Reflective mask blank and method of manufacturing the same

Abstract

To provide a reflective mask blank in which a reference mark can be formed at a relatively low cost with high throughput and the accuracy of position detection by a detector can be improved, and to provide a method for manufacturing the reflective mask blank.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 further comprising a fiducial mark serving as a reference position for detecting a defect position, the fiducial mark being formed on a surface of the reflective mask blank on the same side as the multilayer reflective film, the fiducial mark including at least two parallel line segment pairs each including two concave or convex parallel line segments, the directions of the two sets of parallel line segment pairs are at positions orthogonal to each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a reflective mask blank used in the manufacture of semiconductor devices and the like, and a method for manufacturing the same. [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] Patent No. 5910625 specification [Non-patent literature]

[0008] [Non-Patent Document 1] SEMI P48-1110 (Reapproved 0416) - Specification of Fiducial Marks for EUV Mask Blank Summary of the Invention [Problem to be solved by the invention]

[0009] Non-Patent Document 1 proposes a fiducial mark design combining four large crosses, each 550 μm long and 4-8 μm wide, and seven small crosses, each 100 μm long and 4-8 μm wide. Patent Document 1 also describes that a focused ion beam (FIB) method (hereinafter referred to as FIB) or a lithography method using resist patterning and etching are suitable methods for forming the fiducial mark (paragraph

[0073] ). However, lithography requires the introduction of numerous devices, such as a coater, a lithography machine, a developer, and an etcher, resulting in high introduction costs. Furthermore, FIB processing speeds are slow, making it difficult to create fiducial marks such as those shown in Non-Patent Document 1 at a relatively low cost and with high throughput. Furthermore, narrowing the width of the fiducial mark to shorten processing time poses a problem, such as a deterioration in the positional accuracy of the detector.

[0010] The present invention has been made to solve the above-mentioned problems, and aims to provide a reflective mask blank and a manufacturing method thereof that can produce reference marks relatively inexpensively and with high throughput, and that can improve the accuracy of position detection by a detector. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides a reflective mask blank, comprising: 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; At least a reference mark serving as a reference position for detecting a defect position, which is formed on the same surface of the reflective mask blank as the multilayer reflective film, The reference mark has at least two pairs of parallel line segments each consisting of two parallel line segments having a concave or convex shape, and the directions of the two pairs of parallel line segments are positioned so as to be perpendicular to each other.

[0012] The reflective mask blank of the present invention allows fiducial marks to be produced relatively inexpensively and with high throughput. Furthermore, the reflective mask blank of the present invention allows the detection accuracy of the fiducial marks by a detector to be improved.

[0013] The width of each of the line segments constituting the parallel line segment pair is, for example, 1 μm or less.

[0014] The width of each line segment constituting the parallel line segment pair is not particularly limited, but can be, for example, 1 μm or less. By limiting the width of each line segment constituting the parallel line segment pair in this way, the time required to form the fiducial mark can be reduced.

[0015] In addition, the present invention also provides a method for manufacturing a photosensitive layer, comprising the steps of: 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 detecting a defect position on a surface of the reflective mask blank on the same side as the multilayer reflective film, In the step of forming the reference mark, The present invention provides a method for manufacturing a reflective mask blank, characterized in that the reference mark has at least two pairs of parallel line segments each consisting of two parallel line segments having a concave or convex shape, and is formed so that the directions of the two pairs of parallel line segments are orthogonal to each other.

[0016] The method for manufacturing a reflective mask blank of the present invention can provide a reflective mask blank in which a fiducial mark is manufactured relatively inexpensively and with high throughput.Furthermore, the method for manufacturing a reflective mask blank of the present invention can provide a reflective mask blank equipped with a fiducial mark that can improve the detection position accuracy of the fiducial mark by a detector.

[0017] For example, the reference mark may be formed so that the width of each line segment constituting the pair of parallel line segments is 1 μm or less.

[0018] The width of each line segment constituting the parallel line segment pair is not particularly limited, but can be, for example, 1 μm or less. By limiting the width of each line segment constituting the parallel line segment pair in this way, the time required to form the fiducial mark can be reduced.

[0019] In the step of forming the reference mark, the reference mark can be formed by FIB processing.

[0020] In this way, the fiducial marks and the fiducial mark forming areas can be formed with high precision and at relatively low cost. [Effects of the Invention]

[0021] According to the reflective mask blank of the present invention, the reference marks can be produced relatively inexpensively and with high throughput, and the accuracy with which the detector detects the positions of the reference marks can be improved.

[0022] Furthermore, the method for manufacturing a reflective mask blank of the present invention can provide a reflective mask blank in which a fiducial mark is manufactured relatively inexpensively and with high throughput.Furthermore, the method for manufacturing a reflective mask blank of the present invention can provide a reflective mask blank equipped with a fiducial mark that can improve the detection position accuracy of the fiducial mark by a detector. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 2 is a schematic cross-sectional view of an example of the reflective mask blank of the present invention, in which the reference mark is recessed. [Figure 2] FIG. 2 is a plan view schematically illustrating an example of the arrangement of reference marks on a reflective mask blank of the present invention. [Figure 3] 3A to 3C are schematic diagrams showing examples of the planar shapes of reference marks according to the present invention. [Figure 4] 4A and 4B are schematic cross-sectional views taken along the line AA' in FIG. 3A when the fiducial mark of the present invention is concave and when it is convex. DETAILED DESCRIPTION OF THE INVENTION

[0024] As mentioned above, there has been a need for a technology that can process fiducial marks for reflective mask blanks inexpensively and with high throughput, as well as a technology that can improve the accuracy of fiducial mark position detection by a detector.

[0025] 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) having a reference mark that serves as a reference position for detecting defect positions, formed on the same surface as the multilayer reflective film, and the reference mark has at least two pairs of parallel line segments consisting of two parallel line segments, and is formed so that the directions of the two pairs of parallel line segments are orthogonal to each other, can form a reference mark relatively inexpensively and with high throughput, and can further improve the detection position accuracy of the reference mark by a detector, thereby achieving the present invention.

[0026] 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 on the same surface of the reflective mask blank as the multilayer reflective film, and that in this step the reference mark has at least two pairs of parallel line segments consisting of two parallel line segments, and the directions of the two pairs of parallel line segments are orthogonal to each other, thereby making it possible to form the reference mark relatively inexpensively and with high throughput, and further to manufacture a reflective mask blank with a reference mark, which can improve the detection position accuracy of the reference mark by a detector, and have completed the present invention.

[0027] That is, the present invention is a reflective mask blank, 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; At least a reference mark serving as a reference position for detecting a defect position, which is formed on the same surface of the reflective mask blank as the multilayer reflective film, The reference mark is a reflective mask blank characterized in that it has at least two pairs of parallel line segments each consisting of two parallel line segments of a concave or convex shape, and the directions of the two pairs of parallel line segments are positioned so as to be perpendicular to each other.

[0028] The present invention also provides a method for manufacturing a photolithography system, comprising the steps of: 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 detecting a defect position on a surface of the reflective mask blank on the same side as the multilayer reflective film, In the step of forming the reference mark, This is a method for manufacturing a reflective mask blank, characterized in that the reference mark has at least two pairs of parallel line segments each consisting of two parallel line segments having a concave or convex shape, and is formed so that the directions of the two pairs of parallel line segments are positioned perpendicular to each other.

[0029] The present invention will be described in detail below, but the present invention is not limited thereto.

[0030] [Reflective mask blank] First, the reflective mask blank of the present invention will be described. Fig. 1 shows a schematic cross-sectional view of one example of a reflective mask blank according to the present invention. Note that, although a reflective mask blank for EUV will be described below as an example, the reflective mask blank of the present invention is not limited thereto.

[0031] In FIG. 1, the reflective mask blank 1 first comprises a substrate 10, a multilayer reflective film 20 provided on the surface of the substrate 10 and reflecting exposure light, and an absorber film 30 provided on the multilayer reflective film 20 and absorbing the exposure light, and further comprises a reference mark 40 (which serves as a reference position for defect positions) formed on the surface of the reflective mask blank.

[0032] Although not shown in FIG. 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 a pattern is formed on the absorber film 30. 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. A conductive film may be provided on the back surface of the substrate 10 to function as an antistatic layer during electrostatic chucking. Other functional layers may also be provided.

[0033] Each part will be described below using the embodiment in FIG. 1 as an example, but the present invention is not limited to this.

[0034] 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.

[0035] 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.

[0036] The multilayer reflective film 20 can be formed by, for example, ion beam sputtering or magnetron sputtering.

[0037] 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).

[0038] 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.

[0039] 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.

[0040] 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.

[0041] The absorber film 30 can be formed by, for example, ion beam sputtering or magnetron sputtering.

[0042] 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.

[0043] The protective film can be formed by, for example, ion beam sputtering or magnetron sputtering.

[0044] 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.

[0045] 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.

[0046] The hard mask film can be formed by, for example, magnetron sputtering.

[0047] The thickness of the hard mask film is not particularly limited, but is usually about 5 to 20 nm.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The conductive film can be formed by, for example, ion beam sputtering or magnetron sputtering.

[0052] 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.

[0053] Next, the reference mark 40 will be described.

[0054] The fiducial mark 40 is formed on the same surface as the multilayer reflective film 30 of the reflective mask blank 10. The fiducial mark 40 is a mark that serves as a reference position for detecting the position of a defect.

[0055] FIG. 2 shows an example of the arrangement of fiducial marks 40 on a reflective mask blank. Note that FIG. 2 is simplified for the purpose of explaining the arrangement, but in reality, as will be explained later with reference to FIG. 3, the fiducial marks 40 have at least two pairs of parallel line segments. In the example shown in FIG. 2, the fiducial marks 40 are arranged at each of the four corners on the same side of the reflective mask blank 1 as the multilayer reflective film 20. In the present invention, it is preferable that three or more fiducial marks 40 are formed so that they are not aligned in the same line. However, in the present invention, 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] 3 shows five examples of the shape of fiducial mark 40 in a plan view according to the present invention, but the shape of the fiducial mark in the present invention is not limited to these. In all examples, fiducial mark 40 has at least two pairs of parallel line segments 41-a and 41-b, each consisting of two parallel line segments with a concave or convex shape, and the directions of the two pairs of parallel line segments 41-a and 41-b are positioned at right angles to each other.

[0057] 3(a), the reference mark 40 is composed of two pairs of parallel line segments 41-a and 41-b whose directions are perpendicular to each other, and each pair of parallel line segments is composed of two parallel line segments. The directions Da and Db of the two pairs of parallel line segments 41-a and 41-b are perpendicular to each other.

[0058] The concave and convex shapes of the parallel line segments constituting the fiducial mark 40 are not particularly limited and may be either convex or concave. Figure 4 shows cross-sectional views of the fiducial mark 40 shown in Figure 3(a) along the A-A' cross section, respectively, for concave and convex shapes. For concave shapes, methods for forming the fiducial mark 40 include laser thermal processing or ablation, indentation using a microindenter, lithography, and FIB. For convex shapes, methods for forming the fiducial mark 40 include inkjet printing and the deposition function of FIB. Because the fiducial mark 40 serves as a reference for detecting defect locations, it is desirable to form it using FIB, which enables high-precision processing. In FIB, FIB irradiation of a target area etches the irradiated area, resulting in a concave shape. Alternatively, FIB irradiation while spraying a compound gas onto the sample surface during FIB irradiation allows selective deposition of the irradiated area, resulting in a convex shape. The former is called the FIB etching function, and the latter is called the FIB deposition function.

[0059] 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.

[0060] The shape of the fiducial mark 40 in the present invention is not particularly limited. For example, as shown in Fig. 3(a), two pairs of parallel line segments 41-a and 41-b, whose directions Da and Db are orthogonal to each other, can be arranged to intersect with each other to form a cross shape. In this way, even if the width of the cross is increased, the area to be machined does not change, and it is possible to reduce the machining time compared to when the inside of the cross is filled in.

[0061] The distance L2 between the two parallel line segments that make up each of the parallel line segment pairs 41-a and 41-b is preferably 300 nm or more and 10 μm or less.

[0062] As a variant, the shape of the reference mark 40 may be arranged to form (part of) the outline of a cross shape using four pairs of parallel lines: two pairs of parallel lines 41-a and 41-b whose directions Da and Db are perpendicular to each other, and two pairs of parallel lines 41-c and 41-d whose directions Dc and Dd are perpendicular to each other, as shown in Figures 3(b) and 3(c).

[0063] Alternatively, as shown in Fig. 3(d), two pairs of parallel line segments 41-a and 41-b whose directions Da and Db are perpendicular to each other may be arranged so as not to intersect. In other words, in the present invention, the two pairs of parallel line segments 41-a and 41-b themselves do not necessarily need to intersect each other at right angles, as long as the directions Da and Db of the two pairs of parallel line segments 41-a and 41-b are positioned so as to intersect each other at right angles.

[0064] As yet another modification, as shown in FIG. 3(e), the end points of two pairs of parallel line segments 41-a and 41-b, whose directions Da and Db are perpendicular to each other, may be overlapped to form a rectangle.

[0065] Furthermore, if the fiducial mark 40 is recessed, its depth is preferably 40 nm or more. This ensures sufficient contrast with the surroundings when the inspection machine searches for the fiducial mark 40, preventing a deterioration in detection position accuracy. On the other hand, if the fiducial mark 40 is formed using the etching function of the FIB, the depth is preferably 150 nm or less. This allows the FIB processing time to be kept appropriate, achieving sufficient throughput.

[0066] Since the contrast during detection is improved by making the sidewall angle of the fiducial mark 40 steeper in the cross-sectional shape, when forming the fiducial mark 40 using the etching function of the FIB, the current value is preferably 100 pA or less.

[0067] Furthermore, if the fiducial mark 40 is convex, its height is preferably 40 nm or more. This ensures sufficient contrast with the surroundings when the inspection machine searches for the fiducial mark 40, preventing a deterioration in detection position accuracy. On the other hand, if the fiducial mark 40 is formed using the deposition function of the FIB, its height is preferably 150 nm or less. This prevents pattern collapse due to a large aspect ratio of the fiducial mark 40, and also keeps the FIB processing time reasonable, achieving sufficient throughput.

[0068] The width L1 of each line segment constituting the parallel line segment pairs 41-a to 41-b (the dimension parallel to the direction perpendicular to each of the directions Da to Db) is not particularly limited, but can be, for example, 1 μm or less. By limiting the width of each line segment constituting the parallel line segment pair in this way, the time required to form the reference mark can be reduced. Note that when the sidewall is tapered, the width of the line segment is defined by the full width at half maximum in the cross-sectional profile.

[0069] The length of each of the line segments constituting the parallel line segment pairs 41-a to 41-b (the dimension parallel to each of the directions Da to Db) is not particularly limited, but is preferably 5 μm or more and 1 mm or less.

[0070] An example of the procedure for detecting the reference mark 40 by the detector will be described below using FIG. 3(a) as an example.

[0071] Step 1: Scanning a light beam or an electron beam in a direction perpendicular to the two parallel line segments that make up the first parallel line segment pair 41-a; Step 2: A straight line Da passing through the centers of the two parallel line segments constituting the parallel line segment pair 41-a is obtained from the luminance profile of the reflected light. Step 3: Scanning a light beam or an electron beam in a direction perpendicular to the direction of the first parallel line segment pair 41-a and the two parallel line segments constituting the second orthogonal line segment pair 41-b, which are perpendicular to the direction of the first parallel line segment pair 41-a; Step 4: A straight line Db passing through the centers of the two parallel line segments constituting the parallel line segment pair 41-b is obtained from the luminance profile of the reflected light. Step 5: The intersection of the two straight lines Da and Db in steps 2 and 4 is taken as the coordinate of the reference mark 40.

[0072] By using such a procedure, the accuracy of the detected position is improved compared to when the intersection of the line segments is simply used as the coordinate of the reference mark 40. The reason for this will be explained below.

[0073] Consider two lines, X=X1 and X=X2, parallel to the Y axis. If the detection position accuracy of the X coordinate of each line by a detector follows mutually independent normal distributions with a standard deviation σ, the detection position accuracy of the average X coordinate of the two lines, (X1+X2) / 2, is expressed as σ / √2, which is improved compared to detecting a single line. Based on this principle, by using the intersection of the center lines of the two parallel line segments that make up parallel line segment pair 41-a and 41-b as the coordinates of fiducial mark 40, it is expected that the detection position accuracy will be improved compared to simply using the intersection of the line segments as the coordinates of fiducial mark 40.

[0074] [Method of manufacturing reflective mask blanks] Next, a manufacturing method of the present invention for manufacturing a reflective mask blank of the present invention as shown in FIG. 1 will be described.

[0075] The manufacturing method of the present invention mainly comprises at least the steps of 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 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).

[0076] The manufacturing method of the present invention further includes a step of forming a fiducial mark 40 on the surface on the same side as the multilayer reflective film 20 .

[0077] More specifically, the reference mark 40 has at least two pairs of parallel line segments each consisting of two parallel line segments of a concave or convex shape, and is formed so that the directions of the two pairs of parallel line segments are perpendicular to each other.

[0078] For further details on how fiducial marks 40 are formed, please refer to the above description.

[0079] 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 10 is prepared or after these films are formed, the fiducial mark 40 can be formed with high precision by using, for example, the etching function or deposition function of the FIB. [Example]

[0080] 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.

[0081] 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.

[0082] As preparation, each target was mounted in a sputtering apparatus capable of mounting two targets and discharging either one target at a time or both targets simultaneously, and the substrate 10 was then placed on the sputtering apparatus. In the DC pulse magnetron sputtering, power was first applied to the silicon (Si) target while argon (Ar) gas was flowing into the chamber, forming a 4 nm thick silicon (Si) layer, and then the application of power to the silicon (Si) target was stopped. Next, power was applied to the molybdenum (Mo) target while argon (Ar) gas was flowing into the chamber, forming a 3 nm thick molybdenum (Mo) layer, and then the application of power to the molybdenum (Mo) target was stopped. This process of forming the silicon (Si) layer and the molybdenum (Mo) layer constituted one cycle, and this cycle was repeated 40 times to form the multilayer reflective film 20.

[0083] Next, in order to deposit a protective film on the multilayer reflective film 20, a Ru target was used, and the Ru target was placed opposite the main surface of the substrate 10. While the substrate 10 was being rotated, a protective film in contact with the multilayer reflective film 20 was deposited by DC pulse magnetron sputtering.

[0084] Next, a predetermined portion of the protective film was irradiated with FIB to remove the entire protective film and a portion of the multilayer reflective coating 20. Two line segments, each 500 nm wide and 100 μm long in plan view, were created parallel to the Y-axis (direction Da). These two line segments were designated the first parallel line segment pair 41-a. The spacing L2 between the two line segments was 1.5 μm. Furthermore, a second parallel line segment pair 41-b, parallel to the X-axis (direction Db), was created, parallel to the first parallel line segment pair 41-a, perpendicular to the Da direction at its center. This created a cross shape, as shown in FIG. 3(a), where the Da and Db directions intersect at right angles, and served as the reference mark 40. The machining current was 500 pA, and machining each mark took approximately four minutes. When the fiducial mark 40 was observed with an atomic force microscope (AFM), the depth of the fiducial mark 40 was found to be 140 nm.

[0085] When the coordinate accuracy of each line segment constituting the fiducial mark 40 was confirmed using a Lasertec ABICS E120, the detected position accuracy (3σ) of the X-coordinate of each line segment constituting the first parallel line segment pair 41-a was 39.1 nm and 31.4 nm, respectively, and the detected position accuracy (3σ) of the X-coordinate of the line Da passing through the center of the parallel line segment pair 41-a was 28.2 nm. Meanwhile, the detected position accuracy (3σ) of the Y-coordinate of each line segment constituting the second parallel line segment pair 41-b was 27.6 nm and 22.4 nm, respectively, and the detected position accuracy (3σ) of the Y-coordinate of the line Db passing through the center of the parallel line segment pair 41-b was 20.6 nm. As mentioned above, it was confirmed that by using the intersection of the center lines of the two parallel line segments constituting the parallel line segment pair 41 as the coordinates of the fiducial mark 40, the detected position accuracy was improved compared to simply using the intersection of the line segments as the coordinates of the fiducial mark 40.

[0086] Next, in order to deposit the absorber film 30 on the protective film, a Ta target was used, the Ta target was placed opposite the main surface of the substrate 10, and the absorber film 30 in contact with the protective film was deposited by DC pulse magnetron sputtering while rotating the substrate 10. In this way, the EUV reflective mask blank 1 of Example 1 was produced.

[0087] (Comparative Example 1) As Comparative Example 1, a reflective mask blank 1 of Comparative Example 1 was produced in the same manner as in Example 1, except that the shape of the reference mark 40 in Example 1 was formed as a cross shape (filled in) with a width of 500 nm and a length of 100 μm. At this time, it took about 2 minutes to process each mark.

[0088] In the manufacturing process of the reflective mask blank 1 of Comparative Example 1, as in Example 1, before forming the absorber film, the central position accuracy (3σ) of the reference mark formed on the protective film was confirmed using ABICS E120 manufactured by Lasertec Corporation, and the X coordinate was 36.2 nm and the Y coordinate was 25.2 nm.

[0089] (Comparative Example 2) As Comparative Example 2, a reflective mask blank 1 of Comparative Example 2 was produced in the same manner as in Example 1, except that the shape of the reference mark 40 in Example 1 was formed as a cross shape (filled in) with a width of 1.5 μm and a length of 100 μm. At this time, it took about 6.5 minutes to process one mark.

[0090] To summarize the above results, in Example 1, the detected position accuracy (3σ) of the X coordinate of the straight line Da passing through the center of the parallel line segment pair 41-a was 28.2 nm, and the detected position accuracy (3σ) of the Y coordinate of the straight line Db passing through the center of the parallel line segment pair 41-b was 20.6 nm, which were smaller than the detected position accuracy (3σ) of the X coordinate of 36.2 nm and the detected position accuracy (3σ) of the Y coordinate of 25.2 nm in Comparative Example 1, and it was found that the detected position accuracy (3σ) of the X coordinate and Y coordinate was superior to that of Comparative Example 1.

[0091] On the other hand, the processing time for Example 1 was 4 minutes, whereas the processing time for Comparative Example 2 was as long as 6.5 minutes, and it is clear that Example 1 is superior to Comparative Example 2 in terms of productivity.

[0092] In other words, as is clear from the above examples and comparative examples, the reflective mask blank 1 and its manufacturing method of the present invention make it possible to produce a reference mark 40 at a relatively low cost and with a high throughput, and even if the width of the reference mark is narrowed, the reference mark 40 can be detected without significantly deteriorating the positional accuracy of the detector.

[0093] 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]

[0094] 1...reflective mask blank of the present invention, 10...substrate, 20...multilayer reflective film, 21...layer (Si layer) having a relatively high refractive index to EUV light, 22...layer (Mo layer or Ru layer) having a relatively low refractive index to EUV light, 25...laminated portion (Si / Mo laminated portion or Si / Ru laminated portion), 30...absorber film, 40...fiducial mark, 41-a, 41-b, 41-c and 41-d...parallel line segment pair, 50...main pattern forming region.

Claims

1. A reflective mask blank, 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; At least a reference mark serving as a reference position for detecting a defect position, which is formed on the same surface of the reflective mask blank as the multilayer reflective film, A reflective mask blank characterized in that the reference mark has at least two pairs of parallel line segments consisting of two parallel line segments with a concave or convex shape, and the directions of the two pairs of parallel line segments are positioned so as to be perpendicular to each other.

2. 2. The reflective mask blank according to claim 1, wherein the width of each of the line segments constituting the pair of parallel line segments is 1 μm or less.

3. 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 detecting a defect position on a surface of the reflective mask blank on the same side as the multilayer reflective film, In the step of forming the reference mark, A method for manufacturing a reflective mask blank, characterized in that the reference mark has at least two pairs of parallel line segments consisting of two parallel line segments with a concave or convex shape, and is formed so that the directions of the two pairs of parallel line segments are positioned perpendicular to each other.

4. 4. The method for manufacturing a reflective mask blank according to claim 3, wherein the reference mark is formed so that the width of each line segment constituting the pair of parallel line segments is 1 [mu]m or less.

5. 5. The method for manufacturing a reflective mask blank according to claim 3, wherein in the step of forming the fiducial marks, the fiducial marks are formed by FIB processing.

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