Reflective mask blank and method for manufacturing the same

Abstract

The present invention provides a reflective mask blank with auxiliary marks that can be formed with a simple mechanism and with a low risk of dust generation, in addition to the standard mark. [Solution] A reflective mask blank comprising at least a substrate, a multilayer reflective film provided on the substrate that reflects exposure light, and an absorbent film provided on the multilayer reflective film that absorbs the exposure light, wherein the reflective mask blank is provided with a reference mark formed on the same side as the multilayer reflective film, the reference mark consists of a main mark which serves as a reference position for defect locations, and a group of auxiliary marks arranged around the main mark, the group of auxiliary marks consists of a plurality of auxiliary marks formed at intervals from each other so as to extend in at least one direction from the main mark, and all of the plurality of auxiliary marks are formed to be the same shape and orientation.

Description

Technical Field

[0001] The present invention relates to a reflective mask blank used in manufacturing semiconductor devices and the like, and a method for manufacturing the same.

Background Art

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

[0003] However, due to the continuous miniaturization of device patterns, the formation of further fine patterns has been required, and thus EUV lithography technology using extreme ultraviolet (Extreme Ultraviolet: hereinafter referred to as "EUV") light with a wavelength shorter than that of ArF excimer laser light has come to be used. EUV light is light with a wavelength of about 0.2 to 100 nm, and more specifically, light with a wavelength near 13.5 nm. Since this EUV light has extremely low permeability to substances and conventional transmissive projection optical systems and masks cannot be used, reflective optical elements are used. Also, a reflective mask has been proposed for the mask for pattern transfer.

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

[0005] In EUV reflective masks, if there are concave or convex defects on the surface or within the film, the reflectivity of EUV light decreases at the defect site, making it impossible to obtain the desired transfer pattern during wafer exposure. In particular, if the defect exists within the multilayer reflective film or between the multilayer reflective film and the substrate, even if the height of the defect is only a few nanometers, the disruption of the periodic structure of the multilayer reflective film around it causes 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. Phase defects are difficult to correct because they are located within or beneath the film. On the other hand, defects that exist on the multilayer reflective film or on the absorber film attenuate the intensity of the reflected EUV light, and are therefore called amplitude defects in contrast to phase defects.

[0006] To avoid the influence of phase defects and amplitude defects on the transfer pattern, Defect Mitigation (hereinafter referred to as DM technology), which covers phase defects with an absorber pattern, has been proposed. DM technology is achieved by identifying the defect location in a coordinate system defined by reference marks created on an EUV reflective mask blank through defect inspection, and by having the mask shop measure the reference mark positions and perform appropriate coordinate transformations to obtain the defect location information on the EUV reflective mask blank in the coordinate system inside the mask shop. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6713251 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Patent Document 1 describes a method for forming a low-cost and highly accurate reference mark by dividing the reference mark into a main mark and an auxiliary mark, forming the main mark with a FIB (Focused Ion Beam), and forming the auxiliary mark with indentation using a micro-indenter. It also proposes forming an auxiliary mark that does not damage the substrate and allows for easy substrate regeneration by setting the length of the long side of the auxiliary mark in plan view to be between 200 μm and 600 μm, and the depth to be less than or equal to the thickness of the multilayer reflective film. To form the above auxiliary marks above, below, left, and right of the main mark, the embodiment in Patent Document 1 describes a method in which a micro-indenter is rotated around the main mark. However, in this case, it is necessary to offset the rotation axis of the micro-indenter from the swing axis of the micro-indenter, which complicates the mechanism. In addition, since a rotating mechanism is provided on the substrate, the risk of dust generation increases.

[0009] The present invention was made to solve the above problems, and aims to provide a reflective mask blank having an auxiliary mark that can be formed in the reference mark with a simple mechanism and with a low risk of dust generation, and a method for manufacturing the same. [Means for solving the problem]

[0010] To achieve the above objective, the present invention provides a substrate and A multilayer reflective film is provided on the substrate and reflects exposure light, An absorber film provided on the multilayer reflective film, which absorbs the exposure light, A reflective mask blank comprising at least the following: The reflective mask blank is provided with a reference mark formed on the same side as the multilayer reflective film, The reference mark consists of a main mark that serves as the reference position for the defect location, and a group of auxiliary marks arranged around the main mark. The group of auxiliary marks consists of a plurality of auxiliary marks that are spaced apart from each other and extend in at least one direction from the main mark, The present invention provides a reflective mask blank characterized in that the multiple auxiliary marks are all formed to be the same shape and orientation.

[0011] With the reflective mask blank of the present invention, auxiliary marks in the reference mark can be formed with a simple mechanism and with a low risk of dust generation. Unlike conventional auxiliary marks that require complex mechanisms and high dust-generating risks, the present invention enables a lower-cost and lower-defect reflective mask blank with a reference mark (particularly for EUV reflective mask blanks).

[0012] At this time, the auxiliary mark is It can be defined as a concave shape obtained by inverting a cone shape with a vertex angle of 55 degrees or more, a concave shape obtained by inverting a hip roof shape with a ridge length of 50 μm or less, or a concave shape obtained by inverting a truncated square pyramid with the longest side of the upper surface of 50 μm or less.

[0013] For example, when auxiliary marks are formed by indentation with a micro-indenter, and the depth of the auxiliary marks must be kept below the thickness of the multilayer reflective film, the depth will be very shallow compared to the length (size) of the auxiliary marks in a plan view. In order to obtain the desired shape with good reproducibility, it may be necessary to press the micro-indenter extremely parallel to the substrate. In this case, high precision is required in the mounting of the micro-indenter and the placement of the substrate in order to reproduce the shape. However, if the auxiliary marks (in this case, the micro-indenter) have a specific shape as described above, excessive precision is not required in the mounting of the micro-indenter and the placement of the substrate, and the auxiliary marks will be easier to reproduce.

[0014] Furthermore, the auxiliary mark may be formed on the same layer as the main mark, or on a higher side (away from the substrate) than the layer on which the main mark is formed.

[0015] With this method, auxiliary marks can be formed using the main mark as a guide, making the formation of auxiliary marks much simpler.

[0016] Further, the present invention includes a step of forming a multilayer reflective film that reflects exposure light on a substrate, a step of forming an absorber film that absorbs the exposure light on the multilayer reflective film, and a method for manufacturing a reflective mask blank having at least these steps, the method including a step of forming a reference mark on the same side of the multilayer reflective film of the reflective mask blank, the reference mark including a main mark serving as a reference position for a defect position and an auxiliary mark group arranged around the main mark, When forming the auxiliary mark group among the reference marks, a plurality of auxiliary marks are formed at intervals in at least one direction starting from the main mark so as to be spaced apart from each other, with all of the plurality of auxiliary marks having the same shape and the same orientation, by an indentation method using a microprobe, thereby forming the auxiliary mark group consisting of the plurality of auxiliary marks. The present invention provides a method for manufacturing a reflective mask blank characterized by this.

[0017] According to the method for manufacturing a reflective mask blank of the present invention, the auxiliary marks in the reference mark can be formed with a simple mechanism and a low risk of generating dust. Therefore, it is possible to provide a reflective mask blank with a reference mark that is lower in cost and has fewer defects than in the past (particularly, a reflective mask blank for EUV).

[0018] At this time, as the microprobe, a cone shape with a vertex angle of 55 degrees or more inverted, a gabled shape with a gable length of 50 μm or less inverted, or a frustum of a square pyramid with a long side of the upper surface of 50 μm or less inverted can be used.

[0019] If a microprobe having a specific shape as described above is used as the microprobe, excessive accuracy is not required in attaching the microprobe and installing the substrate, and auxiliary marks can be formed with high reproducibility of the shape.

[0020] Further, when forming the main mark, it can be formed by FIB processing.

[0021] By doing so, it is possible to form the main mark with high precision.

[0022] Also, when forming the auxiliary mark, a defect inspection machine on which the micro pressure element is mounted can be used.

[0023] Some of the defect inspection machines have an indentation function with a micro pressure element mounted. In this case, there is no need to newly introduce a device for forming the auxiliary mark, and the cost can be reduced.

[0024] Also, the auxiliary mark can be formed after forming the main mark.

[0025] By doing so, the auxiliary mark can be formed using the main mark as a guide, and excessive machining position accuracy is not required for the device for forming the auxiliary mark, which is simple.

Effect of the Invention

[0026] According to the reflective mask blank and its manufacturing method of the present invention, it is not necessary to form an auxiliary mark by a complicated mechanism with a high dust generation risk as in the prior art, and an auxiliary mark can be formed. Therefore, it is possible to provide a reflective mask blank with a reference mark at a lower cost and with fewer defects.

Brief Description of the Drawings

[0027] [Figure 1] It is an example of a cross-sectional schematic view of the reflective mask blank of the present invention. [Figure 2] It is a plan schematic view showing an example of the arrangement of the reference marks in the present invention. <00001​​​​​​This is an example of a schematic diagram of the oblique and plan view shapes of the auxiliary mark in the present invention (oblique and plan view shapes of the micro-indenter). [Figure 6] This diagram shows the cross-sectional shape of the auxiliary mark when the micro-indenter is cone-shaped, and a schematic diagram of the substrate surface when the substrate is tilted. [Figure 7] This diagram shows the cross-sectional shape of the auxiliary mark when a miniature indenter is of the hip-roof type, and a schematic diagram illustrating the substrate surface when the substrate is tilted. [Best Mode for Carrying Out the Invention]

[0028] As mentioned above, there was a need for auxiliary marks in the reference marks of reflective mask blanks that could be formed with a simple mechanism and with a low risk of dust generation.

[0029] Therefore, the inventors diligently researched reflective mask blanks and discovered that a reflective mask blank (equipped with at least a multilayer reflective film and an absorbent film on a substrate) has reference marks (main marks and a group of auxiliary marks) formed on the same side as the multilayer reflective film, and the group of auxiliary marks consists of a plurality of auxiliary marks formed at intervals from each other so as to extend in at least one direction from the main mark, and all of the plurality of auxiliary marks are formed with the same shape and orientation, so that the auxiliary marks can be formed with a simple mechanism and with a low risk of dust generation, and a low-cost, low-defect reflective mask blank with reference marks can be made, thus completing the present invention.

[0030] Furthermore, the manufacturing method also includes a step of forming a reference mark (main mark and auxiliary mark group) on the same side of the reflective mask blank as the multilayer reflective film. When forming the auxiliary mark group among the reference marks, by forming multiple auxiliary marks with the same shape and orientation, using an indentation method with a micro-indenter, spacing them apart so that they extend in at least one direction from the main mark, a group of auxiliary marks consisting of multiple auxiliary marks can be formed. This allows for the formation of auxiliary marks on the reference mark with a simple mechanism and a low risk of dust generation, enabling the manufacture of low-cost, low-defect reflective mask blanks with reference marks, thus completing the present invention.

[0031] Embodiments of the present invention will be described below 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. Figure 1 shows an example of a schematic diagram of the reflective mask blank according to the present invention. An example for EUV will be used for the explanation, but the present invention is not limited to this. In Figure 1, the reflective mask blank 1 first has a substrate 10, a multilayer reflective film 20 that reflects exposure light formed on the surface of the substrate 10, an absorber film 30 that absorbs exposure light formed on the multilayer reflective film 20, and a reference mark 40 formed on the surface of the reflective mask blank. Although not shown in Figure 1, 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 pattern formation is made on the absorber film 30. In addition, a hard mask film that functions as an etching mask when dry etching the absorber film 30 may be provided on the absorber film 30. In addition, a conductive film that functions as an antistatic layer when electrostatic chuck is provided on the back side of the substrate 10. In addition, other functional layers may be provided.

[0032] The substrate 10 preferably has low thermal expansion characteristics for use with EUV light exposure, for example, a thermal expansion coefficient of ±2 × 10 -8 Within the range of / ℃, preferably ±5 × 10 -9It is preferable that the substrate is made of a material within the range of / ℃. Furthermore, it is preferable that the substrate 10 has a sufficiently flattened surface, and the surface roughness of the main surface of the substrate 10 is preferably 0.5 nm or less in RMS value, and particularly preferably 0.2 nm or less. Such surface roughness can be obtained by polishing the substrate 10 or the like.

[0033] The multilayer reflective film 20 is generally a multilayer film in which low refractive index materials and high refractive index materials are alternately stacked, and in this case, it is a film that reflects EUV light, which is the exposure light. In the embodiment shown in Figure 1, the multilayer reflective film 20 has a laminated portion 25 composed of multiple layers in which layers 21 with a relatively high refractive index with respect to EUV light and layers 22 with a relatively low refractive index with respect to EUV light are alternately stacked. In this laminated portion 25, it is preferable to periodically stack Si (silicon) in the layer 21 which has a relatively high refractive index with respect to EUV light, and Mo (molybdenum) in the layer 22 which has a relatively low refractive index with respect to EUV light (in this case, the laminated portion 25 becomes a Si / Mo laminated portion). Here, the Si layer 21 and the Mo layer 22 may be layers formed of pure silicon and pure molybdenum, respectively, or they 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 all the way between the Si layer 21 and the Mo layer 22, or only in part.

[0034] The number of layers of Si layer 21 and Mo layer 22 is preferably 40 or more (40 or more layers each), and preferably 60 or less (60 or less layers each). The thicknesses of the Si layer 21 and Mo layer 22 of the Si / Mo laminated section 25 are appropriately set according to the exposure wavelength, with the thickness of the Si layer 21 preferably being 5 nm or less, and the thickness of 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 Mo layer 22 should be set so that a high reflectivity to EUV light can be obtained. In addition, the thickness of each of the Si layer 21 and Mo layer 22 may be constant, or may differ in each layer. The overall thickness of the Si / Mo laminated section 25 is usually about 250 to 450 nm. Furthermore, the multilayer reflective film 20 may have a structure having a Si / Ru laminated portion 25 composed of alternating layers of Si (silicon) layers 21 and Ru (ruthenium) layers 22.

[0035] The material of the absorber film 30 is not limited as long as it absorbs exposure light and can be patterned. For example, materials containing tantalum (Ta) or chromium (Cr) are preferably used as the material of the absorber film 30. Furthermore, materials containing Ta or Cr may also contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Examples of Ta-containing materials include elemental Ta, TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, and TaCONB tantalum compounds. Specific examples of Cr-containing materials include elemental Cr, CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCNB, CrCOB, and CrCONB chromium compounds. A multilayer structure made of these materials is also possible. Furthermore, the absorber film 30 may function as a phase shift mask.

[0036] As mentioned above, a protective film may be formed between the multilayer reflective film 20 and the absorber film 30. The protective film is required to protect the multilayer reflective film 20 from various dry etching and cleaning processes in the reflective mask manufacturing process, the exposure environment when using the reflective mask, and cleaning processes in the regeneration process after use. A protective film containing additive elements such as niobium (Nb), zirconium (Zr), titanium (Ti), and rhodium (Rh) to provide resistance to various processes is preferably used, and a multilayer structure made of these materials may also be used.

[0037] On the side of the absorber film 30 that is separated from the substrate 10, preferably, a hard mask film (etching mask film for the absorber film 30) is provided in contact with the absorber film 30 and has different etching characteristics from 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 remain as a reflectance reduction layer to reduce the reflectance at wavelengths of light used in inspections such as pattern inspection, and may be part of the absorber film 30, or it may be removed so that it does not remain on the EUV reflective mask. As the material for the hard mask film, for example, a material containing chromium (Cr) is preferably used, and it may be in a multilayer structure. A hard mask film formed from a Cr-containing material is particularly suitable when the absorber film 30 is formed from a material containing Ta but not Cr. The hard mask film can be formed, for example, by magnetron sputtering. There are no particular restrictions on the thickness of the hard mask film, but it is usually around 5 to 20 nm.

[0038] A conductive film may be provided on the back side of the substrate 10 as an antistatic layer during electrostatic chuck operation. The conductive film preferably has a sheet resistance of 100 Ω / □ or less, and there are no particular restrictions on the material. Suitable materials for the conductive film include, for example, materials containing tantalum (Ta) or chromium (Cr). Materials containing Ta or Cr may also contain oxygen (O), nitrogen (N), carbon (C), boron (B), etc. Examples of Ta-containing materials include tantalum compounds such as elemental Ta, TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, and TaCONB. Specific examples of Cr-containing materials include chromium compounds such as elemental Cr, CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCNB, CrCOB, and CrCONB. A multilayer structure made of these materials is also acceptable.

[0039] There are no particular restrictions on the thickness of the conductive film, but it is usually around 5 to 100 nm. Preferably, the thickness of the conductive film is formed after the absorber pattern is formed so that the film stress is balanced with that of the multilayer reflective film 20 and the absorber pattern. The conductive film may be formed before forming the multilayer reflective film 20, or after forming all the films on the multilayer reflective film 20 side of the substrate 10. Alternatively, the conductive film may be formed after forming a portion 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, for example, by magnetron sputtering.

[0040] Furthermore, the EUV reflective mask blank may have a resist film formed on the side furthest from the substrate 10. The resist film is preferably an electron beam (EB) resist.

[0041] Figure 2 shows an example of the placement of reference marks. In Figures 1 and 2, the reference marks 40 are placed one at each of the four corners on the same side of the reflective mask blank 1 as the multilayer reflective film 20. However, it is preferable to have three or more marks that are not on the same straight line, and there are no particular restrictions on the location and number of reference marks 40. However, in order to prevent overlap with the main pattern in the EUV reflective mask, it is desirable to form them outside the main pattern formation area.

[0042] Figure 3 shows examples of the shape and arrangement of the main mark and auxiliary mark group that constitute the reference mark in the present invention. As shown in Figure 3, the reference mark 40 consists of a main mark 41 that serves as a reference for the defect location and an auxiliary mark group 42 arranged around the main mark 41, and the auxiliary mark group 42 is composed of a combination of multiple auxiliary marks 43. In Figure 3, the auxiliary mark group 42 (42a, 42b, 42c, 42d) is arranged in four directions: up, down, left, and right of the main mark 41, but the arrangement direction of the auxiliary mark group 42 is not particularly limited. As will be described later, it is sufficient that it consists of multiple auxiliary marks 43 that are spaced apart from each other so as to extend in at least one direction from the main mark 41. For example, it may extend in only one direction from the up, down, left, or right of the main mark 41, or it may extend in two or three directions. By limiting the extension direction of the auxiliary mark group 42, the number of auxiliary marks 43 that constitute the auxiliary mark group 42 can be reduced, leading to improved throughput.

[0043] Since the main mark 41 serves as a reference for defect location, it is desirable to form it by FIB processing (hereinafter simply referred to as FIB) or lithography, which allows for high-precision processing. In Figure 1, the main mark 41 is formed by removing a portion of the multilayer reflective film 20, but it may also be formed by removing the entire multilayer reflective film 20, or by removing the substrate underneath, or by forming it on other layers such as the substrate 10 or the absorber film 30. It may also be formed across multiple layers. However, in order to serve as a reference location for phase defects, it is desirable that it can be used as a reference location in defect inspection of the multilayer reflective film 20, and therefore it is desirable that it be formed on the substrate 10, the multilayer reflective film 20, or the protective film.

[0044] Furthermore, while examples of the shape of the main mark 41 are shown in Figure 4, the shape of the main mark in this invention is not limited to these. As shown in Figure 4, in plan view, a cross shape, circle, rectangle, etc., are possible, and the vertical and horizontal lengths (size) L1 and L2 should preferably be 0.1 μm or more, as visibility will be poor if they are too small. Also, when forming the main mark 41 using FIB, it is preferable that the size be 500 μm or less, and more preferably 100 μm or less, as processing will take time if the size is too large. In addition, the depth of the main mark 41 should preferably be 40 nm or more, as contrast will be poor if it is too shallow, and it is preferable that it be 500 nm or less to minimize damage to the substrate and facilitate regeneration. Furthermore, when forming the main mark 41 using FIB, it is more preferable that the depth be 150 nm or less, as processing will take time if it is too deep. When forming the main mark 41 with FIB, it is preferable that the current value be 100 pA or less, as the contrast during detection is improved by making the side wall angle of the mark in the cross-sectional shape steeper.

[0045] The auxiliary mark group 42 is composed of multiple auxiliary marks 43. Since it functions as a marker for finding the main mark 41, it only needs to be large enough to be detectable by inspection or drawing machines, and its size is not particularly limited. However, specifically, the size L3 of the auxiliary mark group 42 is preferably larger than the main mark, at least 50 μm in size, and at least 1 mm in size (see Figure 3).

[0046] The auxiliary marks 43 that make up the auxiliary mark group 42 may be multiple, and there is no particular limit on the number of them. However, to prevent the loss of their function as markers, it is preferable to have more than a certain number, and to prevent a decrease in throughput, it is preferable to have fewer than a certain number. For example, it is desirable that the number of auxiliary marks 43 that make up each auxiliary mark group 42 be between 3 and 20.

[0047] Furthermore, while there is no restriction on the spacing P1 between adjacent auxiliary marks 43, if the spacing is too wide, it becomes difficult to determine the direction of the main mark 41 relative to a given auxiliary mark 43 within the field of view of the inspection machine or drawing machine, making it difficult for the auxiliary marks to function as markers for finding the main mark 41. Therefore, it is desirable that the spacing P1 between adjacent auxiliary marks 43 be 30 μm or less. For the same reason, it is also desirable that the spacing P2 between the main mark 41 and the auxiliary mark 43 adjacent to the main mark 41 be 30 μm or less. On the other hand, if the spacing P1 between adjacent auxiliary marks 43 is too narrow, the number of auxiliary marks 43 required increases, reducing throughput. Also, the risk of damaging the substrate due to dense indentation during the formation of auxiliary marks 43 increases. Therefore, it is desirable that the spacing P1 between adjacent auxiliary marks 43 be 3 μm or more. Regarding the spacing P2 between the main mark 41 and the auxiliary marks 43 adjacent to the main mark 41, if it is too narrow, there is a risk of damaging the main mark 41 due to misalignment during indentation. Therefore, it is desirable that it be 3 μm or more.

[0048] The auxiliary mark 43 is a component of the auxiliary mark group 42 that serves as a marker for the main mark 41, and is a recess that can be formed, for example, by an indentation method using a micro-indenter. In Figure 1, the auxiliary mark 43 is formed by penetrating the absorber film 30 and a portion of the multilayer reflective film 20, but the layer on which the auxiliary mark 43 is formed is not particularly limited. It may be formed in the same layer as the main mark 41, or in a different layer. It may also be formed across multiple layers. However, when forming the auxiliary mark 43 on the substrate 10, the multilayer reflective film 20, or the protective film, film deposition is required after the formation of the auxiliary mark 43. Therefore, if a defect occurs during the process of forming the auxiliary mark 43, it may become a defect in the film that cannot be removed by washing. For this reason, it is desirable to form the auxiliary mark 43 after the absorption film deposition. Furthermore, it is preferable to form the auxiliary mark 43 after the main mark 41 has been formed. This allows the auxiliary mark 43 to be formed using the main mark 41 as a guide, eliminating the need to require excessive machining positional accuracy from the device that forms the auxiliary mark 43.

[0049] Furthermore, as shown in Figure 3, all of the auxiliary marks 43 constituting the auxiliary mark group 42 are formed with the same shape and orientation. With such auxiliary marks 43, for example, when forming them using an indentation method with a micro-indenter, they can be formed by only the parallel movement of the substrate or the micro-indenter, without rotating the micro-indenter. Therefore, a complex mechanism is not required, and there is no need to provide extra drive parts on the substrate, resulting in a low risk of dust generation. Consequently, a low-cost, low-defect reflective mask blank is produced that is free from dust and other contaminants.

[0050] Furthermore, while examples of the shape of the auxiliary mark 43 are shown in Figure 5, the shape of the auxiliary mark 43 in this invention is not limited to these. Four patterns are shown, with the upper row showing the oblique view of each pattern and the lower row showing the plan view of each pattern. These also serve as examples of the shapes of the micro-indenter (especially its tip) used to form the auxiliary mark 43. The two on the left are inverted conical shapes (the left one is a cone, the right one is a square pyramid). The third from the left is an inverted hipped roof shape. The last one is an inverted truncated square pyramid shape. It is preferable that auxiliary mark 43 be an inverted shape of this type of recess.

[0051] Furthermore, a more preferred form of auxiliary mark 43 is a recess formed by inverting a cone shape with a vertex angle of 55 degrees or more, a recess formed by inverting a hip roof shape with a ridge length of 50 μm or less, or a recess formed by inverting a truncated square pyramid with the longest side of the upper surface of 50 μm or less. This is because it is a shape that can be formed relatively easily and with high reproducibility. A more detailed explanation of this point will be given later.

[0052] Next, the method for manufacturing the reflective mask blank of the present invention will be described. The main steps include, at a minimum, forming a multilayer reflective film 20 on a substrate 10, and forming an absorber film 30 on the multilayer reflective film 20. If necessary, other functional layers such as the aforementioned 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; for example, they can be formed using the aforementioned materials in the same manner as conventional methods (such as sputtering).

[0053] Furthermore, the process includes forming a reference mark 40 (main mark 41 and auxiliary mark group 42) on the same side as the multilayer reflective film 20. Furthermore, as mentioned above, the main mark 41 is preferably formed on the substrate 10, the multilayer reflective film 20, or the protective film. After the substrate is prepared or these films are formed, it can be formed with high precision, for example, by FIB processing or lithography.

[0054] Furthermore, as mentioned above, the auxiliary mark group 42 (multiple auxiliary marks 43) is preferably formed after the absorbent membrane 30 is formed, and in the manufacturing method of the present invention, it is formed by an indentation method using a micro-indenter. At this time, multiple auxiliary marks 43 are formed with the same shape and orientation, spaced apart from each other so as to extend in at least one direction from the main mark 41. The auxiliary mark group 42 is formed by forming multiple auxiliary marks 43 in this way. Because this method involves forming the auxiliary mark group 42 using an indentation method with a micro-indenter, it can be performed at low cost. Furthermore, there is no need to rotate the micro-indenter when forming the auxiliary marks 43, as in conventional methods. Therefore, it can be easily implemented with a relatively simple mechanism, such as one that moves the micro-indenter or the substrate in parallel. In addition, the risk of dust generation caused by drive mechanisms that rotate the micro-indenter can be prevented, and reflective mask blanks can be manufactured with low defects.

[0055] The material that makes up the tip of the micro-indenter that forms the auxiliary mark 43 is not particularly limited, but durable hard materials such as diamond or sapphire are desirable. Although the tip shape of the micro-indenter for forming the auxiliary mark 43 is not particularly limited, in order to stabilize the indentation shape, it is desirable to use a structure in which a cone shape (such as a cone or a square pyramid) is inverted, or a hipped roof shape is inverted, or a truncated square pyramid is inverted, and its vertex, edge, or face is pressed against the substrate, as shown in Figure 5. More preferably, an inverted cone shape with an angle of 55 degrees or more, an inverted hip roof shape with a ridge length of 50 μm or less, or an inverted truncated square pyramid with a long side of the top surface of 50 μm or less should be used. This point will be explained in detail below.

[0056] Figure 6 is a schematic diagram showing the cross-sectional shape of the auxiliary mark at the A-A' cross-section when using the conical micro-indenter shown in Figure 5, and the substrate surface when the substrate is tilted. When the tip of the micro-indenter is conical, consider the change in the shape of the auxiliary mark when the substrate is tilted relative to the indentation direction due to improper mounting of the micro-indenter or improper placement of the substrate, as shown in Figure 6. θ: Angle at the tip of the micro-indenter (apex angle) h1: Depth of auxiliary marks when the circuit board is not tilted h2: Depth of auxiliary marks when the circuit board is tilted L5: Length of auxiliary marks in plan view r: Ratio of h1 to L5 (L5 / h1) α: Tilt of the substrate surface h2 / h1: Rate of variation of the depth of the auxiliary mark due to variations in θ, r, and α. Here, h2 / h1 is expressed by the following equation 1, and the calculation result is shown in Table 1. h2 / h1=cos(θ / 2+α) / cos(θ / 2)…(Equation 1)

[0057] [Table 1]

[0058] It can be seen that the variation in the depth of the auxiliary mark (h2 / h1) is gradual with respect to the variation in α. In other words, it can be seen that the shape of the auxiliary mark is stabilized by making the tip shape of the microindenter a cone. Here, the length L5 of the auxiliary mark in plan view should preferably be 500 nm or more, as visibility will be poor if it is too small. On the other hand, considering substrate regeneration, it is desirable to keep the depth of the auxiliary mark to about the thickness of the film to suppress damage to the substrate, and therefore it is desirable to keep it below 500 nm. In order to satisfy h1 ≤ 500 nm and L5 ≥ 500 nm, it is necessary to set r ≥ 1, and for that purpose, it is desirable to set θ to 55 degrees or more, as shown in Table 1. Furthermore, with such a θ, it is possible to prevent deterioration of durability due to the tip shape of the micro-indenter becoming too thin and to reduce the risk of dust generation due to damage to the micro-indenter when making an impact.

[0059] On the other hand, Figure 7 is a schematic diagram showing the cross-sectional shape of the auxiliary mark at the B-B' cross-section when using the hip-shaped micro-indenter shown in Figure 5, and the substrate surface when the substrate is tilted. When the tip of the micro-indenter is hip-shaped or truncated square pyramid-shaped, pressing its edge or face against the substrate, we consider the change in the shape of the auxiliary mark when the substrate is tilted relative to the indentation direction due to improper mounting of the micro-indenter or improper placement of the substrate, as shown in Figure 7. h1: Depth of auxiliary marks when the circuit board is not tilted h2: The shallower depth of the auxiliary mark when the circuit board is tilted. L5: Length of the base of the auxiliary mark (length of the ridge) r: Ratio of h1 to L5 (L5 / h1) α: Tilt of the substrate surface h2 / h1: Rate of change in depth at both ends of the auxiliary mark due to variations in r and α. Here, h2 / h1 is expressed by the following equation 2, and the calculation result is shown in Table 2. h2 / h1=1-rtanα …(Equation 2)

[0060] [Table 2]

[0061] Compared to the conical shape shown in Table 1, in the hipped shape, as r increases, the variation in the ratio of depth at both ends of the indentation shape with increasing α becomes larger. This indicates that when the length L5 is long relative to the depth h1 of the auxiliary mark, the shape of the auxiliary mark changes due to even a slight inclination of the substrate surface. Considering substrate regeneration, it is desirable to minimize substrate damage by limiting the depth of the auxiliary marks to, for example, the film thickness, and preferably to 500 nm or less. Furthermore, in order to allow a substrate surface inclination α of up to 1 mrad and keep the variation rate h2 / h1 of the depth at both ends of the auxiliary marks within 10%, it is necessary to set r ≤ 100, as shown in Table 2. If h1 ≤ 500 nm, it is desirable that the length of the surface or edge (ridge length) of the micro-indenter pressed against the substrate be 50 μm or less.

[0062] Furthermore, when using a truncated square pyramidal micro-indenter, the considerations are almost the same as for the hipped type. When h1 ≤ 500 nm, it is desirable that the length of the surface or side (the longest side of the top surface) that presses the micro-indenter against the substrate be 50 μm or less. Furthermore, as can be seen from Tables 1 and 2, using a conical microindenter is preferable from the viewpoint of stability of auxiliary mark reproduction (shape stability) because the variation in the depth of the auxiliary mark (h2 / h1) is more gradual with respect to the variation in α compared to using a hipped or truncated square-pronged microindenter. The shape of the micro-indenter described above (especially the cone shape) is preferable because it eliminates the need for high precision when setting up the substrate or attaching the micro-indenter to the mechanism used in the indentation method.

[0063] Here, we will explain again the significance of forming the auxiliary mark group 42. The reference mark 40 can be located using a defect inspection machine (e.g., Lasertec's MAGICS series), a coordinate measuring instrument (e.g., KLA-Tencor's LMS IPRO series), or an electron beam lithography machine (e.g., Nuflare's MBM series). However, if the difference in coordinate systems between the device that creates the main mark 41 and the detector mentioned above is known in advance, the reference mark 40 can be detected relatively easily by inspecting a position that is offset from the design position of the main mark 41 by the amount of the coordinate system difference. In this case, the auxiliary mark group 42 is not necessarily required, and detection is possible with the main mark 41 alone.

[0064] However, it is not always easy for a mask shop to accurately determine the difference between the coordinate system of the device that forms the main mark 41, which is formed by the blank maker, and the coordinate system of the inspection and drawing machines that the mask shop owns. In such cases, the mask shop will use the auxiliary mark group 42 as a clue to find the main mark 41.

[0065] Furthermore, when forming the auxiliary mark 43, it is also possible to utilize the indentation function using a micro-indenter mounted on the defect inspection machine. In this case, it becomes unnecessary to introduce new equipment for forming the auxiliary mark 43, thus reducing costs. [Examples]

[0066] The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited to these examples. (Example 1) A multilayer reflective film 20 was deposited on a substrate 10 made of quartz glass measuring 152 mm square and 6.35 mm thick by DC pulsed magnetron sputtering, using a molybdenum (Mo) target and a silicon (Si) target. The two targets were positioned opposite the main surface of the substrate 10, and the substrate 10 was rotated. The substrate 10 was placed in a sputtering apparatus that can accommodate two targets and can discharge one or both targets simultaneously, with each target mounted on it. First, power was applied to the silicon (Si) target while argon (Ar) gas flowed through the chamber to form a silicon (Si) layer with a thickness of 4 nm, and then the power application to the silicon (Si) target was stopped. Next, power was applied to the molybdenum (Mo) target while argon (Ar) gas flowed through the chamber to form a molybdenum (Mo) layer with a thickness of 3 nm, and then the power application to the molybdenum (Mo) target was stopped. The process of forming these silicon (Si) and molybdenum (Mo) layers constitutes one cycle, and this process was repeated 40 times to produce a multilayer reflective film 20.

[0067] Next, a protective film in contact with the multilayer reflective film 20 was deposited on the multilayer reflective film 20 by DC pulsed magnetron sputtering, using a Ru target, with the Ru target and the main surface of the substrate 10 facing each other, while the substrate 10 was rotated.

[0068] Next, by irradiating a predetermined area of ​​the protective film with FIB, the entire protective film and a portion of the multilayer reflective film 20 in the irradiated area were removed, forming a main mark 41 that was cross-shaped with a width of 1 μm and a length of 5 μm in a plan view. At this time, the FIB current value was approximately 50 pA. Observation by atomic force microscope (AFM) revealed that the depth of the main mark 41 was 100 nm.

[0069] Next, the protective film surface was inspected using a defect inspection machine. This defect inspection yielded Map 1, which includes information on the location of the main mark 41 and the location of defects on the protective film surface. Because the difference between the coordinate system of the FIB that formed the main mark 41 and the coordinate system of the defect inspection machine was known in advance, the main mark 41 could be easily detected by targeting a position where the mark search position was shifted from the design position by the amount of the coordinate system difference. On the other hand, when attempting to detect the mark using the machining coordinates in the FIB coordinate system as the target without considering the difference between the coordinate system of the FIB and the defect inspection machine, the main mark 41 could not be detected within the field of view of the defect inspection machine. As a result, the main mark was detected by searching the surrounding area in a spiral manner, which took longer to detect the main mark 41 compared to when the coordinate system difference was corrected.

[0070] Next, using a Ta target, the Ta target and the main surface of the substrate 10 were placed opposite each other on the protective film, and while the substrate 10 was rotating, an absorber film 30 in contact with the protective film was deposited by DC pulsed magnetron sputtering.

[0071] Next, the surface of the absorber film 30 was inspected using a defect inspection machine. This defect inspection yielded Map 2, which includes information on the location of the main mark 41 and the location of defects on the surface of the absorber film 30. Because the difference between the coordinate system of the FIB that formed the main mark 41 and the coordinate system of the defect inspection machine was known in advance, the main mark 41 could be easily detected by shifting the mark search position relative to the design position by the amount of the coordinate system difference. On the other hand, when attempting to detect the mark using the machining coordinates in the FIB coordinate system as the target without considering the difference between the coordinate system of the FIB and the defect inspection machine, the main mark 41 could not be detected within the field of view of the defect inspection machine. As a result, the main mark was detected by searching the periphery in a spiral manner, which took longer to detect the main mark 41 compared to when the coordinate system difference was corrected.

[0072] Next, a hard mask film in contact with the absorber film 30 was formed on the absorber film 30 using a Cr target, with the Cr target facing the main surface of the substrate 10, and while the substrate 10 was rotating, by DC pulsed magnetron sputtering, thereby creating an EUV reflective mask blank.

[0073] Next, using a micro-indenter with a square pyramidal tip and a 136-degree angle at the tip, multiple auxiliary marks 43 were formed around the main mark 41 transferred to the hard mask film by indentation, thereby forming the group of auxiliary marks 42. During this process, by repeatedly indenting and moving the stage on which the substrate was placed, 10 auxiliary marks 43 (each approximately 5 μm square in size in plan view) were formed on all sides of the main mark, above, below, and to the left and right. The distance P1 between adjacent auxiliary marks 43 was set to 10 μm, and as a result, the size L3 of the group of auxiliary marks 42 was pre-designed to be approximately 140 μm.

[0074] Next, the surface of the hard mask film was inspected using a defect inspection machine. This defect inspection yielded a map 3 containing information on the location of the main mark 41 and the location of defects on the hard mask film surface. Because the difference between the coordinate system of the FIB on which the main mark 41 was formed and the coordinate system of the defect inspection machine was known in advance, the main mark 41 could be easily detected by shifting the mark search position relative to the design position by the amount of the coordinate system difference. On the other hand, when attempting to detect marks using the machining coordinates in the FIB coordinate system as a target without considering the difference between the coordinate system of the FIB and the defect inspection machine, the main mark 41 could not be detected within the field of view of the defect inspection machine, but the auxiliary mark group 42 could be detected. Using the auxiliary mark group 42 as a clue, the main mark 41 could be detected relatively easily.

[0075] The created reference marks 40 were observed using a SEM. When attempting to detect marks using the machining coordinates in the FIB coordinate system as a target, without considering the difference between the FIB coordinate system and the SEM coordinate system, a group of auxiliary marks 42 was confirmed within the SEM's field of view. Furthermore, using the auxiliary mark group 42 as a clue, the center of the reference mark 40 was observed at increased magnification, confirming the presence of the main mark 41. Ten auxiliary marks 43 were found on each of the top, bottom, left, and right sides of the main mark 41, each measuring approximately 5 μm square in plan view, confirming that the shape was formed with good reproducibility. In addition, the auxiliary mark group 42 measured approximately 140 μm, confirming that it was shaped as designed.

[0076] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0077] 1...Reflective mask blank of the present invention, 10...Substrate, 20...Multilayer reflective film, 21…A layer with a relatively high refractive index for EUV light (Si layer), 22…A layer with a relatively low refractive index to EUV light (Mo layer or Ru layer), 25...Laminated section (Si / Mo laminated section or Si / Ru laminated section), 30... Absorbent membrane, 40... Reference mark, 41... Main mark, 42, 42a, 42b, 42c, 42d... group of auxiliary marks, 43... auxiliary mark.

Claims

1. circuit board and A multilayer reflective film is provided on the substrate and reflects exposure light, An absorber film provided on the multilayer reflective film, which absorbs the exposure light, A reflective mask blank comprising at least the following: The reflective mask blank is provided with a reference mark formed on the same side as the multilayer reflective film, The reference mark consists of a main mark that serves as the reference position for the defect location, and a group of auxiliary marks arranged around the main mark. The group of auxiliary marks consists of a plurality of auxiliary marks that are spaced apart from each other and extend in at least one direction from the main mark, A reflective mask blank characterized in that the multiple auxiliary marks are all formed in the same shape and orientation.

2. The aforementioned auxiliary mark is, The reflective mask blank according to claim 1, characterized in that it is a recess formed by inverting a cone shape with a vertex angle of 55 degrees or more, a recess formed by inverting a hip roof shape with a ridge length of 50 μm or less, or a recess formed by inverting a truncated square pyramid with the longest side of the upper surface of 50 μm or less.

3. The reflective mask blank according to claim 1 or 2, characterized in that the auxiliary marks are formed on the same layer as the main marks, or on a layer above the layer on which the main marks are formed.

4. A process of forming a multilayer reflective film that reflects exposure light on a substrate, A step of forming an absorber film that absorbs the exposure light on the multilayer reflective film, A method for manufacturing a reflective mask blank having at least the following: The process includes forming a reference mark on the same side of the reflective mask blank as the multilayer reflective film, the reference mark consisting of a main mark which serves as a reference position for defect locations and a group of auxiliary marks arranged around the main mark. A method for manufacturing a reflective mask blank, characterized in that when forming the auxiliary mark group from the reference marks, a plurality of auxiliary marks are formed by an indentation method using a micro-indenter, with spacing between them so that they extend in at least one direction from the main mark, and all of them are the same shape and orientation, thereby forming the auxiliary mark group consisting of the plurality of auxiliary marks.

5. As the aforementioned micro-indenter, The method for manufacturing a reflective mask blank according to claim 4, characterized in that it uses an inverted cone shape with a vertex angle of 55 degrees or more, an inverted hip roof shape with a ridge length of 50 μm or less, or an inverted truncated square pyramid with the longest side of the top surface of 50 μm or less.

6. The method for manufacturing a reflective mask blank according to claim 4, characterized in that the main mark is formed by FIB processing.

7. The method for manufacturing a reflective mask blank according to claim 5, characterized in that the main mark is formed by FIB processing.

8. A method for manufacturing a reflective mask blank according to any one of claims 4 to 7, characterized in that when forming the auxiliary marks, a defect inspection machine equipped with the micro-indenter is used.

9. A method for manufacturing a reflective mask blank according to any one of claims 4 to 7, characterized in that the auxiliary marks are formed after the main marks are formed.

10. The method for manufacturing a reflective mask blank according to claim 8, characterized in that the auxiliary marks are formed after the main marks are formed.

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