples of materials containing Cr include elemental Cr and chromium compounds such as CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCNB, CrCOB, and CrCONB. Furthermore, a multilayer structure made of these materials may also be used.

[0052] The thickness of the conductive film is not particularly limited, but is usually about 5 to 100 nm. The thickness of the conductive film is preferably formed so that the film stress is balanced with that of the multilayer reflective film 20 and the absorber pattern after the absorber pattern is formed. The conductive film may be formed before forming the multilayer reflective film 20, or may be formed after forming all of the films on the multilayer reflective film 20 side of the substrate 10. Alternatively, the conductive film may be formed after forming part of the films on the multilayer reflective film 20 side of the substrate 10, and then the remaining films on the multilayer reflective film 20 side of the substrate 10 may be formed. The conductive film can be formed by, for example, ion beam sputtering or magnetron sputtering.

[0053] Furthermore, the EUV reflective mask blank may have a resist film formed on the side farthest from the substrate 10. The resist film is preferably an electron beam (EB) resist.

[0054] Next, the reference mark 40 and the reference mark forming area 41 will be described. First, the significance (raison d'être) of forming the fiducial mark formation region 41 will be explained. The position of the fiducial mark 40 is identified by a defect inspection machine (e.g., Lasertec M8650 or ABICS E120) during the reflective mask blank manufacturing process. However, if a defect exists around the fiducial mark 40, the defect may be erroneously detected as the fiducial mark 40. In such a case, the defect position in the coordinate system defined by the fiducial mark cannot be properly acquired, and the defect position cannot be accurately identified with respect to the fiducial mark 40 during the reflective mask manufacturing process, making it impossible to use DM technology, which can lead to fatal abnormalities in the pattern shape transferred onto the wafer. On the other hand, if fiducial mark forming area 41 is provided as in the present invention, when a defect inspection machine searches for fiducial mark 40, it can distinguish between a defect and fiducial mark 40 based on the presence or absence of fiducial mark forming area 41. Therefore, the above-mentioned false detection does not occur, and it is possible to accurately identify the defect position from the detected fiducial mark 40.

[0055] Fig. 3 shows an example of the arrangement of fiducial marks 40 and fiducial mark forming regions 41 on a reflective mask blank. In Fig. 3, fiducial marks 40 are arranged at each of the four corners on the surface of the reflective mask blank 1 on the same side as the multilayer reflective film 20, but it is preferable that three or more fiducial marks are formed that are not aligned in the same straight line, and there are no particular restrictions on the location and number of fiducial marks 40. However, to prevent overlap with the main pattern in the EUV reflective mask, it is desirable to form the fiducial marks 40 outside the main pattern forming region 50.

[0056] Referring to the planar view of Figure 3, an example of the "periphery of the reference mark formation region 41" that is at a different height from the reference mark formation region 41 can be the main pattern formation region 50 as described above, or it can also be an area other than the main pattern formation region 50 (such as the area between the reference mark formation region 41 and the main pattern formation region 50, or the area between each reference mark formation region 41 along the outer periphery of the reflective mask blank 1).

[0057] Fig. 4 shows an example of the relative positions of fiducial mark 40 and fiducial mark formation area 41 in the present invention. As described above, as shown in Fig. 4, fiducial mark 40 is formed so that at least a portion of it is included in fiducial mark formation area 41. The entire fiducial mark 40 may be included in fiducial mark formation area 41 (left and center diagrams in Fig. 4), or only a portion of fiducial mark 40 may be included in fiducial mark formation area 41 (right diagram in Fig. 4). Because the reference mark 40 and the reference mark forming area 41 have this positional relationship, by detecting the reference mark forming area 41 when searching for the reference mark 40, the reference mark 40 can be easily and reliably detected and the defect can be distinguished from the reference mark 40.

[0058] The unevenness of the fiducial mark 40 and the fiducial mark formation region 41 is not particularly limited, and may be convex or concave. The method of forming the fiducial mark 40 and the fiducial mark formation region 41 is not particularly limited, and they may use the same formation method or different formation methods. However, since the fiducial mark 40 serves as a reference for defect position, it is desirable to form it by FIB processing (Focused Ion Beam processing, hereinafter simply referred to as FIB) or lithography, which enable high-precision processing. The fiducial mark formation region 41 can also be formed using a similar method. In FIB, FIB irradiation of the target region etches the irradiated region, making it concave. On the other hand, FIB irradiation while spraying compound gas onto the sample surface during FIB irradiation allows selective deposition on the irradiated region, making it convex. The latter is called the FIB deposition function. In FIG. 1, the fiducial mark 40 is formed by removing a portion of the multilayer reflective coating 20. However, it may be formed by removing the entire multilayer reflective coating 20, or even the substrate underneath, or it may be formed on another layer, such as the substrate 10 or the absorber film 30. It may also be formed across multiple layers. Even when the fiducial mark 40 is convex, there is no particular limitation on the layer on which it is formed. However, in order to use it as a reference position for phase defects, it is desirable that it can be used as a reference position for defect inspection in the multilayer reflective coating 20, and it is therefore desirable that it be formed on the substrate 10, the multilayer reflective coating 20, or the protective film.

[0059] 5 shows four examples of the shape of fiducial mark 40 in a plan view, but the shape of the fiducial mark in the present invention is not limited to these. As shown in FIG. 5, possible shapes in a plan view include a cross, a circle, and a rectangle, and the lengths (sizes) L1 and L2 of the fiducial marks are preferably 0.1 μm or more to prevent them from being too small and reducing visibility. When fiducial mark 40 is formed using an FIB, the size is preferably 30 μm or less, and more preferably 10 μm or less, to prevent them from being too large and requiring a long processing time. Furthermore, the depth of the fiducial mark 40 is preferably 40 nm or more to prevent the fiducial mark 40 from being too shallow, resulting in poor contrast. Furthermore, when forming the fiducial mark 40 using an FIB, the depth is more preferably 150 nm or less to prevent the fiducial mark 40 from being too deep, which would require a long processing time. When forming the fiducial mark 40 using an FIB, the contrast during detection is improved by increasing the sidewall angle of the mark in the cross-sectional shape, so the current value is preferably 100 pA or less.

[0060] As described above, the recesses and protrusions of the fiducial mark formation region 41 need only have a height different from that of the main pattern formation region 50, and their depth (or height) and shape are not particularly limited. If the recess is too shallow, the contrast with the surroundings will be reduced when a defect inspection system searches for the fiducial mark 40, making it difficult to determine the presence or absence of the fiducial mark formation region 41. Therefore, a depth of 1 nm or more is desirable, and 3 nm or more is more desirable. Furthermore, when the fiducial mark formation region 41 is formed using an FIB, if the depth is too deep, the FIB processing time will be extended, resulting in a decrease in throughput. Therefore, the depth of the fiducial mark formation region 41 is desirable to be 10 nm or less, and 5 nm or less is more desirable. Furthermore, if the difference in elevation between the fiducial mark 40 and the fiducial mark formation region 41 is small, the contrast between them will decrease. Therefore, the difference in elevation between the fiducial mark 40 and the fiducial mark formation region 41 is desirable to be 40 nm or more, and 70 nm or more is more desirable. Furthermore, when the fiducial mark formation region 41 is convex, if its height is too low, the contrast with the surroundings will be reduced when searching for the fiducial mark 40, making it difficult to determine the presence or absence of the fiducial mark formation region 41. Therefore, a height of 1 nm or more is desirable, and 3 nm or more is more desirable. Furthermore, when the fiducial mark formation region 41 is formed using the deposition function of an FIB, if its height is too high, the FIB processing time will be extended, resulting in a decrease in throughput. Therefore, the height of the fiducial mark formation region 41 is desirable to be 10 nm or less, and 5 nm or less is more desirable. Furthermore, if the difference in elevation between the fiducial mark 40 and the fiducial mark formation region 41 is small, this will result in a decrease in contrast between the two. Therefore, the difference in elevation between the fiducial mark 40 and the fiducial mark formation region 41 is desirable to be 40 nm or more, and 70 nm or more is more desirable. As described above, the absolute value of the difference in elevation between fiducial mark formation region 41 and the main pattern formation region can be set to 1 nm or more, or even 3 nm or more, or 10 nm or less, or even 5 nm or less, so as to more reliably create contrast between fiducial mark formation region 41 and its surroundings (main pattern formation region 50). Furthermore, the absolute value of the difference in elevation between fiducial mark 40 and fiducial mark formation region 41 can be set to 40 nm or more, or even 70 nm or more, so as to more reliably create contrast between the two.

[0061] Furthermore, the planar shape of the reference mark forming area 41 is not particularly limited, and may be a rectangle as shown in FIG. 4, or another polygon, circle, or the like. As mentioned previously, fiducial mark forming area 41 is used to distinguish between a defect and fiducial mark 40 based on its presence or absence when a defect inspection machine searches for fiducial mark 40. For example, an inspection is performed around fiducial mark 40, an optical image is acquired at coordinates that output a signal strength above a certain level, and if the presence of fiducial mark forming area 41 can be confirmed in the optical image, it can be determined to be a fiducial mark 40, and if the presence of fiducial mark forming area 41 cannot be confirmed, it can be determined to be a defect. For this reason, it is desirable that the size of the fiducial mark formation region 41 in a planar view be smaller than the field of view of the optical image acquired by the defect inspection machine. In this case, the boundary of the fiducial mark formation region 41 can be more reliably displayed within the field of view, making it easier and simpler to determine its presence or absence. For this reason, the size of the fiducial mark formation region 41 is desirably 30 μm or less, and more desirably 10 μm or less. On the other hand, to prevent the size of the fiducial mark formation region 41 from being too small and making it difficult to determine its presence or absence, it is desirably 1 μm or more, and more desirably 5 μm or more. Forming the fiducial mark formation region 41 of such a size makes it easier to search for the fiducial mark formation region 41 and, therefore, to distinguish between defects and fiducial marks 40, further reducing the risk of false detection.

[0062] Next, a manufacturing method of the present invention for manufacturing a reflective mask blank of the present invention as shown in FIGS. 1 and 2 will be described. The main steps include at least the step of forming a multilayer reflective film 20 on a substrate 10, and the step of forming an absorber film 30 on the multilayer reflective film 20. If necessary, other functional layers such as the above-mentioned protective film, hard mask film, conductive film, and resist film can also be formed. The method for forming each of these films is not particularly limited, and they can be formed, for example, using the above-mentioned materials in the same manner as conventional methods (such as ion beam sputtering and magnetron sputtering).

[0063] Furthermore, the method includes a step of forming a fiducial mark 40 and a fiducial mark forming region 41 on the surface on the same side as the multilayer reflective film 20. As described above, the fiducial mark 40 is preferably formed on the substrate 10, the multilayer reflective film 20, or the protective film. After the substrate is prepared or after the film is formed, the fiducial mark 40 can be formed with high precision by, for example, FIB processing or lithography.

[0064] The reference mark forming area 41 can be formed by, for example, FIB processing. By setting the size of the target fiducial mark formation area 41 and irradiating it with FIB, the irradiated area is etched by the FIB and becomes deeper than the area that was not irradiated. The depth can be changed as desired by changing the scanning conditions. Furthermore, by spraying a compound gas onto the sample surface while performing FIB irradiation, selective deposition can be performed on the irradiated area (forming a deposition layer 60). This makes the irradiated area higher than the non-irradiated area. The height can be changed as desired by changing the scan conditions and gas pressure.

[0065] In this way, fiducial mark formation region 41 is formed so as to have a concave or convex shape with a different height from main pattern formation region 50. At this time, fiducial mark 40 is formed so that at least a part of it is included in fiducial mark formation region 41.

[0066] Furthermore, fiducial mark formation region 41 may be formed before or after fiducial mark 40 is formed. When a scanning ion microscope (SIM) image or a scanning electron microscope (SEM) image of fiducial mark 40 is acquired after the fiducial mark 40 is formed to confirm the shape of fiducial mark 40, a convex or concave scan mark is generated in the scan region due to the sputtering effect caused by irradiation with an ion beam or electron beam or contamination. This scan mark may be used as fiducial mark formation region 41. It is desirable to form fiducial mark forming area 41 centered on the central coordinates of fiducial mark 40. By doing so, even if a defect of approximately the same size as fiducial mark 40 exists within fiducial mark forming area 41, it is possible to distinguish between the defect and fiducial mark 40 based on their positional relationship with fiducial mark forming area 41.

[0067] In addition, the preferred forms for the absolute value of the height difference between the reference mark formation area 41 and the main pattern formation area 50 when forming the reference mark formation area 41 and the size compared to the field of view of the optical image acquired by the defect inspection machine are as described above.

[0068] Next, the method for inspecting a reflective mask blank-related substrate of the present invention will be described. The main processes include an inspection object preparation process for preparing a reflective mask blank-related substrate to be inspected, and an inspection process including searching for a reference mark (formed on the same side as the multilayer reflective film in the reflective mask blank product) formed on the prepared reflective mask blank-related substrate, and identifying the defect position based on the reference mark. In the inspection object preparation step, a reflective mask blank-related substrate, for example, the reflective mask blank 1 of the present invention as shown in FIGS. 1 and 2, is prepared. Alternatively, a manufacturing intermediate thereof may be prepared. As the manufacturing intermediate, a thin-film-coated substrate having at least one layer constituting the reflective mask blank 1 can be prepared. More specifically, a substrate on which only the multilayer reflective film 20 is formed, or a substrate on which the absorber film 30 is further formed, can be prepared. Alternatively, a substrate on which the aforementioned protective film, hard mask film, conductive film, resist film, other functional layers, etc. are appropriately formed can be prepared. Here, the inspection method will be explained using an example in which the reflective mask blank 1 of the present invention is prepared. Furthermore, in the inspection process, when searching for fiducial mark 40, the presence or absence of fiducial mark formation area 41 is used to distinguish between fiducial mark 40 and a defect. By utilizing the presence or absence of fiducial mark formation area 41, it is possible to prevent a defect from being mistakenly detected as a fiducial mark 40. Therefore, detection of fiducial mark 40 can be ensured, and the defect position can be appropriately identified based on this. In the inspection process, not only defect position information based on the reference mark can be obtained, but also other necessary information such as the size and unevenness of the identified defect can be obtained as appropriate. [Example]

[0069] The present invention will be explained in more detail below by showing examples and comparative examples, but the present invention is not limited to these examples. Example 1 A multilayer reflective film 20 was formed on a substrate 10 made of quartz glass, 152 mm square and 6.35 mm thick, by DC pulse magnetron sputtering using a molybdenum (Mo) target and a silicon (Si) target, with both targets facing the main surface of the substrate 10 and the substrate 10 being rotated. Each target was mounted on a sputtering apparatus capable of mounting two targets and discharging either one at a time or both simultaneously, and the substrate 10 was then placed on the apparatus. First, while argon (Ar) gas was flowing into the chamber, power was applied to the silicon (Si) target to form a 4 nm thick silicon (Si) layer, and the application of power to the silicon (Si) target was stopped. Next, while argon (Ar) gas was flowing into the chamber, power was applied to the molybdenum (Mo) target to form a 3 nm thick molybdenum (Mo) layer, and the application of power to the molybdenum (Mo) target was stopped. This process of forming a silicon (Si) layer and a molybdenum (Mo) layer constituted one cycle, and this cycle was repeated 40 times to form the multilayer reflective film 20.

[0070] Next, a protective film in contact with the multilayer reflective film 20 was formed on the multilayer reflective film 20 by DC pulse magnetron sputtering using a Ru target, with the Ru target facing the main surface of the substrate 10 and the substrate 10 rotating.

[0071] Next, a predetermined portion of the protective film was irradiated with an FIB, thereby removing the entire protective film and a portion of the multilayer reflective film 20 in the irradiated portion, thereby forming a rectangular fiducial mark 40 having a width (horizontal width) of 1 μm and a length (vertical width) of 1 μm in a plan view. An area having a width of 5 μm and a length of 5 μm, centered on the fiducial mark 40, was then scanned to obtain a SIM image of the fiducial mark 40 and form a fiducial mark formation region 41. The FIB current value used to form the fiducial mark 40 and the fiducial mark formation region 41 was 50 pA. Observation of the periphery of the fiducial mark 40 with an atomic force microscope (AFM) revealed that the fiducial mark 40 had a depth of 100 nm and the fiducial mark formation region 41 had a depth of 1.6 nm (i.e., 1.6 nm deeper than the height position of the main pattern formation region).

[0072] Next, the protective film surface was inspected using a defect inspection machine (Lasertec M8650), and the positions of the fiducial marks 40 and defects on the protective film surface were obtained. When searching for the fiducial marks 40, a rectangle 1 mm wide and 1 mm long, centered on the design coordinates of the fiducial marks 40, was used as the inspection area, and the coordinates of all defects determined to be 0.5 μm or larger in size were extracted. After that, the optical image acquired during inspection was referenced, and defects and fiducial marks 40 were distinguished based on the presence or absence of the fiducial mark formation area 41, and the coordinates of the fiducial marks 40 were selectively obtained. The field of view of the optical image was approximately 30 μm (i.e., the fiducial mark formation area 41, which was 5 μm x 5 μm in size, was smaller than the above field of view).

[0073] Next, using a Ta target, an absorber film 30 in contact with the protective film was formed on the protective film by DC pulse magnetron sputtering while the Ta target and the main surface of the substrate 10 were opposed to each other and the substrate 10 was rotated.

[0074] Next, the surface of the absorber film 30 was inspected using a defect inspection machine (Lasertec M8650), and the positions of the fiducial marks 40 and the positions of defects on the surface of the absorber film 30 were obtained. When searching for the fiducial marks 40, a rectangle 1 mm wide and 1 mm long, centered on the design coordinates of the fiducial marks 40, was used as the inspection area, and the coordinates of all defects determined to be 0.5 μm or larger in size were extracted. After that, the optical image acquired during inspection was referenced, and defects and fiducial marks 40 were distinguished based on the presence or absence of the fiducial mark formation region 41, and the coordinates of the fiducial marks 40 were selectively obtained. The field of view of the optical image was approximately 30 μm.

[0075] Next, a Cr target was used on the absorber film 30, with the Cr target facing the main surface of the substrate 10, and while the substrate 10 was being rotated, a hard mask film was formed in contact with the absorber film 30 by DC pulse magnetron sputtering, thereby producing an EUV reflective mask blank.

[0076] Next, the surface of the hard mask film was inspected using a defect inspection machine (Lasertec M8650), and the positions of the fiducial marks 40 and the positions of defects on the surface of the hard mask film were obtained. When searching for the fiducial marks 40, a rectangle 1 mm wide and 1 mm long, centered on the design coordinates of the fiducial marks 40, was used as the inspection area, and the coordinates of all defects determined to be 0.5 μm or larger in size were extracted. After that, the optical image acquired during inspection was referenced, and defects and fiducial marks 40 were distinguished based on the presence or absence of the fiducial mark formation region 41, and the coordinates of the fiducial marks 40 were selectively obtained. The field of view of the optical image was approximately 30 μm.

[0077] Incidentally, in the above-described Example 1, the main pattern formation region was set as the "periphery of the fiducial mark formation region." However, similar results were obtained when a region other than the main pattern formation region was set. Specifically, even when the region between the fiducial mark formation region and the main pattern formation region, or the region between the fiducial mark formation regions along the outer periphery of the reflective mask blank, was set as the "periphery of the fiducial mark formation region," it was possible to distinguish between defects and fiducial marks and selectively obtain the coordinates of the fiducial marks, just as in Example 1.

[0078] As described above, with the reflective mask blank and its manufacturing method, and the method for inspecting a reflective mask blank-related substrate of the present invention, the presence or absence of a fiducial mark forming area 41 in the mask blank makes it easy to distinguish between fiducial marks 40 and defects when searching for fiducial marks 40 using a defect inspection machine, and the fiducial marks 40 can be reliably detected without erroneously recognizing defects as fiducial marks 40.

[0079] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0080] 1... reflective mask blank of the present invention, 10... substrate, 20... multilayer reflective film, 21...Layer with a relatively high refractive index against EUV light (Si layer), 22...Layer with a relatively low refractive index to EUV light (Mo layer or Ru layer), 25...Laminated portion (Si / Mo laminated portion or Si / Ru laminated portion), 30...absorber film, 40...reference mark, 41...reference mark forming region, 50...main pattern forming region, 60...Sedimentary layer.

Claims

1. A substrate; a multilayer reflective film provided on the substrate and reflecting exposure light; an absorber film provided on the multilayer reflective film and absorbing the exposure light; A reflective mask blank comprising at least a reference mark serving as a reference position for a defect position, formed on a surface of the reflective mask blank on the same side as the multilayer reflective film, and a reference mark forming area for searching for the reference mark, the reference mark formation area is formed at a height different from that of the surrounding area of ​​the reference mark formation area, A reflective mask blank, wherein the fiducial mark is formed so that at least a part of the fiducial mark is included in the fiducial mark forming region.

2. A substrate; a multilayer reflective film provided on the substrate and reflecting exposure light; an absorber film provided on the multilayer reflective film and absorbing the exposure light; A reflective mask blank comprising at least a reference mark serving as a reference position for a defect position, formed on a surface of the reflective mask blank on the same side as the multilayer reflective film, and a reference mark forming area for searching for the reference mark, the reference mark formation region is formed at a height different from that of the main pattern formation region, A reflective mask blank, wherein the fiducial mark is formed so that at least a part of the fiducial mark is included in the fiducial mark forming region.

3. 3. The reflective mask blank according to claim 2, wherein the absolute value of the difference in height between the fiducial mark formation region and the main pattern formation region is 1 nm or more.

4. 4. The reflective mask blank according to claim 2, wherein the fiducial mark formation area is smaller than the field of view of an optical image acquired by a defect inspection machine used to search for the fiducial mark.

5. forming a multilayer reflective film on a substrate that reflects exposure light; forming an absorber film on the multilayer reflective film to absorb the exposure light; A method for manufacturing a reflective mask blank having at least forming a reference mark serving as a reference position for a defect position and a reference mark forming area for searching for the reference mark on the same surface of the reflective mask blank as the multilayer reflective film, In the step of forming the reference mark and the reference mark forming area, forming the reference mark forming region so as to have a height different from that of the surrounding area of ​​the reference mark forming region; A method for manufacturing a reflective mask blank, comprising forming the fiducial mark so that at least a part of the fiducial mark is included in the fiducial mark forming region.

6. forming a multilayer reflective film on a substrate that reflects exposure light; forming an absorber film on the multilayer reflective film to absorb the exposure light; A method for manufacturing a reflective mask blank having at least forming a reference mark serving as a reference position for a defect position and a reference mark forming area for searching for the reference mark on the same surface of the reflective mask blank as the multilayer reflective film, In the step of forming the reference mark and the reference mark forming area, forming the reference mark forming region to have a height different from that of the main pattern forming region; A method for manufacturing a reflective mask blank, comprising forming the fiducial mark so that at least a part of the fiducial mark is included in the fiducial mark forming region.

7. In the step of forming the reference mark and the reference mark forming area, 7. The method for manufacturing a reflective mask blank according to claim 6, wherein the fiducial mark forming region is formed so that the absolute value of the difference in height between the fiducial mark forming region and the main pattern forming region is 1 nm or more.

8. In the step of forming the reference mark and the reference mark forming area, 8. The method for manufacturing a reflective mask blank according to claim 6, wherein the fiducial mark formation area is formed to be smaller than the field of view of an optical image acquired by a defect inspection machine used when searching for the fiducial mark.

9. 8. The method for manufacturing a reflective mask blank according to claim 6, wherein the fiducial marks and the fiducial mark forming regions are formed by FIB processing.

10. 9. The method for manufacturing a reflective mask blank according to claim 8, wherein the fiducial marks and the fiducial mark forming regions are formed by FIB processing.

11. A substrate; a multilayer reflective film provided on the substrate and reflecting exposure light; an absorber film provided on the multilayer reflective film and absorbing the exposure light; A method for inspecting a reflective mask blank-related substrate selected from a reflective mask blank and its manufacturing intermediate, comprising: an inspection target preparation step of preparing a reflective mask blank-related substrate to be inspected; an inspection process including searching for a reference mark formed on the prepared reflective mask blank-related substrate and specifying a defect position based on the reference mark; In the inspection object preparation step, the reflective mask blank-related substrate to be inspected comprises the reference mark, which serves as a reference position for a defect position, and a reference mark forming area for searching for the reference mark, both formed on a surface of the reflective mask blank on the same side as the multilayer reflective film, the reference mark formation area is formed at a height different from that of the surrounding area of ​​the reference mark formation area, preparing the reference mark formed so that at least a part of the reference mark is included in the reference mark forming area; In the inspection step, a reference mark forming area for forming a reference mark on a substrate; a reference mark forming area for forming a reference mark on a substrate;

12. A substrate; a multilayer reflective film provided on the substrate and reflecting exposure light; an absorber film provided on the multilayer reflective film and absorbing the exposure light; A method for inspecting a reflective mask blank-related substrate selected from a reflective mask blank and its manufacturing intermediate, comprising: an inspection target preparation step of preparing a reflective mask blank-related substrate to be inspected; an inspection process including searching for a reference mark formed on the prepared reflective mask blank-related substrate and specifying a defect position based on the reference mark; In the inspection object preparation step, the reflective mask blank-related substrate to be inspected comprises the reference mark, which serves as a reference position for a defect position, and a reference mark forming area for searching for the reference mark, both formed on a surface of the reflective mask blank on the same side as the multilayer reflective film, the reference mark formation region is formed at a height different from that of the main pattern formation region, preparing the reference mark formed so that at least a part of the reference mark is included in the reference mark forming area; In the inspection step, a reference mark forming area for forming a reference mark on a substrate; a reference mark forming area for forming a reference mark on a substrate;

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