Method for manufacturing a reflective mask blank, reflective mask blank and method for manufacturing a reflective mask

Abstract

The present invention relates to a manufacturing method of a reflective mask blank, a reflective mask blank, and a manufacturing method of a reflective mask. Specifically, it relates to a reflective mask blank including a substrate, a multilayer reflective film for reflecting EUV light formed on one main surface of the substrate in order from the substrate side, a protective film, an absorber film for absorbing EUV light, and a conductive film. When a coordinate reference mark is formed on the other main surface of the substrate, a coordinate reference mark is formed on the other main surface.

Description

[0001] Cross Reference to Related Applications

[0002] This non-provisional application claims priority under 35 U.S.C. § 119(a) from Japanese Patent Application No. 2019-166813 filed on September 13, 2019, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to a reflective mask blank and a manufacturing method thereof, and more particularly, to a reflective mask blank suitable for manufacturing a reflective mask having reduced phase defects, and a manufacturing method thereof. The present application also relates to a method of manufacturing a reflective mask having reduced phase defects using the reflective mask blank. BACKGROUND

[0004] In the manufacturing process of a semiconductor device, an optical lithography technique is used in which a circuit pattern formed on a transfer mask is transferred onto a semiconductor substrate (semiconductor wafer) through a reduction projection optical system which illuminates the mask with exposure light. At present, the mainstream wavelength of the exposure light is 193 nm through an argon fluoride (ArF) excimer laser. By employing a process called multiple patterning combining a multiple exposure process and a multiple processing (etching) process, a pattern having a size smaller than the exposure wavelength can be finally formed.

[0005] However, since it is necessary to form a finer pattern, an EUV lithography technique using extreme ultraviolet light (hereinafter referred to as "EUV") having a shorter wavelength than the ArF excimer laser as exposure light is promising. EUV light is light having a wavelength of about 0.2 to 100 nm, and more specifically, light having a wavelength of about 13.5 nm. This EUV light has very low transmissivity to matter, and cannot be used for a conventional transmissive projection optical system or mask, and therefore, a reflective optical element is applied. Accordingly, a reflective mask is also proposed as a mask for pattern transfer. The reflective mask has a multilayer reflective film formed on a substrate and reflecting the EUV light, and a patterned absorber film formed on the multilayer reflective film and absorbing the EUV light. On the other hand, a material before the absorber film is patterned is called a reflective mask blank, and is used as a material of the reflective mask.

[0006] In the manufacturing process of the reflective mask, a pattern is formed by etching the absorber film of the reflective mask blank, and then the pattern is generally inspected. When a defect is detected, the defect is repaired. However, in the case of the reflective mask, in addition to defects derived from the absorber film and the absorber pattern in some cases, there are defects in which the reflectivity is reduced due to a structural disorder of the multilayer reflective film, i.e., so-called phase defects. Furthermore, after the absorber pattern is formed, it is difficult to directly correct the phase defects in the multilayer reflective film.

[0007] In this case, many studies have been made on techniques for detecting phase defects in a reflective mask blank. For example, JP-A 2003-114200 (Patent Document 1) discloses a technique of using a dark field inspection image as a method of detecting phase defects inside a multilayer reflective film by using EUV light. Further, JP-A H6-349715 (Patent Document 2) discloses a technique of using a bright field in an X-ray microscope as a method of detecting phase defects inside a multilayer reflective film by using EUV light. These methods accurately detect phase defects in a multilayer reflective film. In particular, in the dark field detection method using EUV light described in Patent Document 1, phase defects unique to a reflective mask blank having a multilayer reflective film can be detected as a bright point signal with high sensitivity. Therefore, this is a very effective method for determining whether phase defects exist after forming a multilayer reflective film.

[0008] On the other hand, as a method of finally completing reduction of phase defects at the manufacturing stage of a reflective mask even if phase defects remain in a reflective mask blank, for example, JP-A 2002-532738 (Patent Document 3) discloses a technique of improving a projected image in a transfer pattern with an exposure tool by modifying the profile of an absorber pattern when the absorber pattern is formed from an absorber film of a reflective mask blank in which phase defects exist without repairing the phase defects. In this method, it is necessary to accurately obtain the positions of phase defects in a multilayer reflective film based on the coordinates of the absorber pattern after forming the absorber pattern. However, it is difficult to accurately determine the positions of phase defects after forming the pattern.

[0009] Further, WO 2014 / 129527 Al (Patent Document 4) discloses a technique of patterning an absorber film by avoiding the positions of phase defects in the following manner: forming reference marks on the absorber film, obtaining the positions of phase defects in a multilayer reflective film as the positions of irregularities on the surface of the absorber film in the multilayer reflective film, and converting them into position information of the defects with respect to the reference marks, and further modifying drawing data for patterning the absorber film in accordance with the defect position information. In this method, it is not necessary to engrave reference marks into a multilayer reflective film, and therefore it is possible to reduce the risk of generation of particles due to engraving of reference marks. However, in some phase defects, there are almost no structural disorders in a multilayer reflective film that reduce reflectivity as irregularities on the surface of the multilayer reflective film. Therefore, in the inspection of an absorber film, it is difficult to accurately obtain position information of all phase defects. Therefore, a reflective mask blank obtained by this method cannot draw an absorber pattern while avoiding all relevant phase defects, and therefore this method cannot avoid phase defects with high accuracy when forming an absorber pattern.

[0010] Bibliographic list

[0011] Patent Document 1: JP-A 2003-114200

[0012] Patent Document 2: JP-A H 6-349715

[0013] Patent Document 3: JP-A 2002-532738

[0014] Patent Document 4: WO 2014 / 129527 Al

[0015] Patent Document 5: JP-A 2007-200953 SUMMARY

[0016] For example, as a method for detecting and avoiding phase defects with high precision, it is considered to provide a concave or convex mark on a substrate to be used as a reference mark for configuring a coordinate system. According to this method, a multilayer reflective film can be formed on the reference mark formed on the substrate, and the position of a phase defect in the multilayer reflective film is determined with reference to the reference mark in a subsequent phase defect inspection. Further, when an absorber film is formed on the multilayer reflective film on the reference mark, the pattern drawing position for forming an absorber pattern is determined from the position of the phase defect in the multilayer reflective film determined with reference to the reference mark, and the absorber pattern can be formed with the same reference mark while avoiding phase defects.

[0017] However, when each layer constituting the multilayer reflective film is laminated on the reference mark and an absorber film is further laminated thereon, the total thickness of the film stack generally exceeds 300 nm. In the case where the reference mark is deeply buried in the film, it is not expected to determine the position with high precision. On the other hand, the reference mark can be engraved in the multilayer reflective film after the formation of the multilayer reflective film and before the formation of the absorber film. However, it is preferable to continuously form the multilayer reflective film and the absorber film. In particular, if the reference mark is formed by engraving in the multilayer reflective film at this stage, the risk of particle defects in the resulting reflective mask blank increases.

[0018] The present application has been made to solve the above problems, and an object of the present application is to provide a reflective mask blank and a manufacturing method thereof, which can accurately grasp the positions of defects (particularly, fine defects) in a multilayer reflective film after a multilayer reflective film is formed on a substrate, and a protective film is formed on the multilayer reflective film, and which can effectively form an absorber pattern that mitigates the influence of defects in the multilayer reflective film, and highly accurately avoid defects. Further, the present application provides a method of manufacturing a reflective mask, which can effectively form an absorber pattern that mitigates the influence of defects in a multilayer reflective film, and highly accurately avoid defects from such a reflective mask blank.

[0019] To solve the above problems, the inventors have found that, for a reflective mask blank including a substrate, a multilayer reflective film for reflecting EUV light formed on one main surface of the substrate, a protective film, and an absorber film for absorbing EUV light and a conductive film formed on the other main surface of the substrate, when a coordinate reference mark is formed on the other main surface side, particularly, on the conductive film, the coordinate reference mark is not buried in a thick film formed on one main surface of the substrate, the positions of defects such as phase defects in the multilayer reflective film can be highly accurately determined.

[0020] Further, the inventors have found that, by manufacturing a reflective mask blank in which a coordinate reference mark is formed on the other main surface side in such a manner that defects in a multilayer reflective film and an absorber film are inspected once at a stage where the multilayer reflective film and the absorber film have been formed, position information of the detected defects is obtained based on coordinates defined with reference to the coordinate reference mark, and the position information is saved to a recording medium, and then, the absorber film is formed, defects in the absorber film are inspected, position information of the detected defects is obtained based on coordinates defined with reference to the coordinate reference mark, and the position information is saved to the recording medium, the positions of defects can be accurately grasped from information stored in the recording medium. Further, from the position information of defects stored in the recording medium, by effectively forming an absorber pattern that mitigates the influence of defects in the multilayer reflective film, a reflective mask can be obtained from the reflective mask blank, while highly accurately avoiding defects such as phase defects.

[0021] In one aspect, the present application provides a method of manufacturing a reflective mask blank including a substrate, and a multilayer reflective film for reflecting EUV light, a protective film, and an absorber film for absorbing EUV light, which are formed in this order on one main surface of the substrate from the substrate side, and a conductive film formed on the other main surface of the substrate, the method including the steps of:

[0022] (A1) forming a conductive film on the other main surface,

[0023] (A2) forming a coordinate reference mark on the other main surface side,

[0024] (B1) forming a multilayer reflective film and a protective film on the one main surface,

[0025] (B2) inspecting defects in the multilayer reflective film and the protective film formed in step (B1), obtaining positional information of the detected defects based on coordinates defined with reference to the coordinate reference mark, and saving the positional information to a recording medium,

[0026] (C1) forming an absorber film on the protective film after step (B2), and

[0027] (C2) inspecting defects in the absorber film formed in step (C1), obtaining positional information of the detected defects based on coordinates defined with reference to the coordinate reference mark, and saving the positional information to a recording medium.

[0028] Preferably, in step (A2), the coordinate reference mark is formed on the conductive film formed in step (Al).

[0029] Preferably, the method further comprises the step of measuring the flatness of the substrate after step (Bl) and before step (B2) and / or measuring the flatness of the substrate after step (Cl) and before step (C2).

[0030] Preferably, when a defect is detected in step (B2), step (B2) includes the step of creating a processing order of the defect, and saving the processing order to the recording medium together with the positional information, the processing order being typically a priority order of processing the defect, the priority order being determined in accordance with the printability of the detected defect.

[0031] In another aspect, the present application provides a reflective mask blank, the reflective mask blank comprising: a substrate, and a multilayer reflective film for reflecting EUV light, a protective film, and an absorber film for absorbing EUV light, formed in this order from the substrate side on one main surface of the substrate, and a conductive film formed on the other main surface of the substrate, wherein

[0032] a coordinate reference mark is formed on the conductive film.

[0033] In another aspect, the present application provides a set of a reflective mask blank and a recording medium,

[0034] As main components, the reflective mask blank comprises: a substrate, and a multilayer reflective film for reflecting EUV light, a protective film, and an absorber film for absorbing EUV light, formed in this order from the substrate side on one main surface of the substrate, and a conductive film formed on the other main surface of the substrate, and a coordinate reference mark is formed on the conductive film.

[0035] The recording medium records position information of the defects based on the coordinates defined with reference to the coordinate reference marks.

[0036] Preferably, the recording medium further records a priority order for processing the defects, the priority order being determined based on the printability of the detected defects.

[0037] In another aspect, the present application provides a method of manufacturing a reflective mask, the method comprising the steps of:

[0038] a set of a reflective mask blank and a recording medium,

[0039] configuring a coordinate system with reference to the coordinate reference marks formed on the reflective mask blank, and determining positions of the defects of the reflective mask blank in the coordinate system with reference to the position information of the defects stored in the recording medium,

[0040] preparing drawing pattern data to form an absorber pattern by patterning the absorber film,

[0041] evaluating the possibility of processing the defects by retaining the absorber film as the absorber pattern in order according to the priority order stored in the recording medium, and

[0042] forming the absorber pattern by etching and removing a part of the absorber film of the reflective mask blank, thereby retaining the absorber pattern at the positions of the defects whose positions in the coordinate system have been evaluated as the processable defects.

[0043] Advantages of the Invention

[0044] According to the present application, for defects such as phase defects affecting the reflective mask manufactured from the reflective mask blank, the positions of the defects in the multilayer reflective film, especially even if the defects are fine, can be accurately grasped after the multilayer reflective film is formed on the substrate, and further after the absorber film is formed on the multilayer reflective film. In addition, the reflective mask blank can be manufactured by effectively forming the absorber pattern which can mitigate the effects of the defects in the multilayer reflective film and avoid the defects with high precision.

[0045] BRIEF DESCRIPTION OF DRAWINGS

[0046] FIG. 1A and 1B shows an example of a reflective mask, FIG. 1A is a plan view of the profile of the surface side of the reflective mask from which the absorber pattern is formed, FIG. 1B is FIG. 1A is an enlarged sectional view of the device pattern region of the reflective mask in

[0047] as an explanatory diagram, FIGS. 2A-2CA phase defect of the reflective mask is shown, FIG. 2A is a cross-sectional view illustrating a state of a phase defect present in a multilayer reflective film before an absorber film is formed, FIG. 2B is a cross-sectional view for illustrating a state of an exposed phase defect, FIG. 2C is a cross-sectional view illustrating a state of a phase defect covered with an absorber pattern.

[0048] FIGS. 3A-3C Examples of planar shapes of coordinate reference marks are shown, FIG. 3A 、 3B and 3C are a cross mark, a longitudinal line mark, and a transverse line mark, respectively.

[0049] FIG. 4 is a bottom view of a reflective mask blank, in which a coordinate reference mark is formed on a conductive film.

[0050] FIGS. 5A-5E is a view for illustrating each step of manufacturing a reflective mask blank of the present application, FIG. 5A is a cross-sectional view of a substrate, FIG. 5B is a cross-sectional view of a state of forming a conductive film, FIG. 5C is a cross-sectional view of a state of forming a coordinate reference mark on a conductive film, FIG. 5D is a cross-sectional view of a state of forming a multilayer reflective film and a protective film, FIG. 5E is a cross-sectional view of a state of forming an absorber film.

[0051] FIG. 6 is a conceptual view of an inspection tool including an optical system for detecting a film defect and an optical system for detecting a coordinate reference mark.

[0052] FIG. 7 is an explanatory view showing a state of warping or bending of a main surface of a substrate by a conic section.

[0053] FIG. 8 is a cross-sectional view showing a state in which a substrate on which a film is formed is partially tilted at an angle θ.

[0054] FIG. 9 is a flowchart of an example of a method of manufacturing a reflective mask by patterning an absorber film of a reflective mask blank.

[0055] FIG. 10A and FIG. 10B are conceptual views showing positions of a phase defect present in a multilayer reflective film and an absorber pattern of a reflective mask, respectively. DETAILED DESCRIPTION

[0056] The reflective mask blank of the present application includes a substrate, and a multilayer reflective film for reflecting EUV light, a protective film (for the multilayer reflective film), and an absorber film for absorbing EUV light, which are formed in this order on one main surface (front side) of the substrate from the substrate side, and a conductive film formed on the other main surface (back side) of the substrate, which is the opposite side of the one main surface. The conductive film is formed to electrostatically hold the reflective mask on a mask stage of an exposure tool. The thickness of the conductive film is usually 10 to 40 nm. In the above description, the one main surface of the substrate is defined as the front side or the upper side, and the other main surface is defined as the back side or the lower side. However, for convenience, the front side and the back side or the upper side and the lower side are defined among the two surfaces. The two main surfaces (film formation surfaces) are the one main surface and the other main surface, respectively. The front side and the back side or the upper side and the lower side can be replaced. Meanwhile, the reflective mask is formed by patterning the absorber film of the reflective mask blank to form an absorber pattern (pattern of the absorber film).

[0057] FIG. 1A and 1B An example of a reflective mask for EUV exposure is shown as a typical reflective mask of the present application. FIG. 1A is a plan view of the profile of the surface side of the reflective mask on which the absorber pattern is formed, FIG. 1B is FIG. 1A is an enlarged sectional view of a device pattern region of the reflective mask in FIG. 1A and FIG. 1B As shown in Figs. 1 and 2, a device pattern region MDA, which constitutes a circuit pattern of a semiconductor integrated circuit device, is formed at a predetermined position on the one main surface side central portion of the substrate 101 of the reflective mask RM. Alignment mark regions MA1, MA2, MA3, MA4 including marks for alignment of the reflective mask or wafer alignment marks are formed in a peripheral portion other than the device pattern region MDA. Further, a multilayer reflective film 102 for reflecting EUV light, a protective film 103, and an absorber pattern 114 for absorbing EUV light are formed on the one main surface of the substrate 101 (in this order from the substrate 101 side), and a conductive film 105 is formed on the other main surface of the substrate 101.

[0058] It is preferable to use a substrate composed of a low thermal expansion material and having a sufficiently flat surface. For example, the thermal expansion coefficient of the substrate is preferably within ±3 x 10 -8 / °C, and more preferably within ±1 x 10 -8 / °C. The surface roughness (RMS value) of the main surface of the substrate is preferably at most 0.1 nm, and more preferably at most 0.05 nm. In particular, the main surface on which the absorber film is formed at least thereon can be formed with the absorber pattern thereon (for example FIG. 1AThe surface roughness is satisfied on a region of the device pattern area (MDA) in the substrate, preferably across the entire main surface on which the absorber film is formed. Such surface roughness can be obtained by polishing the substrate.

[0059] A multilayer reflective film is a multilayer film composed of alternating layers of materials with low refractive index and layers of materials with high refractive index. For example, for exposing EUV light with wavelengths of 13 to 14 nm (typically about 13.5 nm), a Mo / Si multilayer film can be used, comprising a molybdenum (Mo) layer as a low refractive index material and a silicon (Si) layer as a high refractive index material, alternatingly stacked for approximately 40 cycles (40 layers each). The thickness of a multilayer reflective film is typically... about.

[0060] This protective film, referred to as a capping layer, is provided to protect the multilayer reflective film during the formation or alignment of absorber patterns disposed on the protective film. Materials used for the protective film include, for example, silicon (Si), ruthenium (Ru), or ruthenium (Ru) compounds with added niobium (Nb) and / or zirconium (Zr). The thickness of the protective film is typically about 2 to 5 nm.

[0061] An absorber pattern is a mask pattern that absorbs EUV light and is formed by patterning the absorber film. For example, compounds containing tantalum (Ta) as the main component or compounds containing chromium (Cr) as the main component can be used as the material of the absorber film. The absorber film can consist of a single layer or multiple layers. The thickness of the absorber film is typically about 70 to 90 nm.

[0062] The reflective mask blank may have a hard mask film on the absorber film to assist in the patterning of the absorber film. This hard mask film is typically removed after the absorber pattern is formed, and it does not remain in the reflective mask. Furthermore, a photoresist film (photoresist film) for patterning the absorber film may be formed in the reflective mask blank.

[0063] In some cases of reflective masks, there are defects known as phase defects, where reduced reflectivity results from structural disorder within the multilayer reflective film. The phase defects generated in multilayer reflective films are explained below. FIGS. 2A-2C This is a diagram illustrating phase defects in a reflective mask used for EUV exposure. FIG. 2A This is a cross-sectional view illustrating the phase defect state that exists in the multilayer reflective film before the formation of the absorber film. FIG. 2B It is a cross-sectional view used to illustrate the state of phase defects exposed on a multilayer reflective film. FIG. 2C It is a cross-sectional view illustrating the state of the phase defect covered by the absorber pattern.

[0064] FIG. 2A The state is shown in which, when the multilayer reflective film 102 is formed on the surface of the substrate 101, a convex phase defect 120 is formed through the multilayer reflective film 102 to the protective film 103 formed on the defect, because there is a fine convex portion on the main surface of the substrate on which the multilayer reflective film 102 is formed. The reference numeral 105 represents a conductive film. Although FIG. 2A The case where there is a fine convex portion on the main surface of the substrate 101 is shown, but when there is a fine concave portion on the main surface of the substrate 101, a concave phase defect 120 will be formed. Even when there is a fine concave or convex portion on the main surface of the substrate 101, when the concave or convex shape is slightly flattened by a smoothing action in the process of forming the layers of the multilayer reflective film 102, it is sometimes difficult to exhibit the concave or convex shape on the finally obtained surface of the multilayer reflective film 102 or the protective film 103 in some cases. However, even in this case, if there is a portion of the fine concave or convex shape in the multilayer reflective film 102, the portion functions as a phase defect which produces a certain phase shift to the reflected light and lowers the reflectance.

[0065] When the reflective mask blank is manufactured by forming an absorber film on the protective film 103 in the state where the phase defect 120 is present (as shown in FIG. 2A and then forming an absorber pattern by patterning the absorber film, if there is an exposed phase defect 120 between the adjacent absorber patterns 114 (as shown in FIG. 2B the height of the convex portion or the depth of the concave portion is, for example, at least about 2 to 3 nm, the phase of the reflected light is disturbed and the reflectance is lowered, and thus a defect appears in the projected image of the pattern. On the other hand, when the phase defect 120 is covered with the absorber pattern 114 and the reflectance of the portion of the phase defect 120 is sufficiently low, no defect appears in the projected image of the pattern of the reflective mask. Therefore, when the circuit pattern is formed to cover the portion where the phase defect is present with the absorber pattern in the manufacture of the reflective mask, the defect in the projected image of the pattern caused by the phase defect can be avoided. For this reason, it is important to be able to accurately determine the position (coordinates) of the phase defect present in the reflective mask blank. Further, it is important to be able to accurately grasp the position (coordinates) of the phase defect, which corresponds to the coordinates of the drawing pattern used for forming the absorber pattern, at the time of patterning the absorber film.

[0066] In the reflective mask blank of the present application, a coordinate reference mark is formed on the other substrate main surface side (rear side) opposite to the one main surface side (front side) on which the multilayer reflective film, the protective film, and the absorber film are formed. The coordinate reference mark is a reference (coordinate reference) on a two-dimensional coordinate or a three-dimensional coordinate, and is used to determine the position of a specific site, for example, a site where a defect exists in the reflective mask blank or the reflective mask obtained from the reflective mask blank. Therefore, the coordinate reference mark is usually formed at least at two positions, preferably at least three positions, and more preferably at least four positions. The coordinate reference mark can have a convex shape. However, a concave shape is convenient and is preferably engraved on the substrate or the film to form the mark. In particular, in the case where the other main surface side is a suction surface for applying an electrostatic chuck, it is more preferable to form the coordinate reference mark in a concave shape.

[0067] The planar shape of the coordinate reference mark is not particularly limited as long as its position can be detected by the inspection light of the optical inspection tool. Exemplified are a cross mark 106a as shown in FIG. 3A a longitudinal line mark 106b composed of a plurality of spaced lines (six lines in this case) as shown in FIG. 3B and a transverse line mark 106C composed of a plurality of spaced lines (six lines in this case) as shown in FIG. 3C The size of the mark is not particularly limited. For example, the width can be 50 nm to 10 μm, and the length can be 50 to 200 μm.

[0068] In the reflective mask blank of the present application, the coordinate reference mark is preferably formed on the conductive film. Usually, the conductive film is formed on the other main surface side of the substrate so that an electrostatic chuck can be applied to the reflective mask when the reflective mask obtained from the reflective mask blank is loaded onto the exposure tool. The coordinate reference mark can be formed directly on the substrate. However, it is advantageous to form the coordinate reference mark by processing the conductive film in view of handleability of the coordinate reference mark. In addition, even when the coordinate reference mark is formed on the conductive film, the function of the conductive film is not impaired when the reflective mask is loaded on the exposure tool. This is an advantage of forming the coordinate reference mark on the conductive film. Usually, the concave coordinate reference mark is formed on the conductive film by engraving a portion of the conductive film, particularly a portion of the outer periphery of the conductive film. Usually, the coordinate reference mark is not used for loading the reflective mask onto the exposure tool.

[0069] FIG. 4 is a plan view of the reflective mask blank in which the coordinate reference mark is formed on the conductive film. In this case, the conductive film 105 is formed on the other main surface side of the substrate 101, and four concave coordinate reference marks 106 formed by engraving are formed within each portion of the outer periphery of the conductive film 105 (in this case, specifically in each of the four mark formation regions 116 near the four corners).

[0070] The coordinate reference mark formed on the side opposite to the side on which the circuit pattern is to be formed is used as a common reference for checking the position of a defect such as a phase defect present in the multilayer reflective film, as a position reference for drawing the pattern of the absorber, as a position reference for defect inspection, and other references, without laminating the layers for forming the circuit pattern, such as the multilayer reflective film, the protective film, the absorber film, and other films, on the coordinate reference mark. In addition, since the coordinate reference mark is deeply embedded in each film without laminating a thick film on the coordinate reference mark, high accuracy can be obtained in determining the position. Furthermore, unlike the method in which the absorber film is formed after the coordinate reference mark is formed on the multilayer reflective film or the protective film, the coordinate reference mark is formed on the side opposite to the side on which the circuit pattern is to be formed. Therefore, it is not necessary to perform the processing of the coordinate reference mark after the multilayer reflective film or the protective film is formed, which has a risk of generating particles.

[0071] Next, a method for manufacturing the reflective mask blank of the present application will be described. In the present application, the reflective mask blank is appropriately manufactured by a method including the following steps:

[0072] (A1) forming a conductive film on the other main surface,

[0073] (A2) forming a coordinate reference mark on the side of the other main surface,

[0074] (B1) forming a multilayer reflective film and a protective film on the one main surface,

[0075] (B2) inspecting a defect in the multilayer reflective film and the protective film formed in step (B1), obtaining position information of the detected defect based on the coordinates defined with reference to the coordinate reference mark, and saving the position information to a recording medium,

[0076] (C1) after step (B2), forming an absorber film on the protective film, and

[0077] (C2) inspecting a defect in the absorber film formed in step (C1), obtaining position information of the detected defect based on the coordinates defined with reference to the coordinate reference mark, and saving the position information to a recording medium.

[0078] The method will be described in detail with reference to the drawings. FIGS. 5A-5E is a view for explaining each step of manufacturing the reflective mask blank of the present application. FIG. 5A is a cross-sectional view of a substrate. FIG. 5B is a cross-sectional view of a state in which a conductive film is formed on the other main surface of the substrate. FIG. 5C is a cross-sectional view of a state in which a coordinate reference mark is formed on the conductive film. FIG. 5Dis a cross-sectional view of a state in which a multilayer reflective film and a protective film are formed in this order on one main surface of a substrate. FIG. 5E is a cross-sectional view of a state in which an absorber film is formed on the protective film.

[0079] In step (Al), as shown in FIG. 5A , a substrate 101 is prepared. As the substrate 101, a substrate having one main surface with a predetermined surface roughness and the other main surface is prepared. Next, as shown in FIG. 5B , a conductive film 105 is formed on the other main surface of the substrate 101.

[0080] In step (A2), a coordinate reference mark is formed on the other main surface side. In FIG. 5C the case shown, the coordinate reference mark is formed at a predetermined position in the outer periphery of the conductive film 105. The coordinate reference mark can be formed by etching and removing a portion of the conductive film 105. As the shape of the coordinate reference mark, the same shape of a line mark or a fiducial mark commonly used in a reflective mask can be applied. In particular, after the conductive film and the coordinate reference mark are formed, it is necessary to keep one main surface of the substrate clean. Therefore, if necessary, the substrate can be cleaned after the conductive film or the coordinate reference mark is formed. Even if one main surface of the substrate has been contaminated while the coordinate reference mark is formed, the surface of the substrate itself is easily cleaned by a cleaning process. Therefore, steps (Al) and (A2) are preferably performed before step (Bl).

[0081] In step (Bl), as shown in FIG. 5C , a multilayer reflective film 102 and a protective film 103 are formed on one main surface of the substrate 101. The multilayer reflective film and the protective film can be formed by an ion beam sputtering method, a CD sputtering method, or an RF sputtering method, respectively. FIG. 5C An example in which a convex phase defect 120 is formed in the multilayer reflective film 102 and the protective film 130 is shown.

[0082] In step (B2), defects in the multilayer reflective film 102 and the protective film 103 are inspected, the position information of the detected defects (in this case, phase defects) is obtained based on the coordinates defined with reference to the coordinate reference mark 106, and the position information is saved to a recording medium. The specific method of inspecting defects in this step is described later. In this defect inspection, it is preferable to obtain the information of the detection signal level of the defects as well as the position information, and save it to the recording medium. In addition, a step of measuring the flatness of the substrate can be included after step (Bl) and before step (B2). The flatness can be measured, for example, by detecting the coordinate reference mark using a function for focusing in the optical system of the inspection tool shown in FIG. 6 , and described later.

[0083] In step (C1), as FIG. 5E As shown, an absorber film 104 is formed on the protective film 103. The absorber film can also be formed by ion beam sputtering, CD sputtering, or RF sputtering. FIG. 5E In the absorber film 104, the phase defect 120 obtained by the convex phase defect 120 formed in the multilayer reflective film 102 and the protective film 103 is convex at the location of the phase defect 120. FIG. 5E An example of particles 121 adhering to the surface of absorber membrane 104 is also shown.

[0084] In step (C2), defects in the formed absorber film are inspected, including phase defects, particle defects, and other defects in the multilayer reflective film. The location information of the detected defects is obtained based on coordinates defined by reference coordinate marker 106, and this location information is saved to a recording medium. Defect inspection can be performed in this step using conventionally known methods. For example, such as... FIG. 5E As shown, when particles adhere to the surface of the absorber film, the defect is detected as a particle defect. The location information of the detected defect is obtained and saved to a recording medium. Additionally, a step of measuring substrate flatness can be included after step (C1) and before step (C2).

[0085] Following step (C2), a step of forming a resist film (photoresist film) on the absorber film may be included. According to this method, a... FIG. 5E The reflective mask blank shown is RMB, and it is manufactured, for example, by patterning the absorber film of the reflective mask blank. FIG. 2C The reflective mask shown.

[0086] Next, suitable defect inspection methods for steps (B2) and (C2) will be described. FIG. 6is a conceptual diagram of an inspection tool including an optical system for detecting defects of a film formed on one main surface side of a substrate (defects of a multilayer reflective film, particularly, phase defects in step (B2), or defects of an absorber film in step (C2)), and an optical system for detecting a coordinate reference mark on the other main surface side of the substrate. The inspection tool 200 includes a support member SPT for supporting a film-formed substrate FFS, a mask stage STG, a stage driving unit 201, a defect inspection optical system 202, a defect inspection imaging and control unit 203, an optical system 204 for detecting a coordinate reference mark, an imaging and control unit 205 for detecting a coordinate reference mark, and a control device 206 for controlling the entire defect detection. In steps (B2) and (C2), the object of the film-formed substrate FFS is generally an intermediate product in the process of manufacturing a reflective mask blank or a reflective mask blank. However, an intermediate product in the process of manufacturing a reflective mask or a reflective mask can be used as the object.

[0087] Although not illustrated, the defect inspection optical system 202 and the optical system 204 for detecting a coordinate reference mark include an illumination optical system and a focusing system for irradiating inspection light, respectively. The inspection light used in the optical system 202 for defect inspection can be inspection light having a wavelength of 190 to 540 nm generally applied, and further EUV light having a wavelength of 13 to 15 nm can also be applied. When EUV light is applied, a reflective mirror is used in the illumination optical system and the optical system for inspection. For example, as the optical system for detecting a coordinate reference mark formed on the other main surface side of the substrate, an optical system for a wafer substrate as an object disclosed in JP-A 2007-200953 (Patent Document 5) is known, and this optical system can also be used.

[0088] In FIG. 6 In the case of the inspection tool illustrated, the defect inspection optical system 202 and the optical system 204 for detecting a coordinate reference mark are disposed so that the axes of the lenses are coaxially aligned on the same axis. When defects of a film are detected by the defect inspection optical system 202 after detecting a coordinate reference mark 106 formed on the other main surface side of the film-formed substrate FFS, the positions of the defects can be obtained as position information determined based on the reference coordinate reference mark, and the obtained position information is saved or recorded in a recording medium. Further, information of a detected defect signal level can be obtained together with the position information of the defects. In this case, the information of the detected defect signal level can be saved or written in the recording medium together with the position information of the defects. The coordinate system can be a two-dimensional coordinate system or a three-dimensional coordinate system.

[0089] Specifically, when a defect, particularly a phase defect, is detected, it is preferable to create a processing order for the defect and save or record this processing order along with location information to a recording medium. The processing order can be a priority order for processing defects, determined based on the printability of the detected defect. For example, in step (B2), when detecting a phase defect in a multilayer reflective film, the impact of the reduction in reflectivity caused by the phase defect in the multilayer reflective film (the printability of the defect in the use of the reflective mask) can be evaluated from the signal level information of the detected phase defect. Furthermore, a processing order can be created to prioritize defects that are assessed as having a significant impact on the reduction of reflectivity. In this case, the processing order can be a priority order for processing defects, such as a priority order for covering defects with an absorber pattern by patterning the absorber film during the fabrication of the reflective mask to form an absorber pattern.

[0090] exist FIG. 6 In the case of the inspection tool shown, the support member SPT does not have a structure in which the film-forming substrate FFS is fixed by pressure. The film-forming substrate FFS is simply supported by the support member SPT, and no pressure is applied to the film-forming substrate FFS to deform its shape.

[0091] By forming films such as multilayer reflective films, protective films, absorber films, and other films, the substrate warps due to stress. When simply supporting the film-forming substrate as... FIG. 6 The inspection tool shown is used when the substrate is bent, and the inspection is performed in a bent state. In many cases, the warped or bent shape can be, for example, by... FIG. 7 The quadratic curve shown represents this. In FIG. 7 In the diagram, curve P-P' illustrates the state of the main surface of a substrate with warping or bending. The symbol "L" represents the distance from one of the opposite angles of the substrate to the center of the substrate (i.e., "2×L" corresponds to the diagonal distance), and the symbol "H" represents the amount of warping or bending (height) at the center of the substrate. From these values, the radius of curvature R (the distance from the symbol "O," representing the center of curvature) can be calculated assuming the main surface of the substrate has a quadratic surface shape. The distance L and height H can be obtained by measuring the flatness of the substrate.

[0092] In defect inspection, local tilting of the film-forming substrate causes positional differences between one main surface and another. Therefore, it is preferable to assess the warping or bending of the substrate on which multilayer reflective films, protective films, absorber films, and other films are formed, and to calibrate the effects of local tilting caused by warping or bending. FIG. 8is a cross-sectional view schematically showing a state of a partial tilt angle θ of a substrate on which a film is formed. In this case, when the total thickness of the substrate 101, the multilayer reflective film 102, the protective film 103, and the conductive film 105 is "T", a positional difference expressed as "T x sin θ" occurs in the coordinates between one and the other main surfaces. Therefore, the difference can be calibrated. The angle θ can be calculated from the shape of warping or bending drawn by the quadric surface and the approximate position of the defect detected. Furthermore, the angle θ can be directly calculated based on the method described in JP-A 2007-200953 (Patent Document 5).

[0093] The calibration value can be calculated as follows, for example. In a two-dimensional coordinate system defined with reference to the coordinate reference marks, when the radii of curvature of the quadric surface and the coordinates of the defect with respect to the origin (x = 0, y = 0) are "R" and "x, y", respectively, the calibration value "Δx" in the x direction and the calibration value "Δy" in the y direction due to the inclination of the angle θ are Δx = (T / R)x and Δy = (T / R)y, respectively. When such calibration is applied, information for calibrating the position of the defect can be saved or recorded in the recording medium together with the position information of the defect.

[0094] The position information of the defect in the reflective mask blank is saved or recorded in the recording medium together with the information of the signal level of the defect detected, the processing order (priority order), the information for calibrating the position of the defect, and the like. The reflective mask blank of the present application can be provided as a set of the reflective mask blank (main component) and the recording medium. According to the reflective mask blank in combination with the recording medium, when a reflective mask is manufactured from the reflective mask blank, the position of the defect and the processing order can be determined from the information saved or recorded in the recording medium at the time of patterning the absorber film.

[0095] Next, a method of manufacturing a reflective mask is described. Referring to the flowchart shown in FIG. 9 Examples of a method of manufacturing a reflective mask by patterning the absorber film of a reflective mask blank are explained.

[0096] First, a reflective mask blank and a recording medium or a set including the reflective mask blank and the recording medium are prepared (step S101). The reflective mask blank includes, as main components, prescribed films formed on one main surface and the other main surface of a substrate, and a coordinate reference mark formed on the other main surface of the substrate. The recording medium stores or records position information of defects such as phase defects, information of signal levels of detected defects, processing order (priority order), information for calibrating defect positions, and the like based on coordinates defined with reference to the coordinate reference mark. Examples of the recording medium include a medium that electrically or magnetically records information. The recording medium can be a paper medium in which information is written. Next, a coordinate system is configured with reference to the coordinate reference mark formed on the reflective mask blank, and positions of defects in the reflective mask blank are determined in the coordinate system with reference to the position information of defects stored in the recording medium (step S102). The coordinate system can be a two-dimensional coordinate system or a three-dimensional coordinate system.

[0097] Next, drawing pattern data is prepared to form an absorber pattern by patterning the absorber film (step S103). Next, positions of the drawing pattern are compared with positions of the defects, and the possibility of processing the defects by leaving the absorber film as the absorber pattern, that is, the possibility of covering the defects with the absorber pattern, is evaluated in order according to the priority order stored in the recording medium (step S104). At this stage, if the evaluation result determines that there is no defect that can be processed, or the number of defects is relatively small, the entire drawing pattern that forms the absorber pattern can be rearranged by moving in a predetermined direction. Then, the process returns to step S103, and the drawing position of the drawing pattern can be optimized by executing step S104 again. In this way, the drawing position of the drawing pattern can be optimized to cover defects having a high priority order to the greatest extent, the defects having a high criticality and which should be preferentially covered by the absorber pattern among the defects. In addition, for the influence of local inclination caused by warping or bending of the substrate, the drawing position of the drawing pattern can also be calibrated in the same way as the calibration of the defect positions with respect to the local inclination of the film formation substrate.

[0098] The drawing pattern can be set based on coordinates defined with reference to the coordinate reference mark. For this purpose, a tool for writing the drawing pattern preferably has a function of detecting the coordinate reference mark. If the drawing tool does not have a function for detecting the coordinate reference mark, or the coordinate reference mark cannot be detected, an auxiliary mark can be formed around the absorber film by the drawing tool in advance to be used for setting with the auxiliary mark. A reference mark can be used as the auxiliary mark. In this case, a coordinate system defined with reference to the coordinate reference mark via the auxiliary mark can be configured by obtaining the relationship between the coordinate reference mark and the auxiliary mark with an inspection tool such as shown in FIG. 6. FIG. 6

[0099] ​Next, an absorber pattern is formed by patterning the absorber film (step S105). In particular, the absorber pattern can be formed by etching and removing a portion of the absorber film of the reflective mask blank, thereby retaining the absorber pattern at the location of the defect that has been assessed as a treatable defect according to the location of the defect in the coordinate system.

[0100] This method of manufacturing reflective masks allows for the formation of absorber patterns, minimizing the impact of defects (phase defects) and enabling the fabrication of reflective masks with controlled defect effects. Furthermore, when manufacturing reflective masks using this method, it is not necessary to completely eliminate defects such as phase defects in the reflective mask blank. Therefore, this method effectively increases the yield of reflective mask blanks suitable for manufacturing reflective masks and provides reflective mask blanks with good productivity.

[0101] Typically, a reflective mask obtained by patterning the absorber membrane to form an absorber pattern is provided for inspecting pattern defects in the absorber pattern (step S106). If necessary, the absorber pattern is repaired or calibrated. Conventionally known methods can be used for these purposes, and coordinates defined with reference to the coordinate reference mark of the present invention are preferably used for inspecting defects in the absorber pattern, or for repairing or calibrating the absorber pattern.

[0102] For example, after inspecting the pattern defects of the absorber pattern, such as FIG. 9 As shown, referring to the defect information of the inspected absorber pattern, the location information of the defects stored in the recording medium, and the location information of the drawn pattern, the possibility of residual fatal defects, especially fatal phase defects, in the reflective mask is assessed (step S107). Next, if a fatal defect remains, a calibration amount is calculated to calibrate the shape of the absorber pattern (step S108), and the need to repair the absorber pattern based on the defect information of the detected absorber pattern, and the need to calibrate the shape of the absorber pattern for fatal defects are assessed (step S109). On the other hand, when the absorber pattern is assessed to have no fatal defects in step S107, step S109 is performed directly (step S108 is skipped), and the need to repair the absorber pattern based on the defect information of the inspected absorber pattern is assessed. Next, when it is assessed that it is necessary to repair the absorber pattern based on the defect information of the inspected absorber pattern or to calibrate the shape of the absorber pattern for fatal defects, the absorber pattern is repaired or calibrated (step S110).

[0103] Here, the shape calibration of the absorber pattern is described by showing the absorber pattern of the reflective mask and the location of phase defects present in the multilayer reflective film. FIG. 10A and FIG. 10Bare conceptual diagrams showing the absorber pattern of the reflective mask and the positions of the phase defects present in the multilayer reflective film, respectively. In FIG. 10A and FIG. 10B In both diagrams, the phase defects 120a having a high priority are completely covered with the absorber pattern 114, and the phase defects 120a having a high priority are in a state where the phase defects are not projected as defects when the reflective mask is used. On the other hand, for example, in some cases, the phase defects 120b having a low priority and not covered with the absorber pattern 114 can remain. If the number of defects is large, the possibility of the phase defects 120b not covered with the absorber pattern 114 increases. In addition, if a positional error is caused when the absorber film pattern is formed, the phase defects 120b not covered with the absorber pattern 114 can remain.

[0104] When the remaining phase defects are phase defects present between adjacent absorber patterns, for example, the influence of the exposure tool in projecting the mask pattern can be mitigated by the method disclosed in JP-A 2002-532738 (Patent Document 3), in particular, a method of calibrating the profile of the absorber pattern adjacent to the phase defects.

[0105] Embodiment

[0106] Embodiments of the present application will be given below by way of illustration, not limitation.

[0107] Embodiment 1

[0108] First, a substrate was prepared, and a conductive film (20 nm thick) composed of a Cr-based material was formed on the other main surface of the substrate. Next, a cross mark as a coordinate reference mark was formed in each of the four mark formation regions of the conductive film as shown in FIG. 1B. The coordinate reference mark was formed by etching and removing the conductive film by optical lithography to form a concave mark of 20 nm deep. The width of the line was 2 μm, and the length of the cross line was 100 μm, respectively. FIG. 4 FIG. 3A Next, a cross mark as a coordinate reference mark was formed in each of the four mark formation regions of the conductive film as shown in FIG. 1B. The coordinate reference mark was formed by etching and removing the conductive film by optical lithography to form a concave mark of 20 nm deep. The width of the line was 2 μm, and the length of the cross line was 100 μm, respectively.

[0109] Next, after cleaning the substrate, a multilayer reflective film (280 nm thick) including 40 molybdenum (Mo) layers and 40 silicon (Si) layers alternately laminated was formed on one main surface of the substrate. In addition, a protective film (2.5 nm thick) composed of a material containing ruthenium as a main component was formed on the multilayer reflective film.

[0110] Next, the phase defects present in the multilayer reflective film were measured by using a phase defect measuring device (manufactured by KLA-Tencor Corporation, product name: KLA-Quantum Yield 3000). The measurement was performed in the following manner. First, the phase defects were measured in the four mark formation regions of the multilayer reflective film. Next, the phase defects were measured in the four mark formation regions of the multilayer reflective film. The measurement was performed in the following manner. First, the phase defects were measured in the four mark formation regions of the multilayer reflective film. FIG. 6 ​The inspection tool shown is used to inspect a substrate with multiple reflective and protective films formed on it for defects. First, the origin of the two-dimensional xy coordinate system (x=0, y=0) is set at the center of the other main surfaces of the substrate. Next, before inspecting for defects in the multiple reflective and protective films, the warpage or curvature of the substrate is measured as flatness by focusing the optical system to detect the function of the coordinate reference mark. The result shows that the center of the substrate warps upwards compared to the outer periphery. The substrate measured has a length L of 106 mm and a height H of 400 nm, as shown. FIG. 7 As shown. Therefore, the radius of curvature R of the warp is 1.4045 × 10⁻⁶. 7 mm.

[0111] In this defect inspection, firstly, phase defects in the multilayer reflective film are examined, and the location of the defects is obtained in two-dimensional xy coordinates on other master surfaces. The defect location is calibrated using the obtained radius of curvature R to alter the warp or bending of the substrate, and the defect location information, along with information on the signal level of the detected defects, is stored in a recording medium. Next, after inspecting the multilayer reflective film over the entire predetermined area, the processing priority is determined based on the defect information stored in the recording medium, and this priority is also stored in the recording medium.

[0112] Next, an absorber film (70 nm thick) composed of a material containing tantalum (Ta) as the main component is formed on the protective film.

[0113] Next, using FIG. 6 The inspection tool shown is used to inspect a substrate on which an absorber film is formed for defects. First, prior to defect inspection of the absorber film, the warpage or curvature of the substrate is measured as flatness by focusing the optical system to detect the function of the coordinate reference markers. As a result, it was found that the center of the substrate warped upwards compared to the outer periphery. The measured substrate has a length L of 106 mm and a height H of 550 nm, as shown. FIG. 7 As shown. Therefore, the radius of curvature R of the warp is 1.0214 × 10⁻⁶. 7 mm.

[0114] In this defect inspection, firstly, phase defects in the absorber film are examined, and the location of the defects is obtained in two-dimensional xy coordinates on other master surfaces. The defect location is calibrated using the obtained radius of curvature R to alter the warp or bending of the substrate, and the defect location information, along with information on the signal level detected by the defect, is stored in a recording medium. Using this method, a reflective mask blank is obtained.

[0115] Next, according to FIG. 9The procedure in the flowchart described above manufactures the reflective mask. First, a set of the reflective mask blank (as a main component) and the recording medium is prepared, an electron beam resist is applied to the surface of the blank, and then the blank is mounted on a mask stage of an electron beam drawing tool. Next, the coordinate positions of defects stored in the recording medium are determined with reference to the coordinate reference marks. Next, drawing pattern data for the absorber film is prepared, and the drawing positions of the absorber pattern are optimized to cover the maximum number of defects in accordance with the priority order stored in the recording medium. Then, the drawing pattern arranged optimally is drawn as the absorber pattern on the electron beam resist, and the absorber pattern is formed by a conventional method.

[0116] In this case, since the manufacture from the reflective mask blank to the reflective mask is performed by collectively using the coordinate reference marks formed on the other main surface of the substrate, the position of the defects can be determined with high accuracy. Therefore, the error in the position detection is within 10 nm.

[0117] Comparative Example 1

[0118] After forming the same conductive film as in Example 1 on the other main surface of the substrate, the same coordinate reference marks as in Example 1 are formed on one main surface of the substrate by a general optical lithography method without forming the coordinate reference marks in the conductive film. Next, the same multilayer reflective film, protective film, and absorber film as in Example 1 are formed on one main surface of the substrate to obtain a reflective mask blank. In the manufacture of the reflective mask from the obtained reflective mask blank in the same manner as in Example 1, the measurement of the flatness (correction of warping or bending) and the defect inspection are performed.

[0119] In this case, at the stage after the formation of the multilayer reflective film and the protective film, a film having a total thickness of about 280 nm is formed on the coordinate reference marks, and at the stage after the further formation of the absorber film, a film having a total thickness of about 350 nm is formed on the coordinate reference marks. Since a resist film is formed on the absorber film at the time of manufacture of the reflective mask, the accuracy of the position determination of the defects is low as compared with Example 1. Therefore, the error in the position detection is not obtained within 10 nm.

Claims

1. A method of manufacturing a reflective mask blank, the reflective mask blank comprising a substrate and, sequentially formed on one main surface of the substrate from the substrate side, a multilayer reflective film for reflection of EUV light, a protective film, and an absorber film for absorption of EUV light, and a conductive film formed on the other main surface of the substrate, the method comprising the steps of: (Al) forming the conductive film on the other main surface, (A2) forming a coordinate reference mark on the other main surface side, (Bl) forming the multilayer reflective film and the protective film on the one main surface, measuring a flatness of the substrate by detecting a function of the coordinate reference mark by focusing of an optical system to measure a warp or a bow of the substrate as the flatness, (B2) inspecting defects in the multilayer reflective film and the protective film formed in step (Bl), obtaining positional information of the detected defects based on coordinates defined with reference to the coordinate reference mark, calibrating defect positions based on the obtained warp or bow, and saving the positional information to a recording medium, (Cl) forming the absorber film on the protective film after step (B2), measuring a flatness of the substrate by detecting a function of the coordinate reference mark by focusing of an optical system to measure a warp or a bow of the substrate as the flatness, and (C2) inspecting defects in the absorber film formed in step (Cl), obtaining positional information of the detected defects based on coordinates defined with reference to the coordinate reference mark, calibrating defect positions based on the obtained warp or bow data, and saving the positional information to the recording medium.

2. The method according to claim 1, wherein in step (A2), the coordinate reference mark is formed on the conductive film formed in said step (Al). a processing order of the defects is created, and the processing order is saved to the recording medium together with the positional information.

4. The method according to claim 3, wherein the processing order is a priority order for processing the defects, the priority order being determined based on printability of the detected defects. ​ ​ ​ ​ ​ ​ 3. The method of claim 1, wherein when a defect is detected in step (B2), said step (B2) comprises the following steps: ​ ​

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